Unlike most interplanetary missions, NASA’s InSight lander didn’t make the journey to Mars alone. The MarCO (Mars Cube One) satellites headed into space on the same rocket, and the shadowed InSight all the way to its encounter with Mars. These tiny satellites were not essential to InSight, but they performed their intended functions perfectly. Now, these robotic pioneers have winked out, but that doesn’t equate to failure.

The Mars Cube One satellites, MarCO-A and MarCO-B, coasted along near the InSight lander as it headed for Mars. As the name implies, these were low-cost CubeSats seen most often in low-Earth orbit research. They’re called “CubeSats” because a single unit (or 1U) is a 10-centimeter cube. For more complex experiments, engineers can work with 2U, 3U, and larger designs. The MarCO satellites, nicknamed Eve and Wall-E after the characters in the Pixel film, were 6U designs.

NASA spent a mere $18 million on the two satellites, which is a bargain for something you’re sending into deep space. That was exactly the point — CubeSats have only operated in Earth orbit, but the MarCO mission showed they could also perform at greater distances for many months. The probes had experimental high-gain antennas, but most of the parts were off-the-shelf.

MarCO-A and MarCO-B snapped some photos and relayed communication data for InSight as it landed on Mars late last year. NASA had contingency plans in place in case the MarCO probes failed, but the little satellites came through. Unfortunately, the simple cold-gas propulsion in the CubeSats lacked the power to maneuver them into orbit of Mars. They continued to drift along, pinging NASA on occasion to confirm they were still operational despite having already completed their mission. Now, Eve and Wall-E are silent.

NASA says MarCO-B last made contact on December 29th, and MarCO-A checked in a few days later on January 4th. The agency doubts either probe will phone home again, but this mission could already reshape unmanned exploration of the solar system. Most deep space probes cost hundreds of millions of dollars, but CubeSats are comparatively cheap. The Mars Cube One mission proved that these devices can complete basic tasks in deep space without breaking the bank. We might see many more missions to other planets based on CubeSat designs in the future.

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