Re: Ground-powered Rocket
From: sanman (manofsan_at_yahoo.com)
Date: 11/09/04
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Date: 9 Nov 2004 15:37:04 -0800
Peter Kemp <peter_n_kemp@hotmail.com> wrote in message news:<4g62p01ol7tpjnufij384r47b5jhmvtlhn@4ax.com>...
> Well, one obvious shortcoming is thrust. Electricity does not produce
> thrust, and rockets by definition work by throwing hot gas out the
> back very quickly. So unless you're proposing some kind of ramjet with
> the inlet air heated by electrical means you're going nowhere, and if
> you are proposing that, then as soon as the atmosphere thins you're
> screwed as you've nothing to compress in the ramjet.
>
> So even if you could use this technique to get power to the rocket,
> you still need a conventional rocket motor. At best you save the cost
> of on board batteries/generators, but that's a tiny fraction of the
> launch weight compared to the propellant.
Hiya, well we were previously discussing the VASIMR ion/plasma thrust
rocket (VAriable Specific Impulse Magnetoplasmic Rocket). It can
generate more thrust at the cost of lower specific impulse. This
rocket might be capable of overcoming the Earth's gravity, unlike a
lot of other weaker electric rockets. The only problem is that it
needs a nuclear reactor to power it. Since nobody's going to allow you
to fly a nuclear reactor in the sky, I was pondering what other means
could be found to supply the necessary power requirements for a rocket
of this type.
There are also other types of electric rockets, including Arcjet,
which uses electric arcing to heat a stream of propellant.
Electrically-powered lasers might also be used to heat propellant to
high exhaust velocities.
Another approach for electrically-powered laser which I mentioned
before is the idea of Laser-Wakefield acceleration being used to
generate thrust. Your engine would use an array of solid-state
ultra-short pulse lasers to generate a very high acceleration gradient
via laser-wakefield effect, to shoot ions out at very high velocities.
But this would be a pulsed ion thrust approach, as opposed to
continuous thrust. Laser-wakefield is very new, and I haven't yet
heard anybody suggesting it as a propulsion method, so I thought I'd
suggest it. The high acceleration gradient means your engine could be
more compact, and you'd save engine mass. The high velocity of the
ejected ions would mean lower propellant mass required. The tradeoff
is that you'd need a lot of power, although I'd imagine that the
pulsed thrust could help you manage the overall power requirements.
But if that power could be piped up as electric current via some
conductive channel (laser/ion beam?, conductive exhaust contrail?),
perhaps then this would open up possibilities for propulsion methods
that are otherwise non-starters.
Because I don't see how the current political/environmental/safety
concerns are going to allow you to fly a nuclear reactor in the sky.
- Next message: Rand Simberg: "Re: Scientists against Bush or Swift Boats against Kerry - whom would you believe? Tin cans don't have minds!"
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