Predict how long debris lasts at different altitudes.
A bolt is left in orbit at 800 km. How long does it stay there?
Yes.At that height the atmosphere is so thin that drag takes hundreds of years to bring anything down. Everything ever left at 800 km is still there.
Not quite.That is roughly true at 400 km, where traces of atmosphere still bite. The difference between 400 and 800 km is enormous.
Not quite.There is still a trace of drag. It is slow rather than absent.
Low orbits clean themselves in years. A few hundred kilometres higher, nothing is cleaned at all on any human timescale.
Slide the altitude and see how long a piece of debris lasts.
300 km600 km1,000 km
How long it stays up0.5 years
A human lifetime80 years
300 kmMonths. The station at 400 km has to be boosted regularly for exactly this reason.
How long it stays up25 years
A human lifetime80 years
600 kmDecades. Long enough to outlast the mission and the company that launched it.
How long it stays up1,000 years
A human lifetime80 years
1,000 kmCenturies. This band is where the debris problem is worst.
Why does a few hundred kilometres change the answer so drastically?
Yes.Air density falls roughly exponentially. That makes altitude the single most important fact about a piece of debris, and it is why the choice of orbit is a decision about the next thousand years.
Not quite.They move more slowly. Speed is not what removes them.
Not quite.Slightly, and gravity is not what brings them down. Drag is.
Move the control to see what changes.
A 1 cm bolt hits a satellite at 10 km/s. What does it do?
Yes.Energy grows with the square of speed, so orbital velocity turns a bolt into a weapon. This is why debris too small to track is the part that worries operators most.
Not quite.At orbital speed nothing dents. The impact is closer to a small bomb than to a collision.
Not quite.Both objects vaporise locally at the point of impact.
Put in order how one collision can make a region unusable.
Tap them in order — first to last.
A collision→Thousands of fragments→Spreading orbits→More collisions
A loop that needs no further launches to keep going.Yes.The last step feeds the first. Above a certain density this runs without any new launches — the fragments alone can sustain it, and the region stays hazardous for centuries.
Which of these reduce the debris problem, and which do not?
Designing satellites to de-orbit within a few years of ending service.
Choosing lower orbits where drag cleans up.
Making satellites smaller.
Leaving enough fuel to push a dead satellite out of a busy band.
Tracking debris more accurately.
Yes.Tracking and small size help you avoid or survive collisions; neither removes anything. Only lowering the orbit, or getting out of a busy band, changes how much is up there.
One object shatters into 3,000 trackable fragments. If each has an equal chance of hitting something and one collision produces 3,000 more, how many fragments after two such collisions?
fragments
Yes.3,000 × 3. The arithmetic is why operators talk about a threshold rather than a gradual worsening — past a certain density the count grows on its own.
Lesson complete
Low orbits clean themselves. A few hundred kilometres higher, nothing does.