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ESA's Sentinel-1A satellite narrowly dodges debris

Who left that bit of rocket there? It's getting a bit crowded in orbit

There was a sigh of relief from ESA controllers over the weekend as the Copernicus Sentinel-1A satellite successfully dodged a decades-old rocket fragment.

The debris' closing speed was over 50,000 km/h (∼31,068 mph) and it was expected to come close enough that controllers opted to perform a pair of thruster burns in order to lift the satellite 100 meters (∼328ft) above the predicted point of closest approach.

One of the engineers responsible for flying the spacecraft, Thomas Ormston, summed things up with the inevitable meme.


Controllers had time to plan the maneuver, however, the incident is a reminder of the increasing clutter lurking in orbit around the Earth. ESA described the object as "a 30-year-old fragment", which astronomer Jonathan McDowell identified as being a bit of an old Zenit rocket stage. ESA later confirmed this was indeed the case.

Sentinel-1A, a radar imaging satellite launched in 2014, has run into debris before. One of the solar arrays was smacked with a millimeter-size particle in 2016, resulting in a small drop in power and a sudden change in the orientation and orbit of the satellite. Such small fragments cannot be tracked. However, a lump of rocket stage most assuredly can be.

Unfortunately, the second of the two Sentinel-1 satellites, imaginatively named Sentinel-1B, remains out of action following a problem with the power bus supplying the Synthetic-aperture radar (SAR) instrument. While the spacecraft remains under control, users of the information collected by it were warned to "assume a long-term unavailability of data provision."

"It is however too early to consider a permanent unavailability of Sentinel-1B," said ESA.

Both Sentinel-1A and 1B were launched on Soyuz rockets from Arianespace's Kourou launch site. The next in the series, Sentinel-1C, was planned for launch in 2023 – although given the situation regarding European vehicles flying on Russian rockets, launching on time, let alone bringing things forward, seems unlikely.

Which leaves Sentinel-1A, which has already comfortably exceeded its seven-year mission life.

"With every manoeuver, something – fuel, time, science data – is lost," said the ESA operations team.

And as the clutter increases above the Earth, and current events demonstrate the criticality of orbital infrastructure, "Avoiding collisions alone is not a long-term solution." ®

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