Thermal turbojet power all depends on what type of turbowhatever it is, how strong the reactors are, and what it's using as fuel. If I remember correctly, a true thermal turbojet gets all the power it needs from a reactor directly, no fuel involved, it just uses the air it sucks up as 'fuel'. A turborocket (and thermal turbojets can be made to have multiple 'running modes', so whatever), instead just uses a 'fuel' (like liquid fuel or water) directly.

And yes, they can be really goddamn strong as long as your reactors are good enough. HOWEVER, the main thing isn't thruster POWER, it's thruster EFFICIENCY. that's where turbojets/turborockets can be shit if your reactor isn't powerful enough and you don't have air to burn through: they can get really inefficient, really quick. But, with advancements in reactor technology like I suggested, you could just make the thrust so high, the technical fuel efficiency wouldn't matter.

It could just be that spaceships and stuff have thermal turbojets to use in atmosphere, yet use super-high-efficiency 'Plasma Thrusters' for use in space travel. Acceleration is slower, but space travel can already be slow, so it doesn't really matter if you add another week or two to your interplanetary burn. Plasma Thrusters, while power-hungry as fuck, could also be powered by something that ISN'T onboard, like microwave energy stations.

That'd be a really cool piece of fluff, actually: Spacers have to pay a sort of 'tax' to help maintan giant microwave power stations in orbit around every planet, and in return they get to actually use that beamed power. How it actually works though, basically, make a big-ass reactor, right? Put it into space, then add some giant microwave transmission dishes to it. Aim one of those to the spaceship who requests beamed power. Flip the switch.

On THEIR side, they'd have to have a 'recieving' dish that could transmit the heat energy to simplistic, lightweight onboard generators, (reactors and generators are different things, actually. i'll explain later), which would use the heat energy to generate power for the plasma thrusters.

Then, you wouldn't have to worry about bulky reactor technology to power your plasma thrusters atleast, (though you'd still need one or two for your thermal turbojets), you could just 'rent' power.

And how generators/Reactors work, in extreme laymens terms... Reactors use nuclear fission or fusion, or antimatter, or whatever, to basically make a an amount of heat or particles. They're then put into a generator, which uses that heat or particles to generate power. In essence, flame is also a reactor. A flame-based purification method, would be a 'generator' (but instead of power, it'd 'generate' water).

So, that's how I'd imagine spaceships could work. For atmosphere, just flip on your primary reactor and the attached turbojets, for space, flip on your reactors, OR, just rent some power, to feed your plasma thrusters.

It probably makes no sense, but whatever.

Edit: oh, also, for plasma thrusters and beamed power, you could simply use the space on your spaceship that WOULD be used for reactors and shit to power the plasma thrusters, if you're using beamed power, you could instead simply use that space for more fueltanks and stuff. That's why I think they'd be used for space travel. :S