From: rwallace@unix1.tcd.ie (russell wallace)
Subject: Re: Wreaking a habitat (was Re: Wrecking a Planet
Organization: Trinity College, Dublin
Date: Tue, 12 Jan 1993 01:09:19 GMT

In <1993Jan11.154326.27213@linus.mitre.org> m23364@mwunix (James Meritt) writes:

>In article <rwallace.726538590@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
>}In <1993Jan8.144835.281@linus.mitre.org> m23364@mwunix (James Meritt) writes:
>}
>}>In article <rwallace.726452375@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
>}>}In <1993Jan7.173125.20305@linus.mitre.org> m23364@mwunix (James Meritt) writes:
>}>}>Why bother with total destruction?  Have you considered the results of a
>}>}>number of 5 inch holes drilled through it by very fast gravel?
>}>}
>}>}As I explained in another article, a piece of gravel is not at all going
>}>}to drill a hole in a 1 billion ton O'Neill habitat.
>}
>}>Why on earth would you use one piece of gravel?  Send a gigaton or so of
>}>rock towards it at a few percent of the speed of light.  I don't think
>}>that your "measures" would do much good against a few million foot-wide
>}>holes randomly scattered completely through the habitat...
>}
>}?????!!!!!! A gigaton of rock travelling at a few percent of
>}lightspeed??? Well that would certainly dstroy a habitat! Anything can
>}be destroyed by a sufficiently massive attack. Why not postulate sending
>}100,000 gigantic interstellar battlecruisers instead? Probably cheaper
>}than your suggestion.
>}

>You, at last, catch on.  You are postulating near-infinite capabilities
>against a planetary attack, and near-infinite habitat defenses.  Stay
>consistent.  If you call on magic for the habitat defenses, the attack
>against it should be considered at least as capable.

I'm assuming the attackers and the defenders have the same amount of
money to spend. For an attack on a planet, the attack is more
cost-effective, because the attackers can use cheap bombs and even
cheaper silvered-balloon decoys (or high-speed rocks if you prefer),
whereas the defenders must build orbital weapons platforms, which being
in orbit, are very expensive to build and maintain. On the other hand,
an attack on a habitat must use expensive guided missiles, whereas the
defenders can build guns relatively cheaply, because the guns are being
built and maintained right next to the population and industry.

>}>}gravel. 
>}
>}>Wrong.  The Oort belt, to pick a demonstratable rock-throwing region, is
>}>not close.
>}
>}This is where the maneuvering ability comes in. You can hit a planet
>}from the Oort cloud. You can't hit a habitat from there, because it will
>}have moved a few hundred or thousand kilometres away from its previous
>}orbit by the time a projectile arrives, in a random direction. (For that
>}matter, a habitat being only a few kilometres across, you probably
>}couldn't hit such a small target from the Oort cloud anyway.)
>}

>You cannot maneuver a gigaton habitat outside of a cloud of incoming
>gravel without absurd energy and reaaction masses available.  You are
>calling upon magic of an order not far below a gigaton of rock at a few
>percent of c.  

You only need to impart a delta-vee of 1 m/sec to get the habitat
kilometres out of the way within a couple of hours (less than the time
an attack from the asteroid belt, let alone the Oort cloud, will take to
arrive). 1 m/sec is a *very* long way from the tens of km/sec people
have been casually talking about chucking kilotons of rock around at. I
leave as an exercise to the reader the difference in energy between
moving a habitat at 1 m/sec and moving a comparable mass at relativistic
speeds.

>}>}>}great agility, to be sure, but it means that a guided, powered missile
>}>}>}is needed, not simply throwing bombs on a precalculated ballistic
>}>}>}trajectory. 
>}>}>Unless you are advocating near continuous random changes in acceleration,
>}>}>it fits in much the same category as "planet" - except that the attack
>}>}>could come from any location in the universe, as opposed to less than
>}>}>half for a "moonbase".  There is something reassuring about being able to
>}>}>have your back against a few thousand miles of protective rock...
>}>}
>}>}Presumably the attackers of a planet will have the wit to time their
>}>}attack to hit the right side of the planet.  
>}
>}>That's nice.  So you can cut the time in half, too...  An attack against a
>}>space platform could come at any time.
>}
>}So what? A weapons systems costs the same amount to build, and nearly
>}the same to maintain, whether it is on alert 50% or 100% of the time.

>Not into offense/defense systems, are you.  Wrong.  For an example,
>look at the maintenance costs of an aircraft carrier during flight
>ops and one in mothballs.

Absolutely. Consider in old-time naval war, the fact that a battery of
coast-defense guns was much cheaper than a battleship of equivalent
firepower. The habitat's defenses are like the coast-defense guns, being
built right next to one's population and industry, and not needing to be
activated until an attack is in progress. A force attacking a habitat on
the other hand, would need mobile weapons systems which would incur huge
costs for constant maintenance.  A moon base would also have relatively
cheap defenses, but these would cost little less than those of a
habitat; a coast defense gun costs little more if it needs to be ready
24 hours a day than if it needs to be ready 12 hours a day. This is of
course assuming that the defenders of a moon base know what direction an
attack will be coming from, which is a pretty big assumption. The
defenders of a habitat don't need to know, as they have a 360-degree
field of vision and fire.

>}Also you could send ships around the horizon to hit a moonbase, and the
>}defenders would have no warning. Just land a 0.5-gigaton device behind a
>}mountain a few kilometres away, and the base's defenses are useless
>}(unless they can fire through the mountain). Contrast this with a
>}habitat's 360-degree field of vision and fire.

>You are postulating detection systems for the habitat, while precluding them
>from the planetary system.  Consistency, please.

OK, let the defenders of the moon base have detectors that can pick up
an incoming attack on the other side of a mountain, perhaps by
distributing the detectors, or putting them in orbit. What good will
that do them, when the attackers are on the other side of a mountain,
which the defenders' guns cannot fire through? On the other hand, the
attackers only have to detonate a big enough bomb on the other side of
that mountain for the shock wave to wipe out the base. Space is lousy
for transmitting shock waves, but solid ground is wonderful for the
purpose.

>}>}>}which can be of almost any desired size and power output, with the
>}>}>}habitat's full power generating capacity available, and almost unlimited
>}>}>}heat sink capacity, and the population on hand to maintain it. As
>}>}
>}>}>heat sink, yes.  But terribly vulnerable radiators.  So to zap it, dump silver
>}>}>paint so that it coats the radiator.  And as for the "full power
>}>}>generating capacity", if it is environmental, you couldn't accelerate
>}>}>(read "move") and it could be closed down with black paint.  And if it
>}>}>is internal, so could the planetary base.  
>}>}
>}>}Who mentioned radiators? The heat sink for a fusion gun or whatever
>}>}could simply be the habitat's water reservoir. I think a 10,000-ton
>}>}water storage takn could soak up quite a lot of heat (with bleeder
>}>}valves in case the water got too hot).
>}
>}>Wrong.  If your "beam" is enough to vaporize a few megatons of rock,
>}
>}Megatons? Where are you going to get an attack carrier big enough to
>}throw megatons of rock? You can't throw them from the asteroid belt,
>}because the habitat would have dodged in the long lead time that range
>}would give it.

>Who needs an "attack carrier" (whatever that is)?  There is already
>megaton pieces of rock floating around.  Like, for instance, your
>postulated habitat.  One just recently missed earth, for instance.

What has that got to do with anything? (I'm assuming that the people on
the habitat will have the wit not to do your job for you by accidentally
colliding with an asteroid :-)). I repeat, how are you going to throw
the megatons of rock at the habitat from an adequately close range,
without using an attack carrier (being a ship carrying a rail gun or
equivalent device capable of accelerating large masses of rock to very
high speeds)?

>}>with less than 1% of the beam even hitting the particles, you would
>}>boil your water away long before it worked.  If you happen to have an
>}>ocean available, or a river (read: planet) this might be a viable argument.
>}>As is, nope.
>}
>}Why would less than 1% of the beam hit the particles? Unless you use
>}gravel, in which case the individual particles won't penetrate the
>}shell, in which case you must use such a huge quantity as to vaporize
>}the habitat by the total kinetic energy, in which case the thing becomes
>}unfeasibly expensive (see my comment above about the megaton of rock).
>}Also if you're on a planet with free water, it's also going to have an
>}atmosphere, thus rendering your weapons useless.

>So use gravel.  If each makes a hole in the hull, that's it.  Unless, of
>course, you are proposing disproportionate capabilities (again).

As I pointed out, each gravel (sic) *won't* make a hole in the hull.
Think again.

>}>Hmmm.  Thought - not only would you have to vaporize the rock, you would have 
>}>to divert the the vapor (photonic pressure).  Otherwise you would just wind
>}>up encasing the habitat in vapor-deposited material or STILL destroying
>}>it with the energy transferred - and again wiping it out.  Getting hit with 
>}>a cloud at those velocities would not be a terrific improvement...
>}
>}Not unless the mass is sufficient to destroy the habitat by total
>}kinetic energy - see comments above. Also if you vaporize the rock far
>}enough away, the cloud will have mostly dissipated by that time. And the
>}impact of say 100 tons of vapor would not do any damage (unlike a 100
>}ton rock) because it would be too diffuse.

>I do not agree, for the reasons I gave.  Have you ever fallen a few
>stories into water?  Not much better than hitting rock.  And the recent
>work with the Siberian impact shows that hitting air isn't much better.

I don't happen to be a 1 billion ton space habitat :-). And consider the
total mass of air that was involved in the Siberian impact. How are you
going to throw that mass of material at the target habitat?

>}>}>}opposed to trying to defend a planet; the defences have to be in orbit,
>}>}>}which means they're separated from the population and industrial plants
>}>}>}which are on the ground.
>}>}
>}>}>Only if you are trying to defend the planet, and not just the "special"
>}>}>site.  Most folks I know really wouldn't care if a few cubic miles of the moon
>}>}>get peppered by gravel.  There is a LOT of turf that would count as a "miss".
>}>}
>}>}If an amount of nuclear explosives equivalent to a Dinosaur Killer hit
>}>}the Earth, that would cause a lot of inconvenience to everyone. Plus
>}>}that megatonnage aimed at say Europe would kill quite a lot of people.
>}>}Even not aimed at specific targets.
>}
>}>And if it hit your habitat it would be vaporized.
>}
>}Yes but as I explained, you can't use a bomb-plus-decoy attack on a
>}habitat because the habitat can dodge ballistic weapons given enough
>}time. Instead you must use either missiles (much more expensive) or
>}attack carriers (even more expensive). You could still do it, but the
>}cost of killing even one habitat would be huge, and there are thousands
>}more (assuming the same total population as would fit on a planet).

>And without postulating a technology which would also allow the rock to
>home in on your habitat, the habitat couldn't dodge.  Use the same engines.
>And it would be cheap - no need for life support or a lot of the other things
>needed on a habitat. Face it - a nice place to live is seldom a nice place to
>fight from - and vica-verse.

If the rock is small, the defensive armament will vaporize it. If it is
big (which I think you are assuming it to be), the cost of tossing it
around at those sort of speeds, plus mounting enough defensive armament
on it to prevent the habitat from launching missiles to destroy it (or
at least disable its engines), plus the accomodation for the personnel
to operate and maintain all this equipment, will make it cost a good
fraction of what the habitat itself cost. Plus, it will be seen coming
from a long way off, leaving plenty of time for the defenders to do
something about it, or at least evacuate the habitat, leaving you with
a trade of a very expensive set of engines, armament and life support
system, for a very expensive habitat. Not much point, methinks.

>}"To summarize the summary of the summary: people are a problem"

>Is this your basic problem?  Sounds like some of the environmentalists...

Well, I'm not exactly an environmentalist... :-)

--
"To summarize the summary of the summary: people are a problem"
Russell Wallace, Trinity College, Dublin
rwallace@unix1.tcd.ie
Newsgroups: rec.arts.sf.science