Star Wars wouldn't be the same without the screams of TIE fighter engines or the flashes of brightly colored lasers crisscrossing space battles, but we know that no real space battle would go down the same way. Sound gives outer space character, in Star Wars--and in most science fiction--but real space battles would be soundless and a whole lot less flashy. In fact, they'd probably look nothing like the battles of Star Wars or Star Trek, which are filled with futuristic (but hardly realistic) technology.
An essay on realistic space battles points out that much of popular science fiction bases its space battles on naval battles. Big ships keep their distance, exchanging volleys of fire, while planes buzz around in the sky dogfighting and carrying out bombing runs on the enemy carriers and battleships. Transplanted into space, you get Star Destroyers and star cruisers duking it out with X-Wings and TIE fighters juking around like they're fighting in an atmosphere. In reality, with no friction in space, fighters could turn effortlessly with no loss of momentum, so being positioned behind an opponent wouldn't convey the same advantage it does on Earth.
The essay describes space combat transplanted to Earth like this:
The best terrestrial analogy for space warfare would probably be a battle on a perfectly plain at night, fought between sports cars painted with phosphorescent paint, with machine guns mounted on their hoods. All sides will be aware of the movements of the other. The battles will likely consist of long periods of boredom while the ships chase each other, accelerate towards each other, or vie for an intercept that favors them, punctuated by a few minutes of terror as they scream past each other at many kilometers per second and fire away. The primary weapon will probably be missiles, which will be fired in huge volleys. Depending on the vessels’ relative speeds, a warship will probably need to shoot dozens or hundreds of missiles to be sure of one getting through. In such an exchange, the winner is likely to be the ship with the heaviest missile throw weight, best PD, or both. Victory and defeat will be a question of cold arithmetic: can you can kill all the other guy’s missiles before they reach you and visa versa.
Mutual kills will probably be quite common. As the ships pass within a few tens of thousands of kilometers of each other they may fire lasers at each other. The lasers will be relatively weak weapons, and the aim will probably mostly be to damage the enemy’s sensors, laser turrets, radiators, and other sensitive equipment. A laser battle will be a race to see which ship can cripple the other first, and will be won by the side with the best lasers or best design redundancy. At low engagement speeds the most common strategy is probably going to hamstring the enemy ship as badly as you can with your lasers and then finish it off with missiles. If the engagement leaves survivors on both sides and one side wants to press the attack they will have to do so by burning off their momentum and putting themselves back on an intercept course, basically reversing their present course.
Our favorite ship designs don't make much sense, either. Once you factor out energy shields, nearly every impact from a missile will be incredibly crippling and damaging. Battleships will often be taken out with one-hit kills. Couple that with the fact that ships will be incredibly easy to see against the backdrop of space--the essay notes that powerful engines would likely be detectable as far away as the next solar system--and space battles are unlikely to look like the slugging matches or dogfights we typically see. Visibility and situational awareness in space will far exceed anything we've experienced in traditional warfare. By reading the type of fuel, heat expended, and trajectory of a ship, it will be easy to figure out its exact course and speed.
We may still get our lasers, but they won't be quite as exciting as Star Wars lasers. The essay predicts they'll be used as defense systems against highly destructive nuclear and kinetic missiles, much like the (failed) real Star Wars, or SDI:
A moderately well-focused 100 MW ultraviolet laser will kill the missile in 2-4 seconds at 10,000 km, 20-40 seconds at 30,000 km, and 70-113 seconds at 50,000 km. ... The critical limitation on laser effectiveness at short ranges will probably be the time needed to switch from one target to the next. The actual targeting computer will probably be able to do so very quickly, but remember, we’re talking multi-megawatt lasers with 10 meter mirrors and massive cooling systems here. The turrets these things are mounted in will be literally the size of a house, and I doubt they will be able to rotate to a new target with lightening speed. A delay time of at least 2-3 seconds is probably inevitable.
Another key limitation may be power and cooling. 100 MW is a lot of energy, and most of the high-performance rocket systems a warship may use don’t really lend themselves to being tapped for that kind of electrical power, meaning the ship will probably have to carry a separate reactor to power the lasers. And lasers are notoriously inefficient; the models currently being tested for the US and Israeli militaries have energy efficiencies of 10%, meaning that a 100 MW laser would be using a gigawatt of electrical power and generating 900 megawatts of waste heat, not counting inefficiencies of the power generator itself. As well as their own reactor, they’ll need massive radiators to get rid of all the waste heat they generate. There may be limits to how long you can those things burning. Current military lasers require minutes of cool-down time after a few seconds of firing time, though future systems will probably be much better.
Unfortunately, after dealing a killing blow to the fantasy of sci-fi space battles, the essay targets smugglers and traders, who would likely have no place in a warfaring space civilization. Why? Because their ships could be incredibly lethal, even without weapons.
If your ship weighs 10,000 tons it will impact with a force of 84.8 gigatons. Assuming the blast is similar to an equivalent size nuclear explosion that will cause widespread destruction for hundreds of kilometers around and third degree burns more than a thousand kilometers from ground zero. Essentially, it will wipe out the entire state of New Jersey, and turn the entire northeastern United States into a disaster area. Basically anybody willing to fly his ship into a planet can singlehandedly kill tens of millions of people. And there’s no reason to demand human crews consign themselves to riding a giant kinetic missile into a planet to do this either. You can just take the propellant tanks and engine of a warship, mount a simple targeting computer on it in place of the weaponry and habitat modules, and create a similarly powerful kinetic missile with no need for a crew of would-be suicide bombers.
...What all this means is that the orbital space around a planet will be very tightly watched and defended. ... Incidentally, this probably means you won’t get any Han Solo type free traders in a realistic universe. Even assuming spacecraft are cheap enough for small-time operators to afford (unlikely), even a very slow small craft that putters around in Hohmann orbits will be a potential multi-kiloton kinetic energy missile, and the sort of ship that will get anywhere in less than six months has a destructive potential in the wrong hands that doesn’t bear thinking about. High speed ships will be treated with the same respect that we treat nuclear reactors; they will not be handed out like sporting yachts to anybody who can afford them, even if it’s economically feasible for your average citizen to own one.
Still, space combat will have some glamour to it. You can't deny the cool factor of spaceships using technology like Orion drives, which essentially push ships with the force of nuclear explosions. A "pusher plate" mounted to the back of the ship would bear the brunt of the detonation and send the ship hurtling forward. The ships won't look as cool as the Millenium Falcon, but at least we can count on some pretty amazing propulsion systems to power our interstellar drive-by shootouts.