An ESA satellite avoids the impact of space debris ‘in extremis’

July 15 () –

One of the three satellites of the ESA Swarm mission had to perform an ‘evasive manoeuvre’ on June 30 to avoid the risk of a collision with a piece of space junk.

Swarm is ESA’s mission to unravel the mysteries of Earth’s magnetic field. It is made up of three satellites.A, B and C, known as Alpha, Bravo and Charlie.

A small piece of debris was detected speeding toward Alpha at 1400 UTC on June 30. A potential collision was forecast just eight hours later, shortly after midnight. The risk of impact was high enough that Alpha was repositioned to avoid it.

Take evasive action, known as “collision avoidance maneuver”, it requires a lot of planning. You must verify that you are not moving the satellite to a new orbit that puts it at risk of further collisions and must calculate how to return to its original orbit using as little fuel and losing as little scientific data as possible.

ESA’s Space Debris Office analyzes data from the US Space Surveillance Network and issues a warning of a possible collision to ESA’s Flight Control and Flight Dynamics teams, usually more than 24 hours before the piece of debris gets closer to the satellite. In this case, only eight hours’ notice was received, the ESA reports.

Also, the alert meant that the Swarm team was now suddenly racing against two clocks. Another maneuver was planned for only a few hours after the potential collision and had to be canceled to give Alpha enough time to get out of the way of the debris. That maneuver was also very time sensitive and had to be completely replanned, recalculated and carried out in one day.

Specifically, Alpha and Charlie were raising orbit, as violent solar activity related to the gradual increase in the solar cycle deforms the atmosphere from Earth and threatens to drag the mission out of orbit. Both satellites needed to perform 25 maneuvers over a 10-week period to reach their new higher orbits. One of Alpha’s maneuvers was scheduled for just a few hours after the possible collision.

Alpha was eventually brought to safety from a collision with the piece of debris and has completed her ascent to safer orbits alongside Charlie.