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Thread: The physics of space battles

  1. #1 The physics of space battles 
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    I had a discussion recently with friends about the various depictions of space combat in science fiction movies, TV shows, and books. We have the fighter-plane engagements of Star Wars, the subdued, two-dimensional naval combat in Star Trek, the Newtonian planes of Battlestar Galactica, the staggeringly furious energy exchanges of the combat wasps in Peter Hamilton's books, and the use of antimatter rocket engines themselves as weapons in other sci-fi. But suppose we get out there, go terraform Mars, and the Martian colonists actually revolt. Or suppose we encounter hostile aliens. How would space combat actually go?


    http://gizmodo.com/5426453/the-physics-of-space-battles


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  3. #2 Re: The physics of space battles 
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    Quote Originally Posted by Cyberia
    I had a discussion recently with friends about the various depictions of space combat in science fiction movies, TV shows, and books. We have the fighter-plane engagements of Star Wars, the subdued, two-dimensional naval combat in Star Trek, the Newtonian planes of Battlestar Galactica, the staggeringly furious energy exchanges of the combat wasps in Peter Hamilton's books, and the use of antimatter rocket engines themselves as weapons in other sci-fi. But suppose we get out there, go terraform Mars, and the Martian colonists actually revolt. Or suppose we encounter hostile aliens. How would space combat actually go?


    http://gizmodo.com/5426453/the-physics-of-space-battles


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    This is more science fiction than physics. It is pretty clear that the author has no more than a passing acquaintence with real weapon systems.


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    There would be no explosions or, KaBOOM sound, and no turbo-fan engines.
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    I recall the cold war Soviet killer-satellites blew shrapnel out one side, self destructing. Space shotguns. This makes me think that war would quickly litter orbit with deadly debris, so much that pieces would often collide and bounce apart in random ways. Only armored craft would be safe up there. If this happened in the near future it would severely imperil launches... and if we braved the risk our failures would make matters worse.
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    Lots of interesting ideas on that site, some more practical than others.

    Numsgil started a thread about stealth issues in space a while back. Maybe I'll see if I can dig it up. Most likely maneuvering would not play a very significant role in space combat, simply because you can't dodge most of the weapons your enemy is going to be using. It's not going to be like Star Wars where blasters are firing around willy nilly. Whatever kind of cannon, gun, laser, or whatever your enemy uses, it's going to be computer guided and highly accurate.

    The only way to avoid getting hit is probably just to keep your enemy guessing where you are. Play shell games with decoys that give off heat signatures similar to your ship. Place temporary, cryogenically cooled, barriers between you and your enemy to cover your movements, and hide behind planets and asteroids whenever you can.

    So I think gyroscopes ("CMGs," in the spacecraft lingo) would be a better way to go they could invisibly live entirely within the space fighter hull, and wouldn't need to be mounted on any long booms (which would increase the radar, visible, and physical cross-section of the fighter) to get the most torque on the craft. With some big CMGs, a spacecraft could flip end-for-end in a matter of seconds or less. If you come upon a starfighter with some big, spherical bulbs near the midsection, they are probably whopping big CMGs and the thing will be able to point its guns at you wherever you go.
    Here's the main problem for maneuvering to avoid attacks. Since your enemy can rapidly point their gun in absolutely any direction relative to where they are located, trying to dodge their bullets would be like two modern armies standing in an open field and firing at each other. It wouldn't be a very long battle.
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    Quote Originally Posted by Pong
    I recall the cold war Soviet killer-satellites blew shrapnel out one side, self destructing. Space shotguns. This makes me think that war would quickly litter orbit with deadly debris, so much that pieces would often collide and bounce apart in random ways. Only armored craft would be safe up there. If this happened in the near future it would severely imperil launches... and if we braved the risk our failures would make matters worse.
    Space is really a pretty big place, so collisions with space junk are not as likely as you might think. But they can happen. We already keep track of orbiting junk around Earth. I think there was one report of a satellite that was taken out by a collision, a couple of years ago if I recall correctly.

    The closing velocities for impact with debris are extremely high. Most armor would not be effective. If the junk had any appreciable mass, I would not have conficence in the armor of an Abrams tank, or even a battleship.
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    I was thinking shards of glass, bits of foil and wire. I know the larger stuff is tracked, and we can plan around that, but little objects also bounce off each other, and no predicting where they'll go.

    About how many "shotgun" blasts and exploded satellites do you reckon, before orbit becomes prohibitively risky?

    Could we use nukes to blow all the junk out of orbit?
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    Quote Originally Posted by Pong

    Could we use nukes to blow all the junk out of orbit?
    In order to get it out of orbit, you've got to either accelerate it up to escape velocity, or decelerate it to the point where it falls back into the atmosphere. If you just throw it really far, its speed will adjust with gravity and just form a new orbit.

    Of course, if the direction you throw it in is down, then it will hit the atmosphere on its next orbit, and that will stop it. We'd just want to avoid throwing anything upwards, or sideways.
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  10. #9 It goes BOOM 
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    Space battle will just be like having 2 International Space Stations launching missles, instead of space shuttles, at each other. They would also be very quick because it only takes on tear and the whole entire "spaceattackship" to dissintergrate. Unless everyone on board was wearing a space suit but then again people in space suits floating in space versus a gigantic sized spaceattackship seems preatty obvious who will win considering that bullets will not work in Space and the only arsenal can only come from docking stations that fire missiles.

    Just had a really funny image, MIR vs ISS, I think we all know who will beat those dirty soviets :wink:
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    If you think about it, the best way to dodge in space, for a long range battle, is to just change heading and velocity randomly. Maybe have a computer run some kind of randomization algorithm to make it truly impossible to predict your next position. (Except the computer delays the choices back by about 5 minutes or so, so it knows its own next move.)

    Then it's impossible for your enemy to hit you. They can't see where you are right now, only where you were distance/C seconds ago.
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    I was thinking the most energy efficient means of dodging would be through slinging around moons and planets. A slight thrust yields wide course variation. For example one could bullseye planet Mars most of the way, and in the final approach nudge to fall across the near or far side. You might even deploy a subtle airbrake so as not to reveal escape vector by visibly thrusting.

    Then I thought ships in a fleet could cooperate to slingshot each other, either by their own gravity or better yet mechanically. It would be a sort of dance of the bungee cords.

    Of course defences and regular space travel would exploit gravitational slingshot also. One could swing among three or four bodies indefinitely. Even, I see no reason why just two bodies can't be reused over and over, the craft gaining and losing inertia as necessary.

    One cool implication here is that spacecraft would probably be streamlined to get the most from low flybys.

    Another implication to geek about is that with the growth of space civilizations the relationships of stars would begin to look atomic and even molecular - not in terms of coordinates but in terms of connections. So you'd have your water-form civilizations and your iron-form civilizations, with their characteristic ways of interacting, and so forth.
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    You couldn't repeatedly use gravity slingshots/brakes during space battles since each pass would be several days apart (IIRC).
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    Quote Originally Posted by kojax
    If you think about it, the best way to dodge in space, for a long range battle, is to just change heading and velocity randomly. Maybe have a computer run some kind of randomization algorithm to make it truly impossible to predict your next position. (Except the computer delays the choices back by about 5 minutes or so, so it knows its own next move.)

    Then it's impossible for your enemy to hit you. They can't see where you are right now, only where you were distance/C seconds ago.
    That is why missiles use game theoretic algorithms to determine how to maneuver in the end game. That effectively means that there is no such thing as a long range battle if you use smart weapons.

    You can always predict your "next position" so long as the time interval defining "next" is sufficiently small. There are practical limitations to how rapidly one can change velocity. Changing velocity requires acceleration and acceleratin requires force. If you change velocity fast enough, you die -- it is not the fall that kills you it is the sudden stop.
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  16. #15  
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by kojax
    If you think about it, the best way to dodge in space, for a long range battle, is to just change heading and velocity randomly. Maybe have a computer run some kind of randomization algorithm to make it truly impossible to predict your next position. (Except the computer delays the choices back by about 5 minutes or so, so it knows its own next move.)

    Then it's impossible for your enemy to hit you. They can't see where you are right now, only where you were distance/C seconds ago.
    That is why missiles use game theoretic algorithms to determine how to maneuver in the end game. That effectively means that there is no such thing as a long range battle if you use smart weapons.

    You can always predict your "next position" so long as the time interval defining "next" is sufficiently small. There are practical limitations to how rapidly one can change velocity. Changing velocity requires acceleration and acceleratin requires force. If you change velocity fast enough, you die -- it is not the fall that kills you it is the sudden stop.
    Good point. The human body can only withstand up to about 4 g's of acceleration for more than a moment. Otherwise the retinas in your eyes become detached, and you go blind. There's also the difficulty breathing when you're being smashed up against your seat.
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    Quote Originally Posted by MagiMaster
    You couldn't repeatedly use gravity slingshots/brakes during space battles since each pass would be several days apart (IIRC).
    Because space battles should be at close range? I wish too.
    Quote Originally Posted by DrRocket
    There are practical limitations to how rapidly one can change velocity. Changing velocity requires acceleration and acceleratin requires force. If you change velocity fast enough, you die -- it is not the fall that kills you it is the sudden stop.
    Yes, this is why gravity assist pwns space battles.
    Quote Originally Posted by DrRocket
    missiles use game theoretic algorithms to determine how to maneuver in the end game. That effectively means that there is no such thing as a long range battle if you use smart weapons.
    Well, suppose your fleet is orbiting Mars, and Kojax's is orbiting Venus. You both want to win Earth orbit, you both have smart missiles armed, you're both prepared to "play" any number of ships and missiles within the inner solar system as it also orbits the sun. What's your move?

    I think you'd be a fool to launch smart missiles now since Kojax will contemplate their approach leisurely move to another planet or moon... but I may be wrong.

    Think about the fuel costs, and how to make your opponent spend more fuel in ships and rockets.

    Strategy?
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    I guess whether the slingshot would work would depend on what you're dodging. Light-speed weapons would be too fast for it to make much difference, and smart missiles would be able to compensate. It might matter with dumb-fire missiles and other things though.
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    Quote Originally Posted by MagiMaster
    I guess whether the slingshot would work would depend on what you're dodging. Light-speed weapons would be too fast for it to make much difference, and smart missiles would be able to compensate. It might matter with dumb-fire missiles and other things though.
    It just depends on how unpredictable your movements are, and how far away the two combatants are. If you're 8 light seconds away from your opponent, then they've got 16 seconds to get out of the way before you can hit them with your laser. If you could predict where they were going to be in 16 seconds, and aim your laser accordingly, then they'd be out of luck.

    So, I don't know if gravity slinging will work. A gravitational orbiting pattern can be predicted if you know how fast the object is moving and in what direction. In order to dodge around they still have to use up propellant. However: in orbit, a small thrust can produce large results, so it would certainly conserve propellant to be in orbit, just not totally eliminate the need for it.
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    exactly - fuel would be rather precious for all that maneuvering - i wouldn't want to be 'stranded' in space.

    Good thing is in the low gravity environment you could make very sudden changes to your orientation and not get anywhere near 4 g's - opening the way for some very agile dogfights!

    there might still be a place for more 'conventional' ammunition such as 'flak' guns which will cover a wide area - something a laser might find difficult or be less effective at..........only problem is the recoil could have some interesting side effects but it is relatively easy to make recoiless weapons anyway.
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    There's no way to make a recoilless weapon, especially in space. Even lasers have recoil in space (although generally only a very tiny amount). Missiles can be recoilless if they're just dropped off and allowed to take off afterwards.
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    It's pretty hard to predict what future space battles would look like, since it would really all depend on what the material science etc. is like. Missiles might be nearly impossible to stop, with anyone in the solar system who has a military able to easily blow up anyone else's stuff...or lasers etc. might be able to easily shoot down huge swarms of missiles, making them useless.

    About the only things we can probably be confident of is that:

    1. There probably won't be any stealth. It's just too hard to hide in space.

    2. There probably won't be manned "space fighters" (although there might be unmanned drones).
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    I think there's at least one more thing that would be a safe assumption: there will always be an arms race between offensive and defensive technology, so if missiles are currently unstoppable, all weapons research will be focussed on finding ways to stop them.
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    Quote Originally Posted by MagiMaster
    I think there's at least one more thing that would be a safe assumption: there will always be an arms race between offensive and defensive technology, so if missiles are currently unstoppable, all weapons research will be focussed on finding ways to stop them.
    Fair enough, but that doesn't mean they will succeed...

    For example, missiles that travel at near the speed of light might be nearly impossible to defend against.
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    Lasers are a better example, since they DO travel at light speed and as such will hit you RIGHT as you are become capable of knowing it's coming.
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    How movement was dipicted in Sci Fi shows was mentioened. If I recall, Babalon 5 was the first to show realistic movements in space. A spaceship is not going to track like an airplane or terrestrial jet. I seem to recall Battlestar Galactica, the new one, also dipicting space flight correctly.

    Both... except for it is dead silent in space. No atmosphere to carry sound pressure.
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    Quote Originally Posted by fatman57
    Good thing is in the low gravity environment you could make very sudden changes to your orientation and not get anywhere near 4 g's - opening the way for some very agile dogfights!
    If we are ever going to have any reasonable space travel, I think it's safe to assume G-forces will be eliminated by inertial shields or inertial dampening. Inertial shielding would reduct the power required for manuvering. Inertial dampening would only remove ralative G-Forces.
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    Quote Originally Posted by Arcane_Mathematician
    Lasers are a better example, since they DO travel at light speed and as such will hit you RIGHT as you are become capable of knowing it's coming.
    That's why your only safety would be to constantly change heading/position. Remember that, on the scale of space, light is not an instantaneous effect like it is on Earth. Your enemy can't possibly know your current location, only your location a number of seconds ago. They have to guess your current location on the basis of trying to find a pattern in your past locations.

    If you're moving along under constant acceleration, or just drifting, then you're an easy mark. If you're constantly changing velocity, then we might expect that you'll run out of fuel pretty fast.


    Suppose there are two ships connected by a powerful electric magnet as their tether, with a lot of gyroscopes to preserve their orientations toward each other. Maybe they could push and pull off of each other in order to give themselves seeming random positions? There's no point in targeting their center of gravity, because it's just empty space.
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  29. #28  
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    Quote Originally Posted by kojax
    Suppose there are two ships connected by a powerful electric magnet as their tether, with a lot of gyroscopes to preserve their orientations toward each other. Maybe they could push and pull off of each other in order to give themselves seeming random positions? There's no point in targeting their center of gravity, because it's just empty space.
    Already dubbed it: the dance of the bungee cords.

    Random motion is pretty easy, as in mobiles or chaos pendulums.
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    Quote Originally Posted by kojax
    Quote Originally Posted by Arcane_Mathematician
    Lasers are a better example, since they DO travel at light speed and as such will hit you RIGHT as you are become capable of knowing it's coming.
    That's why your only safety would be to constantly change heading/position. Remember that, on the scale of space, light is not an instantaneous effect like it is on Earth. Your enemy can't possibly know your current location, only your location a number of seconds ago. They have to guess your current location on the basis of trying to find a pattern in your past locations.
    also an attack can come from any direction, unlike on earth where there is less chance of certain directions.

    and you can make recoiless weapons - for example the recoiless rifle! using that principle alone it might be a different scenario for a laser in space as it cannot release its gaseous energy into a void like the recoiless rifle can.

    it might be impossible in space unless countermeasured by thrust from the ship that would be firing at the time.................unless they were in orbit where the kinetic energy from the planetary body could be enough to withstand the energy from the weapon firing at the time, esentially meaning the ship keeps moving along its original path uninterrupted.............???
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    There are no recoilless weapons. The "recoiless rifle" has recoil, just lessened.
    Wise men speak because they have something to say; Fools, because they have to say something.
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    Quote Originally Posted by Arcane_Mathematician
    Lasers are a better example, since they DO travel at light speed and as such will hit you RIGHT as you are become capable of knowing it's coming.
    But lasers would be very hard to aim over long distances, for a variety of reasons. It's not really plausible that you could fire a laser from Jupiter and hit a ship near Earth. Missiles, on the other hand, can actively correct their path as they move to the target. Evasive maneuvers might not help, because the missile will just correct for it.
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    Quote Originally Posted by Wild Cobra
    If we are ever going to have any reasonable space travel, I think it's safe to assume G-forces will be eliminated by inertial shields or inertial dampening. Inertial shielding would reduct the power required for manuvering. Inertial dampening would only remove ralative G-Forces.
    You can have spectacular space travel with only 1 g acceleration. With 1 g constant acceleration, you can go from Earth to Mars in just 4 days, or the solar system to the Alpha Centauri in about 3.5 years.
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    Quote Originally Posted by Arcane_Mathematician
    There are no recoilless weapons. The "recoiless rifle" has recoil, just lessened.
    I might have to go along with the scientific view on this one but I can still aggravate!


    What would 1 g acceleration be equivalent to?
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