Wasn't it Russell Wallace who wrote:
>It was suggested recently that stealth in space might be countered by
>sensors that look for a stealthed vehicle randomly occulting a star,
>causing the star to wink out for a moment. This is an interesting
>concept, so I ran some very rough calculations to try and figure out if
>it makes sense. All figures order of magnitude only.
>
>Assume the targets being looked for are 10 m.
>
>Suppose diffraction limits the range to 1 million km.
>Then the fraction of the sky occulted is (1e1 / 1e9)^2 = 1e-16.
>
>Suppose there are 1 billion stars visible enough to be used for the
>purpose. (i.e. the target isn't careless or unlucky enough to wander in
>front of another galaxy, so we're using only the visible stars in our
>own galaxy.)
>Then the probability of occultation is 1e-16 * 1e9 = 1e-7.
>
>But the target is moving. So it has to travel 1e7 times its own length
>to have a reasonable chance of occultation.
>1e7 * 10 m = 100,000 km, which is less than the originally assumed
>range, so the concept looks workable, unless I'm making a mistake
>somewhere?
>
>If the target is bigger, or you use shorter wavelength light (both of
>which seem plausible) then the range will be greater.
I imagine that an occultation caused by a 10m target at a range of 1
million km might look rather similar to one caused by a 1 km asteroid at
a range of 100 million km.
I guess you need to have a complete accurate catalogue of all the
asteroids and comets in the system before the technique becomes usable.
You can use the device to build such a catalogue, but it might take a
while. You'd still get false positives from things like long period
comets coming into range, and comets breaking up so that the fragments
end up in slightly different orbits to what your catalogue predicts.
--
Mike Williams
Gentleman of Leisure
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