ESA's next technology-testing CubeSat will be fitted with two tiny butane-powered thrusters, making it the agency's first miniature satellite with the capacity to move through space under its own power. GomX-4B, and near-twin satellite GomX-4A are set to launch from China on February 2nd next year.
Mass is a key consideration when determining the cost and feasibility of putting a satellite in orbit – the lighter the satellite, the cheaper it is to get into space. Therefore, naturally, the lightweight and flexible nature of a CubeSat makes it a popular choice for companies and space agencies looking to test new technologies. Beyond this, the invention of CubeSats has had the effect of democratizing space by providing a new, cheap and relatively accessible option for universities and smaller enterprises.
The probes are so small and light that they do not require their own rocket, and instead can be housed as a secondary payload in the faring of a launch vehicle carrying a larger, heavier conventional satellite.
In this case, the GomX twins will be nestled in the tip of a Chinese Long March rocket, riding shotgun into orbit with China's Seismo-Electromagnetic Satellite (CSES-1). The primary payload is designed to predict earthquakes by observing subtle changes in Earth's ionosphere that manifest prior to the onset of the devastating events.
Any given CubeSat is comprised of one or more standardized 10 x 10 cm (3.9 inch) units, that can be equipped with an array of experiments and instruments. GomX-4B and its partner are built from six of these units, making each of the dynamic duo roughly the size and shape of a cereal box.
GomX-4B has been outfitted with a hyperspectral imager capable of imaging Earth in 45 different spectral bands with the goal of collecting environmental data. Also on board is a small navigational tool known as a startracker (which is used by orbital probes and telescopes to determine their orientation in space), tools to observe the damage done to technology by cosmic rays, and a radio receiver designed to detect signals from air traffic.
The probe also plays host to two pairs of miniaturized cold gas thrusters arrayed down one side. The entire thruster system takes up the space of roughly one CubeSat module.
In spite of this, the little thrusters are capable of shifting the 8-kg (17-lb) probe at a speed of 15 m/s. The thrusters can be fired separately or in pairs, for anything from minutes up to an hour.
"The fuel is stored under pressure, then released through a tiny rocket nozzle. Even though it's cold gas, we achieve a substantial velocity change by using liquid butane that turns to gas as it exits," comments Tor-Arne Grönland, head of the Swedish firm NanoSpace, which supplied the thrusters. "Storing it as a liquid, like in a cigarette lighter, allows us to pack as many butane molecules as possible inside the small available volume – its liquid form being some 1,000 times denser than its gas."
GomX-4B will make use of its thrusters to test satellite communications, both in terms of linking with its partner CubeSat, and terrestrial stations. Soon after separating from the upper stage of the Long March rocket, GomX-4A & B will orientate their antennas to face one another.
The probe will then fire its thrusters, gradually moving farther away from GomX-4A. The CubeSats will check their intersatellite link once every 100 km (62 miles) up to a distance of 4,500 km (2.796 miles) to test their effectiveness.
"We'll do different kinds of burns: long, short, pulsing and throttling up and down," says Grönland. "It's important to do these things early in the mission then again late on, to show it can survive and perform well in space."
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