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Comment by loonster | Hacker News Reader

We got the Hubble after they made spy satellites about the same size. Maybe there is the equivalent of the JWST looking down at us?

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JWST would be totally useless as a spy satellite. It sees in IR. It is in space specifically because IR does not penetrate the atmosphere very well. That applies when looking down equally as up. Everything from the mirror and sensors to the entire cooling operation is optimized to see that IR blocked by earths atmosphere. So any spysat version wanting to actually see through that atmosphere would share almost nothing in terms of design or parts.

This is what real spysats looks like. They make JWST look like a toy.

https://en.wikipedia.org/wiki/Orion_(satellite)

"is according to NRO director Bruce Carlson "(...) the largest satellite in the world".[3] It is believed that this refers to the diameter of the main antenna, which might be well in excess of 100 m (330 ft)."

I think its kind of amazing how little is known about Orion. Not even the manufacturer is publicly known.

Impressive job keeping secrets.

Its not only in space, but very far away from the Earth and the Moon, so it doesn't become saturated with IR. That apart, there is a lot of important IR a spy satellite would search for. The heat signature from a fighter jet is much larger that its visual signature, for example.

IR is how satellites see clouds at night. Seems to work pretty well.

Weather-related sats see the clouds because IR is blocked by moisture, the stuff that clouds are made of. Spy sats generally want to see things that are not made of water.

Yawn. https://www.usgs.gov/special-topics/water-science-school/sci...

Depends? Humans are made out of water (mostly) ;->

Orion is a spy satellite for radio frequencies ("sigint satellite"). While it is massive, it's not an optical spy satellite and certainly does not have <10cm resolution.

JWST is fairly old tech now so probably better - by better I mean in some colloquial sense based on the passage of time, i.e. JWST would be pretty useless pointed at the earth one imagines.

Pointed at earth from k2 it would be useless.

But a similar diameter in the same orbit as current spy satelites may be able to resolve objects 1/3 of the size. If OP is correct about 10cm, that would place it at around 3.7cm.

It still is incredibly poor compared to what a high flying aircraft could capture, much less a drone spraying chemicals.

There are other considerations. The atmosphere is wobbly. You can have a mirror 100f across. That won't help the distortion. The only option is active optics, mirrors that adjust in real time, something very hard to on the ground let alone in space.

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