Military Spacecraft Designations

[tkdguy]

Re: Military Spacecraft Designations

 

Looking back at some old notes, I notice I once considered these classifications:

 

Class 1 Spacecraft: Large vessels, front-line combatants

 

Class 2 Spacecraft: Medium-sized combat support vessels, also used for long-range patrol and exploration

 

Class 3 Spacecraft: Small vessels used as escorts and for short-range patrols

 

Class 4 Spacecraft: Personal (1-2 people) spaceplanes

 

Not very imaginative, I know, which is why I never continued using them. But do you think they would work?

[megaplayboy]

Re: Military Spacecraft Designations

 

At first' date=' sure. But the advent of any ship that could take a hit or mount any sort of serious point defence would end their usefulness - speed is no defence in space. Real warships would eat them like popcorn.[/quote']

 

Well, not speed in a linear sense, I suppose. But if you posited a beefed-up inertial dampener(providing for superior maneuverability), plus a thrust/vector randomizer(ship alters its acceleration/deceleration randomly during flight, as well as juking slightly in random directions, all for the purpose of making computer plotting/tracking nearly useless), on top of the usual ECM/cloaking mumbo-jumbo, you could create a class of ships that, at the very least, are "harder to hit".

[CptPatriot]

Re: Military Spacecraft Designations

 

The smaller sized craft would keep their current names. Fighters, bombers, gunships.

 

The larger sized craft would be the real problem as we don't currently have an analogue for them.

A carrier still seems like the most likely name for a vessel that carries smaller vessels though Traveller did provide us with another name: Tenders

 

I'm just trying to imagine a nuclear powered Air Force controlled fighter tender in the USAF.

[Cancer]

Re: Military Spacecraft Designations

 

If space travel is slow (months to years for long-leg travel), then escort duty is like WW2 naval war (but even more so, since in WW2 supply and escort cruises were weeks in duration, not months), long periods of boredom with rare episodes of terror.

 

Thing is, space trajectories are deterministic in that sort of tech. Newton lets you -- and everyone else -- forecast your flight path almost from the moment you leave orbit. That means small differences in engine capacity (both peak thrust and duration over which the engine can operate) and in payload (since mass directly "offsets" thrust in a sense) can operate over long periods of time. Strategically, you can have lots of "bait and switch" possibilities in terms of supply convoy dispatching and "commerce raider" dispatching.

 

Cargo vessels and their escorts could mount detachable ballast for both tactical and strategic defense. Tactical, because that could be metal armor that can be shed at will, so your ships can shrug off more punishment. Strategic, because by detaching that ballast en route you can gain in maneuverability, opening up alternate options for trajectory, perhaps cutting significant time off the trip duration. The interceptor's strategic consideration has to include trying to guess what the convoy's combat capacity is, how much maneuver power and endurance the targets have in both the tactical and strategic sense. There is always going to be some point in time after which the interceptor can no longer decline action, but for the much of the time the interceptor can study the targets, see if they can detect their masses and engine thrust capacity, and guess at their armament and protection. If it turns out the defenders will be too tough for them, then they can abort the mission and never get close, so they are safe from combat risks; what they lose is on the strategic level, the deployment of those combat resources for an extended length of time with no gain if they decline action.

 

This puts a very strong emphasis on intelligence, since light-travel time is always much less than ship-travel time; if your agents can learn the exact load and capacity of all the ships in a convoy, then you can tailor one or more interceptor forces to be assured of tactical superiority if they do successfully intercept.

 

I am assuming here that a planetary-orbit base is going to be large enough that it will always have enough firepower and short-range (that is, not interplanetary) war spacecraft to stand off anything but a "combined fleet". Given that self-contained environment support for long-haul travel is a significant cost in mass and power, I think that's a fair assumption.

 

I find myself thinking it would be very nice to gang up a "real" Solar System ephemeris with a program capable of doing the multiple restricted 3-body problems so you can compute spacecraft trajectories "correctly". Tthat way you could examine real trajectories that result from various assumptions about spacecraft parameters for your chosen game-time epoch range. While the ephemeris is easy to come by, the trajectory/astrogation code is not. Sigh.

[Zeropoint]

Re: Military Spacecraft Designations

 

Is "maneuvering" really a meaningful part of combat in a realistic near-future setting? Detection ranges will be measured in AUs, and weapon ranges in hundreds of thousands of kilometers. There's no terrain, and because of the relative ease of turning a ship as opposed to moving it, effectively no facing. Any ship can hit any other ship on the map at any time.

[Clonus]

Re: Military Spacecraft Designations

 

Is "maneuvering" really a meaningful part of combat in a realistic near-future setting? Detection ranges will be measured in AUs' date=' and weapon ranges in hundreds of thousands of kilometers. There's no terrain, and because of the relative ease of turning a ship as opposed to moving it, effectively no facing. Any ship can hit any other ship on the map at any time.[/quote']

 

Well if you are going to fire a missile from a hundred thousand kilometers away and the target can see the launch manuevering out of the destination radius of the missile is rather important. It's not a dog fight. You'd be chugging away for hours to get out of the missile's range since it would conserve some reaction mass for when it got within striking range.

[Old Man]

Re: Military Spacecraft Designations

 

Is "maneuvering" really a meaningful part of combat in a realistic near-future setting? Detection ranges will be measured in AUs' date=' and weapon ranges in hundreds of thousands of kilometers. There's no terrain, and because of the relative ease of turning a ship as opposed to moving it, effectively no facing. Any ship can hit any other ship on the map at any time.[/quote']

 

I'm not sure detection ranges will be measured in AU. Look at how hard it is to spot an incoming asteroid that's the size of a house. A military spacecraft built with present-day technology would be stealthy and have other low-observable features. Probably the best way to detect one would be in infrared, since it has to radiate heat, although I can think of ways to reduce the IR signature for a few minutes, or screen it from a particular direction.

 

This is important since lasers have very very long range in space, and are virtually instantaneous. You'll know when your ship is detected, because it will explode.* In that way, I imagine "real life" space combat will resemble sub combat in a lot of ways, only more instantaneous. It's all about the sensors.

 

Functionally I envision spacecraft units to be similar also, with bombardment/ground attack units meant to hit targets planetside, observation/recon units meant to find them, and interceptor/attack/killersats meant to kill them. There would also be transports--low-observable military ones, and sitting duck civilian ones.

 

*Probably not right away... it'll take a few seconds for lasers to burn through, even in space. But they will screw up your sensors and solar panels right off the bat, and then what are you gonna do?

[Zeropoint]

Re: Military Spacecraft Designations

 

Well if you are going to fire a missile from a hundred thousand kilometers away and the target can see the launch manuevering out of the destination radius of the missile is rather important.

 

It's also rather impossible if the missile has better acceleration and delta-v than you do.

 

I'm not sure detection ranges will be measured in AU. Look at how hard it is to spot an incoming asteroid that's the size of a house.

 

A spaceship would most likely be larger than a house, and would certainly be a lot hotter than a chunk of rock that's had millions of years to achieve thermal equilibrium. As far as detecting ships goes, it's my understanding that with current tech, the Space Shuttle's engines could be detected as far out as Pluto. If you can detect a ship's engines, it doesn't matter if you can't see it when it's coasting; you already know where it's going.

 

Also, ask Nyrath about stealth in space.

[megaplayboy]

Re: Military Spacecraft Designations

 

As I said, if a ship can randomly alter its rate of acceleration/deceleration, profile/orientation, make miniscule and random alterations to its trajectory on a constant basis, you can create position uncertainty for enemy plotting and tracking of your ship. At distances of greater than a light second, the sensors will say "it's accelerating..no, wait it's slowing down, heading 090...wait, heading 089, now 091..." you have a general idea of where it will be, but your laser now has a chance to hit the target that's significantly less than 100 percent.

[Clonus]

Re: Military Spacecraft Designations

 

It's also rather impossible if the missile has better acceleration and delta-v than you do.

 

That's only true at shorter ranges. At the kind of long ranges where the missile has to coast most of the distance and the defending ship has many hours to maneuver while it coasts, it wouldn't be that difficult to turn it into a miss. The real problem of course is that in reality the attacking ships would launch several missiles to bracket the defender. And that would be impossible to avoid unless you evade one while shooting down another.

[dmjalund]

Re: Military Spacecraft Designations

 

sunds like one would use short range anti-missile weapons

[The Weapon]

Re: Military Spacecraft Designations

 

As I said' date=' if a ship can randomly alter its rate of acceleration/deceleration, profile/orientation, make miniscule and random alterations to its trajectory on a constant basis, you can create position uncertainty for enemy plotting and tracking of your ship. At distances of greater than a light second, the sensors will say "it's accelerating..no, wait it's slowing down, heading 090...wait, heading 089, now 091..." you have a general idea of where it will be, but your laser now has a chance to hit the target that's significantly less than 100 percent.[/quote']

 

Sure you can jink, a little bit but you can't stealth and you can't really maneuver for strategic/tactical position. Every time you accelerate you give away your position and velocity which means that you give away your future position for a long time. Eventually chaos theory says your position alter from the predicted but by that time you won't know where you you'll be either.

 

Altering position by even 10m in the two seconds it takes for the radar to get back and the beam to arrive requires accelerating by 10 m/s. Doing that every second for an hour requires 36 km/s of delta-v. That's about 140 times more energy than remaining weight (after using the reaction mass) of the ship in TNT. Even at 36 light-seconds (over ten million kms) you still need 1 km/s per hr. Now assuming you're closing at say 30 km/s (which is _really_ fast) this hour would bring you 108,000 km or .36 light-seconds closer. By the time you're 10% closer you'll have had to expend 11 times the energy of remaining ships weight in TNT. Bear in mind if you're closing that fast you'll want a LOT of delta-V left for when you get into "throwing cat litter" range. Cat litter at 30 km/s is deadly and should be dodged at all costs.

 

Maneuvering might have value if it's designed to stop beams hitting the same place on ablative armor. This is known as "scribbling the beam" or at least it might be if people take up this marvelous neologism. Beams vaporize armor so the trick is to make sure they don't hit the same part for long enough to go through. If you're doing that though it's probably best to push/pull parts of your ship forward/backward relative to each other and spin/yaw/pitch a lot. It's not worth wasting reaction mass most of the time.

[The Weapon]

Re: Military Spacecraft Designations

 

That's only true at shorter ranges. At the kind of long ranges where the missile has to coast most of the distance and the defending ship has many hours to maneuver while it coasts' date=' it wouldn't be that difficult to turn it into a miss. The real problem of course is that in reality the attacking ships would launch several missiles to bracket the defender. And that would be impossible to avoid unless you evade one while shooting down another.[/quote']

 

Nope, if the target maneuvers during the "coasting" phase the missile can see it easily and counter any delta-v you add. If it's got more delta-v you still end up with the exact same relative velocity after you both burn. The delay between target maneuvering and missile maneuvering adds means the closest interception point is a(target)/2 * t(delay)^2 further away. To correct for this requires changing velocity by about (change in interception distance)/(time to interception) or (a(target)*t(delay)^2)/(2 * (time to interception). This assumes instant acceleration for this maneuver, but the difference isn't that much. For example a missile closing at 30 km/s 10 lightseconds away with negligible reaction delay to detecting a burn would need only an extra .1 m/s to catch up with a ship that burned at 20 Gs for 10 seconds. As lightspeed delay gets less this gets worse. Basically you need as close as makes no difference to the same delta-V or better acceleration to avoid being in the killzone.

 

Anti-missile maneuvering isn't about stopping the missile hitting, it's about stopping it dodging. The more acceleration and delta-V it uses keeping up with you the less it can use in the last few dozen kms where you fire everything you've got at it. Unless of course you just use nukes as point defense, in which case it can dodge all it wants, at less than 100 km the nuke kills it anyway.

[Sundog]

Re: Military Spacecraft Designations

 

Beam weapons have better range in space since there's less particulate interference, but they're still subject to decoherence over sufficient distance. More importantly, the farther you want a Laser weapon to go before decoherence problems set in, the larger the emitter has to be - which becomes a problem because emitters are delicate, making them a serious problem for Damage Control. I have a strong suspicion that energy weapons will be prmarily used for point-defence work and close-range fighting - missiles will be the weapon of choice for extended range combat, though kinetic-kill weapons (such as coilguns) would also be useful against anything that can't maneuver. And smart, two stage missiles (cruise bus followed by sprint bus) would be very hard to evade.

[Ian Mackinder]

Re: Military Spacecraft Designations

 

The forum for the 'Eclipse Phase' rpg has a couple of threads going on space combat (... and other things) which may be of interest here.

 

Most early posts on the first thread are of no consequence - bleatings about how the game should not have any space combat component - but it picks up later.

 

http://www.eclipsephase.com/eclipse-phase-space-ship-combat-game

 

http://www.eclipsephase.com/get-your-stealth-or-how-can-my-firewall-team-sneak-enemy-habitat

[megaplayboy]

Re: Military Spacecraft Designations

 

Nope, if the target maneuvers during the "coasting" phase the missile can see it easily and counter any delta-v you add. If it's got more delta-v you still end up with the exact same relative velocity after you both burn. The delay between target maneuvering and missile maneuvering adds means the closest interception point is a(target)/2 * t(delay)^2 further away. To correct for this requires changing velocity by about (change in interception distance)/(time to interception) or (a(target)*t(delay)^2)/(2 * (time to interception). This assumes instant acceleration for this maneuver, but the difference isn't that much. For example a missile closing at 30 km/s 10 lightseconds away with negligible reaction delay to detecting a burn would need only an extra .1 m/s to catch up with a ship that burned at 20 Gs for 10 seconds. As lightspeed delay gets less this gets worse. Basically you need as close as makes no difference to the same delta-V or better acceleration to avoid being in the killzone.

 

Anti-missile maneuvering isn't about stopping the missile hitting, it's about stopping it dodging. The more acceleration and delta-V it uses keeping up with you the less it can use in the last few dozen kms where you fire everything you've got at it. Unless of course you just use nukes as point defense, in which case it can dodge all it wants, at less than 100 km the nuke kills it anyway.

 

Hmm... Well, if the missile is, say, 30 light seconds away, then it need only randomly alter its vector once per 15 seconds(assuming the target is firing lightspeed weaponry at it). As it gets closer, then it needs to increase the frequency of its delta-V alterations. In the original case we were talking about the equivalent of a torpedo boat, a vessel with small crew and no armor, mostly just an engine and fuel tank with a couple pylons for ordnance. If it approaches the target in such a way, then releases its payload at a critical range(and said payload has an extremely high delta-V, shortening the window of opportunity to destroy it), then its only need is just to get close enough to have a chance for the ordnance to do its job. If it's attacking a larger target en masse, employing ECM and decoys, so much the better for the chances of success. The "torpedos" might even be more heavly shielded than the ship itself, so that they can take a single hit and keep coming, or so that the defensive laser is required to linger too long on single targets.

[Clonus]

Re: Military Spacecraft Designations

 

The very fact that missiles need a lot of acceleration to do what they do (or get zapped by point defense) suggests that they can't have all that much delta-v by comparison with ships designed to shuttle at low acceleration high delta v for months between planets

[dmjalund]

Re: Military Spacecraft Designations

 

The very fact that missiles need a lot of acceleration to do what they do (or get zapped by point defense) suggests that they can't have all that much delta-v by comparison with ships designed to shuttle at low acceleration high delta v for months between planets

They could keep most of this acceleration until they come close to their target

[Zeropoint]

Re: Military Spacecraft Designations

 

The very fact that missiles need a lot of acceleration to do what they do (or get zapped by point defense) suggests that they can't have all that much delta-v by comparison with ships designed to shuttle at low acceleration high delta v for months between planets

 

Keep in mind that a missile doesn't have to be very big, making it cheap to give it a large mass ratio.

[The Weapon]

Re: Military Spacecraft Designations

 

Hmm... Well, if the missile is, say, 30 light seconds away, then it need only randomly alter its vector once per 15 seconds(assuming the target is firing lightspeed weaponry at it).

 

Ok, I think you meant if it was 15 lightseconds away it would only have to randomly alter it's vector once every 30 seconds. Typos are the bane of fourrums.

So displacement (x) provided by a random delta-v would be:

x = v(delta)*t/2 {t= delay time including each way lightspeed delay}.

Making the v(delta) required for s meters displacement at t=30s:

v(delta) = 2x/30s =x/15s.

Since this has to happen every 30s the random acceleration required is:

a = x/450 m/s^2 = 2*x/t^2

So how much would that add up to in delta-v over the whole approach run? Well the time between random displacements and the delta-v required for them to be effective are both reciprocals of the delay, hence of the distance. The acceleration required is:

a= 2*x/t^2

Now keeping up such a dodge for time needed to get .1 ls closer to the target, even at 30 km/s closing velocity would require a delta-v of:

1000s * a = 2000x/t^2 = 2.22222x/s^1 at 15 ls.

 

So to calculate the delta-v needed to dodge for t seconds from range = d at v closing velocity we integrate the acceleration with respect to time and get:

 

v(delta) = xc/d *(1/(d-vt)-1/d)

c = speed of light obvious.

 

At least I hope that's right. Don't know how to put integration maths on this format.

 

My feeling is that dodging in space is horribly expensive at ranges where anyone would hit. At 1/2 a lightsecond you need over a G of acceleration to even dodge by 5m. At 30 km/s closing it would take 1000 seconds to get from .5 to .4 ls requiring over 10 km/s of dodging delta-v. Even adding in a half second of reaction delay (a long time) would only drop this to 2.5 km/s. The missile still has to dodge closing from .4 to .1 ls so even with a .5 second reaction delay you still need well over 10 km/s in the last to protect a 5m target. Even a half meter target still needs more than 1 km/s to dodge even under these generous assumptions.

 

As it gets closer, then it needs to increase the frequency of its delta-V alterations. In the original case we were talking about the equivalent of a torpedo boat, a vessel with small crew and no armor, mostly just an engine and fuel tank with a couple pylons for ordnance. If it approaches the target in such a way, then releases its payload at a critical range(and said payload has an extremely high delta-V, shortening the window of opportunity to destroy it), then its only need is just to get close enough to have a chance for the ordnance to do its job. If it's attacking a larger target en masse, employing ECM and decoys, so much the better for the chances of success. The "torpedos" might even be more heavly shielded than the ship itself, so that they can take a single hit and keep coming, or so that the defensive laser is required to linger too long on single targets.

 

If the missile is more heavily shielded than the ship itself then the ship won't survive going closer to release the missile. Since the only reason to keep the missile on board is to prevent it being taken out why go close? The missile has no limit on range remember, just on delta-v? Adding delta-v by the ships movement just means that you have to accelerate the whole ship, slow it down and then push it in the other direction to avoid going close enough to be lasered.

[Clonus]

Re: Military Spacecraft Designations

 

If the missile is more heavily shielded than the ship itself then the ship won't survive going closer to release the missile. Since the only reason to keep the missile on board is to prevent it being taken out why go close? The missile has no limit on range remember, just on delta-v? Adding delta-v by the ships movement just means that you have to accelerate the whole ship, slow it down and then push it in the other direction to avoid going close enough to be lasered.

 

There's no real reason apart from tradition to launch them from ships at all.

[megaplayboy]

Re: Military Spacecraft Designations

 

There's no real reason apart from tradition to launch them from ships at all.

 

Well, it might reduce the engine/fuel requirements, plus, well, my physics may be rusty, but wouldn't a ship traveling at, say, 100km/sec and launching a missile in the general direction of its forward motion be imparting some of that forward motion to the missile, even before the missile's engines engage?

I suppose, in the alternative, one could have solar-orbiting launch platforms which fire the missile toward the enemy at the point when the vector of the platform is optimal(i.e., when its orbital velocity at that moment is highest in the direction of the target), and then the missile just engages its engines to break orbit and head straight toward the target, engaging maneuvering thrusters and countermeasures in inverse proportion to the remaining distance to target.

[dmjalund]

Re: Military Spacecraft Designations

 

some concepts of space-mines a re predeployed missiles

[The Weapon]

Re: Military Spacecraft Designations

 

some concepts of space-mines a re predeployed missiles

 

There would be floating energy weapons or kinetic-kills weapons (guns left lying around) and predeployed missiles. Just leaving bombs around hoping that someone will get close enough won't work in something as big as space.

[megaplayboy]

Re: Military Spacecraft Designations

 

I have starship designations up to "Ultra Dreadnought", and then two groupings of largely unused designations--Titan-class ships and Crusher-class ships, there are Super Titans and Ultra Titans, and then there are Planet Crushers, Star Crushers and Galaxy Crushers.