When NASA's Mars Reconnaissance Orbiter reaches the Red Planet next month, it will immediately seek out areas where water once flowed, try to identify habitats where ancient life might have thrived, and start mapping the entire planet in unprecedented detail. But the orbiter's arrival at Mars will also set the stage for a new epoch in spacecraft telecommunications. Its onboard Electra UHF relay transceiver [see photo, " "] will serve as an engineering test bed for new communications and navigation technology that will be required for all future orbiters, landers, and rovers, to provide the faster data rates required for transfer of information from rovers and landers on the Martian surface to orbiters circling above.
The early Mars landers, like the 1976 Viking and the 1997 Mars Pathfinder, sent data directly back to Earth using X-Band antennas that could manage no more than 1 to 10 kilobits per second of data. But when Spirit and Opportunity landed on Mars in January 2004 to explore its surface, they carried cameras that could produce dramatic panoramic pictures representing 500 megabytes of data. Accordingly, rather than transfer data straight back to Earth, their X-Band system first transferred data to the Mars Global Surveyor and Mars Odyssey orbiters, which were equipped with UHF transceivers that could support transfer rates of up to 128 kb/s.
In the new system to be tried out with the Mars Reconnaissance Orbiter, once the orbiter receives data from a lander or rover it will transmit the information back to a series of large radio telescopes located on Earth, the Deep Space Network. The orbiter's 3-meter-long high-gain antenna and 100-watt transmitter will be able to send data at up to a maximum of about 6 megabits per second at the minimum Earth-to-Mars distance of 55.7 million kilometers and roughly 0.6 Mb/s at the maximum distance of 401.3 million kilometers. The Mars Reconnaissance Orbiter has 160 gigabits of solid-state memory and a processor able to operate at up to 46 million instructions per second, to store and manipulate data obtained from craft on the surface of Mars.
The first Mars rover to make use of the Electra system will be the Phoenix Mars Lander, scheduled to land in the north polar region of Mars in May of 2008. But because this lander was built using spare parts from the canceled 2001 Surveyor Lander mission, it is not outfitted with an antenna capable of communications with Earth. Instead, Phoenix will transmit all its data to Electra on the Mars Reconnaissance Orbiter, which will forward it to Earth.
The 2009 Mars Science Laboratory rover will be the most sophisticated rover ever sent to Mars and will also be the first rover to have its own scaled-down version of the Electra transceiver, called Electra-Lite. Built as part of a successful partnership between NASA's Jet Propulsion Laboratory, in Pasadena, Calif., and the Space Division of L-3 Communications Cincinnati Electronics, in Mason, Ohio, Electra will carry the first in-flight reprogrammable software designed for use in a long-lived Mars telecommunications relay infrastructure.
Thus, it "offers a highly capable, flexible, and evolvable framework for relay communications in support of Mars exploration," says Chad Edwards, the Mars chief telecommunication engineer at JPL. New error-correction codes can be implemented at any time during a mission, and protocols can be modified in response to unforeseen developments.
Besides serving as a transceiver for all Mars missions currently planned, Electra will also provide a navigational or locational beacon for incoming spacecraft or any craft on the surface of Mars. Electra will make a precise measurement of the Doppler shift of the UHF radio signal from such craft as the orbiter passes overhead, revealing speed and distance from Mars, or location on Mars.