Inside a spherical cagelike structure, a small platform slowly spins as if floating. A single, bright lamp illuminates the scene, simulating the Sun. This setup constitutes the European Space Agency’s brand new facility for the testing of CubeSats – small satellites, usually no larger than a shoebox and weighing only a few kilograms.
This space-simulating facility, built for ESA by University of Bologna and Nautilus – Navigation in Space, is part of the Attitude and Control System (AOCS) & Pointing Systems laboratory at ESTEC, the Agency’s technical centre.
Just like any piece of machinery destined for space, CubeSats undergo rigorous testing on the ground, in conditions resembling space as closely as possible.
Andew Hyslop, ESA’s AOCS engineer, explains: “We can test attitude control systems separately or integrated in a complete CubeSat. An attitude control system is a combination of sensors, software and actuators that will make sure a CubeSat is in the right orientation when floating in space.”
To simulate the state of microgravity, the facility relies on an air bearing system – a device blowing a continuous stream of air upwards and creating a stable, invisibly thin air gap, allowing the platform suspended above it to float.
The CubeSat under test – or, in this case, its attitude control system – is mounted on this hovering platform.
“The system works out its orientation using Sun sensors, a magnetometer and a gyroscope. To stimulate the first, our setup includes a Sun lamp,” Andrew adds.
“However, Sun sensors tend to be susceptible to Earth’s ‘trickery’ – meaning some of the sunlight reflected from the Earth can be mistakenly interpreted as coming directly from the Sun. To take this effect into account, our facility includes an albedo lamp.”
Metal coils wrap around the curved bars that form the cage, simulating Earth’s magnetic field inside the structure. “As the spacecraft orbits our planet, the magnetic field it encounters keeps changing. Our metal coils replicate that.”
Andrew taps the hovering platform gently to initiate a spin. “To perform a test, we place the system on the air bearing in its starting orientation and optionally give it an additional tap. Then we let the attitude control system take over, stop the spin and get the platform back into the correct orientation.
“Like most attitude control systems on satellites in low Earth orbit, this one here uses reaction wheels to reorient itself. When these wheels start spinning, the spacecraft will spin in the opposite direction – according to conservation of angular momentum.
“Additionally, the floating platform is equipped with small reflective markers, which are being tracked by two cameras fixed to the top of the cage – this system gives us information of the platform’s true orientation. We can then compare this information to what the platform itself detects, to ensure its measurements are accurate,” Andrew notes.
The lab team recently finished testing and commissioning the facility to get it ready for its first customers. ESA CubeSat projects will soon be able to make use of it to gain confidence in their attitude control systems before flight.