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Space travel

 
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dph_of_rules
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PostPosted: Thu Jun 19, 2008 12:12 am    Post subject: Space travel Reply with quote

In the sci-fi stories, what are the most common types of 'engines' that transport people over vast distances in short periods of time? Which one(s) have the closest barring on reality?
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ttallan
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PostPosted: Thu Jun 19, 2008 12:11 pm    Post subject: Reply with quote

The ion engine and the solar sail are both based on real science, though currently they both have some impracticalities. The ion engine is real, it's been used to propel space probes. It can go for the long haul, but the actual thrust wouldn't be enough to launch from Earth gravity. Solar sails are a simple idea, and the technology exists (there have been several attempts already to launch a solar sail, though I don't think they were successful?), but to move a spaceship you'd need to build a sail, in space, that would be hundreds of miles across, and we don't have the ability to do that yet.
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dph_of_rules
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PostPosted: Thu Jun 19, 2008 10:32 pm    Post subject: Reply with quote

Thanks. I figured the problem with harnessing the power of solar wind would be a scale problem.

As far as the ion cannon goes, I'm aware of Newton's laws. Small particles times lots of speed equals moderate force.

Given the neglible amount of friction in traveling through the space, the question really isn't Can we get there, but how soon can we get there? With minimal friction in space, once you get enough momentum to overcome gravitional forces, that would be it, right?
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Alitorious
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PostPosted: Fri Jun 20, 2008 10:06 am    Post subject: Reply with quote

This might help: http://www.projectrho.com/rocket/rocket3c.html

Atomic rocket is, like, one of my favouritest sites evar. Smile

The ion engine is very efficient, but its maximum thrust is so low because of the nature of the electric drive. Pumping up the voltage makes the ions spit out the back faster, but you can only have the voltage so high before arcing occurs in your engine (lightning/spark effects).

Even without friction hampering your momentum, gravity is nasty enough. Remember that you have to use fuel to go both uphill and downhill any gravitational field, like the Sun's. (If you're heading to Mercury, there are actually circumstances where it would be more fuel efficient to go through Jupiter first, then slingshot back to Mercury.)
The questions most of the time actually probably go like this:
"Do we have the fuel to get there?"
"Do we have the fuel to stop?"
and then we get "How long will it take to get there?"
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dph_of_rules
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PostPosted: Fri Jun 20, 2008 1:51 pm    Post subject: Reply with quote

Oh yea, I forgot about the problem with stopping.
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spambot
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PostPosted: Fri Jun 20, 2008 8:32 pm    Post subject: Reply with quote

This seems to be another one of those topics where the more of a science fantasy or comedy the story is the easier it is to explain away. I don't think I've even touched on the subject in my comic, as it's not vital to the plot to have them explain it.

Personally, I've always felt the most realistic are the kind where they can't quite make it faster than light, so the crew has to go into suspended animation, which then makes that an issue of plausible technology. A lot of these seem to become lose-lose for story telling when you dwell too much on the hard science of it.
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dph_of_rules
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PostPosted: Sat Jun 21, 2008 2:23 pm    Post subject: Reply with quote

I understand the need for finding faster methods of transportation in the future, but I like the idea of finding new alternative means of propulsion.
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zortic
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PostPosted: Sat Jun 21, 2008 9:49 pm    Post subject: Reply with quote

Hybrid Hyperdrives?
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Last edited by zortic on Sun Jun 22, 2008 7:59 am; edited 1 time in total
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dph_of_rules
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PostPosted: Sun Jun 22, 2008 1:03 am    Post subject: Reply with quote

Actually I was thinking about magnetic propulsion system. Create a strong magnetic field some distance away from your space ship and let magnetic forces give your ship thrust.

I don't quite understand the idea behind a gravitional impulse system, the technology the Minbari (B5) uses on their ships.
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Arioch
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PostPosted: Mon Jun 23, 2008 2:54 am    Post subject: Reply with quote

The issue with magnetic propulsion is that you're still limited by Newton's third law; you need something to "push" against, whether your motive force is magnetism or electricity or something else. You need to throw something out the back of your ship so that your ship can be pushed in the opposite direction. This need for "reaction mass" is what ultimately limits all realistic forms of propulsion, because the amount of reaction mass needed to reach any kind of useful velocity is horrendous (to the point where any vessel must be 99% fuel). This is why you hear a lot of talk in science fiction circles about "reactionless" drives.

The idea behind a gravity drive is that you somehow create a gravity well in front of your ship, and the ship "falls" toward it. The warp drive in Star Trek works on a similar principle, warping space around the ship so that the ship is propelled through it. The biggest problem I have with these kinds of drives is that the effect of warping space is not going to be limited to just your ship; if your ship is creating a gravity well, then other things are going to be attracted to it as well as your ship.

The Outsider version of the reactionles drive uses the properties of the inertial damper. Ships that travel at very high accelerations must have some way of cancelling out this crushing acceleration so it doesn't kill the crew. Some more realistic milieu use things like liquid tanks to protect the crew, but those ships with crews that fly in shirtsleeves like Star Trek must have some sort of artificial gravity or inertial dampening device that reduces or cancels out the forces of acceleration on the crew (and probably on the ship itself). If such a device can reduce the effect of acceleration on the ship and crew, then it makes sense that a similar device could work in the opposite way, that is, increasing the effect of acceleration on the reaction mass that you're firing out the back of your drives. So although the drive does use reaction mass, it can get a huge acceleration effect on a very small amount of fuel.
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Alitorious
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PostPosted: Mon Jun 23, 2008 10:09 am    Post subject: Reply with quote

One other thing to watch out for is just how lethal drive plumes can be. The engine becomes more efficient the faster the exhaust particles go - so in theory the most efficient drive can cheaply shoot out its exhaust particles at a considerable fraction of the speed of light.

But then there are these weapons called particle beams - they are most efficient when they can shoot particles out the front end at a considerable fraction of the speed of light.

The only difference between a good rocket engine and a good particle beam cannon is that the weaponized version needs to maintain a cohesive stream.

See: http://www.projectrho.com/rocket/rocket3x.html#propulsion
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Entity325
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PostPosted: Mon Jun 23, 2008 10:12 am    Post subject: Reply with quote

the problem with using a fluid tank to protect your crew is that it does nothing for your insides, so beyond a certain G-force level, you're still going to have your liver trying to fall out the back of your spine.

Handwavium inertial dampeners work better, even if we have no clue how they would possibly work using current technology.
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