Re: Space warfare- fighter ship design

Logan Kearsley wrote:
>"IsaacKuo" <mechdan@xxxxxxxxx> wrote in message
>news:1126795415.134052.283340@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

>>Nit: low orbit implies HIGH relative velocities. Orbital
>>velocities are higher the lower you go. It's like fighting
>>inside a tornado. Orbital mechanics dictate high velocities,
>>and the tug of gravity whips around velocity vectors into
>>violent crossing paths.

>Low orbit implies high orbital velocities. That doesn't
>necessarily mean that the ships have to have high
>relative velocities,

While certainly not necessarily, the way orbital mechanics
works seems to make it far more likely. It takes special
effort to wrench yourself into a close matching orbit with
a destination. You can't just drift toward the destination
slowly and then gently brake when you get close. The way
orbital mechanics works is that a modest thrust changes
your orbit slightly--and then that's it! You don't get to
drift gently from one orbit to another. You can slowly
change your orbit by applying thrust, but once you stop
thrusting your orbit stops changing. Period.

It's takes so much effort to match orbits in low orbit
that I can't imagine anyone doing it unless they absolutely
had to. There are so many more crossing solutions which
don't demand so much delta-v expense.

Note that to perform a significant change in orbit, it's
often easiest to boost OUT of low-orbit, perform a small
thrust while in high orbit, and then reinsert yourself
back into low orbit. Of course, if all you care about
is an intercept path, there may be no reason for you to
worry about that final re-insertion maneuver.

>And in low orbit, a significant portion of the sky is
>out of view, being blocked by the planet.

A problem easily remedied by having more than one
sensor platform.

>And it seems to me that, if one is using missiles
>instead of lasers, one would want to be in a similar
>orbit to one's opponent so as to minimize the amount
>of delta-v each missile needs.

If you want to minimize the amount of delta-v the
missile needs, then you can lob missiles "down" at
him from high orbit. All the missiles need to do
is negate your own slow orbital velocity, and they
simply fall down to intercept the target.

>>Well, even in an old fashioned "broadside battle" between
>>warships politely sitting at rest with each other, the
>>plausible velocites of the missile projectiles themselves
>>will be high enough to result in hypervelocity impacts.
>>I'm thinking in terms of terminal velocities on the order
>>of 10km/s, rather than 1km/s (in other words, about an
>>order of magnitude faster than typical terrestrial combat
>>projectiles).

>Could you explain why?

Because Earth escape velocity is over 10km/s. If
we're talking seriously about space combat, then
presumably we have the technology to economically
boost a lot of stuff off Earth. I thus presume
the existence and development of SOME technology able
to launch a lot of stuff economically at 10km/s with
high thrust (at least 1gee, obviously).

Obviously, 10km/s is a perfectly acheivable velocity
for chemical rockets, but with hefty mass ratios.
Light gas guns have acheived greater than 10km/s
muzzle velocities, but with puny payloads and
extreme inefficiency. MPD thrusters have also been
used to accelerate puny payloads for hypervelocity
impact research. None of these are yet serious
contenders for economic mass space launch with
current technology, of course.

Maybe advanced chemical rockets will be the key to
economical space launch. Maybe it will be laser
launch. Maybe some sort of nuclear rockets. Whatever
it will be, it might be equally applicable to space
missiles. OTOH, maybe not--for example, nuclear rockets
may be expensive and won't scale down well to
disposable missiles.

>>>A nuclear warhead, I imagine, would best be used to
>>>do a soft-kill, intending to irradiate the fragile
>>>bags of water inside the enemy craft and/or knock
>>>out delicate circuitry.

>>A dubious method of attacking a spacecraft which may
>>already need heavy radiation shielding for the crew
>>from natural radiation.

>One might reasonably expect that shielding designed
>to protect against natural radiation alone would be
>somewhat overwhelmed by a directed nuclear
>blast as relatively short range.

Natural cosmic radiation is pretty nasty stuff,
a lot harder than the soft stuff nuclear bombs
output. It's too hard to shield against for a
short mission to Mars and back, but if we've got
people spending entire careers in space, the dosage
might mandate heavy shielding.

With that sort of thick shielding, even a short range
nuclear blast will be absorbed. However, at short
range that just means the radiation shielding itself
will explosively vaporize, blowing up the ship...

Actually, though, the crew might not need such heavy
radiation shielding. Future medical technology may
cure cancer and maybe even radiation sickness. If
cancer is cured, long term radiation exposure isn't
such a big deal.

>>Nukes are more effective in space than in an atmosphere.
>>An atmosphere is essentially free armor, absorbing a
>>lot of the nuke's energy and transforming almost all of
>>the remaining energy from highly penetrative high energy
>>radiation into relatively non-penetrative wind and
>>low energy blackbody radiation.

>In space, though, you can be protected at a
>suitable distance by radiation shielding that
>wouldn't have a chance of standing up to the
>mechanical stresses imposed by an atmospheric
>shockwave.

At any given distance, the energy per square meter
in the radiation for a space detonation is greater
than the energy per square meter of an atmospheric
shockwave. What's more, it only goes down with the
inverse square of the distance.

In fact, it takes THICK armor to block radiation.
Nuclear bomb tests in the Pacific showed that the
metal hulls of old warships could survive the
shockwaves of nearby nuclear blasts (including the
powerful underwater shockwaves!). The radiation,
however, would have killed anyone inside.

Isaac Kuo

.

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