Re: retrieving material from asteroids

royls@xxxxxxxxx wrote:

:On Tue, 28 Feb 2006 08:29:49 GMT, Fred J. McCall
:<fmccall@xxxxxxxxxxxxx> wrote:
:
:>"Mike Combs" <mikecombs@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
:>
:>:"Fred J. McCall" <fmccall@xxxxxxxxxxxxx> wrote in message
:>:news:gpv202pm5o5usqj40nb814t70nvqkdajam@xxxxxxxxxx
:>:>
:>:> The big problem with the whole 'mass driver' concept is that you're
:>:> spraying rocks at high speed out into orbits which will potentially,
:>:> at some future time, intersect some other vehicle. Not sure it's a
:>:> great idea even if you grind it up into fine dust first.
:>:
:>:True, but interplanetary space is already criss-crossed with small grains of
:>:matter traveling at high speeds. So the only sensible question that needs
:>:to be answered is: Are you increasing an already-existing hazard to a point
:>:where the gains don't justify the increased risk. We might could do a
:>:significant amount of activity in this way before the contribution we're
:>:making to the problem becomes significant.
:>
:>Except most of what you're spraying out is probably going to wind up
:>intersecting places where you want spacecraft at some point in the
:>future.
:
:An exhaust rock intersecting a place for one second per century where
:there is a spacecraft one second per millenium is not a problem.

Throwing them fast enough to put them into 1,000 year orbits, are you?
Unlikely.

And everything is not a problem ... until it is.

:>:One way to mitigate this problem entirely would be to ensure that all of
:>:your reaction mass is ejected at a speed in excess of solar escape velocity.
:>:Although I've heard it said that the scenario is a lot more energy efficient
:>:using larger volumes of lower velocity reaction mass.
:>
:>That high a velocity with a mass driver is, uh, unlikely.
:
:That depends on what kind of mass driver you use, but it it true that
:lower exhaust velocity is more energy-efficient.

And leaves more rocks where they are likely to be hit more frequently.

:>:In the High Frontier proposal, they only recommended using regolith for
:>:reaction mass until the orbital ore refineries were up and running. Past
:>:that point, they recommended switching over to liquid oxygen, which would
:>:vaporize after release (and we'll be producing more of it than we need).
:>
:>And there's a reason for not sticking with filling your transfer
:>orbits with rocks.
:
:It takes a lot of rocks to "fill" a transfer orbit. Remember, we're
:not talking about earth orbits, here, but orbits around the sun, which
:are several orders of magnitude larger.

You don't have to FILL them. Why do we worry about debris in Earth
orbit? Surely it would take huge quantities of debris to fill those
orbits.

--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
.

Relevant Pages

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