Re: Missiles in Space Combat?
- From: Luke Campbell <lwcamp@xxxxxxxxx>
- Date: Tue, 20 May 2008 17:47:17 -0700 (PDT)
On May 20, 5:13 pm, Mike Williams <nos...@xxxxxxxxxxxxxxxxxx> wrote:
Wasn't it Tim Little who wrote:
Also, in space you don't need to make your missiles pointy and
slipstreamed. If you suspect that your enemies have anti-missile lasers,
you can stick a big laser reflector on the nose. Three mirrors at right
angles. If someone shines a laser at the missile, a tiny fraction of the
energy gets through the mirrors but the main beam bounces off all three
mirrors and gets sent back almost exactly to where it came from, causing
more damage to your enemy than they do to your missile.
There are several reasons why it doesn't work that way. The first is
that at intensities where lasers are capable of burning missiles, they
rapidly roughen and pit mirrors, turning them from surfaces that
specularly reflect to surfaces that diffusely scatter the incident
laser radiation. Not to mention making the mirror a lot less
reflective, so they rapidly get burned through. A mirrored surface
could reduce the effective range of the anti-missile laser somewhat,
by preventing melting at the extreme range of the laser, but it will
not give significant benefits well inside the laser engagement range.
The second reason is more fundamental. Lasers start out with wide
beams at telescopes that point, direct, and focus the beams. There
are two reasons for this - first, it keeps the beam intensity on the
scope optics low enough that the telescopes don't melt (or even
soften, or otherwise fail due to the heat). The second is that the
wider the beam starts out, the better it can focus. For example, a
beam one micron light focused from a 1 meter telescope can be focused
to a 10 cm spot at 100 km distance, while the same beam focused
through a 10 meter telescope can be focused down to a 1 cm spot at the
same distance. Now consider the beam when it hits the corner
mirrors. It is focused to as tight of a dot as it is possible for the
scope to focus. If it is intense enough to cause damage, this will be
a spot which is much smaller than the beam diameter at the scope.
Remember that narrow beams do not focus well - so the reflected beam
diverging from the corner mirrors will not be able to keep a tight
focus because it starts out so narrow. In fact, by the time it gets
back to the scope, it will be as wide as the original beam, which is
low intensity enough that it cannot cause damage to the scope. This
is a fundamental limitation imposed by the wave nature of light, and
you cannot get around it (well, I suppose you could, in principle,
take the incident beam and send it through a series of optics until
the beam is very wide, and then focus it with a wide aperture mirror
back at the target. Now you need active target tracking and precision
beam control as well as large, heavy, wide aperture telescopes on your
missiles - a lot more complicated than just mounting a corner mirror,
and since a spacecraft can typically mount a bigger beam pointing
telescope than a missile, your missile will still be burned up before
it can damage the target spacecraft).
Luke
.
- References:
- Missiles in Space Combat?
- From: Ingo Siekmann
- Re: Missiles in Space Combat?
- From: Mike Williams
- Re: Missiles in Space Combat?
- From: Tim Little
- Re: Missiles in Space Combat?
- From: Mike Williams
- Missiles in Space Combat?
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