On 1 m=E4rts, 04:01, Mike Williams <nos...@[EMAIL PROTECTED]
> wrote:
> 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 =3D 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 =3D 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 =3D 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.
>
For a single sensor, sure.
For a pair of sensors 100 m away from each other, they are very
different. Since the stars are infinitely far away, the shadow is
about as big as the object that casts it.
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