response 1 of 32:

Aug 12 17:41 UTC 1996

Slinging something off the Moon is a fairly simple engineering
task.  The speed to orbit the Moon is only about a mile per second,
and the vacuum is good enough that you can pretty much ignore
drag.  Lack of drag means that the payloads can be about any
convenient size or shape.  Small payloads require little energy
and can be slung at a high, continuous rate.

Slinging something off of Earth is, ah, more difficult.  First,
orbital velocity is about 5 miles a second, so the energy requirement
is 25 times as high.  To get through the atmosphere, you need a
minimum size.  It needs a heat shield or else it's going to suffer.

I've seen proposals for catapults to launch bulk items into orbit.
The canisters would be about the size and shape of a telephone pole
and carry a foot or so of graphite on the forward end.   IT would be
launched at about 6.5 miles per second and lose about 1.5 miles per
second on the way up.

Engineering such a beast would be difficult.  The payloads are big
and infrequent instead of small and frequent.  The energy and power
demands are much bigger, power storage is a problem, sonic booms,
the catapult has to be protected from the plasma produced when
the payload slams into air, you've got environmental issues...
Not to mention that the demand for the bulk commodities which are
the only things which can take such a rough ride (thousands of
gravities) isn't there yet.

So yes, in principle it can be done.  But the engineering, economic
and political problems mean it probably won't be any time soon.

response 3 of 32:

Aug 12 20:02 UTC 1996

Thanks, russ..

I had been hoping that some new technologies had evolved.. *sigh*

I presume, then, that it would be less economically feasible than current
launchs? How about switching to strict H2&O engines?

response 5 of 32:

Aug 12 20:43 UTC 1996

Hm...got me thinking...suppose you were sitting on the moon, feeling
bored, and partook of a few lunar brewskies.  With nothing better to
do, you decide to shoot the earth.  With a regular .22 caliber rifle,
do you think your bullet would be able to hit the earth's atmosphere?

response 7 of 32:

Aug 12 22:07 UTC 1996

Hmmm...maybe if you first place a few small dense masses in lunar orbit (black
holes would be dramatic, but lumps of neutronium ought to suffice), and you
were a real sharp shooter, you might be able to use the slingshot effect to
staircase you pellet out of the moon's gravity well.

response 9 of 32:

Aug 12 22:28 UTC 1996

Sum, but not nearly enough.  The moon only rotates once a month after all.
It's not a fast spinner.

response 11 of 32:

Aug 13 06:44 UTC 1996

in the case of the moon, i'd think not.  (without actually doing the math)
the gravity is only one sixth, but the drag effect of air resistance is
infinitessimal above three inches

response 13 of 32:

Aug 13 12:56 UTC 1996

And now for another topic transplanted from item #79:

Mining the asteroid belt.

It's a subject which has often appeared in science fiction stories
and comes up regularly in proposals from space enthusiasts and
companies in the industry.  Yet nobody seems to *do* anything
about it.

Probably because it's not quite as easy as it looks, and when
you're trying to get money for a venture, uncertainty's a killer.

In item 79.21, pfv mused:
>hmm...
>
>       Drives and automation... A good computer system, hardened.. An Ion
>       Drive, even a Fission Drive.. Lightsails... Long lags between
>       "deliveries".. 

All sorts of issues with this one.  Good computer systems are hard
to come by.  The technology advances, but the same sub-micron chips
which make them cheap also make them more vulnerable to radiation
effects.  Ion drives:  You may be able to get 10,000 lb-sec of thrust
per pound of propellant, but if you're trying to push a million tons
of asteroid, a ton of propellant only gets you about 10 cm/sec of
delta-V.  Ion drives are starting to make appearances on geosync
communications satellites, but NASA has never flown one on a deep space
mission.  (Something about "never used one for propulsion before, so
why should we be the first?" aka chicken/egg.)  Lightsails:  Nobody's
ever flown one, and they'd produce a few Newtons of force per square
kilometer of area.  Maximum.  You won't move anything very fast.
Getting one built, launched and deployed without tangling is going to
be quite a learning process, you can bet.

>       Taking along some H-bombs and simple-minded Guidance Systems: kick
>       the ore toward the Moon/Earth Orbit and let the GS finetune the
>       flight.. Flying "Catchers Mitts" (the design is old L5 related).

The H-bomb idea would be great for giving small pushes to bodies
which threaten to strike Earth, and deflect them just enough to
miss us.  Trying to use them for anything else would likely run
afoul of one or another test ban treaty (and you don't even want
to ask about the paperwork and background check for purchase).
The "catcher's mitt" concept doesn't apply to asteroid capture;
it is a rather specialized idea for capturing relatively slow-moving
slugs of moon dirt at a site over the far side of the Moon, not
whole asteroids winging in at escape-velocity-plus.  It was designed
out of Kevlar, which stops bullets, not meteors.

>       "The Man Who Corrupted Earth" covers a lot of the socio-economic
>       horrors, too.. What happens when someone parks an asteroid
>       in orbit containing more nickel-iron than Man has ever even mined?

What happens?  Well, the world price of nickel takes a dive.  I suppose
that this brings cities-full of cars running on nickel-hydrogen
batteries a bit closer to plausibility, but you never know.

So let's see.  Light sails big enough to do the job almost
certainly couldn't be made and launched, not as a first attempt.
Ion drives would require many tons of propellant, too costly
to launch.  Nuclear pulse, not politically feasible.  What's left?

The concept being pushed in the late 70's/early 80's by the Space
Studies Institute was to take propellant from the asteroid itself.
Using a page from the moon-mining handbook, they proposed building
a catapult and just slinging pieces of asteroid.  Action/reaction;
for every slug of rock slung one way, the rest of the asteroid
gathers a bit of speed the opposite way.  You might use up half or
so of your rock, but you get there.  Unfortunately, you can't
launch anything that big in one piece, so it would have to be
built on-site.  Building a catapult of substantial size takes a
crew, and launching a crew and the supplies to sustain them would
cost a lot of money and take a lot of engineering.  Which brings
it back to money.

The real problems are political and financial.  The political
problems with landing the fruits of your labor might be considerable;
if you think that nuclear power plants had problems in the courts,
I think it would be a church picnic compared to the brouhaha over
bringing down space stuff.  Everyone with an interest to be damaged,
e.g. nickel mine owners, would be paying lawyers to get you shut
down.  And in that sort of climate it's unlikely you'd ever get the
venture capital to get off the ground.  The Christic Institute
wasn't able to prohibit NASA from flying Galileo only 100 miles
from Earth, but there wasn't any money at stake.  Now think about
fat fees for lawyers and campaign money for politicos....

response 15 of 32:

Aug 13 21:35 UTC 1996

Could you repeat that please???  *rotfl*

response 17 of 32:

Aug 13 22:15 UTC 1996

Won't happen.   Washington will shut the venture down as soon as
it looks like an arms race in rubber-band guns is developing, and
they'll establish treaties to restrict world trade in latex to
prevent hostile governments and punks from getting too much.

response 19 of 32:

Aug 14 07:38 UTC 1996

the sick thing is .... #18 really happened.
  
the NucTestBanTrty however .. .could be modified to allow vessels
exceeding the thrust of escape-velocity restrictions ... so that
nothing could/would "fall" back to earth. ????????????
  
<<is this linked from science.cf? >>
  
there is a large puddle of rocket-scientist brains working on the
engineering and physics for stuff liek this ... it will take salesmanship
adn 'will' to make it happen in our life time.
  
and i hope it happens

response 21 of 32:

Aug 14 17:18 UTC 1996

("science" still points to the melvin conference, so I assume that
 the conf does not exist yet.)

response 23 of 32:

Aug 16 00:45 UTC 1996

I'm pretty sure I read once that some test ban treaty explicitly prohibited
the detonation of nulear devices in space.  Maybe that has been ammended to
allow detonation for thrust?

That Black Horse idea sounds like a death trap.  The German military used a
similar set of fuels for the ME-163 Kommet rocket fighter.  The one of the
two fuel components was caustic enough that a spoonfull would make a nice
tunnel through your thigh if you sat still enough.  The other burst into
violent flames on contact with almost all organic substances such as clothing
and flesh.  Together they produced a wonderfully powerful explosion.  If any
of you know of a Kommet pilot who lived through his 'Kommet tour', and doesn't
look just like Freddy Krueger, I'd like to know his name.  So on that note,
*you* fly the blackhorse, I'll watch.  

Oh, and I forget one or both of those fuels also had a nitroglycerin reaction
of exploding at the slightest bump.  Have fun...  >:}