Even as the InSight lander heads to Mars, it is being accompanied by two test cubesats, the first such smallsats to ever fly an interplanetary mission.
The MARCO mission objective is a challenging one. The team will provide a dedicated relay during Mars InSight’s descent to the surface of the Red Planet on November 26, 2018. Rather than entering orbit, the CubeSats will pass 2,175 miles (3,500 kilometers) from Mars during the larger mission’s crucial landing phase. Mars will be 97.5 million miles (157 million kilometers) away at the time, making for an 8.7-light-minute communications lag from Mars to the Earth. The lag means that NASA engineers will need to wait 8.7 minutes to see whether the landing was successful, equivalent to Curiosity’s “seven minutes of terror;” meanwhile, if all goes well, MARCO will have a front-row seat to the show. While the success of the InSight mission isn’t dependent on MARCO, the CubeSats will provide a black box data recorder of all aspects of the mission’s descent.
If these cubesats succeed in accomplishing their engineering test missions, their true innovation will not be engineering but cost reduction. If they prove that cubesats can be designed as interplanetary probes, the costs to build and launch such missions will be drastically reduced. Not only do cubesats routinely use cheaper off-the-shelf components, they are far lighter than standard satellites, which means a smaller, cheaper rocket can launch them.
The data-relay test of these cubesats however is quite important, nonetheless. See my post above.