Idea for FTL

[VarrusTheEthical]

Space fortresses do exist in my setting, I just call them planets. From the point of view of an invading fleet, a planet is a gigantic carrier and missile battery. You could have tens of thousands of missile bases buried into the planet's mountains, and on wet ships or submarines in the oceans. Since my missiles use the same drives as starships, they have the range to pelt a fleet from a distance. And they would never run out of missiles because they could just build more. The main issue would be fueling them. The planet can also sortie fighters against the enemy, attacking either the fleet itself or it's supply line, since fighters have the range an endurance to go pretty far.

It is a massive undertaking overwhelm a well defended, industrialized planet. Usually when a fleet invades a system, it's not to do anything to the planet itself, but to establish local space superiority and the destroy as much space based industry as possible. Solar power statites, space factories, ship yards, orbital gas mining. Basically the objective being to destroy the system's ability to project interstellar power, rather than conquest itself.

Now since I'm a space fighter fanboy, in my setting I think the way they would deal with a space fortress is to use a massed fighter and bomber attack. The objective would be to try and disable the largest weapons with saturation nuclear strikes by the bombers. The fighters would work to try and suppress the point defenses of the starfortress, as well as any fighter screen it may have. Once enough of the fortress' firepower has been disabled, I would move in my battleships, using their main KE weapons to bombard the asteroid as they approach. Once I get a few battleships close enough, and felt that the starfortress' defenses were weak enough, I would have the battleships turn their drives on the starfortress, roasting it until the surface melts.

[Number Theoretic]

Another argument in favor for space fortresses is waste heat managment: the whole asteroid can be used as a heatsink, which allows you to install and operate waay more terawatt-range lasers than any battleship could afford. Because of the much bigger heatsink, it can fire the same number of lasers as a battlefleet for a longer time, before heat needs to be radiated away. And of course it can easily fire as many missiles as the whole battelfleet.

The only thing, that can be a real danger to space fortresses - well, apart from a really big invading fleet - could be a relativistic kill vehicle that flies insanely close to the speed of light. Calculating the necessary fraction of c to escape a given reaction time is left as an exercise for the reader but in theory, it could work: you only know that a laser hits you when it's too late. Which can be approximated, given that the energy necessary to shatter an asteroid is extremely high. Put into kinetic energy, the resulting kill vehicle can be unstoppable, given that the fortress does not expect the
assault from a certain direction. Becaue then, it can be averted by the interceptor drones mentioned by Destructionator.

[Purple]

Hm... a hypothetical question. How much do these missiles of yours accelerate? And what's their mass? I mean, I can't see it being pretty for the environment when millions of rockets all fire at once no mater what drive you are using.

[VarrusTheEthical]

@ Purple

Well, say the missiles are about the the size of a Delta IV rocket. 60m tall, 5m diameter. I would assume a chem rockets for the first stage to get the rocket safely out of the atmosphere before lighting its fusion drive. As for fusion drives, aneutronic reactions such as He3-deuterum would be preferable, but a dirty deuterium rocket would also work in a pinch. And to be fair, I doubt even a million rockets would be as bad for the atmosphere than say, cool-fired power plants. At least as long as you don't use the nuclear drive in the atmosphere.

I'd imagine a the fusion drive would be throttle able. If you're target is far away, 1g acceleration should be sufficient. If you keep that acceleration constant, it would be less than two hours before you crossed lunar orbit. On terminal approach, or if the enemy close at launch, start moving at up to 20-30 gs? Perhaps it could be a 3 stage missile, first stage is a chem booster, second stage is a 1g "cruising" stage, and then a third stat 20-30g terminal stage?

At the velocities such a missile could reach, you may be better served by using kinetic kill vehicles rather than nukes.

[Number Theoretic]

How about a shaped charge nuke? Your missile might then need to aim in the right direction for the shaped charge to be effective, but it reduces the danger, that your nuke gets shot down by PD before it can get into effective range.

[VarrusTheEthical]

Shaped charge nukes are the norm of my setting. The primary munition for a space bomber, for example, is a freefall space bomb with a shaped charge. A squadron of 12 bombers can drop a little less than a 150 warheads in an expanding cone, that a sluggish vessel like a battleship typically will not be able to escape. Further, because the bombs are completely passive and covered in radar absorbent materials, they would be harder for PD to detect, track, and destroy.

[VarrusTheEthical]

Note: battleships were actually pretty fast, historically. There's a lot of the same scaling factors that apply to space too - there's really no reason that a battleship needs to be slow, and there are reasons it can do better than smaller ships.

Well its not that Battleships are slow, they just don't have great acceleration and cant change their vector very fast. The logic is that with battleships, the emphasis is on the heaviest armament and armor possible at the expense of performance. One G of acceleration is considered enough because it will get you where you need to go pretty quickly and provide comfortable gravity for the crew. If you want to have a ship that's quicker on it's feet, your going to need to sacrifice either guns or armor. Which is essentially what a battle cruiser is.

Also, since battleships are the biggest warships, you're going to run into problems with scaler laws. The largest battleships are already going to be pushing the limit of my setting's material science. You have to remember that if a 10 megaton starship is accelerating at 1g, that means there's 10 million tons resting on the engines. So if you try to push the ship to higher accelerations, then run the risk of essentially having the whole ship collapse on itself. Since fighters and bomber are only about 150 tons, they can get away with 10g+ without the same issues as larger ships.

Also, the reason I need carriers is because space fighters and bombers are too small for FTL drives. In normal space, fighters have almost indefinite endurance. The pilot can be kept in hibernation during any downtime, only to be awoken during combat.

Though to be honest, I want Space Fighters because they are really cool.

[VarrusTheEthical]

In regards to space fortresses, I think that a planet has all the advantages of an asteroid based fortress, but on a far larger scale. And the atmosphere of a planets is more of an advantage than a liability to me. It's an added layer of protection against both lasers and kinetic weapons, and will help hide your land, sea, and air forces. As for sensor issues, that can be mitigated by the use of satellites, or even high flying aircraft. And if the enemy shoots down your sats? Build new ones and launch them into space with cheap chem rockets.