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Comment by ck2 | Hacker News Reader

Is bouncing radar from above on an active commercial airport an okay idea?

The vast majority of SAR satellites are below 500W and have a beam "footprint" of about 5km by 5km at minimum.

Imagine 5 100W lightbulbs reflected and focused to channel as much light as possible onto a 25 square kilometer field from hundreds of kilometers away.

The planes are fine.

yes, received power is inversely proportional to the distance squared. it's hard to overstate how ridiculously small the amounts of power are at play with spaceborne SAR systems.

Sure, happens all the time. Synthetic aperture radar satellites operate in different bands than air traffic control radar, so there is no risk. Your house is scanned at least once every few days from wide swath radar satellites like Sentinel-1.

What for?

https://en.wikipedia.org/wiki/Sentinel-1#Applications

Sounds like some disaster response, some scientific, and some commercial uses.

And, obviously, lots of military uses.

I don't know how it's applied in practice, but apparently the treaty establishing ESA specifies that its space activities will be "for exclusively peaceful purposes" and they apparently have no missions that are classified or have any declared military purpose.

I think there are other non-ESA European (and national) agencies that work on military use of space. For example, there's apparently an "EU Satellite Centre" based in Spain that is concerned with military use of space (and is not part of ESA).

https://en.wikipedia.org/wiki/European_Union_Satellite_Centr...

I do imagine that military users can probably buy or access data from ESA sources on the same terms as civilian users and that they probably do so.

Sorry, yes, I meant non-ESA, just satellites in general.

They have much much better resolution though. They can detect car plates, and probably also people looking up.

Do they? From the declassified Trump photo, it seems like the maximum resolution is a few tens of cm, very far from detecting car plates.

Remember that the CIA has 4 hubble's, the fifth spare one they did donate to point outwards. Of course their capabilities are highly classified, but it leaked.

That's NRO rather than CIA.

https://en.wikipedia.org/wiki/2012_National_Reconnaissance_O...

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