A squadron of starships avoid space debris as they climb to escape the sun’s wrath.

Artist’s impression of the Swarm, the European Space Agency’s first constellation of Earth observation satellites. Credit: ESA-P. Karl, 2013

Pressure is mounting on the European Space Agency’s Mission Control Center. A European Space Agency (ESA) satellite avoided mysterious space debris that was spotted hours before a possible collision.

This means a critical step in the spacecraft’s ongoing journey to safe skies must be quickly rescheduled, as violent solar activity associated with intense solar cycles is distorting Earth’s atmosphere and threatening to pull the satellite out of orbit…

swarm? bug?

Not exactly – the swarm is actually ESA’s task of detecting the puzzle of Earth’s magnetic field. It consists of three satellites, A, B and C – affectionately called Alpha, Bravo and Charlie.

what happened

A small piece of man-made scrap orbiting our planet – known as space junk – was spotted hurtling towards Alpha on June 30 at 4:00 pm CET (10:00 am EDT). From the runway, a possible collision was predicted just eight hours after midnight. The risk of impact was enough that Alpha needed it to get out of the way quickly.

Constellation Swarm is the European Space Agency’s first constellation Earth observation satellite. His mission is to discover one of the most mysterious aspects of our planet: the magnetic field. Credit: ESA-P. Karl, 2013

There is garbage in space?

A lot. Fragments of old rockets and satellites and pieces of debris left over from past collisions and chaotic avalanches litter our planet. Each small fragment can cause severe damage to a satellite, while large fragments can destroy the satellite and create large amounts of new debris.

Is this the first time this has happened?

That day? Box. Already? Of course not. Each of ESA’s satellites is expected to perform an average of two evasive maneuvers per year – and that doesn’t include all the warnings they receive that don’t end up requiring evasive action.

Impact of Rangers Part 1 in Space

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

So what’s the problem?

Executing an evasive action—known as a “conflict avoidance maneuver”—takes a lot of planning. You must verify that you are not moving the satellite into a new orbit that puts it at further collision risk, and you must calculate how to return to your original orbit using the least amount of fuel and losing the least possible amount of scientific information.

The European Space Agency’s Office of Space Debris analyzes data from the US space surveillance network and alerts ESA flight control and flight dynamics teams to potential collisions, usually more than 24 hours before the debris approaches the satellite.

In this case, we only got eight hours notice.

Worse, the warning meant that Team Swarm was now running against two hours. Another maneuver was planned hours after the potential collision and had to be canceled to give Alpha enough time to move away from the wreckage. This strategy was also very time sensitive and had to be completely re-planned, recalculated and executed within a day.

What were the other tricks?

Alpha and Charlie were climbing to escape the wrath of the sun. Both satellites had to make 25 maneuvers over 10 weeks to reach their new higher orbits. One of the alpha maneuvers was scheduled hours after the potential collision.

Solar Cycle 25 NOAA Forecast

Solar Cycle 25 Forecast, NOAA, July 2022. The number of sunspots on the Sun’s surface waxes and wanes during a solar cycle of about 11 years. Our star is currently entering a very active period of its 25th solar cycle. Credit: NOAA

Wait, does the sun kill satellites?

Our Sun is now entering a very active part of the solar cycle. This activity increases the density of the Earth’s upper atmosphere. Satellites go through “dense” air, which slows them down and forces them to use limited fuel on board to stay in orbit. Alpha and Charlie were moving into a less dense part of the atmosphere where they could remain in orbit and hopefully collect science data and extend the mission for many more years!

What would have happened without this strategy?

Alpha could have drifted towards Charley and the orbits of the two satellites would have crossed soon. This would have left the Swarm’s overall mission “intersected”, limiting the ability to do science until Alpha and Charlie could rebuild for another round of maneuvers.

Is the swarm okay now?

The Swarm team gains reaction time for an Olympic sprinter’s competition. Together with the flight dynamics team at ESA’s Mission Control Center, they planned and executed the evasive action in just four hours, then replanned and executed another maneuver within 24 hours.

Alpha is now safe from being hit by this piece of debris and completes his ascension to heaven safe alongside Charlie. But there’s a lot of debris, and it shows with little caution that it could threaten a satellite.

Laser Ranging Station at Tenerife Green Laser

The European Space Agency’s (ESA) Laser Measurement Center in Tenerife points its green laser at the sky. Credit: ESA

How does your team keep track of all these collision alerts?

With new technologies, more sustainable behavior and taking responsibility for space debris very seriously. ESA is developing new technology to track more debris, developing new mathematical tools that will help us plan, execute and work on the rules guiding ever-increasing strategies that we and other satellite operators have to limit the amount of new debris that exacerbates the problem. We are even working on ways to capture large pieces of debris and eject them from orbit using SpaceClaw.”

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