Two CubeSats, MarCO A and MarCO B, have gone where no CubeSats have gone before: beyond low Earth orbit. MarCO A and B—short for Mars Cube One—traveled to the Red Planet in a mission to prove that the tiny satellites can be useful in deep space.
The MarCO satellites made the journey alongside NASA’s InSight lander. According to NASA, the lander successfully touched down on Mars just before 3 p.m. ET on Monday, 26 November. InSight will break new ground as it probes deeper into Mars’s surface than previous landers, in order to explore the composition of the planet’s interior.
Not to be outdone, however, MarCO did more than set a new distance record for CubeSats. The two satellites have potentially changed how NASA puts rovers and landers on other worlds.
“What MarCO looks like will probably pave the way for future deep space CubeSats,” says Nacer Chahat, an antenna engineer for MarCO at NASA’s Jet Propulsion Laboratory (JPL), who wrote for IEEE Spectrum about the challenges that came with designing MarCO’s antennas. MarCO’s success in passing on information from InSight while the lander touched down opens the door for a “bring your own communication relay” approach to future missions.
In the past, when missions to Mars like the Phoenix lander or Curiosity rover reached the planet, they relied on orbiters already in place like Mars Odyssey and the Mars Reconnaissance Orbiter (MRO) to send information during the critical minutes of descent. Referred to by NASA engineers as “7 minutes of terror,” the descent of any mission to the planet’s surface is when one of any number of things could go wrong.
The trouble with using existing orbiters to keep Earth informed about a mission’s status is that the orbiters often have to be guided into a new orbit to do the job effectively. This takes time away from their own missions, uses up extra fuel, and shortens their life-spans.
The amount of time it takes for the orbiters to send the information back to Earth is also not ideal. According to Chahat, if NASA and JPL were waiting for MRO to send updates on InSight’s status, it would take 3 hours to know how the lander was doing due to transmission times and data processing.
Instead, the MarCO satellites used a technique called bent-pipe relay to send data back to Earth in near real time. Rather than clean and encode the data, bent-pipe relays just amplify the signal after converting it from an uplink to a downlink frequency. With bent-pipe, JPL knew what had happened to the lander with a delay of only 8 minutes and 7 seconds—the amount of time it took for the signal to physically travel from Mars to Earth.
The hope is that future missions can use CubeSats with bent-pipe relays to easily provide real-time communications for the critical moments during entry, descent, and landing, instead of shuffling other orbiters into position for just a few minutes of work.
InSight’s 7 minutes of terror began when the lander separated from the cruise stage that’s carried it and protected it all the way to the Red Planet. After taking a few minutes to orient itself, the lander activated its radar to help it spot the ground. Then, the legs deployed and the lander jettisoned its heat shield before releasing its parachutes. “The whole thing is super quick,” says Chahat.
In all, MarCO did its job in about 19 minutes. The satellites started sending telemetry about 7 minutes before InSight’s entry, continued sending it during the lander's 7-minute descent, and stopped about 5 minutes after touchdown. In those 19 minutes, the CubeSats kept JPL informed in as close to real time as possible. JPL is still relying on MRO to confirm the data that MarCO has sent.
Aside from proving that a “bring your own communications relay” approach can work for future missions, the MarCO satellites also demonstrated several new engineering tricks. The reflector antennas, which have already been in use for several months with excellent gain, according to Chahat, are flat antennas designed to mimic a parabolic dish while taking up far less space.
The ultrahigh-frequency loop antenna that received data from InSight was also designed specifically for the MarCO satellites, as was the Iris V2 CubeSat Deep-Space Transponder that enabled the CubeSats to communicate with NASA’s Deep Space Network on Earth.
MarCO B snapped a picture of Mars (and part of its own reflector antenna) after InSight landed. Photo: NASA
The MarCO satellites even took time to take pictures of Earth and Mars during their trip—a brief side project which was not originally part of the plan, according to Chahat.
MarCO may be the first CubeSats in deep space, but they won’t be the last. “There are different advantages that come with CubeSats,” says Chahat. “For specific mission goals, they can be useful.” Their small size, simplicity, and cheapness makes it easy to send spares on the mission for redundancy, and there are some constellation-based applications that could be feasibly done only with CubeSats.
NASA’s upcoming Exploration Mission-1—the first flight of the new Orion spacecraft on the Space Launch System—will carry three different CubeSat projects into deep space. Chahat is also hoping that there will be an opportunity to put a CubeSat in orbit around Mars as an independent orbiter to see how long it survives and how well it performs.
These missions, and others, will owe some of their success to the MarCO satellites and what JPL engineers learned from them during InSight’s landing. For the satellites themselves, however, they’re continuing past Mars after doing their 19-minute job.
The last thing they sent back to Earth was an image that InSight took 2 minutes after landing. The image was taken by the instrument-context camera located under the lander deck, and confirmed that the lander had settled in a spot that enabled it to conduct its research.
Now, MarCO A and B will drift farther into deep space, having already paved the way for CubeSats to follow them well beyond Earth. “We like to say that MarCO is a pathfinder for future missions,” says Chahat.