Micro Satellites on their way to Mars

NASA is sending two CubeSats to Mars. CubeSats are one of the most promising candidates for the current trend towards small and cheap, multi-purpose satellites and space probes. These new devices are about the size of a shoebox. If these types of devices are successful they could save a large amount of money. The most expensive part of space travel is getting the payload up into space. The smaller and lighter micro-satellites can be fit into the gaps of the cargo-hold when conventional large satellites or probes are launched.

^{Artists impression of one of the MarCO CubeSats by NASA, JPL (public domain)}

Currently, NASA is sending the InSight landing craft to Mars. This is a conventional probe about the size of a normal car, weighing more than 750 kilograms. It is due to land on Mars’ surface this November. In a first, NASA launched two CubeSats alongside the InSight lander. These CubeSats, known as MarCO-A and MarCO-B will follow the main spacecraft. They are designed to relay information about InSights approach and landing on Mars back to Earth. They are not critical to the mission of the lander but they are an experiment, whether or not these small probes can be reliable and useful for future missions.

Last month, on May 9th 2018, MarCO-B was already in the news as the first CubeSat to take a picture that contains both Earth and Moon. This picture was taken to celebrate the milestone of the micro-satellites reaching the 1 million kilometres (about 620,000 mi) mark away from its home planet. The image shows Earth and Moon as small dots in the sky and is a homage to the Pale Blue Dot image taken by the Voyager spacecraft over 28 years ago.

^{Image of Earth and Moon taken by the MarCO-B (Wall-E) CubeSat by NASA, JPL (public domain)}

The two crafts, MarCO-A and MarCO-B are trailing the InSight lander on its way to our neighbour planet. This also involves any course corrections that the main spacecraft has to undergo to make sure that it hits its target. The NASA engineers had to be inventive because the traditional technology for the thrusters needed for any course correction was too big to fit on the tiny crafts. The went for a solution involving a small canister of compressed gas that is released upon command. The gas jet is enough to alter the trajectory of the lightweight devices.

The gas that is used in the thrusters is a gas that is also commonly used in fire extinguishers. This form of propulsion has similarities to a scene in the Walt Disney movie Wall-E in which the main character uses a fire extinguisher to propel himself through space. As a result, the researchers at NASA decided to nickname the two micro-probes Wall-E and Eva.

During the past week, MarCO-A and MarCO-B performed their first course-correction. The manoeuvre went without a glitch for the first of the two partners in space. MarCO-B, on the other hand, had some small problems. Due to a leak in the thruster valve, the thrust from the gas jet was smaller than expected. The scientists had already detected the leak because it created a small, uncontrolled thrust on the spacecraft. After the first course correction, the scientists decided to analyse all the data they had gathered. They are planning to initiate multiple small thrusts during the coming weeks to countermeasure the errors in the trajectory. They are confident that MarCO-B will be on its correct path at the end of June.
When the two probes reach Mars they will relay data from InSights landing back to Earth. After this, the two friends will have completed their mission. Hopefully, they will have shown that CubeSats can be used as support vehicles for other long distance missions. While the failure rate is probably going to be higher than that for conventional large spacecrafts, the reduced size and lower cost will more than make up for the shortfall.