Is there life on Mars?
Was there once life on Mars?
How is the geology and evolution of the planet similar to and different from that of Earth?
Where is the best place on the planet for humans to visit?
These are questions that robotic missions to the red planet are being designed to help answer. Our project represents a piece of that effort -- a UHF "proximity-link" radio that sends data to a Mars orbiter (picture at right), which then relays the data back to earth. The project is funded by the Mars Technology Program office at Cal Tech’s Jet Propulsion Laboratory under a contract from the National Aeronautics and Space Adminstration. The goal is to develop a highly miniaturized, low-mass, low-power radio transceiver for future robotic "scout" missions. As part of the "Base Technology" group of projects, the Mars Proximity Microtransceiver provides an enabling factor in the design of new classes of scout vehicles such as aerobots (balloons, airplanes) and small networked-landers / probes. Potential applications also include low-cost backup communcations and telemetry on rover designs and proximity links in future earth/moon and outer-planet missions.
Proximity Link Communications
Existing transceivers carried aboard the highly-successful Mars Exploration Rovers (MERs), popularly known as Spirit and Opportunity, are manufactured by L-3 Communications. These radios measure approximately 2000 cm3, weigh approximately 2 kg, and consume about 5 Watts on receive and 45 Watts on transmit. The radios operate at UHF (400 MHz transmit and 440 MHz receive frequencies) according to CCSDS Proximity-1 protocols and send science data to the orbiters through a small omnidirectional "whip" antenna on the rover (shown circled in green). With 10 Watts of transmited RF output power, the resulting signal levels at the orbiter are on the order of -110 dBm, supporting data rates of up to 256 kbps, depending on the geometry of the orbital pass. Received signals downlinked from the orbiter are sent at nominal rates of 8 kbps to provide good margin for critical command reception. The radios reside physically within the Warm Electronics Box (WEB) of the MER body (below the solar panels), which keeps them at or above -55 degrees centigrade. Details of the proximity link and other systems which made the MERs so successful can be found in Article 10 at the DESCANSO website.
The radio being developed in this project is not a replacement for those currently in use. Rather, it is an alternative design opening up new possibilities for scout craft development. The goals of the project are to reduce the size, mass, and power of the communication system by at least two orders of magnitude. In addition, the project aims at operating the electronics outside the traditional warm-box. To achieve these capabilities, certain levels of performance are traded off. First, RF output power will be 100 mW to 1 Watt, translating to a modest reduction in transmitted data rates relative to existing higher-power designs. Second, the micro-transceiver will support only half-duplex operation, sacraficing some ranging capability. Finally, the digital packet processing is scaled back within the transceiver and must be assisted by the host-vehicle's microcontroller to perform such functions as go-back-N ARQ. In return for these limitations the size/mass/power parameters will be only 10 cm3, 10 gms (PCB form-factor version), and 0.05 W on receive / 0.3 to 3 Watts on transmit. When combined with other scientific instrument miniaturization efforts and scout vehicle concepts currently under development, a wide area of new opportunities is enabled. Possiblities range from sending large numbers of airborne vehicles in a single launch, to developing small expendable probes and networked lander-craft. With these capabilities, significantly higher percentages of the planet's surface can be explored than ever before.
Microtransceiver Performance Goals
The following table summarizes the target specifications for the Proximity Microtransceiver.
Transceiver circuits are currently in development. While the basic parameters in this table are believed to be accurate, final performance parameters are subject to change. Please consult project personnel for the latest specifications before applying this information in scout proposals or designs.