AquaAlmond Productions

Alternatives to chemical rockets

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What do you think is the most likely contender to be the "next-gen" space travel method? We haven't gone much beyond chemical rockets In the duration of the history of space travel. I think EM drive could be a possibility but at the moment we don't know quite a bit enough about it to utilize it. Tell me what you think will be the alternative to chemical rockets in the comments!

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I think chemical rockets will be used for a long time in space travel. They provide high thrust, and are somewhat efficient. 

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The intermediate step would be chemical propellant, non chemical fuel. In other words, chemicals must still be used as propellant, but the energy comes from somewhere else. For example, hydrazine has a crappy specific impulse of 220 seconds but if you heat it up with an electric arc, it gives you a specific impulse of over 500 seconds.

The difficulty is finding a source of heat energy that is lightweight other than an unshielded nuclear reactor.

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If we grow up, then a 1960s Orion NPP could get a large crew to Mars in four weeks. In the 60s.

But, if we don't grow up, then we'll probably have to wait until we get fusion. Even for drives like the EM drive, you still need energy. And unless you want to use rare fissionables in a reactor, then fusion is the way to go.

Funny how fission relies on rare materials and fusion relies on the most abundant materials in the universe.

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Ion thrusters are already in use.  Difficulty: they are strictly for cargo (read s  l  o  w).  There are other methods that might work better in the lab, but getting something that will work significantly better (read at speeds suitable for human travel) will inevitably require more power than you can conveniently supply (or cool).

Don't underestimate the ability to ship all your supplies early without needing full chemical rockets to get them there.

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1 hour ago, AquaAlmond Productions said:

What do you think is the most likely contender to be the "next-gen" space travel method? We haven't gone much beyond chemical rockets In the duration of the history of space travel. I think EM drive could be a possibility but at the moment we don't know quite a bit enough about it to utilize it. Tell me what you think will be the alternative to chemical rockets in the comments!

I'd say ION space tugs, then possibly beamed power. Nuclear fission based stuffis going to be impossible to get to space.

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1 hour ago, sevenperforce said:

 

The intermediate step would be chemical propellant, non chemical fuel. In other words, chemicals must still be used as propellant, but the energy comes from somewhere else. For example, hydrazine has a crappy specific impulse of 220 seconds but if you heat it up with an electric arc, it gives you a specific impulse of over 500 seconds.

The difficulty is finding a source of heat energy that is lightweight other than an unshielded nuclear reactor.

Chemicals have a higher energy density in terms of bond energies than can be recovered from battery or capaciter. The only strategy that competes with that is energy density in atomic decay, the problem with nuclear reactions however is they are often difficult to start and once started almost impossible to completely stop.

23 minutes ago, wumpus said:

Ion thrusters are already in use.  Difficulty: they are strictly for cargo (read s  l  o  w).  There are other methods that might work better in the lab, but getting something that will work significantly better (read at speeds suitable for human travel) will inevitably require more power than you can conveniently supply (or cool).

Don't underestimate the ability to ship all your supplies early without needing full chemical rockets to get them there.

With fusion energy they might be able to travel between waypoints in space with human cargo. The problem with ion drive is to really take advantage of them you should use a high ISP drive, but to take advantage of high ISP thrusters that are capable of >1 ma one needs alot of power, and solar cells at their best are too heavy and need to much associated structure.

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23 minutes ago, sevenperforce said:

I wonder what kind of performance you could get out of a solar-thermal hydrazine ducted rocket.

You could get the same thing with hydrazine normal and separate ION thruster system.

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VASIMR is an ion engine, though its design is a bit different than the ones in use today.  IMO that's definitely the one that makes it into space near-term.  And if you have enough power you can scale up VASIMR.  It would require a nuclear power plant, but the hurdles to making that happen are more political than technical.

After that some sort of fusion drive is probably likely, but I don't think any of us will live to see it.  We might see a gas core nuclear rocket, but I wouldn't hold my breath on that one.

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Chemical energy per mass ~= 10 MJ/kg
Nuclear energy per mass ~= 108 MJ/kg

Intermediate would be ~= 104 MJ/kg.
Such energy capacitor would mean an SSTO Daisy Cutter inside a grenade launcher,
which would mean a world-wide tsunami of wars and incidents when nobody even knows who had launched the missile from another hemisphere and then, in turn, fires at a presumable target.

Thanks to the Universe, there is a great gap between chemical and nuclear energy densities.
 

Edited by kerbiloid

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7 hours ago, sevenperforce said:

I wonder what kind of performance you could get out of a solar-thermal hydrazine ducted rocket.

You would run hydrazine engine in the atmosphere?

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1 hour ago, kerbiloid said:

Chemical energy per mass ~= 10 MJ/kg
Nuclear energy per mass ~= 108 MJ/kg

Intermediate would be ~= 104 MJ/kg.
Such energy capacitor would mean an SSTO Daisy Cutter inside a grenade launcher,
which would mean a world-wide tsunami of wars and incidents when nobody even knows who had launched the missile from another hemisphere and then, in turn, fires at a presumable target.

Thanks to the Universe, there is a great gap between chemical and nuclear energy densities.
 

There is potentially something with that energy density - nuclear isomer. Weather or not you can actually trigger the isomer to release all their energy on demand is questionable though.

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Various forms of ion engines for low mass cargo and uranium fission reactors heating up hydrogen for more massive stuff. You can't beat up physics.

But I think classical hypergolic fuels will hold on for a long time.

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9 hours ago, tsotha said:

VASIMR is an ion engine, though its design is a bit different than the ones in use today.  IMO that's definitely the one that makes it into space near-term.  And if you have enough power you can scale up VASIMR.  It would require a nuclear power plant, but the hurdles to making that happen are more political than technical.

One of the last nuclear thermal rockets the Russians prototyped used a rather small 198MW reactor IIRC. Now, that's for heating hydrogen instead of producing electricity, but I wonder if that reactor could be the starting point for a reactor capable of powering Vasimir engines.

But in any case, Vasimir engines work in orbit, but can't lift payloads into orbit

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6 hours ago, Shpaget said:

You would run hydrazine engine in the atmosphere?

...yes. Why not?

Hydrazine is deadly toxic in its liquid form, but its exhaust is completely harmless. 

A solar-thermal hydrazine rocket would have a theoretical maximum specific impulse of 617 s, even without any air augmentation or secondary atmospheric combustion. 

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7 hours ago, Shpaget said:

You would run hydrazine engine in the atmosphere?

We run stuff just as deadly as straight hydrazine in the atmosphere all the time.  Протон is an entire rocket filled with unsymmetrical dimethylhydrazine and dinitrogen tetroxide.  Many of the earlier U.S. storable ICBMs, before we figured out how to make decent solid rockets, used Aerozine50, a 50/50 cut of straight hydrazine and UDMH.

Edited by regex

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An impulse of 617 seconds affords a propellant mass fraction of 72.5%. Of course, actual performance would be lower, but atmospheric augmentation/combustion could probably compensate enough to bring it back up to that; hydrazine exhaust is 13% pure hydrogen by mass (67% by volume). 

A delta-body with a parabolic-concave surface on one side (painted with a super-low-density reflective paint) and a blunt-body re-entry surface on the other side could probably make it work with structural integrity to spare.

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15 hours ago, tsotha said:

After that some sort of fusion drive is probably likely, but I don't think any of us will live to see it.  We might see a gas core nuclear rocket, but I wouldn't hold my breath on that one.

Actually, parts of a Fusion engine have already been tested, and if I'm not mistaken, we actually do already have the tech to build a Z-Pinch fusion rocket.

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3 minutes ago, SargeRho said:

Actually, parts of a Fusion engine have already been tested, and if I'm not mistaken, we actually do already have the tech to build a Z-Pinch fusion rocket.

Really!? Why aren't we funding the $#!t out of this!?

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