Inspired by Cecil’s column for today:
We know (or someone does), I presume, the specs for the Hubble Space Telescope – 2.4 meter primary mirror, 0.3 meter secondary mirror, focal length of 58 meters.
We know that spy satellites pass, at the low point of their orbits, 175 miles (280km) above the earth.
Based on those numbers, assuming that a spy satellite had the Hubble telescope inside it, what would be its maximum (minimum?) theoretical resolution (assuming no atmospheric interference)?
“No comment.”
Dunno, but I’ll bet they’re a helluva lot better than they were in the late '80s, when Cecil wrote his column. Still, they have their limits, or we’d have found those pesky WMDs in Iraq by now…
Here’s an earlier thread on spy satellites.
A pixel resolution of 2" on the ground is about the limit. With a stationary target, good seeing conditions, and nasty synthetic aperature calculations it might be possible to improve that by a factor of 10.
Hubble is pretty old. Are its optics still first-rate? I was under the impression that the science/manufacturing processes of optical devices continues to improve, resulting in ever-improving, albeit diminishing, resolution.
Is there a difference between satellites (like the Hubble) which are meant to look into deep space (e.g. the distance to the object is infinite) and satellites which are meant to look a finite distance?
From a finite point of view, the light rays from your object aren’t very parallel; your mirror would have to be elliptical, not parabolic.
There’s nothing to prevent an array of satellites looking at something, then digitally combining the pictures. Since you’d have different angles, you could get rudimentary 3D images. Sensors outside the visible light spectrum would also increase the data available.
A lot of the improvement results from so-called “adaptive optics”.
Hubble’s performance is pretty close to the theoretical limit already. Theoretical limit imposed by the size of the aperture, that is - the only way to improve resolution is to use a larger aperture (larger mirror).
A few hundred miles is pretty close to infinity, in terms of optics. I don’t think it requires a different optical design. But there would be countless differences in the design detail. You’d need a completely different set of tracking sensors, and an instrument package optimized for high speed. A spy satellite telescope would also need adaptive optics to get anywhere near the theoretical limit. (The Hubble wouldn’t benefit from it, since it doesn’t look through the atmosphere.)
If you told him, would you have to kill him?
If so, I think we can sacrifice just one doper for a little extra knowledge.