GURPS Space: Stardrives

[Diomedes]

One of the things that's fallen out of the discussion of SF space settings is the importance of how you get around. Apart from dictating the movement of the players, it dictates the setup of the universe.

So I thought this might be a good time to brainstorm fictional stardrives and figure out what's "gamable."

Here's my first idea:

Hyperspace/Catapult Drive

The hyperdrive portion of this is fairly standard; you have to get far enough away from large gravitational bodies like planets and stars, calibrate your drive for your destination, and press enter. It's fairly slow; 200c will take you about a week to get to Alpha Centauri, plus the time you spend getting out of the inner system, and getting into the inner system of your destination.

So it was with great joy that people discovered "hyper nodes" in several nearby systems. Hyper nodes are features of space-time that, when properly stimulated (i.e., with the careful application of energy), will fling a starship on its way, at a much greater speed (~3500c). The distance is variable up to a maximum for each node, as is the direction, so careful calculation is required beforehand.

One limitation of the nodes is that travel is mostly one-way. You can only get back if your destination happens to have a node of its own, of sufficient range to reach the original. If not, you have to use hyperdrive to get home. Of course, if the system has a node of insufficient range, you can still use it to take a shortcut and reduce your travel time.

Most trips consist of using hyperdrive to reach a suitable node, and often navigating to several nodes on a long voyage. If you're lucky, each node is within range of the last one; more often, you go as far as you can and cover the difference on hyperdrive.

The advantage of this system is that it allows choke points, which are useful to empire builders and pirates. But it also allows people to take the slow-but-direct route, or go off the beaten path for exploring, smuggling, hiding, and other things PC's may want to do.

The disadvantage is that keeping track of the nodes and their ranges would be a pain (probably requiring a computer program or applet), though not as much of a pain as placing the nodes in the first place!

Questions? Comments? Ideas that would make it more or less of a pain?

[Anthony]

One variant I've considered, which has some considerable utility with respect to solving Fermi's Paradox, is something sort of like a B5 drive, though more restricted. The basic way it works is that ships can only enter or leave hyperspace (or whatever you choose to call it) at a jump point, and that jump points are (a) normally synthetic, and (b) last pretty much forever once created. My instinct is that a jump point is either just a micro black hole, or perhaps something more exotic like a ring singularity, but either way, is pretty much indestructible once created. Creating such gates probably implies gravitic superscience, though not necessarily anti-gravity or full-fledged creationless drives as such (tractor/pressor beams, or perhaps force beams, seem more likely). It would be nice, if a good handwave can be found, if the region in which you can enter/leave hyperspace is fairly large (planet-sized), as that makes smuggling more practical. You can also sensibly handwave size limits on ships, or even throughput limits on jump points.

The advantage, here, is that any place that a ship can exit hyperspace must be interesting, because the presence of a gate implies something capable of creating a gate -- at least, sometime within the last fourteen billion years. It also means you can have alien races who haven't contacted Earth, and maybe don't know about us, because we haven't created a gate.

Depending on the exact properties of hyperspace, this may support hyperspace pirates. If gates can only be detected at relatively short distances (relatively short on hyperspace scales, anyway) this also supports exploration. I'd also be strongly tempted to toss psionic powers into the blender, as some form of excuse to keep robotic probes under control.

[Diomedes]

A simpler hyperdrive:

Quadratic Hyperdrive

Navigation is easy with this drive. You simply get your starship on the right heading, speed up to a decent clip, and engage the drive. In hyperspace, your effective speed is modified by 200,000. At the other end, you have to slow down again.

Two interesting consequences fall out of this drive:

1) The fastest trip of a given distance will involve spending a quarter of the time speeding up, another quarter slowing down, and half in hyperspace.
2) Assuming the above ratio, the distance travelled is proportionate to the square of the time involved.

Both these facts assume that the starship has sufficient ∆V to speed up and slow down again; otherwise, it can go no faster, and the ratio of time to distance becomes linear after that point.

The high velocity on has on exiting hyperspace means that warships will have limited tactical options upon arrival, unless they can manage to match velocity with their targets from interstellar distances. So popping into orbit from nowhere is probably out.

This drive is simpler than the previous one; no nodes to create choke points. The quadratic relationship between time and distance means that an interstellar empire can spread pretty far, while still requiring a decent amount of time to get around the core.

[Diomedes]

Originally Posted by Anthony

The advantage, here, is that any place that a ship can exit hyperspace must be interesting, because the presence of a gate implies something capable of creating a gate -- at least, sometime within the last fourteen billion years. It also means you can have alien races who haven't contacted Earth, and maybe don't know about us, because we haven't created a gate.

The catch is that any place that a ship can exit hyperspace must be interesting to the original builders. For instance, I happen to think Terra is a pretty interesting place, but it didn't even exist fourteen billion years ago. And if we don't have a gate, we're kinda stuck here.

[Anthony]

Originally Posted by Diomedes

The catch is that any place that a ship can exit hyperspace must be interesting to the original builders. For instance, I happen to think Terra is a pretty interesting place, but it didn't even exist fourteen billion years ago. And if we don't have a gate, we're kinda stuck here.

I'm not assuming that the technology to build a gate was only known to the ancients -- I'm assuming all the modern races have built their own gates, it's just that there are also gates that are millions or even billions of years old.

[Diomedes]

Originally Posted by Anthony

I'm not assuming that the technology to build a gate was only known to the ancients -- I'm assuming all the modern races have built their own gates, it's just that there are also gates that are millions or even billions of years old.

That is a bit different... how would you build a gate? If you can build them in hyperspace, then you have to build the gate before you know whether there's anything interesting on the outside, unless you send a sublight ship to take a look around – and report back to your descendants. If gates are cheap enough to build, then you may as well put one in every star system before finding out if there's anything interesting.

On the other hand, if you have to build them in realspace, then you have to send a slowboat – which means that most gates will be old.

[Anthony]

Originally Posted by Diomedes

That is a bit different... how would you build a gate?

With great effort. It's not something PCs would ever be doing.

Originally Posted by Diomedes

On the other hand, if you have to build them in realspace, then you have to send a slowboat – which means that most gates will be old.

Most will be old, sure. Not necessarily ancient, though; it depends on the temporal distribution of alien races with the ability to create gates. It's probable that there won't be any gates more than a billion years old anywhere near sol.

[Diomedes]

A third (because the other two weren't complicated enough!):

Hopscotch Catapult

This uses the same mechanics as the Quadratic Drive, but all the energy for the jump has to be put in when you engage the drive. That means you can't go into hyper until you have enough juice in your capacitors, and the size of those capacitors limits how far you can go in a single jump. As does how much energy the hyperdrive can stand to be fed into it.

For a further wrinkle, most ships are limited to six jumps per trip, by a method I haven't figured out yet. Since it takes 24 hours to build up enough charge for a full 12-hour jump, ships have to spend half their time coasting through interstellar space – easy prey for pirates.

[thrash]

Originally Posted by Anthony

One variant I've considered, which has some considerable utility with respect to solving Fermi's Paradox, is something sort of like a B5 drive, though more restricted.

This description also has some similarities to the drive used in Morioka Hiroyuki's Seikai no Monshou novels. See, e.g.: http://www.geocities.com/Tokyo/Shrin...ai/planar.html

[Agemegos]

Originally Posted by Diomedes

A simpler hyperdrive:

Quadratic Hyperdrive

Navigation is easy with this drive. You simply get your starship on the right heading, speed up to a decent clip, and engage the drive. In hyperspace, your effective speed is modified by 200,000.

Effective speed in what frame of reference?