Actually About STL-Only Interstellar Travel

[David Johnston2]

As I was saying, in order to reach ramjetting speed, you'd need about 9 tanks of reaction mass minimum, which plus the other required systems, would leave you with about one spare section that you could use for sensors or cargo or a second habitat or something. That's by the book which doesn't take into account that the density of the interstellar medium varies and Sol happens to be plopped right in the middle of a bubble of thin medium.

It's actually unlikely that a Bussard ramjet could get a ship up to relativistic speed. The faster you go, the more energy you have spend on accelerating the gas you are taking in by ramjet. This creates drag that will balance your thrust. I seem to vaguely recall 17% C as a maximum figure, but I have no idea how they calculated it. It would depend on how fast your maximum exhaust speed was.

Of course with a realistic fusion torch it would take a very long time to accelerate up to that maximum in the first place. If you were just hopping between nearby suns, you'd need a superscience reaction drive. Really reactionless drive would be an awful lot easier.

[malloyd]

Originally Posted by David Johnston2

It's actually unlikely that a Bussard ramjet could get a ship up to relativistic speed. The faster you go, the more energy you have spend on accelerating the gas you are taking in by ramjet. This creates drag that will balance your thrust. I seem to vaguely recall 17% C as a maximum figure, but I have no idea how they calculated it. It would depend on how fast your maximum exhaust speed was.

Right. Since you are collecting hydrogen primarily,assume you can fuse it to helium, find the energy that will produce, and dump that entirely into the helium produced, and you can calculate the exhaust speed.

But note that imposing a drag speed limit depends on an analogy to jet engines that doesn't necessarily hold - specifically that you can't recover the relative kinetic energy of the swept up material. For a jet engine that slows down the incoming air by collision with a diffuser, this is of course true, it shows up as heat in the diffuser. For an interstellar ramjet, where you are slowing it down by interaction with an electrical or magnetic field, this is almost unavoidably partially false - and indeed you probably have to remove that stored energy from your scoop field somehow even if you are going to waste it just to keep your field shape under control.

[David Johnston2]

Now with a reactionless drive or a JAFAL drive, you can have the actual potential for an interstellar civilisation, albeit a loose one. You can have warships that may take twenty years to get where they are going, but once they do, can slap around colonies that have gone astray as far as the homeworld is concerned or fight similarly sluggish alien fleets. You can have actual interstellar trade via nomadic worldships. Space missionaries can spread the word, whatever their word might be. So that's the way I'd go.

[sir_pudding]

Originally Posted by David Johnston2

Now with a reactionless drive

Of which there are actually some plausible hard-ish handwaves for.

[David Johnston2]

Originally Posted by sir_pudding

Of which there are actually some plausible hard-ish handwaves for.

If you squint real hard. Were I running an STL game I'd probably talk vaguely about "dark energy/matter" and leave it at that.