I was lately reading about making pictures of ISS. The pictures are not really great from "home telescopes".
I was wondering what the usual altitude of espionage satellites is, given those pictures of i.e. cars are pretty detailed.
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Sign up to join this communityI was lately reading about making pictures of ISS. The pictures are not really great from "home telescopes".
I was wondering what the usual altitude of espionage satellites is, given those pictures of i.e. cars are pretty detailed.
That's a great question! So your question is: why are images taken from observation satellites much better than the typical images of the ISS taken from the ground.
The answer is:
Reconnaisance satellites are at similar altitudes to the ISS. The ISS is at 330-400 km, recon sats are in elliptical orbits with a perigee on the order of 250 km.
The big difference is the optics. A photo recon satellite has a telescope with a mirror 2.4 m in diameter (dimensions similar to the Hubble space telescope). Ground-based telescopes that big would have a hard time taking photos of the ISS because they can't be moved quickly enough to keep the ISS in sight.
This is the best ground-based photo of the ISS I've seen yet. It was made with a 0.64 m telescope:
This site lists exposure times of around 1/250 s. Bigger telescopes will use shorter exposure times.
I suspect the main reason large telescopes haven't been used to take pictures of the ISS is that observation time is at a premium: every observatory has a waiting list of people doing actual science. Taking time out to take pictures just for fun wouldn't sit well with the telescope's users.