Speed drives only make sense when there is a static frame of reference. The classic version that we all have a degree of experience with is the road. When a thing is moving with respect to such a frame of reference, it's quite possible to bleed that difference for energy - there are electric cars that do it all the time with generator braking. The thing that drives the hardtech scientists adsolutely batty and/or fascinates the hell out of them is that they can't seem to touch this *particular* frame of reference with anything that isn't at least a good 10% or so handwavium - and anything that *has* handwavium is, by its strange and inconstant nature, *entirely* unsuitable for performing repeatable experiments with. They've been trying anyway. When they do use the 'wave, they've found, the results perfectly support whatever theory the professor has espoused most recently. In a couple of cases, behavior has changed dramatically, multiple times over the course of a single experiment, as he was "trying to explain". A small but growing group of researchers have decided that the only conclusion that makes sense is that scientific devices, when exposed to handwavium, must frequently develope rudimentary sentience and communications abilities, but hide them, and that those stealth AIs have a prediliction to *like* the professor, or perhaps are merely easily persuaded by him.
Thrust accelleration: First, I apologize for the sheer fuzziness of the following math. I will be rounding like a bad man. Now we have a "pretty dern close to top speed" speed drive maxxing out at about 0.1c with maybe a bit more for making the ship Really Rather Small and the engine Really Rather Big. Engines can be optimized a bit for either high-grav or low-grav, and the asteroid belt is pretty much always going to be low-grav. Lets say your average speed-pure racing hull has a top speed on the flats of .12c and isn't good for really much of anything other than racing and, perhaps, escape/evade/high-speed courier work. (this is a *conservative* estimate). You can amp that up further with the right sorts of Wacky And Experimental Tech, but those inevitably have equally wacky drawbacks that you get to wrestle with *while* hurtling from point to point at your ship's top speed. Let's say that *your* hull, as it's not a pure speed-build, only manages to drag 0.11c out of its drives. This isn't as bad as you might think, because people aren't rolling along at top speed on the maneuverability challenges anyway. In those cases, the limiting factors are pilot reaction and ship responsiveness - and if you push out too far and fail, you tend to pancake yourself on a rock. So, you're out on the flats, up against some guy in a generic speed build. He cranks it up to 1.2 at the same time you crank it up to 1.1 and you're off. Obviously, you want to beat this guy, and your baby is going to take a few moments of careful massage to rev up to top speed and then disengage the speed system and fire up the accelerator. In order to beat this solidly, you want to pull out a coasting speed of 1.3, and for whatever reason, you can afford to shove about 10% of your total ship's mass out the back for this particular leg. You're going to have to shove it out at about .2c to get the job done. If you need to use it to decelerate any at the end, that's going to be 5% here and 5% there, which means .4c relative for the stuff pouring out the back. This is potentially doable, given exactly the right rolls on the "nifty handwavium devices" table, but it does have some implications. At least it's something to think about.
Thrust accelleration: First, I apologize for the sheer fuzziness of the following math. I will be rounding like a bad man. Now we have a "pretty dern close to top speed" speed drive maxxing out at about 0.1c with maybe a bit more for making the ship Really Rather Small and the engine Really Rather Big. Engines can be optimized a bit for either high-grav or low-grav, and the asteroid belt is pretty much always going to be low-grav. Lets say your average speed-pure racing hull has a top speed on the flats of .12c and isn't good for really much of anything other than racing and, perhaps, escape/evade/high-speed courier work. (this is a *conservative* estimate). You can amp that up further with the right sorts of Wacky And Experimental Tech, but those inevitably have equally wacky drawbacks that you get to wrestle with *while* hurtling from point to point at your ship's top speed. Let's say that *your* hull, as it's not a pure speed-build, only manages to drag 0.11c out of its drives. This isn't as bad as you might think, because people aren't rolling along at top speed on the maneuverability challenges anyway. In those cases, the limiting factors are pilot reaction and ship responsiveness - and if you push out too far and fail, you tend to pancake yourself on a rock. So, you're out on the flats, up against some guy in a generic speed build. He cranks it up to 1.2 at the same time you crank it up to 1.1 and you're off. Obviously, you want to beat this guy, and your baby is going to take a few moments of careful massage to rev up to top speed and then disengage the speed system and fire up the accelerator. In order to beat this solidly, you want to pull out a coasting speed of 1.3, and for whatever reason, you can afford to shove about 10% of your total ship's mass out the back for this particular leg. You're going to have to shove it out at about .2c to get the job done. If you need to use it to decelerate any at the end, that's going to be 5% here and 5% there, which means .4c relative for the stuff pouring out the back. This is potentially doable, given exactly the right rolls on the "nifty handwavium devices" table, but it does have some implications. At least it's something to think about.