NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/sci/crypt/6629

Text File | 1993-01-11 | 3.5 KB | 70 lines

Newsgroups: sci.crypt
Path: sparky!uunet!cis.ohio-state.edu!zaphod.mps.ohio-state.edu!howland.reston.ans.net!spool.mu.edu!agate!overload.lbl.gov!dog.ee.lbl.gov!network.ucsd.edu!qualcom.qualcomm.com!servo.qualcomm.com!karn
From: [e-mail] (Phil Karn)
Subject: Re: KH-11 pictures -
Message-ID: <[e-mail]>
Sender: [e-mail]
Nntp-Posting-Host: servo.qualcomm.com
Organization: Qualcomm, Inc
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Mon, 11 Jan 1993 07:05:08 GMT
Lines: 57

In article <[e-mail]> [e-mail] (Germano Caronni) writes:
>Isn't there a possibility to place some mirrors up there, align their
>positions by measuring distances between them with laser or whatsoever,
>and then computationally combine the so won pictures ?

I thought about this some time ago, because it would be the only way
to overcome the fundamental limits on what you can do from orbital
altitude with something that can fit inside the payload fairing of a
launcher like the Titan (commonly used to launch spy payloads out of
Vandenburg).

To get better resolution, you'd have to increase the effective
diameter of your telescope -- there's no way around this. You'd have
two basic approaches: a folding mirror of some kind, and the coherent
combining through some sort of signal processing of the light
collected by multiple telescopes spaced some distance apart.

In the first case, you'd have to build a folding mirror that could
deploy automatically in space and maintain alignment to a small
fraction of an optical wavelength. Ground telescopes have been built
from multiple mirrors, each under computer control, and I understand
it works. But considering the severe weight constraints and the
constant thermal stress from the 90 minute day/night cycling in polar
orbit, this seems like a tall order.

In the second case, you'd have to record the actual phase of the
incident photons on each telescope so you could combine them
coherently (i.e., simulate what happens in a single, large telescope).
I don't think the technology is ready for this yet. Remember that the
Space Telescope came from the same industrial base as builds these
things...

This is not to say that it's *impossible*, only that it's probably not
feasible or cost-effective with present technology. You also have to
ask what the use would be of all this extra resolution. One of the
problems they already have with spy satellites is sifting through the
flood of information they produce, and doubling the resolution
quadruples the amount of data they have to deal with.

And you have to consider the competition, such as a stealth airplane
designed specifically for reconnaissance. Airplanes can get a lot
closer to the subject than satellites, and they let you easily change
the instruments to suit the mission. They can also loiter in one spot
for a long time.

Now if you could keep the existence of such a plane secret, perhaps by
retiring your known spy airplanes with great fanfare and issuing a
cover story about how they've been completely replaced by satellites,
then you might actually be able to use it repeatedly before your
adversary even begins to suspect you have it. Of course, you might
have to make up another cover story to explain all those sonic booms
heard on a regular basis here in Southern California...

I know, this is getting pretty far afield from cryptography...

Phil