Re: Space travel with lasers
From: George Dishman (george_at_briar.demon.co.uk)
Date: 12/30/04
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Date: Thu, 30 Dec 2004 17:49:51 -0000
"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:41d42a9e$0$41726$ed2e19e4@ptn-nntp-reader04.plus.net...
> In sci.physics Dave <noemail@hell.gov> wrote:
>> .... My laser or maser propulsion
>> now is refined. You set up a nuclear or solar powered master laser which
>> powers a series of mass produced slave repeaters spaced out. The slaves
>> have large arrays that gather the diverged beam, concentrate it, and
>> resend
>> it to the next slave. In between missions, the slaves are powered in
>> series
>> from the master to "recharge" them for boosting signal and maneuvering
>> for
>> next mission and placing new slaves, but they are mostly passive in
>
> <snip quoted message incorrectly placed at bottom>
>
>
> Some problems.
> If you've got 100 stations, then admittedly, you can drop the lens sizes
> to
> around 1% of the radius of one big lens.
> This takes the lens from around 50Km, to .5Km.
Each one gives a short impulsive boost. To even out
the power use an array of lasers at each station
starting with their beams much smaller than the
target and distributed over the surface. As the
distance increases move the beams towards the
centre. As they overlap, the centre will be pushed
hardest giving a natural concave surface which,
with a bit of spin, should improve stability. Space
the stations so that, as one reaches the limit of
it's ability to focus, another takes over.
> But, if one fails, you're screwed.
Build 101 or more. Each one that fails only loses a
fraction of the end speed and you can switch off the
last few when the speed reaches the planned value.
Redundancy is a good thing. If a single laser design
fails, the whole launch is aborted.
> If the efficiency of a repeater is 95%, then at the far end, you get 0.59%
> of the input power out.
> So, to avoid that inefficiency you're going to need to at least double the
> size of each lens.
Definitely, each should be autonomous using it's own
solar panels.
> Energy storage is a big problem, there is no real way at the moment to do
> much better than large tanks of hydrogen and oxygen burnt to form water,
> then recycled back.
> But, this is utterly useless for a photon drive.
With the right choice of chemical components however,
it might be possible to produce a chemical laser.
Failing that, use the H and O in a fuel cell to power
it.
There are ways to get round most of the problems but
it would still be a huge undertaking and planning the
orbits of the stations so that they were all in the
right location as the probe passed would be a nightmare.
It could be done but I still think the passive approach
has a lot going for it, even though it would be a bit
slower.
<snip>
> Especially when you compare something that's relatively possible to get to
> to
> maintain, with something impossible to get to.
>
> My first cut at an interstellar launch system would be medusa-based.
> You take a large heat-resistant parachute.
> Now, it's connected to a payload, and forms a typical parachute shape,
> with
> the payload away from the line of flight.
>
> Now, shoot a nuclear device forward into the parachute, and detonate it,
> pushing the parachute forward.
> Repeat until required velocity attained.
>
> If you also tip a device out the back every so often, then you have a
> string
> of bombs ready to power the next vehicle coming along.
That means carrying the mass of the bombs with you so is
no better than the rocket equation. If we can go beyond
current technology, manufacture a block of anti-lithium,
it only(!) needs a method of slowing down anti-neutrons,
and carry that as your fuel. Collect interstellar hydrogen,
react some with the anti-lithium and use the energy to
accelerate the remainder of the hydrogen in a cyclotron
to relativistic exhaust speed. As they say, nothing
impossible, it's just engineering ;-)
George
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