Minutes of the
Mars Relay Flight Test Workshop
1996 June 07
Jet Propulsion Laboratory
Pasadena, California

Prepared by John L. Callas

Background

The Mars Relay Flight Test will be a two-way test of the Mars Relay onboard the Mars Global Surveyor and Russian Mars'96 spacecraft. The test is planned to occur shortly after spacecraft launch while each spacecraft is near the Earth. The Flight Test will involve the support of the UHF-capable worldwide radio amateur community. The Workshop summarized here is in support these tests.

Introduction and Workshop Information

Dr. John L. Callas opened the Mars Relay Flight Test Workshop and welcomed the participants. In attendance were 27 outside (non-JPL) participants and approximately 15 JPL staff. Most of the attendees are radio amateurs. Two of the visitors were from outside the United States; one from Canada and one from France. The French visitor was AndrŽ Ribes of the Centre National d'Etudes Spatiales (CNES), the French Space Agency. AndrŽ Ribes is the CNES chief RF engineer who developed the Mars Relay. CNES provided the Mars Relay system to the NASA and the Russian Mars Programs.

Mars Exploration Educational and Public Outreach

Dr. Cheick M. Diarra of the JPL Mars Exploration Education and Public Outreach Office spoke briefly on the efforts of his office. He summarized some of the activities and products being generated by his office. These include efforts to distribute Mars spacecraft data (images, etc.) over the Internet as the data are received at JPL, and the development of special educational tools to permit students at various grade levels to interact with the data and produce their own scientific results. Other activities include production of information sheets, CD-ROMs, and presentation materials. The principal thrust of his office is to more meaningfully involve students and the public in the exploration of space, particularly Mars. Therefore, it was appropriate for the radio amateurs to learn of these activities since the Mars Relay Flight Test does have a significant public outreach component in itself. Those interested in learning more about JPL, Space Exploration and Mars Exploration, and Public Outreach efforts, can access the JPL Homepage on the Internet at http://www.jpl.nasa.gov/. From there one can navigate to each of the JPL Project Homepages.

Mars Exploration Program

Glenn E. Cunningham (WA6TPT), Project Manager of the Mars Global Surveyor Project and the Mars Surveyor Operations Project, gave a presentation on Mars Exploration. Mr. Cunningham briefly summarized previous missions to Mars by both the United States and Russia. From 1960 to 1992 there have been 26 missions to Mars from both nations. The first successful mission was the JPL Mariner 4 Mission launched in 1964. Since that time NASA has launched a total of 8 successful missions. The last US mission to Mars was Mars Observer launched in 1992. Contact with Mars Observer was lost just 3 days prior to arrival at Mars in 1993 August.

Since Mars Observer, NASA and JPL have been developing an ambitious, low-cost program to return to Mars. This program will be a decade long exploration of Mars with two spacecraft launches to Mars every opportunity (about every 25 months). The first missions will be the Mars Global Surveyor Mission to be launched in 1996 November and the Mars Pathfinder to be launched in 1996 December. The total funding for the entire Mars Program is less than $200 million per year. This funding must cover the cost of developing and launching two spacecraft every two years and operating all active spacecraft at or en route to Mars over the duration of their mission. After the completion of the series of orbiters and landers, a Mars sample return mission is being considered for launch around the year 2005.

Mr. Cunningham reminded the audience that Mars Global Surveyor (MGS) uses many frequencies onboard the spacecraft. There are the X-band frequencies (around 8 GHz) used for the primary spacecraft communication with the Deep Space Network (DSN) to send commands to the spacecraft, return telemetry from the spacecraft, and to provide navigation and tracking of the spacecraft. There is a Ka-band (approximately 32 GHz) experiment onboard MGS to test this band for future deep-space telecommunications use. And finally, there is the UHF Mars Relay to be used for relay operations at Mars between MGS and small stations and landers placed on the surface of Mars.

Mars Exploration Missions

Wayne J. Lee, mission designer for the Mars Surveyor Program, presented an overview of the current Mars Missions. The first mission to launch is Mars Global Surveyor (MGS). The launch period of MGS opens on 1996 November 06. MGS will take approximately 10 months to travel to Mars on a Type II trajectory. After arrival at Mars MGS will aerobrake about Mars to place the spacecraft in a low-altitude polar orbit about the planet. From an altitude of about 400 km above the surface, MGS will perform a systematic study of Mars for at least one Martin year (687 days).

The second mission to launch will be Mars Pathfinder. The launch period opens on 1996 December 02. Pathfinder will take approximately 7 months to arrive at Mars on a Type I trajectory. Pathfinder will use a combination of aerobraking, parachute deployment, rocket motor firings, and airbag inflation to provide a controlled landing on the surface of Mars of a lander system and microrover. Once safely on the surface, the microrover, named Sojourner, will independently explore the region around the landing site.

Late in 1998, two more missions to Mars will be launched, the 1998 Mars Surveyor Orbiter and Lander. The orbiter will take up an orbiting position similar to MGS. The lander will attempt to land very close to the edge of the South Polar Cap on Mars below 71 degrees South latitude. The lander will investigate the historical climate and volatile record contained the Polar Cap's layers.

Mars Global Surveyor Science

Dr. John L. Callas discussed the individual science instruments on Mars Global Surveyor. Each instrument is fixed to the spacecraft body. With the exception of the two Magnetometers (MAG) and the Ultrastable Oscillator (USO) all others are mounted on the nadir panel of the spacecraft. The nadir panel is that side of the spacecraft which is held fixed toward Mars as the spacecraft rotates about the planet.

The camera, referred to as the MOC, consists of two camera systems, a wide angle camera and a narrow angle camera. Using a linear charge coupled device (CCD), each camera collects an image as a long strip in a push broom fashion. The wide angle camera will provide two-color (red and blue) horizon to horizon, global coverage of the planet each day. The narrow angle camera will provide selected high resolution images of the surface with a resolution of approximately 1.4 meters per pixel.

The Thermal Emission Spectrometer (TES) is a multi-wavelength infrared remote sensing instrument. It incorporates a Michelson interferometers that collects infrared spectra of the surface and atmosphere. From these measurements, the mineralogical composition of the surface can be mapped globally to a ground resolution of about 2 kilometers. With limb (horizon) and nadir scans, the atmospheric structure (temperature, pressure, etc.) of Mars can be in investigated continuously. Additionally, the seasonal advance and retreat of polar caps can be monitored.

The laser altimeter, referred to as the MOLA, collects altitude measurements ten times per second as the spacecraft orbits the planet. By firing a semiconductor laser towards the surface and measure the time of flight of the backscattered light, the spacecraft altitude can be measured to a precision of about 2 meters. When combined with spacecraft tracking, a global topographic map of Mars can be obtained with a vertical resolution of about 30 meters.

The Electron Reflectometer (ER) along with the MAG will search for an internally generated magnetic field, or possibly a remnant or crustal field, at Mars. The presence or absence of a field provides insight as to the internal structure of the planet and the planet's origin.

The USO is used as a frequency reference for the X-band communication system. The radio signal from the spacecraft is accurately monitored from the ground. As the spacecraft orbits the planet, changes in the radio signal strength and frequency reveal characteristics of the Martian atmosphere and gravity field.

The final instrument is the Mars Relay (MR). This subsystem is a UHF transponder designed to provide a communication link between MGS and landers placed on Mars my other missions. Designed and built by CNES, the French Space Agency, and provide to NASA, the Mars Relay uses a 1.3 watt beacon at 437.1 MHz to alert ground stations that the spacecraft is within view, and two receive frequencies at 401.5 and 405.6 MHz to collect ground telemetry at either 8 kilobits or 128 kilobits per second. The Relay uses the memory of the MOC to buffer the received Mars surface station data into the MGS telemetry system for playback to Earth.

Mars Relay Flight Test Description

Dr. John L. Callas then gave background on the use of the Mars Relay, a detailed description of the Mars Relay subsystem and operational use at Mars, and a detailed explanation of the current design of the Mars Relay Flight Test. (A detailed set of viewgraphs covering these subjects is contained in the Mars Relay Flight Test Workshop briefing package.) The objective of the Mars Relay Flight Test is to verify, while en route to Mars, the two-way functionality of the Mars Relay onboard the NASA Mars Global Surveyor and Russian Mars'96 spacecraft. The approach is to enlist the UHF-capable assistance of the worldwide Radio Amateur Community in carrying out this Flight Test of the Mars Relay shortly after launch.

Detection of the Mars relay Beacon has been tried before. Earth-based detection of the Mars [Balloon] Relay was attempted during the search for Mars Observer after contact was lost with the spacecraft in 1993 August. Several large antenna facilities around the world supported a search. Unfortunately after several attempts over many months, no signal from Mars Observer was ever detected.

Mars Global Surveyor will launch in 1996 November carrying a new CNES Mars Relay. To assure proper post-launch functionality of the Relay, a two-way flight test is being planned. The specific objectives of the test are:

- To verify the Mars Relay operational modes by observing at Earth the Beacon subcarriers, designated RC1, RC2, RC3 and TC;

- To confirm the far-field antenna pattern with Earth-based measurement of the beacon signal strength as a function of spacecraft rotation;

- To verify the Mars Relay receiver functionality with a radiated simulated, Earth-based Small Station signal with subsequent observation of the Relay TC signal lock-up, and a measurement of bit error rate as a function of signal level.

The Mars Relay Flight Test is currently being scheduled for Mars Global Surveyor approximately 20 days after launch, and possibly with the Russian Mars'96 spacecraft sometime soon after the test with MGS. At 20 days after launch, MGS is approximately 6 million kilometers distant from Earth. At these distances the 1.3 watt, 437.1 MHz Beacon signal from the Mars Relay is of sufficient signal level for detection by radio amateurs with large antenna systems (gain > 21 dBi).

The Mars Relay Flight Test will have three parts. The first part will be to activate the Mars Relay in the Beacon CW mode. This mode broadcasts the 1.3 W Beacon as a pure tone at exactly 437.1 MHz. This will maximize the amount of power in a single [carrier] frequency. The mode will be active for a period of at least 24 hours. While en route to Mars, the MGS spacecraft rotates about its X-axis once every 100 minutes. Furthermore, the X-axis is pointed off the Earth by approximately 30 degrees. The combination of these two effects is to produce a Beacon signal that modulates in strength with the spacecraft rotation. This feature provides an opportunity to observe different parts of the Relay's antenna pattern as the spacecraft rotates. The peak gain for the Mars Rely antenna on MGS is about 2 dBi.

After completion of this part of the test, the second part will be to activate different modes of the Relay. Each mode will be active for at least 100 minutes to allow the spacecraft to complete one full rotation. With the activation of these modes the Relay signal will drop by several dB as the Beacon is frequency modulated (FM) with one of four subcarriers. Only those radio operators with the largest antennas will be able to detect these signals from MGS. The Russian Mars'96 spacecraft Mars Relay has an antenna with 12 dBi of gain, making the signal from Mars'96 more easily detectable by radio amateurs with smaller antennas, even during this phase of the test.

The third part of the Mars Relay Flight Test will be an active uplink from the 46 meter antenna at Stanford University. The Stanford antenna will be instrumented with equipment to simulate a signal from a Mars lander. The signal will be radiated with sufficient power (~2.5 kW) to match the expect signal levels received from landers on Mars by the Relay. The radiate signal will contain a pseudo-random number (PN) sequence as the transmitted data. This data can then be analyzed to determine bite error rate (BER) after the received data is returned to Earth, via the spacecraft's X-band downlink to the DSN in the case of MGS, or via the Russian ground stations in the case of Mars'96. Additionally, those radio operators with large antennas will be able to observe the TC subcarrier modulation in the Beacon signifying the Relay receiver lock-up on the radiate signal from Stanford.

The Flight Test will be coordinated from JPL. JPL will control the operation of the MGS spacecraft and will provide instruction to Stanford for the operation of the radiate uplink. JPL will coordinate with the Russians as to the operation of the Russian Mars'96 spacecraft. JPL will generate and distribute the position (range, RA and DEC) and Doppler shifts and Doppler rates for the MGS spacecraft. This same information will be asked of the Russians in support of testing with Mars'96. JPL will serve as the collection site for observations provide by radio amateurs around the World. The received Mars Relay telemetry from MGS will be analyzed at JPL and at CNES in France. The Relay data collected aboard the Russian Mars'96 spacecraft will likely be analyzed by the Russians and CNES.

Several sites with large antennas are currently planning on supporting these tests. Stanford University's 46 meter antenna will be the only site radiating a signal to the Mars Relay on either spacecraft. Simultaneously Stanford will also be receiving the downlink signals from the Mars Relay. The Apple Valley (CA) Regional Science Center is working with JPL to re-instrument the Goldstone 34 meter standard antenna (DSS-12) to receive the Relay signals. The Algonquin 46 meter antenna in Canada with help from radio amateurs is also planning to support the Relay tests.

Frequency Allocations and Spectrum Management

Paul E. Robbins, of the Spectrum Management Group at JPL, discussed the issues associated with spectrum management and frequency allocation. JPL has made an official request for allocation of spectrum to conduct the Mars Relay Flight Test to the National Telecommunications & Information Administration (NTIA). The NTIA is the U. S. Government agency responsible for spectrum management of government frequencies. The NTIA has received the request and has asked the user community for comment on the request. Some of the frequencies to be used during the test fall within bands that have user activity. Members of the user community in Southern California have been made aware of this test and are supportive. Final approval from the NTIA to proceed with the Mars Relay Flight Test is expected later this year prior to the launch of MGS.

Radio Amateur Activities

Professor Michael Owen (W9IP) of St. Lawrence University in Canton, New York discussed various radio amateur activities supporting the Mars Relay Flight Test. The most likely radio amateur activity will utilize the Algonquin 46 meter (150 foot) antenna facility in Canada. Professor Owen is working with the facility operators and the amateur community to support the tests. Several other radio amateurs across the continent have large UHF antenna configurations capable of also supporting the Relay tests.

Professor Owen discussed the type of equipment necessary to detect the Mars Relay signals. A large antenna configuration tuned for 437.1 MHz is required. The signals transmitted (and received) by the Mars Relay are right-hand circular polarized (RCP). Antennas can either be right circular polarized, or even linearly polarized if the system can tolerate a 3 dB polarization loss. A series of connected crossed yagi antennas is one possibility. A configuration of four 15-element crossed yagi antennas can achieve 21.5 dBi of gain at 437.1 MHz.

To minimize noise and maximize the signal, a preamp connected close the antenna is required. Commercial high electron mobility pseudomorphic transistor (HEMPT) low noise amplifiers (LNA) are available at reasonable costs (~$100). These LNAs achieve high gain and system noise temperatures as low as 85 Kelvin. After the preamp the signal can be mixed and filtered down to audio baseband. Consideration should be given to Doppler effects associated with the relative motion of the spacecraft and the rotation of the Earth when choosing the mixer local oscillator (LO) frequency and the baseband width.

Many multimedia home computers or computers with audio processing cards can digitize audio signals to 16 bits with sampling rates of 44 kilosample per second per channel. This permits the digitization of baseband to as much as 22 kHz. Digital Signal Processing (DSP) software has been developed to perform Fast Fourier Transforms (FFT) on the digitized data for spectral analysis. Some of this software is available commercially.

Tracking of the spacecraft across the sky is an important issue. Professor Owen has made available shareware software that will assist amateurs in tracking the MGS and Mars'96 spacecraft on any given day for any amateur location. The software calculates the local azimuth and elevation settings for the spacecraft current position. For antennas with gains of 21.5 dBi the half-power beamwidth (HPBW) is roughly 15 degrees. Therefore continuous (active) pointing of the antenna is not necessary. Periodic repositioning may be sufficient to track the spacecraft across the sky.

Stanford's Mars Relay Flight Test Effort

Dr. Ivan Linscott of the Stanford Center for Radar Astronomy presented a description the Stanford 46 meter (150 foot) antenna facility. The Stanford facility has been used to support a number of research efforts over its years of operation. It has been a valuable astronomical research tool, probing the Galactic and intergalactic regions at multiple wavelengths. It has also conducted searches for several missing or disabled spacecraft, in addition to its effort to locate Mars Observer, with extremely fine sensitivity. The facility also contains a 30 kW UHF transmitter and feed system. This transmitter will be employed to perform the active portion of the Mars Relay Flight Test, the radiated uplink of a simulated lander signal.

In addition to the hardware assets of the Stanford facility, the Center for Radar Astronomy has developed and employed several analytical tools for extracting weak and varying signals from a significant noise background. Such techniques may permit the identification of a signal, such as the Mars Relay Beacon, several octaves below the background level. With the availability of commercial analysis software and powerful home computers, it is reasonable to consider applying these analytical tools to the digitized data collected by amateurs on their UHF equipment. Additional RF equipment will be required to digitize a complex waveform. However, many multimedia computers have two audio channels (left and right) to digitize the I and Q signals associated with a complex waveform. This possibility of complex signal analysis represents an enabling technology for weak signal detection by radio amateurs in general.

Open Discussions and Conclusions

The proximity of the spacecraft to Earth shortly after launch represents an opportunity to ask the UHF radio amateur community to participate and assist in the Mars Relay Flight Test. The expected signal levels are within the reach of amateurs operating antenna systems with 21.5 dBi of gain when listening for Mars Global Surveyor or an antenna as small as 10 dBi of gain when listening for the Russian Mars'96 Mars Relay signal due to its Relay's higher antenna gain (12 dBi).

The development of advanced analytical tools, like those from Stanford University's Center for Radar Astronomy, greatly enhances the ability for amateurs to detect very weak signals, if such tools can be successfully implemented for digitized signals by individual amateurs on their own equipment.

JPL will continue to work with the radio amateur community to help realize the developments in support of the Mars Relay Flight Test. Continually updated information on the Mars Relay Flight Test can be found on the MGS Homepage at http://mgs-www.jpl.nasa.gov/. The JPL Open House was held on the following two days, Saturday and Sunday. Many of the Workshop participants attended the Open House.