How to determine a good star travel speed?

[Xavier Onassiss]

There are a couple of ways to deal with "in system" travel and FTL drives. Having a lower limit on distance traveled is one. Another is to go the route used in Traveller: the FTL drive won't work if it's too close to a planet/star. And the drives used in 2300AD work at sub-light speeds when they get close to a star/planet. You could also put a minimum "transit time" on hyperspace jumps, which would quite often make it faster to travel in normal space, if the ship has a good torch drive.

 

I went with a variation on Traveller's method: FTL drives won't work within a certain distance of a planet or star, but this varies with ship size. Smaller vessels can operate their drives much closer in, while larger ones have to shut down their drives farther away. Multiple FTL drives in close proximity will also interfere with other: the larger the drives, the greater their zones of interference. Aside from that, I allowed FTL travel within a system. Using the drives I mentioned above, travel times range from 5 to 8 seconds per AU. (Followed by a lengthy shuttle ride from wherever your FTL drive shut down to your final destination....)

 

The above guidelines yielded some interesting results:

 

Small starships can emerge from hyperspace within striking distance of a planet's surface, but large ones can't. No "first strikes" by massive war fleets.

 

A "first strike" mission can only have so many small starships; their FTL drives will interfere with each other.

 

It's fairly easy to prevent "first strike" missions by parking one large ship with an FTL drive in low orbit over a potential target. Its FTL drive will bollix up the drive of any approaching strike ships.

 

A large warship can't operate in close formation with other large warships; it needs to carry its own close escorts. (But there aren't any "fighters" in this setting; they're fairly large gunboats.

 

Bulk cargo carriers and large passenger vessels can't reach the habitable zones of most systems; they must rely on deep-space way stations and FTL shuttles to transfer passengers and cargo to and from the system's main population center.

 

The small-ish starships which Player Characters tend to operate can escape pursuit from larger vessels by jumping into the "shallows" of the system where the larger ships' FTL drives won't operate.

 

Blockade runners, smugglers, etc. who are "just passing through" and wish to avoid being intercepted by system patrol vessels have very limited time. As soon as they emerge from hyperspace, the energy from their emergence (it's a highly visible signature) begins to propagate through local space, at 500 seconds (8.33 minutes) per AU. So the clock is ticking, and they have to re-calibrate their drive and transit out-system again before the interceptors spot it, or they've got a fight on their hands. (If the local squadrons have FTL, they'll reach the PCs' ship quickly once they spot them: 5 to 8 AU per second as stated above.)

 

So I've gotten a lot of mileage out of in-system FTL in my campaign. Individual results may vary.

[sinanju]

Regarding "first strike" capabilities, something we see in David Weber's Honor Harrington universe is something I think would be fairly common in any space-faring civilization. The "Eridani Accords" are a (virtually) universally-agreed treaty. ANYONE who uses a kinetic kill weapon (i.e, throwing or dropping big rocks) on a habitable planet will be hunted down and exterminated by EVERYONE ELSE. And they'll stop whatever else they're doing (including fighting with each other) to do it.

 

Such attacks can be very hard to see coming and difficult-to-impossible to stop. After all, it's just a big rock flying through space without power, and if it is being used a weapon (as opposed to simply falling through the system like a normal asteroid) it could be traveling at godawful speed, making that much harder to detect (or stop if it is seen) before it strikes.

 

 

[Xavier Onassiss]

I've always wondered how the Eridani Accords would be enforced. Relativistic weapons are not only difficult (or impossible) to detect or stop; they can be hard to trace as well. And I'm wandering off-topic a bit here....

 

Hyperspace travel raises a similar problem with regards to first strike capabilities; it might even make things worse. Accelerating a projectile close to light speed takes a lot of time and energy, but opening a "jump gate" for your war fleet to emerge a kilometer above the enemy's capitol city could be a lot faster and easier. (Basically, it comes down to what universe you're in, and how careless the author is.) And again, in a setting where this sort of thing is possible, how would a treaty banning it be enforced? Better to come up with a good reason to explain why it's just not possible, period.

[sinanju]

I've always wondered how the Eridani Accords would be enforced. Relativistic weapons are not only difficult (or impossible) to detect or stop; they can be hard to trace as well.

 

Good question--and good point. In fact, without too much of a spoiler...such a weapon does get used in one of the books. And yes, trying to figure out who did it is much harder than anyone thought.

 

And I'm wandering off-topic a bit here.... Hyperspace travel raises a similar problem with regards to first strike capabilities; it might even make things worse. Accelerating a projectile close to light speed takes a lot of time and energy, but opening a "jump gate" for your war fleet to emerge a kilometer above the enemy's capitol city could be a lot faster and easier. (Basically, it comes down to what universe you're in, and how careless the author is.) And again, in a setting where this sort of thing is possible, how would a treaty banning it be enforced? Better to come up with a good reason to explain why it's just not possible, period.

 

That's specifically why Jerry Pournelle made use of of "jump points" in his fiction. The FTL drive only works in those places, and only to go to and from specific places. So there's no possibility of fleets jumping into orbit without warning and blasting you back into the stone age. Once they arrive in-system, they have to slog across space the old-fashioned way, which gives you time to react.

[dmjalund]

relativistic weapons would be just as hard to start as they would be to stop

[Nolgroth]

There are a couple of ways to deal with "in system" travel and FTL drives. Having a lower limit on distance traveled is one. Another is to go the route used in Traveller: the FTL drive won't work if it's too close to a planet/star. And the drives used in 2300AD work at sub-light speeds when they get close to a star/planet. You could also put a minimum "transit time" on hyperspace jumps, which would quite often make it faster to travel in normal space, if the ship has a good torch drive.

 

I went with a variation on Traveller's method: FTL drives won't work within a certain distance of a planet or star, but this varies with ship size. Smaller vessels can operate their drives much closer in, while larger ones have to shut down their drives farther away. Multiple FTL drives in close proximity will also interfere with other: the larger the drives, the greater their zones of interference. Aside from that, I allowed FTL travel within a system. Using the drives I mentioned above, travel times range from 5 to 8 seconds per AU. (Followed by a lengthy shuttle ride from wherever your FTL drive shut down to your final destination....)

 

The above guidelines yielded some interesting results:

 

Small starships can emerge from hyperspace within striking distance of a planet's surface, but large ones can't. No "first strikes" by massive war fleets.

 

A "first strike" mission can only have so many small starships; their FTL drives will interfere with each other.

 

It's fairly easy to prevent "first strike" missions by parking one large ship with an FTL drive in low orbit over a potential target. Its FTL drive will bollix up the drive of any approaching strike ships.

 

A large warship can't operate in close formation with other large warships; it needs to carry its own close escorts. (But there aren't any "fighters" in this setting; they're fairly large gunboats.

 

Bulk cargo carriers and large passenger vessels can't reach the habitable zones of most systems; they must rely on deep-space way stations and FTL shuttles to transfer passengers and cargo to and from the system's main population center.

 

The small-ish starships which Player Characters tend to operate can escape pursuit from larger vessels by jumping into the "shallows" of the system where the larger ships' FTL drives won't operate.

 

Blockade runners, smugglers, etc. who are "just passing through" and wish to avoid being intercepted by system patrol vessels have very limited time. As soon as they emerge from hyperspace, the energy from their emergence (it's a highly visible signature) begins to propagate through local space, at 500 seconds (8.33 minutes) per AU. So the clock is ticking, and they have to re-calibrate their drive and transit out-system again before the interceptors spot it, or they've got a fight on their hands. (If the local squadrons have FTL, they'll reach the PCs' ship quickly once they spot them: 5 to 8 AU per second as stated above.)

 

So I've gotten a lot of mileage out of in-system FTL in my campaign. Individual results may vary.

Some great ideas here. In fact, these guidelines solve most of the FTL "problems" without glossing over them.

[Xavier Onassiss]

relativistic weapons would be just as hard to start as they would be to stop

True enough; all it takes to stop them is putting a good-sized planet in their path....

 

 

[Sundog]

relativistic weapons would be just as hard to start as they would be to stop

Nah, starting one just requires a disposable, high-impulse engine and a rock to attach it to.

[Cancer]

relativistic weapons would be just as hard to start as they would be to stop

Though solid rocks that can stand that kind of push are rare. The asteroids don't qualify, except perhaps the largest three or four. After that, you're down to big moons.

[Xavier Onassiss]

relativistic weapons would be just as hard to start as they would be to stop

...and the keyword here is "relativistic" which means you'll need delta-V of nearly 300,000 kps *before* factoring in the effects of relativity. Your payload gets more and more massive as you approach light speed, which only makes things worse. (But your reaction mass also gets more massive... does that help at all? This stuff makes my friggin' head hurt, seriously.)

[Cancer]

It's your campaign, so you can set it up however you like. In Pournelle's (and Webers' and others' universes) naturally occurring jump points are of fixed distances--they simply exist (or don't exist) between Point A and Point B. And you can only jump to Point B from Point A. Anywhere else and you just burn up a lot of fuel and go nowhere. That's rather different than the Traveller approach, where as long as you're far enough from a star (or planet), you can jump out from anywhere. That difference will radically alter how navigation (and warfare) works. In fact, Pournelle set up his fictional universe to require jump points precisely because he felt that if a ship can jump in anywhere from anywhere, there's no real hope of mounting a defense. The enemy can pop in, hammer your planet, and pop out again. With defined jump points, you can fortify them against attack.

 

The issue of shedding excess heat in hyperspace... That's an issue in normal space, in the real world. One of the reasons the space shuttles spent so much time in orbit with the cargo bay doors open was so they could more effectively radiate excess heat from the shuttle's interior. Space is already either very hot (or very cold). Is hyperspace even warmer?

 

Maybe it isn't an issue of dumping heat. Maybe hyperspace has bad effects on human beings (and aliens). You have to start making CON saves if you stay in hyperspace too long--or you become hysterical/catatonic/otherwise useless, or you have to be sedated. In that case, military vessels might select crewmen who have the highest resistance, and/or use drugs, to tough it out. Commercial vessels will just drop out of hyper periodically to rest. (And if unfriendly folk know this, and know where they tend to do that...piracy could be a possibility.)

 

Larry Niven limited the distance vessels could travel in hyperspace with the idea of the "blind spot". Human eyes can't see hyperspace. If you look out a window at hyperspace, your mind tries to blot it out, so you don't see the window, just a blank expanse of bulkhead. And it works on your nerves. Even the best pilots, who don't even try to look outside--they just navigate by instrument--need to drop out of hyper occasionally to look around and reassure themselves that the real world still exists.

Shedding heat in space is hard because you can only radiate it, which goes at a limited rate (black-body radiation) and the only way to lose heat faster is to have more radiatng area. Conduction and convection are not effective in space. You are free to pick what you want for hyperspace, of course.

[Cancer]

relativistic weapons would be just as hard to start as they would be to stop

Actually, I haven't seen a workable treatment of a relativistically-moving body with variable acceleration. That takes GR, and I've never done much of that. I do know I wasn't successful in finding a treatment that gave the onboard clock time for the canonical accelerate-out, then reverse thrust and apply acceleration the other way for the 2d half of the trip. The special relativity treatments I know assume constant velocity between moments of infinite acceleration.

[PaycheckHero]

I do I seem to recall reading a story where the author mentions sending "message torpedos' date='" which I think is precisely what would happen.[/quote']

 

The old Starfire board game had something like that, and Weber probably used it elsewhere. I think they were called, "courier drones" were used to send messages through jump points and uninhabited systems.

Yeah, anyone who can go to the stars can automate things, and the old stories have aged really poorly on that point. I believe the specific author I was thinking of was Hal Clement, who of course would go to extremes to introduce as few impossible plot-devices as he could. Naturally he had to have an FTL travel method (which, significantly, always stays well off-screen), but he surely wasn't going to also introduce FTL radio. I don't quote him as a source otherwise, though, because none of his stories are about space travel per se (they are about the places you could get to if you had FTL travel, and ultimately about science and how the universe works).

[PaycheckHero]

That difference will radically alter how navigation (and warfare) works. In fact, Pournelle set up his fictional universe to require jump points precisely because he felt that if a ship can jump in anywhere from anywhere, there's no real hope of mounting a defense.

 

I hadn't heard that, but it makes perfect sense. Piper was his friend, so he knew all about Piper's universe favors offense. A few ships can raid well-defended systems, and do so repeatedly in Space Viking. The story purpose of that is that it fits his historical models--the title of SV makes the model for that story clear, and so the Sword-Worlds discover they can raid the old Federation worlds precisely like Vikings discovering that the English keep valuables in indefensible abbeys on tiny little islands in the North Sea. I can see why Pournelle would want to make his model a bit different. Also, as I said Pournelle knows more science and cares more about using it. OTOH, Piper's universe is more cinematic. If I were doing a story in one of them, I'd probably do Piper. For one thing, role-players like to be free agents answering to no one, and that's much more like Piper's universe during the period of SV.

[PaycheckHero]

relativistic weapons would be just as hard to start as they would be to stop

While I'm quite rusty, you certainly do not need GR for variable acceleration. You need it when space is curved, which either means extremely compact objects (neutron stars, black holes) or relativistic velocities of masses with enough quadrupole moment to emit gravity waves. You can get qualitative pictures of constant acceleration by drawing world-lines that asymptotically approach 45 degrees, but quantitatively I think you'd have to do some integration. it might not be a nice integral either.