dietz%USC-CSE@USC-ECL.ARPA (02/13/84)
Watching news accounts of the New Jersey's shelling of Lebanon, it
occurs to me that this job could be done from space with mass drivers.
A kilogram of mass, falling to earth from infinity, has a kinetic
energy of over 62 million joules, about the same as the explosive
energy liberated by 15 kilograms of high explosive. The energy from
geosynchronous orbit is almost as high. To put this number in
perspective, 62 million joules is enough energy to lift 62 metric tons
of matter 100 meters, if it were to be converted into potential energy.
That 1 kilogram of mass will dig a big crater, assuming it survives the
atmosphere.
Mass drivers being discussed for lunar mining have a mass flow of about
10 kilogram/second at a velocity of about 2 km/sec, with mass being
accelerated in 1 kilogram chunks. Orbital velocity at geosynchronous
orbit is about 3 km/sec, so a mass driver with an exhaust velocity of
around this much is needed to put mass onto trajectories intersecting
earth.
Assuming a 10 kg/sec mass flow, the geosynchronous mass driver can
deliver the equivalent of 150 kg of high explosive to the earth each
second, or .54 kilotons per hour.
In contrast, a shell from the New Jersey's 16" guns has a mass of about
a ton; around 500 shells were dumped on Lebanon in a 12 hour period.
(I'm not sure how many of these shells were 5" shells.) This
comparison isn't really fair because a large number of small explosions
will do more damage than if the same explosive force is detonated in a
smaller number of large explosions; blast damage scales as the 2/3
power of explosion energy. Taking this law at face value, and assuming
the New Jersey can fire one 16" shell every 30 seconds, the mass driver
has about 18 times the firepower.
At 11 km/sec, the ultrahypersonic projectiles will be in the atmosphere
for only a few seconds. Some mass loss to ablation is acceptable. The
projectiles should be long and thin to minimize drag forces, yet should
be designed to fragment when a solid surface is encountered so their
energy is deposited near the surface.
>From 40,000 km away, accuracy is a problem. Assuming an average
velocity of 5 km/sec, the projectiles will reach Earth in under three
hours. This time can be reduced at the cost of a larger mass driver
and higher power requirements, but remember that projected mass drivers
for asteroidal mining have exhaust velocities of ~10 km/sec. Engineers
working on lunar mass drivers are confident that lateral velocity
errors of only a few meters per hour are achievable, leading to an
error of perhaps 10 meters after three hours. Longitudinal velocity
errors are harder to correct. An error of 1 meter/second will cause
the projectile to arrive about 1 second off the target time; the
earth's motion will cause the target to move 450 meters during this
second. This problem can probably be solved by arranging for
"achromatic" trajectories that focus projectiles of slightly varying
velocities. Errors due to atmospheric forces will be neglible if the
projectiles enter head-on; maintaining projectile orientation could be
a problem (spin? tail fins?). All other errors (deviations from
symmetry in earth's geoid, lunar and solar gravity, magnetic fields,
light pressure) can be accounted for fairly precisely.
Assume that most of the projectiles land in 1 km x 1 km area. During a
24 hour bombardment, some 864,000 projectiles will be launched, or one
projectile for every 1 or 2 square meters of target area. Saturation
bombing indeed.
Mass for projectiles would most likely come from nickel-iron asteroids
(for density). Retrieving the asteroid is no problem with the mass
driver assumed here. The asteroids would also yield ballast mass to
anchor the mass driver in orbit against the reaction produced when the
it is fired, and to shield the mass driver against hostile attack.
Power requirements are not excessive. Launching 10 kg/sec at 5 km/sec
requires 125 megawatts of power (at 100% efficiency). A nuclear source
is probably best.
The mass driver could defend itself against attack by shooting clouds
of sand at oncoming missiles or satellites, or by shooting projectiles
at larger targets. Sand injected into earth-intersecting orbits would
be a nice touch for the 4th of July.rpw3@fortune.UUCP (02/18/84)
#R:sri-arpa:-1664800:fortune:10200012:000:475
fortune!rpw3 Feb 17 23:25:00 1984
"[Mycroft:] ... throw rocks at 'em! [Manuel:] Get serious, Mike..."
See Robert Heinlein's novel, "The Moon Is A Harsh Mistress", for an
interesting scenario of a possible war using falling-rock weapons.
He notes that accusations of nuclear arms use could arise from the
extremely high energies released.
Rob Warnock
UUCP: {sri-unix,amd70,hpda,harpo,ihnp4,allegra}!fortune!rpw3
DDD: (415)595-8444
USPS: Fortune Systems Corp, 101 Twin Dolphins Drive, Redwood City, CA 94065kcarroll@utzoo.UUCP (Kieran A. Carroll) (02/20/84)
* Has anyone else on the net, upon hearing O'Neill's idea for using mass-drivers throwing away tiny pellets of reaction mass ( say little buckets of lunar dirt) as a high-efficiency rocket-engine, had the thought, -Kieran A. Carroll ...decvax!utzoo!kcarroll "Good Lord, who wants to fill the solar system up with billions more meteorites, especially around what will eventually be a crowded shipping region, the earth-moon region? Won'rt the probability of hulling your ship increase dramatically?" Well, if so, I've just thought of the solution to this problem. Just accelerate your reaction-mass to greater than solar-escape velocity, and they'll go away and never come back. If they hit a planet with an atmosphere, they'll burn up. All you'll have to be careful of is that you don't aim your exhaust stream through a high-traffic area. Perhaps one of the "rules of the road" of the future will be that you aren't to point your exhaust directly towards the earth ( for fear of hitting low-orbit satellites), or towards the moon ( so as not to hit the mining base that sends up the fuel that you're using).
henry@utzoo.UUCP (Henry Spencer) (02/26/84)
Kieran asks:
Has anyone else on the net, upon hearing O'Neill's idea for using
mass-drivers throwing away tiny pellets of reaction mass ( say little
buckets of lunar dirt) as a high-efficiency rocket-engine, had the thought,
"Good Lord, who wants to fill the solar system up with billions
more meteorites, especially around what will eventually be a crowded
shipping region, the earth-moon region? Won'rt the probability
of hulling your ship increase dramatically?"
Actually, O'Neill thought of this. The first part of the answer is
that there is so much natural debris around that it's hard for human
activities to increase it much. The second part is that there are
fairly easy ways to handle the problem, which should probably be used
to prevent a problem developing in the long term. Specifically...
The mass-driver's big virtue is that it can use most anything as
reaction mass. So you can choose something that will be relatively
inoffensive. Early on, the choice of propellant will be constrained
by what's available, such as aluminum dust from ground-up shuttle
external tanks. The problem can be minimized by spraying a static
charge onto the dust as it leaves the mass-driver; this will make
the dust particles disperse. Later, the propellant of choice is
liquid oxygen extracted from lunar/asteroidal rock. The LOX simply
boils off into vacuum after release, leaving no debris at all.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henryal@ames-lm.UUCP (Al Globus) (02/27/84)
The article I'm replying to is too long to include here, but the basic idea is that you can blast Earth from space with mass drivers. This sort of thing is the reason we must keep weapons out of space. If we don't, a lot of people are going to suffer. One of them might be you. The U.S.S.R. has proposed a treaty banning weapons from space. This is currently before the U.N. I believe it is strongly in our interest to negotiate, sign, ratify, monitor and enforce such a treaty. Let's not blow it, this is our last chance.
judd@umcp-cs.UUCP (03/01/84)
.
The old problem arises again. If you ban weapons from space how do you
verify compliance?? This is even harder in space since many usefull tools
are also weapons (eg. small rocket engines).
An uninforcable treaty is rather usless especialy if *you* are willing
to play by the rules but the others are not (specificly the SU, a very
paranoid lot).
Judd Rogers
--
Spoken: Judd Rogers
Arpa: judd.umcp-cs@CSNet-relay
Uucp:...{allegra,seismo}!umcp-cs!juddrichard@sequent.UUCP (03/04/84)
>> The old problem arises again. If you ban weapons from space how >> do you verify compliance?? This is even harder in space since >> many usefull tools are also weapons (eg. small rocket engines). This would indeed be a problem, if the primary concern were weapons to be used against other space entities. But the weapons that are the primary concern are those that have the power to effect earth-based objects, or missiles/planes in flight. Anything with this kind of power is still neccessarily large - farily easy to detect. The only type of space-space weapon of concern is a satellite-killer. This poses a more serious problem, but still, "tools" won't usually qualify as anti-sat devices. If the ban you're speaking of is, indeed, a personal-weapons ban, measures on the order of the airline security checks should do for quite some time. ___________________________________________________________________________ The preceding should not to be construed as the statement or opinion of the employers or associates of the author. It is solely the belief... from the confused and bleeding fingertips of ...!sequent!richard
cozadde@trsvax.UUCP (03/19/84)
#R:sri-arpa:-1664800:trsvax:56000009:000:1526 trsvax!cozadde Mar 19 11:38:00 1984 To: richard What difference does it make to the people on the ground in Moscow, Washington DC, Leningrad, or New York whether it was a ballistic rock or a cargo carrier packed with food, medical supplies, spare parts, etc. if it falls out of high orbit. Any physical object that can generate concentrated and directed energy is a weapon (this includes biological and chemical). Therefore, ANY object in orbit that has control over its position is a weapon. This includes mass- drivers used for mining operations, transportation (as in The Moon Is A Harsh Mistress) or space drives, Solar Power Stations (the microwave power transmission beam could be easily converted to a 'death ray' with the proper motivation), communication satellites (jamming and propaganda), etc. Remember the Soviet Union has been trying to have the Space Shuttle declared as a strategic weapon since STS-1 landed. They consider it in the same catagory as the MX-1 'Peacemaker'. So, before we go charging off to sign a whole bunch of 'let's stop it before it spreads' treaties, lets find out what it is that we want to stop and what the Soviet Communist Party wants to stop. Remember the corollary to the NRA motto"Guns don't kill people, people kill people." Corollary:"Guns just make it easier (physically and psychologically) to kill people." The difference between a weapon and a tool is the ease of use for its intended purpose. lt. of marines ...microsoft!trsvax!cozadde ...ctvax!trsvax!cozadde