[quote=mdk]
Not necessarily. Planet-to-orbit is a massive energy barrier (I mean you've seen how much rocket it takes to put a shuttle into LEO). Planet-to-interstellar missiles would have to be... I mean.... we're talking *enormous* amounts of power required. The more logical process would be to send tools of production into space -- something like a construction drone, sent out into the asteroid belt to convert space rocks into materials, materials into space stations, stations into shipyards, etc. So what's the advantage of doing something like that, well, A, it dramatically reduces how much mass you need to carry off your planet, which is a big deal. But secondly, it opens the door for space travel as a means of power-projection. Think 'carrier battlegroups' in naval theory.... Carriers are essentially portable airfields, and massive ships like these would function as portable planets. You'd park it in orbit around a sun, and you'd immediately enjoy vast physical advantages over any planet-bound (or planet-orbiting) forces in the system -- primarily, firing weapons from a ship will always consume less energy than firing weapons from a planet, because of gravitational considerations. So, if you can BUILD such a ship -- which only a select few could, on account of (again) physical barriers to access and the costs involved -- you could very conceivably use them to build an empire. For reference the British built a global empire in an era of sailboats and carrier pigeons... these things are certainly possible, for the men who can pull it off.
[/quote]

Except that there are two key differences between a space empire in space and the British empire which was not in space.

[b]#1:[/b] The time disparity isn't even remotely comparable. Even at light speed the closest solar system is [url=http://www.astro.wisc.edu/~dolan/constellations/extra/nearest.html]Proxima Centauri[/url], that's still 4.2 [b]years[/b] away at the speed of light. None of the closest [i]ten[/i] solar systems are even remotely acceptable candidates for life. (At least, life as we know it, and which would be useful for anything from Earth.) This is at light speed. Getting there by modern propulsion would take around... [b]72,000 years[/b]. Even at 1/10th light speed, which isn't anywhere near achievable for humanity at the moment, it would take us 42 years to get to the closest system, which isn't remotely inhabitable.

Maintaining an empire when it would take decades, or even centuries, to just send and receive orders, would be insanely prohibitive to the maintenance of any sort of long range space fleet. Leave alone the fact that during the reign of the British Empire, technology moved slowly. If technology continues to change and upgrade at the rapid pace it is now, even 10-20 years from now the targeting computers used on those war ships would be antiquated toys put into calculators for small children. And yes, for space combat, at the sheer range that it would go on at, you would need targeting computers, human beings wouldn't cut it.

[b]#2:[/b] Then there's the fact that despite the higher cost of firing defensively from a planet against an offensive fleet, planets have two advantages that fleets do not have.

[i]#1:[/i] Fleets would be easy to see coming from (literally) decades away. Especially since you can't hide heat in space, one of the [i]coldest damned places we know[/i], because even if you can disguise ships with heat retaining alloys, you certainly can't do that for your engines, which have to expunge heat emissions. Unless you invent an engine or method of propulsion not driven by heat, in which case, by then, technology in general will have evolved to the point of being able to monitor the entirety of the night's sky through networked satellites.

[i]#2:[/i] Planets don't realistically run out of ammo. Ships certainly do. At least, ships would far, [i]far[/i] sooner than planets would. Because push comes to shove, you could fire giant rocks into space to intercept incoming missiles using advanced targeting computers and it would do the job.

This is not mentioning that it would still be cheaper to mass produce cheap interception methods to ballistics weaponry and arm them on satellites/fire them into space manually, than it would be to mass produce war fleets capable of laying siege to an entire planet. Especially if you use those same construction ships/drones to just... Drag the asteroids back to the planet and build even more satellites and ammunition in orbit... Instead of wasting a significant portion of it on hulls, engines, fuel, etc.

Traditional fleet combat, or ballistics weaponry, when put to the sheer scale of space, is irrelevant nonsense. Wars would be fought on a planetary scale, because fighting over the sheer amount of distance in space would be insane and impractical. Especially since there's quite literally vast emptiness between you and the incoming fleet, so it's not like you can't see them coming.

Now if you can break the light speed barrier with ships, then fleet combat comes back into play, because you can't see them coming... But if you break the light speed barrier, you just broke the back of one of the key principles of hard sci-fi, and moved into soft sci-fi. Something far more malleable. :sun

EDIT

Though I suppose I should quickly expand on something I said before: "From my primitive point of view." What the future holds is likely so far beyond my comprehension as to make it outright alien to me. With the way technology and society is marching on, who could have imagined instantaneous communication available to everyone across the entire planet for just 10 dollars a month? Or access to the entire world's vast collection of public knowledge in over twenty different languages, all accessible in your pocket? Such things must be like magic to men of a hundred years ago. A hundred years from now, the technology we will have will be like magic to a very likely dead me. Leave alone two hundred or three hundred years from now.

All I can do is contemplate the future and all its potential wonders. I will never [b]know[/b] it.