Re: Snow-trail drive

Alex Holden wrote:

I'm not sure why the fuel needs to be "at rest". During the acceleration phase, the fact that the fuel is already moving in the direction of travel (and the nearer to the end of the trail you get, the faster it is going) reduces the velocity difference between the colony ship and the fuel, which reduces the drag. When decelerating, the fuel is moving towards the colony ship, which increases the drag, but that's exactly what you want. Whether it would remain in alignment after it's been dropped or tend to drift away from the intended trajectory is one of the things I'm not sure about.

If it's not "at rest," it's moving at interstellar speeds, and the ship can't catch up with it. If it's just left at the current speed of the seeder ship, then the different chunks are moving at different speeds, making the problem worse. Either way, even in the best case, the fuel chunks that this ship is going to catch are going to be massive (if they weren't massive then there would be little benefit) and moving very fast relative to the main ship -- tens or hundreds or thousands of kilometres per second.

Engineering the "catcher's mitt" is the tricky part, but at least it's much more likely to be buildable in the near future than a Bussard Ramjet scoop.

That's not really saying much, since Bussard ramjets are nearly pure fantasy at this problem. In fact, they have a very similar major engineering problem, which is collecting interstellar (or intergalactic) hydrogen moving at relativistic speeds relative to it.

During the acceleration phase, collecting the fuel imparts a drag similar to the force you'd need to exert if you'd carried the fuel with you (not quite as large, because as already discussed, the fuel is moving in the direction of travel), but you gain because you don't need to carry an asteroid sized fuel tank with you in order to "burn" an asteroid's worth of fuel, and you don't need to carry fuel or a tank to carry the fuel for the deceleration phase, or fuel to accelerate the fuel you're going to use for deceleration.

Well, you don't gain that during the acceleration phase. Both are equally important.

I don't know enough to guess if in the future fusion motors will be able to be fueled by Hydrogen extracted from water. If they won't, then the fuel will need to be carried with the ship, but at least you save by not needing to carry the reaction mass with you.

Extracting the hydrogen means electrolysis, which means using energy, which means using fuel! Now you're adding more inefficiency factors into the mix.

A decent fusion drive is already easily capable of 0.1 c deltavee with no difficulty. An efficient one could handle 0.2 c. Very efficient ones might be able to get to 0.3 c or 0.4 c (with a ship that is mostly fuel, giving very high mass ratios). There's really no need for this convolution.

--
Erik Max Francis && max@xxxxxxxxxxx && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
  But since when can wounded eyes see / If we weren't who we were
  -- Joi
.

Relevant Pages

  • Re: Snow-trail drive
    ... Either way, even in the best case, the fuel chunks that this ship is going to catch are going to be massive and moving very fast relative to the main ship -- tens or hundreds or thousands of kilometres per second. ... The main ship won't have any trouble catching up with the ice crystals because it will be using the fuel supply to accelerate at a much higher rate than the trail-layer did. ...
    (rec.arts.sf.science)
  • Re: How to get Chelsea Tractors off the Roads
    ... Moving the goalposts again? ... rather shows up the 'official' fuel consumption figures. ...
    (uk.rec.driving)
  • Re: more whining
    ... If it keeps moving, tax it more. ... The truck driver said they had a serious ... said, no - he actually buys fuel from out-of-state ...
    (sci.electronics.design)
  • Re: Snow-trail drive
    ... interstellar space, drop material such that it will be at rest with respect to the two stars? ... phase, the fact that the fuel is already moving in the direction of travel reduces the velocity difference between the colony ship and the fuel, which reduces the drag. ... When decelerating, the fuel is moving towards the colony ship, which increases the drag, but that's exactly what you want. ...
    (rec.arts.sf.science)
  • Re: space travel
    ... I'm still not moving. ... well here goes, i make my mega-uber-space ship warp both space and time, ... it take atleast 2 month to travel to mars today. ... > we biuld somekind generator which stretch out the spacetime continuum ...
    (sci.space.policy)