Re: Orion Drive space battle


Rhysy wrote:
Isaac Kuo wrote:
[...about 1m thick metal hulls...]
There's no chance of it handling larger hypervelocity projectiles,
but it would more or less completely block background radiation
(which is a good thing). It would also handle the explosion of
a nearby nuke, making the pusher plates superfluous.

Wouldn't you still need a way to reduce the accleration from the nuke
to a survivable level ? If I recall correctly the bomb plasma impacts
the ship over about a millisecond. If it has sufficient effect to
increase the ship speed by 1m/s, that would cause a 1 million tonne
ship an acceleration of 100g.

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.

As an added bonus, any minor weapon damage to the outer hull
doesn't transmit shocks to the more sensitive protected
equipment within.

Are ships viable with such massive deadweights ? Smaller, ~10,000 tonne
ships planned as having only 25% payload + about 25% deadweight, so
seems plausible, assuming don't need to scale up pusher/shock absorbers
proportionally with increasing overall
mass.

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.

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.

Larger, >1,000,000 tonne "Super Orions" typically starships
(albeit bad ones), sacrificing payload for speed, hence comparision
invalid. In reality would probably use Medusa/Classic Orion/Mini-mag
hybrids, so probably not worth worrying about too much.

Talk no more about starships. Orion is a rather dubious
option for interstellar propulsion even making optimistic
assumptions. Anything Orion style drive suitable for
interstellar travel will be very highly specialized for
that purpose. It would bear as much resemblance to an
interplanetary Orion style drive as a Concorde supersonic
airliner bears to an M1 Abrams Main Battle Tank (both of
these essentially derive their power from internal
combustion turbines--that's where the similarities end).

So ideally, would like (at some point - not continuously) to have
enemies within 10km of each other. If can't think of good excuse, will
show victors approaching enemy wrecks (or debris) after the battle.

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.

[...laser stuff snipped...any of Luke Campbell or Erik Max
Francis or John Schilling or others would be better with
those numbers...]

But, maximum angular resolution of 3m telescope is 1.932e-7 radians.
Smallest missiles are 5m long by 0.6m wide. Angular size of missiles :
s = r*? Where s = length of arc = 0.6m, r = distance, ? = angle
subtended = 1.932e-7
r = s/? = 0.6/1.932e-7 = 3105 km - Maximum distance can target
missiles (assuming no interferometers).

[uncertain if angular resoultion would really mean objects smaller than
a.res aren't at all visible, but it should definately make them very
hard to target]

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).

Or, with rapid-fire unguided projectiles plus
silo-launched missiles, easily capable of defeating laser defences at
3000km. Gauss cannons may rapid-fire missiles with high speed plus
enough delta-v rocket capability to act as guided missiles without
expending much propellant cannon-launched rockets - plausible ?).

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.

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.

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.

2) Allies have other defensive systems - guns as directly targeting
missiles or launching mass volleys of nukes (together with their own
missiles).
ABL takes 3-5 seconds to destroy a target but is experimental and does
not have a great honkin' fusion reactor powering it. Targeting time I
can't find, so maybe giving lasers an unfair disadvantage for those who
love numbers. Still, the essence of the
power of a laser defense system - able to handle thousands of missiles
in minutes - is there.

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. Even with a high Isp 10,000sec rocket, a 2.8:1
mass ratio is only enough fuel for 10,000 seconds of 1gee
maneuvering. That's less than 3 hours. Now, imagine that
the Soviets try to rush in and close the range at 20km/s.
That takes 5.75 hours. So, three hours into their rush,
they're still well over 100,000km away and completely out
of fuel. That means they're unable to continue dodging and
unable to compensate for the allied fleet making a minor
sideways maneuver to prevent them from ever closing the range.

What's more plausible is that the Soviets use other
countermeasures to make long range laser fire too tedious.

At 3000km range, beam radius = 0.3m, equivalent to about 0.3 sq m with
beam power 1100MW/sq m. Assume 1m thickness of armour. Volume to steel
to be cut = 0.3*1 = 0.3 cubic meters = 300,000 cubic cm. Heat of
vapourization = 60KJ/cm^3. Heat needed = 18,000 MJ. Delivering 300MJ
per second. 300 * ? = 18,000 => Burn time = 60 seconds. In reality will
be less with pulsed lasers. On the other hand have only calculated by
heat of vapourization - need to heat up metal AND melt first, requiring
more heat than calculated. Estimate additional heat :

It's more efficient to use pulse lasers to cause a
surface explosion that sends fragments of armor spalling
off the inside into the internal components. This can
be countered by using spaced or composite armor construction
rather than simple solid hull plates. As you can tell,
it takes incredible amounts of energy to actually melt
through a target.

Countermeasures to laser damage can be quite interesting
and complex. One simple countermeasure is to simply
rotate the ship. This can force the enemy to either
eat through a large swath of armor just to get to the
interior, or be patient with waiting around for the
same spot to be available from the same angle each time.
Note that you can get better protection from thick
spaced layers of armor than from a thin dense layer.

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.

But one hole in hull will not be lethal if ship has airtight
compartments. Time to slice ship in 2 ?

With pulse lasers, you wouldn't want to slice the ship
in two. What you'd really like to do is fire a series
of quick pulses at the same spot. The initial pulses
mostly just damage outer layers, but then pulses which
hit the interior will cause mostly internal explosions
which could severly damage the whole ship. This is
what you would LIKE to do. Your lasers may simply not
be powerful enough to do so.

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.

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".

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.

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.

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.

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.

Specific tactics

2) Line of battle tactics. Each ship approaches the missile-firing
range and fires its entire supply (or substantial fraction thereof) at
once, then retires from the laser range. Waits to see the effect of its
missiles on the opponent. Minimizes time Soviets are in
effective range of lasers (or could fire before even in range at all),
but perhaps not so efficient - assuming missiles go for speed rather
than maneuvering, some won't have enough delta-v left after main burn
to attack any other ships. Subsequent ships come in
and proceed with the same tactic. Once all missiles gone may resort to
close-range gunfire against survivors. But, if Allies are not in
similar deep line but are in a closer plane, lasers may easily be
capable of dealing with any number of missiles one enemy ship can
launch, as could have 192 turrets all independelty targetting and
destroying missiles (will have 8 ships per side). With this many
turrets, at 600s available time with 10 seconds targetting time per
turret, lasers can deal with 11,500 missiles - or 23,000 with 5 seconds
targetting time. So line much less effective against plane.

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.

Other questions :
What does the damage from an Excalibur-style bomb-powered laser look
like ? Powerful enough to penetrate 1m armour, or better to target
individual exterior systems i.e. weapons ?

Plausibly, not powerful enough to do either. It's
a terrifically inefficient weapon which was hoped to
"soft kill" ICBM electronics by spraying the entire
area with x-rays.

What do the "lasing rods" actually look like ?

They'd be hair thin but extremely stiff. Plausibly,
this requires placing a hair thin lasing "string" on
a stiff tube of structural support (like a long
graphite straw).

Is it necessary to use multiple rods, or could 1
big rod give more power by intercepting more of the X-rays, or would it
be better to have multiple rods targeted on the same spot ?

One big rod could intercept more X-rays, but unfortunately
the beam will end up unfocused and so the amount of
X-rays actually delivered to the target will be lower.

Multiple rods targeting the same spot will also suffer
from interference, but not to the extent of a single
thick rod.

How are these rods targeted, anyway ?

They are physically pointed at the target.

Checking nyrath's site, "On a target at ten megameters, it would
deposit about 300 kJ/cm2 over a spot 200 meters wide." Is this for each
rod ? 1 sq cm of 1 m thick steel needs 1cm2 * 100cm depth * 60KJ/cm3 =
6,000 KJ. So may burn through about 5% of the depth over the whole ship
- suggests if ship isn't destroyed it certainly isn't going to look
pretty afterwards. Cooling fins would be obliterated, missile turrets
and guns destroyed, silos probably clogged with melted debris. Guess
crew would be OK. But not sure if it means each rod does this or
combination of whole (hoping it means combination of all rods, would
prefer to show multiple beams on target).

That sort of performance sounds incredibly optimistic.

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

Isaac Kuo

.

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