((OOC: we have basic fusion now that can produce as much power as it takes in.
Nope, We don't. We don't even have operational fusion plants that can theoretically produce energy. The National Ignition facility reported that they would reach a theoretical break even before the end of last year, but they didn't. Iter will have a ten for 1 ratio, but is far from finished, and hasn't got a generator to retrieve the energy.
And i think really the only way we could travel quickly in space is to have Fusion.
The Vasimir and it's cousins might be plasma based engines, but those don't need fusion. Besides, a standard fission drive works too and is vastly cheaper, and safer.
Also, yes, the big plant has a nuke plant. Fusion-fission hybrid.]
And what might this be? I mean, fusion and fission operate on vastly different principles and with tremendously different temperatures. Combining them is nearly impossible, and always a bad idea. It's essential that a fission plant doesn't go over a 1000 degrees (depending on reactor type. But even gas based fission doesn't go above 10 000). Fusion meanwhile, occurs at temperatures of 15 million degrees (in the sun), or at 150 million degrees in human build plants.
[So, first off, we aren't on an alien planet. We're on Mars. We've colonized it way before the Kai arrived(evidenced by holdfasts). Secondly, we sure as hell better have fusion, and I wouldn't put it past having antimatter reactors, because my melee weapon fucks with gravity. Unless we managed to steal that from the Kai(which has a shitton of other implications), the technology is pretty far advanced, especially what with the part where there's space battles(boats weren't commonly used for fighting in the way we think of it for a long ass time). We can use a factory, but we can use it for a short period of time, then sabotage it and run like crazy fuckers with tanks that we built in the factory.]
It might be called a gravity hammer, but that doesn't mean it actually manipulates gravity. Marketing terms exist after all. A magnetical or gyrostability effect seems much more likely. Otherwise you'd have a massive plothole. Though if we do have gravititational technology, fusion becomes a lot more effective, and vastly more dangerous. Most importantly, you could dramatically increase the pressure at which it operates, turning it into a miniature sun.
Don't forget that the factory contains massive amounts of enemies. It's probably working full time for them.
[Nope. Possible? Yes. Vast amounts of energy? Yes. Dangerous as fuck? Yes.]
[It's something that would, like, power a Deathstar or an Orbital Military Academy. It's too dangerous for almost any use. Highly-efficient sol-voltaic(meaning a combination of photo- and thermo-voltaic that relies on sun/star light), well protected fusion generators, the fuel-less zero-point energy generators, and even coal power plants would be preferred. Coal plants don't explode if someone trips the wrong breaker.]
[But I do still like the idea. It'd probably have a fusion plant attached to kickstart the particle accelerator, which would create antimatter which would be annihilated as soon as it was created to prevent a buildup. The net gain comes from the fact that creating the anti-matter takes energy, but maybe 120% of the energy that is released by the anti-particle, and the energy comes from the annihilation of the normal particle. Safety measures would try to ensure that you know, people didn't explode just for existing near it. Gravity fields would be a requirement, the particle accelerator would have to be able to shut down at a moment's notice to prevent creating anti-matter when the energy can't be harvested.]
[I think of it like a continuous EPG]
Sadly, 50% of a matter anti matter reaction's energy is released as unusable fast particle neutrons. Also, you could increase the efficiency massively, by taking away the middle man (antimatter) and just firing the PArticle Arcellerator at a fissile material of choice.