July 21, 2024

A satellite will hurtle down to Earth this week and no one knows quite when or where it’s going to land — but there’s no need to worry. In the space sector, this is standard operating procedure. 

The satellite in question is the European Space Agency’s ERS-2. Launched in 1995, the spacecraft set new standards for Earth observation. It was also an extremely durable machine. Despite an original mission life of just three years, ERS-2 made it to the ripe old age of 15 before its operations were terminated in 2011. 

Although the satellite was still functioning nominally, ESA initiated a de–orbit to mitigate the proliferation of space junk — a growing threat as rocket launches surge.

The descent began with a sequence of 66 deorbiting manoeuvres. This consumed all the satellite’s remaining fuel and lowered its average altitude from 785km to 573km, which reduced the collision risks. 

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ERS-2 was then “passivated” — a process that removes the energy sources that could cause fragmentation or explosions. The remainder of the journey was then left to the cosmos.

As an uncontrolled re-entry, ESA couldn’t determine the exact date of the return to Earth, but predicted that it would happen within the next 15 years. 

Thirteen years later, the big day is almost here. ERS-2 has begun plunging into the lower layers of the atmosphere, where it will start burning up. But the precise time — and location — of the arrival on our planet remains unclear.

Graph showing the declining altitude of the ERS-2 satellite ahead of its re-entry