An artist’s view of Swarm, the European Space Agency’s first constellation of Earth observation satellites. Credit: ESA-P. Karel, 2013

Pressure is building at the European Space Agency’s mission control center. A European Space Agency (ESA) satellite steers clear of a mysterious piece of space junk that was spotted just hours before a potential collision.

This means that a vital step in the spacecraft’s ongoing journey to a safer skies must be quickly rescheduled, as violent solar activity associated with the intensification of the solar cycle distorts Earth’s atmosphere and threatens to drag the satellite down out of orbit…

swarm? from bugs?

not exactly – swarm It is actually the task of the ESA to detect Earth’s magnetic field puzzles. It consists of three satellites, A, B and C – affectionately known as Alpha, Bravo and Charlie.

what happened?

A small piece of man-made junk orbiting our planet – known as space debris – It was spotted hurtling towards Alpha at 16:00 CET (10:00 AM EDT), on June 30. From the track, a potential collision was predicted just eight hours later, just after midnight. The chance of impact was large enough that the Alpha needed it to get out of the way — quickly.

constellation swarm. Swarm is the European Space Agency’s first constellation of Earth observation satellites. Its mission is to uncover one of the most mysterious aspects of our planet: the magnetic field. Credit: ESA-P. Karel, 2013

There is junk in space?

a lot of it. Fragments of old rockets and satellites and little bits of debris left over from past collisions and chaotic avalanches revolve around our planet. Every small piece can cause serious damage to a satellite, while larger pieces can destroy the satellite and create a large amount of new debris.

Was this the first time this had happened?

that day? Can. Ever? No way. Each of the ESA satellites should perform an average of two evasive maneuvers each year – and that doesn’t include all the alerts they receive that don’t end with the need for an evasive action.

The image shows the solar array of Sentinel-1A before and after the impact of a millimeter particle on the second panel. The diameter of the damaged area is about 40 cm, which corresponds to this structure with an impact fraction whose size is less than 5 mm. Credit ESA

Then what’s the big deal?

Doing an evasive act – known as “Collision avoidance maneuver– It requires a lot of planning. You need to check that you are not moving the satellite into a new orbit that exposes it to the risk of further collisions and you have to calculate how to return to your original orbit using the least amount of fuel and losing as little scientific data as possible.

The European Space Agency’s Office of Space Debris analyzes data from the US space monitoring network and raises the warning of a potential collision to the ESA’s flight control and flight dynamics teams, usually more than 24 hours before the piece of debris approaches the satellite.

In this case, we only received eight hours’ notice.

Even worse, the alert meant Team Swarm was now suddenly racing against two hours. Another maneuver was planned only a few hours after the potential collision and had to be called off to give the Alpha enough time to move away from the wreckage. This maneuver was also very time sensitive and had to be completely re-planned, recalculated and executed within a day.

What was the other maneuver?

Alpha and Charlie were climbing to escape the sun’s wrath. Both satellites needed to perform 25 maneuvers over 10 weeks to reach their new, higher orbits. One of the Alpha maneuvers was planned for a few hours after the possible collision.

Solar Cycle 25 Forecast, NOAA, July 2022. The number of sunspots on the surface of the Sun increases and decreases in solar cycles of about 11 years. Our star is currently entering a very active period of its 25th solar cycle. credit: NOAA

Wait, the sun is killing the satellites?

Our sun enters a very active part ofsolar cycle‘ Immediately. This activity increases the density of Earth’s upper atmosphere. The satellites run through “thicker” air, which slows them down and requires them to use limited fuel on board to stay in orbit. Alpha and Charlie were moving to a less dense part of the atmosphere where they could stay in orbit and hopefully collect scientific data for many more years and extend missions!

What would have happened had it not been for this maneuver?

Alpha could have drifted toward Charlie and the orbits of the two satellites would have crossed soon enough. This would have left Swarm’s overall mission ‘intersected’, limiting her ability to do science until another set of maneuvers realign Alpha and Charlie.

Is swarm okay now?

Team Swarm earned reaction time for an Olympic sprinter competition. Working with the Flight Dynamics team at the ESA Mission Control Center, they planned and executed the evasive action in just four hours, and then re-planned and executed the other maneuver within 24 hours.

Alpha is now safe from hitting that piece of wreckage and has completed his ascent to safer skies alongside Charlie. But there’s a lot of debris out there, and it shows with little warning that it could threaten a satellite.

The European Space Agency (ESA) Laser Measurement Station in Tenerife directs its green laser into the sky. Credit: ESA

How do your teams keep up with all these collision alerts?

With new technology, more sustainable behavior and by taking responsibility for space debris very seriously. ESA is building new technology To track more debris, developing New math tools This will help us plan, execute and act on the rapidly growing number of evasive maneuvers guiding rules Which limits the amount of new garbage that we and other satellite operators add to the problem. We’re even working on ways to capture larger pieces of debris and remove them from orbit using “space claw“.