Spinning into control

To make the situation even more challenging, in safe mode, Solar Orbiter can only use its back-up communication antenna.

The back-up antenna can move ‘up and down’ in one axis, but not ‘left and right’ in the other. This prevents a number of potential complications, but it also means the whole spacecraft must rotate in order to point the antenna in certain directions.

The solution is ‘strobing’ – if Solar Orbiter ever finds itself in safe mode and unable to locate Earth, it will begin to roll around one axis while keeping its heat shield pointed safely at the Sun.

“In strobing mode, Solar Orbiter emits a signal with a special ‘tone’ – a beacon in the darkness of space,” says Lakey.

“Eventually, this signal will sweep across Earth. As soon as we detect it at one of our ground stations, we can assess the situation, work out what caused the safe mode and carry out our problem solving and recovery operations.”

That’s the theory, anyway. During Solar Orbiter’s four years in space, it has never had to rely on a strobing recovery – and it has never been tested in flight.

Until now.