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Propelled by Water, Powered by Sun

Mon, 12/09/2013 - 4:13pm
Melissa Fassbender, Associate Editor

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The team's design of a 5 kg 3U CubeSat with CAT engine performing initial testing in Low Earth Orbit. A solar-powered spacecraft could someday average over 1 billion miles per gallon using only water for fuel, thanks to a new technology being developed at the University of Michigan’s Plasmadynamics and Electric Propulsion Laboratory.

View: Kickstarter of the Week: Mini Satellite is Propelled by Water

The group of researchers are developing a new rocket propulsion system, the CubeSat Ambipolar Thruster (CAT). With the help of Kickstarter backers, the team at the University of Michigan is hoping to test the technology on a CubeSat, a tiny satellite that costs up to 10,000 times less to develop and launch than a conventional satellite.

“The design of the CAT engine is quite unique,” explains Assistant Professor Ben Longmier.

The quartz plasma liner supported by plastic stand. The gaseous propellant enters from the left, is ionized into a plasma in the bottle shaped region, and accelerated out of the nozzle to produce thrust. The engine produces thrust through the expansion of a super-heated 350,000°C plasma, an ionized gas that can be accelerated to produce thrust. The gas could be one of many, including water vapor. It is turned into plasma for thrust by a radio frequency antenna. The force generated by the thruster is low, but very efficient.

While plasma thrusters have been used for decades, its size has limited use. The team’s new design scales down the previously demonstrated technology to make it practical for CubeSats, with a weight of less than one pound.

Read: The Future of Thrust Technology is Ion Propulsion

“In order to optimize efficiency of our device and reduce the mass, we have to go to the very edge of what most material can do,” says Longmier. “This means using specialized materials that can withstand the intense heat and power loads and the manufacturing of a unique set of permanent magnets for the nozzle.”

They turned to 3D printing for parts that couldn’t be machined. “Our solid silver antenna is only possible because of unique 3D printing process from companies like Shapeways,” explains Longmier. “We are a research and development lab, so we are continually engineering new parts that don’t exist and machining them and 3D printing them. We then assemble them into a working prototype or engineering unit and test it until it breaks. We then repeat the process until we have a system that can hold up in our extreme environment.”

The team has recently partnered with the company to further develop 3D printing for different spacecraft applications. Specifically, using 3D printed titanium parts that would reduce a thruster’s mass and increase its strength to weight ratio.

CAT Engine Specifications:

  • Up to 2 mN thrust for 10 W (20 mN for 100 W pulsed).
  • Up to 20,000 m/s plasma exhaust velocity.
  • Up to 10 W continuous (or higher power when pulsed).
  • >90% efficient solid-state DC to RF converter.
  • Expected engine lifetime, >20,000 hrs of operation.
  • Expected propellant: iodine or water.
  • Expected propellant mass: <2.5kg (for a 3U CubeSat).
  • Permanent magnet converging-diverging nozzle.

A computer design of the CAT engine with the power system and propellant tank. After launching as a secondary payload on a larger satellite, a camera on the CubeSat will provide visual diagnoses of the plasma thruster. Later determining if the thruster is operational, the camera will turn towards Earth providing backers with a view from space.

The team has already passed their goal of $50,000, raising more than $66,000 with 11 days left to go.

“We have two main goals with this project,” says Longmier, “First, we would like to make space exploration affordable and sustainable. And secondly, we’d like to open it up to the community and have people be a part of the process.”

For more information, visit www.kickstarter.com.

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