This segment of the program supports the development of robotics to satisfy the planned requirements for exploration of planetary surfaces. These plans call for robotic reconnaissance and exploration systems traversing the Mars terrain. During such missions robots will explore potential landing sites and areas of scientific interest, place science instruments, and gather samples for analysis and possible return to Earth. The robotic systems required for these operations will require high levels of local autonomy, including the ability to perform local navigation, identify areas of potential scientific interest, regulate on-board resources, and schedule activities, all with limited ground command intervention. The objectives of the tasks within this segment of the program are to develop these abilities, as well as conduct research into mobility systems, miniature mechanisms, planning, and on-board navigation. Specific applications are to the Mars Pathfinder, Mars Global Surveyor project and other programs planned by the Space Science user community.
Mars Pathfinder Planetary
Rover
Long Range Science
Rovers / Remote Geologist
Automated Geologist
Natural Landmark Navigation
Lightweight
and Survivabile Rover
Nano-rover Technology
Development
Exploration of Small
Bodies
Micro-Lander Dexterous
Manipulators
Robotic Subsurface
Explorer
Planetary Aerobot Technology
Technology Transfer Roadmap Details
Mars PathfinderThe Microrover Flight Experiment (MFEX) is a flight experiment to validate autonomous mobile vehicle technologies, whose primary mission is to determine microrover performance in the poorly understood planetary terrain of Mars. The microrover is planned to be delivered, integrated with the Mars Pathfinder (MPF) lander, and land on Mars on July 4, 1997 following a seven-month cruise through interplanetary space. After landing, the microrover is deployed from the lander and begins a nominal 7 sol (approximately 7 day) mission to conduct technology experiments such as determine wheel-soil interactions, autonomous navigation and hazard avoidance capabilities, and engineering characterizations (thermal control, power generation performance, etc.). In addition, the microrover carries an alpha proton x-ray spectrometer (APXS) which when deployed on rocks and soil will provide element composition. Lastly, to enhance the engineering data return of the MPF mission, the microrover will image the lander to assist in status/damage assessment.
The microrover is a 6-wheeled vehicle of a rocker bogie design which allows the traverse of obstacles a wheel diameter (13cm) in size. Each wheel is independently actuated and geared (2000:1) providing superior climbing capability in soft sand. The front and rear wheels are independently steerable, providing the capability for the vehicle to turn in place. The vehicle has a top speed of 0.4m/min.
This year, the Mars Pathfinder activiity will:
complete integration of the 'Sojourner'
rover with the Mars Pathfinder lander
support launch of the Mars Pathfinder spacecraft
assess the health of the 'Sojourner' rover during
the cruise phase of the Mars Pathfinder mission
train team members in preparation for the landed
surface phase of the mission
participate in the landed surface phase of the
mission through the operation of the 'Sojourner' rover on Mars
accumulate, analyze and prepare reports on the
data collected during the operation phase of the mission
initiate publication of the reports on the results
of this mission.
Background:
FY97 is the fifth and final year of the MFEX task. In the prior four years,
the requirements and design of the MFEX
rover have been completed
two vehicles have been assembled: the System Integration
Model (SIM) and the Flight Unit Rover (FUR or 'Sojourner')
a program of test and qualification has been completed
certifying readiness for integration with the Mars Pathfinder lander and
for flight
'Sojourner' was delivered to the cape and began
the process of final integration with the lander in preparation for launch.
the workstation for command generation and image
display during the surface operation phase of the mission was designed,
implemented and integrated with the Mars Pathfinder ground data system
Approach:
In completing the integration of the 'Sojourner' rover with the Mars Pathfinder lander, the MFEX team will support the:
integration and test of science instrument
(APXS) sensor head with sources on the rover. This will include mechanical,
electrical and data measurements taken after integration to the rover is
completed
update of the flight software on 'Sojourner' through
parameter, code or stored sequence changes approved by the Mars Pathfinder
project. Any update will be tested and certified as correct in execution
on the SIM vehicle. Upon completion of the update a read-out of the on-board
stored software and parameter state will be performed and the result archived
as the baseline software load for the 'Sojourner' vehicle.
integration of the modem with the lander electronics
and test of the rover/lander communication system in the vicinity of the
lander. Such testing will include a measurement of BER and detemination
of the requirement for attenuation in the signal path to ensure reliable
communication in the stowed/landed and cruise configuration of the lander
and rover.
mechanical attachment to the lander mounted rover
equipment (LMRE) and tiedown of the rover on the lander petal, which will
include test and any retentioning after tiedown.
participation in a bioassay of the lander. Results
of the bioassay may include retreatment of rover surfaces and additional
assay as necessary.
participation in electrical checks between lander
and rover during staged assembly of the lander with the aeroshell, cruise
phase and launch vehicle.
Upon completion of this set of activities a prelaunch test on the launch pad will be conducted certifying that the rover is ready for launch. Results of this test and the prior set of integration and test activities will be reported at the mission readiness reviews scheduled for 10/24/96 and 11/27/96.
The MFEX team will support the Mars Pathfinder project during any rework, retest or troubleshooting associated with preparation for launch. This will require the presence of an engineering team at the cape through the launch window, until spacecraft launch.
Upon launch, the nominal mission plan affords two opportunities for test of the 'Sojourner' vehicle during the cruise phase of the mission. One is scheduled for 12/16/96 and the second for 6/16/97. These tests will be health checks which will allow assessment of the state of the vehicle system (as is possible) in the cruise configuration. Team members will collect and analyze the data during the opportunity and report to the Mars Pathfinder project on the state of the vehicle.
The cruise phase of the mission also affords additional opportunity for access to the 'Sojourner' rover. Testing and operation of the SIM vehicle may result in a recommended update of the stored software prior to initiation of surface operation at Mars. Upon approval of the project, such update will be incorporated at an opportunity during this phase of the mission.
The MFEX team will support the Mars Pathfinder project during its preparations for operations during the landed surface phase of the mission. This activity will include :
development of the nominal scenario for
the first 30sols of surface operation
support in the definition of experiments and utilization
of data collected by the 'Sojourner' rover during its operation for 'cross-disciplinary'
science conducted as part of the mission
participation in training exercises conducted with
the operations team. Such training exercise involve both team personnel
on station, and configuration and use of the SIM vehicle in support of 'real-time'
execution of mission sequences
In addition to the project directed training exercises, MFEX team members will schedule and participate in an independent set of training exercises with the objectives of :
training team members in the roles and responsibilities
for downlink data analysis, uplink command generation, experiment planning
and coordination with the lander system
rehearsing time critical functions, ensuring performance
on the nominal mission timeline
developing skills for anomaly detection, analysis
and recovery planning
anticipating modification of command sequences
for execution of key mission objectives and analysis of vehicle response
in a variety of terrain conditions.
To assist in achieving this last objective, some of these training exercises will be performed in a 'field test' environment chosen for similarity to expected Mars terrain conditions.
Supporting the data analysis to be performed by team members during these training exercises (and during the mission), Labview and WEB-based tools will be developed for data display and trend analysis which will assist in evaluation of the state of the vehicle system. These software tools will be integrated with the data analysis workstations and certified as ready for the mission operation. In addition, certain enhancements of the rover control workstation used for image display and command generation will be performed to streamline command sequence development and ensure correctness and completeness of command sequences.
Finally, team members will participate in the landed surface operation beginning at landing on 7/4/97. Two shifts of personnel will cover the 7day per week schedule of operation of the rover during this phase of the mission. The prime mission phase for the rover will complete within the first 7 days. It is anticipated however that rover operations will continue for at least one month and possibly longer (3 months). Plans call for support of team members in operation of the rover throughout an extended mission phase.
During landed surface operations, data is collected from the rover and lander which supports the ten technology experiments to be conducted during this mission. These experiments characterize the rover engineering performance in the Mars environment and assist in imaging and soil mechanics experiments as part of the science objectives of the mission. The main science goal of the rover mission is deployment and gathering of spectra data from the APXS instrument on soil and rocks in the terrain. Lastly, images will be taken by the rover of the lander as part of the engineering assessment of the lander performance.
MFEX team members, including LeRC experiment participants, and Pathfinder science team members will be participating in the evaluation of the data collected during the mission and the generation of reports on the results. A certain degree of this analysis will be performed during the operation phase of the rover mission. At the completion of the operation phase the final reports will be prepared and submitted for publication.
Key Milestones:
Mission readiness reviews - 10/24/96, 11/27/96
Final payload health check - 11/21/96
Launch - 12/2/96 (first day of 30-day launch window)
1st in-flight health check - 12/16/96
2nd in-flight health check - 6/16/97
Landing - 7/4/97 (beginning of landed surface ops)
Completion of prime mission - 7/11/97 (7 sols of
nominal operation)
Point of Contact:
Jake Matijevic
Jet Propulsion Laboratory
Pasadena, CA 91109
818-393-7804
jake.matijevic@jpl.nasa.gov
Long Range Science RoversThe science rover task combines both research and actual system demonstrations as a means of pushing the state of existing autonomous vehicle technologies for long range traverses for scientific exploration of the surface of Mars while maintaining flight program relevance. While the primary focus is research, the planned system demonstrations and scientist directed field tests provide a means of testing the robustness of the technology components within a viable mission scenario/environment. The task will have three distinct components: Rover System; Science System; and Ground System. In addition to the integrated level-I milestones described in the following each subsystem will have its separate level 2 milestones. Level-II milestones are planned to occur about six months prior to the integrated level-I milestones to show the readiness of new technologies in each subsystem.
This task develops long range science rovers with the goal of covering tens of km for long duration missions currently envisioned for sample return from Mars. Enabling technologies are long-distance non-line-of-sight navigation; autonomous confirmation of goals and concatenation of commands; rock fracture and sampling devices; and deployment of multiple instruments. Current microrovers have several limitations that preclude more ambitious science rich missions. They have very limited range (10s of meters), are not capable of sample acquisition and manipulation (i.e., soil and rock acquisition, subsurface access, pointing and burial of instruments), have limited science packages onboard, are designed for short term missions (10 days), and require careful and repetitive ground monitoring and control (limited autonomy).
There is great interest in the science community to explore Mars by landing near interesting geographic areas and moving to pre-selected targets. Rovers are valuable since they can compensate for landing errors, and provide the mobility to visit several sites. At each site, it is desirable to place instruments against outcrops or loose rocks, search an area for a sample of interest, and possibly collect rocks and soil samples for return to Earth. Long traverse will also provide an opportunity to make observations and measurements along the way providing access to a wide variety of rocks from different areas.
This task develops small prototype rovers that will carry several science instruments. It is envisioned that the mass of the flight rover will be 10- 20 kg and that of the science payload 5 - 10 kg. One challenge will be to increase the science payload to rover mass ratio and at the same time achieve long-range and autonomous science experiment goals. This rover will have the capability to perform macro and micro imaging, visual and near-infrared spectroscopy, instrument pointing, sample acquisition, and manipulation. The rover will also carry several yet to be defined science instruments. This task will emphasize scientist involved field testing and long traverses so that relevant onboard and ground based automation tools for realistic surface exploration of Mars are developed. Ames Research Center is collaborating in this task by providing virtual reality displays and ground-based science data analysis and visualization.
An important element of this task is the development of robust autonomous navigation algorithms and associated hardware and software to enable the rovers to traverse to designated locations. Current capabilities lack intelligence required to make global decisions for navigation in Viking Lander II type terrains and cannot determine rover's position particularly for long range traverse.
This task will increase the traverse range of microrovers by 50 times in FY 97, 200 times by FY 98, 500 times by FY 99 and 2500 times by year 2000 relative to Rocky 7's 20 meter nominal FY 96 traverse. The science instrumentation will be increased by a factor of 3 and 4 in FY 96 and 98, respectively. A major contribution of this task is the development of autonomous science experiments with and without a lander.
Technical Approach
This technology development program combines both research and actual system demonstrations to advance the existing autonomous vehicle technologies for future Mars missions. While the primary focus is research, the planned system demonstrations and scientist directed field tests provide a means of testing the robustness of the technology components within a viable mission scenario and environment. The task has three distinct components: Rover System; Science System; and Ground System.
This task evolves the Rocky series rovers to provide a mobility system that is capable of housing additional science instruments, sampling devices, and a mast system for landerless operations. Rocky 7 rover incorporates new elements which allows for soil sampling, mast based panoramic imaging, and sun sensor based navigation. Extensive testing is done both at JPL's Mars Yard and in the desert. The Rocky 7 rover will be upgraded to include technologies that emerge from another rover task that emphasizes lightweight advanced materials, survivability of mechanical components, and thermal issues. This upgraded rover, called Rocky 8, will also includes new elements such as rock sample acquisition, rock polishing and fracturing devices to prepare samples for science experiments and return to Earth.
New navigation strategies and associated hardware and software will be developed to provide robust navigation is rocky terrains. Current behavior based algorithms lack high-level decision making abilities to guide the rover in densely distribute rock fields. Another important research emphasis of this task is to develop techniques to better estimate rover's position both for science activities and global navigation.
The science system provides emulated and actual science instruments that are of interest to the science community. This system develops control capability to traverse and point or place science instruments on specified targets using high-level commands from a ground station. This system also develops onboard autonomous technologies to analyze onboard science data and enable return of only the significant portion to Earth. Opportunistic science experiments will be developed based upon science goals onboard.
The ground system develops an Internet based advanced operator interface enabling many scientists to observe and provide inputs for day-to-day operation of a Mars rover without physically being present at JPL for long duration missions. This interface also provides a simple and essentially free tool for the science community and the general public to observe all rover returned images and the data and at the same time they arrive. This system also enables selected students to participate in rover operations.
Major milestones:
FY 1996:
Development and integration of at least three science
instruments - Q2
Command sequencing and Web-based science target
designation - Q3
Navigation capability for long-range traverse via
the integration of a sun sensor - Q3
On-board monitoring and confirmation for each science
activity - Q4
Autonomous position localization from the lander
via image differencing - Q4
Integrated demo, multiple science operations
for each uplink command using a lander (Level 1 milestone) - Q4
FY 1997:
Development and integration of a 3 DOF mast to
Rocky 7 - Q1
200 m field testing of Rocky 7 with scientist participation
- Q1
1- 2 km field testing (Level 1 milestone)
- Q3
Integration of new light weight mobility system
with Rocky 7 chassis - Q4
FY 1998:
Development of Rocky 8 rover - Q3
Improved navigation algorithms for VL-II terrain
- Q3
Terrain map building and use of virtual reality
to visualize terrain and science data - Q3
Development of a sampling system and sample storage
capability - Q3
Increased autonomy via improved sensing - Q4
4 km field testing of Rocky 8 rover (Level
1 milestone) - Q4
FY 1999:
Rover position estimation using beacon system -
Q1
Rock fracturing and sample selection - Q3
Increased autonomy for science experiment (several
experiments per uplink) - Q4
10 km field testing and science operations
(Level 1 milestone) - Q4
FY 2000:
50 km field testing, hands-off operation (Level
1 milestone) - Q4
Related university contracts which deliver hardware and software to this task are:
MIT, Rod Brooks: Mars Exploration Automated Geologist
MIT, Ken Salisbury: Vision and Touch Guided Grasping
Caltech, Joel Burdick: Advanced Navigation
Collaborative/Other Supporting Work:
Ames Research Center: Virtual Reality
Washington University (Professor Ray Arvidson, and others): Field testing
Professor Goestar. Kligelhofer (Institut fur Kernphysik, Germany): Moessbauer Spectrometer
SoHar Inc: Web Based Interface (SBIR)
Mars Office of JPL: International student involvement
JPL In-Situ Center of Excellence: Infrastructure
Lightweight survivable rover task: Materials and thermal technology
Points of Contact:
Samad Hayati
Jet Propulsion Laboratory
Pasadena, CA 91109
(818)354-8273
Samad.A.Hayati@jpl.nasa.gov
Automated GeologistObjectives
To develop autonomous capabilities using behavior-control methods to enable new classes of planetary exploration missions. The products of this task will feed into the Long Range Science Rover task outlined above.
Approach
The approach is to couple the physics of a robot and its interaction with the environment with relatively simple computational schemes that modulate these dynamics. This leads to very robust systems that can operate over a wide variety of conditions as they vary from the baseline.
Under NASA/JPL sponsorship MIT has developed a micro-rover testbed with an integrated compliant manipulator. Vision based navigation, vision based target approaching and manipuluation have been, or will have been, demonstrated by the beginning of this task. In particular the navigation system has been tested at the MIT AI Lab indoor "moon yard", at JPL's indoor Mars facility and at JPL's outdoor "Mars yard".
The 5 to 10 Kgm rovers navigate autonomously using vision. Rather than use structured light this task concentrates on purely passive lower energy approaches---lower energy in that no lasers are needed, and lower energy in that very little computation is needed. Many individual vision agents will compute desired actions from simple properties of the image. The actions will be combined to produce local navigation strategies. Additionally a manipulator with series elastic springs in the actuators will be used with these rovers. It couples the physics of a real spring with the behavior of a virtual spring to allow for advanced compliant tasks with the arm, such as hammering, splitting, and coring. We will work towards coupling the vision system and the arm, for vision guided manipulation of samples.
Focus and Directions
Subtask 1. Software for automated geologist mission
Integrate the target approaching with the
navigation system so that exploration can continue autonomously without
operator inputs.
Demonstrate a selective target acquisition
system that finds target samples with a variety of different characteristics.
Demonstrate vision based rock sample manipulation.
Show a complete integration of the first
three elements in an example autonomous geologist scenario.
Demonstrate and test the full geologist
scenario in the JPL Mars Yard (Level 1 - November 1997)
Subtask 2. Hardware for automated geologist mission
The MIT micro-rover is operational, but our early experiments suggest a number of improvements that will make the demonstrations of automated geology much more viable. Additionaly we propose starting a transition of our compliant manipulator technology to JPL.
Develop a second generation multi-purpose
gripper for the onboard manipulator. In particular we will include a wrist
degree of freedom. Fortunately this can be accomodated in existing empty
space in the current lower arm link.
Develop with JPL a transition plan for a
compliant manipulator to be installed at JPL. The main choice is whether
to use the 4/5 DOF arm on MIT's micro-rover, or a more capable derivative
6 DOF arm that MIT has developed. (Level 1 - September 1997)
Point of Contact:
Rod Brooks
Massachusetts Institute of Technology
Cambridge, MA 02139
(617) 253-5223
brooks@ai.mit.edu
The general objective of this task is to develop and demonstrate visual perception technology for robotic navigation through a science site. This technology will enable robotic vehicles to traverse a science site, visiting rocks or other objects designated as targets, without use of lander cameras, despite poor dead reckoning, and without range sensors.
The current state-of-the-art in navigation through a science site is the Mars Pathfinder rover flight experiment, which guides rover motions based on images acquired by lander cameras. This approach is not viable for science sites out of sight of the lander cameras. Later Mars Surveyor flights call for traverses of 100 km or more, well out of sight of lander cameras.
The technical objective of this task is to enable rovers to travel from designated target to designated target, arriving within 3 cm of the targets, close enough that a manipulator can easily reach them.
Approach
The approach will locate and track features from the rover's on-board cameras, and determine the rover position through triangulation and filtering against dead-reckoned estimates of vehicle motion. Relative navigation about a science site will be achieved by tracking distinct image features, such as prominent rocks or ledges, and computing vehicle position in a local coordinate frame.
The components of the system will include the following.
1/ Landmark detection, based on color and texture.
2/ Landmark tracking, using correlation and sum-of-squared-difference operators.
3/ Relative position estimation, using the Approximate Transformation approach pioneered by P. Cheeseman and implemented by G. Thomas, and using classical maximum likelihood estimation.
The system will be tested in extensive field experiments conducted at the CMU Moonyard and at selected Ames sites.
Planned Milestones
In Year 1, the task will concentrate on two subtasks: visual tracking and relative position estimation. The milestone for tracking is to demonstrate visual prediction and verification techniques for keeping track of the image coordinates of up to 5 distinct targets such as rocks. The targets may exit and enter the field of view. The milestone for position estimation is to demonstrate a relative accuracy of 30 cm.
In Year 2, the task will extend the tracking and relative position estimation techniques developed in Year 1. For tracking, the task will demonstrate locking onto up to 10 distinct targets, representing a two-fold improvement over the Year 1 result. For position estimation the task will demonstrate a relative accuracy of 3 cm, representing a ten-fold improvement over the Year 1 result.
Also in Year 2, the task will demonstrate automatic selection of geological targets around a natural site 20 meters in diameter that enables the accuracy of relative position estimation to improve over time while traversing the site.
Relation to Other Tasks
The Natural Landmark Navigation task is a subtask of the Perception for Advanced Robot Interfaces (PARIS) task at Ames Research Center. Both the subtask and the task contribute to the strategic objective of enabling terrestrial scientists to experience, explore, and gather information about remote environments, especially the surface of Mars. The subtask will deliver software and written materials to Ames, and will support field trials using the Marsokhod and other rovers.
Point of Contact:
Martial Herbert
Carnegie Mellon University
Pittsburgh, PA 15201
412-268-2585
hebert@cs.cmu.edu
Lightweight
and Survivable RoversObjectives
This task develops, demonstrates and quantifies new technologies that will enable low mass, volume, and power (m/v/p) Mars surface mobility in diverse terrain and latitudes. We conceive and implement new integrated system architectures for mobile sample selection, packaging and return functions of the Mars Surveyor Program (MSP), and missions beyond. FY97 work focuses on creating a rover prototype for the Mars Sample Return (cf. MSP '05). The function of this vehicle is to quickly retrieve, e.g., in as little as one diurnal cycle, as much previously cached material in near proximity to a companion ascent vehicle as possible. We benchmark such systems in earth-simulated science operations, performing component-level tests under Mars-relevant environmental conditions. Work of this task began in FY96; results to date are illustrated by the LSR-1 integrated technology prototype in the photo above, shown along-side NASA's recently launched Mars Pathfinder (PF)/ Sojourner microrover flight experiment (MFEX).
The need for enabling advances in low m/v/p rover technology is apparent in recent mission planning of the Mars Program Office (MPO) and MarsSWG/Mars Expedition Strategy Group (MESG). Mars in situ science opportunities are limited by available, affordable mass/volume payload of given launch access options. E.g., the MSP '98 lander allocates a total of only 20 kg and 70 liters to science, with further packaging constraints due to the backshell geometry. Within such costly launch resources, rover design must be optimized for terrain mobility, range, duration, instrumentation, etc. While future long range science rovers (LRSR) may be heavier (15-to-50 kg), they must in turn allocate significant portions of their mass, power and volume (external and thermally enclosed) to science instrumentation and computing. At the other functional extreme, sample retrieval rovers (SRR) -- as will be used in precision-landed, short range Mars Sample Return science activities, wherein precursor missions have amassed sizable cached samples to be collected and protectively quarantined -- will compete sharply with ascent vehicles for launch mass and volume. Thus, light, small, strong, fast rovers will be important assets for sample returns. To the degree that such small rovers can further can allocate mass for contingency sampling and sensing, their science value will be enhanced. Indeed, they will potentially create an important niche for planetary/cometary micro-spacecraft based science exploration. In general, enabling technologies that shift the balance of launched mass/volume/power from the robot to science payload will be key to increased exploration capability, regardless of total launch access payload.
Technical Approach:
We have organized our LSR activities along several enabling technology lines:
1. reduced stowage volume & rover mechanization approaches
2. high strength-to-mass structures and materials innovations
3. high power-to-mass actuation with reduced gearing volumes
4. improved thermal isolation and vehicular survivability
5. reduced computation & power use in sensing and control
The first thrust develops rover mechanical architectures that stow to small fractions of their operational volume, with benefits of increasing rover terrainability from given launch volume, and/or freeing launch resources for additional science. Example: Mars VL2 (~18% surface area rock coverage) or better mobility within 70+ liters (cf. Sojourner). Building on experience with four and six-wheel designs (incl. team participation in MPF/Sojourner), we seek to develop a low mass, collapsible wheeled mobility system (wheels and running gear) that stows to 25% its operational volume. FY96 work demonstrated a first concept collapsible hybrid metal/composite wheel stowable to 30% volume (LSR-1 wheels above, shown prior to final bonding of 2D composite growsers). FY97 efforts develop a complementary collapsible running gear; out-year efforts investigate alternative rover kinematics, deployment mechanization, and novel approaches to mass/volume-saving "WEB-less" thermal structure integration.
Closely coordinated with this work, the second thrust (leveraged in part from the JPL Micro Lander Dexterous Manipulators task) pursues the creation, machinability and environmental testing of light composite materials from which to fabricate mobility and chassis elements. Success - the innovation of new environmentally robust, easily formed/machined 3D (isotropically strong) and 2D/3D (selectively strengthened) composite processes - could reduce vehicle mass up to 50%, improve DTCE match in integrated rover structural design, ameliorate chemical interface effects, etc. FY96 work developed the LSR-1 six-wheel rigid running gear as a first proof of principle (2D composite linkages and a 3D machined composite joints). FY97 efforts will produce collapsible running gear noted above. We are also developing improved material processes and higher strength:mass gear for high payload LRSR applications (note: the LSR task delivers a lightweight LRSR mobility system as a FY97 milestone). Significant research problems remain open in this effort, including selection of an optimal matrix (resin), definition of process cure cycles for high yield and low work machining, evaluation of relevant static and dynamic loading properties, lubricant interface behaviors in Mars relevant thermal/atmospheric conditions, radiation effects relative to matrix formulation, etc. The general direction is toward - with accompanying thermal design advances below - development of an all-composite, ultralight rover mechanical architecture. FY96 trends are encouraging: the 100 cm x 70 cm six wheel LSR-1 mobility subsystem, with actuation, weighs less than 3 kg.
The third thrust explores alternatives to rover actuation by conventional brushed/brushless DC motor and planetary gearing (cf. Sojourner). High torque-density, high non-actuated holding force, reduced gearing complexity/weight, and multiplexed drive (multiply actuated degrees of freedom, wheels, arms, etc. by one motor) are of interest. Cumulatively, such advances will reduce rover actuation mass, lower power requirements, and enable new small rovers capable of very high payload (e.g., fast/highly efficient sample return). One promising actuation approach, being developed in concert with the JPL Micro Lander Dexterous Manipulators task, MIT, and an industrial TCA partner, is a new class of space-targeted rotary ultrasonic motor (USM). FY97 work provides a first prototype for such a motor, and initiates its environmental characterization; FY98 work will continue environmental analysis and demonstrate the motor within a functional wheel drive assembly. Pending positive outcome of these studies, FY98-99-outyear work will develop/demonstrate mobility and performance characteristics of a small USM actuated rover platform (1-3 in-lb), as well as provide proof of concept for scaled-up USM designs (5-15 in-lb) supporting larger, long range rover mechanization. Finally, we will investigate the development of lighter, longer lived gears, their mechanical characterization in relevant environments, concentrating on plastic alternatives to metals and their tribology.
The fourth thrust develops thermal mechanization approaches to use of rovers in colder, more extreme Martian environments over longer duration. The primary emphasis is more robust thermal control, to be implemented without increase in rover mass, significant reduction of science volume, or increased rover integration complexity/reliability issues. Initial results are very promising, During FY96 we conceived an approach to integrated rover thermal/structural design, wherein the Warm Electronics Enclosure/Box ("WEE/B") was implemented in sheet-and-spar glass epoxy, carrying all non-mobility mass (via rocker pivot cups affixed directly to its sides, cf. LSR-1 photo above). Within this design we introduced: 1) a new opacified aerogel insulator (walls) that reduces thermal losses up to 30%, and 2) in cooperation with a NASA Mars Exploration Technology (MET) program innovation in thermal materials, a means of Phase Change Material (PCM)-based thermal stabilization that reduces temperature swings from -40-to-40 C to -40-to-0 C for nominal Mars environments. By comparison to the MPF Sojourner flight rover, the new WEE achieves almost twice the isolated volume at given mass. FY97 begins a environmental characterization of this WEE concept, including finite element model-based analysis, and consideration of WEE interactions with relevant power sources such as new Li-ion low temperature batteries being developed in the aforementioned MET program. FY98 develops improved cabling interface design (a major source of rover heat losses) through introduction of a new conformable "cable tunnel" enabling multiple WEE assemblies/re-integration without loss of thermal integrity. Out-year work shifts the rover design paradigm to "WEB-less integration": decentralized thermal controls relying as much as possible on ambient electronics and localized thermal reservoirs/heating for temperature stabilization. The system payoff is potentially great - ultra-light, agile rovers, stowable to flexible and very small form factors.
The fifth thrust focuses on developing sensing and controls suitable to small, light, low power rovers. FY96 work developed, optically modeled and experimentally demonstrated first proof of concept for a novel "spot-pushbroom" active terrain sensor: near-infrared, quickly pulsed laser diode emissions are diffractively projected to a linear array of spots that "sweeps" the rover frontal terrain during a traverse. As imaged onto forward looking CCD cameras, and selectively scanned - at reduced computation by comparison to passive stereo correspondence ranging (a ranging mode requiring significant terrain featuring/texture) -- the projected spot positions can be analyzed (inverse geometric reconstruction) to estimate terrain topology. FY97 work develops related speed-up and reactive hazard avoidance algorithms. Complementing this, enabling the sample return function, we develop a baseline approach to visually detect and localize (position/aspect) a cache for SRR terminal approach and pick-up. FY98-99 work develops continuous terrain estimation, to enable predictive hazard avoidance and safe path traverses during fast area-wide searches for sample caches, and combines visual active-and-passive ranging modes (pushbroom and stereo) for improved terrain and cache discrimination. (Note: navigation developments are coordinated with the Long Range Science Rover task, including common software). Work of the last area draws on research of NASA-funded contracts at MIT (S. Dubowsky) and USC (G. A. Bekey), respectively in physically based planning of mobility strategies, and rover multi-sensing.
Major Milestones:
FY 1996:
Develop collapsible rover wheel concept
and prototype - Q2
Develop and demonstrate laser spot-pushbroom sensor
- Q3
Develop thermal/structural integrated WEE prototype
- Q3
Develop, demonstrate, and evaluate for local area
science sorties (10 meter dead-reckoning, MarsYard) in various VL1/2 class
terrain, a new light, volume-efficient rover mobility design, having a 20
cm, dia. collapsible wheel stowing to ~30% operational volume (Level
1) - Q4
FY 1997:
Develop engineering design for Sample Retrieval
Rover (SRR) - Q2
Develop WEE models (FEM) and perform low-temperature
tests - Q3
Develop and demonstrate a collapsible mobility
frame concept - Q3
Develop a LSR-based long range mobility sub-system
(e.g., as consistent with 30-50kg LRSR/'01 applications) - Q3
Develop and implement an approach to visual cache
acquisition (navigation to cache site, cache localization, and pick-up)
- Q4
Design and implement a Sample Retrieval Rover (<8
kg with cache), demonstrating it in simulated near-field (<100 meters)
operations for navigation, localization, pick-up and transport of a cached
sample of known location (Level 1) - Q4
FY 1998:
Develop and demonstrate high-strength, thermally
robust mobility platform components based in hybrid light 2/3D composites
- Q2
Conceive, design, implement, and test a conformable
"cable tunnel" for low thermal loss WEE computing/science integration
- Q2
Develop a LSR-based thermal/structural integrated
chassis prototype (e.g., for 30-50 kg LRSR/'01 applications) - Q3
Develop and evaluate USM-based wheel actuation
concept - Q3
Develop and demonstrate fast visual terrain estimation
and mobility control for area-wide cache search - Q4
Demonstrate an end-to-end "find-cache"
rover sequence: survey a nominal 100x100m^2 area, localize a sample from
a previous mission, and return this package to a simulated ascent vehicle,
with assumed containerization/quarantine constraints (Level 1) -
Q4
FY 1999:
Develop an ultra-light all-composite, collapsible
mobility platform (incl. long-lived, low-temp. plastic gearing) - Q3
Develop and prototype a new chassis concept for
"WEB-less" distributed thermal controls and electronics/science
interfaces, used in conjunction with an ambient computing implementation
- Q3
Develop and demonstrate techniques for multi-sensor
terrain mapping, predictive mobility, and hazard recovery strategies (incl.
FY97/98 developments of MIT and USC contracts) - Q4
Conceive, design, and environmentally characterize
a "WEB-less" ultra-light, highly stowable microrover (target:
2-4 kg, 10 liters) for extended duration operation (9-12 mos.); demonstrate
for MSR cache retrievals, and simple science/sampling (Level 1) -
Q4
Out Years:
Develop a telerobotics technology framework and system demonstration paradigm
for opportunistic science by one or more cooperating small, functionally
specialized lightweight utility rovers, in support of 2005-beyond landed
MSR missions (precision landing capability assumed): E.g., 2-to-5 kg, 5-to-50
liter (stowed) LSR's performing wide-baseline stereo terrain mapping, beacon
triangulation and/or self -beaconing; near-lander scout, survey, science
instrument transport-emplacement-collection; long range piggyback as a deployable
science module, multi-km carrier and local comm. support for nanorover )
Actuator and thermal development for extended
habitation at mid-to- high latitudes (thermal cycling, tribology and intermittent
ops. issues) - FY00, Q2
Micro-miniature sampling mechanization for collection,
and ad hoc containment of multiple pristine surface samples over an area
- FY00, Q3
Terrain map building/traverse by multiply situated
rovers (fusion of partially uncalibrated, moving sources) - FY00, Q4
Low power techniques for subsurface sample extraction
in more favorable terrains (incl. mechanization to secure, stabilize and
release the rover) - FY01, Q2
Demonstrate advances in integrated mechanical performance
of an ultra-light rover and with active surface/sub-surface sampling tools,
applying same to the simulated extraction, containment, and cached return
of multiple small pristine samples (Level 1's) - FY00/01, Q4
Current Grants or Contracts:
The JPL Planetary Telerobotics element supports work at MIT/AI lab (R. A. Brooks; J. K. Salisbury), MIT/Mechanical Engineering (S. Dubowsky), and Univ. So. California (G. A. Bekey) with which we have established collaborative design and experimentation efforts in several key areas. These include vision and touch guided grasping for rover based sampling functions (MIT-jks), techniques for compliant actuation (MIT-rab) and high-precision long-reach manipulation (MIT-sd), physically based modeling and robust synthesis of rover mobility tasks (MIT-sd), experimental definition and benchmarking of rover mobility (USC), and multi-sensor fusion for robust rover navigation in Mars environments (USC).
Collaborative/Other Supporting Work:
Work leverages other tasks of both the NASA TR and MET Programs. This includes USM actuation and small composite sampling arm concepts under development in the TR Planetary Dexterous Manipulators task (cf. MLDM task FY96); also application of novel thermal materials (PCM), and low temperature batteries being developed in the MET Survivability technology thrust.
Points of Contact:
Paul Schenker
Jet Propulsion Laboratory
Pasadena, CA 91109
(818)354-2681
paul.s.schenker@jpl.nasa.gov
NanoRover
Technology
The second class of rovers are very lightweight--on the order of 10gms. In this task we will work closely with JPL to develop a generic platform which can accomodate a variety of JPL produced micro instruments. We will use ideas developed earlier in the program to have many of these very small rovers cooperate, without any global control system. Rather, local communication and signalling will be used to have a provably correct set of global behaviors emerge. MIT developments will be demonstrated on the MIT Ant Farm.
Recent advances in microtechnology and mobile robotics have made it feasible to create extremely small automated or remote-controlled vehicles which open new application frontiers. One of these possible applications is the use of nanorovers (robotic vehicles with a mass of order 100 grams or less) in planetary exploration. Such vehicles could be used, for example, to survey areas around a lander, or even to conduct long-range missions of exploration doing surface chemical analysis or looking for a particular substance such as water ice or microfossils. The objective of this task is twofold: to create a useful nanorover system using current-generation technology including mobility, computation, power, and communication in a ~100 gram package, and also to advance selected technologies which offer breakthroughs in size reduction, mobility, or science return.
NASA Code-S planetary missions have been under increasing pressure to reduce their launch mass requirements so that less expensive launch vehicles can be used. To achieve those aspects of scientific exploration requiring mobility, any rover component of the science payload must compete effectively in terms of mass against other payload options. Nanorover technology would allow some mobility-based science surveys, such as mineralogic classification or the search for water ice or other volatiles, microfossils, or other entities at or very near the surface with a small, perhaps negligible fraction of the science payload for Mars Surveyor class missions. This latter point makes it conceivable that nanorovers could fly as a secondary payload on most landers using whatever mass margin is left over at launch time. Alternatively, they could be the prime payload of microlanders for Mars, small bodies, or the moons of the gas giant planets. The vehicle developed thus-far in the Nanorover Technology task is considered as the only serious candidate for NASA participation in the Japanese MUSES-C mission which will return a sample from the asteroid Nerius, launching in early 2002. The chairman of the NASA Small Body Science Working Group (as well as of the MUSES-C Science Working Group) Joe Veverka has stated that "the value of [NASA/ISAS] cooperation would be increased dramatically by the inclusion of a NASA-provided, scientifically instrumented microrover". He further states that the science goals of the [1 Kg max] rover will be to make "texture, composition and morphology measurements of the surface layer at scales smaller than 1 cm, investigations of lateral heterogeneity as such small scales, investigation of vertical regolith structure by taking advantage of disturbances of the surface layer by microrover operations, and to measure constraints on the mechanical and thermal properties of the surface layer." The nanorover was also recently demonstrated for the Committee on Planetary Exploration (COMPLEX) of the National Academy of Sciences, who expressed considerable interest and excitement at the possibility of these relatively low-cost, high-science return missions.
Technical Approach:
This task has first established a credible science instrument suite which can be integrated within the mass and power budgets of a nanorover, and then proceeded to design the other elements of the rover into a highly integrated "sciencecraft" system. Alternative instruments of many sorts were considered; a multi-band visual imager with near-IR point spectrometer has been selected. This combination is the lowest mass, highest science return instrument complement which can be integrated at acceptable cost, which works in Earth test environments, and which involves no radioisotopes or ionizing radiation. Using the Active Pixel Sensor 256x256 imaging array developed in the JPL MicroDevices Laboratory (MDL), the camera with filter wheel will give images in a number of spectral bands in the visible out to about 1 micron with resolutions as high as 10 microns per pixel. By covering the wavelength range of 1-2.5 microns, the near-IR spectrometer will give mineralogic data on a huge variety of possible minerals including important clays and carbonates. As part of the MUSES-C activity, an Alpha-Proton X-ray Spectrometer (APXS), miniaturized from the one being flown on the Sojourner rover, is being actively considered as a third instrument. This science complement would give essentially complete and unambiguous mineralogic and morphologic information about the target sites visited.
This task has developed a high-mobility vehicle configuration which can meet the mission and science requirements. This "posable bogie" concept is for a self-righting and/or upside-down-operable articulated vehicle chassis. It includes the ability to recover from overturning as well as body pose control for camera/instrument pointing, sampling, or other functions. It accomplishes this with a remarkably simple, top/bottom and right/left symmetric mechanism which has a small number of moving parts and very low mass. Motors, which are normally the most massive single element of a miniaturized vehicle chassis, are only needed for the wheels; the additional degrees of freedom which accomplish the other functions are entirely actuated using these same motors. Operation in extremely low gravity (e.g. on the surface of an asteroid) can be accomplished since no free pivots are used (which would have too much friction to articulate freely in a microgravity environment). No prior vehicles are known which combine many or most of the desirable features achieved in this design:
can operate upside down
can intentionally flip over and recover
from accidental overturning
can place the body flat on the ground (e.g.
for sensor placement)
can lift wheels and set them on top of obstacles
(instead of pushing the wheel against the obstacle and requiring enough
traction to lift the wheel against gravity)
are actuated only by one gearmotor for each
wheel (no additional motors are needed to actuate the additional degrees
of freedom)
allows torque from the gearmotor driving
one wheel to assist another wheel when extra torque is needed
can articulate to keep all wheels providing
optimum traction even in arbitrarily low gravity fields
can "hop" and reorient the body
during ballistic hops in very small gravity fields
The main chassis of the vehicle is composed of two printed circuit boards, which on the inside face have all the electronic components mounted, and on the outside have the solar cells, radio antennas, proximity sensors, etc. The kevlar circuit boards plannned for the flight version are very strong, light, and have low thermal expansion, and so make good structural members. These circuit boards are used as the "optical bench" of the camera and spectrometer, thereby making maximally efficient use of available mass. This is a special case of the "sciencecraft" development philosophy: perform maximal cross-utilization of all components to maximize science return while achieving necessary engineering functions.
One particularly good example of this maximal cross-utilization is the focus mechanism of the camera. Interviews with planetary scientists confirmed that a sequence of images is needed to establish scientific context when a science target such as a rock is approached. Each image should have a scale no more than 2-5 times smaller than the previous image. At the finest scale, the images must give a resolution of better than 10 microns per pixel if most crystal boundaries are to be seen and cleavage angles measured. These constraints can be shown to require that there must be a mechanical focus mechanism which can be positioned accurate to about 1 part in 1000 over a lens stroke of about 3 cm.
The existence of this focusing mechanism has profound consequences for the configuration of the spectrometer. Conventional wisdom in the flight community is to use detector arrays to avoid the mechanical scanning which historically was used to multiplex a point detector over a span of wavelength or a spatial dimension. However, because we already plan to have a precision scanning mechanism for camera focusing, we can use it also to scan an "inexpensive" (but still many $K) point detector over the infrared spectrum. This also increases the performance, because 1000 element IR detector arrays (the effective number needed to equal the performance of the mechanical scan mechanism) do not yet exist (and even the 256 or 512 detectors are too expensive for this task).
The optical elements needed to meet the science requirements set the overall scale of the vehicle developed in the first two years of the Nanorover Technology task at about 15 cm. This scale sets the area of the top surface, which is used as the solar panel. This collection area sets the available power budget (Pathfinder plans 7mW per sq. cm.), which will be greater than 0.5 watts for four to six hours per day for most Mars mission scenarios. This power level is barely adequate for direct communication to orbiters around Mars, and thus this scale vehicle is attractive for several mission scenarios. (A similar situation arises in the case of the MUSES-C mission, where the entire power budget of the first generation nanorover is needed to allow any communication at all with the Japanese orbiter.) Key elements of research for the next generation nanorover (about half scale and one-eighth the mass of the first generation) include reducing the volume required for the instruments, building actuators smaller than the smallest commercially available gearmotors (and which can also withstand the thermal/vacuum requirements of Mars and small body missions), creating behaviors which can effectively utilize the posable bogie chassis to achieve the full potential of its mobility and instrument-pointing capability, developing and implementing advanced dust control techniques to keep the optical surfaces effective in a dusty environment, and developing and implementing flight qualifiable means for communicating which meet the mass and power requirements of the nanorover.
Major Milestones
FY 97
Prototype Nanorover operational with posable
bogie mechanism - Q2
Optical bench test of camera and IR spectrometer
- Q3
Miniaturized wheel motor able to withstand
thermal/vacuum reqs - Q4
Tetherless Nanorover (of order 100s gm)
operational with imaging and near-IR spectrometer (level 2 milestone)
- Q4
FY98
Posable bogie incorporating flight microactuator
designed - Q2
Miniaturized instrument complement defined
- Q3
Advanced electromagnetic and mechanical
dust sensing and control to clear optical surfaces of dust (level 2 milestone)
- Q4
FY99
1/2 scale posable bogie prototype - Q2
Miniaturized instrument complement prototype
- Q3
Long-range Nanorover operational miniaturized
by factor of 2 in scale (factor ~8 in mass) over FY'97 prototype (level
1 milestone)- Q4
Other Agency Sponsored Activities:
This task, which focuses primarily on the engineering issues for practical rovers, is coordinated with a NASA-funded behavior-control research task led by Professor Rodney Brooks of MIT, which concentrates on advanced miniaturized but non-flight mobility systems and software architectures for autonomous and cooperative behavior. Both annual and ad-hoc exchange visits are conducted which coordinate infusion of MIT technology into this task.
Points of Contact:
Brian Wilcox
Jet Propulsion Laboratory
Pasadena, CA 91109
(818) 354-4625
brian.wilcox@jpl.nasa.gov
Exploration Of Small BodiesObjectives
The objectives of this task are to develop the enabling technologies necessary to accomplish in-situ scientific studies of small interplanetary objects such as comets and asteroids. Planned research of these small bodies faces a number of key challenges. Landing in the extremely low gravity environment (ranging from 10-4 to 10-2 m/sec2) requires a method of retaining the Lander to the surface, and rendezvous impact energy must be absorbed without causing the Lander to merely "bounce off". The near absence of gravity, and the assumed aggregated morphology of comets, holds the promise of the most rugged terrain ever to be autonomously landed upon. Science goals require that the Lander cannot cause sublimation of the substrates to be sampled. Surface and subsurface sampling will impart forces that may eject the Lander from the body (as may surface sublimation). Therefore, to meet the objectives of this task a Landing System has been configured to accommodate rugged terrain, provide "low rebound" impact absorption and to anchor the Lander to the surface, with all elements designed to operate at 120°K. A Drill and Sampling System is in development to acquire and transport subsurface materials to science instruments, again entirely under cryogenic operating conditions. The near term objective will be to develop these systems for "single site exploration" using an integrated prototype tested in the relevant environments. The objective in the out years will be to investigate the technologies necessary to accomplish "multiple site exploration."
This task has applicability to a number of proposed Discovery and New Millennium missions to comets and asteroids. Particularly relevant is that this task has been conceived to develop technology that meets the low mass, low power and low cost requirements of the new wave of smaller "science-craft". The Landing System promises to be a robust but low cost approach and may be extrapolated to planetary landings as well. The Drill and Sampling System will be applicable to planetary missions such as Mars Exploration. A number of key technology developments of this task are directly applicable to cometary lander mission designs such as Champollion, currently undergoing development by NASA Code S.
Approach:
Considerable study resulted in the conclusion that an articulated, three legged Lander configuration would provide the most robust design and meet a key requirement for cryogenic operating temperatures. This approach of using a deployable leg configuration is similar to landers of the past in providing a large footprint that will react against the overturning moment from horizontal landing velocities and accommodates high relief in the terrain. The proposed Lander leg is a new design, consisting of a tripod of damping struts and a footpad with a pyrotechnically-fired tethered anchor, integrated with a winch mechanism. This would be a "smart" Landing System, in which embedded sensors in the basebody, footpads and anchors will control the winch motors to arrest Lander tip-over under extreme terrain conditions. By using the existing gyros in the basebody, added accelerometers and a controller, a dynamically stable landing can be assured that minimizes the force that each anchor must retain. This effort is a key advancement in the state of the art, as previous Landers used rocket propulsion to provide a stable rendezvous with the surface and had the stabilizing force of gravity to arrest tip-over. "Low rebound" damping struts, using vacuum-qualified polyurethane foam, have been developed that provide significantly less returned energy than the aluminum honeycomb dampers of Viking and Apollo. A pyrotechnic device to fire tethered anchors into substrates that range from 10-4 to 102 MPa compression strength and provide adequate retention force is in development. Another key technical challenge is to develop the integrated winch system which must allow the anchor to fly free, yet grasp the tether, arrest potential Lander roll-over and retain the Lander to the surface for drilling. Extensive ADAMS kinematic modeling has demonstrated the capability of this system to provide a stable Landing.
The Drilling and Sampling System also must successfully operate against a wide range of substrate properties and at cryogenic temperatures. Closed loop control has been integrated in the mechanism to allow this "adaptive" drill to choose the correct drilling parameters for the entire range of substrate properties and to limit the forces that must be resisted by the anchoring system. The Drill Controller will enable the attainment of useful scientific information by recording the data received from the embedded control sensors. The Drill Mechanism will be calibrated against a number of terrestrial minerals and comet simulants. Scientific information such as hardness, density and data on inclusions or porosity can be obtained by the performance of mechanical tests on an unknown substrate by the Drill.
Initial efforts in the remote sensing of the landing terrain and on-board autonomous hazard avoidance will be funded through this task. To be investigated will be the required software tools to identify potential landing sites that are free of hazards, evaluate the perceptual stability of the landmarks and to verify that the features can be tracked by a descending Lander. This effort will utilize a 3-D model of a comet or asteroid rather than image maps obtained from an orbiter. Monte carlo simulations will be performed to verify the stability of proposed landmark features against varying illumination and viewing angles, and whether the features are likely to be tracked reliably during descent.
Milestones
FY97
Calibrate Drill System adaptive controls
to known substrates. FY97, Q1
Demonstrate/verify sealing of anchor pyro
device in cryo-vac. FY97, Q2
Complete brassboard anchor tether &
winch system. FY97, Q3
Fabricate, assemble and test integrated
anchor & winch system. FY97, Q4
Perform cryo-vac verification tests of autonomous
Drill & Sampling System. Obtain 20% mass reduction in Drill Mechanism
(Level 1 Milestone). FY97, Q4
Perform "end-to-end" Lander system-level
test demonstrating "smart landing" with integrated sensors. The
capability target is to perform landing sequence (anchor firing and winch
operation) autonomously to demonstrate a dynamically stable landing (Level
1 Milestone). FY97, Q4
FY98:
Design and analyze lander mobility system
and develop control concepts, including retention to surface requirements.
FY98, Q2
Demonstrate Lander mobility conceptual model
(hopping or crawling), verifying impact absorption and surface retention
(Level 1 Milestone). FY98, Q4
FY99:
Integrate mobility systems into Lander testbed
and demonstrate impact absorption, retention and mobility (Level 1
Milestone). FY99, Q4
Point of Contact:
Donald R. Sevilla
Jet Propulsion Laboratory
Pasadena, CA 91109
818 354-2136
Donald.R.Sevilla@jpl.nasa.gov
Micro-Lander Dexterous ManipulatorsThis task develops new robotic system concepts and technologies for planetary surface science. The primary applications are sample acquisition functions of the NASA Mars Surveyor Program (MSP). When integrated with future lander platforms and roving vehicles, technology products of this task will enable scientists to dexterously view, probe, freshly expose, acquire, and containerize surface and near surface samples -- for in situ analysis and protective containerization and return to earth -- thus advancing knowledge of Martian geologic and biologic evolution, climate, and prevailing resources.
As shaped by interests of the Mars science community (e.g., Mars Science Working Group - MarsSWG), the range of Mars Surveyor Program (MSP) mission activity spans the upcoming Mars '98 polar lander (MVACS) to a 2005 sample return with rover based sample collection & caching activities part of the planned '01 and '03 mission sets. Robotics, essential to enabling envisioned lander and mobile science sample collection and analysis, will confront fundamental challenges in mass/volume/power reduction, while also addressing requirements for dexterity, survivability, operational range (rover) all relative to nominal daily communication downlinks from unstructured, highly variable physical environments. There does not at present exist enabling technology solutions to span envisioned MSP requirements.
Among these requirements are frequent in situ interactions with the planetary surface:
close-up viewing (micro-camera and/or imaging
spectroscopy)
analytic probing (point spectrometer or
meteorology sensor)
instrument emplacement (APX, NMR, Mossbauer
spectroscopy)
material extraction (trenching, abrasion,
coring and granulation)
sample-exposure-acquisition-manipulation-and-containment
(grasp-and-turn-for-view, pick-and-place, expose and collect)
The goal of this task is to provide breakthrough robotic solutions for known Mars community surface/near-sub-surface sampling interests, working within projected MSP mission design constraints. Beyond this MSP-driven goal, we more generally seek to develop a core of reference robotic component technologies robotic concepts, actuators, material processes, and benchmarks that may provide a baseline for mass/volume/power (m/v/p) efficient sampling on other solar system bodies. Mars Surveyor '98 landed science package constraints are illustrative of challenges that will drive these developments the NASA MSP'98 Science AO/PIP guidelined a nominal mass/volume/power/cost budget of 20 kilograms/70 liters/25 watts (day average)/$20M. Of the proposing science teams, most allocated 20-40% resources to robotics. It was generally held that lander deck robotic science operations should be 5Kg/10L(stowed)/10+ W at 20-30% of science cost with two or better meter reach to the near field. The '01 mission m/v allocation is potentially greater (under AO/PIP specification process at this time), with far greater expectations of the long range sampling rover facility it is intended to host. Thus, there are significant pressures to develop cost efficient, very lightweight, highly volume efficient robotic mechanization, as this task has already done for Mars'98. NASA has now committed aggressively to rover-based missions for '01-05 (and after) Mars explorations. It is thus imperative maximize the strength, dexterity, and function of rover sampling assets relative to mass/volume allocable to on-board science instrumentation and cached samples. Further, MarsSWG interests in climate, life, and resource in situ analysis span the equatorial to polar (> -70 S) regions over both changing seasons and full diurnal cycles -- potentially subjecting robotic components to extreme temperatures (<-100 C) and thermal shock, as well as atmospheric, chemical and radiative/UV degradation considerations. We note also that recent Mars '01 science planning more strongly emphasizes fresh rock exposure, and we are accordingly including appropriate sampling arm effector concepts/devices are explored in our FY98 task work.
Technical Approach:
We have broken our attack on the task objectives into three closely linked task thrusts -- robot design & mechanization, advanced robotic materials, and advanced actuators. The class of robotic science operations we investigate are diverse, and will require well-coordinated advances not only in these mechanization areas, but also sensor-based robotic control for remote unstructured, uncertain environments (e.g., task-adaptive contact interactions with highly variable media, visually guided positioning, etc.). In this Telerobotics Program task, we focus on enabling mechanization issues. We conduct complementary R&D of the latter sample acquisition automation & control strategies in a related task of the Mars Exploration Technology Program (See "MET/Sample Selection and Packaging," NASA PBS 1.6.1.3). The PDM task is in its third year of activity, and we outline a plan that will conclude efforts in FY99, approximately in alignment with earliest projected MSP '03/'05 technology "freeze" points. We present the task sequentially, briefly recapping relevant prior FY95-96 outcomes, detailing our ongoing FY97 work as motivation for further advances, next describing the proposed FY98 main thrusts, and finally summarizing further directions and rationale for FY99 developments. At the end of this section, we list corresponding yearly Level 1 Milestones, FY95-99.
FY95 work developed a lightweight, stowable lander-manipulator, MarsArmI -- a 3-dof lab gas-deployable segmented (telescopic) composite link robot. MarsArmI uses brushed DC terrestrial motors, highly geared planetary/harmonic metal joints, and a one-dof actuated "back-hoe" style effector for open face trenching. We demonstrated (coordinated motion) open loop joint position control of trenching, end-of-arm viewing, and point spectroscopy.
FY96 work made major advances in arm (and rover!) enabling component technologies. We developed MarsArmII, similar to MarsArmI, but 40% lighter, having a pitchable wrist d.o.f. and powered effector, the entire assembly of all-composite construction. The multi-function effector includes an opposable jaw gripper (>10 in-lbs at tip), micro-viewing camera, and active abrader (DC-motor driven) for shallow exposure of fresh rock. The enabling composite, developed within this task, and also utilized to create the LSR-1 vehicle (Lightweight Survivable Rover task), utilizes an air lay-up 3D carbon fiber preform and resin transfer mold process, tunable in thermal/mechanical properties by choice of matrix (epoxy, polycyanate, etc.). This "black Aluminum (JPL/Caltech NPO filed)" composite is machinable through conventional metal shop practice, enabling formation and integration of complex, mass-versus-stiffness optimized parts.
A major feature of the FY96 MarsArmII deliverable was first integrated use and precision control of the ultrasonic (USM) rotary actuators being developed for space-qualified applications within this task. We employed three such 6 in-lb USMs in MarsArmII (and a related 1 in-lb device in the wrist pitch joint), and through the companion MET/Sample Acquisition task developed accompanying servo and inverse kinematics positioning controls. These controls included visually- referenced operator designation in a stereo workspace of target sampling objectives, and a new higher-level task control architecture enabling dexterous, adaptive actions: This "Goal Oriented Behavior Synthesis (GOBS)" intelligent control architecture is a task-extensible approach to programming critical sampling skills such as trenching, rock sampling, close-up viewing, rock/soil probing, etc., wherein the robot in real time can sense and correct for its errors/uncertainties in position and force (see references, 10/18/96 TRIWG task report). This provides task robustness, enabling the task to proceed autonomously, adjusting to a priori unknown environmental circumstances. As a specific example, MarsArmII was utilized under GOBS-based control to demonstrate adaptive impedance control for trenching, wherein the robot, discovering ground plane mis-positioning relative to visually designated location, changing soil simulant conditions, and/or hard sub-surface obstacles, recalibrated its local workspace and computed an adaptive trajectory to complete the trenching task. As later discussed, we are generalizing this capability for use in rover-based dexterous sampling in FY97, to be first implemented on the FY97 Level 1 deliverable, MicroArmI (shown above in very early mock-up, mounted to LSR-1). Relative to the FY96 USM developmental work itself there were several important advances achieved by a joint JPL/MIT (N. Hagood)/Quality Materials Inspection, Inc. (Costa Mesa, CA, based TCA partner) team: 1) created and characterized various rotary ultrasonic motors (USM) as potential mass/volume/power-optimal solutions for a wide class of planetary robotic (and small spacecraft) applications -- this entailed significant design, fabrication, and laboratory test/trade studies of materials, emphasizing the critical rotor-stator interface design for high-efficiency wave transduction and thermal DTCE match; 2) conducted first cryo-vacuum tests of a USM, with successful operations to ~ -50C; 3) developed a highly accurate FEM design tool (modal analysis, drive frequency, etc.), and validated in parametric experimental studies and in situ analytic/diagnostic electronic speckle pattern interferometry (ESPI); 4) demonstrated, with MIT, two new high-power motor designs, one reaching 16 in-lb in preliminary tests, a best result reported to date.
FY97 shifts the task focus from large lander arms to scaled-down rover-based sampling arms. As general goals, we seek to develop robots of 1-2 Kg class, .5-1.0 meter extent, and capable of as much lift/force-to-mass as possible. The general arm architectures remain like those successful to date in our MarsArmI&II/Mars'98 concept three or four degree-of-freedom, serial link, independently actuated manipulators, incorporating as much end effector functionality as consistent with rover m/v/p constraints. There are two applications & integration foci for these small arm developments: rover sample acquisition and rover sample return. In the first area we are initiating development of an arm intended to become a prototype of a light sample selection & caching arm for the Mars '01 and '03 rovers. As such, members of this team are currently participating in a Mars'01 facility Rover Design Team definition effort (D. Shirley/MEP). As discussed in more detail in the FY98 LSR (Lightweight Survivable Rover) task proposal, JPL is developing a next-generation lightweight "Rocky" series vehicle, to integrate end-FY98, utilizing a rover mechanical architecture derived from LSR efforts, and an arm deliverable from this PDM task. We demonstrate first rough proof of concept with MicroArmI, the FY97 Level 1 task milestone deliverable. MicroArmI is a 4 d.o.f., all composite, commercial USM (1 in-lb Shinsei motor) driven manipulator of t/s/e configuration, pitchable wrist and multi-purpose, gripping end-effector. This arm of .7 meter full extent, 1.25 in link diameters, and 1.25 Kg mass -- will be mounted and demonstrated on the LSR-1 platform to perform the following science functions:
sample acquisition and on-board storage
(sample caching concept)
trenching and digging of rover soils surrounding
the rover
sample manipulation including in-situ rock
manipulation (flipping, turning, etc.) and transfer of rock to on-board
science instrument
fresh rock exposure using an end-effector
mounted Dremel-type tool (initial investigation into the feasibility of
tool and method)
close-up visual inspection of with end-effector
mounted micro-camera
integrated force feedback operations for
sample handling tasks
The remote operator visually designates target samples within the MicroArm-I workspace through the stereo camera pair nominally used for the obstacle-avoidance aspect of rover navigation (we are investigating other more novel visual designation/servo/ranging concepts in the MET/Sample Acquisition task, including use of a novel JPL-developed arm-borne 3D imaging sensor). Note that MicroArmI implements (computationally practical) inverse kinematics and force and task adaptive controls (via integral arm strain gauges), by comparison to the prior simple forward joint controls of MarsArmI or Rocky7 sampling. We note also that the JPL/QMI first-developed low temperature USM (FY97 Level 2 deliverable) will be integrated into MicroArmI for operational demonstration/evaluation.
MicroArmI is a first-cut late-FY96/FY97 PDM technology development path for an all-composite small arm. We cited above two small arm applications, the second of which is Mars sample return. For this second function, the LSR task is developing a new concept light rover (FY97 Level 1 deliverable) requiring a very light and strong cache retrieval arm, one which can grow to perform basic opportunistic science. We are using this target application to drive next generation design of MicroArm technology, MicroArmII -- a development which leverages knowledge gained from the design and fabrication of MarsArm II, MicroArm I, and the MVACS flight arm for Mars'98 (the last of which has provided useful feedback/data/material-samples in areas of 2D composites and motors/tribology). MicroArmII is like MicroArm I in that it has a t/s/e configuration (to initially incorporate a simple single d.o.f. end effector for sample cache grasping), but will be "in-line," having no offset in the pitch joint. The motivation here is to improve stiffness of the arm and address issues associated with cabling. The elbow joint and the shoulder joint will not be restricted severely in rotational range, with each approaching 270 degrees of range. MarsArmII is to be made of a new superior, stronger 3D composite substrate from SEP, for which we are currently developing a baseline process. Intrinsic to the MicroArmII construction will be the use of "Flexprint" cabling instead of traditional round wire cables. Flexprint cables are made by directly depositing and etching copper on a substrate of Kapton (a high temperature polyimide plastic from Dupont extensively used in space) and then covering with another layer of Kapton. Rather than creating an external wire harness and routing it around and through the arm, the light and compliant flexprint cables (or circuits) will be bonded internally to the tubes and joint structure. This will result in up to 75 % reduction in mass of the cabling harness and connectors (which can be 25% or more of system mass), and provides for a safe integration of the flexprint to the arm structure. Beyond this integration of power and signal lines, we will explore flexprint as an R&D paradigm for implementing "smart sensors" (viz., integral and potentially distributed temperature, strain, vibration, etc., sensors to be used in conjunction with closed loop compensating controls) as well as distributed thermofoil heaters. Such MultiFunctional Structures (MFS) will potentially create a new architecture for flight robots. This year our effort will be simple, integrating only cabling and force sensors into the MFS, but the experience base should help us in FY98-99 to expand the MFS emphasis into both arms and rovers. MicroArm II will be actuated by flight-relevant DC permanent magnet brushed motors that come assembled with a planetary gearbox and magnetic encoders. The output torque of the actuator assembly is almost 2 in-lb, driving directly into the same harmonic gears used in MicroArm I, and potentially providing payload:mass > 3:1. The MarsArmII design addresses the dusty nature of Mars, incorporating intrinsic mechanical seals into all rotating joints. We note in summary that MicroArmII will provides the following capabilities on the forthcoming LSR sample retrieval rover (SRR/FY97): 1) retrieval of sample cache from an expired long-range science rover; 2) storage of the sample cache container on-board SRR; and 3) a stable mechanical platform for wrist mounting of the SRR goal-recognition camera.
We next outline our planned FY98 work, describing first the continued development of robotic sampling arms/effectors; then, we give multiyear development perspectives for the enabling technology work in composite materials and high performance motors.
MicroArm architectures: Two thrust areas within mechanism design will be
addressed. The first area is design and fabrication of a flight-targeted,
low mass, all-composite rover science arm and end-effector. The second area
is exploratory development of synergistic arm-deployed, rock exposure mechanisms.
Recall that the above-discussed MicroArm-II has only a simple gripping mechanism
for purpose of acquiring a sample cache container. Extending this concept,
we will develop a flight-relevant, multi-functional end-effector. This design
will use integrated cabling/sensing technology developed for MicroArmII,
will incorporate a means to generically grip (clam shell scoops), and offer
a means of securely grasping/aligning mechanical interfaces of a deployed
tool, instrument, cache container, etc. The related arm architecture --
to be finalized in cooperation with the end-user Long Range Science Rover
task -- will be based in strengthened hybrid-2/3D composite designs and
include trade studies on use of the new JPL high-torque, low-temperature
USM actuators versus conventional DC motors (more below under these topical
technology areas). We will evaluate arm assemblies in relevant thermal environments.
The integrated arm-effector will be called MicroArm-III, to be integrated
with the LSR-derived Rocky 8 FY98 mechanical rover architecture. The second
thrust addresses the yet unsolved problem of exposing fresh rock for science
investigation and sample collection. To address this problem, we will develop
a high-dexterity, rock exposure mechanism (REM) that is deployed by a rover-mounted
arm to the rock surface of interest. The mechanism will be mounted on the
rover frame and power to the REM will be provided through a spring-loaded,
retractable tether. The operational scenario for this mechanism is as follows:
the robot arm grips the REM and guides the mechanism from its stowed location;
the REM (now within the grasp of the robot arm's end-effector) is positioned
against the rock sample of interest; once the rock exposure procedure is
completed the REM is placed back in its stowed position by the robot arm.
The actual mechanism for completing this rock exposure may possibly be a
cutting tool (saw), a chipping mechanism, or an explosive (pyro) mechanism.
There are several advantages to this operational approach. First, the robot
arm is not continually burdened with the task of carrying around the REM
and the cabling of the REM is kept separate from the arm cabling. Thus the
effective functionality of the robot arm's end-effector is enhanced not
by adding the REM to the end-effector itself, but instead by providing the
ability to deploy the REM using the existing end-effector design. Secondly,
the dexterity of the REM is enhanced. As opposed to rover-fixed designs,
the REM can be positioned anywhere within the operating workspace of the
rover-mounted manipulator. Finally, the feedback sensors that alread exist
within the robot arm can be used to control directly the dynamics associated
with the rock exposure event (sawing, chipping, etc.). The design of the
REM will also include a collection basket that will collect the chips that
fall from the cutting tool of the REM while sifting out any dust produced
by the cutting process. These chips can then be transferred via the manipulator
to a sample collection device located on the rover body for further science
investigation. Personnel carrying out this work have participated/led in
the seminal SAAP task study for Mars sample extraction, and are well-informed
in the salient issues of tool fatigue & abrasives wear, cutting/impact
design, actuation-power cycle optimization, etc. In addition to the design
and fabrication of the REM, a study into the effect of the dynamics of the
rock exposure event on the manipulator/rover system needs to be conducted.
This study would need to insure that the forces and vibration environment
experienced by the manipulator/rover system do not adversely effect the
performance of the entire system. In particular we note our collaboration
with the MIT/J. K. Salisbury task on force-referenced perception and control
of sampling device interactions with hard/variable media including the fresh
rock exposure; given the known difficulty of efficient coring/chipping extractions
and challenges of power delivery from light, potentially compliant platforms/arms,
the MIT mechanical design and controls expertise will be very valuable.
Advanced materials: This work concentrates on development of novel environmentally robust 2 and 3-dimensional composite materials from which to realize the above discussed lightweight sampling arm, effector, and rover designs. There is an established technology base of high strength 2D composite processes which underlie the fabrication of arm links and rover struts in typical buckling and torsional loads. In FY96 we investigated and to some degree optimized such material systems as a function of different resins, forming processes, and cure cycles. Our testing to date using epoxy and polycyanate resins at both cryogenic and room temperatures revealed a modest (~10-20%) difference in relevant mechanical/thermal properties. This minimal difference, along with task budget constraints, lead to the conclusion that this is a secondary line of research for FY97. Work in this area will re-intensify in FY98 as we evaluate flight-relevant environmental exposure effects (primarily UV light and radiation). A much more central line of work is our development of a new class of 3D composite begun in FY96 a machinable, tappable material that we believe will enable creation of new robots and rovers of higher structural rigidity at 20-50% lower overall mass. In FY96 we invented a first such prototype process based in resin transfer molding (RTM) of a B. F. Goodrich furnished lower density 3D random air lay-up carbon fiber preform. Using this JPL developed material, we constructed many primary load-bearing components of both MarsArmII and LSR-1. During processing of the materials, we observed in some bulk process material samples lower than expected strength, and cracking/delamination/celling (cf. TRIWG 10/96 report for specifics). We believe, based on FY96 coupon tests, that there is a much better alternative in SEP "Novoltex (SPC)" high density material. We are developing and will characterize in FY97 -- for both initial mechanical and thermal environmental performance -- a new RTM process for this material. If this material proves suitable, we will undertake a thorough FY98 mechanical characterization and process optimization of the material, also characterizing its salient UV/radiation effects. We emphasize that this 3D composites work is fundamental, in both the materials R&D sense and applications importance to robot and rover designs; we have found few external reports of related work. In passing we note that we have identified several new possibilities for 3D preforms, should the SEP process prove suboptimal. Another planned and potentially major advance in our 3D material development, is selective stiffening/strengthening by a directionally hybridized lamination of 1D and 2D material onto the load paths of a 3D orthotropic composite component. As a final note, we will characterize design trades between more conventional aluminum (or titanium) versus 3D composite part forming. This will demonstrate potential mass, interface DCTE matching, structural rigidity, and environmental stability gains.
Advanced actuator development: We are developing rotary ultrasonic motors (USM) as a hypothetically superior alternative to conventional DC brushless actuators. Rotary USMs are high-torque density piezoelectric devices of low fabrication complexity; major drive elements are formable in batch process; and, the underlying mechanization is conceivably survivable at extended life cycles over a full range of anticipated Mars ambient surface science conditions (operating in physical principle to near 0K!). USMs have additional advantages of self braking (non-backdrivability), and inherently low operating speeds at high torques, thereby facilitating reduced gearing mass and making them very attractive for rover wheel actuation. As design targets, we seek to develop and demonstrate a piezoelectric rotary motor having 5-to-10x DC brushed motor torque-density, 10x reduced no-load speed, at comparable volume. As part of this effort, we will characterize motor performance and critical design parameters under salient Mars operating conditions (as to material, structural, and electrical issues, e.g., DTCE effect on close-tolerance mechanical/electrical interfaces, and discharge-arcing-breakdown phenomena in reduced atmospheres). We note that at this time, there are few design tools for the systematic analysis and synthesis USMs an important accompanying contribution of this task. Work is being performed as a JPL-led tripartite collaboration between Dr. Yoseph Bar-Cohen (JPL), Prof. Nesbitt A. Hagood IV (MIT/Aero &Astro)., and JPL TCA partner Quality Materials Inspection, Inc. (Costa Mesa, CA). It is significant that QMI has begun the first US commercialized development of USM technology (currently centralized in Japan for OEM electronics/appliance applications, and limited to nominal 1-to-6 in-lb motors of purely terrestrial relevance and simple open-loop controls). The collective JPL/MIT/QMI effort targets a rotary motor concept for space environmental application, in capabilities ranging 1-50+ in-lb (the highest reported result to date being ~15 in-lb, with no prior literature in space applications): technical challenges include conceiving new transduction architectures to increase motor torque density (JPL/MIT), developing a stator-rotor interface robust to DTCE and cryo-vac degradation effects (JPL/MIT), creating motor designs that reliably scale to larger size, e.g. 3" dia. and 15-30 in-lb upward (MIT), providing first analytic design framework for design of such motors (JPL/MIT), development of experimental tools for run-time in situ dynamic characterization of such devices (MIT, cf. electronic pattern speckle interferometry--EPSI) and innovation of batch manufacturing processes and supporting driver electronics that will carry higher-power commercial USMs to broad-scope, inexpensive application (QMI/JPL). JPL has conceived a novel, patent-pending reverse segmented and stacked USM design for ferroelectric poling of the USM stator; this concept has potential to greatly increase torque-density (up to x10) and largely alleviate differential temperature effects on motor interface mechanical stability (thought to be the primary degradation/failure mode for experimentally observed low temperature efficiency loss and seizure). Further, the new JPL motor design is amenable to batch process in readily available low cost commercial piezoelectrics (compare Japanese manufacturing processes using more costly single re-poled piezoelectric rings). JPL has now a patent pending for this invention, which we have recently reduced to practice in one first-cut prototype. Further, JPL/MIT has developed a high-quality dynamical finite element model of USMs -- simulation of the piezo-mechanical structure upon which a flexural traveling wave mode is electrically transduced, interacting frictively with the rotor, exciting bi-directionally controllable rotation at variable speed. This enables a significant characterization/ design/ visualization of modeled motor operating frequencies, modal properties, relative conversion efficiency, etc (cf. the earlier photo of "technology development"). In FY95, we developed the experimental foundations for space ultrasonic motors, including the design of a cryo-vac test system and we started to develop a finite element analytical model for interactive design of USMs; with MIT we demonstrated/evaluated a novel larger USM design concept. In FY96, we completed the development of the Mars relevant cryo-vac system and its programming to allow measuring torque vs. speed as a function of temperature down to 120K and vacuum down to 2x10-2 torr. A commercial 1-in-lb Shinsei motor (USR-30E3) was tested and was found to maintain a relatively uniform operation characteristics down to stall at -48 deg. C under vacuum. This has been a surprising and important result since the manufacturer rates the motor as inoperable in vacuum or below -10 deg, C. -- it gives preliminary evidence that inherent DTCE mechanical stability of USM designs may be quite adequate to achieve very low temperature operation. Further, we developed the above-noted key analytical design tools for USM and showed excellent agreement with EPSI interferometric measurements that were made at MIT, thus showing an important closure between our new theoretical design tools and experimental validation/optimization. In FY97 the emphasis is on making a first baseline space-targeted 1-in-lb USM that will be installed on the MarsArmI and testing its operation at low temperatures and vacuum. Efforts are made to employ stack actuators while overcoming frequency limitations that are associated with the inherently increased electric capacitance. In FY98 our USM development program focuses sharply to analytically and experimentally characterizing the low temperature failure modes of USMs, and those mechanical/electrical factors that would be causal in limiting motor life cycle in particular temperature/environmental regimes (including ambient atmosphere). Work on small low-temperature USMs targeted to robot/rover application will include objectives of: 1) 50% torque increase over the FY97 small arm motor design (through model-based design optimization and experimental trials); 2) development and demonstration (with QMI, Inc. TCA partner) of miniaturized drive electronics consistent with flight m/v/p constraints; 3) definition of a USM concept design appropriate to Lightweight Survivable Applications in potential support of the Rocky8-long range science rover/Mars'01, and LSR-sample retrieval rover; and 4) same, for applications for rover-borne rock exposure and subsurface coring/drilling applications (for which USM have potentially very attractive operating curves). FY99 work will continue this effort to actual development of a thermally validated development and demonstrations of items "3" and "4".
At task level, the FY99 work will concentrate on extending the successful base of arm/effector lightweight, survivable component technologies in this task to broader sampling science objectives. A pivotal development, much emphasized in recent science working group discussions (cf. Mars Drilling Workshop, JPL/Caltech, Jan 28, 1997, Org.: J. Cutts) would be creation of means for sub-surface sampling from a rover. We will develop a low mass (1.5-5.0 kg) all-composite USM actuated drilling/coring architecture for (.5-2.0 meter stroke) applications, designing new USM-based force-velocity servo controls, and characterizing control structure interactions as can be expected from such a low mass, flexural body, high torque, low speed system. If successful, this architecture (given its component environmental robustness as proven in prior years of task activity) should be of broad space science applicability. Working in a complementary direction, we will continue the "REM" corer/chipper system miniaturization (.5-1.0 kg). Finally, based on component level concept work to be initiated in FY98, we will investigate approaches to mechanizing more agile underground sample recovery technique. Such dexterity strategies -- e.g., a segmental borer (viz., individually actuated inch-worm articulated links as one reference concept) -- wherein, given unpredictable subsurface soil densities, rock inclusions, porosity, permafrost characteristics, etc., sampling can proceed unhindered to significant depths (1-2 meters). This highly articulated manipulator design, as deployable from a lander or larger rover, would have inherently good stowage characteristics, and offers intriguing opportunity for both onboard science instrumentation and multiple sample containments, and offers a functionally complementary direction of R&D from Subsurface Explorer tethered underground vehicles.
Major Milestones :
FY95 Level 1: develop a three degree of
freedom arm [composite links, metal joints] capable of two meter full extent
reach and stowage volume reduction into a nominal 10 liter space (via gas
deployable segmented links). Demonstrate the arm in simulated Mars lander
operations such as sample acquisition [May 95]
FY96 Level 1: conceive, design, fabricate,
and experimentally test a new lightweight, high-strength all-composite three
degree of freedom robotic arm. Demonstrate the arm in representative lander-based
dexterous sampling tasks, and quantify mechanical and material properties
of the new enabling composite technologies. As a design goal, reduce arm
mass approximately 30% from a similar hybrid composite-body/metal-joint
arm architecture [Aug 96]
FY97 Level 1: develop, integrate, and evaluate
under task-level controls an all-composite arm, utilizing new JPL/QMI-MIT
high-torque ultrasonic motor designs, advancing 3D RTM composite strength
and reliability, and characterizing the enabling motor and material technologies
under realistic space environmental conditions. Demonstrate this arm in
representative dexterous sampling and sample-return processing tasks [Sep
97]
FY98 Level 1: develop, demonstrate, and
experimentally evaluate a lightweight, flight-targeted micro-sampling arm
(1.0+ kg/.6 m class) based in low-temperature (- 60-100 degrees C) actuation
and 2-D/3-D hybrid high-strength composite architecture, and characterizing
functional elements (e.g., an operative all-composite arm joint/link complex)
in relevant thermal environments. This development will include: 1) design,
implementation, and test of a multi-function science end-effector with active
tooling for fresh rock exposure; 2) integration of a high-fidelity task
positioning control (visually referenced); 3) instrumentation for closed
loop force response (via embedded strain sensors); 4) realistic demonstration
in science-advised scenarios for fresh rock exposure/extraction from a light
rover platform [Sep 98]
FY99 Level 1: conceive, develop, and demonstrate
in relevant simulated media a low mass (1.5-5.0 Kg), composite body, USM-actuated
subsurface drill/corer architecture for rover-borne sub-surface sampling
applications (.5-2.0 meter), innovating as needed new USM-based force-velocity
servo controls, and characterizing control structure interactions as can
be expected from such a low mass, flexural body, high torque, low geared
system [Sep 99]
Milestones by quarter
FY95
Collapsible MarsArmI concept - Q2
Hybrid 2D composite-link/Al-joint arm -
Q3
JPL/MTU Visually servoed sampling (CSM)
- Q4
MarsArmI lander demo (joint control) - Q2
& Q4
FY96
MIT dual rotor USM - Q1 & Q3 (rev)
JPL 3D low density RTM composite ("ALC")
- Q2
USM (Shinsei) low temperature tests - Q2
JPL/MIT USM FEM & parametric experimental
studies - Q3
All composite joint and link fabrication
- Q3
MarsArmII demo (IK controls/stereo sample
designation) - Q4
FY97
JPL high density RTM composite (SEP-"SPC")
- Q2
MicroArmI low density composite build -
Q2
JPL/QMI reverse segmented USM & low
temperature tests - Q3
MicroArmII high density build for sample
cache retrieval - Q4
MarsArmI rover-based dexterous sampling
demo - Q4
FY98
Hybrid 2D/3D high strength composites -
Q2
Characterization of composite environmental
exposure factors - Q3
Rock Exposure Mechanism (REM) concepts &
development - Q3
MicroArmIII flight concept arm build (flexprint/sensors)
- Q3
Low temperature JPL segment/stacked USM
& integrated arm test - Q4
MicroArmIII effector/REM integration and
rover science demo - Q4
FY99
USM-based actuators for rover wheel and
sub-surface applications - Q3
USM extended life cycle operations/optimization
- Q3
Collapsible composite body corer/drill architecture
definition - Q3
Rover based subsurface sampling/control
demo - Q4
Current Grants or Contracts:
The JPL Planetary Telerobotics element supports work at MIT/AI lab (R. A. Brooks; J. K. Salisbury), MIT/Mechanical Engineering (S. Dubowsky), and Univ. So. California (G. A. Bekey) with which we have established collaborative design and experimentation efforts in several key areas. These include vision and touch guided grasping for rover based sampling functions (MIT-jks), techniques for compliant actuation (MIT-rab) and high-precision long-reach manipulation (MIT-sd), physically based modeling and robust synthesis of rover mobility tasks (MIT-sd), experimental definition and benchmarking of rover mobility (USC), and multi-sensor fusion for robust rover navigation in Mars environments (USC).
Collaborative/Other Supporting Work:
Work leverages other tasks of both the NASA TR and MET Programs. As described
above in the "Technical Approach," this task works closely with
the MET/Sample Selection & Protection thrust to develop supporting sensor-based
controls for remote robotic science. The PDM task provides the TR Long Range
Science Rover (LRSR) and Lightweight Survivable Rover (LSR) tasks with light,
dexterous arms for their respective sample selection & caching and sample
cache return functions.
Point of Contact:
Paul Schenker
Jet Propulsion Laboratory
Pasadena, CA 91109
(818)354-2681
paul.s.schenker@jpl.nasa.gov
Robotic Subsurface Explorer
The objective of the is task is to create a device which can maneuver in the expected regolith (e.g. soil, permafrost) of planetary bodies such as Mars or comets, penetrating to depths of meters to hundreds or thousands of meters depending on the soil properties, and making in-situ measurements of the soil composition and chemistry. One specific objective of this task is to demonstrate that a self-contained vehicle can reach depths much greater than that achievable with any reasonable-mass drill rig attached to a lander.
The subsurface composition and chemistry of deep subsurface material on Mars, comets, or other solar system objects is of intense scientific interest. The surface of Mars is known from the Viking missions to have considerable soil-like surface covering; estimates are that the volume of all ejecta from the observed craters would cover Mars to a depth of a few Km. This mixture of soil, rock and ices probably becomes impermeable at some depth (a Km or so) and therefore would support pressure buildups below which water could liquefy under volcanic heating. Liquid water and the chemical disequilibria associated with volcanic springs would be the natural abode of any life forms which might have descended from the putative fossils discovered in the SNC meteorite AHM84001. Building a vehicle which could locate and investigate these sites on Mars, within the mass and budget constraints of plausible near-term missions, would be one of the greatest scientific enterprises in history. Even if this goal proves elusive, cometary cores are likely to consist of ices, silicates, etc. which this same vehicle could explore with relative ease, due to the expected factor of two or more reduction in the compressive strength of the anticipated worst-case cometary materials and the tendency of the icy comet material to fracture more easily. Although current Level-3 requirements include Subsurface Explorers for modest mission concepts, missions to search for extant life kilometers deep on Mars or to explore the deep interiors of comets are both scientific endeavors which have not heretofore been seriously considered by the science community because they think it is impossible. The demonstration of technology which enables these missions would be "technology pull" in the most intense use of the phrase and lead to missions which could revolutionize our knowledge of the evolution of life and of the formation of the Solar System.
Technical Approach:
An all-percussive mobility approach has been adopted for the Subsurface Explorer (SSX). This approach is potentially very simple, compact, reliable, and low power. A simple set of experiments with an all-percussive industrial demolition hammer has provided extremely promising results which encourage further development of this approach. Evaluation of the device indicate that it functions by an electric motor spinning a flywheel which runs a crankshaft to a hammer which impacts the demolition spike. No spring or ratchet release mechanisms are used. The flywheel/hammer effective mass is about 1 kg with a velocity of 5 m/s, causing the hammer to impact the ~700 gram spike at 30 blows per second. In tests, this device was able to easily penetrate soil (at 10's of cm/sec) and to pulverize rock, splitting a 1/2 meter diameter basalt rock in half in less than 1 minute. Smaller rocks, such as 10 cm granite blocks, cleave in one to two seconds. The energy of each blow is about 12 joules and the momentum is about 5 nt-s. We therefore seek in our design to deliver comparable or greater blows, both in energy and momentum, to the front of the SSX. Instead of delivering these blows at 30 Hz using 1200 watts, power limitations will force us to deliver them at about 1 Hz, using about 20-30 watts supplied to the SSX over a long (e.g. 1 Km) and yet low mass (e.g. 1 Kg) tether. These power levels are consistent with what might be available from a modest surface lander of the size used for the Mars Surveyor missions.
In addition to the percussive mobility approach, there is another way that subsurface penetration rates may be dramatically increased. If, as expected, there are volatile materials such as water ice mixed in with the terrain, then it should be possible to melt and electrolytically separate some of the atomic constituents of these volatiles into gasses. In the likely case of water ice, this would result in the generation of hydrogen and oxygen gas. The hydrogen would diffuse readily into almost any terrain, but if the terrain is strong the oxygen would build up significant pressure. It might be possible to build up sufficient pressure to effectively support the sidewall and overburden pressures (analogous to one of the functions of drilling mud in conventional terrestrial deep drilling applications) and perhaps even further to generate sufficient overpressure to assist in fracturing the rock ahead of the vehicle. One can imagine that the vehicle could use this gas generator to create a "bubble" of gas with such extreme pressure that it becomes the primary means for fracturing the medium, with the percussive system needed only for porous and therefore weak terrain where it's performance is excellent. Development of this gas generator and demonstration of its effectiveness in likely Mars and comet simulant will be a major research effort of this task.
Another problem needing an innovative solution is the requirement to move the pulverized medium from the front of the vehicle to the rear. We propose to use ultrasonic excitation (as has been demonstrated in many drilling/coring applications) to "fluidize" the dust and allow it to flow freely along the sides of the vehicle. Small channels may need to be fabricated into the surface of the vehicle to enhance this effect. Creation and refinement of this subsystem will be another the major research effort of this task.
A final area of research in this activity is the sensing of the terrain ahead of the vehicle, and the steering of the vehicle into the easiest terrain and/or the most scientifically interesting terrain. The percussive mobility system provides "free" acoustic excitation of the soil ahead of the vehicle, thereby providing a means for sensing the soil properties ahead of the vehicle. An acoustic sensor in the vehicle, along with an array of sensors on the surface (perhaps deployed from the lander via Nanorovers) would provide an acoustic image of the subsurface environment. Using techniques similar to those employed on Earth for oil prospecting, these active seismic measurements could be used to map individual rocks near the vehicle or layered structures or fluid bodies much deeper below (e.g. the hydrothermal regions which would be the natural abode of extant life if it exists on Mars). This information would be used to steer the vehicle along the easiest path to the most exciting science sites.
The payload volume of the Subsurface Explorer will contain microinstruments developed in the JPL MicroDevices Laboratory (MDL). This will include Raman spectroscopy and mass spectroscopy, as well as analytical chemistry instruments. The Mass Spectrometer will use laser ablation to vaporize a small spot on the sample surface. The resulting plasma will be channeled into a electrostatic ion trap which is tuned for a specific mass-to-charge ratio (associated with each isotope). After a very brief period, the only molecules remaining in the trap are those with the selected mass, with all other isotopes dissipating. The quantity of material in the ion trap is measured, and the ion trap is returned for the next isotope to be measured. Arrays of microscopic ion traps are currently in development and being fabricated by MDL. The high vacuum needed for the mass spectrometer is maintained by a "getter" which is an ultraporous material which adsorbs tremendous quantities of gas, and which can occasionally be regenerated by desorption and thermal entrainment. The samples enter the system through a hole perhaps only 10 microns across, so that the choke flow rate of atmospheric gas is relatively low.
Major Milestones
FY 97
Evaluation of percussive hammer energy/momentum
requirements - 2Q
Selection of hammer/nose materials - 2Q
Fabrication and test of percussive mobility
subsystem - 3Q
Demonstrate Subsurface Explorer moving
vertically of order 1 m in loose sand while performing useful scientific
measurements (level 2 milestone) - 4Q
FY98
Fabrication and test of tether/power subsystem
- 2Q
Fabrication and test of steering/control
subsystem - 3Q
Fabrication and test of integrated science
subsystem - 4Q
Demonstrate Subsurface Explorer moving
vertically of order 10 m in loose sand while performing useful scientific
measurements (level 2 milestone) - 4Q
FY99
Demonstration of acoustic/electromagnetic
hazard avoidance - 2Q
Demonstration of ultrasonic dust fluidization
for transport around vehicle - 3Q
Demonstrate Subsurface Explorer moving
vertically 10-100 m in undisturbed desert terrain while performing useful
scientific measurements (level 2 milestone) - 4Q
FY00
Cold chamber testing of Subsurface Explorer
- 2Q
Demonstration of electrolytic gas generation
and lubrication from volatiles - 3Q
Demonstrate Subsurface Explorer moving
vertically 10-1000 m in undisturbed natural permafrost while performing
useful scientific measurements (level 1 milestone) - 4Q
Current Grants or Contracts:
A full-time graduate student at MIT (Brian Anthony) under Professor Kenneth Salisbury is performing evaluation and integration of acoustic and/or electromagnetic terrain sensing under this program.
Collaborative/Other Supporting Work:
Other funding from the NASA sensor technology program has and will support the development of microinstruments such as the Raman Spectrometer and the Mass Spectrometer, as well as the chemical sensors. The Subsurface Explorer task pays for integration of these instruments into a fully functional robotic system and performs system-level performance tests, demonstrations and analysis. If co-funding were not available, much of the system-level functionality would be demonstrated with bench-top science instruments connected to the Explorer via the optical fibers in the tether.
Brian Wilcox
Jet Propulsion Laboratory
Pasadena, CA 91109
(818) 354-4625
brian.wilcox@jpl.nasa.gov
The objectives of this task is to develop the enabling telerobotic technology to accomplish global in-situ scientific investigations of planetary surface and atmospheric environments using aerobots (robotic balloons). Although there are many technical challenges to flying aerobots at any planet, this research focuses on the following telerobotic-related challenges:
Real-time determination of the location and state of an aerobot: As an aerobot moves through the atmosphere, it must track its own global position in order for the data it collects to be scientifically and operationally useful. To determine its location, an Aerobot on Mars or Venus will be forced to use a variety to techniques such as sighting of celestial objects or use of camera images of the surface. In either case, it will be critical to know the attitude of the aerobot's swinging instrument platform to do the necessary location calculations. The coupling of attitude estimation and global position determination is more complex and demanding than that for typical interplanetary spacecraft or rovers.
Controlling the vertical motion of an aerobot: Since an aerobot moves along with the winds horizontally, it must be able to control its vertical motion in order to be able to control its motion through an atmosphere in general. For Venus (and the Earth) research is under way to study using fluids which change phase and provide significant renewable control of buoyancy and hence vertical motion. For Mars (due to the atmospheric structure) such approaches are not possible so the focus there is on the smart use of ballast drops for vertical motion control for obstacle avoidance and path modifications. Research is necessary to understand how to achieve various desired vertical trajectories such as descents to landing, hovers, and related motions. Other related issues which need to be addressed are how to deploy an aerobot from a planetary entry probe and how to safely land an aerobot and retrieve scientifically data from the surface.
Predicting and Planning global-scale paths: In order for an aerobot to be a useful scientific exploration vehicle, it should have the ability to move to a desired location or scientific target on the planet. This may involve using known wind structures at different altitudes to "tack" on the winds to adjust its ground track. It may also involve more extensive global path planning and execution. There will be numerous scientific targets that will be of interest to the scientific community. It is likely that aerobots will operate in one of several autonomous modes. A likely mode is an "opportunistic" mode in which the aerobot maintains a prediction of its probable path and can modify it (using the winds) to change its path to fly over or land at nearby scientific targets. In other modes, more extensive path planning (probably requiring several circumnavigations of the planet) will be required to move to a specific target of interest. In either case, path prediction and planning will be a core technology necessary to make aerobot missions scientifically valuable.
The general approach in this task is investigate each of these items in simulation first and then to validate them with Earth-based test flights and then later on in actual preliminary mission to another planet (possibly a New Millennium mission).
Technical Approach:
Autonomous State Determination: Unlike earth-based systems, where Global Positioning System (GPS) technology has considerably simplified the state determination problem, autonomous knowledge of a aerobot position and velocity on other planets requires the use of a combination of inertial, celestial, ground imaging, altitude, and radio metric sensors. Not all of these sensors or the associated state estimation methods are applicable on all planets, and nor are they available at all times and phases of a mission. The data from these sensors, each with their distinctive periodic and a-periodic characteristics, and multiple data rates, must be combined in an Autonomous State Estimator in order to provide the best possible estimate of the current position, predictions of the future trajectory, as well as revisions of estimated positions in the past. On Venus, the basic approach is to rely on a combination of inertial state propagation, ground imaging for frame-to-frame motion estimation and map correlation, and radar altitude profiles correlation to topography. The challenge of precision inertial sensing with low-mass, low-power components is partially overcome by developing estimation algorithms that exploit the unique pendulum dynamics of a Venus aerobot. Ground-imaging has more utility at night where the Venus terrain is visible in the 1 micron band anytime the aerobot descends below the clouds (47km). During daytime, however, the terrain is visible only below about 17km because of the atmospheric dispersion of sunlight. Frame-to-frame motion estimation relies on distinguishable features that can be located within successive image frames and does not need a global map. In the case of Venus even global correlations of images to maps can be attempted since the IR images is expected to be strongly correlated to the altitude of the terrain because of the high lapse rate in the atmosphere. Finally, radar altitude profiling of the surface and correlating of these profiles to terrain maps also provides an indication of aerobot position. Overall performance of position estimation to within 30 km appears feasible. On Mars, the primary approach is to utilize celestial sensing of the sun, moons (Phobos, Diemos) and the stars (only at night). The key technical challenge is to achieve high-precision, simultaneous celestial sensing from a low-mass, swinging platform while accommodating the wide visual dynamic range of the various celestial targets. Precision tilt estimation using inertial sensors is important since errors in tilt directly affect the precision of the celestial observations. Celestial sensing under optimum conditions (i.e. all targets are visible) leads to relatively high accuracies (e.g. within 2 km). When higher precision target-relative positioning is required, correlation of landmarks to maps can be employed near the target locations. Frame-to-frame imaging or doppler radar can be utilized for velocity estimation, which is used to reduce the uncertainty in the celestially based position estimates.
Mobility and Control: Achieving a significant degree of control over the vertical motion of aerobots requires significant developments in the areas of buoyancy control system design, vertical motion modeling, and vertical trajectory optimization and execution. One focus of this task is to design the hardware components that are part of a Venus-applicable buoyancy control system based on a fluid which changes phases from liquid to gaseous and back at some altitude in the atmosphere. Past passive balloon tests here on Earth have used unmixed commercial fluids such as R114 to achieve a limited amount of buoyancy control. Research is underway to identify mixtures of fluids that have improved buoyancy control features. A second focus of this task is to improve the modeling of the thermodynamic components of the system that control the aerobots vertical motion. Vertical motion models need to be developed for aerobots at Venus. A basic model will be developed in a planned Venus Mission Study which will be conducted in calendar 1997 on JPL IR&D funds. This model will form the basis for a more advanced Venus vertical motion model. Once this model has been developed, Venus specific vertical trajectories will be studied. Models for an aerobot's vertical motion at Mars have been developed on other tasks. Further research is needed to investigate the ability of ballast drops to control the vertical motion at Mars. One result of this research will be a better understanding of the granularity of the ballast needed for various operational requirements (such as obstacle avoidance and trajectory modification). The aerobot trajectory analysis and optimization will happen in two phases: (1) Preliminary development in simulation which will produce nominal trajectory profiles which can be used in other activities, such as path prediction and planning. (2) Test trajectory generation and execution on Earth-based, Venus-applicable demonstration flights. As these technologies mature, more of the functionality will be moved from the ground to on-board autonomous control. In FY98 and beyond we plan to investigate using a landing snake for safe landings and to capture useful scientific data about the surface that the snake contacts. Other areas of research in the coming years include how to best deploy an aerobot from a descending planetary probe or aeroshell.
Autonomous path prediction and planning: This technology requires
the integration of several components: improved vertical motion models,
useful vertical motion trajectories, global wind models, and path planning
techniques. In the beginning, simulations will be used to develop and test
the necessary components, such as path planning based on canonical trajectories
derived from trajectory optimizations and simplified global wind circulation
models. Increasing levels of fidelity and flexibility in all components
will be incorporated to improve the accuracy and usefulness of the path
planner. A second thrust of this activity will be to shift the path prediction
and planning techniques from off-line simulations to on-board, autonomous
path prediction and planning tools. Various techniques for using path planning
capabilities will be investigated to improve the ability of the aerobot
to respond to scientific targets of interest. This will include studying
various "modes" of operation (as mentioned in the technical objectives
section). For Mars, tradeoffs in path planning capability versus ballast
granularity and use will be studied. In particular, if the ballast is composed
of scientific drop-probes (such as micro penetrators), tradeoffs will be
examined to decide whether to make the probes complex (and heavy) or simple
(and light) and the possible mobility and scientific benefits of each approach.
Technical Milestones:
Venus Applicable Milestones :
Autonomous State Determination:
Demo Inertial State Propagator accuracy better
than 80 km over 8 hrs - 98Q4
Demo Topo Map/IR Image Correlator for nighttime
pos est within 30 km - 99Q3
Demo Topo Map/Altitude Profile Correlator for pos
est within 30 km - 00Q2
Demo Long Duration System Flight with better than
30 km pos est - 01Q2
Mobility & Flight Control:
Demo Vertical Control to Hold Altitude within 0.5
km for 15 minutes - 98Q4
Demo Soft Landing Closed-Loop Control for Impact
Velocity < 3 m/s - 99Q4
Demo landing snake operations for safe landing
in winds up to 2 m/s - 00Q4
Path Prediction/Planning:
Simulate Venus Plan/Control with landing 30 km
from 500 km distant target - 97Q4
Demo Vertical Planner to achieve alt/time state
within 0.5 km/15 min - 98Q4
Demo Downrange Landing Planner to land within 10
km of target - 98Q4
Demo Lateral Planner to adjust ground track by
5km - 99Q4
Demo Cross-range Landing Planner to land within
25 km of nearby target - 00Q4
Demo Global Motion Planner to adjust latitude 5
deg, change hemisphere - 01Q4
Mars Applicable Milestones:
Autonomous State Determination:
Demo High-Accuracy Tilt Sensing better than 1 mrad
- 98Q2
Demo Terrain Range Sensing with 1% Accuracy using
Radar/Laser Altimeter - 98Q2
Demo Celestial Sun Sensor System for position within
30 km - 98Q4
Demo Celestial Star/Moon Sensor System for position
within 10 km - 99Q2
Demo Ground-Track Velocity Estimator with 0.1 m/s
accuracy - 99Q3
Demo Map/Landmark Correlator for target relative
position within 2 km - 00Q2
Demo Long Duration Stratosphere System Flight,
3+ days, 2 km pos est - 01Q2
Flight Control & Sequencing:
Demo Science Camera Trigger at optimum swing angle
(within 1 deg) - 98Q4
Demo Sensor-based Ballasting within 2-5 km of hazard
- 99Q2
Path Prediction/Planning:
Demo Vertical Trajectory Predictor of motion within
0.3 km - 98Q4
Demo Global Circulation Model Based Predictor (inc.
ballast) for 50 day mission - 99Q4
Demo Ballast Planner to achieve 50% ballast savings
for peak avoidance - 00Q2
Point of Contact:
Jonathan Cameron
Jet Propulsion Laboratory
Pasadena, CA 91109
818-354-1189
Jonathan.M.Cameron@jpl.nasa.gov
with any comments, criticisms
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