As to the speed issue poeple got on me on: any weapon moves fast. I was talking about repeatable speed. Mass drivers would have terrible trouble with keeping up a volume of fire; I don’t believe they can easily or cost-effectively replace modern and will-soon-come artillery, which must be able to put a great many shots into the air before any of them hit, and all must hit *extremely * accurately. And that’s talking artillery, let alone hand weapons.
Now, IMHO a more practical idea involves using a very large, very long fixed-emplacement railgun to shoot vehicles into space. This obviates the need for extensive fuel tank boosters. You could potentially put on onto a mountain and basically shoot up at an angle. It would probably be far safer than conventional launches since you’re not sitting on giant bomb. Likewise, you can make larger, tougher, (read: heavier) ships, which will make re-entry safer.
You’d still need to be sitting on a small bomb, though. Any closed orbit which intersects the planet once is going to intersect it again. If you want to stay up for a while, then you have to do something to change orbits once you’re up there, and that means firing rockets.
Yes, but look at how much fuel they burn up getting there. most of the space shuttle’s launch weight is in the massive rocket boosters. By comparisons, the fuel onboard is a drop in the bucket.
True but the acceleration you (or the object) would experience being fired out of a rail run I think would pulverize most anything not solid. Humans, electronics and so on would have serious issues staying in one piece if someone tried to shoot them/it into orbit from the earth
I doubt a rail gun would be as visually spectacular as, say, a missile firing/hitting. The coolness factor comes into play more in your head knowing what you are doing.
What part of “very long” didn’t you understand? Maybe you don’t quite understand what a railgun is: you accelerate an object over the entire length of the barrely by magnetic attraction and then repulsion from specific points. It would probably be less acceleration at any one point than strapping a rocket to your buttocks and lighting the fuse, such as we do now.
Heh, I don’t really have much to add at this point (hence my silence up till now), but I wanted to thank everyone for contributing so much to the discussion.
This is something I often worry about; I’ll start a thread in the interest of seeing what people have to say, and contribute as long as I have something meaningfull to add. But sometimes the thread goes on for a while after I don’t really have anything else to say, so I’ll just lurk. But I’ve read in a couple different discussions on this board that it’s considered rude not to comment on a thread you started, and I’m often unsure what to do about it.
What you’re describing would be a coilgun, rather than a railgun. A railgun operates differently, and would be extremely ill-suited towards launching anything except, perhaps, kinetic-kill weaponry, into space. For one thing, as far as I know there’s no such thing as ‘slow’ acceleration with a railgun.
A coilgun, or electromagnetic induction cannon, on the other hand, can be tuned to provide slow, steady acceleration (rather than the wham-bam-thank-you-ma’am railgun), and would suit the purpose you describe. But it’d have to be pretty damn long. Personally, I think a loop design that switches you onto a launch track when you’ve achieved enough velocity would be the only workable way to go, if people could take it without hurling their breakfasts.
Basically, much more than 1g acceleration is not going to be viable for passengers. I’m too tired to do the math right now, but it’d take a while to get to escape velocity at only 1g; a few miles of track would not surprise me.
I agree they could and probably should call it that. But for whatever reasons, they usually don’t. I won’t try to correct them. Aside from which, 1 g acceleration is plenty in a railgun with a large enough barrel. In an actual coilgun, a large enough circuit should make it quite easy for people to hold their lunches.
Large enough is right. My best guess would be that you’d need a circuit with a fairly large radius. But that’s only a gut feeling; I have no idea what centrifugal (centripetal?) force amount is enough to cause The Hurling.
BUT! Doing a little math, I can tell you that it would take a little less than 1 minute at 1g to reach escape velocity, and you’ll need about 11 km of track – if my figures (and calculations) are correct
Escape velocity: ~11.2 km/s
One G acceleration: 9.8 m/s
This is not very accurate; I have not factored in friction from the atmosphere, so I guarantee it needs to be higher, but I have no idea how much faster you need to move.
Somehow this doesn’t ‘feel’ right, but if it’s not I don’t know enough about physics (oh, the shame!) to calculate it correctly. Maybe a more smarter Doper can check me?
And I don’t know why I’m still posting in this thread; I think I’m the only one who cares about this junk anyway. Heh.
The only things you need to keep a mass driver (coil gun or rail gun) going are magnetically reactive materials to form into slugs, and power. If you’re postulating SF spaceships that can run around at anything like a useful velocity, you probably don’t have a problem with the power requirements. Chemical propellants, on the other hand, take manufacturing facilities, precautions against explosions, access to multiple chemicals, as well as the implied dependency on all that stuff that you can’t easily get in orbit or farther out.
It makes sense to have, say, asteroid miners armed with railguns rather than rifles because those are easily produced with the materials they’d have readily available. In those circumstances, chemicals would be much rarer and difficult to obtain than power and metals.
Plus, you can get something moving a shitload faster with a mass driver than you can with a chemical propellant. It depends on how long of a track you want to make and how much power you’re able to dump into the acceleration magnets. If you’re talking about spaceships that are hundreds or thousands of meters long, that could be a pretty long track, and with a (as yet) magical fusion reactor you’ve got as much power as you want, up to the limits of your materials. Chemical reactions are limited by the rate that the gasses can expand.
The disadvantage of lasers is that they’re not especially efficient at transferring energy, and even with really powerful ones you’d have to keep it on target for a while to get that energy into what you wanted to fry. Countermeasures like thermal shielding and polished surfaces could have some success, as well as simple tactics like spinning so that the laser can’t irradiate a single area very well. Kinetic energy weapons, on the other hand, impart their energy all at once if they hit at all.
All that being said, with current technology there are some problems that really need to be worked out to get any kind of mass driver to be a more practical tool. The fact that advantages are there will keep people working toward overcoming those problems, but it’s anyone’s guess as to whether they’ll find good solutions in a relatively short amount of time.
