(semi)hard sci-fi propulsion

[The Dark]

Highly hypothetical question here:

IF a graviton particle exists, and IF there is a method of interacting with it (i.e. generating or destroying gravitons), THEN could that be used for such things as artificial gravity without rotation and lessening of inertia for purposes of additional acceleration from identical reaction mass? I realize the energy requirements would be very high, but it would seem that this would allow for a much smaller reaction mass tankage, if an energy generator could cause the remaining reaction mass to have more effect than the original remass pre-graviton dampening.

Of course, this is probably all pseudoscience BS, which is why I'm asking.

[SirNitram]

The problem with using gravity, even gravity particles, is that it requires mass.

[The Dark]

The problem with using gravity, even gravity particles, is that it requires mass.

If you mean reaction mass, I figured it would, but it would give a way to reduce the necessary remass needed for accelerations. If you meant something else, I'm afraid you've confused me.

[SirNitram]

What I mean is, if you want 1G of gravity, you must has as much mass as Earth. If you want gravity to accelerate you, you must effectively permenantly position a massive object in front of you to fall towards.

[The Dark]

What I mean is, if you want 1G of gravity, you must has as much mass as Earth. If you want gravity to accelerate you, you must effectively permenantly position a massive object in front of you to fall towards.

Ah, I understand. *Tosses another idea into the trashcan before starting a new short story. * Thanks for explaining.

[Enlightenment]

If I follow you right, then an Ion engine even though right now we can't make one with the acceleration to be practical for manned flight.

The acceleration limits for ion drives more in the realm of physical limits rather than matters of engineering. It is highly unlikely that high-thrust ion drives will ever be built.

The best bet going for space propulsion is antimatter. Unlike 'lets bend reality' hypothetical concepts, antimatter propulsion is very well grounded in physics. Given enough engineering time and effort it will work and will yield enough thrust at a sufficently high specific impulse to get around the solar system with ease. Antimatter is also quite sufficient for STL interstellar travel.

Nuclear fusion drives are another option. They are cheaper than antimatter but have lesser performance and are harder to build. Fusion drives are good enough to get around the solar system but their interstellar performance is marginal.

[The Dark]

Another possible choice for interstellar travel is a solar sail. Even though the acceleration isn't great, it can still outperform conventional chemical rockets if traveling past Mars and would be a cheap form of early STL interstellar travel while we work the kinks out of fusion or antimatter (since it would currently take years to produce the antimatter for one ship).

I recommend Louis J. Friedman's book on solar sailing, though I don't recall the title. Look up his name, should be something like "Starsailing."

[Slartibartfast]

Another possible choice for interstellar travel is a solar sail. Even though the acceleration isn't great, it can still outperform conventional chemical rockets if traveling past Mars and would be a cheap form of early STL interstellar travel while we work the kinks out of fusion or antimatter (since it would currently take years to produce the antimatter for one ship).

I recommend Louis J. Friedman's book on solar sailing, though I don't recall the title. Look up his name, should be something like "Starsailing."

With a solar sail, the amount of thrust decreases the farther you get from the sun. Using it for anything except thrust inside a stellar system is useless.

[greenmm]

Not to burst your bubble... but did you even notice that those were hypothetical drive systems? Or that it was pointed on the very same page that they'd have to even develop working theories to create the science that would allow such a drive to be designed? Heck, for that one drive system, they don't even know for sure if "negative energy" exists.
Not to mention that there is no theory, let alone science or technology, that allows us to even generate artificial gravity in space, so expecting us to be able to change the gravitational properties of local spacetime are sheer fantasy.

The closest thing we have to a working interplanetary/interstellar drive system right now is the electric/ion drive systems that NASA has been testing, and even that isn't ready for manned space travel.

Sorry to burst your bubble but did you notice the (semi) before hard science? Or the fact that this is a SCI FI forum? what are you? stupid? of course they're fucking hypothetical, if it were in SLM then it that would be an issue. This is Other sci-fi. idiot.

And semi-hard means they have to have some sort of grounding in reality, even if still theoretical. Those drive systems haven't even made it past the hypothesis level yet, let alone made it into scientific theory.

I'm not saying it's impossible to use them... but you have to make sure it doesn't sound like another bit of Trek technobabble, or it won't qualify as "semi-hard".

[greenmm]

If I follow you right, then an Ion engine even though right now we can't make one with the acceleration to be practical for manned flight.

The acceleration limits for ion drives more in the realm of physical limits rather than matters of engineering. It is highly unlikely that high-thrust ion drives will ever be built.

The best bet going for space propulsion is antimatter. Unlike 'lets bend reality' hypothetical concepts, antimatter propulsion is very well grounded in physics. Given enough engineering time and effort it will work and will yield enough thrust at a sufficently high specific impulse to get around the solar system with ease. Antimatter is also quite sufficient for STL interstellar travel.

Nuclear fusion drives are another option. They are cheaper than antimatter but have lesser performance and are harder to build. Fusion drives are good enough to get around the solar system but their interstellar performance is marginal.

I think you mean the best bet for power generation, not propulsion. Unless you plan on ejecting the antimatter behind you like a rocket engine -- in which case you've still got the equivelent of an ion engine.

As for getting higher speeds out of the ions, it's the same principle behind most acceleration equations: you increase the time you spend accelerating (in this case, by making the thrust chamber longer), you increase the rate at which the ions accelerate (in this case, by making the attracting or repelling charge stronger), or you combine the two.

This is a case where antimatter, or even nuclear fusion, power generation would be helpful. The more power you can pump into the charge plates, the faster the ions will squirt out the back, and the more thrust the engine will generate.

[Neko_Oni]

I really like the Solar Sail idea. Has an elegant feel, though obviously it's only useful close to the sun. There's another version a Mag Sail, saw it on the NASA website, uses the solar wind to push against a magnetic field which moves the ship. BTW anti-matter worries the hell out of me, since it's default state is blow the crap outta everything around it.

[Enlightenment]

I think you mean the best bet for power generation, not propulsion. Unless you plan on ejecting the antimatter behind you like a rocket engine -- in which case you've still got the equivelent of an ion engine.

You're confusing a lot of concepts here. A full explanation would be rather complicated so I'm just going to direct you to a few websites where you can see what I'm talking about

Antimatter propulsion:

http://science.msfc.nasa.gov/newhome/he ... ov97_1.htm
http://science.nasa.gov/newhome/headlin ... pr99_1.htm
http://www.transorbital.net/Library/D001_S01.html
http://www.engr.psu.edu/antimatter/

Ion engines:

http://www.southpole.com/headlines/y2000/ast15jun_1.htm
http://www.jpl.nasa.gov/technology/features/ion.html

In summary, ion engines are a specific type of drive where an ionized gas is accelerated using electricity. Antimatter drives react antimatter with matter and use the thermal energy, explosive force, and/or reaction products for propulsion. They are completely different technologies.

As for getting higher speeds out of the ions, it's the same principle behind most acceleration equations: you increase the time you spend accelerating (in this case, by making the thrust chamber longer), you increase the rate at which the ions accelerate (in this case, by making the attracting or repelling charge stronger), or you combine the two.

Again, there are physical limits involved here. Ion engine thrust is dependant on the area of the charge grids; getting decent thrust requires utterly huge charge grids and a huge quantity of power. See
http://groups.google.com/groups?selm=5k ... put=gplain
for gory details including the math.

[gravity]

From that website, the most likely and practical approach seems to be laser-powered sails. But to get enough power to send a manned ship, it would probably be necessary to construct a huge network of solar panels in space (a fractional version of the original Dyson Sphere concept). Still, it might be practical eventually if none of the anti-gravity type stuff pans out, and asteroid mining/and or space elevator gets going.
Colonizing our own solar system first is probably a better bet, unless we discover an earth-like planet very nearby.
Hmm, assuming solar panel efficiency of 80% (50-70% ones are currently in development), that means about (based on data from http://www.911-strike.com/solar.htm) 4166666666667 square meters (4,166,667 square km) of solar panels will be needed, massing about 378787878788 kg (378787 teratons) which is probably way to much to actually manufacture anytime in the near to mid future. (note: this is required to send a spaceship big enough to house humans by laser-sail method to Alpha Centauri in 10 years).

[kojikun]

Solar Sails:

Ok, these are possibly the most feasibly resent propulsion system. Why? Because while they do loose accelerative ability the further from the sun they go, they GAIN it the closer the get. Inverse square. If the sail is 1/3 the distance from earth, orbitting mercury, it could provide 9 times the thruster. And also for longer, because it travelling further.

Nuclear and Solar Thermal Rockets:

Both of these use heat to boil hydrogen and heat it to 2200 degrees (C or F im not sure but im betting F because steel melts below 1000C). Nuclear Thermal Rockets, or NTRs, work by pumping hydrogen past the fuel rods in a nuclear reactor. Los Alamos tested various NTRs back in the 60s, getting upwards of 5000 gigawatts generated.

Solar Thermal Rockets do the same thing, minus the reactor. They use mirrors to reflect sunlight. Because the lack the radiation of the NTRs, theyre safer, and weigh less. The mylar-aluminium mirrors would also reduce the weight. Both of these have realistic specific impulses of about 900 seconds, twice what hydrogen burning rockets provide.

Solar Farms:

Gravity, your mentioning of solar farming is good, but you over estimate the size needed. You also need to provide figures for power. For fun I've calculated the size and power generated by your 4.16 trillion square meter collector.

Circular radius is an astounding 1.15 THOUSAND KILOMETERS.
Side of a square is nearly double that at about 2 thousand km.

Power generated by your 4.16 trillion square meter collector is 728 TERAWATTS. Earth as a whole presently consumes about 8.5 terawatts, so unless you plan on founding colonies on 77 other worlds, a 1150 km collector is far from necessary.

And as for your weight calculations, thats not a necessity. Using a large mirror, made of the same stuff solar sails are made of, you would be able to reflect a whole lot of light onto a small number of solar panels. Mylar-aluminium is the same material used in those foil birthday balloons.

[Peregrin Toker]

What about negative matter, which was theorized to exist?? If I recall correctly, this hypothetic negative matter repulses normal matter, and using this, negative matter can be used as a propulsion method for spaceships so they can reach 70% the speed of light!!

I'll soon go get the book at the library where I read about it.

[ClaysGhost]

What about negative matter, which was theorized to exist?? If I recall correctly, this hypothetic negative matter repulses normal matter, and using this, negative matter can be used as a propulsion method for spaceships so they can reach 70% the speed of light!!

I'll soon go get the book at the library where I read about it.

If this exotic matter ever becomes available, the best use propulsion-wise would probably be in making wormholes.

[Peregrin Toker]

If this exotic matter ever becomes available, the best use propulsion-wise would probably be in making wormholes.

Artificially generated wormholes also seem like a good propulsion idea to me. (although they would require INSANE amounts of electricity to generate!)

[ClaysGhost]

Artificial, as in, without the use of exotic matter? How would you do that? Electricity is certainly not exotic and would not therefore stabilise the mouth of the wormhole?

[His Divine Shadow]

With a solar sail, the amount of thrust decreases the farther you get from the sun. Using it for anything except thrust inside a stellar system is useless.

Use in conjunction with a giant laser?

[Neko_Oni]

They use the giant laser array in Mote in God's Eye (it outshines a dim star while its operating). However you still have to slow down at the other end if your using it to travel interstellar.

[Peregrin Toker]

Artificial, as in, without the use of exotic matter? How would you do that? Electricity is certainly not exotic and would not therefore stabilise the mouth of the wormhole?

Artificial as in not natural. In fact, I could easily have said "man-made wormhole" instead.

[Slartibartfast]

With a solar sail, the amount of thrust decreases the farther you get from the sun. Using it for anything except thrust inside a stellar system is useless.

Use in conjunction with a giant laser?

That would be interesting. I have a RPG book which gives several realistic propulsion systems for ships (it's a shipbuilding resource, it neatly separates components into hard-sci-fi and the rest), don't remember exactly but it makes reference to the laser propulsion.

[Pu-239]

Look here too:
http://www.itsf.org/index.php?PAGE=broc ... index.html

[kojikun]

Negative matter is theoretical at best, fanciful at worst. Theres no evidence that it does exist or that its even possible for it to exist. Its not like antimatter where you can make it at CERN or something. Its pure theory.

That said, its best use (without getting into strange physics regarding wormholes) is as a reactionless drive (which doesnt violate conservation of momentum or energy because of.. strange physics).

The drive would work like this: take a bit of negative matter, stick it behind your craft, and the ship moves away from it. Its not like two magnets which would push one another away from a common center, its the opposit kind of. The normal matter moves away from a common center of mass and the negative matter moves TOWARDS the common center. So the ship moves forward at an ever increasing rate. Theoretically, it might be possibly to reach C using such a drive because negative matter requires energy to slow it down whereas it speeds up as it looses energy (sounds much like tachyons at FTL speeds). Equally, negative matter has negative momentum. So as the momentum of the ship increases, the momentum of the negative matter decreases and the whole contraption speeds up. The negative mass of the negative matter would also negate the mass of the positive matter giving the whole thing 0 mass and potential C or FTL abilities.

Thats an idea...

[gravity]

Solar Farms:

Gravity, your mentioning of solar farming is good, but you over estimate the size needed. You also need to provide figures for power. For fun I've calculated the size and power generated by your 4.16 trillion square meter collector.

Circular radius is an astounding 1.15 THOUSAND KILOMETERS.
Side of a square is nearly double that at about 2 thousand km.

Power generated by your 4.16 trillion square meter collector is 728 TERAWATTS. Earth as a whole presently consumes about 8.5 terawatts, so unless you plan on founding colonies on 77 other worlds, a 1150 km collector is far from necessary.

And as for your weight calculations, thats not a necessity. Using a large mirror, made of the same stuff solar sails are made of, you would be able to reflect a whole lot of light onto a small number of solar panels. Mylar-aluminium is the same material used in those foil birthday balloons.

But according to the NASA site mentioned earlier in this thread, 10000000 gigawatts of laser-thrust power is required to get to Alpha Centauri in 10 years, which is a lot more than 728 terrawatts. And that mass was based on the lightest currently existing solar cells, though that could improve in the future.