Using a moon based rail gun as a weapon
Input Output Centres
I was wondering whether anyone could settle an argument I'm currently
having with some friends
Is it feasible to have a rail gun on the moon that could accelerate
large rocks (100 tonnes?) to hit the EARTH at extremely high velocity's
(11 km per second??) to flatten cities
I do not believe this possible/practical for the following reasons
a) Any rock launched would spend days reaching its target as it would
have to spiral into a decaying orbit around the earth (the rock cannot
change course once it is launched)
b) The amount of damage it would do would not compare to a nuclear
weapon (or even a large conventional bomb)
c) 100 tonnes if not that heavy (compared to a missile)
d) 11 km per sec is fast but not that fast
e) Seem like a very expensive weapon to me
W Vander Wilp
>From: Input Output Centres <ioce...@tcns.co.uk>
>Subject: Using a moon based rail gun as a weapon
>Date: 28 Feb 1996 16:37:52 GMT
>I was wondering whether anyone could settle an argument I'm currently
>having with some friends
>Is it feasible to have a rail gun on the moon that could accelerate
>large rocks (100 tonnes?) to hit the EARTH at extremely high velocity's
>(11 km per second??) to flatten cities
There are several science fiction novels that use this idea. "The Moon is a
Harsh Mistress" comes to mind. In reality such a weapon wouldn't be worth
the effort of construction since we can't get out to the Moon all that
easily and we're quite capable of killing ourselves without its help. :(
In science fiction, however, it's usually assumed that it is lunar settlers
who are deciding to bombard the mother world so getting to the Moon isn't a
problem. Assuming an appropriate weapon system is built then:
>I do not believe this possible/practical for the following reasons
>a) Any rock launched would spend days reaching its target as it would
>have to spiral into a decaying orbit around the earth (the rock cannot
>change course once it is launched)
Why is there a need for a decaying spiral orbit? Just take the rotation of
the Moon (not much) and its orbit around the Earth into account and fire the
rocks "straight" at the Earth. Okay, so they can only impact on the side
that (accounting for travel time) faces the Moon but the Earth
rotates once a day so every point on Earth is targetable once every twenty
four hours. By anology a comet or near Earth asteroid wouldn't need a
decaying spiral orbit to hit the Earth, just an intercept trajectory.
>b) The amount of damage it would do would not compare to a nuclear
>weapon (or even a large conventional bomb)
Kinetic energy = 0.5 m v^2
For a 100 tonne rock travelling at 11km/s this is:
KE = 100 000 kg * (11 000 m/s)^2
= 1.21 * 10^13 J
A megatonne is, I believe, equivalent to about 50g of matter:
E = mc^2 = 0.05 (2.99*10^8) = 4.47*10^15 J
So you're looking at something like a hundredth of a megatonne. Not exactly
nucelar weapon caliber but nothing to sneeze either.
Given, however, the rock has a density of about 3.5tonnes/m^3 a 100 tonne
rock only has a diameter of about 3.8m. A 10 000 tonne rock has a diameter
of about 17.6m. Such a rock would have 100 times the kinetic energy upon
arrival (ie. be on the order of a megatonne). This is a lot more bang
without the rock being too much bigger. (The rail gun would have to be a
lot more powerful, of course.)
>c) 100 tonnes if not that heavy (compared to a missile)
Most missiles don't use kinetic energy for their killing power so I don't
see how this is relevant.
>d) 11 km per sec is fast but not that fast
>e) Seem like a very expensive weapon to me
Assuming there are people living on the Moon with a reason to build such a
weapon (in "The Moon is a Harsh Mistress" they wanted to force Earth to
grant them independence) the expense becomes much, much smaller. Plus
people seem willing to shell out big bucks for military schemes (witness the
Cold War).
The 11km/s is largely "free" energy provided by Earth's gravity. All the
Moon settlers have to do is get the rock free of the Moon's gravity and
headed in the right direction and it will naturally fall "down" to Earth.
Thus once the launching system is built, there is a virtually unlimited
and practically free supply of ammunition in the form of lunar rock. I
wouldn't want to be on an Earth that had to fight off an infinite artillery
barrage. A single rock wouldn't destroy a large city but even a relatively
small number would make a big mess.
------------------------------------------------------------------------------
W Vander Wilp
Dani Eder
>Is it feasible to have a rail gun on the moon that could accelerate
>large rocks (100 tonnes?) to hit the EARTH at extremely high velocity's
>(11 km per second??) to flatten cities
>I do not believe this possible/practical for the following reasons
>a) Any rock launched would spend days reaching its target as it would
>have to spiral into a decaying orbit around the earth (the rock cannot
>change course once it is launched)
It depends on your point of reference. If you launch a rock off the
Moon opposite the Moon's orbital motion, it will be at rest with
respect to the Earth. Then it falls straight down. It would typically
take several days to fall, and from a ground oberver's point of view
the rock would appear to be spiralling in, but that is an artifact of
the Earth's rotation. Also, who says you can't put some guidance
thrusters on the rock to steer it in?
>b) The amount of damage it would do would not compare to a nuclear
>weapon (or even a large conventional bomb)
Well, something falling from that height has about 15 times it's weight
in TNT in energy, so you have 1.5 kilotons of TNT. That's about 1/10
of the energy in the Hiroshima bombing. Nowhere near what a cruise
missile or ICBM carries (450 kiloton warheads), but a heck of a lot
more than a conventional bomb.
>
>d) 11 km per sec is fast but not that fast
>e) Seem like a very expensive weapon to me
It depends. There are lots of rocks on the Moon, so you aren't going
to run out any time soon. Our current nuclear arsenal wasn't cheap either
(hundreds of billions of dollars).
Gordon Johnson
>I was wondering whether anyone could settle an argument I'm currently
>having with some friends
>Is it feasible to have a rail gun on the moon that could accelerate
>large rocks (100 tonnes?) to hit the EARTH at extremely high velocity's
>(11 km per second??) to flatten cities
>I do not believe this possible/practical for the following reasons
>a) Any rock launched would spend days reaching its target as it would
>have to spiral into a decaying orbit around the earth (the rock cannot
>change course once it is launched)
>b) The amount of damage it would do would not compare to a nuclear
>weapon (or even a large conventional bomb)
>c) 100 tonnes if not that heavy (compared to a missile)
>
>d) 11 km per sec is fast but not that fast
>e) Seem like a very expensive weapon to me
Biggest argument against it would be its own vulnerability to one
guided missile from Earth. These things take time and effort to build
(and replace if bombed)
Gordon Johnson
Scottish genealogical consultant
Kin...@wintermute.co.uk
Henry Spencer
>>Is it feasible to have a rail gun on the moon that could accelerate
>>large rocks (100 tonnes?) to hit the EARTH at extremely high velocity's
>>(11 km per second??) to flatten cities
>
Sigh, it also comes up quite regularly in the sci.space.* newsgroups,
usually with enthusiastic discussion by people who (like the SF authors)
ignore some of the practical problems.
>So you're looking at something like a hundredth of a megatonne. Not exactly
>nucelar weapon caliber but nothing to sneeze either.
Actually that's definitely nuclear-weapon caliber -- that's 10kT, roughly
the yield of the Hiroshima bomb. Many people do not realize that most of
today's nuclear warheads are well under a megaton. Really big nuclear
bombs are heavy and inefficient and have never been built in quantity.
The biggest bomb the US ever tested was 15MT, and that was an accident --
it was supposed to be 5MT (!). The biggest bomb the US ever deployed in
operational service was 9MT, and it is long obsolete.
>The 11km/s is largely "free" energy provided by Earth's gravity. All the
>Moon settlers have to do is get the rock free of the Moon's gravity...
That trivial little requirement is one of the practical problems I alluded
to above. When you study schemes like this carefully, you find that the
energy cost of launching the rocks is rather large. It's smaller than the
impact energy, but only by something like a factor of 20. While that is a
useful amplification, it does mean that you need a very substantial input
of energy: about 0.5kT to produce that 10kT impact. Almost certainly,
you are better off using that 0.5kT more directly, and forgetting about
the rocks.
>headed in the right direction and it will naturally fall "down" to Earth.
Not quite -- launching the rock exactly to lunar escape velocity will leave
it in orbit around the Earth, just like the Moon. You also need to kill
most of its orbital velocity.
>Thus once the launching system is built, there is a virtually unlimited
>and practically free supply of ammunition in the form of lunar rock...
Which cannot be launched except with the aid of very large amounts of
very expensive energy.
Bear in mind that if you don't want the nasty Earthmen to bomb your
launching system fairly promptly, you have to keep its location secret.
That means you don't get to use solar power, because the collecting areas
needed are much too large to hide. It also makes it very awkward to use
nuclear power, because there's a lot of waste heat in the conversion step
and disposing of that without advertising your location is seriously
difficult. (If you want to launch a 100t rock about once an hour, that
requires about 200MW of continuous power -- plus a suitable storage
system, of course -- which implies circa 400MW of waste heat. That's
really hard to hide.)
Heinlein could just wave his hands and allude to a big fusion power plant
powering his military launcher, but in the real world it's not so easy.
--
Space will not be opened by always | Henry Spencer
leaving it to another generation. --Bill Gaubatz | he...@zoo.toronto.edu
Sea Witch
>Why is there a need for a decaying spiral orbit? Just take the rotation of
>the Moon (not much) and its orbit around the Earth into account and fire the
>rocks "straight" at the Earth. Okay, so they can only impact on the side
>that (accounting for travel time) faces the Moon but the Earth
>rotates once a day so every point on Earth is targetable once every twenty
>four hours. By anology a comet or near Earth asteroid wouldn't need a
>decaying spiral orbit to hit the Earth, just an intercept trajectory.
Yup, and it is better to do it that way, because the impact velocity
is much, much higher.
>So you're looking at something like a hundredth of a megatonne. Not exactly
>nucelar weapon caliber but nothing to sneeze either.
Now the way I learned this stuff, 1/100th of a megatonne is 10
kilotons -- just a little smaller than the weapon that leveled
Hiroshima. Indeed, nothing to sneeze at -- call it a tactical nuclear
weapon. Drop a few of those on good ole NY, and it will be very flat.
>Assuming there are people living on the Moon with a reason to build such a
>weapon (in "The Moon is a Harsh Mistress" they wanted to force Earth to
>grant them independence) the expense becomes much, much smaller. Plus
>people seem willing to shell out big bucks for military schemes (witness the
>Cold War).
The 'weapon' in question was an adapted civilian launch system -- like
an Atlas in reverse :).
>The 11km/s is largely "free" energy provided by Earth's gravity. All the
>Moon settlers have to do is get the rock free of the Moon's gravity and
>headed in the right direction and it will naturally fall "down" to Earth.
>Thus once the launching system is built, there is a virtually unlimited
>and practically free supply of ammunition in the form of lunar rock. I
>wouldn't want to be on an Earth that had to fight off an infinite artillery
>barrage. A single rock wouldn't destroy a large city but even a relatively
>small number would make a big mess.
One rock wouldn't totally destroy a large city, but it would put it
out of commission for a long while. You are also forgetting that such
an impact would trigger fire storms. All that asphalt is quite
flammable when you heat it to a few thousand degrees... The fire
storms would level any city. Or make it a few rocks just to make sure.
Pierce Nichols
L. Parker
>Is it feasible to have a rail gun on the moon that could accelerate
>large rocks (100 tonnes?) to hit the EARTH at extremely high velocity's
>(11 km per second??) to flatten cities
>
I can't answer for the exact circumstances you described, but have you
considered the damage that could be done by much smaller missiles, say
about 10 grams, moving at .99 c?
Whether or not it could penetrate atmosphere may be pretty much
irrelevant, thermal shock alone would be pretty bad, and space borne
infrastructure such as communications satellites would be sitting ducks.
There are more kinds of weapons than those which only kill directly....
L. Parker
David Thomas Richard Given
>large rocks (100 tonnes?) to hit the EARTH at extremely high velocity's
>(11 km per second??) to flatten cities
>
>
>
>a) Any rock launched would spend days reaching its target as it would
>have to spiral into a decaying orbit around the earth (the rock cannot
>change course once it is launched)
Who says it has to be in orbit? Just throw it in as near to a straight
line as it can go. You'd have to place your rail gun accordingly, of course.
>b) The amount of damage it would do would not compare to a nuclear
>weapon (or even a large conventional bomb)
>
>c) 100 tonnes if not that heavy (compared to a missile)
>
>d) 11 km per sec is fast but not that fast
It's the total kinetic energy that counts. at (mv^2)/2, 100 tonnes at
11000 m/s is 6.05E12 joules. Six *terajoules*. This is all going to get
converted into heat on impact, and will produce quite a large fireball. I
can't remember how many joules per megaton of TNT for fission/fusion
weapons, but I'd wager this is equivalent to a pretty large one. And the
radiation is negligable.
>e) Seem like a very expensive weapon to me
*Expensive*? It's just a big chunk of rock, for goodness' sake! You'll
have to put some metal sheathing on it to be able to grip it with your
magnetic fields, but that's cheap. The only energy you're expending is
that used to launch it. Remember, in order to launch a `conventional' nuke
from the same place, you'll have to expend the *same* amount of energy to
launch. And you'll also have to build a nuclear warhead of whatever kind,
which is quite expensive.
--
-------------------------------------------------------------------------------
Why do people surf the Information Superhighway? Won't they get run over?
http://www-hons-cs.cs.st-andrews.ac.uk/~dg
Sun-Earther David Daton Given of Lochcarron
Pat
Henry Spencer <he...@zoo.toronto.edu> wrote:
>>And you'll also have to build a nuclear warhead of whatever kind,
>>which is quite expensive.
>
well actually since the cold war ended, nuclear materials are
just darn cheap, not to mention, that nuclear handling facilities
may be cheaper to build on the moon. Lot's of vacuum, so handling the
chemistry may be safer, no-one to go nuclear over spills and
not a lot of eyes around or easy detection methods.
pat
--
One mans desperate mundane existence is anothers technicolor - Tik
Martin Jones
: >>P.S. I assume you've read Moon is a harsh Mistress by R A Heinlein...
: >>I'm afraid he doesn't consider the possibility of a counterattack against
: >>the launcher all that well. Still - well worth a read.
: >>
: >He had the Looneys build a second launcher underground except for the exit,
: >which was an extinct volcano, one of many in the area. And everyone was
: >told an incorrect location (lat & long) for the site...
Oops - my apologies - it's obviously been too many years since I last read it
.. however I don't remember the rocks having any form of engine strapped
onto them at all - so couldn't you "just" trace back the paths followed by
the incoming rocks and get a pretty good guess as to where the launcher must
be. - then if it's on the side facing earth you can watch the area closely
for the next launch to pinpoint your target, otherwise you might need some
form of small inconspicuous craft for a closer watch of the probable launch
site.
Anyway - obviously time to go dust off my copy of one of the better Heinlein
Novels :)
Martin.
Pat
David Thomas Richard Given <dt...@st-andrews.ac.uk> wrote:
>In article <Dnux0E.ro%spen...@zoo.toronto.edu>,
>Henry Spencer <he...@zoo.toronto.edu> wrote:
>>In article <4hdalt$c...@mtinsc01-mgt.ops.worldnet.att.net> JWMo...@worldnet.att.net (Wayne Morris) writes:
>>Heinlein's books typically are superficially correct, but he seldom did
>>in-depth homework, and there are some real howlers to be found when you
>>look with a really critical eye. (The lunar advertising scheme in "The
>>Man Who Sold The Moon" relies on scattering black dust on parts of the
>>lunar surface, but even at the time the story was written, it was well
>>understood that the Moon's surface is *already* coal-black -- it looks
>>bright only because it is in brilliant sunlight and is seen against a dark
>>sky.) Heinlein's fiction should not be relied on as a source of technical
>>information.
how about the other approach? Scatter Bright aluminum particles on the
Dark surface and count on indirect lighting when the surfaces are in
shadow, or would the light intensity be too low from earth scatter.
Luminous paint?
doyle%PROBLEM_WITH...@beaver.cs.washington.edu
> Luminous paint?
> pat
My sister says she has a friend that for a million dollars or so could
project holograms on to the moon.
mdk@@meteorology.ho.bom.gov.au
Martin wrote:
>Oops - my apologies - it's obviously been too many years since I last read it
>... however I don't remember the rocks having any form of engine strapped
>onto them at all - so couldn't you "just" trace back the paths followed by
>the incoming rocks and get a pretty good guess as to where the launcher must
>be. - then if it's on the side facing earth you can watch the area closely
>for the next launch to pinpoint your target, otherwise you might need some
>form of small inconspicuous craft for a closer watch of the probable launch
>site.
>
>Anyway - obviously time to go dust off my copy of one of the better Heinlein
>Novels :)
>
> Martin.
There were rockets strapped to the rock so that the target could be changed
in flight, which they did (remember - hit Cheyenne til it didn't exist, then
belt someone else?).
Edward Bornstein
>: In article <wa2iseDn...@netcom.com> wa2...@netcom.com (Robert Casey) writes:
>: >>P.S. I assume you've read Moon is a harsh Mistress by R A Heinlein...
[ text sold for Hong Kong Dollars ]
>Oops - my apologies - it's obviously been too many years since I last read it
>.. however I don't remember the rocks having any form of engine strapped
>onto them at all - so couldn't you "just" trace back the paths followed by
>the incoming rocks and get a pretty good guess as to where the launcher must
>be. - then if it's on the side facing earth you can watch the area closely
>for the next launch to pinpoint your target, otherwise you might need some
>form of small inconspicuous craft for a closer watch of the probable launch
>site.
The rocks did have engines, solid fuel rockets, IIRC. These were used
by Mike and his "idiot child" (both computers) to adjust trajectories to
make course corrections, retarget, and abort strikes. Note: abort usually
meant retargeting into an ocean or lake away from shipping lanes, though
sometimes rocks could be diverted into a permanent orbit.
Radar installations on the Moon were used to track the rocks.
One radar was at the secret catapult site, but was used sparingly.
The main, publicly known catapult and radars were used exclusively
until it was destroyed by missiles and bombs launched by Federated
Nations (FN) spacecraft. The secret catapult was used only after this,
when no FN ships orbiting the Moon were above the horizon. The
possibility of the FN locating the secret catapult by radar from Earth
or Earth orbit was not mentioned.
However, it seems likely that the FN had no inkling of the secret
catapult's existence until the rocks continued to arrive after the main
catapult was destroyed. No doubt the FN could have located and
destroyed the secret catapult eventually. However, within a few days
there was a political decision to grant Luna's independance.
An important point is that the FN military was complacent, careless,
and contemptous of "a rabble of convicts" throughout the war. This
was discussed in alt.fan.heinlein recently in reference to the FN's
tactics during the earlier ground assault on Lunar warrens. The FN
would certainly have won a long war, which was why Free Luna's
goal was to press for a early political solution.
- Captain Button - but...@io.com
Burns Fisher
In article <1996Mar15.1...@ucl.ac.uk>, m...@bsm.bioc.ucl.ac.uk (Martin
|>: In article <wa2iseDn...@netcom.com> wa2...@netcom.com (Robert Casey)
writes:
|>: >>P.S. I assume you've read Moon is a harsh Mistress by R A Heinlein...
|>: >>the launcher all that well. Still - well worth a read.
|>: >>
|>: >He had the Looneys build a second launcher underground except for the exit,
|>: >which was an extinct volcano, one of many in the area. And everyone was
|>: >told an incorrect location (lat & long) for the site...
|>
|>.. however I don't remember the rocks having any form of engine strapped
|>onto them at all - so couldn't you "just" trace back the paths followed by
|>the incoming rocks and get a pretty good guess as to where the launcher must
|>be. - then if it's on the side facing earth you can watch the area closely
|>for the next launch to pinpoint your target, otherwise you might need some
|>form of small inconspicuous craft for a closer watch of the probable launch
|>site.
|>
|>Novels :)
Actually they did have some small engines. I don't recall if the normal wheat
packages had them (I think so), but the rocks certainly did, so that Mike could
knock out of the way the rocks heading for country A when A recognized Free
Luna.
Nonetheless, there was no mention of evasive maneuvers, and you are probably
right that in reality it would not be that hard to find the launch point.
Burns
Thomas Kalbfus
projectiles to penetrate the Earth's Atmosphere. Alternatively
it could be designed to fire Nuclear Warheads. I don't like
this idea of turning the moon into a battleground, it could
hinder mining operations. Verifying Nuclear treaties would be
much more difficult once a large portion of humanity lives and
works in space.
The Solar System is a large place and there are many
places to hide a nuclear bomb factory, or even a city of one
million people manufacturing bombs. The only question is why
civilizations would want to nuke each other in outer space when
so much is free for the taking. The environment of space is
tough enough without people up there trying to kill each other.
Thomas Kalbfus
defense system. The projectiles shot from the moon would have
to travel from the moon to the Earth in less than 30 minutes in
order to shoot down the missiles before they reached their
targets and thats not counting the missiles launched from
submarines. Remember it took 4 days for an Apollo space ship to
reach the moon. Any projectile shot from the moon would have to
travel 200 times as fast.
Julian Bordas
contrast on the moon veiwed from the earth is neglible. Luminesent painr could be
the go though
Julian
--
TK2 Summer Tour. Paddle Mania is back
Wayne Morris
but anyone interested in a fictional description of this very subject
should read the novel _The_Moon_is_a_Harsh_Mistress_ by Robert
Heinlein published in the mid 60's. A very similar thing is described
in the book, and while I have not checked the "facts" presented,
Heinlein's books are noted for technical accuracy.
Wayne Morris
JWMo...@worldnet.att.net
>launch. And you'll also have to build a nuclear warhead of whatever kind,
>which is quite expensive.
Henry Spencer
>...anyone interested in a fictional description of this very subject
>should read the novel _The_Moon_is_a_Harsh_Mistress_ by Robert
>Heinlein published in the mid 60's. A very similar thing is described
>in the book, and while I have not checked the "facts" presented,
>Heinlein's books are noted for technical accuracy.
Unfortunately, Heinlein pulled major boo-boos occasionally -- he worked
hard at getting things precise (that is, doing calculations of how stuff
would work) but not too hard at getting things accurate (that is, filling
in background knowledge so he'd know whether the assumptions behind the
calculations matched reality). TMiaHM has some real howlers in it. It's
great reading if you don't examine it too closely, but it should **not**
be trusted on technical matters.
In particular, TMiaHM's catapult design glosses over problems of power
generation and heat dissipation, which are severe for a concealed lunar
catapult.
--
Americans proved to be more bureaucratic | Henry Spencer
than I ever thought. --Valery Ryumin, RKK Energia | he...@zoo.toronto.edu
Steve Willner
True, of course. Not least the economics. Heinlein exposes a lot of
the problems himself in a (much) later story.
> In particular, TMiaHM's catapult design glosses over problems of power
> generation and heat dissipation, which are severe for a concealed lunar
> catapult.
True enough, but to be fair, the catapult in the story was built to
launch payloads to Earth, not as a weapon. It was used as a weapon
because it was available and nothing else was. I don't remember any
attempt to conceal the catapult; certainly Earth would have known its
location.
When he wrote a story involving a lunar base _purpose built_ for
launching weapons, Heinlein had it use nukes. (I believe the story's
title was _Requiem_.)
--
Steve Willner Phone 617-495-7123 swil...@cfa.harvard.edu
Cambridge, MA 02138 USA