On Feb 29, 4:12 pm, Russell Wallace
<russell.wallace.nos...@[EMAIL PROTECTED]
> 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?
It's better than that. The system would have lots of sensors at wide
separations, so, as a rough approximation, divide the reasonable
travel length by however many sensors you have in total.
Each occultation event only gives you a line along which the object
could exist, so you'll want at least two sensors active within a
fairly short period of time to locate an object in space (with only
two, this gives the potential of false positives if two different
objects just happen to produce events with very close occultation
lines, but the chance of that drops as you add more sensors), and you
probably want at least three points (so, at least six occultations) to
get a trajectory for an object, and effectiveness for those
requirements is obviously reduced. But, again, just add more sensors.
100 sensors spread out over, say, the volume of the Earth-moon system
ought to much more than make up for those stricter requirements.
-l.
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