On its seven month journey from the Earth to its November 26th landing on Mars, NASA’s InSight Lander had two little friends to keep it company. Called Mars Cube One (MarCO), and designated as MarCO A and MarCO B, the briefcase-sized CubeSats were launched from the Centaur upper stage of InSight’s Atlas V launch vehicle. They flew in close formation with InSight and provided additional communications capability during the successful landing of InSight onto the Martian surface.
CubeSats are not new. They are a class of spacecraft that are based on a standardized small size and often use off-the-shelf technologies. Their relatively low cost and mission specific nature allows them to be made by university students. Hundreds have been launched into Earth orbit using extra payload mass available on launches of larger spacecraft.
Pictured is an artist's rendering of the twin Mars Cube One (MarCO) spacecraft as they fly through deep space. The MarCOs relayed images from the Martian surface minutes after the InSight Lander touched down. (Image source: NASA)
According to a NASA news release, “The basic CubeSat unit is a box roughly 4 inches (10 centimeters) square. Larger CubeSats are multiples of that unit. MarCO's design is a six-unit CubeSat. Each of the two spacecraft has a stowed size of about 14.4 inches (36.6 centimeters) by 9.5 inches (24.3 centimeters) by 4.6 inches (11.8 centimeters).” The MarCO spacecraft mark the first time that CubeSats have been sent outside of Earth orbit.
The MarCO CubeSats flew independently of InSight and their propulsion system used compressed R236FA gas—a common propellant used in fire extinguishers. According to NASA, “Each MarCO has eight thrusters that can release this cold-gas propellant in different directions from a single, shared tank. The thrusters will operate for trajectory adjustments and for de-saturating the reaction wheels.” The MarCO spacecraft pioneered CubeSat use of propellant for attitude-control reaction wheels. NASA noted that Earth-orbiting CubeSats typically control their attitude with electromagnet devices that “push” against Earth’s magnetic field, an option that was not available to MarCO in deep space.
Two MarCO CubeSats were deployed for redundancy, but both operated perfectly on the trip to the Red Planet. Each was positioned approximately 6,200 miles away, on either side of the InSight spacecraft, for safety. Although not necessary for the success of the InSight Mars mission, the extended flight and landing provided an opportunity to test the concept of adding CubeSats to future missions.
During InSight's entry, descent, and landing (EDL) operations, the lander transmitted information on the UHF (ultra-high frequency) radio band to NASA's Mars Reconnaissance Orbiter (MRO) flying overhead in Mars orbit. MRO forwarded EDL information to Earth using a radio frequency in the X band. Because MRO cannot simultaneously receive information over one band while transmitting on another, however, confirmation of a successful landing could be delayed by more than an hour before it's relayed to Earth using the MRO. Because MarCO's softball-size radio provided both UHF (receive only) and X-band (receive and transmit) functions capable of immediately relaying information received over UHF, pictures from Mars could be received just minutes after the lander touched down onto the planet surface.
Following the landing, both MarCO CubeSats continued in their elliptical orbit around the sun. Their electronics and propulsion systems were expected to last for a few weeks after leaving InSight behind and continuing on their Mars fly-by.
Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.
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