Comment by steve19 | Hacker News Reader

Comment by steve19 | Hacker News Reader

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The optical equipment I work with has improved so much since the 70s that I find it hard to believe spy sat technology has not.

I am not sure that the U2 is still used for surveillance. I think it is now used for research purposes. The much more modern Lockheed SR-71 Blackbird has been retired. Either the DoD is relying on sats or UAVs or the rumored next-gen spy plane is deployed [0]

Even if sats can take hi-res photos, there are still plenty of good reasons to use spy planes. Capturing visible light from space only works if the target area is not covered in cloud, spy sats are very hard to hide (it can be done in the short term but amateurs eventually find them) and they can be shot down (in a war with China, you bet the spy sat will be knocked out within hours of the first hostilities), spy planes can carry SIGINT gear as well.

That said, there are plenty of good reasons not to use spy planes and rely solely on sat intel. If you plane crashes it is a diplomatic and technological disaster. Unlike the stealth Blackhawk crash at Bin Laden's compound, spy planes don't carry a squad of seals equipped with C4 to destroy the valuable top secret technology.

[0] http://en.wikipedia.org/wiki/Aurora_%28aircraft%29

I think the limiting factor is the air, not the lens. That's why astronomers put telescopes in space (to avoid the air completely), or use a huge array of cameras and postprocess it.

I'd expect the big gains are in stitching together lots of signals, possibly over time, and extracting interesting features automatically. I'd think resolving stuff over time can only be done if you already know what you are looking for (to avoid massive dimensionality problems), or for static features. Still, that's an interesting subset.

Just like you can link a bunch of smaller telescopes on the ground to compensate for air distortion and get a significantly higher resolution, it should be possible to do the same with a bunch of satellites looking down.

But then you have to deal with parallax from nearby objects on the ground. That would limit its usefulness in hilly, mountainous or urban environments.

That's something computers are really, really good at.

The cameras don't have to be too widely separated. A little time and space helps a lot. The main problem is that this reduces your areal coverage as you're dedicating multiple sensors to a single sensing target.

Photostacking. Kalman filter. Differential.

U-2s are still in use, though they're in the process of phasing them out. They are still being used in a recon role (though no longer the same way as in the Cold War). They can still fly higher than Global Hawks, and there still aren't -that- many Global Hawks around.

It's easier just to jam the satellites directly instead of shooting them down. In the case of anything less than a full-on shooting war it leads to much less diplomatic trouble as well.

What optical equipment are you working with, if I may ask?

You can't use commercial focal planes in space. Rad hardened space hardware development moves slower than consumer.

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