Re: Missiles in Space Combat?

On May 26, 5:58 am, SolomonW <Solom...@xxxxxxxxxxxxxx> wrote:
In article <2d2cdff2-6c12-460a-9e05-
3c99574da...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Alien8...@xxxxxxxxx says...



On May 25, 8:20 am, SolomonW <Solom...@xxxxxxxxxxxxxx> wrote:
In article <Hi7_j.162244$rd2.79851@pd7urf3no>, bryan.derk...@xxxxxxx
says...

SolomonW wrote:
In article <262c2103-86ba-48b8-a6c5-e3388e32c5e2
@x1g2000prh.googlegroups.com>, lwc...@xxxxxxxxx says...
In any event,
no, there isn't a minimum frequency (zero frequency EM "waves" are
common, we call them static electric or magnetic fields). If, as I
suspect, you are talking about a maximum frequency, there is no known
maximum frequency either. It is just that there is no known physical
mechanism to generate photons with such an absurdly high frequency.

Yet for a weapon designers, the shorter the pulse the better. In theory
he cannot do better then that.

Only when you're focusing solely on one single measure of "better". When
building a weapon system you have to consider many factors, and the
mechanisms necessary for cranking the quality of your laser pulse up to
such unreasonable levels will come at the expense of other things.

What factors are you thinking of? The energy level can be the same.

The many "expenses" of operating the weapon system- How expensive is
it to build/test/field in large enough numbers to equip all your
ships; how large/massive is it (which costs you shielding to protect
it and fuel to move it, not to mention having to take its moments of
inertia into account when maneuvering); how robust is it (if it breaks
easily, why bother with it?); how much maintenance it needs (which
costs you man-hours and tools/parts storage); how "obvious" it is (as
in does it exhaust a bright energetic plume of say hot hydrogen
fluoride with every shot); does it have "expendable" parts (to get
very energetic photons you may need a so-called sacrificial lasing
medium like the old nuke-pumped xray laser idea); oh, I could go on
for hours.

Indeed. It certainly will be a major challenge.

You have not demonstrated that your 'single measure of "better"'
will be worth the effort; or for that matter, possible.

We have now the technology to make femtoseconds lasers. Soon we will
have attoseconds lasers.

Useful for physics research, but not obviously so for weapons
applications.

The bottom line is that a dead-simple shotgun firing buckshot can
kill an incoming missile just as dead as an "advanced society's" super-
duper laser, and is a whole lot cheaper (yes, assuming you can get the
buckshot where it needs to be in time to kill the missile).

Lasers would have some advantages.

Buckshots will be heavier.

The better to impart the desired (damaging) momentum to the target.

Buckshot would more effect the motion of the ship firing it.

If a warship can't absorb the delta-vee imparted by a departing
charge of buckshot it has no business in the battlespace.

It would require mass drivers.

Much less complex than any equally-dangerous laser.

It would be more detectable.

How do you figure that?

Less parts.

You have not presented an equally-dangerous laser design for
critique. Claim provisionally rejected.

If you were trying to design an ideal bomb to maximize the amount of
explosive yield for its mass, as another example, you might say that it
should be composed of 50% matter and 50% antimatter. But if the
containment systems have to be made so light and fragile as a result
that it can only be moved at microgee accelerations, well, perhaps the
more _usable_ solution has less antimatter and more robust containment.

Sort of agree. Whatever the containment is, it will not be matter or
antimatter. A clever way of doing it is to make the missile antimatter
and use the matter of the target.

Dandy. Now, what do you make your shipboard missile magazines and
launchers out of?

The antimatter has to be kept separate from the mass on the ship too
whatever the design of the antimatter bomb.

That's basically what I asked you to address. Any ideas?

Indeed. And we are limited to pulses of several femptoseconds or more
because we use lasers that emit in the near infrared, with a
wavelength of around 1 micron. So long as our best chirped pulse
amplification lasers operate in the near infrared, we will never get
pulses shorter than several femptoseconds.

Advanced society, I expect will do better.

Magic isn't a good basis for an objective comparison.

I think we can agree that an advanced society will be able to do better
then we can. The question is how much better.

You are assuming near-magical technology for your missile defense
system, forgetting that in real wars, both sides tend to acquire very
similar levels of technology very quickly. If they don't it isn't a
war; it's a slaughter. You better start thinking about how to defend
against near-magical missiles.

(a)

Indeed.

No matter what technology difference between two groups are they cannot
see a laser coming towards them.

So? Once fired, your position is given away. If your first shot
isn't a killshot you've put yourself at hazard for no obvious gain.

For instance, suppose someone throws missiles at you made of doped
hydrogen-isotope ices at a couple microKelvin, driven by an atom-laser
firing a coherent near-c beam of supercold helium as reaction mass.
The stealth-faceted shell is a Bose-Einstein condensate meaning you
have to heat all of it to affect any of it; burning holes in it like a
metal-skinned missile simply isn't possible. The guts is deuterium-
tritium ices compressed in kiloTesla magnetic fields just short of
fusion density and impact sets the whole mass of the missile into
fusion.

How will you spot them coming? You can't bounce photons off them,
their exhaust plume is invisible, and they're too small to occult
anything worthwhile.

How will you stop them if you can't _see_ them?

see above (a)

I will add here that missiles, unlike laser beams, can maneuver to
make it harder to backtrack their launch point.

But it would be so much easier and amazingly more efficient to use a
much longer pulse (say a picosecond or so) that was made up of visible
or near UV photons, so all the energy would be absorbed by the surface
and could be used to blast through the missile's skin to the
vulnerable components underneath.

If possible you will want to by pass the skin and hit a component
underneath.

Could be prevented by making the skin out of the same material as the
internal components, if nothing else.

You would on the skin use reflective materials and spin it to spread the
heat.

Wait, you're claiming x-ray/gamma ray lasers- at those wavelengths
there _are_ no such things as "reflective" materials except at
glancing angles.

Exactly which is part why you would try to get high frequency laser
pulses?

Yes...

The higher the frequency of the laser, the thicker the shielding
required.

At those frequencies secondary radiation is generated that will kill
electronics; more shielding is _worse_, not better.

Depends how much shielding you have! Antimatter can be used for the
shielding remember with nano constructions, the electronics can be very
small. Another possibility would be a dumb bomb which would not have
electronics.

How does antimatter armor help? As far as I know photons can't tell
the difference between it and ordinary matter.

Earlier you suggest the beam cover the missile cross-section so that
rotation is pointless; that makes the entire illuminated surface emit
secondaries into the internals.

Dumb bombs are just great big buckshot which you weren't very
enthusiastic about above.

Getting a single photon with
megajoules of energy is so far gone beyond anything we can currently
do it is silly to think about it in this context of realistic missile
engagements.

A single I would agree, but a lot is different.

But the big difficulty is not in the number of the photons, it's in
getting any photons _at all_ up to that energy level.

Gamma rays of sufficiently high energy have a tendency to spontaneously
decay into electron/positron pairs, for example. I imagine this makes
them rather hard to work with. I'm not an expert in the field, but I
imagine pushing the energy higher just opens up a bigger zoo of
fundamental particle/antimatter particles for things to fall apart into.

We are talking lasers, so this effect is not important. But are you sure
about this? I would expect the reverse. The higher energy of the Gamma
ray, the more stable it will be.

To start with, what exact lasing mechanism are you thinking of using
to generate your coherent beam of "sufficiently high energy"? All that
I know of tend to be rather destructive of the lasing medium.

http://www.mpq.mpg.de/lpg/research/attoseconds/attosecond.html

Very cool, but the output beam isn't coherent (no cavity mirrors
around the final Helium gas jet); in other words it isn't a laser. The
beam will spread to uselessness at weapon-useful ranges we're
discussing.

Even that assumes the device can be scaled up to dangerous (to a
target) power levels, which I'm not very confident of. One thing you
must keep in mind with high-output lasers (or any energy-projecting
weapon, for that matter) is that their internal structure must handle
their own output power, plus whatever waste heat they generate due to
not being 100% efficient. I notice many gratings and mirrors in the
beam path and gratings in particular are not known for being good at
handling large amounts of power without absorbing respectable (in this
case hazardous) fractions of it.

Also, the output is stated to be XUV which is "extreme ultraviolet",
not x-ray or gammas; there's a huge difference.

As I said, the only ways I've ever heard of to generate weapon-
worthy coherent x-ray/gamma beams is nuke-pumped sacrificial devices.

And yes, gammas decay into particle/antiparticle pairs but require a
"nearby" nucleus to do that (any photon can decay into a particle/
antiparticle pair of the same total energy, but the minimum is the
rest-energy of the electron/positron pair meaning you need a 1.02 MeV
gamma ray to get them). OTOH there's always a few stray atoms floating
around in space, meaning the path of your laser beams will be filled
with scattered, Doppler-shifted, recombination radiation pointing
straight back at you, making you that much bigger a target.

If your general position is not known, why fire a missile?

To strike the enemy, of course. One does not win by hiding.


Mark L. Fergerson
.

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