NASA tried a communications experiment with its latest mission to Mars, and it turned out spectacularly well.
On Nov. 26, as the probe known as InSight plummeted through the Martian atmosphere on its way to the planet's surface, two miniature spacecraft — known collectively as MarCO — relayed telemetry from InSight to Earth, assuring all those watching that the landing of the probe was proceeding successfully and was soft.
In the past, spacecraft were only able to transmit back to Earth simple tones during a landing. Those tones would change for major milestones, such as parachute deployment, the firing of landing rockets or touchdown.
This time, as InSight team member Christine Szalai called out altitudes from the control room in the Jet Propulsion Laboratory in Pasadena, she was reading off actual data from InSight's onboard radar. It was live play-by-play, bearing in mind that the radio signal from Mars took approximately eight minutes to reach Earth.
The MarCO spacecraft are what are known as cubsesats. These are standardized minispacecraft. The cubesat model first appeared in 1999, as part of a program aimed at making it easier for university students to get projects into space.
The original cubesat was just 4 inches on a side, and weighed less than 3 pounds. Later versions allowed multiples of the original dimensions. The MarCOs are the size of six of the original cubesats stacked together.
NASA initially was interested in cubesats for their educational value, but the space agency has begun to see them as more broadly valuable.
"MarCO was primarily a technology demonstration," explains JPL mission engineer Anne Marinan. "There were brand new components and technologies that we flew for the very first time in deep space."
The MarCO satellites use a new kind of antenna to help a low-powered radio signal reach the Deep Space Network antennas back on Earth. They also rely on a new kind of propulsion system.
Marinan says the new technology hasn't always worked perfectly — one of the thrusters kept leaking, making the spacecraft hard to steer. But "it worked perfectly when it had to," she says.
The MarCOs and InSight left Earth on the same rocket last May. The two minisatellites then trailed close behind InSight on its way to Mars.
Marinan says the success of the MarCO in relaying InSight's signal may help make small, inexpensive satellites a regular partner of planetary landing missions.
After its relay mission was over, the MarCOs sailed past Mars; they'll go into orbit around the sun. Marinan says the research team on Earth will check in on the cubesats from time to time, just to see how long they last.
InSight, on the other hand, is just starting its mission to explore the interior of Mars. It's expected to operate on the Martian surface for about two Earth-years.
Marinan, who only recently earned her Ph.D., says MarCo was her first assignment at JPL. So, what do you do for an encore when your first mission worked so well?
"I am actually putting together another spacecraft," Marinan says. It's another miniature satellite, this time with its own science mission: to study a near-Earth asteroid.
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