Swarm dodges collision during ascent to escape the wrath of the sun - Parabolic Arc

Swarm dodges collision during ascent to escape the wrath of the sun – Parabolic Arc

Artistic view of Swarm. (Source: ESA–P. Carril, 2013)

ESA mission update


ESA mission control is under pressure. An ESA satellite dodges a mysterious piece of space junk discovered just hours before a possible collision.

Now, a crucial step in the spacecraft’s ongoing journey to safer skies must be quickly postponed as intense solar activity associated with the ramp-up of the solar cycle is distorting Earth’s atmosphere and threatening to knock it out of orbit…

Into the deep

A swarm? Of mistakes?

Not quite – Swarm is ESA’s mission to unravel the mysteries of the Earth’s magnetic field. It consists of three satellites, A, B and C – known affectionately as Alpha, Bravo and Charlie.

Swarm is ESA’s first Earth observation satellite constellation. (Source: ESA–P. Carril, 2013)

What happened?

On June 30th at 16:00 CEST a small man-made piece of debris was discovered orbiting our planet – known as space junk. A possible collision was predicted just eight hours later, just after midnight. The risk of an impact was so high that Alpha had to dodge quickly.

There is garbage in space?

A lot of that. Old satellites, rocket parts and small pieces of debris left over from previous collisions and messy separations. Any small piece can seriously damage a satellite, larger ones can destroy a satellite and create a large amount of new debris.

Is this the first time this has happened?

This day? Maybe. Ye? No way. Each of our satellites is required to perform an average of two evasive maneuvers per year — and that’s not all of the alerts we receive that don’t require an evasive maneuver.

The image shows Sentinel-1A’s solar array before and after a millimeter-sized particle hit the second panel. The damaged area is approximately 40 cm in diameter, consistent with the impact of a shrapnel less than 5 millimeters in size for this structure. (Source: ESA)

Then what’s the big deal?

Performing an evasive maneuver—known as a “collision avoidance maneuver”—requires a lot of planning. You have to make sure you don’t put the satellite in a new orbit that exposes it to other collisions, and you have to calculate how to get back to your original orbit with as little fuel and science data as possible.

ESA’s Space Debris Office analyzes data from the US Space Surveillance Network and alerts ESA’s flight control and flight dynamics teams of a potential collision, typically more than 24 hours before the debris comes closest to the satellite.

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

Worse still, the alarm meant the Swarm team was now suddenly racing at two o’clock. Another maneuver was planned just hours after the possible collision and had to be canceled to give Alpha enough time to duck under the debris. This maneuver was also very time-sensitive and had to be completely re-planned, re-calculated and carried out within a day.

What was the other maneuver?

Alpha and Charlie climbed to escape the sun’s wrath. Both satellites had to perform 25 maneuvers over a 10-week period to reach their new higher orbits. One of Alpha’s maneuvers was planned just hours after the potential collision.

The number of sunspots on the sun’s surface waxes and wanes in solar cycles of about 11 years. Our star is currently entering a very active phase in its 25th solar cycle. (Source: NOAA)

Wait, the sun is killing satellites?

Our sun is entering a very active part of its “solar cycle”. This activity increases the density of the Earth’s upper atmosphere. Satellites fly through “thicker” air, which slows them down and requires them to use less onboard fuel to stay in orbit. Alpha and Charlie moved to a less dense part of the atmosphere where they will remain in orbit and hopefully continue collecting science data for many years and mission extensions!

What would have happened without this maneuver?

Alpha would have drifted towards Charlie and the orbits of the two satellites would soon have crossed. This would have caused the entire Swarm mission to “squint” and limited their ability to do science until another series of maneuvers realigned Alpha and Charlie.

Is Swarm okay now?

The Swarm team worked with a reaction time that rivaled that of an Olympic sprinter. Working with ESA’s Mission Control Flight Dynamics team, they planned and executed the evasive maneuver in just four hours and replanned and executed the other maneuver within 24 hours.

Safe now from colliding with this piece of debris, Alpha has completed his ascent to safer skies alongside Charlie. But there’s a lot of debris out there, and it shows how little advance notice they can threaten a satellite.

With all these collision alerts, how are your teams keeping up?

With new technology, more sustainable behavior and by taking our responsibility for space debris very seriously. We’re building new technology to detect more debris, developing new computational tools to help us plan and execute the rapidly growing number of evasive maneuvers, and working on policies that limit the amount of new debris we and other satellite operators are adding to the problem. We’re even working on ways to grab larger pieces of debris and use a “space claw” to remove them from orbit.

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