In the current column here Cecil informs us that spy satellites have a resolution of 6 inches. Of course that column dates from 1987. Have things improved any? Can newspapers be read from orbit yet?
There are limits imposed by the laws of physics.
There are also limits caused by the atmosphere. Remember how we put a telescope in space so we could see the stars without having to go through the atmosphere? Well, it works both ways.
Per the commercial sats, however, the resolution has increased to about a meter. But you probably already knew that…
Now the satelites can just go online to read the articles, rendering the park bench obsolete.
Are you saying that six inch resolution is pretty much the best we can do? (Not that I’d be surprised if it was.)
I’d read somewhere (sorry, no cite), that the resolution was currently up to (down to?) 3-4 inches.
this site suggests that resolution may be as good as 7.17 centimeters ( 2.8 inches).
http://www.law.berkeley.edu/journals/btlj/articles/vol6/Steele/html/reader.html
(it’s a legal article on privacy issues,and quotes another source in a footnote for the 7.17 cm data. I have no idea how reliable that source is)
Dear Cecil and friends; Three mirror sets were made for space telescopes. Two sets were made by Eastman Kodak for delivery to the US military. One set was made by Perkin-Elmer for delivery to NASA’s Hubble. Theoretical resolution for ground targets is apx. 0.75 inches. High technology “adaptive optics” that can compensate for atmospheric distortion may be able to deliver this number. So a newspaper headline is not out of the question.
I remember watching something on the news when I was in Chicago, Channel 2, I believe (CBS). They said that the gov’t had satellites that could read the serial numbers of a dollar bill.
Adaptive optics work by sending a light signal (laser) into the atmosphere, measuring the distortion of a received signal, and modifying accordingly. (It works fine for ground telescopes looking up, not at the horizon.) Besides the fact that the laser would be noticed on the ground, you need a power source, a fair sized laser and deal with a few other issues. (For example, the ground would probably be the primary “mirror” for the reflected signal, not the atmosphere.) I suppose you could locate a laser on the ground, near the object of interest, and send a pulse from the ground to the satellite, but that would be tricky and hard to pull off near your average park bench.
That, and if you’ve got the infrastructure to put that laser on the ground, you could just have the guy with the laser walk over to the park bench in question with a Polaroid, thus saving you a lot of money on your big expensive satellite. I suppose in principle, you could find something already in place near your target which you know to be a point source, and base your adaptive optics on that, but that would be very difficult, and if your opponent (whomever you’re spying on) caught on, they could very easy manipulate that source to ruin your images.
There’s also the problem that a satellite in low Earth orbit is going to have to track a lot faster than any ground-based astronomical telescope, which is going to make adaptive optics even harder. You could, of course, get around this by going to a geosynchronous orbit, but that’s a much further distance away, and would require a prohibitively large mirror.
You’re still a long way off from being able to read a newspaper headline. A theoretical resolution of .75" means that two objects .75" square set .75" apart would be recognizable as distinct objects. At that resolution, you’d be hard-pressed to pick the headline out from the rest of the paper and figure out how many words it had. You’d need resolution an order of magnitude better to actually read it.
Well, that depends on the headline.
WA-
(headline continued on page 2)
But they wouldn’t have to read that newspaper from space. They’d have copies up there already, right?