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Old 08-March-2006, 06:14 AM
Pete Albrecht Pete Albrecht is offline
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Default Something in Blackstar story doesn't add up

OK, this is a minor point and doesn't directly negate anything else in the story, but...

In the Aviation Week story, at http://www.aviationnow.com/avnow/new...s/030606p1.xml there is the paragraph

"The spaceplane is capable of carrying an advanced imaging suite that features 1-meter-aperture adaptive optics with an integral sodium-ion-sensing laser. By compensating in real-time for atmospheric turbulence-caused aberrations sensed by the laser, the system is capable of acquiring very detailed images of ground targets or in-space objects, according to industry officials familiar with the package."

Unless I completely misunderstand the physics alluded to here, that won't work. The sodium laser trick involves firing off a laser to excite sodium atoms way up in the atmosphere (or better said, above just about all of it), something like 60 miles? up. Yup. just found it. http://www.astro.caltech.edu/palomar/AO/
This creates an artificial "star." By monitoring the artificial star's behavior, one can compensate a ground-based optical system in real time (one form of "adaptive optics") to correct for atmospheric aberration.

But if you are already above the atmosphere, firing a laser at sodium atoms at the top of the atmosphere, below you, will do you absolutely no good in imaging ground-based targets. The aberrations are caused by stuff happening well past the atoms you've just excited, almost all of it in the first few miles above the surface. And I can't see it helping image space objects either unless for some reason one is trying to shoot obliquely through the atmosphere.

As for the rest, well, there have always been secret projects, it's a fairly safe bet that there are recent secret projects we don't know about, and others underway right now, and that when we finally, inevitably hear about them, we'll be amazed. Maybe this is real. Maybe not. We'll know when they let us know. And by the time they let us know, they'll already be working on something even more amazing.

Pete
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