Hard sci-fi space crew sourcebook

[lwcamp]

Originally Posted by z0boson

GURPS space is mainly focussing on world creation, which is kind of useless in a campaign without FTL drives.

There are ways to get FTL-like behavior without breaking physics as we currently understand it. These mainly involve using general relativity to mess with space-time geometry. In essence, you never go faster than light speed, but you can take short-cuts.

There are various limitations that methods discovered so far impose. For example, you don't really have the freedom to go wherever you want, but rather you put down well-defined "short-cuts" before hand that form "railways" to your destination.

The best understood of these methods - wormholes - are something like jump-gates. Wormholes conserve energy (and thus mass), momentum, angular momentum, and electric charge locally. Thus, if your spacecraft masses 100 tons and you go through a wormhole, the wormhole end that you go through gains 100 tons of mass and the wormhole end that you come out of loses 100 tons of mass. If you go through at high relative speed, the wormhole end you go through absorbs your momentum and gets a kick in the direction you were moving, and the wormhole end you come out of gets a kick opposite your direction of motion as it recoils from the momentum of your spacecraft suddenly appearing. And so on. Since quantul mechanics seems to forbid isolated spots of negative mass, this probably means that wormhole controllers will need to be careful about balancing the mass through their wormholes.

General relativity messes with both space and time. Consequently, you can get some rather counter-intuitive effects based around what people naturally assume about time. There are good reasons to think that no space-time geometry can let you go back to meet yourself along your own past time-line, so you don't get paradoxes or true time travel (probably, this does not yet have a general proof). You can, however, get apparent time travel in a given coordinate frame. With wormholes you can exploit this so that, for example, you only have to wait a few months from the time of launch to go visit a star that is tens of light years away if you launch the wormhole fast enough (if you do this, you will essentially be going tens of years into the future in your home reference frame when you step through to visit the star, because it will have taken tens of years to travel that distance in your reference frame. This seems like time travel, but because of speed of light limits you can't go back to meet yourself before you left so it is all good). Usually, these jumps in time can be ignored by setting up a standard clock time that is continuous through the wormholes - this makes things easier on the players so they don't have to wrap their minds around how general relativity plays with time. It does mean that closed loops of wormholes that lead back to where they started require careful planing to keep them from becoming time machines (which would break the weakest wormhole in the loop, and possibly damage the others, just as it was about to become a time machine).

Because momentum is conserved locally around wormholes, wormholes themselves make rockets if you shoot stuff through them. For example, make a wormhole and put one end in space and the other on the ground. Keep all your propellant and rocket nozzles on the ground, but just shoot the jet of exhaust from the rocket through the wormhole, and the wormhole end in space is propelled along by the rocket due to the impulse it gets from the jet shooting away opposite the direction of acceleration - just like a normal rocket. As the wormhole loses mass, you can even efficiently propell it using a large ground-based laser to form a photon drive, allowing you to reach relativistic speeds. You can even give it an initial boost by charging it up, reducing its mass to something microscopic, and launching it out of a particle accelerator at relativistic speeds.

This all has the consequence that the wormhole mouth itself is all the spacecraft you need, and all the equipment - thrusters, propellant tanks, sensors, communications equipment, weapons, and the like, stay comfortably back at home. The wormhole is controlled by staff at mission control, rather than crew on a bridge - and thus they can go home to their families at the end of their shift because they are still on their home planet.

When you start applying realistic science to these things, you end up with some delightfully off-the-wall consequences that don't seem much like the standard space opera tropes, but do allow you to go have adventures on distant planets.

Luke