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Thursday, April 2, 2015

Electric Propulsion Gives Cube-Sats Mobility in Space

As reported by MIT Technology Review: Natalya Brikner, CEO of the startup Accion Systems, holds an impossibly small spacecraft thruster in the palm of her hand. It looks more like a computer chip than a rocket—a gold-coated square of silicon the size of a dime.

Accion’s thruster has 480 barely visible nozzles etched into the surface of that silicon. It relies on a type of electronic propulsion that to date has only been used on a few space missions. An electric field is used to accelerate charged particles, normally using ions generated from a gas propellant, to create thrust.

Accion’s thruster has 480 barely visible nozzles etched into the surface of that silicon. It relies on a type of electronic propulsion that to date has only been used on a few space missions. An electric field is used to accelerate charged particles, normally using ions generated from a gas propellant, to create thrust.


Dozens of Accion’s thrusters can be packaged, along with a fuel tank, into a space propulsion system about the size of a deck of cards. Brikner says the technology, which will be launched into space on its first satellite in July, will make it practical to add propulsion to low-cost satellites that are as small as a tissue box, making them considerably more useful.

Microsatellites have largely been used for research, but commercial applications are gaining traction (see “Startup Plans Constellation of Tiny Monitoring Satellites”). The commercial potential of the technology was highlighted last year by Google’s $500 million acquisition of Skybox, whose small imaging satellites weigh 5 percent as much as conventional ones.

The capabilities of such satellites have been limited in part because they typically cannot maneuver themselves. Propulsion systems have proved difficult to shrink. Conventional thrusters tend to lose efficiency and power at small sizes, and they can double the size of a small satellite, making it too expensive to launch into space.

The systems normally used to ionize gases for electronic propulsion are also typically bulky. But Accion eliminated some of this bulk by using an ionic liquid (a salt that’s liquid at room temperature). “We don’t have to do any ionization in space; it’s done already on the ground,” Brikner says.

Adding propulsion to microsatellites could allow clusters of them to fly in formation, allowing them to mimic the performance of much larger and more expensive satellites for applications such as imaging. Propulsion could also help microsatellites maintain orbit instead of slowly deorbiting, allowing them to last up to 10 times longer.

Other companies, including Aerojet Rocketdyne and Busek, are also developing miniaturized thrusters for small satellites. “It’s a micro space race to see who will launch these things into space first,” says Paulo Lazano, director of MIT’s Space Propulsion Lab, where the basic technology behind Accion was developed.