I think you got it all wrong. Take into consideration that this is a fiction novel, and that their technology is thousands of years beyond ours.
Well yeah, but it still follows basic science. Its part of Suspension of Belief.
fighters are useful -they are meant to defend against Fighters/Bombers before they reach either bombing range of your home fleet or reach attacking range of your bomber group.
The devil is in the details, my friend. In an atmosphere, that would be correct, in the vacuum of space, it isn't. Here is why, the bigger ships with their bigger engines can maintain vastly greater acceleration and velocity, and thus out run them as their is no drag.
The fighter in order to make an intercept must use a planet or moon to slingshot him at a faster speed, even then it won't be enough. The fighters therefore need to box their targets in so they can intercept, even then the big ships just by turning one degree can simply avoid the intercept.
By the time we develop strike craft of our own, we should be able to provide some viable fuel source to last for long dogfights and sorties.
The problem is thrust, not fuel then. A bigger ship generates more thrust, more angular velocity, and can accelerate faster.
also, fighters would be equipped with some type of anti-strike craft weaponrey, like a rapid-firing railgun or Space torpedoes. It is true, though, that they would be of little use to anti-ship attack unless outfitted with such weaponrey, but that would be a multirole strike craft.
Could be useful against Frigates, but not against capital ships more than a kilometer long.
Before I begin, I must explain what stress is. Mechanical stress is expressed in units of force divided by area, and it is conceptualized as the load acting normal to a plane surface, divided by the area of that plane surface.
The diagram shows a bar which is being stretched. We call this "tensile stress", and it's the simplest possible situation in stress analysis. The little arrows show the force acting on the bar, and of course, it's spread out over the entire area of the bar's cross-section. This cross-sectional area is often referred to as the "load-bearing area". For example, if the load-bearing area is 5 m² and the bar is supporting a 100,000 ton mass against the force of gravity, then the stress would be roughly 2E8 N/m², or 200 MPa (structural steel yields at ~260 MPa, in case you're wondering).
The critical factor is the load-bearing area. The length of the bar doesn't help at all, and you can verify this with an experiment. Get a length of good high-quality rope, tie one end to a solid post, and try to pull on the other end until it breaks. Does it matter how long the rope is? No. You could cut a 100 foot length and it would be no stronger than a 1 foot length. So the moral of this story is that the load-bearing capacity of our bar is affected by changes in width or height, but not by changes in length. If you scale the bar up by a factor of 100, then its volume will increase by a factor of 1 million but its load-bearing area will only increase by a factor of 10,000.
Why does size matter then? Size matters because of gravity and acceleration. If you're building an immobile space station in a zero-gravity environment (such as Mir), size doesn't matter. But if you're building a ship, then things become a whole lot more complicated. When that ship accelerates or enters the gravity well of a planet, the resulting forces will be proportional to its mass. Its mass, in turn, is proportional to its volume.
It doesn't take a genius to see the problem here: when you scale something up, the mass increases faster than the area. Mass will define load, and area will define load-bearing ability. If load increases faster than load-bearing ability, then we have a problem. For example, if you scale up a building by a factor of 10, it will get 1000 times heavier but it will only get 100 times stronger.
This problem isn't restricted to stress analysis; technological devices which apply force also don't scale with volume. For example, a hydraulic cylinder's maximum force is dependent on the piston area, not its volume. If you take a hydraulic cylinder and precisely scale it up 10 times in every direction, it will be 1000 times more massive but it will only exert 100 times more force. The same is true of biological systems such as muscles, for which the predominant strength determinant is cross-sectional area.
In general, if you scale up an object, its strength will increase with the square of the size multiplier, but its mass will increase with the cube of the size multiplier. That's why Galileo knew, many centuries ago, that there's a "proper size" for everything. You can't scale something up without radically altering the design, and when the size of an object reaches extreme levels, it becomes infeasible regardless of design.
Case Study: The Executor
Executor-Class Star Dreadnoughts are good examples of the engineering difficulties posed by large-scale starship construction. Let's look at the specs:
Length: 17.6 km
Width: ~6.5 km
Thickness: ~1.7 km
The Executor decelerated at a rate of roughly 30 km/s² in ROTJ along with the rest of the fleet, so what kind of force would be required? If we assume 10% solidity and iron construction, the ship's mass would be well over 35 billion tons. In order to accelerate that much metal at 30 km/s², its 13 engines would have to generate around 8E16 N apiece. Each engine is 300 meters wide, so the outlet pressure would be around 1.13 TPa. An engine of such outlet pressure, scaled down to a pair of 10x10 meter squares and attached to the back of, oh, say, a 4.5 million ton starship would accelerate it at more than 50,000 m/s².
Even if we ignore the engines and look only at the structure of the ship itself, it would have to be enormously strong in order to simply survive this rate of acceleration. Let's take its cross-sectional area at the thickest point to be roughly 5.5 million m². If the ship is 10% solid, this would mean there is roughly 550,000 m² of metal which has to withstand a total of more than 1E18 N of force, for a resultant stress in excess of 1.8 TPa (nearly 7000 times the yield stress of structural steel). In fact, even if it were a solid block of metal, it would still have to be made out of a material which is 700 times stronger than structural steel in order to survive the acceleration without permanent deformation!
We also know that the Executor can survive the gravity of a planet even when it's powered down, because an Executor-class ship was buried for years under a mountain range on Coruscant. However, the stresses imposed on its frame from its high sublight acceleration would be much higher than the stresses imposed by the weight of a mountain range, so the ship's ability to survive its own engine output is still its most impressive attribute (particularly during hard turns such as the one in ROTJ, which would impose bending moments on the ship's frame). It must be constructed out of impossibly strong materials in order to hold it together.
(special thanks to Micheal Wong for explaining to me everything involved in space combat)
As for the capital ship, i believe you may be wrong with the capital ship being faster than all the others. it all has to do with newton's third law (hopefully i do not have to explain it), therefore a a small, light frigate needs less energy to move forward and to accelerate than a large, two kilometer long behemoth, although at a certain point, if the engine is large enough and can still fit in the Capital ship, or it can even emit enough energy, the capital ship would be able to move faster than most ships. but then think how long it would take to slow down the thing, and how much fuel would be wasted.
Gravity isn't an issue in space, and its a very weak force even on planetary surfaces. Electromagnetism is the ruling force in space and the bigger thrust of the Captal ship's engines win out.
it is good to go with a slow moving flagship than a rampaging bull. The only stresses the ship itself has to face is stopping and going - no friction in space, and inertia only applies to loose objects that are not welded down inside, but a good artificial gravity and pumping systems for any liquids should solve that.still, we will not be sure what is right and what rules apply to space - and more importantly space combat - unless we prove it in real space, away from any body that emits it's own natural gravity. That will be years from now, so we entrust science and science fiction to answer these questions...by the way, great story, 8/10! I hope you get online soon!
Real scientists and engineers already know what space combat will be like. A cursory google search will show them up. Start with Micheal Wong's excellent Stardestroyer.net or http://www.projectrho.com/rocket/rocket3x.html#nuke for excellent information.