It's nice to be a gov't employee who's got the day off due to the inauguration of a new boss! Means I've got time for a long post.
I haven't seen any source that indicates or suggests that spaceships use repulsorlift for traveling through space. And ships have been known to travel in the middle of nowhere, very far away from any object...
There are several. The best is the Battle of Coruscant in RoTS. Take a look at the apparent size of Coruscant, how it doesn't move under the combatants, and really watch what happens to the Invisible Hand as the battle progresses. If Coruscant is roughly Earthlike in size (and sources appear to agree that it is)...then you can conclude several things from watching that battle:
1. The part we see in the movie takes place roughly several hundred kilometers up (you can tell from the amount of sky it takes up)
2. The part we see in the movie takes place in a *stationary* location above Coruscant. This is confirmed by the novelization.
3. These two things mean that those ships aren't "in orbit" in the true sense of the word: i.e. they're not flying around the planet so fast that the force of gravity on them is counteracted by "centripetal force" (quotes because it's not really a force in a physics sense).
4. If the ships are not in orbit, something is exerting force on them to hold them at that altitude. If it was rocket propulsion, their nozzles would probably be pointed at the ground yet most of the vessels are "level" with respect to the horizon. The repulsors are the ONLY other propulsion system mentioned in canon sources. Note that (when Invisible Hand loses power, she starts falling out of the sky. Also, note that local gravity on Invisible Hand becomes "down" i.e. where Coruscant is. That would not happen if they were in orbit. They'd be "weightless". Instead, when the ship pitches forward, everything falls to the forward bulkhead).
5. Finally, the planet is turning beneath them yet they are staying over one place on the surface. Yet all the ships are pointed everywhich way. If they were using rocket propulsion to stay over the same spot on Coruscant, they'd need to all be thrusting the same direction, meaning they'd all have to point generally the same way. This implies that they can use their repulsors to provide some lateral acceleration in addition to the force just holding them in the sky.
There is also a piece of written G-Canon (the Star Wars novelization written by "G" himself). Page 115-117 gives the range of repulsorlift operation from a "typical" habitable planet is six planetary diameters. Read the
wookiepedia article on repulsorlifts for a slightly more complete statement...though it doesn't quote the actual original novelization source. Saxton quotes it on his website
as well here. Read the section of Saxton's Technical Commentaries on
ISD Propulsion. He also thanks a Mr. Ken McClintock for reminding him of the importance of repulsorlift for planetary operations...but all this was written long before RotS and there's nothing on the Technical Commentaries site yet about that battle.
Don't get me wrong: Dr Saxton is a brilliant guy and I love his stuff...but...he's an astrophysicist not a rocket scientist. He appears to study natural relativistic jets...I can't blame him for looking at the ISD's ion engines because they're basically just artifical relativistic jets. *I* only noticed it on my third viewing of RotS. And the only reason that I noticed it at all was I'd gotten two postgraduate level degrees in spacecraft engineering and astronautics since the first time I saw the movie (yes, I am a poster child for Navy education. They've been very very nice to me. Go Navy!). You really have to think about this stuff alot before it all clicks. Specifically, one class project in trajectory analysis that a buddy of mine and I did was figuring out how much rocket thrust you need to "hold yourself up" in low Earth orbit. It's ridiculous and you couldn't do it for long with any rocket I'm familar with (including theoretical fusion or antimatter rockets).
And ships have been known to travel in the middle of nowhere, very far away from any object...
True. That's why they *also* have rocket propulsion.
I've considered doing this, but I think it would be potentially unbalancing; it'd probably work better for a game with true 3D battles.
I wouldn't change a thing. The reason I like the repulsorlift theory is that it makes sense (assuming repulsorlift is possible at all) both from an "engineering" perspective as well as following continuity in the games. If tweaked right, repulsor as primary drive allows everyone to be "correct". Your EAW/FOC battles all take place WELL within Lucas' "six planetary diameters" if the worlds are roughly Earth like in size so you're fine.
But one you pass a certain speed, it would be impossible to engage an enemy in combat, so let's just consider each unit's top speed as the top speed for effective combat operations.
That's a good one that I've not heard before! Works very well on first blush...have to think about it some more.
Wook seems to favor it being the top speed to prevent significant micrometeorite damage...
You can look at the energy of micrometeorite impact and SW particle shielding should be able to stop it. If they can survive flying through the relativistic jets behind their own cap ships (watch, they do) then a micrometeorite impact is nothing. IMHO this explanation is not useful.
Speaking of trench runs, if there really is no top speed barrier, wouldn't the numbers on the targeting computers go down at an increasing rate (which I'm not sure they do), or does the proximity of the Death Star somehow muddle that logic?
Yes...if Luke's "we're going in full throttle" means "max acceleration" the numbers should go down at an increasing rate. The DS proximity might limit relative speed because it will take a certain amount of time to pull out of the run.
Edited by feld, 20 January 2009 - 05:25 PM.