CubeSats to Mars and beyond
CubeSats have gone from curious toys to capable tools. When CubeSats started flying a decade ago, many dismissed them as best suited for training students given their limitations. Advances have expanded their capabilities in areas as diverse as imaging the Earth and studying space weather, attracting greater interest from scientists and venture capitalists.
(It's helped that CubeSats have gotten bigger, too, using that original 10-centimeter-cubed form factor as a building block for larger spacecraft, particularly the “3U” variant about 30 centimeters long.)
All of that activity and interest involving CubeSats, though, has been primarily limited to spacecraft in Earth orbit. Some scientists and engineers have started to explore what CubeSats could do beyond Earth orbit, including missions to the Moon and near Earth asteroids, with mission concepts being developed for launch later in the decade. But that interest is accelerating, with the first interplanetary CubeSat mission now under construction for launch next year, and concepts for increasingly ambitious missions under study.
That first interplanetary mission is now slated to be a JPL project called Mars Cube One, or MarCO. A pair of 6U CubeSats roughly 12 by 24 by 36 centimeters in size, the MarCO spacecraft will hitch a ride on next March’s Atlas V launch of the InSight Mars lander mission. Deployed from the upper stage of the rocket, MarCO-A and -B will coast in interplanetary space on the heels of InSight.
MarCO’s mission unfolds when the spacecraft arrive at Mars in September 2016. As InSight enters the Martian atmosphere, it will transmit telemetry at eight kilobits per second on a UHF band too weak to be detected back on Earth. The MarCO cubesats, flying by Mars at an altitude of 3,500 kilometers, will receive those UHF signals and retransmit them on X-band frequencies back to Earth in real time.
MarCO won’t be the only relay for InSight during landing: the Mars Reconnaissance Orbiter (MRO) will also listen for the UHF signals for transmission back to Earth. However, MRO can’t simultaneously receive and transmit, so it will store InSight’s entry, descent, and landing telemetry for later retransmission back to Earth, a delay of an hour or more. MarCO will be able to relay the telemetry without delay.
MarCO is considered an experimental mission: one that provides a useful capability in support of InSight, but not an essential one. “MarCO is an experimental capability that has been added to the InSight mission, but is not needed for mission success,” said Jim Green, head of NASA’s planetary science division, in a June press release about the mission.
MarCO has come together quickly, JPL’s Andrew Klesh said in an August 11 presentation at the annual Conference on Small Satellites at Utah State University in Logan. It passed a mission concept review last October, allowing work on MarCO to begin in earnest. “We have a launch delivery date of December 1st of this year,” he said, with assembly of flight hardware starting the week of the conference.
For a CubeSat, MarCO is rather complex. “It’s quite a deployable mission,” Klesh said. Two solar panels deploy from either side of the spacecraft, generating 35 watts of power at launch, decreasing to 17 watts at Mars. A UHF antenna deploys from the bottom of the spacecraft to receive the InSight transmissions. A large “reflectarray” antenna unfolds from the top to transmit the high-gain X-band signal back to Earth.
MarCO is rather large for a CubeSat: the 6U form factor is only now starting to be used for missions, and at a mass of 14 kilograms, it’s far heavier than the typical 1U or 3U CubeSat. However, it makes use of much of the technology, from spacecraft subsystems to launch vehicle deployers, developed to support the broader CubeSat community.