An Advanced Propulsion Overview

by Paul Gilster on September 4, 2009

Both Tau Zero Foundation founder Marc Millis and JPL’s recently retired Robert Frisbee appear in an article in the Smithsonian’s Air & Space, where voyages to distant places indeed are discussed. Nothing is further from Earth, the article notes, than Voyager 1, which travels at a speed (almost 17 kilometers per second) that would get it across the US in a little under four minutes. Point that spacecraft toward Proxima Centauri and the journey at this speed would take 73,000 years. Clearly, something has to give, and writer Michael Klesius runs through the options.

From Ideas to Engineering

Voyager is actually headed in the vague direction of the constallation Camelopardalis, and won’t come near anything stellar in several hundred thousand years. We’d like to get mission times to a nearby star down to decades so that scientists and engineers working on the project could live to see its outcome.

How to achieve that is a question that has been at the back of Bob Frisbee’s mind for a long time now. To Alpha Centauri in just decades? Years? “We can see the theoretical possibilities of these things happening, but we just can’t get the engineering there,” Frisbee notes in the article, but he points out that this kind of brainstorming was what we used to do when thinking about a moon voyage, and that was a journey we made. It may take several generations of brainstorming but the ideas continue to fly.

Building a Breakthrough Concept

Let’s hope the Air & Space article provokes public discussion as it runs through the background of advanced propulsion studies in the 1990s, when wormholes were seriously tackled and warp drive began to be written up in scientific journals. Miguel Alcubierre’s concept of a spacecraft riding what is essentially a wave in spacetime kicked off a resurgence in breakthrough propulsion that led materially to projects like NASA’s Breakthrough Propulsion Physics, run by Millis until its termination in 2002. Funding issues are always problematic, but Tau Zero continues to probe these matters, and Frontiers of Propulsion Science, co-edited by Millis and Eric Davis, shows that the ongoing conversation is robust indeed.

Says Millis:

“I think back to the era of Dirac and Schrödinger and Einstein. When they were having their pivotal meetings and sometimes heated debates, they weren’t being funded for that work. They were just doing it because that’s what they did. And they made significant advances… And I’m thinking to myself, Well, it would be great if we got funding, but even if we don’t, when we talk amongst ourselves and debate things and encourage each other to write papers, we’re going to make progress.”

That kind of progress is what Tau Zero is about. Not that robust funding is out of the picture — we are building a philanthropic model for the foundation that should be able to tap private sector sources (with all the good things that follow from not being channeled through endless layers of bureaucracy). But keeping an eye on the issues and encouraging debate is bound to produce good outcomes, if only in the synergies that result from putting propulsion theorists with good ideas in continuing contact.

Options for Infrastructure

But before we go to the stars, we’ve got to build up our capabilities right here in the system. On that score, the article is also noteworthy for its examination of NERVA, a nuclear thermal rocket design that Klesius describes this way:

It would produce thrust the way chemical rockets do: by heating a propellant—in this case, hydrogen—and ejecting the expanded gas through a nozzle. Instead of heating hydrogen through combustion, however, the nuclear rocket vaporizes it through the controlled fission, or splitting of atomic nuclei, of uranium. Because nuclear fuel has a greater energy density, it lasts a lot longer than chemicals, so you can keep the engine running and continue to accelerate for half the trip. Then, with the speedometer clicking off about 15 miles per second — twice the speed reached by returning Apollo astronauts — you’d swing the ship around to point the other way and use the engine’s thrust to decelerate for the rest of the trip. Even when factoring in the weight of the reactor, a nuclear engine would cut the transit time in half.

NERVA was a promising technology that delivered 850 seconds of thrust — twice the efficiency of chemical rockets — in 1960s-era tests, but the program faded in the 1970s. You’ll find more on NERVA, and on Franklin Chang-Díaz’ work on VASIMR, in Klesius’ article. Neither NERVA nor VASIMR has interstellar potential, but in terms of opening up the Solar System for exploration and infrastructure building, these are solid options to investigate.

An Insurance Plan for Human Survival

I like the Chang-Díaz quote that ends the piece:

“The space program began the day humans chose to walk out of their caves. By exploring space we are doing nothing less than insuring our own survival.”

Indeed. And all the technologies described here point to ways of making the insurance policy pay big dividends. Klesius writes about a fusion-powered 180-day trip to Jupiter, one dependent on breakthroughs in fusion itself and in materials science. Build the infrastructure here in the Solar System and gradually push the envelope outwards. It’s a plan that could pay off one day in making that journey to Proxima Centauri via fusion, antimatter or other means, and crossing the gulf in a single human lifetime.

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Pat Galea September 15, 2009 at 16:41

“there has been an active and ongoing investigation of far more theoretical ideas like wormholes and warp drives”

The way I look at this far-off stuff is that even if it is pushing the boundaries of what we can think about – even theoretically – it is still useful because it gives us ideas about what we need to be thinking of right now.

So, for example, when we look at wormhole concepts, we know darn well that we ain’t going anywhere with them for the next thousand years (usual caveat for exceptional events applies). But we can look at the ideas to see whether they are total non-starters (e.g. they are not consistent with physics as we understand it, perhaps in subtle ways), or whether we can see certain things that we need to understand better in order to make any progress – even purely theoretical – in getting a solid picture of how the physics hangs together. Whichever way it pans out, we are either a little bit closer to getting these systems working, or we have achieved a slightly better understanding of the scope of the physics. Either is good.

It may be that we end up with some research ideas that we can carry out now; perhaps this research is experimental (e.g. particle physics), or observational (e.g. astronomy), or maybe purely theoretical. This research is targeted, in the sense that we carry it out with a goal in mind.

However, none of this is to suggest that the far-out research should take precedence over the short-term stuff. *Both* types are needed. Furthermore, I’d add (riffing on the theme of a recent CD post) that we also need some ‘wacky’ research to exploit the wholly unpredictable serendipity.

Ronald September 15, 2009 at 17:31

Duncan,

concerning your philosophy with regard to discovering versus inventing the laws of nature, I think I disagree, but it may largele be a matter of wording;

“Some people think, there is something like the true nature of the cosmos, and that the natural laws of, say, physics are something we *discover* by observing natural phenomena.”
No, not just some people, exactly that *is* science, the process of discovery through research. I think there is a misunderstanding here. The ‘laws of nature’, physical laws are (nearly) always simplified and abstracted *models*, descriptive approximations of a reality that can be tested (i.e. demonstrated, verified, reproduced) and amended. The practical application of the laws of nature are called technology and that is what is invented.

Contrary to some popular belief, Newton did not ‘prove Galileo wrong’, not did Einstein ‘prove Newton wrong’, but rather amended or expanded. They presented (even) better or expanded models and approximations for describing testable reality.

“Physical laws are not discovered like we discover stones, plants, animals, stars, light, etc, when we look outside”
Well, we do, but indirectly. Physical laws themselves are not discovered as such, and could not, because they are abstractions, but by studying the very real objects that you mention (and many others).

After all, in your post to James, you also mention things like “real physics”, evidence and reality.

But again, maybe we mean the same in different words.

george scaglione September 16, 2009 at 9:40

hello all,don’t want to beat this topic into the ground with a stick but in regard to alot of what has been mentioned above : just yesterday i finished reading a book “quantum enigma” by doctors bruce rosenblum and fread kuttner.a wonderful study of quantum physics.at the very end,to my mind,the make the point of how little or rather – how much physics there still is still to understand!! ergo,wormholes,warp drive! the way to understand the way to do it might “only” be one heck of alot of learning away!!!! this is what i think.all the very best everybody your friend george scaglione

george scaglione September 17, 2009 at 9:53

paul, yes we do and righttfully should have room a plenty for the more speculative! lol sorry to say – even putting a “man on mars” is currently a little too speculative for my blood. sorry to have to say so,your friend george

Duncan Ivry September 17, 2009 at 13:18

Ronald: “concerning your philosophy with regard to discovering versus inventing the laws of nature, I think I disagree, but it may largele be a matter of wording;” “No, not just some people, exactly that *is* science, the process of discovery through research. I think there is a misunderstanding here.”

It’s not *my* philosophy, and, yes, there is a misunderstanding, and it is a matter of wording.

Contrary to your opinion there are indeed theoriticians of science and (may be a minority of) physicists thinking the way about science, I tried to describe. Just as an information for you (not trying to prove anything) : I learned this, when studying mathematics, physics, and theory of science at university years ago. It was and still is a normal part of the lessons told at this university, and at some other universities, in my country, and, with variations, in other countries. I even ;-) successfully passed an examination on theory of science as a minor subject.

I know, many physicists think, there is one and only one opinion about what science *is*. But this is only a certain lack of knowledge. Clearly stated: when practicing physics and when using the results of physics, in most cases and most of the time theory of science is not important; there is not fight between schools of thought; there are no lunatics running wild.

I think, discussing this topic more deeply on this website is not appropriate. My apologies go to Paul Gilster for having occupied so much of his estate! I won’t continue.

Administrator September 18, 2009 at 9:51

Duncan Ivry wrote:

I think, discussing this topic more deeply on this website is not appropriate. My apologies go to Paul Gilster for having occupied so much of his estate! I won’t continue.

Actually, I think this is fascinating. Don’t feel that you have to close down the discussion, Duncan, unless you just want to.

Ronald September 19, 2009 at 15:57

Paul,

I presume you are aware of this? Looks exciting!

http://nextbigfuture.com/2009/09/path-unification-of-general-relativity.html

Duncan Ivry September 20, 2009 at 11:00

Thank you to Paul Gilster for being so generous, and to Ronald for the link. I always look for — and already know several — lectures on physics presented on the web by universities of good standing. By the way, when listening to video lectures, I, as someone who’s first language isn’t English, more often than not have difficulties understanding Americans. It’s less difficult, when having them in front of me (but even then impossible sometimes). Leonard Susskind, on the contrary, gives an example of enunciating his words clearly. A further difficulty for me is, of course, writing in a foreign language about a sophisticated topic concisely and precisely. It costs much time, and I have work to do ;-) By the way, thank you to everybody for being patient.

Administrator September 21, 2009 at 14:46

Ronald wrote:

I presume you are aware of this? Looks exciting!

http://nextbigfuture.com/2009/09/path-unification-of-general-relativity.html

Ronald, I think Woodward’s ideas are interesting though naturally the Machian interpretation of inertia is quite controversial. BPP looked at Woodward and we have sections on him in Frontiers of Propulsion Science — I also interviewed him for the Centauri Dreams book. So yes, am interested, but will want to read through the most recent stuff before commenting, and in any case I may want to hand the relevant comment off to Eric or Marc.

Do note the number of ifs here in Brian’s first post:

If the Mach Effect is real [mass fluctuations) and behaves as theorized (with some experimental confirmation) by James Woodward and the effect scales up as expected then we can create reactionless drive.

All of these things are being investigated but we have a long way to go for conclusive results. Naturally, we follow this work with interest.

george scaglione September 22, 2009 at 14:16

duncan thank you very much for the above.our administrator,paul gilster is 100% correct that sometimes misunderstanding is just part of the discussion and in no way does that mean that the discussion itself should be shut down! english duncan,is,my first language and i am not so bad at it.however does that mean that i can not be and have not been misunderstood?you bet! lol happens on a weekly basis.thank you too for your patience. i will now read your comments from a whole different point of view.sometimes there is a bump in the road but all of us are still heading in the same direction.all the best my friend,george scaglione and by the way?what was that first language!? :) g

ljk October 17, 2009 at 0:30

Some realistic nuclear spaceship designs here:

http://www.projectrho.com/rocket/rocket3ap.html

Chip Burcham November 28, 2009 at 17:06

Dual Reusable Fuel Transit Drive

This type of transit drive should work by reusing the fuel in two loops. Fuel is pumped into the left and right combustion chambers. Next the fuel provides thrust for the spacecraft, four action forces numbered 1 and two reaction forces numbered 2 causing the ship to have a temporary net movement of zero. The left and right aft exhausts then move along the inner left and right aft curves of the return pipes creating two forces (numbered 3) that move the ship forwards (the left and right forces of 3 cancel each other out). The left and right exhausts then move along the return pipes and hit the ends of the return pipes at midship bulkhead with gas forces numbered 4 moving the ship forwards. Now, the pushing panels (forces 5) move the gases left & right to where they meet gas forces 1. Next, panel forces 6 push the gases (1 & 4 gas forces) back into the combustion chambers exerting an opposite and equal reaction (forces 7) on the ship pushing it forwards. Then panel forces 6 are slowly pushed back into position by forces 8 moving the ship a little bit backwards.

Forces 1 & 2 cancel each other, forces 3 & 4 are not cancelled, left and right forces 5 cancel each other, forces 6 & 7 cancel each other, forces 8 & 9 cancel each other. If any of you want to continue explaining why this design won’t work, then explain what forces cancel forces 3 & 4, otherwise please say my design can work.
________forward bulkhead____________________
_____midship bulkhead_______________________
|4^**__|5>__**9**|***********9***__<5|*^4*|
|*^*|*******|*8**|**********|*8*|******|*^*|
|*^*|*******|*7^*|**********|^7*|*****|*^*|
|*^*|*******|**6*|__________|*6*|******|*^*|
|*^*|*******|****|****Fuel***|***|******|*^*|
|*^*|*******|*^*|=Pumps*=**|^*|*******|*^*|
|*^*|********\^1/***********\1^/*******|*^*|
|***|********/**\************/**\*******|***|
|***|********|**|************|**|*******|***|
\***\________/**/************\**\_______/***|
*\3___________2/**************\2_________3/
________aft bulkhead_______________________
Left and right combustion chambers
Asteriks used to provide spaces.

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