The European Space Agency’s Swarm mission is made up of three spacecraft circling Earth to study our planet’s magnetic field. And recently the small constellation had to make an emergency maneuver on short notice to avoid a potential collision with space debris.
This kind of move is far from unprecedented. ESA says each of its satellites has to make a collision avoidance maneuver two times a year, on average. What is unusual is that this dodge came with very little notice, and as Swarm was already climbing to safety from another threat.
When the alert came that a piece of space trash was coming too close for comfort, two of the three satellites were in the process of moving to a higher altitude to avoid damage from the sun.
The sun has been moving into the active part of its eleven-year cycle when more and more powerful solar flares can bombard Earth’s upper atmosphere. This increases the density where the satellites orbit, slowing them down, burning more fuel and threatening to drag them back to the surface. So the satellites were in the midst of a ten-week process of moving to higher orbits.
In the midst of this, a hunk of orbiting junk was detected on June 30 that threatened to collide with one of the spacecraft only eight hours later.
That’s a very short amount of time to plan an evasive maneuver. Such a move typically requires a lot of checking that the alteration doesn’t put it at risk of other collisions and also figuring out how to get back to the original path it’s supposed to be on when the threat has passed.
ESA planned and conducted the evasive action in only four hours and then Swarm got back to climbing less than a day later.
So the danger has passed, but only for now, as there’s more debris than ever far above our heads.