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This may not sound like much, but the spacecraft was rotating at five times its maximum when under control.“The data coming down from Integral was choppy, coming in for short periods due to it spinning. They are offered for download solely for.The reaction wheel was reactivated by teams on the ground, but the spacecraft kept spinning at an average rate of about 17 degrees per minute (roughly one rotation every 21 minutes), as well as wobbling unpredictably about its axes. These desktop background (wallpaper) images contain the intellectual property of Microsoft and other third parties.
The reason for this is still not completely understood but is thought to be associated with a ‘star tracker occultation’ or ‘blinding’ which wasn’t handled correctly by the satellite’s control systems – effectively when Earth gets in the way of the spacecraft’s view of the stars, which it uses to orient itself.The team repeated the previous days steps to stabilise the spacecraft and return to a Sun pointing position, this time without getting in the way of the star trackers. By late afternoon, the commands were sent and immediately showed success, but another three long hours passed before the satellite was fully under control and out of immediate danger.An artist's impression of the mechanisms in an interacting binary system“Most of the Control Team were working from home at this point – I was following operations from the train! – and worked until four in the morning to get the spacecraft fully stable, back into position and facing the Sun to recharge its batteries.”Unfortunately, a few hours later as the team reconvened to discuss the next steps, the spacecraft once again started to rotate, its reaction wheels again turning at high speed. Next step – stop the spinning.With support from industry experts, the team at ESOC analysed the state of the reaction wheels, coming up with a series of commands to change their speed and brake the spinning satellite. Step by step, by turning off various instruments and non-critical components, this increased to more than six hours. First estimates of the charge remaining before blackout and the loss of the satellite was just three hours.
After doing a simulation, we tested it on the spacecraft. We checked with our flight dynamics colleagues and the theory indicated it would work. It was a solution that had never been tried before.“I didn’t believe it was possible at first. With the mode now disabled, the Control Team are working on a new automatic rescue sequence that should mimic many of the operations carried out after this anomaly, only much faster.When the propulsion system failed, the team realised they would have to learn to manoeuvre the four-tonne satellite using its highly sensitive reaction wheels alone, to dump energy at regular periods and counteract forces on the spacecraft, including the gentle shove from the Sun’s light.
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