Originally, a dedicated, hardware system handled Integral’s rescue operations and directly controlled the thrusters when the safe mode was triggered. The team’s new approach listens for the alarm signal generated by this circuit but then re-routes it through the spacecraft’s primary ‘brain’ – the central on-board computer.

There, a newly developed algorithm receives the alert and determines how to control the reaction wheels to spin Integral to safely point towards the Sun.

This system was tested in flight for the first time on the real satellite on 2 March 2023, when Integral’s Flight Control Team deliberately rotated Integral away from the Sun and triggered the new safe mode, which successfully returned the spacecraft to its original safe orientation.

“Part of these tests involved making sure that the primary onboard computer can handle the new workload, as the 20-year-old computer was not designed to handle this extra effort,” says Jim Martin, who led the development of the new safe mode at ESOC.

“We closely monitored the computer’s vital signs during the operation to make sure that the new safe mode doesn’t impact any of the brain’s other duties, such as handling the science data gathered by Integral’s instruments.”