Whay would real-life war spacecraft look like?

[EzinX]

Q-thrusters might have major drawbacks. Essentially they are trying to manipulate virtual matter that is barely even there. The energy to do this may always be extremely high, and the apparatus very large and massive.

If you look at this paper and assume a power density of 1 kilogram per kilowatt for your power plant (possible with theoretical bleeding edge nuclear designs) and that future advances let Q-thrusters weigh 1 kg per kilowatt of power used, and the same power efficiency (0.1 newton per kilowatt), then you arrive at the following numbers (again, I'm assuming that future engineers can do 10 times better in both power generation and Q-thrusters than we can do today):

Assume the ship is 1/3 power reactor (including the radiator mass), 1/3 engines, and 1/3 everything else. Then, for 3 kilograms worth of ship, you have 0.1 newtons of thrust from the main engine that is 1/3 of the ship. F=ma, 0.1 = 3*a, a = 0.033333 m/s. That's 0.33% of 1 G acceleration. A quick bit of figuring shows it would take 30 days to reach Mars with this, which is no better than you can do with a top end VASIMR.

Sure, that tiny force will add up over time enormously. What I've described here would make interstellar travel practical, and would also make relativistic missiles that wreck planets possible.

But you will have trouble dodging incoming fire, it's actually going to take a while to transit to Mars, and your spaceship would probably want to have an orion drive or something for dodging incoming fire. The Q-thrusters would be helpful in that once you are out of propellant you could recover the ship if you're willing to wait long enough, assuming you still have power and at least 1 working Q-thruster.

Regarding radiators : no need to dump coolant. That's one of the things that there actually is a clever solution for. Use this drop radiator calculator. Assume you are using liquid tin as the coolant at 1000 kelvin. Let's say we're making 5 gigawatts thermal, and the space along the hull of the ship where the drops fly free is 100 meters long. Then we need just 4 booms each 18 meters long, half sending and half receiving. Calculating the mass of the pumps, compressors, total volume of liquid, and plumbing is beyond the scope of this message board, but even using 1987 assumptions it's less than 1 kg per kilowatt of heat rejected.

Dumping coolant is super bad and I think most warships would be designed to never do this even when at maximum power output and taking extraneous heat from enemy laser fire.

Edited December 3, 2014 by EzinX

[nyrath]

Sorry I'm coming into the discussion late.

The various weapons seem have been discussed, with the glaring exception of the casaba howitzer. This is a weaponized version of the nuclear pulse units used by the Orion nuclear pulse engine. It is a nuclear shaped charge directing about 85% of the blast energy in a narrow burst at the target.

I have a few notes here:

Introduction to Space Warfare

Detection in Space Warfare (but first read Nicoll's Law)

Introduction to Space Weapons

Conventional Space Weapons

Exotic Space Weapons

Defenses in Space Warfare

Space Warship Design

Space Warfare Strategy and Tactics

Planetary Attack

[Mazon Del]

EzinX: The main reason why the Q-Thruster (still, assuming it works, really really want it to work...) ends up being better then VASIMR despite their similar thrust/weight ratios and such, is simply that the ship using a Q-Thruster no longer has fuel concerns. Which means that the act of forcing them to dodge means nothing except that it will take them slightly longer to reach their target. I'm assuming the ship in question of course has something like a nuclear reactor. Effectively fuel-less for 10+ years of operation. As a result, most of the text in my giant wall of it previously is meaningless. The tactics laid out there depend on the idea of forcing your enemy to waste enough fuel such that they are either unable or unwilling to complete their mission (completing it could mean the crew ends up in a solar orbit far away from help with not enough fuel to reach anywhere that they could even surrender at). The second aspect of the tactics still ends up being decently valid, as it is easier to heat up the ship with what amounts to a flashlight beam from a maser than it is to hit it with a railgun round, eventually the crew will succumb if not the hardware.

As far as what I was saying about coolant. I wasn't actually stating to dump coolant itself, I was stating to dump FUEL, utilizing it as a coolant. If your fuel source is anything cryogenic or volatile at elevated (but not extreme) temperatures, then as the ship heats up you are going to be boiling some off and will have to vent the excess to prevent the pressure in the fuel tank from reaching dangerous levels. Since you have to do this anyway, I was saying you might as well use it in some way that lets the escaping fuel take more heat with it.

The liquid droplet cooling system I have always somewhat enjoyed as a concept, but it has some issues, especially for a warship. Passed a certain phase in the combat, the warship is likely going to be relatively constantly changing vector and orientation. Unless you contain the droplets in some sort of physical tube (which I imagine would drastically reduce the effectiveness of the system, even if IR transparent) any time you turn or shift 'position' you'd be losing the droplets. Of course the way to ensure you don't lose any is by turning the flow off, sucking up the rest, then continuing. Depending on how long this process takes, it could result in a net gain of thermal energy rather than a net loss. Remember, the other guy is presumably looking for any situation where you are 'standing still' to focus all of his lasers on you for maximum heating. Additionally, I would assume that you could only really utilize the droplet booms on the opposite side of your ship from the enemy. Either their beams will heat up the droplets instead of letting them cool (in which case collecting them gives you heat) or they simply reduce the effectiveness of the droplets (in which case, nevermind, go ahead and do them).

Earlier in your post you mention that the acceleration provided by the Q-Thruster in your math is about 0.33% of 1 G of accel. That is perfectly fine for dodging the slow stuff (railguns, missiles, etc) over combat distances of thousands of kilometers or larger (the larger the better of course). Terminal changes though (quick turns/translations to dodge incoming missiles and close railguns and eventual laser fire) it might behoove your ship to have something that can do quick bursts even at the expense of having an expendable fuel. But the Q-Thruster still provides you with the game changing fuel-less main engine. Remember, the idea of making the enemy waste his fuel is only really helpful if it means he won't end up getting anywhere he wants to go without it. If all you do is reduce his maneuverability, this was still helpful but his mission is still possible.

[EzinX]

Sorry I'm coming into the discussion late.

The various weapons seem have been discussed, with the glaring exception of the casaba howitzer. This is a weaponized version of the nuclear pulse units used by the Orion nuclear pulse engine. It is a nuclear shaped charge directing about 85% of the blast energy in a narrow burst at the target.

Your site lacks a key calculation : changing the Z-value of the nuclear shape charge payload, what does it do to the angle of the resulting stream of particles?

Also, wouldn't a nuclear accelerated particle stream dissipate just like any other stream of particles over distance? I'm not convinced this weapon would have more than a few kilometers of range no matter how powerful the nuclear warhead driving it was.

[Mazon Del]

Your site lacks a key calculation : changing the Z-value of the nuclear shape charge payload, what does it do to the angle of the resulting stream of particles?

Also, wouldn't a nuclear accelerated particle stream dissipate just like any other stream of particles over distance? I'm not convinced this weapon would have more than a few kilometers of range no matter how powerful the nuclear warhead driving it was.

What it likely does for you is lets your missiles be less accurate, but still have a chance at hitting the target. They just get in range, point in the right direction, hope for the best. A bit like the Honor Harrington laser warheads.

[nyrath]

Your site lacks a key calculation : changing the Z-value of the nuclear shape charge payload, what does it do to the angle of the resulting stream of particles?

Also, wouldn't a nuclear accelerated particle stream dissipate just like any other stream of particles over distance? I'm not convinced this weapon would have more than a few kilometers of range no matter how powerful the nuclear warhead driving it was.

If you ever find the equation for the relationship between Z and the blast angle, let me know. I'd like to know myself.

Apparently it is still classified.

Yes, of course the blast will dissipate, as long as the blast angle is greater than zero. The blast will dissipate with distance proportional to the tangent of the blast angle.

The casaba howitzer was a candidate for President Reagan's Strategic Defense Initiative. So it had a theoretical range suitable to pick off Soviet ICBMs coming over the horizon.

The estimate I saw was 6.276 × 10^12 joules per bolt, which is quite a bit better than any laser weapon currently on the drawing board.

[EzinX]

If you ever find the equation for the relationship between Z and the blast angle, let me know. I'd like to know myself.

Apparently it is still classified.

Yes, of course the blast will dissipate, as long as the blast angle is greater than zero. The blast will dissipate with distance proportional to the tangent of the blast angle.

The casaba howitzer was a candidate for President Reagan's Strategic Defense Initiative. So it had a theoretical range suitable to pick off Soviet ICBMs coming over the horizon.

The estimate I saw was 6.276 × 10^12 joules per bolt, which is quite a bit better than any laser weapon currently on the drawing board.

On your website, you have an example where you analyze "plasma weapons". A super heated stream of material heated by a nuke probably acts like plasma, with the lighter electrons driven off. That means that electrostatic repulsion between the protons would shove the stream apart very rapidly, soon dissipating it to harmless levels. The total energy doesn't matter if by the time it reaches the enemy ship it's so dispersed that 99% or more of the energy doesn't even impact with the target.

Anyways, if we had that relationship between angle and Z, it would be straightforward to calculate the energy per area for a target at a given distance, and then determine how destructive it would be. Shame it is classified.

[Bill Phil]

Hey! The Atomic Rockets guy is here!

Now we're cooking!

BTW nyrath, I really think your website idea is a good one. I learned quite a few things there. Thanks.

Although, spacecraft maneuvering like aircraft isn't very far-fetched. If your point of reference is a space station, you can use thrusters like wings and fly like a plane. It's not very effective, but it can be done.

[problemecium]

I'm sad this thread doesn't have more pictures :C

[KerikBalm]

Yes, of course the blast will dissipate, as long as the blast angle is greater than zero. The blast will dissipate with distance proportional to the tangent of the blast angle.

Wouldn't it be proportional to (distance*sin (theta))^2 ?

the radius of the "beam" would increase by distance * sin (theta)

And of course, if you double the radius of the beam, its area increases 4 fold (2^2) because the area of a circle is proportional to R^2.

So the energy density of the beam should be something like 1/ (distance * sin(theta))^2

No?

[nyrath]

Wouldn't it be proportional to (distance*sin (theta))^2 ?

Yes, you are correct. I was speaking off-handedly.

[nyrath]

Although, spacecraft maneuvering like aircraft isn't very far-fetched. If your point of reference is a space station, you can use thrusters like wings and fly like a plane. It's not very effective, but it can be done.

Well, yes. And aircraft can be maneuvered as if they were old-school seagoing battleships, trying to cross the "T" and firing broadsides. Airplanes do not maneuver that way because it is not very effective, and contrary to their nature.

[Frozen_Heart]

Every time someone suggests spacecraft fighting like aircraft or battleships I just facepalm.

[nyrath]

Having a fleet has no purpose, except making your belongings easy target for a big nuke. The only meaningful case is to defend an asteroid mining facility or the earth itself ^^,

but even then you don't need to stack them side by side like boats.

Keep in mind laser weapons even missiles can hit from huge range in space very accurately

Depends upon what you mean by "fleet". Conventional nuclear weapons radiate damaging energy isotropically which is good for taking out lots of ships in a compact formation. Unfortunately this means the damage is subject to the inverse-square law. Nuclear weapons detonated on Earth, that is in a place with an atmosphere, do most of their damage with "blast" (i.e., the x-rays are absorbed by the air, this superheats the air, resulting in blast). There ain't no air in space so the damage has to be done with x-rays.

Bottom line is if your spacecraft is more than about a kilometer from a standard sized nuclear weapon, the only damage it will suffer is some scorched paint. So you can have lots of ships in a compact formation if by "compact" you mean "spaced with two kilometers of separation"

http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Nukes_In_Space--Warhead

Yes, lasers can hit targets from huge ranges.

Problem 1: while lasers are not subject to the inverse square law, they are subject to diffraction. This has much the same effect, weakening the power density of the beam with range.

http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Laser_Cannon--Equations

Problem 2: if the targets are maneuvering (i.e., dodging), and the range becomes more than a few light-seconds, you will not be able to hit the target except by accident. You will only see where the target was, not where it is right now. And not where the target will be when the laser bolt finally gets there.

http://www.projectrho.com/public_html/rocket/spacewardefense.php#id--Evasive_Maneuvers

[nyrath]

Doesn't matter how weak the laser is. In space it doesn't lose power with distance. It could hit a missile launched from the moon in about a second if it was orbiting the earth. Maybe a missile could be designed with a system of heat sinks and radiators though.

Unfortunately that turns out not to be the case.

As mentioned before, while lasers are not subject to the inverse square law, they are subject to diffraction. Which has much the same effect.

http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Laser_Cannon--Equations

[nyrath]

Chances are a missile won't have as much deltav as a full-fledged spacecraft, so the target can easily change it's velocity and get a completely different orbit. The missile most likely doesn't have the deltav to intercept.

Although, if the missile is S-IVB sized....

Yes, this is called a "torch missile."

The point being that it is much easier to have a deltaV of X if the item does not need mass for crew, life support system, consumables, habitat modules, and so on. A missile with more deltaV than a full-fledged spacecraft would be cheaper than the full-fledged spacecraft.

Of course a torch missile is more expensive than a conventional missile. But a torch missile can chase the target all over the solar system, and cannot be evaded because it has more deltaV. Even if it takes a few months.

Torch missiles cannot be evaded, you have to destroy them with point defense or something.

[nyrath]

Personally I believe the first "space warships" would simply be some common craft for the time repurposed for a military action. the reason being is space is expensive and you can waste a lot of money and resources speculating on how it would all go down.

Agreed. Much like the Eagle transporters from the TV show Space 1999. They were cargo vessels that got laser weapons stuck on with duct-tape. The analogy is how the original wood and fabric biplanes were gradually adapted to be used as war machines in WW1

http://www.projectrho.com/public_html/rocket/spacewarship.php#id--Ship_Design_Analysis--Arthur_Majoor's_Analysis

[nyrath]

Every time someone suggests spacecraft fighting like aircraft or battleships I just facepalm.

Yeah, me too. Personally I blame Star Wars and the Wrath of Khan movie.

http://www.projectrho.com/public_html/rocket/spacegunexotic.php#id--Space_Fighters--Role

[KerikBalm]

Yes, so thats why we want large focusing arrays, high frequencies (upto X rays) and ships in formation to form phased arrays - I'm unsure of how close the formation needs to be to derive significant benefits from acting as a phased array.

Could a grid of ships 10km apart, firing at a target 15,000,000 km away, function as a phased array? What difference would it make if they were 1km away.

I suspect it has something to do with the difference in the firing angles- as the beams must overlap as they spread - but if the individual beams are converging on the same point, they won't have to be very wide to start overlapping and having constructive interference.

I do know that the smaller the distance, the better (the interference starts earlier), but I don't know exactly how close they really have to be.

Obviously if the angle between Ship1-Target-Ship2 is 90 degrees (ship1 and ship 2 are firing at the same target), there won't be any beneficial effect.

The closest thing I can think of to a "fighter" is a scout with large sensor arrays for its side, that will preceed a larger ship.... and if you do have massive death cannons firing out to several AU, I suppose it could supply targetting data for such a vessel.

The smaller the vessel, the closer it can get before detection, generally speaking, so maybe scouts and anti-scouts.... but they'd all be basically snipers, not dogfighters.

Edited December 4, 2014 by KerikBalm

[nyrath]

The thing that commonly gets ignored in futuristic depictions of space combat is the awkward necessity for huge heat radiators.

Weapons like lasers, particle-beam weapons, coilguns, railguns, and the like requires huge amounts of power. Nuclear reactors that can supply such power will also generate huge amounts of waste heat.

The weapons will generate waste heat as well.

Laser cannon are notoriously inefficient. Free-electron lasers have a theoretical maximum efficiency of 65%, while others are lucky to get a third of that. This means if your beam power is 5,000 megawatts (five gigawatts), and your cannon has an efficiency of 20%, the cannon is producing 25,000 megawatts, of which 5,000 is laser beam and 20,000 is waste heat! Ken Burnside describes weapon lasers as blast furnaces that produce coherent light as a byproduct. Rick Robinson describes them as an observatory telescope with a jet engine at the eyepiece.

The only three ways of getting rid of heat are convection, conduction, and radiation. And the first two will not work in space since space is a vacuum.

This means you are stuck with using huge heat radiators.

The problem with heat radiators are that not only are they huge targets, they are very difficult to armor.

http://www.projectrho.com/public_html/rocket/spacewardefense.php#radiators

The thinking is that when going into combat, the spacecraft will retract their radiators and rely upon internal heat sinks to temporarily store the waste heat. Trouble is that they probably will not be able to store more than a few minutes worth of heat.

If a ship's heat sink fills up, the ship has a choice of:

[1] The ship melts, killing everybody aboard and destroying the ship

[2] The crew surrenders, "striking the colors" by extending their radiators and ceasing fire.

[nyrath]

Could a grid of ships 10km apart, firing at a target 15,000,000 km away, function as a phased array?

That is a very good question. Alas it is above my pay grade. I'm unsure about phased arrays at optical frequencies.

[Mazon Del]

For phased arrays the distance between the ships is not so important as much as ensuring that the distance between the emitters is exactly the distance necessary for the waves to build on each other and constructively form your more powerful wave. The other issue you have is needing to have VERY precise timing for this. Imagine needing two events on opposite sides of the Earth to happen within nanoseconds of each other (only slightly exaggerated). Certainly possible to do, but hard. And that is with STATIONARY objects.

But yes, a grid of ships 10km apart could function as a phased array if you got the timing right and the distance was right (if the distance isn't perfect, you can compensate by adding a time offset, which means that your timing is even more critical than it already was).

Mostly the difference you get from the 1km away vs the 10km is that the beam will be tighter (and thus more powerful) as opposed to fatter (and less powerful). BUT, you "should" be able to compensate for this with localized timing and direction. But there are reasons why the vast majority of phased array systems on Earth tend to be fixed panels with known spacing. Primarily because that way you don't have to do all these weird calculations to compensate for wonky offsets and such.

Ideally the separate elements in a phased array should be as close as the physical dimensions of hardware allow. That said though, there isn't anything stopping them from being an arbitrary distance apart provided that the power of the transmitters is sufficient for the signals to actually overlap usefully where/when you want it. (IE: If your transmitters are so far away that the constructive signal is only barely noticeable above the background radiation, was the project really worth it?)

[KerikBalm]

Yea, well, as I think about it, it depends when the beams start to overlap. If you don't have overlap until half the distance to target(of course it is not all or nothing), then you've lost half the effect, no?

And of course, reducing the distance to something arbitrarily small gets you just a single emitter, as the ideal. Of course it may be more practical to have smaller emitters. You could have a fleet of "cruisers" instead of one large "dreadnaught", but the cruisers could form a phased array and act as if they had 1 large super gun.

Yes, this does require incredible precision, even more so as the wavelength decreases I would think.

A partial solution to the spacing effect, I think may be analagous to old musket lines, where you could have 3 lines firing (prone [rarely though], kneeling, and standing).

Instead of being a grid forming a "wall", you could have multiple "grids" in front/behind of others.

ie

>

...>

>

...>

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instead of

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As far as the phasing, it should be nearly identical, but the ship separation is increased (not that I would expect an AoA weapon to be effective against such a formation that is engaging targets at 1 AU)

As far as radiatiors....

If you outrange the enemy, radiate away, you only want to retract those if the enemy is in range.

Bigger fleet = bigger phased array = bigger range = larger standoff range = no incoming fire.

You don't armor artillery guns, you just have a pair of wheels and a truck pull them (sure, there is some armored self propelled artillery).

Of course, this is sort of interplanetary/heliocentric warfare... fighting in the orbit of earth would be quite different.

And since Nyrath is here... regarding stealth in space... yes I know, there is no true stealth in space... directional radiation is addressed, and you have to know where your enemy is not in order to use it.. and how can you know that if stealth works.....

I submit for consideration that radiating perpendicular to the ecleptic is a pretty good place to radiate, as it takes a lot of dV to get an observer in position, its probably the least likely place to be detected.

I also submit for consideration that the first one to get "360 degree" converage up can acheive stealth by denying the opponent such coverage

But I also conceed that any significant maneuvering is going to leave a plume of hot exhaust that gives you away. Maybe you can hide from a purely earth based force by thrusting when there is an occuluding body (like the other side of the sun), or when the sun is your backdrop - but these would have to be strategic moves, not tactical moves during a battle.

[problemecium]

I've been musing on the heat issue and wondered about whether that "waste" heat can be piped somewhere and used for something. Obviously we can't make a perpetual motion machine, but there's no reason I can't heat my shower water with waste heat from a nuclear reactor (ignoring radiation). Perhaps the engines could exchange heat with the weapons systems to increase the temperature (and thus specific impulse) of the exhaust, or some of the heat could be used to make an infrared laser.

Or as another solution, how about having the radiators radiate into a reserve of compressed fluid and vent it as plasma when it gets saturated? That could even be used as a short-range weapon (against whatever might be trying to fist-fight the ship, which isn't likely to be much, admittedly).

[EzinX]

The thing that commonly gets ignored in futuristic depictions of space combat is the awkward necessity for huge heat radiators.

Your own website describes droplet radiators and links to a droplet radiator calculator. Liquid Tin droplets at 1000 Kelvin allow for a pretty compact radiator. You'd have to turn off the droplet radiator and collect the droplets before making maneuvers not along the plane created by the 2 radiator booms (and have enough thermal mass on the ship to not burn up right away without coolant for a brief period). That might make for an interesting tactical option - obviously, in an emergency you could make your turns and lateral maneuvers without turning off the droplet flow and just eat the coolant loss.