MadSci Network: Physics

Re: Would explosive weapons be effective in space?

Date: Wed Jan 11 20:20:54 2006
Posted By: David Coit, Aerospace Engineer, Naval Air Warfare Center - Weapons Division
Area of science: Physics
ID: 1136496454.Ph


There are several ways a warhead can eliminate a threat, and the preferred
method will depend on the type of target. For a sophisticated electronic
target, it might be effective to use an electromagnetic pulse (EMP) to
induce a high current through its sensitive electronic parts, frying them.
High heat or pressure can make an absolute mess out of "soft targets" (a
euphemism for "people"). Some things, such as heavily armored tanks, can be
disabled with a shaped charge that can penetrate the armor and maybe bounce
around inside to maximize the damage. Most warheads are capable of
eliminating threats in multiple ways, and are not designed to simply "blow
them to pieces." 

For example, the 500 pound MK-82 is a staple of modern air forces, even
though it has been around since the early 1960s. If it scores a direct hit
on a building, its nearly 200 pounds of high explosives are enough to do
significant damage to the structure and anything inside. However, it is
also effective against smaller, more mobile targets because even if it
misses by a little bit, the 300 pounds of other material that surrounds the
explosive will fragment and fly at high velocity in all directions. I know
what you're thinking: maybe the MK-82 is effective, but its big brother,
the 2000 pound MK-84, is just plain awesome. I agree, but this was just an

This finally brings me around to answering your question. Determining how
effective a given warhead would be against a given target can be extremely
difficult. There are many sophisticated analytical and statistical methods
for calculating this quantitatively, but it's always good to back up your
calculations with real experiments, and both are done in the real world.
Many people would think that designing and carrying out these experiments
would be about the coolest job ever, and I am here to tell you: they are
right! But I digress. My point is that your question is difficult to answer
even if you specify a weapon and target, and you're asking generally about
any possible future weapon and target. I think maybe the best way to answer
your question is to discuss the basic methods I outlined above in a
qualitative way. 

If you are very accurate and can score a direct hit, just about any
machinery can be disabled by explosives alone. You mention in your question
that explosives generate a shock wave in an atmosphere, and that's true,
but any detonation generates a shock wave in the detonating material. That
shock wave spreads outward and carries material at high speeds, even if the
detonation occurs in a vacuum. If you are close enough, and have enough
explosive power, you will do damage. However, it will probably not be
economical to disable space-based threats purely with explosives. Adding
material that will fragment and send shrapnel towards your target gives you
a lot of bang for your buck. Even a small piece of metal traveling at very
high speed can tear apart the target and prevent it from functioning. This
is true both in the atmosphere and out of it. It doesn't matter if you
accelerate the fragments with electromagnetic forces (as in a railgun) or
with conventional explosives, this has been the preferred method for
eliminating enemy threats since the invention of the sling (granted, we've
gotten a lot better at slinging things). Since conventional explosives are
a simple, effective, and relatively cheap way of throwing shrapnel, I don't
see them becoming obsolete even if future threats are in the vacuum of
space. That's not to say we won't develop new weapons. For example a laser
can be very fast, powerful, and has an advantage in that it is easy to
change its aimpoint by a large amount simply by moving a mirror a little
bit. The technology isn't quite here yet to make it economical, but there
is a lot of research going on. 

Still, the future you are asking about is decades away, and it's always
tricky to predict where technology will be that far down the road. How many
people in the 1970s would have predicted the internet or the personal
computer? The real test will be to wait a few decades and then go back and
watch some of these old movies again. Unfortunately the only thing I'm sure
will be the same is that human beings will be fighting each other because
they are both greedy and vengeful. 

David Coit

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