Re: Orion Drive space battle


Rhysy wrote:
OK, I should probably have determined the relative
velocities/distances. However I really don't find these tens of
thousands of kilometers distance or up to 100km/s velocities quoted at
all plausible. No-one's going to fight a battle if there's time to
dodge the enemy missiles, or even just leave the combat zone
altogether. It makes no sense.

Except that the missiles are guided. You try to dodge them, they
follow you. You try to leave the combat zone, they follow you.

Now there is the question of whether the missiles have the delta-V that
the main ship has. If you cannot pack an orion drive or other nuclear
drive on the missiles, then the orion drive main ships can run away
given enough time/distance. On the other hand, if the missile's drive
has anywhere near the performance of the main craft's drives, the
missiles have a huge advantage at maneuvering. The reason is that the
main craft will only expend about 1/4 their delta V to close with a
target, because the crew all want to get home and they need to expend
another 1/4 of the delta V to slow down at (or after) the mission
objective, 1/4 to accelerate back towards home, and 1/4 to stop at
home. The missiles don't care about getting home. They don't care
about stopping. They can exhaust all their delta-V in one sprint to an
intercept course with the target. Here, "intercept" is one of those
nice military euphamisms for crashing into the target (or at least
getting within a few km, so the KK ball bearings or nukes or whatever
can do their work)

At lower distances, the high relative
velocities I also find highly dubious as I doubt any system is every
going to be perfect to ever be able to accurately target anything at
those kinds of speeds.

There are technical chalenges, but they seem quite doable. The U.S.
military has repeatedly demonstrated this ability (although there were
technical glitches at first). Hitting small target with another small
target at 20 km/s is doable, and this is a direct hit. If you only
need to detonate a nuke within 100 meters or so, or send a cloud of
ball bearings out in a swarm that is 100 meters across by the time of
impact with the craft, it gets much easier.

Strangely though, people have also raised issue with the unguided
weaponary (which only amounts to a few guns anyway - I barely even
mentioned it in the battle plan).

Your description made the missiles seem to be unguided. If they are
guided, you will not loose accuracy by jinking about during approach
(but while jinking may help in dodging incoming kinetic projectiles, it
will not help against lasers).

Yet others think that unguided ball
bearings are going to be devastating weapons !

The ball bearings themselves are unguided, but the missiles that
deliver them are not. closing at 20 km/s (say), and releasing the BBs
from 200 km out, the ball bearings drift for only ten seconds before
encountering their target. They are launched with enough precision to
give a cone centered on the current position of the craft, and over a
wide enough cone that in that half second, the craft has no chance of
accelerating away from the cone in time. Detonating closer to the ship
means you get more densly spaced ball bearings, but gives the craft
more time to shoot down the missile, something of a trade off.

Secondly, this
idea of low-mass ball bearings being used to cripple warships is not
plausible in my opinion.

100g ball bearings being fired at 100km/s do have the KE of WWI
battleship shell, but weren't those filled with explosives too ?
Moreover these ships are rather larger than WWI vessels both in size
and mass. As for the claim that a mere 10g ball bearing could be
deadly, this is simply wrong, it doesn't have enough energy. Even if
you did, somehow, get your high-speed tiny ball bearings fired at high
energy from a great distance to hit the enemy, it seems dubious that
such small objects would necessarily have the same effect as a larger
shell.

A single ball bearing is probably not going to be a ship killer.
That's why the missile carries tens of thousands of them, and releases
them in a swarm. Remember, too, after discharging the BBs, the main
body of the missile is still closing at 10 to 100 km/s. There's no
reason the drives/reactor/fuel tanks/etc can't also be guided during
that last second or so. The BBs cause many small holes and wipe out
surface emplacements (turrets, scopes, sensors, heat radiators). This
may cripple or mission kill the craft. If it doesn't, the collision
with the main body of the missile will destroy the craft - I mean
destroy it. Reduce it to drifting fragments and chunks, or at least
put so large a gaping hole in it that it is no more than a drifting
hulk. The difference is that the defending craft has maybe an extra
ten seconds to shoot down the main body of the missile, while blasting
10,000 BBs out of the sky is hopeless.

Finally, as I've said, I don't find these immensive velocities
plausible (I would stress that this is not from orbital considerations,
just from a tactical point of view).

The side armed with missiles and kinetic weapons will want as high of
velocitiy as possible, to enhance the hitting power of their weapons
and to give the other side less chance to shoot the weapons (and the
opposing craft!) down. Targeting will not be a problem, as has been
demonstrated with modern technology.

Dodging to avoid lasers is not so implausible I think - a moving target
is simply harder to hit. However that is something that can be changed,
if necessary.

It has been repeatedly demonstrated with military test lasers (google
for THEL, MTHEL, ABL, MIRACL), with astronomical telescopes, with
radars (across interplanetary distances, even), military sensors
(trying to scan or "paint" hostile evading targets) that putting a beam
of electromagnetic radiation exactly where you want it is a
technologically doable challenge. The only way to dodge is at very
close ranges and high velocities, where your movement is so fast that
the scope can't slew about in time to track you. Farther away, the
beam will be on target.

"A chemical warhead to spread fragments may be far deadlier
than a nuclear warhead for anti-spaceship work. " - that's an
interesting point, but you'd have to somehow deliver the chemical to
the interior.

I think the idea was to use the warhead to spread fragments of the
missile toward the target craft - the ball bearing cocept again.

" There's no good reason to wait until you're in knife range of the
enemy if you're
armed with a machinegun. " - but as you say the missiles may take an
hour to reach their targets, this analogy doesn't hold. A knife takes a
finite amount of time whereas a machine gun incapacitates instantly -
that's the whole point of the gun. The enemy isn't going to stand idlly
by for an hour being shot at.

They can try to dodge if they want, but the missiles will track them
and home in on them. Note that even if the enemy manages to outrun the
missiles, you have made him waste a valuable resource - his delta-V.
If he does not have enough propellant to finish his mission, you've
won. He may not even have enough propellant to get home, in which case
the other side is now out some very expensive craft that will need to
be replaced.

"Visually, you will not see any beam, but you will get a powerful green

flash (or continuous green flare, depending on the dwell time) where
the beam is incident on the missile. " - showing the beam is another
artistic necessity, I think. The audience needs to see clearly what's
happening, and OK, I like a nice lightshow. :)

And I will sadly shake my head and be disappointed, just like every
time I see supposedly "realistic" space battles that show visible
beams.

Now there is a way - after the first few pulses have blasted bits off
the other guys, you can get gas and dust and smoke and fragments
escaping into space that the beam has to go through to hit the target.
The light scattered from these gases and particulates can give a
visible beam for a short distance before the target. You can get neat
dynamic effects as the beam flickers into and out of visibility as the
gas jets intercept it, as debris drifts into its path and flares
brightly before vaporizing, and so on.

But really, if you are trying to make a realistic clip, just see where
invisible beams takes you. You get fancy light shows from the flashes
and sparks and incandescent debris at the target.

"No need to align the whole ship, just point a scope. " - the big laser
is probably the one design element I can still alter, since it's been
shown in the closed position throughout. It could instead be labelled
as a docking port/lifeboat hangar, or something. I guess whether you'd
need a laser cannon rather than a turret would depend on how much power
you can channel through a small area without burning your own system.

Not really. The advantage of a scope is so overwhelming everyone will
want to use one, and mirrors can be so reflective (99.9% or more at a
known wavelength) and large (so the beam is spread out more and heats
the mirror less) that any plausable laser can be guided and focused
with a scope. Note that the ABL, with a multimegawatt laser, is
focused through a scope with a diameter of about a meter.

At
closer range unguided weapons may at least tie up the enemy defenses
whilst other weapons do the main damage.

Even the close range weapons will probably have guidance and minimal
maneuvering capabilities. Just a small chemical rocket with 100 m/s
delta-V can mean the difference between having an incoming missile
dodge (because it can) and smacking that rocket out of the sky.

the nukes referred to in that context are small, sub-kiloton
nukes, and very large (~1 million tonne) spaceships.

To me, a sub-kiloton weapons nuke in space sounds completely pointless.
A 0.1 kT and a 100 kT nuke both require the same amount of plutonium,
the same amount of triggering explosives, the same amount of neutron
and radiation reflectors, tritium and berylium, and etcetera. For the
same expense and mass, you can have a 100 kT fission bomb. For not too
much more mass, you can have half a megaton or more fusion bomb. This
gives you longer kill ranges and causes more havoc in general.

The point of 0.1 kT bombs is to limit collateral damage. For this kind
of engagement, you don't need to worry about collateral damage.

Quick check (snipped check)

You don't need to melt the entire craft to destroy it. Mechanical
damage in the form of shocks is much more effective at breaking up
objects than thermal means. Smash, don't burn. Or, in the case of
impulsive vaporization, smash by burning (but it is the smash that does
the damage).

I therefore sumbit that no plausible KE weapon under any remotely
plausible circumstances has any chance of causing a kill to warship of
specified design.

A half ton missile impacting at 20 km/s will handlily take it out, no
questions asked. 10,000 ten gram ball bearings at 20 km/s will
puncture and perforate it and cripple many of its surface emplacements.

Note that unlike some other posters, I am not convinced that a ten gram
hypervelocity projectile will cause significant damage to the main body
of an armored warship. Sure, you've got huge heaps of kinetic energy,
but you've not got very much momentum. Momentum is what keeps things
going in one direction. The greater your ratio of KE to momentum, the
more spherical the resulting explosion and the less penetration into
the interior you will get. You can carve out a lot of craters on the
armored surface, though.

In particular, armor designed to protect spacecraft from hypervelocity
projectiles will probably use some variation on the whipple shield -
have a think outer layer of armor, a gap, and then several thick plates
separated by gaps. The impact with the thin outer layer vaporizes the
projectile, and the resulting plasma and re-condensed debris spreads
out before impacting the first inner layer. The inner layer absorbs
much of the impact, and will do so more easily because of how much the
debris has spread, but if it also fails, it will slow down and spead
out the debris even more before encountering the next layer, and so on.
These sheilds seem to be quite effective against orbital debris in
near earth orbit. A large or fast enough projectile will of course
defeat the armor, but it is considerably more effective than a solid
armor slab.

Luke

.

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