Predicting when orbital debris will come down

What is it about?

There are more than 10,000 active satellites circling Earth, joined by far more pieces of defunct spacecraft, broken rocket bodies and collision fragments, which are drifting slowly towards Earth under the effect of atmospheric drag. Accurately predicting how quickly this descent occurs is crucial for anyone tracking or removing debris. Solar storms make this much more difficult: the sun's outbursts heat and expand the upper atmosphere, thereby intensifying the drag experienced by every object in low Earth orbit. We developed a method that uses each object's orbital history to calibrate its drag model. When applied to eight catalogued debris objects in the first half of 2024, the simulated orbital heights matched historical records with an error margin of less than 10%. Then came the severe solar storm of 10–11 May. Orbital decay rates increased by 233–266% during its main phase. One notable result was that objects orbiting at 500–600 km fell seven times faster than those just 60 km higher, due to the steep drop-off in atmospheric density with altitude, compounded by the shape and mass of each object. This reliable knowledge changes what operators can do: predicting when and where debris will re-enter becomes more feasible, thus improving collision warnings for active satellites.

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Photo by Jeremy Straub on Unsplash

Photo by Jeremy Straub on Unsplash

Why is it important?

In May 2024, a solar storm sent debris orbiting at 500–600 km into decay seven times faster than objects just 60 km above. This difference is explained by the steep drop in atmospheric density at these altitudes. For mission operators and debris trackers, a reliable predictive model is a valuable tool for safer orbit management. However, the method still relies on constant drag assumptions, and future work must consider how attitude and orientation change as objects tumble.

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