ESA Sentinel 1A: Collision Avoidance maneuvre to avoid dead satellite

At the end of the first day after the launch (4 April): all deployments have been executed during the night and completed early in the morning at the beginning of the first ‘day shift’.

As the first day shift nears its end, a serious alert is received: there is a danger of a collision with a NASA satellite called ACRIMSAT, which has run out of fuel and can no longer be manoeuvred.

A collision avoidance manoeuvre during LEOP has never been done before, and has not been simulated.

The satellite had not yet reached its ‘normal pointing mode’, the ESA team could not manoeuvre it before this milestone was reached.

But there was no alternative. After a brief team consultation Juan, the ‘day shift’ Deputy Flight Operation Director, decided to start preparing the satellite in case a manoeuvre was needed, and it was to be executed by his colleagues on the night shift.

It is decided to manoeuvre Sentinel-1A. Its orbit altitude needs to be changed to escape the chaser satellite (debris).

The manoeuvre takes 39 seconds. The sequence of commands was uplinked during pass 37 over Alaska/Svalbard/Kiruna/ at 04:33 UTC for execution at 05:14 UTC, outside visibility.

The atmosphere was tense and the Main Control Room was filled with suspense.

All eyes were watching the big screens on the wall, waiting for a sign, good or bad.

As the satellite approached Troll ground station on the next pass and the telemetry started to scroll down in the twilight of the control room, the team held their breath.

But there was no need for concern. The satellite was in Orbit Control Mode and the GPS on-board showed a change in its orbit status.

The manoeuvre had been a complete success. The collision and premature end of the mission had been avoided. Just another day in the office for the ESA Flight Operations team.

But it does highlight the need for continued vigilance in the debris littered orbits around the Earth. A more permanent solution is vital to allow the continued use of Earth orbits for scientific research.