Artist rendering of the GomX-4 pair in formation around Earth - Credit: GomSpace

The European Space Agency (ESA) demonstrated the use of a butane based cold gas propulsion system to adjust the orbit of the GomX-4B CubeSat. During the mission GomX-4B was able to maintain formation with its twin, GomX-4A, up to 4500 km away. The two CubeSats also tested an inter-satellite radio link between each other and Earth. These tests are verifying the operation of a planned CubeSat constellation.

GomX-4B is a 6U CubeSat (measuring 30 cm by 20 cm by 10 cm) weighing 8 kg that includes an inter-satellite communication system, a hyperspectral imager, a star tracker (HyperScout), and the butane based cold gas propulsion system. The spacecraft contains four 1 mN thrusters that fire in pairs while keeping one set in reserve. For comparison, many existing CubeSats use a monopropellant (i.e. hydrazine) for propulsion that provide more thrust (up to 1 N) but a lower specific impulse (lower efficiency). Gomx-4B's propulsion system allows it to adjust its orbital speed by a total of 10 m/s (about the speed of kicking a ball).

Butane cold gas thruster system used on the GomX-4B that has four 1 mN thrusters and two titanium tanks for storing butane. Takes up two half-CubeSat units in size. - Credit: Nanospace

The spacecraft stores 130 grams of liquid butane in two spherical titanium tanks. The butane is stored as a liquid to increase the amount of material stored. The cold gas thruster system takes up two half-CubeSat units on one side of the spacecraft.

While not the first CubeSat to include an on-board propulsion system, it is the first to operate a butane based cold gas thruster in orbit. This further demonstrates the capability of cold gas propulsion technology. Other CubeSat propulsion systems proposed include electric thrusters, electrospray thrusters, warm/cold gas systems, monopropellant systems, solid rocket motor systems, electrolysis of water systems, and solar sails [Zondervan et al., 2014].

Roger Walker, head of ESA’s Technology CubeSats, holding a 3D printed model of GomX-4B, which while the size of a cereal box, is the largest CubeSat ESA has yet flown - Credit: ESA-G. Porter

GomSpace manufactured the GomX-4 spacecraft, with both launched on February 2, 2018 from Jiuquan, China. GomSpace is starting development on GomX-5, a 12U follow-on CubeSat. GomX-5 will further evaluate CubeSat maneuverability and high speed communication links. It is scheduled to launch in 2021.

Developing reliable and efficient CubeSat propulsion systems is essential for precise formation flying. Potential missions with this technology include communication constellations, deorbiting space debris, and near-Earth object mining. The CubeSat industry will continue to deliver innovative solutions for propelling CubeSats on ever more expansive missions.

References

http://www.esa.int/Our_Activities/Space_Engineering_Technology/Mission_accomplished_for_ESA_s_butane-propelled_CubeSat
http://www.rocket.com/cubesat
Zondervan, Kevin, et al. "CubeSat solid rocket motor propulsion systems providing delta-Vs greater than 500 m/s." (2014).

Other CubeSats