Hi, interesting discussion, I played a bit around with the OP's numbers. I admit your calculations makes projectile weapons look very attractive, but theres some other things to consider, if you want physical realism and speeds of 1/10 c = 3*10^7 m/s:

You figure constant velocity, so I assume the missiles are fired by some gun onboard our ship. If our ship is 100m across (as our adversary), and the gun-barrel runs the whole length of the ship. Firing the missile will involve accelerating it by:

a = v^2 / (2 * r) = (3*10^7 m/s)^2 / (2 * 100 m) = 4.5*10^12 m/(s*s) ~ 4.5*10^11 g.

If the missile masses a millionth that of our ship (say 100 kg vs 100000t), conservation of momentum will give our ship a backwards acceleration of about half a million g's !
Of course, at these speeds a missile could be much smaller and still deadly.

If we assume the missile has its own propulsion, and accelerate all the way to the target (300000 km = 3*10^8 m), we get:

a = (3*10^7 m/s)^2 / (2 * 3*10^8 m) = 1.5*10^6 m/(s*s) ~ 150000 g.

Only a very sturdy sensor and guidance system should be fitted to this bird

In a game it would be OK to invent some magic "recoil-dampening" technology to make these missiles possible, but you should be consistent. Eg the ships you're shooting at should be able to take far more powerful evasion than 1 m/s. And whatever super energy-plant that powers these missiles or launchers could be fitted to power energy-weapons like x-ray/gamma-lasers etc.


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"It''s always useful when you face an enemy prepared to die for his country. That means both of you have exactly the same aim in mind." -Terry Pratchett

[edited by - deformed rabbit on August 7, 2002 2:32:15 PM]

deformed rabbit: Thanks for working out those calcs. I was going to look into the feasability of having projectiles that fast, but it looks like it would need some extreme technology to pull it off. I''m trying to stay away from made up technology as much as possible. So far, I''m allowing some sort of hyper-drive (with restrictions that limit it to interstellar areas only) and a vacuum-energy power plant that would provide unlimited energy, but with a finite power.

I did some quick calculations to find out how accurate you need to aim the big gun to hit a 100 m target at 300,000 km. I got 2^10-5 degress, or 0.07 arc seconds. I''m going to do a little research to see what accuracy current servos can give.

The missile''s momentum need not affect the launching ship''s, although doing so would give it even greater velocity. But therein lies the problem: the faster the missile is going, the easier it is to dodge. The slower it goes, however, the easier it is to shoot down. Thus, missiles with all the technology to have a decent hit rate would be more accurately call drones. They would need to be able to maneuver very quickly and accurately. In order to turn at sufficient angular velocities, they would need to either redirect thrust from the main engine or use chemical thrusters. They''d also need lots of fuel. They''d need a computer onboard to locate the ship. It would most likely be able to dodge; pure projectiles have easily predictable trajectories and so are easy to shoot down with good sensors. It may be useful for them to carry onboard weapons in case they don''t score a direct hit, they''d still be able to do some damage. The computer would need to calculate the distance to the target, so that it could explode if it got close enough to do damage but not close enough to contact.(a fission or fusion or antimatter powered missile would make a very powerful projectile).

As for pure missiles, how about launching several at the same time, with the same velocities, but with extreme payloads--fission, fusion, or antimatter. Launching them in a spherical configuration that corresponds exactly to the outer sphere mentioned in the first post. They all then detonate their high-yield explosives. Everything in the center of the sphere would be hit. Actually, the missiles would detonate before they surround the ship, so that their shockwaves reach the center of their configuration when the missiles would have surrounded the ship. Depending on how cheap extreme explosives become, this might be a viable option. Then imagine a machine gun like rate of fire for these.

Or how about drones that have smaller yield weapons and orbit the defending craft? If they are sent from the attacking ship to the defending ship, they simply fire their rockets in a slow burn starting when they''re beginning to overshoot the defending ship and always turn to face the ship. This causes them to orbit at their maximum weapon range, but incidentally, to always face the ship. Then, they could fire their projectile weapons, burning more vigourously when they start to fire in order to offset recoil. Imagine a cloud of such drones surrounding a target.

I just did some checking on servo moter accuracy. The ones the use to position large telescopes are incredibly accurate, 5 arc secs absolute and 0.5 arc secs differential. I''m sure in the future gaining a couple orders of magnitude is not unreasonable.

I ran deformed rabbit''s calculations with some new data. If we take a ship that is 1 km in length with a mass of 50 million metric tonnes firing a 1 kg projectile with a speed of 10% the speed of light, the ship experiences a recoil acceleration of 0.1 g. Since this is about the max acceleration I wanted capital ships to have to begin with, it all seems to work out. I feel kinda like an WorldCom accountant.

So a point blank range of 300,000 km seems to be acceptable for ships of about 1km in length. To put that distance in perspective, the average distance between the earth and moon is 384,467 km.

anonymous-
excellent point that if it''s as easy for the attacking ship to calculate how to hit the defending ship, it is even easier for the defending ship to know the projectiles path. I was wondering if it would be possible to shoot down a high speed projectile....even if it was going at near relativistic speeds.

korvan-
I think you are right with the submarine warfare analogy. I think realistic space combar will mostly be an affair of trying to find each other. I think victory will mostly go to the person who gets in the first shot that hits. If you make it realistic, I don''t know how a vessel would be able to survive most of today''s destructive firepower. Look at what happened to England in the Falklands war. One little exocet missle took out a destroyer (and a frigate I think). I''m not sure that even the armor of a battleship would have done much good against a good anti-ship missle. In the future, I think this will only get worse.

If you really extrapolate even further...you would want to build the smallest possible ships. As I said, I think ships will be able to at most take 3-4 good hits and be out of commission. The largest ships will be transport ships to bring supplies, and maybe some kind of tender ship.

Speaking of tender ships, you can have something like large transport craft which carry other fighters or mechs inside. This will have sufficient size for fuel for changing vectors. Think of them as boarding party vessels, or as tender craft for smaller fighters.

One last thing to remember is that not all space battles are going to be happening at extremely fast speeds. In fact, I''d say that most will NOT. Most space battles will be taking place near solar systems and in high orbits above planets. Essentially the space vessels will need to slow burn into system so they can drop off troops or simply bombard a planet. Vessels will not be able to fight at extreme velocities if they need to drop in system. And I seriously doubt any naval battle will be fought in deep (extra solar) space. Battles will congregate around defending planets or bases, and consequently speeds will be reduced.

Don''t forget about the recent advances in armor made by the British( and promptly excoverted by the American''s) Which allow the new generation battle tanks to survive a volley of cruise missiles with a great survivability ratio. Also, if you are using a near-futurist point of view, say projecting only 50-75 years in the future the anticipated power plant should be a gravity engine.(or so it is said) which carries the additional breakthrough of an inertial bubble being created around the vessel, or missile it propels. Thus the ability to travel in a straight line at 1/10 the speed of light and to immediately reverse course at an equal speed.

Dreddnafious Maelstrom

"If i saw farther, it was because I stood on the shoulders of giants."

Sir Isaac Newton

The main problem with a hyper-velocity cannon, is that very little of its energy is transfered to the target ship. The shell just punches a small hole straight through and keeps on going. The thinner the material the shell has to go through, the less energy it uses. So a heavily armoured ship actually would take more damage than a lightly armoured one.

Now, that same shell hitting, say, an astroid base would transfer all of its energy in the impact creating an emormous explosion, about five times as powerful as a similar sized hydrogen bomb.

A shell that was rigged to explode inside the ship would be devestating, but given the insane acceleration the shell has to undergo, only a solid shell could survive. For arguements sake, lets say that the 1kg shell I mentioned in an earlier post was deformed during the firing to atain a final diameter of 1 meter. The target ship would then have a 1 meter tunnel bored right through it.

If this hit a structual member of the ship, it would be unable to withstand accelerations from either its engines or main guns. If it hit a main gun while it was charging up to fire, the resulting electrical explosion would tear the ship to pieces. It would be like setting off a nuclear bomb inside. So, your big ships would be at their most vulnerable when firing their weapons.

The smaller the ship, the more compact its critical systems would be. A large ship would be easier to hit, but a small one would have a greater chance to inccur critical damage. With no such thing as shields, and armour being useless, having top notch damage control teams could be your best defense.

The target ship could certainly detect the firing of a main gun, but if the shell was made out of a stealth material, it would be invisible. My earlier calculations regarding a point blank range assumed the target would begin evassive action the moment it detected the firing of a main gun. Even at a distance of 300,000 km, there is a 90% chance of hitting.

In orbital situations, it would be possible to place a planet between you and the enemy. Assuming the enemy is approaching the planet to invade, some sort of orbital ambush would be possible.

Even if the position of the projectile is unknown, its possible trajectories could be saturated with explosives. With a rough estimate of the capabilities of the gun, however, even this is unnecessary. The countermeasure to this is to vary the velocity, but it would always be less than its maximum, and the volume of possible positions could still be saturated. Basically, then, the best way to fire would be to fire exploding projectiles that detonate everywhere between here and the enemy ship.

An interesting question, though is whether or not to fire on the edges of this volume, or the dead center. A dead center explosion would not deflect a dead center shot, but an off-center explosive would have less deflecting power than a dead center explosive, to all but dead center shots. And off-center shots would still lack deflecting power for shots that go through the center.

I think it''s kinda stretching it to say a projectile can undergo hundreds or thousands of G''s, and still be undetectable.

You don''t need to destroy the projectile(although I suppose that would work, too, if from a long enough distance), you just need to deflect it.

What about shrapnel? If a missile explodes in such a way as to saturate the volume of possible locations of the enemy ship, couldn''t you just send a whole bunch of these missiles continuously? The solution of course, is to explode something at the point where the missile should be, but a solution to that problem is to vary the distance at which it explodes, filling more or less than the volume, exploding off center, and so on. The dilution of shrapnel density could be compensated by rapid fire. I suppose you''d call it a vacuum flak gun.

I''m inclined to believe that all this means that the attackers still win, or perhaps mutually assured ship destruction. Unless, of course, you introduce shields.

I think its possible to imagine an ultra-high-velocity gun with near-future technology, but not with projectiles of any kind, even AP-rounds break up during the extreme acceleration.

It would be more like a beam weapon with the beam consisting of particles, protons, apha-particles or electrons accelerated to a fraction of lightspeed by a humongous electrical field (Apparently, an ordinary TV-tube can accelerate electrons to 1/3 c ). This will behave much like an energy-beam on the way to the target, ie unguided flight, straight line trajectory, dispersion increasing with distance. Once the beam reaches it will probably behave quite different from an energy beam, I don't really know enough physics to say very much, but eg alpha-particles hitting something made out of a heavy metal like lead will generate quite deadly secondary radiation.

All three types of weapons: energy-beams, fast particle-beams and slower homing missiles have their advantages and shortcomings. I think you could make up a reasonable near-future technology, where all three weapon-types are relevant to space-warfare, to make gameplay more varied.

Its not unreasonable to imagine a more conventional missile, with sensors and guidance system, in the near future accelarating at about a 100g's. Note that it might be a bad idea for a missile to approach a target too fast, if the target manages to dodge the missile, the missile will have to spend a lot of time decelerating and accelerating back to the target, and in the meantime it might be hit by countermeasures. Note that a fusing system that detonates the warhead if it misses the target also suffers from high speed with respect to the target. The speed at which the cloud of shrapnel expands is finite, and the center of this cloud follows the trajectory of the missile.
If the missile moves at 1000km/s and the explosion expands at 10km/s (don't know if this is reasonable, but its more than any nuclear explosions I've seen recordings of), and the warhead passes within 1km of the target, the warhead needs to predict all this and detonate 100km in front of the target for the explosion to be able to even graze it.


I can imagine an attacker firing a 1-2 punch of missiles: a kinetic killer accelerating all the way to the target, hoping that the target will not detect the missile until its to late to evade, and a missile with a warhead and a guidance computer, which starts decelerating halfway to the target and is able to maneuver for a kill once it get to the target (if it survived).



[edited by - deformed rabbit on August 8, 2002 1:45:32 PM]

For the lasers, think of this. You want them to travel at the speed of light. For realism, take this into account. I''m 300,000km from you and I shoot at you. When are you going to see the shot fired? Pretty much as it hits you. I''m not real sure that it matters. It''s kind of like me trying to dodge a bullet. It''s just not going to happen. Not only is it moving too fast to see, I don''t have the reflexes anyway. I think that reducing their power over distance is a good idea though.

Missles are a different story. I can see them long before they reach me, so I can dodge. But a capital ship shouldn''t be able to dodge a homing missle. Having fighters shoot down the missles/torpedoes might be an option. As would a chaff cloud to distract and disorient them.

As for the accuracy, I understand that servos can be very very accurate, but how fast do they move? I''ve worked with servos before and the larger the server, the slower it moves. If you have a small fighter that''s moving at 50km/sec, I rather doubt that unless the fighter holds steady, the turret would be able to lock on with any great degree of accuracy. Perhaps they get much better in the future though, as do the laser cannons.

Something else you could have is light powered energy particles. You fire a ''laser'' (imaging Dr. Evil there) at the enemy and it''s actually a uranium bullet powered by light. So, it''s a projectile, but it moves extremely fast, but slow enough that you can see the trail of light and have a (very small) chance of actually dodging it. Just an idea I guess.

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