Mars Cube One (or MarCO) is a Mars flyby mission consisting of two nanospacecraft, of a size that JPL has referred to as a "6U CubeSat", that is planned for launch in 2018 or later alongside NASA's InSight Mars lander mission. Mars Cube One is intended to provide a communications link to Earth for InSight during mission critical entry, descent, and landing when InSight will be out of sight from the Earth. Mars Cube One is expected to be the first spacecraft built to the CubeSat form to operate beyond Earth orbit.
The launch of Mars Cube One is being managed by NASA's Launch Services Program. The launch was originally scheduled for 4 March 2016 on an Atlas V 401, but the mission was postponed to 2018 after a major test failure of an InSight instrument.
The two "MarCO" CubeSats (A and B), are identical. They measure Template loop detected: Template:Convert/x (about 10.5x the volume of a 10x10x10 cm 1U cubesat) with one of them serving as backup. They will fly by Mars during the landing phase and relay InSight's telemetry in real time. MarCO is a technology capability demonstration of communications relay system.