Topics of Discussion

• A scientific rational for autonomous systems

• A systems approach to autonomous stations- view from spacecraft integration

• Remote ocean floor observatories

Past Experiences and Lessons Learned

Carol Raymond, Jet Propulsion Laboratory

Many investigators have years of experience with autonomous systems in extreme environments. Careful design and engineering is crucial for a successful system, however, much can be learned from practical experience. Unanticipated feedbacks have occurred within systems, winds and temperatures have proved more extreme than anticipated, and methods for data retrieval or system deployment have changed with time. Accounts of successes and other experiences from current investigators will prove invaluable in formulating recommendations for future autonomous systems within polar regions and other extreme environments.

The most extreme example of systems that survive hostile conditions for long periods is spacecraft. Talks will address experiences investigators have had with spacecraft that could be pertinent to our problems with autonomous systems on Earth. The challenge will be to identify cost-effective solutions that aerospace engineers have identified that can be transferred to terrestrial applications.

Ocean floor observatories are under development for siting in sea floor boreholes and at active spreading centers such as the Juan de Fuca Ridge (under the NSF RIDGE program). The Juan de Fuca Ridge has been selected for focused development of a comprehensive ridge crest Observatory. Two segments within the ridge have been chosen for focused long-term sea floor instrumentation. The Ocean Seismic Network (OSN) Experiment will emplace a broadband borehole seismometer in a cased borehole paired with a sea floor seismograph at the same location. The borehole has been dubbed B3S2 (BroadBand Borehole Seismic System) and the seafloor and buried broadband system is called BBOBS (BroadBand Ocean Bottom Seismograph).

Topics:

Past experiences and lessons learned
Scientific autonomy
Operational autonomy
Operations/controllers

Bill Nesbit, Communications Supervisor (O&M), Antarctic Support Associates

The range of options for powering polar autonomous systems includes both passive sources like solar and wind, and active sources like fuel cells, propane and diesel generators. Environment will be the biggest factor in limiting the design of passive systems. Solar power is not a viable option during the dark polar winters, nor is wind an option in still regions such as the Antarctic polar plateau. Diversified power sources (e.g. wind and propane, or wind and solar) are one way to overcome temporal variations in the source strength of passive systems. Restrictions in weight and size might further limit choices for particular applications. In all cases temperature extremes will determine the key design parameters. Battery freezing points depend on the electrolyte mixture and charge level, thus, both must be carefully controlled. Batteries may also outgas acid vapors if overcharged, which can adversely affect other components within the system. To prevent outgassing, the charging system must be regulated with temperature compensation. Finally, a properly designed system needs a mechanism for safely venting exhaust gasses from active systems and batteries without compromising the thermal insulating barrier.

Ray Dibble, Professor Emeritus, Geophysics, Victoria University, Wellington, New Zealand

On Ross Island, Antarctica, the Mount Erebus Volcano Observatory (MEVO) group, led by Prof P.R. Kyle of New Mexico Tech, operate a seismic telemetry net on the 3800m volcano, powered by solar panels and auxilliary wind generators. The seismic signals are automatically digitised at McMurdo and FTP'd to NMT and VUW each night. Year round operation is achieved with Gel/cell batteries on the Mountain, which have low self discharge rates, and excellent tolerance to complete discharge at temperatures as low as -50 deg C. Part time attention by the Science Technician at McMurdo, and yearly servicing of the equipment on the Mountain enables nearly 70% data recovery. All the equipment components are available off the shelf at low prices, and have withstood the environmental conditions and volcanic gases remarkably well. Some of the batteries have been in service for 15 years, and storm damage is rare. Equipment specifications will be provided, including the conversion of DC powered computer fans to auxilliary wind generators.

Similar techniques have been used to operate a television station at the Crater Rim to monitor the activity in the liquid Lava Lake from 1986 to 1990, and to record the infrasonic signals at the Windless Bight Array, powered by a Radioactive Thermoelectric Generator on loan from NSF.

Topics:

Solar
Wind
Fuel Cell
Batteries
Propane
Generators
Regulators - temperature compensation, low voltage cutoffs, hysteresis
Flywheels
Heat Pipes

Henry Awaya, Senior Thermal Engineer, Jet Propulsion Laboratory

Yi-Chien Wu, Jet Propulsion Laboratory

 

The thermal control of an instrument in the Antarctic poses multiple challenges for the instrument designer/implementer. The Antarctic environment is very harsh by Earth's standards and encompasses temperatures ranging from a balmy 0 degrees centigrade all the way down to -60 or -70 degrees centigrade and with wind conditions ranging from still air to velocities of raging windstorms. The sun is either very low to the horizon or below the horizon. One interesting aspect of Antarctic weather (especially at high elevations) is that the temperature ranges resemble those in the fair latitudes of Mars.

The first instinct is to heavily insulate the instrument to protect it from the potential cold, however, heat from power utilizing instruments and support equipment must be removed to avoid an over heat situation. Thus, the problem of thermally controlling an Antarctic instrument becomes one of balancing the changing environment against the variation incurred within the instrument box.

To construct a thermal model, the environment must be characterized first, and the configuration of the instrument/assembly must be thoroughly understood. The power levels generated within the instrument must be known as a function of time. This model can first be used as a predictor of thermal performance. Pre-application tests can help "tweak" the model. Finally, the model is validated/refined and can be correlated with reality when actual instrument data becomes available.

Topics:

Environmental Considerations (Antarctic, Mars, Deep Space Comparisons)
Temperature Control Range (Heat Rejection/Heat Retention Philosophy)
Thermal Analysis/Thermal Design of GPS/Data Box Assembly
Thermal Data Retrieved (Discussion and Comparison with Analyses)
Applications to Future Missions

Gregory E. Dace, President, Acumen Instruments Corporation

Autonomous science missions employ data systems to perform many critical tasks. These tasks include data collection, processing, and storage; system monitoring and control; and data retrieval operations. Extreme environments impose unique requirements on data system design that dictate which functions the system must perform and how each function is implemented.

Data requirements vary greatly among experiments being conducted in extreme or polar environments, so data systems should be designed with the expected volume of data in mind. Some systems, such as those for meteorological experiments, collect only a few hundred bytes of data per day (making cost per megabyte only a minor issue), while others (e.g. seismic) collect megabytes per day, requiring the use of low-cost high-capacity storage media.

Deployment in Antarctica can expose systems to extremes in temperature, pressure, and vibration that can adversely affect components. For instance, disk drives are not specified to operate below 0 degrees C, nor do they survive the high altitudes of the polar plateau. Flash memory proves robust in these conditions, but is prohibitively expensive for high capacity systems. Electrostatic discharge (ESD) is another common source of problems in the extremely dry Antarctic conditions. All electrical systems must be built to withstand this harsh environment.

Extreme environments limit data retrieval opportunities. Remote data retrieval is an attractive option, but communications systems are expensive and limited in data bandwidth, making them suitable only for transferring small amounts of data at present. Data compression and/or on-site data reduction can make remote data retrieval practical. Data volume may necessitate archiving data on site for periodic retrieval by field personnel. Systems that archive data for on-site retrieval must provide simple and expedient download mechanisms such as removable media, equipment swapping or high-speed data transfers (e.g. SCSI, Ethernet, FireWire, USB).

Limited development resources (e.g. time and funds) often force compromises in these specifications. As system complexity increases, more failure points are introduced and more resources must be devoted to development and testing. Testing is the most important ingredient for successfully completing a scientific mission in extreme environments, so systems need to be simple enough to provide adequate time for thorough testing and personnel training.

Topics:

Loggers - high and low capacity
Storage media - disk, flash memory, tape
Static State of health information
Sample handling

Ngoc Hoang, President, NAL Research Corporation

There is a requirement for a satellite communications system that could supplement, complement or even replace some of the current communications techniques used in polar regions. These include the high data rate NASA Tracking and Data Relay Satellite System (TDRSS), the INMARSAT maritime satellite network, the Argos data relay satellite system, high frequency (HF) radios and some of the old government satellites operating beyond their original design lives. There are shortcomings associated with each of these systems. However, they are the only available options that provide vital voice and data links within the polar regions. For example, HF radios are the best means for on-demand contact between McMurdo and South Pole operations and for communicating with aircraft supporting the station. With these systems, however, blackouts can occur for days due to disturbances in the ionosphere caused by solar activity or due to strong interference from the Earth's magnetic field. Another example is the use of the Argos system for the collections of meteorological data from drifting buoys in the Arctic Ocean or from the Automatic Weather Stations (AWS) and Automated Geophysical Observatories (AGO) in Antarctica. Argos has demonstrated its great potential for the collection of atmospheric data, but it also has many disadvantages including one-way communications, non-continuous temporal coverage, low data transmission rate, long message latency and high cost due to low volume markets. Another example is that a geosynchronous (GEO) satellite will experience orbital inclination over time due to gravitational fields of the sun and the moon if station-keeping corrections are not made. Thus, a GEO satellite at the end of its operating life will tend to drift north-south at an inclination rate of about 0.8 degrees per year allowing direct line-of-sight view of both north and south poles a few hours a day. The National Science Foundation has been taking advantage of these "old" GEO satellites such as ATS-3, LES-9 and GOES-2 to provide a temporarily solution for voice and data communications in the polar regions.

A variety of commercial low-Earth orbit (LEO) satellite communications systems produced by the private sector are now in, or will soon achieve, operational status that may provide solutions for the South Pole Station and other Antarctic and Arctic locations. They will offer considerable research opportunity for autonomous science platforms applications in remote regions including two-way communications, real-time data transmissions, global coverage and reduced costs. They are much closer to Earth; therefore, low-power lightweight transmitters and receivers and omni-antennas can be used. NAL Research Corporation is currently developing a satellite data relay system for remote science platforms utilizing commercial LEO satellite transceivers. The system will allow two-way real-time data collection. In addition, science platforms can be monitored, adjusted and re-calibrated by scientists at their home laboratories or institutions.

Satellite
Radio modem
H/F

Michael Brennan, Northern Power Systems, Inc.

In finalizing an autonomous system the various sub-systems (communications, data acquisition, power) must be put into a physical framework that meets form and fit requirements. These include size, bulk, weight, operator controls, making the pieces work together, managing the thermal environment for the pieces, etc. Heating, cooling, electromagnetic interference, venting, or other problems may arise when a group of electronics are packed into a tight space. Environmental issues such as shock, vibration, splash, spray, or wind must be taken into account when designing the completely integrated unit. The housing of the system must be able to withstand transport, and temperature extremes and high winds within its local environment.

Packaging is where the "system" part of system integration comes into any project. The talk will focus on desiging environmental enclosures (packaging) for extreme environments - such as Antarctica and space. While most system designs are fairly consistant in specification, I've found over the years that each system has its own set of unique attributes (factors) that if overlooked can result in poor performance and even failure. I plan to show slides of several remote autonomous sites and discuss these factors and how they influenced the integration and packaging of each system.

Topics:

Enclosures
Insulation
Construction materials
Size
Off-the-shelf vs. custom
Maritime applications - rime ice, etc.

Last modified on 3/11/00 by Maggi Glasscoe (Maggi.Glasscoe@jpl.nasa.gov)