While recent Mars missions have been relatively successful, they still suffer from the fact that they're a hundred million miles from Earth and communications are limited – especially during the critical minutes of landing. Built by the Jet Propulsion Laboratory (JPL) in Pasadena, California, MarCO is a technology demonstrator made of six CubeSat units measuring 14.4 x 9.5 in x 4.6 in (36.6 cm x 24.3 cm x 11.8 cm) that is hoped can fill this communications gap.
InSight (short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) and the MarCO spacecraft are scheduled to launch in March 2016 Vandenberg Air Force Base, California atop an Atlas V rocket. After liftoff, the MarCO spacecraft will separate, deploy solar panels and antennas. They will fly to Mars independently of the InSight spacecraft and will provide status information to mission control after the lander touches down on September 28, 2016.
This information is not necessary to the mission because it will also be relayed by NASA's Mars Reconnaissance Orbiter (MRO), but it will not only demonstrate the feasibility of the technology, but also return the information an hour earlier than the MRO.
NASA says that if this demonstration proves successful, it could lead to "bring-your-own" communications for deep space missions to Mars and beyond.