Re: Orion Drive space battle

Jarrod : Ah, thanks very much ! I was expecting them to be implausibly
heavy, never mind implausibly light. Not sure you could really get tens
of thousands of crew in and still have room for other systems, but
probably not worth quibbling over.
"Assume the ship needs a delta-V of 250,000 km/s and this is equal to
the effective exhaust velocity"
You did mean 250km/s... right ?

IsaacKuo wrote:
The large metal hull will flex and bend to an extent, rather
than act as an infinitely rigid object. Nevertheless, it
will transmit sound and other vibrations, so the crew could
be in for a terribly unpleasant experience. It'd be like
sitting inside a big bell when it's rung.

So, it could be a good idea to vibrationally isolate the
main crew compartments and less ruggedized equipment (perhaps
including all sensor and weapon systems other than the gauss
cannons). You could do this by designing the ship as a shell
within a shell. The outer thick hull along with ruggedized
nuke magazines acts as a shock absorbing "pusher plate".
This is attached to a shock isolated pressurized inner hull
via internal tethers.

Another very interesting idea, never considered flexible (non-sailing)
spaceships before. It works for bridges, so I don't see why not.

The bigger you get, the less you need to worry about the
pusher plate mass. There's some particular "sweet spot"
for the best size of a pulse unit. This dictates some
particular best size for a pusher plate. The pusher
plate requirements don't get any bigger as you scale up
the ship.

Excellent ! Looks like these things might just fly !

What can kill you, however, is the mass of the structure
required for the ship itself. As you scale up a design,
the "strength" of the metal structure seems to get weaker
in proportion.

Or, then again...

Talk no more about starships. Orion is a rather dubious
option for interstellar propulsion even making optimistic
assumptions.

Completely agree there.


A desire to fire missiles from short range to limit the
time for laser defenses to react is good. Just keep in
mind that it's a double-edged sword. You're giving the
enemy all of the benefits of a short range knife fight
also.
....
Objects smaller than the angular resolution are visible,
and they can still be targeted precisely. Against the
black background of space, it still appears as a bright
dot and the center of this dot can be determined to
arbitrary precision.

In order to get a 3d fix on the target's position, you
need another view from a different angle (for binocular
vision triangulation) or you need another sensor capable
of determining distance (like radar).

I suspected something like that might happen. Can I assume other
countermeasures employed to get ship safely into continuous
laser-saturation range ? The 3000km range I would think is still
reasonable given the available missile payloads.

Cannon launched missiles are an interesting idea with
a lot of potential benefits, but also a lot of technical
challenges. Designing a missile to survive the shock
of firing is a challenge, but if you can figure it out
you could potentially send more munitions downrange for
less overall mass and less overall cost.

I really like the idea of firing "dumb" guided missiles.
This is a spinning projectile fired out of a "rifle" with
some sort of sideways pointing thruster. This could be
a shell filled with an ablative material; this shell has
a nozzle hole in one side and a transparent base.
Upon firing, the "rifle" sends the shell hurtling
more or less at the target. The firing ship tracks both
the target and the shell. Sideways course adjustment
thrusts are performed by firing a timed laser or microwave
pulse at the shell. This pulse vaporizes a bit of the
ablative filler material, and as the gas escapes out of
the sideways nozzle it produces a sideways thrust.

These "dumb" guided shells have no moving parts and no
delicate electronics so they can survive the shock of
firing easily. They also don't have any chemical
explosives, so they can be used as part of the armor
protection scheme.

The main problem with "gun" launched missiles is that
they plausibly have low muzzle velocities. Even with
an advanced electromagnetic linear accelerator, it
takes really long barrels to reach decent velocities
with reasonable accelerations. But for short range
work, I think it has potential.

Definately sounds a viable option for the short-range phase. Think I'll
assume cannon-fired missiles doable for long-range phase (only for
Gauss cannons, maybe also for Allied guns which are a bit larger).
Directly using propellant without an engine sounds like a good way to
save mass and would add less cost to each shell so could be used for
the larger numbers needed for the smaller gun shells.

So
from 3000km, Soviets should have capability to substantially
oversaturate lasers. Does not guarantee kill :
1) So many missiles, some are simply bound to miss.

Maybe some small number of malfunctions, but very
few will miss such a large target unless damaged
by enemy fire.

Exactly what I was thinking - only a few misses, I just don't like the
idea of 100% accuracy (call it a pet hate). Not enough to really affect
the battle, just something to show to remind people that occaisionally,
things just break, even in the future.

2) Not all may be lethal-yield nuclear, some may be cheap chemical
explosives - tie up lasers for minimal cost (Allies can't see which
ones are nukes), launched first to 'shield' higher-yield weapons - may
damage Allied cooling fins and laser turrets.

I still don't see the benefit to using nuclear
warheads offensively. The minimum size/mass of a
nuke is substantial. I think you'd do a lot better
by having that much mass used for sacrificial laser
shielding. This boosts your chances of getting
through the defenses in the first place, and once
you get through and hit the target, it's dead even
with no warhead.

Wikipedia lists the smallest nuke mass as 23kg with a yeild up to 1kt.
The maximum yeild-to-weight is apparently 4Mt/tonne (though, on a much
larger device - I don't know the actual masses of, say, a many-kiloton
bomb - but Davy Crockett is listed up to 40kt/tonne). Whereas at the
5km/s velocities here would lead to about than 3 tonnes TNT energy per
tonne of projectile (any links on the damage 1 tonne TNT can do ?).
Nukes also don't have to detonate on impact, if the yeild is high
enough. Assuming pessimistically that the missiles here have the same
payload and speed as the Exocet, being of similar size, they could
deliver at least 7kt by proven Davy Crockett nuke standards. If the
payload was inert, energy would be less than 1 tonne TNT. A dramatic
performance increase is needed for these small missiles to be useful.

Using the payload for extra propellant would help, but with the size of
the missiles here I don't think more than a few extra km/s at the very,
very most would be likely. Whether you could get sufficient extra mass
on the projectiles for them to better withstand the lasers, given laser
power, I will do as you suggest and wait for wiser minds to check. I
would inclined to disagree since there appears to be more than
sufficient energy available even to vaporize, which is an overestimate.
Still, it seems possible that you may be able to get more energy per
unit mass with nukes than using dead projectiles, at least at these
speeds. For the larger weapons that might be sufficiently powerful to
do KE damage, why not put a nuke in anyway ? Should it, for whatever
reason, not manage to actually impact, it can still detonate.

Problem : lasers may easily target ship directly at 3000km range.
Maximum range at which Soviet ship resolved by 3m telescopes :
r = s/? = 80/1.932e-7 = 414,000 km
But probability of hit due to lightspeed lag = 0.01, assuming 1g
acceleration available to Soviets. Equivalent to about 1%. Hence, need
closer range.

I think it's best if you forget about the possibility
of dodging laser fire. 1gee is REALLY HARD to keep up for
a long time.

Ah, my mistake - I plugged the numbers into the equation on nyrath's
site without actually considering what it meant.

Another countermeasure particularly suitable for defense
against long range fire is to simply repair damage.
With spaced armor shells, it's possible to replace
plates with robots or space suited crew behind the
outer shell. With foam-like armor, it's possible for
two ships to support each other with "foam hoses".
The damaged ship simply rolls to face the damaged area
toward the other ship. The other ship sprays foam onto
the damaged area.

Interesting, but wouldn't the two ships have to be incredibly close
together for this to be viable ?

Major unkown is how much easier pulsing the lasers
makes destroying things.

It can make things a heck of a lot easier to destroy
things, but conversely you can assume that the pulsed
laser technology available just isn't all that great.

That'll do nicely ! :D

Have assumed Americans facing Russians head-on, but calculated drilling
through armour as if were facing side-on.

I really don't like this. This is "one dimensional
thinking".

No, just very back-of-the-envelope. Can't spend months doing the
precise calculations, even if I knew how. Besides in this case, if the
lasers were drilling head on, it would take longer.

I've noted several times already that both sides will
split apart into at least two taskforces so that they
can attack the other side from more than just one angle.
If you concentrate all of your forces into a single
taskforce, then the enemy has many options for
putting its "best side forward".

Instead, you want to engage the enemy from at least
two different directions at once. This guarantees
that you can pick and choose your targets at will,
and limits the enemy's options to concentrate his
defenses.

Mmm... I may have misunderstood this, but if they're BOTH in two
taskforces, two groups have engaged one, the remaining group is free to
engage as well, bringing it back into essentially a 1-on-1 melee. Since
each side can see exactly what the other's doing at massive distances
no one taskforce is likely ever to be engaged with more than one other
similar taskforce. No-one will deliberately risk engagment at 2:1 odds
against.

Allies - may want to maintain distance to destroy as many lasers as
possible. Could try and "retreat" at such a speed that the missiles
can't catch them up, in which case the Russians accelerate and the
whole thing degenerates into a farcical race rather than
a battle. Will ignore this option.

A retrograde battle is more tactically interesting
than you think. One the face of it, it seems like
the guy who's retrograding has the advantage--his
missiles take less time to reach the enemy and they
hit him harder. However, in a fleet action the
retrograding fleet also has fewer tactical options.

In the chasing fleet, any ship which gets damaged
can trivially retreat behind the battle line simply
by reducing thrust. The enemy is forced into deciding
whether to turn its attention to a fresh ship while
the damaged ship conducts repairs, or to continue
firing at the damaged ship from longer range.

The retrograding fleet has no such option. If a ship
is damaged, the only way for it to "retreat" from the
battle line is for the rest of the fleet to slow down
(making the entire fleet more vulnerable to enemy fire).
If a ship's drive is damaged, it will either slow down
the entire fleet or it gets left behind--where it's
easy pickings for the chasers.

OK, I'll give that option some further thought.

Inital attack proceeds as follows between 2 ships : Russians bombard
Allied ship with thousands of missiles and unguided/semi-guided
projectiles.

Unguided projectiles are a waste of time. Only a
vanishingly small number of them will even be headed
toward the target.

Very well, forget the unguideds at long range.

Laser defences take out the vast majority of such
missiles, however, a significant number still make it through simply on
sheer numbers. As the missiles get closer the low-yield missiles use
the last of their propellant and accelerate, reaching close enough to
detonate or even impacting. Velocity will not be enough to cause damage
(to hull) in itself but explosive power will be able to damage cooling
fins and laser turrets.

I didn't find this plausible before; I still don't find
it plausible. If missiles actually impact the target,
plausibly it's dead. If you can vaporize it with a nuke
just before impact (like 100-1000m away), then the
resulting plasma blast could have terminal effects like
you desire. This high velocity plasma would more or
less bounce off the thick metal hull plating, but could
seriously damage radiators and laser turrets.

Impact is only lethal with the velocities stipulated here using a nuke.
Whether ALL the small missiles would be nukes depends on how cheaply
the things can be made. If you can increase the chance of nuclear
success by using cheaper chemical rockets then there would be some
value in it.

If your hull-scouring nuke does not actually destroy the hull, do the
crew survive ?
(if no, then no further action need be taken, if yes, then further
attacks by larger weapons may be needed, if the Russians are feeling
particularly merciless)

3) Any other ideas...?

The Allies have a mixed armament which at first seems to
put them in a strange predicament--their lasers work best
at long range, but their missiles work best at short range.
Should they keep the range open and just use their lasers,
or should they get closer to use the missiles also?

There's a less obvious solution which is to launch all
the missiles from long range, and use them as an independent
"fleet". While the laser ships stay further away, the
missile swarms can operate much closer to the Russians.

Now that I think is probably a valid reason for a mass-missile launch.

Other questions :
[lots of very good answers]
How are these rods targeted, anyway ?

They are physically pointed at the target.
What I meant was - how do they know where the target is, and how are
they turned ?

That sort of performance sounds incredibly optimistic.

Can't speak for that - any second opinions ?

And I don't even want to think about the idea of
"visible X-ray laser beams".

Ah well, we'll just have to diasagree on that particular thorn. ;)

.

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