Using GURPS Spaceships as a model: Onno Meyer wrote: > * STL uses a range of reaction engines (plus lightsails for exotic > jobs). Usually fusion rockets or optimized fusion rockets, since > water reaction mass is almost free. Fusion rockets are relatively > easy to detect. > > * A typical commercial craft is 33% unloaded ship, 33% reaction mass > and 33% cargo. If it goes from low orbit of one world to low orbit > of another, travel speed is a quarter of total delta-V, about 16 > km/s. That means each STL trip means a week or so of coasting.
6 fuel tanks for a fusion drive would get you 29 mps (46 km/s) of Delta-V for a TL9 fusion rocket using water, and an acceleration of 0.015G per engine system. An average trip would involve roughly three days of burn-time overall (during which your average speed would be 7mps), and an indefinite number of days of coasting time (during which your average speed would be 15 mps). During the burn-time, you'd cover 0.02AU; during cruise time, you'd cover 0.015AU/day. For ships that take multiple drive systems, divide the burn-time by the number of systems taken, and divide the burn-time distance by the square of that. Rapid-response military ships might splurge and go with a TL9 Orion Drive; Delta-V would be the same (though much more expensive), but acceleration would be 2G per engine system - not useful for speeding up the long-distance travel times by much; but potentially quite useful in the firefight, if for no other reason than that they can dedicate more of their hull mass to weapons and armor. Burn time would be just over half an hour, during which no appreciable distance would be covered; cruising speed would still be 0.015AU/day. Except... Instead of lightsails (0.0001G per system), go with magsails (0.001G per system); rapid-response ships might even be equipped with a Mag-Orion combination, generally using the magsail to get around when there's no urgency or to speed up the so-called cruise time; such a system would generate approximately 0.54 mps per day of mostly free delta-V per magsail system. One week, and such a system would match the total delta-V of one fuel tank. Indeed, such a ship could plot an "intercept course" that involves using up all of its fuel to get to a ship in transit, moving at an average speed of 0.022AU/day (50% faster than normal) before accounting for the mag-sail, and then rely entirely on its magsail to get home afterward. In fact, the mag-sail is useful enough that civilian ships might invest in it, too. And if the average travel time is over a week, it would probably be worthwhile to replace one of the fuel tanks with a magsail system: same or better effective delta-V, probably an improved travel time, and more of a safety net if something goes wrong. Just don't lose the magsail. > * FTL is by hyperdrive. Hyperdrive works only far away from planets > and suns (to the order of 10 million miles / 0.1 AU). Hyperdrives > are fairly precise, very hard to detect, but come with an > inconvenient calculation/preparation time. A commercial ship would take roughly six days to reach a 0.1-AU threshold, and then another six days to approach the destination. Minimum interplanetary travel time looks like it would be closer to two weeks. > * Pirates are up to 60% reaction mass, three times the delta-V, and > they go to the trouble to refuel in the outer system before a > hunt. Note that military ships can do likewise, and with vastly superior acceleration. > The pirates lurk just outside the FTL exclusion bubble, with a > constantly updated 'hyperdrive solution' to jump out. They wait > until an inbound freighter has burned the third quarter of its > delta-V reserve before they try an intercept. > > The freighter might detect the pirate and call for help, or there > are patrols out there, but the numbers game makes it likely that > the pirate can intercept the freighter before a warship can get > the pirate. Dumping cargo is an option, but then the pirate can > try to salvage the abandoned stuff (possibly even legally, since > it did nothing more illegal than speeding). The pirate is going to have to burn a considerable amount of delta-v matching vectors with the target, since said target will probably be moving outbound from the planet at 0.015 AU/day, or more. The good news (for the pirate) is that the target probably won't have the delta-v needed to evade. -- Jonathan "Dataweaver" Lang _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
