13 April 2018
GomSpace hopes to show that two is better than one, as its two-cubesat GOMX-4 mission moves from commissioning to demonstration phase. By flying in tandem formation and able to communicate with each other and ground stations, GOMX-4A and -4B can cover a large geographic area; the Danish small satellite maker described the per-satellite price as “very competitive…making it economically feasible for a country like Denmark to add even more nanosatellites to the monitoring of the Arctic area” – an increasing priority as global warming opens previously inaccessible areas to growing activity from ships, aircraft researchers and tourists.
The two 6-unit, 8kg satellites are nearly identical, carrying AIS ship tracking and ADS-B aircraft tracking transceivers, visual and hyperspectral camera and a new version of the software defined radio system tested on the GOMX-3 satellite, launched from the International Space Station in 2015. The European Space Agency owns -4B. Its sister unit, -4A, was built for the Danish defence ministry under a separate contract, with the Danish Defence Acquisition and Logistics Organisation (DALO) and Technical University of Denmark (TUD) as partners.
Marking the commissioning at an event in Aalborg, where GomSpace has its headquarters and a ground station, chief executive Niels Buus called -4B “our most advanced satellite to date”.
For station-keeping, the satellites are equipped with a new cold-gas propulsion system built by GomSpace-owned NanoSpace of Sweden. In their 500km polar orbit, with 5-day revisit time, the two units are being gradually separated, eventually to a distance of 4,500km – a limit being set by an operating concept that could in future define a constellation of 10 or more satellites equally spaced around the same orbital plane, according to ESA.
GOMX-4B carries an ESA experiment to test components for radiation hardness, and a miniaturised star tracker from ISIS (Innovative Solutions In Space) of Delft, Netherlands. The hyperspectal camera, called HyperScout, was developed by Cosine Research, also in the Netherlands, through ESA’s general support technology programme. That camera, says Roger Walker, who heads ESA’s technology cubesat initiative, “images Earth in 45 different spectral bands, gathering a wealth of environmental data – so much so, in fact, that the camera must perform its own processing to drastically reduce the amount needing to be sent back to the ground.”
The two satellites’ ability to communicate with each other is a key feature, to help future cubesat constellations relay data quickly to users on the ground. Flying at 500km and 7.5km per second, there are only three “windows” per day in which to transmit images and signals from ships and aircraft to the ground station in Aalborg.
The GOMX-4 satellites were launched as secondary payloads on 2 February on a Chinese Long March 2D rocket from the Gobi desert. The primary payload was China’s Seismo-Electromagnetic Satellite – CSES-1 – designed to scan the ionosphere for precursor signals of earthquakes.