Re: Space warfare- fighter ship design
- From: "IsaacKuo" <mechdan@xxxxxxxxx>
- Date: 6 Sep 2005 22:53:11 -0700
Logan Kearsley wrote:
>"IsaacKuo" <mechdan@xxxxxxxxx> wrote in message
>news:1126017573.398491.152820@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>Logan Kearsley wrote:
>>>I think I have come up with a fairly good design for
>>>defensive ship/drone for space warfare.
>>>Tell me what you think:
>>I think you've started with the wrong priorities.
>>If the design of military equipment so far is any
>>indication, a space warship will be first and
>>foremost a spaceship, and a weapons platform
>>a distant second.
>>The dominant design requirements will be those
>>which any spaceship will require--the drive systems,
>>power systems, thermal regulation systems, radiation
>>management, and life support (if manned). In
>Right, I agree with most of that. I wasn't thinking of this as being a
>primary space battleship, though, just a fighter.
Even "fighters" need a propulsion system, and all of
the other stuff. The challenges are even greater,
because it is either small and/or cheap and/or compact,
or they aren't "fighters", in any traditional sense.
>Either something that, if
>manned, would be launched from a larger space warship, or, if unmanned,
>would be launched from a manned fighter that just acts as a bus to get them
>to the battle and a control center, which would in turn be launched from the
>main warship.
I fail to see how this somehow removes any need for an
effective propulsion system.
One possibility which I have toyed around with is that
of externally powered space "fighters". It's a technologically
sexy idea--you put the big power reactors on your "carrier",
and it beams power to the little "fighters". Unfortunately,
when I ran the numbers it looked like the sheer amount of
power required made it very unfavorable looking compared
to local power generation (in the form of nuclear pulse units;
VERY powerful!).
>>particular, the drive system will impose the
>>fundamental design of the spaceship.
>On the internals, I'll agree with that. As far as the exterior, though, most
>of the time you could just expand the sphere until it's big enough to hold
>whatever shape and size of engine you want.
As I noted below, with the example of a nuclear rocket,
it's not necessarily just a matter of physically fitting
the drive inside your ship's hull. Other advanced
propulsion concepts also have such design constraints.
Ablative Orion style propulsion, one of my favorites,
is by definition external, and dominates outer hull of
the spacecraft. Even traditional orion style propulsion
dominates at least one side of the craft. Magsail
propulsion involves a huge exposed wire loop. M2P2
propulsion engulfs the spacecraft within plasma
which obviously has profound design implications
for all of the sensors and weapon systems.
>>>The weaponry would consist of a phased array of
>>>laser diodes covering nearly the entire surface of
>>>the sphere.
>>It may be impossible to acheive coherence in the first
>>place, but even assuming the technology is acheived,
>>it may be impossible in practice to maintain coherence
>>while under enemy laser fire.
>Can you explain why?
Because pulses of enemy laser fire will induce vibrations
and thermal stresses which plausibly make it impossible
to maintain a coherent beam.
>Saying that this is the case, that just says to me that certain fighters
>will be restricted in the direction of their fire until other ships can take
>out / distract the offending enemy laser.
The problem is that it's plausible for the lasers to
simultaneously be take each other out.
Both side's lasers could be defocused too much to
effectively deal out directly damaging firepower, but
to nevertheless still have sufficient firepower to
defocus the other side's lasers. In the meantime,
other weapon systems may be dealing out the decisive
blows.
>>Fish-eye lens cameras would be of dubious value, since
>>they'd have low resolution and sensitivity. Large
>>aperture telescopic optics would give you high resolution
>>and high sensitivity. Sure, it takes time to scan all
>>around, but distances in space are very very big, and
>>as such it takes a long time for stuff to move across
>>one's field of view.
>Since I was assuming these to be sub-units, not self-sufficient battleships,
>I figured that in best conditions, they'd just have to be able to find a
>laser-painted target.
Over the distances of plausible space combat, you'd still
want telescopic optics. Consider that even with the puny
distances involved in today's terrestrial combat, laser
guided bombs/missiles use telescopic optics. (I'm not
talking about beam riders, of course.)
>>In real life, attitude adjustment flywheels tend to be
>>small and compact, so as to minimize the space and weight
>>used. However, we're talking about satellites which
>>carry little/no on board propellant.
>Well, I wanted quick reaction times to point the engine
>wherever needed.
Given the distances involved in plausible space combat,
I question the need. Stuff just doesn't move very fast
across the field of view.
>>For an interplanetary spaceship, there are going to be
>>large propellant tanks--some sort of internal circulation
>>propellers could provide attitude adjustment as long as
>>high precision isn't required.
>True, but high precision is required, and this wouldn't be interplanetary.
No, high precision is NOT required for just pointing the
main engine vaguely in the desired direction. The design
you are proposing uses attitude adjustments purely for
pointing the engine (which doesn't need high precision).
The weapon system points itself, essentially.
This isn't like the Hubble telescope, where the entire
hull needs to be pointed with astronomical precision.
>It would be carried interplanetary distances by something else- just a
>fighter, not a battleship.
It still needs a lot of propellant, otherwise what's the
point? One idea for justifying the use of "space fighters"
is that the carrier has a low thrust high Isp drive, while
the fighters have a high thrust low Isp drive (like
chemical rockets). This implies that the fighters still
need to be dominated by their propellant tanks--possibly
even more so than the carrier.
If the space fighters lack mobility, then they're really
just anchoring the carrier in place for no particularly
good reason. The carrier would pop them out, and then
is forced to stay and wait for them to land before making
any serious course change. It would make more sense for
there not to be any fighters in the first place, and to
physically mount the weapon systems to the carrier's
hull.
>>Every time we run heat rejection numbers here on
>>r.a.sf.science, high power equipment simply can't
>>be run for a significant time on an internal heat
>>sink.
>Significant time meaning, minutes, seconds?
>Just a few minutes at a time ought to be enough, I'd think.
For a serious laser weapon, much less than a minute.
Depending on how powerful the laser is, maybe just a
few seconds or less. If you're going to be playing
around with these ideas, they really don't scale down
very well. You'd be much better off doing it with
your big "carrier" than with some "space fighters".
>>>The engine, however, could itself be used as an active
>>>cooling system, by running the propellant pipes
>>>around/through the heat sink or whatever components
>>>need cooling before injecting the propellant into the
>>>engine.
>>This suffers from the same problem as internal heat
>>rejection--the only difference being that you are
>>throwing the heat sink overboard while you're at it.
>>Also, you're probably reducing the Isp of the propellant
>>down to chemical rocket levels...but the point is moot.
>>The vibrations from operating the rocket in the first
>>place plausibly spoil your beam coherence and your aim
>>anyway.
>So don't operate the engine while firing. Fire the weapon, use propellant as
>coolant, then when you're done firing run the pre-heated propellant through
>the engine.
This would mean having a "temporary heat storage", for which
your propellant is almost certainly not a good thing to use.
Your propellant is presumably hydrogen, good for its physical
property of expanding a lot when heated. That's great for
where you want that expansion (in a rocket nozzle). That's
not great for where you don't want it (in a temporary heat
storage "tank"). For you "temporary heat storage", it makes
more sense to use a chunk of metal, through which are
cooling tubes (for propellant to flow through).
>But, why would that reduce the Isp to pre-heat the propellant?
Because of enthalpy limitations.
>>This is actually issue number one! First, figure out
>>the propulsion system--all else is secondary. Think
>>about real life warships. Sailing warships looked
>>like sailing ships. Paddlewheel warships looked like
>>paddlewheel ships. Piston warships looked like
>>piston steamships. Turbine warships look like turbine
>>ships. The propulsion system can't just be some
>>afterthought in the design.
>All of those had terrestrial design constraints, though. They had to be
>designed to support their own weight, aero/hydrodynamics, etc. In space, why
>not just use a spherical shell large enough to enclose everything you might
>need?
Because the equipment you need may not work best within
the confines of a spherical shell. There are many
potential considerations.
>>>I was thinking perhaps either a gas-core nuclear
>>>rocket or a VASIMIR engine,
>>For there to be any point to either, you need a
>>high power heat rejection system. You can't just
>>try to use the waste heat to preheat your propellant.
>>This was a mistake I myself made, and it was pointed
>>out to me that enthalpy limitations would reduce
>>the Isp of such an engine down to the levels of a
>>plain old solid core engine (i.e. low enough to be
>>self cooling).
>Oo. That could be a problem, then. Of course, it's a problem for any
>warship- how do you keep your heat rejection system out of enemy laser
>beams?
More or less, you don't. I tend to favor self cooling
propulsion and weapons systems for space warcraft
concepts.
>>Note that for a modest increase in volume/mass/complexity,
>>a solid core nuclear thermal rocket can be designed to
>>be a dual mode reactor (either a thermal rocket for thrust,
>>or a power reactor recycling "propellant" through a
>>condenser/radiator).
>Why do say only solid core? I'd think any heat-producing apparatus could be
>run as a powerplant as well, including a gas-core NTR.
For more advanced types of reactors, the considerations for
making them dual mode may or may not be a "modest" increase
in volume/mass/complexity.
For example, some gas core fission rocket design concepts
assume the ship's acceleration as part of the design--it
provides a sort of "artificial gravity" which buoyantly
separates the heavier uranium core from the lighter hydrogen
coolant. To make a dual-mode version, there would have to
be another sort of artificial gravity, perhaps involving
spinning the reactor or spinning the entire ship.
>>>On a completely different note, though, as long as
>>>I'm talking about high-tech weaponry, how does this
>>>sound for producing a coherent neutron beam: get a
>>>slug of fissionable/fertile material and cool it to BEC
>>>temperatures. Trigger a nuclear reaction in the usual
>>>way, by injecting a small number of excess neutrons
>>>in one end, and the whole slug should decay at the same
>>>time, in the same direction, throwing out a huge flux of
>>>coherent neutrons, right?
>>I am unaware of any sort of "lasing" effect with the
>>neutrons of a fission reaction.
>I was thinking of a standard lasing effect. I was thinking more along the
>lines that a BEC behaves like a single super-atom, so if you trigger it to
>decay, shouldn't all of the component atoms decay at the same time and in
>the same direction?
I have no idea. Hopefully, someone else here does...
Isaac Kuo
.
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