You have to be really careful how you apply "realism" to spaceships/space combat. Why would you risk lives when you could easily make an unmanned ship or missile? It's not like it'd be hard to do. There's not a lot of complex physics in space. No pesky air resistance, gravity or other messy things screwing up your AI. It just has to take into account it's relative speed, its position and heading, and then use its sensors to keep track of it's opponent.

I'd just build a swarm of missiles, program them to hit whatever target I decide, and send them off. They can probably accelerate/manouver much better than manned ships, and you'd have a hard time defending against all of them. Then when everything you have has been blown to pieces, I could fly in and take possession of the remaining debris and ruins. If they can get up near the speed of light, they'll be practically impossible to detect and destroy. And they don't have to carry any real payload, since at that speed, practically anything can cause a lot of damage. So all you need is an engine, a fuel tank and some navigation system, and you have a weapon that's basically impossible to defend against, and doesn't even risk the lives of my own soldiers.

Of course, that's a fairly obvious strategy, and my opponent would probably do the same. That means we could both get killed. Not very much fun.

Anyway, about your original suggestion. Would a big huge armored ship really be worth it? Do you think its armor would actually help it? (How would it "move very fast" anyway? It sounds like it'd have a lot of mass, meaning lots of inertia) But wouldn't most sci-fi weapons be able to blow it to bits anyway? If I fire a small slug at it at, say, 80% of the speed of light, I doubt you'll have much left of your ship. Would it make more sense to use lots of smaller faster and lighter armored ships?

Here's my take on "realistic" spacecraft (say within the next 100 years or so). I'm positing real world physics here, so no reactionless drives.

1) The ships will be fairly small.
2) They will have few to no human crews.
3) Combat will take place at extremely long ranges using energy weapons.
4) Combat will take place at relatively slow speeds.
5) *Fighters will not be used in space-to-space battles

Explanations:
1) Small ships will require less fuel and hence can travel further. I posit that solar sails or laser sails will be the main method of intra-solar travel, while traditional chemically propelled or maybe atomic detonation devices will be used for high speeds burns. In my own game system, I have posited a reactionless drive system that utilizes the Zero Point engery field (google it). Some physicists believe that this real field is what causes inertia. If we can create a drive system that can tap into the ZPE, then you could conceivably "push-pull" through this modern day "ether" that's the ZPE.

2) The quickness of decision-making simply won't allow for human crews to be that efficient anymore. If you posit robotic technology, then having human crews becomes even less sensible. The reaction time of a computer controlled ship will be far greater than that of a human. Taking into account a slightly reduced Moore's law, and/or quantum computers, and you can have decision-making computers that can decide and interface with ship controls far faster than a human crew could (even if they could somehow jack-in). Add in the maintenance upkeep and logistics for human crews (life support, food, crew quarters) and it just doesn't make sense.

3) The range at which ships can detect each other purely through passively radiated EMF signals (whether infrared or something else) will make sneaking up nigh impossible. Hence, combat will take place at incredibly long ranges. Given that the primary weapon systems will be energy weapons for several reasons (not needing to stock ammunition, not having explosive ammunition on board, and the weight/volume savings), we now have the premise for #4.

4) Combat will be slowly paced because if your ship is moving fast, it can't turn fast. If you can't change your vector quickly, then your enemy can better predict where your ship will be from momment to moment. Since most weapons will be energy weapons at extreme range, this will give only a split second to make course corrections. This supports yet another reason why human crews are unlikely...ships without human crews can perform high-G moves that humans wouldn't be able to take.

5) Because of the long ranges, fighters are somewhat useless. Most fights will be over by the time the fighters made their acceleration burn to get within firing range of the target. However, fighters will probably take on an important planet-based role. The asterix is there because it's possible for them to be of use in ambush situations. In my own game world, thanks to the ZPE engines that produce extremely little heat (ZPE energy usage can "violate" laws of thermodynamics because the energy is coming from "outside" of the system) fighters can be almost powered down and lay in wait.

So you won't see the fancy Newtonian-approved acrobatic displays of ships blasting each other with humans barking orders to one another. Instead, it will be a very cold, calculating and quiet affair like space itself.

This is just a general post on the topic.

By 'realistic' I'm going to assume, like everyone else seems to, that you mean slower-than-light. I'll also assume that reactionless drives (as someone else pointed out) are still beyond the horizon. So, we have two huge constraints right there. Two direct results would be:

1. Ships would avoid planets like the plague. A planet means a relatively huge gravity well to contend with, which would place even worse constraints on fuel and maneuverability (mainly from a lower orbit to a higher one).

2. The farther away from the enemy at which you can win, the better. In space, time is fuel, and both are precious. Ship commanders will need at all times to conserve their reaction mass (whatever it may be) as much as possible.

Drives requiring reaction mass would mean that the fuel-to-mass ratio would be as low as possible (i.e. maximum fuel and minimum mass). Depending on what kind of reaction mass you're working with, this is more or less of a constraint.

At relativistic speeds, the amount of mass something has is not as important as how fast it is going. This is true for even subrelativistic speeds. I once read that an object the size of a pencil eraser orbiting Earth collided with a satellite and vaporized(!!!) it. So, drones (the likely weapon in near-future space combat, basically a guided missile) are likely to be as small as possible.

Furthermore, these drones will be (as many others have suggested here) unmanned. There are two reasons for this: an unmanned vehicle can undergo vastly higher accelerations than a manned one, and a manned vehicle requires much more mass (life support, actual person(s), etc.) than an unmanned one.

Even better, a drone wouldn't necessarily have to make accelerations from (essentially) rest to relativistic speeds. A probable tactic would be for a ship travelling toward a star system at relativistic speeds to release some drones before it decelerates. That would allow the drones' onboard fuel to be dedicated entirely to maneuvering and (possibly) deceleration.

A projectile travelling close to the speed of light would be very difficult to detect, because at any point at which one could detect it, it would actually be much closer. However, I wonder if a projectile's accuracy rate is inversely proportional to its speed. That is, I wonder if it would be just as easy for a ship to move out of the projectile's course.

Finally, shields would be vastly preferred to armor. Armor is always passive, while shields can be either active or passive. Furthermore, shields can have much longer range than armor. In fact, shields would be a necessity on *any* relativistic ship, because there could be many objects in space which could destroy the ship while it is travelling at relativistic velocities. Another consideration is, given the speeds at which drones would travel, it is likely that any armor would be rendered meaningless. So, the probable configuration would be little or no armor, mainly just to keep the ship structurally intact, and as much shielding as possible.

Another tactic for such ships would be to 'mine' the area around it to a certain range. This could be an extension of its shielding system, whether permanent or temporary. The permanent version would be a constellation of small objects moving with the ship a certain distance away from it, hopefully to catch any objects which could collide with the ship before they would reach it. The temporary version would, again, be for the ship to release these objects only upon decelerating to non-relativistic speeds.

Hope that's some stuff for y'all to work with.

- Rob

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Original post by RobAU78 1. Ships would avoid planets like the plague. A planet means a relatively huge gravity well to contend with, which would place even worse constraints on fuel and maneuverability (mainly from a lower orbit to a higher one).

I'd disagree with this one, at least as far as combat is concerned. I'd go as far as to say that combat will simply never happen except within a fairly short distance of a planet.

The reason for this, is that planets are really the only points likely to be of interest to anyone, and therefore the only place where forces are likely to clash. Deep space is so unbelievably vast that the chances of two forces clashing randomly is essentially nil, and it's so empty there's no other reason for them to fight in it.

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Original post by Sandman I'd disagree with this one, at least as far as combat is concerned. I'd go as far as to say that combat will simply never happen except within a fairly short distance of a planet. The reason for this, is that planets are really the only points likely to be of interest to anyone, and therefore the only place where forces are likely to clash. Deep space is so unbelievably vast that the chances of two forces clashing randomly is essentially nil, and it's so empty there's no other reason for them to fight in it.

Of course you're right that "planets are really the only points likely to be of interest to anyone." However, I don't think two (or more) species would have to fight over a planet *near* that planet. They would certainly have to have forces within the general vicinity (i.e. in the planet's solar system), but the farther they are from the point of interest at which they can achieve victory (likely the total annihilation of the other's/s' forces), the better. So, I agree that there would be little (if any) conflict in deep space, and most battles would take place "in-system," as it were. But I still think that the major battles would not take place *in orbit* around contested planets.

- Rob

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Original post by Dauntless 4) Combat will be slowly paced because if your ship is moving fast, it can't turn fast.

Umm, why not? That may be true of atmospheric aircraft that turn by essentially trading speed in one direction for speed in another, but spacecraft do not work that way. Even the concept of "turning" doesn't really translate well to spacecraft. If a spacecraft thrusts at an angle to it's current velocity vector, the only factor governing how quickly that vector will change is the amount of thrust that can be applied. Of course, the ship may first have to rotate itself before it's able to thrust in a new direction, but the ability to do that quickly is a function of the shape of the ship and the placement and power of the thrusters. The current speed makes no difference whatsoever.

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Original post by CombatWombat The point I'm trying to make, is what is the difference of a projectile and a ship in space? The ship/projectile can sort of be looked at as a two-stage vehicle, where the first stage is nearly obsolete. Faster response times of having a launch vehicle in the area of conflict are nice, but how long does it take to actually get there? Probably hundreds up to millions of years. (Again, why a 'realistic space combat game' would be a terribly boring thing). Why not just shoot first and not get out of bed?

I think you are assuming combat between enemies who are in different solar systems, while I and Plasmadog were speaking of combat inside one solar system. In which case, millions of years is certainly an overstatement; you can reach Mars from Earth in (IIRC) two years even on a highly efficient orbit.

Even between solar systems, though, I think you don't want to be launching robots. By the time they get there, the enemy's technology will be vastly improved; how could your ancient, steam-powered robots compete? You would have to send an entire microcosm of your society, capable of improving its weaponry en route, so it would stand a chance when it arrived. Which might make for an interesting RPG, if a part of the Fleet decided it didn't want to die in a war declared five generations ago.

But getting back to combat inside one solar system, I think it's not so trivial as all that to hit a target - even a planet-sized one - at distances of AU. There are limits to how good a brain you can build for your missile, if you want to build them in sufficient quantities to fight a war; whereas humans can be produced in nine months by unskilled labour. Why not send along a few human brains to direct your missiles, cope with enemy surprises, and accept his surrender, then?

Plasmadog-
Even though space offers no friction as a counter-resistance against the hull of the ship, you still have to account for the acceleration of the thrusters versus the inertia of the ship's own mass as well as the equal but opposite force generated by the thrust accelerators. Apply too much acceleration against a weak structual part of the ship, and you'll snap it in half. The inertial mass of the hull itself acts as a counter-resistance to the acceleration. Imagine this for a second. You have a super-hero trying to lift a battleship off the ground. Assuming he's strong enough, there's a problem with this....the ship would either crack in half, or the hero would just act like a nail driving through the ship. In this case, it's obvious that gravity is acting as a downward force. But relatively speaking, that's no different than if the hero was pushing forward (Newton's second law IIRC). So when the ship has to burn its thrusters at an acute angle to make a steep turn, that acceleration still has an equal but opposite force. If that opposite force is applied to the ship's weak structural side, that could be bad ( depending on how the ship was designed....I guess the safest structure for a ship would indeed be a sphere).

In fact, in gravity situations, frictional forces actually help you turn. Think for a moment of how hovercraft turn versus a car. The frictional forces of the tires on the pavement act as a gripping force that actually improves handling. The hovercraft on the other hand has almost no friction, and you can think of hovercraft as a 2d "gravityless" environment. Hovercraft turn by pointing their fans in a different direction. And the handling characteristics of hovercraft are pretty poor. Same thing for aircraft...the air drag and air resistance actually can help the turning characteristics (to a degree). Obviously, it can't do very acute turns, but

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Let's say your rocket will take 1 minute to reach the target, and that the target's thrusters can accelerate it at a speed of 10 m/s. From a sitting position, the target will move roughly 60*10 meters. That means that your target's expected position after a minute is a sphere .6Km in radius.

I'm not a math major so correct me if I am wrong, the above calculating assumes a max SPEED of 10 m/s. Wouldn’t an acceleration of 10 m/s give you something much larger (no friction in space)? Something like 18300 m?

Aside from that I think the biggest problem is not how far away the target is but how fast the projectile is traveling in relation to the target.
You are standing on a high way and a motorcycle is barreling down on you at 100 mph. If you time it right, at the last second you can step/jump either left or right and the motorcycle will wiz on by. It's turning radius prevents if from being able to make a curse correction fast enough to hit you at the last second.

[Edited by - Kars on October 13, 2004 2:02:45 PM]

Everybodies already touched on most of the important topics, but I'll throw out a few thoughts too.

Inertia will be one of the biggest things you need to consider when designed "realistic" spacecraft. It affects how quickly they can accelerate, decelerate, and rotate. The faster something is, or the more massive something is, the more inertia it has, and thus the harder it is to maneuver or change velocity.

Ships will be designed to make the optimal use of space and resources as possible. On earth, we have things like air, water, or ground that affect the design of function of a craft. Space has few constraints like this. There's no reason to be aerodynamic, for example. On the other hand, the function of the ship will determine its design.

For example, a ship that would be required to rotate and move quickly might be designed something like a giant "jack" - a center sphere or structure that houses the engines and computers, while struts extend in every direction with thrusters on the ends. By placing these thrusters out away from the center, rotational torque is increased, allowing the ship to rotate much faster than if the thrusters were towards the center.

Ships won't have human crews, and that's been discussed already. In short, computers will be advanced enough to do whatever they need to on their own.

To house humans will be a complete waste of resources - humans require air, food, water, and large amounts of empty space. Humans generate waste. To keep temperatures regulated will take excessive amounts of energy. Ships will need additional shielding to protect the humans from radiation, further adding to the weight and/or energy requirements of the ship.

Future ships will get rid of humans entirely and use all that extra space and energy for more productive things, like better computers, faster engines, or more weapons.