From: Mike Lorrey (mlorrey@yahoo.com)
Date: Wed Oct 23 2002 - 20:01:46 MDT
--- "Robert J. Bradbury" <bradbury@aeiveos.com> wrote:
>
> On Tue, 22 Oct 2002, spike66 wrote:
>
> > Assume you
> > decide to grind up part of the asteroid to use
> > as reaction mass to accelerate the remaining part.
>
> Fine. Even if I reduce a 5m asteroid to a 2m asteroid
> if I can capture it in a controlled orbit it has
> transformed itself from a hazardous mass in space
> to a useful mass in space.
2 meters worth has. The rest of the asteroid is now a stream of high
speed gravel and/or ions. So long as this stream is traveling faster
than solar escape velocity, this is copacetic (and so long as this
stream is not in line with Earths orbit around the sun.)
>
> > It is a tradeoff, depending on how much energy is
> > available and how much mass you decide to throw away.
>
> Yes, I understand this and clearly at the current time you
> have perhaps 3 choices (a) our existing ion thrusters;
> (b) our existing LH2 LOX engines; (c) our existing LOX
> and kerosene engines. I believe the Zubrin Mars refueling
> scheme was based on an as yet untested (or at least not
> commonly used) fuel.
The Zubrin Mars refueling scheme entails, AFAICR, using Martian water,
CO2, and energy (nuke or solar) to manufacture hydrocarbons and either
LOX or H2O2. In the absence of water resources on Mars, which to date
are now thought to be far greater than when Zubrin first wrote his
book, the mission was going to settle on something less energetic,
which, given an, I think, .35 g gradient, should still do the trick (if
you consider how puny the rockets for the lunar lander were to get back
in orbit, and they had a 1/6th g gradient to deal with).
In addition to the three you listed, there is also the mass driver
option, which has been in development going back to O'Niel's
colonization research projects in the 70's. Use a mass driver as a
propulsion method, tossing away pieces of gravel at high velocity. No
complex chemistry, no need for chemical purity for ion engines.
>
> If its a hazard you don't care how much mass you have to
> consume to deflect it (witness the Rafal/Eugene discussions
> on whether nuclear weapons would be effective in deflection).
> I'm interested in using semi-hazardous masses as a test suite
> to produce useful deflection strategies and at the same time
> turn the semi-hazardous masses into something useful for
> space development.
That 100m pseudo-moon just discovered isn't a hazard, according to the
orbital mechanics. Every time it gets close, our own gravity sends it
spinning away again. Nor is it's eccentricity a problem, energy wise.
If you plan on using asteroid material as reaction fuel, and solar/nuke
power to electrify a mass driver propulsion system, the only earthly
energy demand is that to get this system out to this asteroid. How long
do you want to take to do this? If you put most of the equipment on a
slow gravity assist trajectory, you can send an Artemis style manned
scooter up later for fast trajectory transfer of the human crew of the
asteroid.
>
> What I am interested in here is whether we currently have
> the means to turn hazardous mass into useful mass? As far
> as I can tell that requires knowing how much delta-v needs
> to be applied to the object (including derotating it if
> that is currently the situation in which it is in) and
> then getting it into an orbit that allows the Earth-Moon
> to capture it.
We do. What is lacking is the political will to use it.
Imagine a cosmic 9/11: A 100 meter asteroid, heretofore unknown by
astronomers, strikes the earth and wipes out Kennebunk, Maine, killing
thousands of the most well connected people in the country, whose
families and friends control a majority of the economic clout in the
country. How quickly do you think it will take Bush to pony up $100
billion annually for the sort of program you envision?
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