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Propulsion

Larspeart

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Feb 28, 2003
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Okay, we all know that this, more then anything, is the one thing that is most hindering exploration, whether manned or unmanned, of outer space. To date, our farthest probe from Earth is STILL IN THE SOLAR SYSTEM after 26 years of top speed cruising (Voyager 1).

With that in mind, what kinds of solutions are we working on, and even more, what are some of the best thoughts and ideas? Humans have always been enamored with speed, so. . . that's have at it! What are the thoughts on solving the Propulsion Problem?



:)
 
I've heard nuke power would be the best propulsion system that we currently have the technology for. Unfortuately we can't build them because of some ridiculous anti-nuke treaty that says "no nukes in space."
 
Actually, half the probes that we currently have are nuke powered, last I knew. Even recently lauched probes are using plutonium.

I think it goes beyond just the power source. the power source would either be ambient (solar, stellar, or the controversial 'Dark Matter/Dark Energy') or nuclear. It is the method and kind of propulsion I think that is most important, and currently lacking.
 
Nuclear (or is it nukuler) WEAPONS are illegal. Perhaps semantics could get us past that to allow building an Orion craft, powered by nuclear explosions. Another nuclear option, powered by a reactor in this case, is ion, although it's not as efficient (lower specific impulse) as Orion. This is what's proposed for the JIMO mission.

Other than that, solar sails, microwave beams, and Rosie O'Donnell's singing voice have all been proposed...

did
 
Larspeart said:
Actually, half the probes that we currently have are nuke powered, last I knew. Even recently lauched probes are using plutonium.
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Alrighty. I'm an idiot. Just talkin' out my @$$.

What we need is an infinite improbablity drive.
 
Larspeart said:
Actually, half the probes that we currently have are nuke powered, last I knew. Even recently lauched probes are using plutonium.
Click to expand...

They're powered by radioisotope thermoelectric generators, and only for their experiment and system power - for propulsion, they still use chemical rockets. Nothing nuke-propelled has been launched, though Deep Space 1 did use a solar-electric ion engine.

did
 
Ion drives are tempting, in that they are cumulative in action. They steadily just increase in speed until the fuel runs out. Still, as pointed out, they are ineffecient.

The Orion model has some promise, but it is still thinking too inside the box (if you can believe that). simply doubling or tripling our speed is not nearly enough. We need to find ways to increase it at least 10x's to have any kind of real impact. Remember that in my earlier example, Voyager is STILL in the Solar System after 26 years. 1/3ing that means that would be a 'mere' 8 years.
 
Larspeart said:
We need to find ways to increase it at least 10x's to have any kind of real impact. Remember that in my earlier example, Voyager is STILL in the Solar System after 26 years. 1/3ing that means that would be a 'mere' 8 years.
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If we're not willing to wait years, we're not going to leave the solar system until we get faster than light travel. If we're just talking about tooling around in the solar system, I think chemical rockets will do fine for quite a while, especially if we can figure out a way to manufacture cheap fuel off Earth.
 
You want high Delta V you need power and reaction mass. You carry power and reaction mass, you need a big ship. Build a big ship you need more power and reaction mass. Catch 22

Answer, pick up the fuel and reaction mass en route.
Bussard ramjet.
 
Inertial propulsion relys on accelerating mass to produce acceleration of the ship in the opposite direction. As pointed out above, the more mass you start out with the more mass you have to accelerate along with the ship. So, use a nuclear reactor for power to accelerate particles scooped from space. Sort of a giant ram jet. The mass of particles may be low, but you could accelerate continuously for a long period of time and you don't have to carry the mass with you....

I see Soapy Sam beat me too it...
 
Soapy Sam said:
You want high Delta V you need power and reaction mass. You carry power and reaction mass, you need a big ship. Build a big ship you need more power and reaction mass. Catch 22

Answer, pick up the fuel and reaction mass en route.
Bussard ramjet.
Click to expand...

Problem: Bussard scoop, in the act of accumulating fuel, incurs a drag penalty as speed increases - all those otherwise handy bits of hydrogen must be compressed and accelerated from a relative standstill to the speed of the Bussard-equipped vessel. Phooey.

did
 
Yes. Ehen the exhaust velocity matches the scoop velocity you hit the wall. But how fast might that be? My knowledge of this is all from science fiction, so don't quote me.
 
Problems to overcome:

Any form of reaction drive must carry fuel onboard, therefore to get more speed you need to eject the fuel faster.

Chemical rocket engines are already close to the theoretical efficiency limit therefore the only solution to go faster is to carry more fuel.

Ion drive will be subject to the same problems, it has very high exhaust gas speeds, but little thrust, but over a long period of time the speed will build up and exceed that of a chemical rocket.

I suspect that a futuristic engine that can accelerate it’s exhaust fuel to near light speed would be the ultimate limiting factor. If this could be achieved with large quantities of fuel then a very fast ship could be built possible to some fraction of light speed (one tenth perhaps, like the Orion project).

Note this is all still to slow for interstellar travel.
 
I'm aware of solar sails, and that they work by using the momentum of photons to accelerate. So, is it feasible to build a ship that runs by firing a laser out the back? You know, conservation of momentum and all that.
 
Soapy Sam said:
Yes. Ehen the exhaust velocity matches the scoop velocity you hit the wall. But how fast might that be? My knowledge of this is all from science fiction, so don't quote me.
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Theoretically? You can approach (but not reach) c, depends on how long you want to accelerate. And don't forget that you can't use the ramjet to slow down. You can however brake against the galaxy's magnetic field.
 
Cecil said:
I'm aware of solar sails, and that they work by using the momentum of photons to accelerate. So, is it feasible to build a ship that runs by firing a laser out the back? You know, conservation of momentum and all that.
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I read a David Brin short story that had ships that did that. In the story interstellar travel and communication took so long that it was done by gigantic artificially intelligent space ships that basically just flew around carrying souveniers and messages to wherever they visited. The ship that was the main character fell into a black hole and came out in the center of the universe. The spot where the big bang happened and the universe expanded from. So far away from everthing that it was stuck there. It's a good story with great descriptions of the mighty engines shooting pure laser light out into space to propel the ship.
 
Anyone remember E.E. "Doc" Smith? "Bolts of quasi solid lightning, blasting through the luminiferous ether".

They don't do that any more.
 
I can't see how a Solar Sail could be at all fast or effecient. First off, you steadily DECREASE thrust (if you can call it that) the further from the Sun you get, thus losing speed. Once past the Termination Shock of our solar system, you get the OPPOSITE effect, in that all the ambient 'wind' from the rest of the galaxy's stars are pushing against you.

Solar sails have never impressed me.

It seems that Nuclear is the best method that we have in the practical sense currently, but that is still FAR too slow to accomplish anything. As put earlier, tooling around the solar system is an ENTIRELY different matter then interstellar. I have nothing against us finding ways of getting to Jupiter, Neptune, etc faster/cheaper/safer, but that still isn't putting us very far.

In a hundred years, Voyager will STILL be in the Suns direct vicinity, Galactically speaking. It won't even be remotely near any star (except for Planet X), and 5 generations will have died on Earth to get that far.

To me, that just rings as pathetic.
 
That's why you use a laser instead, and as new laser tech becomes availabel you can just keep adding ne emitters without needing to remove/replace old ones (though of course you can still do that). They don't even have to be particularly powerful or efficient.

While thrust from the Sun is steadily decreasing the advantage is still that most of your ship is payload and since (presumably) you're not in a hurry the low acceleration isn't a problem.

I will grant that a solar sail is not the best way for shipping live, concious people.

And if we're going to get technical, outside of a ramjet, an A/M proplusion system is the best way to go.
 
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