Efficient Fuel

[Barry Scott]

The human race are going to have to use more efficient fuel and invent spacecraft that will travel much faster than they do now, if we are ever going to colonise the galaxy, or even universe. I was wondering what are the chances of humanity spreading out of our solar system in the next millennia, and also is anit-matter the only fuel that comes close to 100% efficiency?

[InfiniteNow]

You might wish to check out the Search feature within Hypography. This might give you some ideas and clear up some issues on things which have been discussed here already.

http://hypography.com/forums/search.php


Cheers.

[UncleAl]

The Starflight Handbook, Mallove, Matloff, 1989.

There is no existing or extrapolated engineering that will get humans out of the solar system. Nobody is going to Mars, either. The atmosphere is equivalent to a yard thickness of lead shielding (mass/area, plus no pair production from light nuclei, plus time delay of flight). 100% of long duration flight astronauts and cosmonauts (and most of the rest) get radiation cataracts - and they are still shielded by the Earth's magnetosphere.

Thermodynamics has a lot to say about making piles of antimatter. It ain't gonna happen, even if you could safely store it. Even if you had it, antimatter would not be nearly an adequate starship fuel. Stuff moves form momentum, mv. Energy is proportional to mv^2. The "better" the fuel, the more of its energy is wasted.

If you want to go interstellar slumming you need entirely different physics.

[CraigD]

Originally Posted by Barry Scott

I was wondering what are the chances of humanity spreading out of our solar system in the next millennia, and also is anit-matter the only fuel that comes close to 100% efficiency?

The ”photonic rocket” wikipedia article gives a good synopsis of the limits of rocket performance, as does its article on specific impulse, and hypography’s own ”Relativistic Rocket: The rest of the story...” thread. My all-time favorite work on the subject is the late Robert Forward’s ”Indistinguishable from Magic”. Though a proponent of antimatter powered rockets, Forward believed that they would be useful only for surface-to-space and interplanetary use.

I think UncleAl’s “ain’t gonna happen” summary of the problem is, lamentably, likely an accurate one. The engineering challenges of interstellar travel are staggering, greater than any ever faces by science. However, history has shown that even the most reasonable pronouncement of impossibility often prove wrong, so I’m not entirely without hope for interstellar travel becoming a reality within our lifetimes.

[Barry Scott]

Thnks for the reply's

[Roadam]

Well, we already have an interstellar travel, only that the crafts are have only started their way(voyagers...). And of course it is really slow.

As for all traveling, one has to consider how quick does he want to come somewhere and how much energy he wants to spend.

Magic is still wainting to be discovered, doesnt it?

[UncleAl]

http://www.neofuel.com/optimum/
Optimum rocket performance for self-contained fuel and oxidizer

The best propellant exhaust velocity is about 2/3 of mission delta-V.

[CraigD]

Originally Posted by UncleAl

http://www.neofuel.com/optimum/
Optimum rocket performance for self-contained fuel and oxidizer

The best propellant exhaust velocity is about 2/3 of mission delta-V.

The linked to paper by Zuppero is a wonderful read. It’s not, however, about “optimum rocket performance for self-contained fuel and oxidizer”. It is about the optimum exhaust velocity for a ship where only the energy supply need be self-contained. Although this energy could be supplied by a combustible fuel and oxidizer engine, in isn’t required, or even desirable, for it to be. Zuppero’s example assumes that the energy would be supplied by a nuclear [fission] reactor – that is, a nuclear thermal rocket, and that the propellant is water obtained on the Moon, and launched into lunar orbit to fill the ships tanks “like a gas station”.

With this design, propellant (water) is cheap, abundant, and easy to store, while energy (the nuclear reactor) and the spacecraft structure itself, which is must be launched from Earth, is expensive, so the design goals are either to move the maximum payload (in Zupperro’s example, from Earth or Moon orbit to Mars) with the minimum of energy, or move a given payload in the minimum time. For both scenarios, the optimum exhaust velocity is about 2/3 (0.6275…) of the required change in velocity (V), for the trip, though the V is higher for the “fast, light” trip than for the “slow, heavy” one. For a given trip, there is a minimum V below which the trip is impossible.

For the trip between stars on which this thread is focused, this low-exhaust velocity design is not very useful, because there are presumed to be no “gas stations” with which the ship could be supplied by propellant along the way. Energy, on the other hand, can in principle be relatively abundant (in the form of “beamed energy” supplied by a solar-system based facility, or a very energy-dense fuel such as antimatter). So, in a high-velocity interstellar trip, energy is “cheap”, propellant “expensive” (infinitely so, as it’s presumably unobtainable), so the design goals become to have the greatest possible exhaust velocity, which is discussed at some length in the ”Relativistic Rocket” thread.

Note that I say “presumably” throughout the above, because I strongly suspect that a workable high-speed interstellar spacecraft will not be a rocket with either energy source or propellant self-contained, but some sort of “beamed” system, where both are supplied to a comparatively small spacecraft by a comparatively large solar-system based “projector”)

[Roadam]

We still can make generation ships, or make hibernation beds. This way you dont need much veilocity to reach someplace quickly.

The only thing is that when that ship would reach its destination, there would probably be already much faster ships.

[Moontanman]

Originally Posted by UncleAl

The Starflight Handbook, Mallove, Matloff, 1989.

There is no existing or extrapolated engineering that will get humans out of the solar system. Nobody is going to Mars, either. The atmosphere is equivalent to a yard thickness of lead shielding (mass/area, plus no pair production from light nuclei, plus time delay of flight). 100% of long duration flight astronauts and cosmonauts (and most of the rest) get radiation cataracts - and they are still shielded by the Earth's magnetosphere.

Thermodynamics has a lot to say about making piles of antimatter. It ain't gonna happen, even if you could safely store it. Even if you had it, antimatter would not be nearly an adequate starship fuel. Stuff moves form momentum, mv. Energy is proportional to mv^2. The "better" the fuel, the more of its energy is wasted.

If you want to go interstellar slumming you need entirely different physics.

Space craft can be shielded from space radiation by a powerful magnetic feild or even low density material sheilding. A magnetic feild strong enough give enough sheilding would need a nuclear reactor to generate the power. It can be done if we use nuclear power. No other energy source is practical

Michael