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CAT Project Aims to Propel CubeSats to Space with Water

By Wesley Fenlon

Water, superheated to plasma, could provide the cheap, efficient propellant needed to send small satellites out into the solar system.

CubeSats, the small, square, inexpensive satellites loved by startups and academics, are changing how we study the Earth and space. For example, Skybox Imaging wants to massively increase the satellite coverage of Earth's surface with a fleet of CubeSats. Once the small satellites hitch a ride with an outgoing spacecraft, they can relax in Earth's orbit and collect data. But what if they could leave Earth's orbit and journey to Mars, or beyond? Wouldn't that require them to be far more expensive? Not according to Benjamin Longmier, Ph.D., who's heading up the CAT project. His solution: Propel CubeSats with water.

CAT stands for the CubeSat Ambipolar Thruster. Longmier and a team at the University of Michigan’s Plasmadynamics and Electric Propulsion Laboratory are developing a thruster that converts water into a plasma propellant, which will help CubeSats break free from Earth's orbit and head out to parts unknown. Solar panels provide CAT with a constant renewable energy source.

Image credit: University of Michigan

It all sounds great, but CAT isn't a reality yet. The project has some private funding, but a crowdfunding drive in July failed to bring in the $200,000 Longmier. Now the team has relaunched its Kickstarter with a more conservative $50,000 goal. That $50,000 will supposedly be enough to get the project started, using the traditional propellant of xenon gas in place of water for early engine testing. If CAT hits its stretch goals, or brings in more money, the team hopes to bring it to NASA's Technology Readiness Level 8, making it worthy for a jaunt out into the solar system.

The Kickstarter page claims CAT could propel an 11 pound CubeSat the 80,000,000 miles to Mars using 5.5 pounds of fuel. It explains the technology, stating "Just like a normal rocket that produces thrust from the burning and expansion of hot gases, CAT produces thrust from the expansion of a super-heated 350,000 °C plasma stream. Plasma is an ionized gas that can be accelerated to produce thrust (F=ma). The force generated by this thruster will be very low (micro-newtons) but very efficient. The engine will be turned on for long durations, accelerating the spacecraft to much higher velocities than a typical chemical rocket."

The project page also lists out some of the many possible uses for mobile, exploratory CubeSats. They could easily move around the Earth, providing Internet coverage or gathering weather information. They could give us the same kind of weather readings in orbit around other planets. Given how much we've learned from each individual probe sent to Mars, imagine how much more we could learn from a fleet of CubeSats orbiting the planet. $50,000 is just a small step in that direction--the stretch goals estimate needing $1,750,000 to get a CubeSat on its way to Mars--but that's still remarkably cheap compared to just about everything else in the field of space exploration.