Butane-Propelled GomX-4B Smallsat Mission Success for ESA and Manufacturer GomSpace

The GomX-4B — ESA’s largest, small cubesat yet flown — has completed its mission for the Agency, testing out new miniaturized technologies including: inter-satellite link communication with its GomX-4A twin, a hyperspectral imager, star tracker and butane-based propulsion system.

An artistic rendition of the GomX-4 smallsat pair.

Image is courtesy of GomSpace.

ESA is making use of the standardized 10 cm. cubesats for testing new technologies in space. GomX-4B was ESA’s first six-unit cubesat, double the size of its predecessor GomX-3, built for ESA by GomSpace in Aalborg, Denmark, who is also the builder of GomX-4A for the Danish Ministry of Defence. The cubesat pair was launched in February of 2018 from Jiuquan, China.

GomX-4B’s cold-gas thruster system takes up two half-cubesat units at one side of the nanosatellite, with two spherical titanium tanks filled with liquid butane. It has four 1 mN thrusters, typically to be fired in pairs while keeping one set in reserve.

Photo is courtesy of Nanospace.

GomX-4B used its butane cold gas propulsion system to maneuver away from its twin, flying up to 4,500 km. away in a fixed geometry — a limit set by Earth’s curvature and representative of planned smallsat constellation spacing — to test inter-satellite radio links allowing the rapid transfer of data from Earth between satellites and back to Earth again.

Supplied by the Swedish branch of GomSpace, the propulsion system allows the cubesat to adjust its orbital speed in a controlled manner by a total of 10 m/s — a speed equivalent to a kicked football.

In another first, GomX-4B acquired the first hyperspectral images of Earth from a cubesat. Cosine Research in the Netherlands and their partners constructed the hand-sized HyperScout imager for ESA. This divides up the light it receives into many narrow, adjacent wavelengths, gathering a wealth of environmental data. The mission also proved that hyperspectral image processing can be performed aboard, to reduce the amount of data needing to be transmitted down to Earth. High-quality image acquisition requires good pointing accuracy and stability, so GomX-4B also trialed a miniaturized star tracker developed by Dutch cubesat manufacturer ISIS to orient itself by its surrounding starfield, turning itself using fast-spinning reaction wheels. A final experimental payload gathered data on how orbital radiation affects computer memories.

Observing in 45 visible and near-infrared spectral bands, the HyperScout hyperspectral imager was launched in February 2018, aboard ESA’s cereal box-sized GomX-4B smallsat. HyperScout has been developed by cosine Research in the Netherlands.

Photo is courtesy of the company.

The large amount of flight data returned by the mission is being analyzed as a source of lessons learned to guide the development of follow-on smallsat missions, starting with GomX-5 whose 12 unit design begins next month at GomSpace.

The GomX missions are funded primarily by Denmark in the ‘Fly’ element of ESA’s General Support Technology Program to develop and prove leading edge space technologies. ESA has a trio of Technology cubesats from Belgium planned to fly during the new year: Qarman to gather atmospheric reentry data, Simba to monitor Earth’s radiation budget and Picasso to monitor the troposphere and stratosphere.

Executive Comment

Roger Walker, who oversees ESA’s Technology cubesats, said that this multi-faceted mission has performed extremely well in flight. What its results demonstrate is that European cubesats are now ready for operational deployment, as the first generation of cubesat constellations in LEO for a variety of applications. The post-flight review has declared ESA’s in-orbit demonstration mission a success, but in fact GomX-4B’s story is far from over. GomSpace, the manufacturer of the satellite, continues to operate the smallsat, while GomSpace’s subsidiary in Luxembourg will be in charge of mission exploitation. In spite of all the orbital maneuvering, GomX-4B still has a lot of fuel. Of the original 130 grams of butane, only 13 grams were consumed during the mission.

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