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Telecom Closing Comments [Image]

Let's reflect on what we've learned about Mars Microrover Telecommunications and see what the future may hold for other Rover missions.

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Before we bid "farewell", a few words on what we learned during this project and then a discussion on the telecommunication systems for future Mars missions.

What We've Learned....

Our telecommunication team gained plenty of valuable experience during this project. We accomplished the bottom-line goal of this project, which was to deliver a functional communication system within budget and on time. The radio modems and antennas were not fancy, but they are functional as required. We encountered many challenges along the way, some expected, some not. We expected the challenges of the space radiation environment, the harsh temperature, shock and vibration environment. The unexpected problems were mainly due to undefined electrical interfaces with other systems, and a few anomalies during systems testing. We certainly attempted to establish these interface agreements early in the project, but a few issues always came up as the different systems were being built and tested with each other.

Future Mars Telecommunications systems, Challenges and possible solutions...

Future Mars rover missions will demand more challenging requirements on the telecommunications systems. These rovers will be required to cover longer distances from their lander spacecrafts. In some cases, over-the-horizon communication will be required. These future rovers will continue to have mass and DC power constraints. The DC power availability will most likely remain the same, if not decreased. Which means, the radio link will have to be made more reliable over farther distances, with lower DC power available. The cold Martian environment will continue to be a challenge. Future rovers are expected to operate over longer periods of time. Compared to Sojourner's requirement to operate for 7 days, future rovers are expected to operate for several weeks and perhaps months. Hardware fatigue from temperature cycling is the main problem with these longer missions. There remains of course space radiation problems as well. With the trends toward limited budgets and funding for these future rovers, the need to use commercial grade hardware will probably continue.

The step to take towards addressing the challenges above is "miniaturization" of the telecommunication system. Smaller hardware usually means less DC power consumption and/or more power efficient systems. Smaller hardware systems are more thermally rugged. Smaller components are much easier to keep thermally stable, or to keep warm, should it become necessary. With the recent advances of the wireless industry, personal cellular phones and the like, the future rover telecommunication systems should perhaps take advantage of this technology growth.

Future Telecommunication Relay Systems at Mars...

There are five broad classes of future Mars exploration systems which will require telecommunication relays similar to that carried by the Pathfinder lander for the Sojourner microrover:

  • Full-size long-range rovers, derivatives of the Sojourner microrover, which will be capable of long traverses across Mars, far beyond the radio horizon seen by their landers. A long-range rover will be carried aboard the 2001 Mars Lander currently in its development phase. This will be the Mars Surveyor '01 Lander and Rover mission. Its goal is to characterize the terrain over a much larger area, covering tens of kilometers. This rover (likely modeled after Rocky VII) will need a more complex "over-the-horizon" telecommunications system enabling it to communicate with the lander and the Mars Surveyor '01 orbiter. There are many different possibilities for this type of telecommunications system. One possibility is to use a single UHF link for lander and orbiter telecommunications. Another possibility is to use a single radio with dual frequency operation, one UHF frequency for communication with the lander and an L-band (1 to 2 GHz) frequency for communicating with the orbiter. This type of dual-frequency communication may require two different antennas on the rover, one for omni-directional UHF communications with the lander and one low-gain, broad-beamwidth antenna for overhead orbiter communications. A UHF link to the lander can take advantage of some of the Sojourner hardware heritage, and an L-band link makes it possible to use a flat microstrip antenna array for orbiter communications, reducing rover solar array shading. For 2003 there are plans to send yet another lander and rover to mars. This will be the Mars Surveyor '03 Lander and Rover mission. There will also be a Mars Surveyor '03 orbiter. This rover will also explore a much larger area of mars looking for a prime landing site for a future sample return mission, perhaps as early as 2005. Long-range rovers will probably be carried on all subsequent Mars landers as well.

  • Mars Microprobes, the first of which will be carried aboard the 1998 Mars Surveyor Lander. The Mars Microprobes are surface penetrators which are released on a direct, ballistic descent through the Martian atmosphere. The first generation of Microprobes are to make direct measurements of the material into which they have embedded themselves; subsequent versions may carry other instruments such as seismometers which require direct coupling to the Martian surface.

  • nanoRovers, cigar-box-sized rovers with masses of less than 1 kg, but which nonetheless carry a capable set of science instruments for imaging and measurements of the composition of surface minerals. A nanoRover is to be carried by the Japanese MUSES-C spacecraft to the asteroid Nereus in 2002, and duplicates may be carried aboard Martian landers beginning with the 2001 Mars Lander. This rover is baselined to communicate with the hovering MUSES spacecraft at a frequency of about 1.9 GHz through a circularly polarized patch antenna.

  • Balloons and aerial connaissance craft, of a nature not yet fully defined, for deployment at Mars sometime after the year 2000.

  • Manned expeditions.

    These five types of Mars exploration systems in fact require two distinctly different relay paths. The nanoRovers will operate in the vicinity of their host lander, just as Sojourner does. These "lander-local" relay applications employ the infrastructure of their landers to accomplish the long-range transmission to and from Earth. Because nanoRovers are of a size such that an antenna at the 459.7 MHz frequency used by Sojourner would overwhelm the basic vehicle, a move to higher frequencies (shorter wavelengths) is necessary. The system baselined for the nanoRover operates at 1902 MHz. It takes advantage of technology and components developed for the Japanese Personal Handyphone System and the European Digital Cordless Telephone system, much in the same way that Sojourner utilized Motorola commercial hardware in volume production targeted for the terrestrial short-haul data transmission market.

    Of the remaining types of Mars exploration systems, all will need "comm-to-orbit", that is, communication relay to and from Earth, not by way of a lander but by way of an overhead orbiting satellite or group of satellites. The majority will require a two-way communication link with Earth, to send data and receive commands. Additionally, most will require radiometric position determination, referenced to the instantaneous and known position of the orbiting relay platform to localize their surface position and thereby to give context to the data they are acquiring. The first comm-to-orbit system will be demonstrated by the Mars Microprobes, utilizing a French-designed Mars Balloon Relay System which is currently enroute to Mars aboard the Mars Global Surveyor spacecraft. This system is quite limited in its capabilities, for it does not support the forward command path or radiometric position determination, only data relay back to Earth. It operates at 401 MHz and 437 MHz, and it has set a de facto operating-frequency standard for all near and intermediate timeframe comm-to-orbit relay systems. Fortunately, the Martian exploration systems discussed so far that will need comm-to-orbit are all large enough to accommodate antennas for this frequency range.

    One can appreciate upon reflection that the very nature of comm-to-orbit relay systems involves not only the surface exploration elements below but also an orbiter or orbiters overhead. There must be a synergy between the infrastructure capabilities of the orbiter (hardware and orbit as chosen) with the data volume, rates, and allowable latency established by the surface (or airborne) elements. Detailed studies are being conducted right now by the Telecommunications and Mission Operations Directorate at JPL in concert with their consulting engineering firm, Stanford Telecom, to assess these needs and to design an evolutionary system architecture that will grow to fulfill the needs of upcoming missions, both robotic and (eventually) manned. Along these lines, a recently discussed goal is to have a dedicated Mars Relay Satellite system in place to support the first manned mission to Mars which is capable of live High Definition Television transmissions of the surface operations: we at JPL are ready for the challenge.

    Thank You and Farewell from the Mars Microrover Telecommunications Team

    Telecom Team 1-4 [Image]

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    All information on this site, including text and images describing the Rover is copyright 1997, Jet Propulsion Laboratory, California Institute of Technology and the National Aeronautics and Space Administration.

    This page was last updated Friday October 3, 1997.
    Web Author: Scot Stride, NASA-JPL, Telecommunications Hardware Section 336

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