Friday, March 12, 2004


I was in a discussion today about the use of lasers in adaptive optics for telescopes.

For adaptive-optics-capable telescopes operated by the US and its partners (if any), before a laser is fired through the atmosphere to determine the correction needed for atmospheric distortion, permission has to be obtained from the US Air Force.

You might think "well that makes sense, we don't want any planes shot down, or pilots blinded," but you'd only be partially right. The US Air Force's main concern becomes somewhat clearer when you find out that they want you to ask for permission to fire a laser into the sky from anywhere, at any time. Even from Antarctica (yes, there are over-Pole flights). And now, even if you have no connection to US funding or projects.

They are worried about their satellites.

Not only that the satellite might be blinded, but that an unexpected laser blast from a foreign country might be misinterpreted.

Do LIDARs have to ask for permission? I bet the LIDAR installation in Camag├╝ey, Cuba, doesn't ask. They happily blast away with their old Soviet equipment almost nightly. Perhaps the beam doesn't get that high.

It ocurred to me that of course the USAF is not going to release the TLEs for the orbits of their satellites so that each telescope operator can decide whether or not to fire the laser. That would give away the location of the satellite at all times. But, consider the following:

Permission probably means a satellite is not present. Given enough data on when and where permission is given, determining satellite orbit probabilities is possible. It's the type of inverse problem that we are starting to get very good at. And that's not good news for the INTEL community. It's not an immediate problem, because adaptive optics technology is still fairly sparsely distributed - but you can bet that like other techniques, adaptive optics using lasers will proliferate. And if you can collect permission slips, the problem will be a cinch.

Here's a look at some of the big-bucket concepts floating around. My favourite name has to be the "OverWhelmingly Large" telescope, OWL.