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Let's go to Mars

Two CubeSats fly to Mars and call the landing live

MarCO-A and MarCO-B, 13.5 kilograms each, were the first CubeSats ever to leave Earth orbit — and they carried InSight's descent telemetry home live at 8 kilobits per second.

Two engineers holding a briefcase-sized spacecraft mock-up between them, its flat solar panels folded out to either side.
A full-scale mock-up of a MarCO CubeSat, held by JPL engineers Joel Steinkraus and Farah Alibay. The flight articles were this size. · Image: NASA/JPL-Caltech

InSight's landing signal reached Pasadena at 19:52:59 UTC on 26 November 2018, roughly eight minutes after touchdown, the time light takes to cross from Mars. Telemetry from a landing is relayed live by an orbiter overhead, or played back later; this time two objects the size of briefcases were flying past the planet.

MarCO-A and MarCO-B were 6U CubeSats, 36.6 by 24.3 by 11.8 centimetres folded and 13.5 kilograms each, built at JPL from largely commercial parts for a reported 18.5 million dollars the pair. They launched with InSight on an Atlas V 401 from Vandenberg on 5 May 2018, then flew their own trajectory, the first CubeSats to operate beyond Earth orbit. Eight cold-gas thrusters ran on R-236FA, a hydrofluorocarbon also used in fire extinguishers — hence the names Wall-E and EVE, after a film robot that flies with one.

They carried no science instruments, only a UHF receiver, an X-band transmitter, a flat folding reflectarray antenna and engineering cameras. The job was to catch InSight's 8 kbit/s UHF stream during entry, descent and landing from about 3,500 kilometres away and push it straight out to the Deep Space Network unstored: a bent pipe across 146 million kilometres. Mars Reconnaissance Orbiter recorded the descent but returned it afterwards, and Odyssey's confirmation that InSight's solar arrays had unfurled reached Earth about five and a half hours after touchdown.

MarCO-B leaked propellant almost from liftoff and needed constant attention to stay pointed. It worked anyway. On 2 October, from 12.8 million kilometres out, its wide-angle camera returned the first image of Mars taken by a CubeSat, a small red dot with its own antenna in frame; at 12:10 p.m. PST on landing day it took a parting shot, 7,600 kilometres past the planet and receding.

MarCO-B was last heard on 29 December 2018 and MarCO-A on 4 January 2019, drifting on solar orbits beyond Mars.