Jon replied to me: > Check to see if some sort of space sail can be used to improve fuel > efficiency; at the very least, a mag-sail should be able to save on > fuel by acting as a braking system. The question is if it will save > enough fuel to be worth its mass.
Good idea, but I don't think the numbers work out. To brake a 15,000 ton ship from 0.02 c in less than a decade, I need 63 tons of magsail thrust -- more than 10,000 tons of sail. That mass is better spent on reaction mass for the existing drives. The new Spaceships rules are much more friendly, but I want my design to work in both editions. > If you're going for a generation ship, consider the Habitat modules > from VX2 (I think). You might even go with a small metallic asteroid > reshaped into a hollow cylinder: sure, it's a significant amount of > mass; but it's also a wide-open space, which will benefit the > colonists. Those modules are from GURPS Traveller, IIRC, not part of the official Vehicles 'canon' ... > Instead of installing ten fusion reactors to power the ship's systems > for 2000 years, just carry additional reactor fuel. It certainly > won't mass anywhere near as much as nine additional reactors. And Roger wrote regarding that: > It all depends on whether the limit on the reactor's lifespan is fuel or > embrittlement of the components. I'm inclined to assume it's set up to > be both; this suggests that refuelling a reactor wouldn't work, but that > the lifespan is from ignition. > > I suspect, though, that you could get away with three reactors: one > live, one hot spare, and one undergoing maintenance. Add a big > workshop... But can the workshop rebuild fusion reactor parts? By giving them 200 years of fuel, Vehicles implies that fusion reactors can last at least that long without a total rebuild. GT Starships has more detailed rules, but again those might be setting-specific. Besides, I'll get away with 10 MW for a 200-man ship, mostly life support and radar, so a TL10 reactor is just two tons. And I would have to pull the stats for reactor fuel out of thin air, too. Back to Jon: > GURPS Space gives advice on the minimum population for a start-up > colony; your generation fleet (it needn't be one ship, and probably > shouldn't be) should probably have a bit more than that. After all, > the fleet itself is essentially a colony already. 4E Space suggests 10,000 colonists. My tentative numbers come in at $20M per person. Ugh. And HK Piter wrote: > You might want to check out GURPS Biotech for 4e. One of the > sample game backgrounds details a kind of Generation fleet that > journeys to Draconis or some star like that. They used hollowed > out asteroids hollowed out and fitted with fusion engines for > the ships, and a comet mounted with fusion engines for spare > volatiles. Since you want to make a ship, make the ship, and > just have a spare asteroid and/or comet mounted with engines as > a mini fleet. Two objections to that. The Biotech fleet was written to make a Biotech background, with some iffy reasoning -- why would faster growth make the fleet run out of heavy metals, but not out of volatiles which were ALSO required for braking? And those ships are on the scale of towns, not on the scale of vehicles. _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
