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Engines to reach the orbit and - later - other planets

Posted by: Ekkehard Augustin - Tue Jul 20, 2004 7:53 am
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Engines to reach the orbit and - later - other planets 
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Post Engines to reach the orbit and - later - other planets   Posted on: Tue Jul 20, 2004 7:53 am
The teams competing for the XPRIZE are using chemical drives and engines. That's sufficient for suborbital flights. But orbital flights are requiring much more propellant - and that means much more weight...

Assumed private use of nuclear drives is allowed - is it financial and technical possible for private enterprises and teams to use such drives outside the atmosphere to reach the orbit, to decelerate for leaving to the surface or to start out of the orbit for the moon or other planets?

Are there advantages of weight in using nuclear drives? Is it possible to construct nuclear drives a small as chemical drives? Might private firms allocate the Know How needed within five to ten years?



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Post    Posted on: Tue Jul 20, 2004 6:51 pm
The short answer for nuclear rockets is no-way! The government would never allow it, and private firms couldn't raise the money to develop the know-how in 5-10 years.

But I still think this thread asks an interesting question. What kind of engine technology do people on this board think will be the marketplace winner.

Well, I don't know what propellant will win, but I bet the rocket will be a multi-stage pressure fed design. When reading about minimum cost design I came across an interesting quote, but I can't remember where I saw it now. Basically, it said there is never any justification for a pump fed rocket. Lower stages should be low cost and low performance so pressure fed is okay. Upper stages can justify more cost for higher performance, but they operate in vacuum so low chamber pressures give very little performance penalty. So upper stages can be pressure fed too at very low pressure.


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Post    Posted on: Tue Jul 20, 2004 7:44 pm
yea, "no way" is about right. barring fusion engines, you really have to be at least in LEO to use a nuclear engine, and then you'd have to be careful of satellites and stuff if it puts out much radiation at all. nuclear is the answer for vehicles that don't ever have to enter the atmosphere, but until we have something that is much cleaner than any of the current possible designs, it won't work for getting to orbit. besides, while nuclear can put out immense amounts of thrust at good isp, it weighs a whole lot more than a simple chemical engine. you really need to have something big to even consider nuclear propulsion (power is another thing though). obviously if people start researching it though that'll likely change fairly fast, so no telling what'll be best in the future.

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Post    Posted on: Wed Jul 21, 2004 2:24 am
I am in favour for a non-conventional first stage either by aircraft launch or maglev like what is proposed for the ESA Phoenix program.

The big Russian AN-224 looks like a good platform to start with.


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Post    Posted on: Wed Jul 21, 2004 3:18 am
The guy who wrote this article: http://www.nuclearspace.com/a_liberty_ship10.htm seems to think that a nuclear powered ship could be launched from the surface. He's talking about an ISP of over 3000.

While I think it's a very interesting concept and the articel nicely covers the advatages of nuclear over chemical I somehow don't think it's as good as he thinks it is. The environmentalists would reflexively have a collective heart attack if anyone tried to build such a ship, even if it was as safe as this guy believes. So there'd be a massive outcry against it and most likely a lot of political pressure to put a stop to it.

For the time being nuclear ships to orbit are just not going to happen. I think even a technically successful fusion drive would have a mess of PR problems likely to stop that as well, even if it was some sort of super clean helium3 based system.

At this point in time some sort of gravity control is just as likely. 20, 30 or maybe 50 years from now things may be different but short of some sort of extreme need you just will not see any nuclear ships to orbit.


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Post    Posted on: Wed Jul 21, 2004 7:49 am
There's the problem of the Nuclear Non-Proliferation Treaty..
While it's purpose isn't for this, it may have wording in it that would make any signatory countries liable to not allow a company to engage in any drive with the word 'nuclear' in it.


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Post    Posted on: Thu Jul 22, 2004 12:41 am
It's my understanding that the Non-Proliferation Treaty does not exclude power plants, people only get worried when it seems that a particular country might be trying to refine fissionable material enough to make a bomb out of it. It shouldn't forbid something that doesn't go kaboom. And there are countries not as fearful of nuclear power as some people here are. The idea is potentially feasible, but still many hurdles to be leapt.


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Post    Posted on: Thu Jul 22, 2004 1:58 am
That's interesting, I didn't know that.


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Post    Posted on: Thu Jul 22, 2004 6:27 am
The most important question concerning the Non-Proliferation Treaty and Space is wether there are countries not being part of it. That has been the reason why I didn't into account the treaty and only asked if private firms may be able - in a future of five or ten or fifteen years - to develop and use nuclear drives outside the atmosphere.

But now the question is involved - what about Texan? May he find out, which countries are not being part of the treaty and what is perhaps forbidden to private firms by it? It would be interesting.



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Post    Posted on: Fri Jul 23, 2004 1:44 am
Does the NPT prevents the launch of nuclear electric systems? ie RTG's for power generation and not direct propulsion.


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Post    Posted on: Fri Jul 23, 2004 8:54 am
At least nuclear power sources are not forbidden by the treaty - Cassini-Huygens has a nuclear power source and has been launched by NASA.

There has been a heavy public debate by the Greens about that intending to prevent that launch I remember.

So this means that it is allowed to get radioactive materials to space - to do that really has been a politicum in the past. Since Cassini-Huygens that might have changed.

Are the radioactive parts of nuclear power sources fit to be used in nuclear drives too or do the latter require another kind of nuclear material?



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Post    Posted on: Fri Jul 23, 2004 8:46 pm
Here's an opinion from a lowly computer programmer who knows almost nothing about propulsion:

I think the "next big thing" in propulsion technology will be something we haven't really thought of yet. It's the same with computer technology: Faster and smaller isn't going to be good enough for much longer. We're at the point of really needing an evolutionary step. In computers, consider the Palm, Pocket PC, and new generation of cell phone/pda's. What's holding them back is not our ability to make things smaller and faster -- it's that no-one has really come up with a way to throw out the keyboard. Whoever finally comes up with the next evelution in input/output will win the market.

Propulsion (in my admitedly ignorant opinion) is in a similar situation. You engineers can quote the formulae of thrust, wieght, etc... nothing is going to suddenly make it cheaper. That's why I love the really crazy ideas out there being generated by the X Prize -- Balloons taking you up so far, etc.

It's going to be some "crazy" idea that goes completely outside the normal mode of thinking about propulsion that will finally take us to the next level.

Am I completely off base?

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Post    Posted on: Mon Jul 26, 2004 9:45 am
You are right - the next evolutionary step is required. At the NIAC-Site there are a lot of documents studying many thoughts and ideas. But light sales, magnetic sails etc. don't work at launches form planets - they only are working if the spacecraft already is in space.

I remenber only two ideas providing new solutions for launching - the space elevator and a concept of a space-based spacecraft diving into the atmosphere and catching a payload transported by airplane to a sufficient altitude.

But the next step mustn't be searched for in propulsion only - may be propulsion alone doesn't provide the solutions needed. The next evolutionary step has to be searched for in organization, transportation, coordination and infrastructure too. It may be dependent of all this together as a whole - there should be search for synergies where ever there is chance to find them. I have in mind a special aspect of transportation but it has to be discussed in another section of this message board and I have to wait a liitle bit I think.



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Post    Posted on: Mon Jul 26, 2004 2:16 pm
I like the idea of space-built craft swooping down to pick up cargo from earth-bound vehicles. I heard somewhere (maybe it's one of the X Prize teams) about an idea that involved a system of baloons. The idea is that there would be a "station" baloon floating very high up. Balloons would bring vehicles, suplies, etc. from the ground to the station. Rockets would then launch from the station into orbit, etc. That definitely intrigued me.

I also think you are correct about the organizational structure, etc. New paradigms rarely come in old structures -- and when they do, the old structures rarely survive them.

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Post    Posted on: Tue Jul 27, 2004 3:29 am
Yeah, about those balloons. They float from helium, right? I coulda sworn that I've read in a journal somewhere about how the world is running out of readily available sources of helium from the ground and that in 20 years it could be considered rare. And now they want to fill huge balloons with a large portion of it? Seems a bit wasteful.


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