Conceiving the Laser-Fusion Starship

by Paul Gilster on November 16, 2012

When young Rod Hyde, fresh out of MIT, started working on starship design in mid-1972, there were not many fusion-based precedents for what he was up to. He had taken a summer job that would turn into a career at Lawrence Livermore National Laboratory, but right off the bat he was involved with Lowell Wood and John Nuckolls in a concept that would use a battery of lasers to create fusion reactions whose energy would be channeled out the back of the ship by magnetic nozzles. Wood and Nuckolls had been developing their ideas for years, after Nuckolls first began to ponder how to use laser fusion micro-explosions to drive a spacecraft.

Now the duo had a kid who had spent his previous summers working in a beet cannery, a recruit for Livermore who had run up high grades at MIT and had shown he could work like a demon once he put his mind to it. This would be his first technical job. Hyde went into full gear on containing the plasma from the fusion explosions with a magnetic field. If they could ignite fusion, the three researchers were looking at specific impulses of 300,000 seconds and maybe as high as a million.

The figure was staggering. The amount of time it takes one pound of fuel to produce one continual pound of thrust gives you the specific impulse figure. It’s one way to measure rocket performance. Putting the work of Hyde, Wood and Nuckolls in context, consider that the main engines of the Space Shuttle can turn out a specific impulse of about 455 seconds. Hyde couldn’t talk about the specifics of the fusion pellets and laser ignition in this engine when he presented it in late 1972 at a conference of the American Institute of Aeronautics and Astronautics in New Orleans, but even the declassified version made quite a splash.

Image: We’re still trying to turn fusion into a reliable power source here on Earth. Pictured are the pre-amplifiers of the National Ignition Facility at LNLL. Will we ever find a way to use inertial confinement fusion powered by lasers on a spacecraft? Credit: Damien Jemison/LLNL.

A Memorable Conference

Remember, this was shortly before Daedalus, the British Interplanetary Society’s starship design project that began in 1973. Daedalus would go on to develop a concept around inertial confinement fusion ideas produced by Friedwardt Winterberg, a theoretical physicist at the University of Nevada in Reno. In later years, Hyde would question some of the Daedalus work, about which more in a moment. For now, let me quote Thomas Heppenheimer, who wrote about the New Orleans conference and the starship design in his book The Man-Made Sun (Little Brown, 1984). Heppenheimer says the paper took the conference by storm:

Hyde stood up there at the podium and laid it all out: the physics, the design concepts, the calculations, the performance equations. Almost nobody in the audience had the background to follow him. Still, the paper was a blockbuster, for it had about it the aura of classified technology. People didn’t know much in those days about laser fusion, though it was considered quite a hot topic, but nobody could say why. Also, the word got around that Wood had had a hard time getting the paper cleared through classification so that it could be released. The government had just barely, and reluctantly, let it out. Then the requests for copies of the paper started pouring in.

And pour in they did. Wood had ordered two hundred reprints and surely thought he had grossly overestimated the demand, but the papers were gone in two months and the starship designers were sending out copies from the lab’s copy machines. The 19-year old Hyde found his paper being sought out by the White House and the National Security Council. Hyde would go on to develop a much longer report based on the paper, spending the ensuing years developing how the laser would work and covering details from radiation shielding to power equipment.

Radiators and Starship Design

Yesterday I ran an image from the film Avatar to accompany the first of these articles on Hyde, Wood and Nuckolls’ ideas. The choice was deliberate because the ISV Venture Star has what many cinematic starships lack: A set of radiators. Think about the fact that while a rocket of any kind will produce heat, a vehicle like the Space Shuttle is also cooled by the flow of hydrogen fuel (over 440 pounds of hydrogen per second). Fusion engines can’t shed their heat as readily. They demand radiators that will glow red-hot as they carry the heat away. Hyde saw this early in the game and spent a lot of time working on the radiators and their supporting equipment.

The engine design that Hyde took to New Orleans was based on inertial confinement fusion as conceived by Wood and Nuckolls, a concept intended to move far beyond Orion, with its nuclear devices exploded behind the spacecraft to drive it forward. The new design would use frozen pellets of deuterium/tritium, each weighing 0.015 grams, 500 of which would be exploded by lasers every second. The result would be a tiny fireball whose charged particles would be turned into the exhaust beam by magnetic coils. The fireball would in turn press the magnetic field to induce current in a pickup coil, flowing into a capacitor whose discharge would fire the lasers.

When Hyde later looked at the Daedalus papers, developed not long after his initial work with Wood and Nuckolls, he balked over the issue of the fuel pellets, thinking that the design was unworkable. The Daedalus designers had based their pellet design on unclassified literature, but Hyde knew there was a great deal more about pellet design than could be reported in the press. When he ran the BIS’ pellets through the LASNEX computer code then in use at Livermore, he found they produced little thrust, and if re-engineered to create thrust, would melt the engine.

With breakeven fusion proving a tougher nut to crack than appeared likely in the 1970s, it’s almost wistful to look back at some of the excitement these methods produced in that era. Thomas Heppenheimer talked of using the Hyde/Wood/Nuckolls design to boost a spacecraft to ten percent of the speed of light for a flyby mission to a nearby star, diverting to another after the first encounter. A probe to Barnard’s Star, for example, would reach its target in 64 years, after which it would be re-deployed toward 70 Ophiuchi, which it would reach some 92 years later.

Today we’re re-examining the whole concept of inertial confinement fusion, with ongoing work at the National Ignition Facility located at Livermore. In starship terms, the Icarus project is massaging the Daedalus report to bring it up to speed with current thinking and technology, even as the question of flyby probes is giving way to a realization that without a means of decelerating, we’ve spent vast amounts of money on mere hours of close-in data. Whether the intense work that resulted in Hyde’s final designs will ever pay off in terms of an actual mission to a star remains to be seen, but the ideas he worked with at Livermore continue to be a vital part of interstellar studies, energizing continued work on the conundrum of fusion propulsion.

For more on all this, the original conference paper is Hyde, Wood and Nuckolls, “Prospects for Rocket Propulsion with Laser Initiated Fusion Microexplosions.” AIAA Paper 72-1063, American Institute of Aeronautics and Astronautics, November 1972.

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railmeat November 16, 2012 at 11:39

I still think a fly-by mission would be worthwhile, it is asking a lot to get to a start and slow down there too. A fly-by of Proxima Centauri then Alpha Centauri B would be a huge accomplishment and, I believe, would create a lot of interest in interstellar space flight. Sputnik did not actually do anything useful, but it did start the space age.

ljk November 16, 2012 at 12:22

While searching for the Hyde, Wood and Nuckolls paper online, I came across this interesting read online here:

http://fti.neep.wisc.edu/pdf/fdm1287.pdf

“Fusion Space Propulsion – A Shorter Time Frame Than You Think”, by J. F. Santarius of the Fusion Technology Institute, University of Wisconsin at Madison, December, 2005.

Plus this paper for good measure:

http://www.fas.org/sgp/othergov/doe/lanl/docs1/00189777.pdf

ljk November 16, 2012 at 12:57

More online goodies found while searching for the 1972 paper:

“A Laser Fusion Rocket for Interplanetary Propulsion” by Hyde, 1983:

http://www.osti.gov/bridge/servlets/purl/5619090-M1gt9T/5619090.pdf

A related paper to the above by Orth from 1998:

http://www.boomslanger.com/images/istuifp.pdf

“MICF: A Fusion Propulsion System for Interstellar Missions” by Kammash and Cassenti (cannot find a year but am guessing early 1990s):

http://www.boomslanger.com/images/istuifp.pdf

The authors of the above paper claim their method could send a flyby probe 10,000 AU in just 28 years.

“An Intertial Fusion Propulsion Scheme for Solar System Exploration” by Kammash and Galbraith, 1991:

http://deepblue.lib.umich.edu/bitstream/2027.42/87799/2/754_1.pdf

“VISTA: A Vehicle for Interplanetary Space Transport Application Powered by Inertial Confinement Fusion” by Orth, 2003:

https://e-reports-ext.llnl.gov/pdf/318478.pdf

“A Spherical Torus Nuclear Fusion Reactor Space Propulsion Vehicle Concept for Fast Interplanetary Travel” by Williams et al, 1998:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990020975_1999011467.pdf

“Pure Nuclear Fusion Bomb Propulsion” by Winterberg, 2008:

http://arxiv.org/ftp/arxiv/papers/0803/0803.3636.pdf

For good measure, here is an excerpt from a technical book on various kinds of rocket propulsion:

http://catdir.loc.gov/catdir/samples/wiley031/00027334.pdf

ljk November 16, 2012 at 13:05

One more paper. This 2003 work is authored by the three gentlemen from the 1972 paper, plus one M. Ishikawa and some guy named Edward Teller…

http://www.dauvergne.com/spanish/images/Teller%20paper.pdf

Greg November 16, 2012 at 14:47

The one thing that I see as an issue with any laser based ICF engine is the pellet delivery mechanism. It has to deliver the pellet at the point where the lasers converge, each and every-time, at a very high rate. Obviously, if it is off by just a little the fusion compression most likely not occur.

GaryChurch November 16, 2012 at 15:56

“-a concept intended to move far beyond Orion, with its nuclear devices exploded behind the spacecraft to drive it forward.”

Unfortunately there is no “far beyond”; the laws of physics are crystal clear on “confining” fusion and it is only going to happen in a star using gravity. The only other place fusion will work as advertised is in a bomb. Stan Ulam thought outside the confinement box by going around confinement problems with bombs. It is a stroke of genius still unappreciated by a public with little imagination or knowledge of basic physics.
Nuclear Pulse Propulsion and Freeze and Revive sleeper ships are the only starships we will see for a century or two.
That second generation is the small black hole engine; it is the only other candidate and will require hundreds of square miles of solar energy devices generating more energy than the earth currently uses to manufacture them.
We are in the position of Jules Verne who had the beginnings of complex technology to work with in predicting submarines, heavier than air flight, and traveling to the moon.
We have an understanding of how to travel to the stars but are dragging our commercial airline/star trek baggage around the subject.

Adam Crowl November 16, 2012 at 17:06

An updated version of the Spherical Torus fusion spaceship can be found in this paper: Realizing “2001: A Space Odyssey”: Piloted Spherical Torus Nuclear Fusion Propulsion
…the performance is a bit low for a starship, getting an effective exhaust velocity of 3,000 km/s. Fusion burn-up fraction is only ~2.2%, about 8 times less than “Daedalus” was predicted to achieve. Hyde’s assessment of “Daedalus” sounds very pertinent to “Icarus” – any references? I’ve heard that claim for years, but never knew the source.

Adam Crowl November 16, 2012 at 17:43

Hyde’s 1983 paper makes several points about the “Daedalus” design:

(1) Secondary reactions make D-He3 pellets produce many more neutrons than the “Daedalus” designers had hoped.

(2) The thrust efficiency of a hemispherical engine bell is 50% at most, not the 95% assumed by “Daedalus”

In a follow-up paper from 1986 Alan Bond & Anthony Martin address the first point, pointing out certain modifications to their initial pellet design. However I am not sure they addressed the thrust efficiency question. That does imply a significantly lower performance. Japanese researchers have tweaked thrust efficiency towards ~75-80%, but not the high hoped by the “Daedalus” designers.

Interestingly Freeman Dyson’s seminal paper on fusion bomb interstellar travel only assumed ~50% thrust efficiency. He also assumed a perfect fusion burn, resulting in an effective exhaust velocity of ~15,000 km/s. Less perfect fusion performance would perhaps approach the “Daedalus” range of ~9,000-10,000 km/s.

Adrian Mann November 16, 2012 at 17:57

Radiators – working with the Icarus team has made it clear to me that one of the major problems in spacecraft design is heat management. Whenever I see a fictional spacecraft these days, my second question is “Where are the radiators?”
Great articles and thanks for all the links to the papers – I’ll be getting and reading all of them – I can only guess how much I’ll be able to understand!

GaryChurch November 16, 2012 at 19:20

I read Star Warriors and found it interesting but it did not change my worldview the way Project Orion did. Probably the most amazing book I have ever read- and it was panned by the critics. But then, critics said Prometheous was a great movie and I thought it stunk.

My magnum opus on space exploration;
http://voices.yahoo.com/water-bombs-8121778.html?cat=15
It has never generated much interest which puzzles me. I think this is the way to go. Of course, everyone has their own idea about the next step. The Ayn Rand in space commercial crew zealots are an especially unsavory bunch I have had nothing but trouble with for several years. They howl and moan at any suggestion that only vast governmental resources can build the atomic spaceships necessary to establish off world colonies (and enable star travel).

lurscher November 16, 2012 at 19:26

@GaryChurch, do you have a link to that estimate of “hundreds of square miles of solar energy devices” to generate micro black holes? I saw an estimate once that you need at the very least 10^40 or 10^45 watts of radiation energy entering into a spherical region in order to create black holes, and our sun only provide 10^26 watts. Maybe you have another method in mind that doesn’t involve radiation?

Robert Horley November 16, 2012 at 19:51

I’ve been hearing about fusion engines all my life and how they have been ‘proven’ conceptually at Livermore. However I’ve never heard of anyone building an actual proof of concept model in the real world. What’s the problem? Do the test ban treaties even forbid rocket engines?

Astronist November 16, 2012 at 19:53

I am skeptical about diverting flyby probes from one star to another. While this works beautifully for planets, at interstellar speeds the gravity of even a star is almost invisible to a spacecraft. It either needs to slow down to get much of a gravitational change to its course, or execute that change propulsively. In either case, I would have thought that the large extra propulsion burden would be much better used slowing down so as to get into orbit at the first target star (and send a different probe to the second one). The more so as the main function of a robotic probe, as I see it, is to conduct surface exploration of planets in the target system in order to obtain the ground truth which is totally inaccessible to even the largest telescopes based in the Solar System.

Stephen

Brett Bellmore November 16, 2012 at 19:53

I actually find impact fusion more plausible. No problem attaining pretty much any standoff distance you want, and the fuel pellets are not complex. (Which is important when you’re going to need to manufacture billions of them, at a high pace.) Further, delivery of kinetic energy to the “bullet” is likely to be more efficient than any laser would probably be, and even contributes slightly to the engine’s thrust.

Finally, since the burn, once initiated, is proposed to be 1 dimensional, the same mechanisms can drive arbitrarily greater fusion yields, by adopting high aspect ratio targets.

Astronist November 16, 2012 at 20:02

Your image of part of NIF is a useful reminder that controlled fusion as an electrical power source is also in development, and the fraction of the world’s population who would thank us for fusion for electrical power is probably rather larger than the fraction who are hoping to see its rocket applications. But even within the development of interstellar spaceflight, fusion for electrical power would be extremely useful. Perhaps at this stage we should concentrate a little less on the rocket application and a little more on establishing whether or not fusion is competitive with fission, solar power or fossil fuels for running cities?

Adam Crowl November 17, 2012 at 3:13

Bond & Martin’s reply to Hyde’s critique:

Recently Hyde [4] has made a valuable contribution to the
ENPR literature, considering a laser fusion rocket for interplanetary
propulsion. Among other topics, the question of
fuels was discussed and Hyde chose all deuterium, using DD
reactions to produce the power.
This choice was based upon Hyde’s assessment that DD selfburn
within a DHe3 pellet will account for about 15 per cent
of the reactions, producing neutrons either directly or indirectly
via DT reactions. Also, any neutron capture by He3 will produce
a T and most of this will burn, even in the outer regions of the
pellet. Also, at temperatures relevant to DD or DHe3 burn
(around 100 keV in Hyde’s analysis) there is copious production
of X-rays due to bremsstrahlung. For Hyde’s pellet about 15
per cent of the energy which is produced escapes as X-rays.
Thus, Hyde’s explicit conclusion is that there is no advantage
to be gained by using DHe3 rather than DD, and his implicit
conclusion is that the Daedalus vehicle will fail as a result of
heat loading on the thrust chamber.
Following the publication of Ref. 4, the authors have reviewed
the questions of pellet burn and neutronics in the case of the
Daedalus pellets. It is still thought that the heat loadings of a
DHe3 pellet can be controlled.
The Daedalus pellets have high compression factors of 1,000
for the first stage and 2,000 for the second. At these compressed
densities, the neutron thermalisation mean free paths are about
0.2 mm for 14 MeV neutrons from DT and about 0.06 mm for
2.4 MeV neutrons from DD. The energetic neutrons formed
will be thermalised to the mean temperature of the pellet in its
compressed state before escaping. If this compression has been
carried out efficiently, then the regions where the neutrons are
thermalised will be in the Fermi degenerate state, with a
temperature of about 1 keV. The capture cross section via the
(n,p) reaction in He at this energy is sufficiently large that
neutron attenuation factors of 1E-13 and 1E-10 should be present,
for the first and second stages respectively.
The situation will be different in the case of any 14 MeV
neutrons born in the outer regions of the pellet, as a result of
DT reactions, where the T is produced via neutron absorption
on He. As Hyde correctly points out. most of this T will burn
and the neutrons will escape largely unattenuated. This point
was overlooked in the Daedalus study. but it is a relatively
trivial modification to pellet design to make the outer layers
depleted in deuterium, so that any tritium produced will not
be able to react.
Finally, X-rays. In the large pellets considered in Daedalus
(with compressed radii of about 1.8 and 0.7 mm) the authors
believe that the X-ray source is only a surface one, with a brief
period of emission when the burn front reaches the pellet radius
and pellet disassembly occurs. Most of the X-rays produced
will be strongly attenuated by self-absorption via inverse
bremsstrahlung in the compressed pellet. The pellets considered
by Hyde, on the other hand, had a compressed radius of
somewhat less than 0.2 mm, and a correspondingly larger
fraction of the X-rays produced would be expected to escape
from the pellet.
Nevertheless, we wrote in the Daedalus Report [2, p.S60]
“simulation of the implosion of large pellets of DHe3 via the
use of sophisticated computer codes was an area to which the
study could not contribute … The remedying of this state of
affairs would be a valuable service to the cause of nuclear pulse
propulsion.” We are still strongly of this opinion, and would
urge that such work be done if at all possible.

Would be good to see this suggestion taken up.

Max November 17, 2012 at 6:17

I don’t think starships will be propelled by nuclear fusion, at least not directly. Beamed propulsion (SailBeam etc.) seems to be a more realistic proposition. In addition to that it also allows for higher speeds with greater power levels.

GaryChurch November 17, 2012 at 14:46

“-do you have a link to that estimate of “hundreds of square miles of solar energy devices”

the link to their paper is easy enough to google.

Brett Bellmore November 17, 2012 at 15:02

I don’t think that fusion will be the primary propulsion for departure from the solar system, but any star ship that’s not a flyby is going to need a propulsion system for coming to stop at the destination, and for mid course corrections. While mag-sails might help for the former, (And will be deployed anyway for protection against interstellar gasses.) you’re still going to want a high ISP propulsion system on board with plenty of delta V.

Nobody is going to launch a star ship that relies on chemical rockets at any point.

Robert Horley November 17, 2012 at 15:19

I’ll repeat the question I i plied in my last posting. Has anyone anywhere actually managed to ignite a single fusion pellet in the laboratory?

Paul Gilster November 17, 2012 at 16:37

GaryChurch writes:

the link to their paper is easy enough to google.

Not without an author or other reference. In any case, I can’t find it — can you give the citation?

GaryChurch November 17, 2012 at 16:49

http://arxiv.org/pdf/0908.1803.pdf

Excerpt:
“Using the formulae from the section above, we find that a black hole with
a radius of a few attometers at least roughly meets the list of criteria (see
Appendix). Such BHs would have mass of the order of 1,000,000 tonnes, and
lifetimes ranging from decades to centuries. A high-efficiency square solar panel
a few hundred km on each side, in a circular orbit about the sun at a distance of
1,000,000 km, would absorb enough energy in a year to produce one such BH.
A BH with a life span on the order of a century would emit enough energy
to accelerate itself to relativistic velocity in a period of decades. If we could let
it get smaller and hotter before feeding matter into it, we could get a better
performance.
In Section V below, we discuss the plausibility of creating SBHs with a
very large spherically converging gamma ray laser.”

Wojciech J November 17, 2012 at 16:51

Astronist:
“The more so as the main function of a robotic probe, as I see it, is to conduct surface exploration of planets in the target system in order to obtain the ground truth which is totally inaccessible to even the largest telescopes based in the Solar System.”

Actually a flyby probe would be a waste of time and resources. With hypertelescopes you get pretty close ground resolution. You can also service the telescopes and continually improve them. A probe is one shot only. It really offers nothing that telescopes can’t provide-and for much bigger cost.
The only reason to send a probe would be if we were planning to send a ground mission as well. But that wouldn’t be a fly-by probe.

Brett Bellmore November 17, 2012 at 22:29

“I’ll repeat the question I i plied in my last posting. Has anyone anywhere actually managed to ignite a single fusion pellet in the laboratory?”

I personally regard Bikini Island as a “laboratory”, but if by that you mean tiny ones? No, though they’ve reached the point of fusion occurring.

qraal November 18, 2012 at 0:20

As I pointed out to Shawn Westmoreland and Louis Crane, the black hole starship needs a gamma-ray reflector to concentrate the energy sufficiently. The spectra of black holes in the size range of interest for star-flight is largely unknown due to the necessary simplifications and lack of data at such high energies. Louis was hoping to get a clearer picture from his quantum gravity theory, but I am unsure what the current status of that work is.

Paul Gilster November 18, 2012 at 14:48

I remember when you were talking to Dr. Crane about all this, Adam. Fascinating stuff, and for those who would like more, here is Adam’s article on the black hole idea:

http://www.centauri-dreams.org/?p=11751

Brett Bellmore November 18, 2012 at 15:11

A black hole with a mass in the neighborhood of 1e6 tons would be putting out maybe 10e17 watts of power. A welding arc runs to 10e5 watts per square centimeter. So, roughly speaking, the radiation from this black hole would be equivalent to direct contact with a welding arc at about 9 km away.

Better be a pretty efficient gamma ray reflector!

Gregory Benford November 18, 2012 at 15:46

Most distressing in laser fusion is the many billions spent with no result at Livermore and elsewhere. I left Livermore because I didn’t want to work on it, suspecting it would fail. It has. The instabilities can’t be offset enough. Optimism became an easily caught disease that wasted a lot of money and talent.

It was never a serious power generating idea, as we all knew in the 1970s. It’s a weapons simulator, one that can be bested by simply testing fission triggers underground, rather than waste $6 billion/year for 20 years, as we’ve done, to do simulations etc as “Stewardship.”

Magnetic confinement fusion remains the plausible path.

GaryChurch November 18, 2012 at 19:24

“I don’t think starships will be propelled by nuclear fusion, at least not directly.”

There is molecular energy, atomic energy, and nuclear energy; fire, fission, and fusion. Beyond these sources are anti-matter and gravitational force in the form of black holes. The electromagnetic spectrum can also be used to facilitate thrust in different forms.

Chemical energy can get us outside the magnetosphere to the Moon without contaminating the Earth’s atmosphere too much. The Moon can be used as a giant beamed energy base to allow cheap lift and cheap outward bound missions. The Moon can also supply Thorium for reactors in the outer solar system and act as a safe base from which to launch nuclear missions to establish colonies using those reactors.

The Fission Fragment engine is a promising device but relies on an expensive Americium isotope. It might be useful in the future for something if this substance becomes cheaper. Not now. Fusion energy in the form of Pulse Propulsion is a way to establish colonies in the solar system and also a way to slow down at the end of a centuries long star voyage. Bombs can also be used for excavation and power generation where practical.

Beam propulsion can be used to eventually provide cheap access to space from Earth, a solar system highway of accelerators and decelerators, and a way to send a Star Ship on it’s way. As it stands, such a Starship would need to carry bombs to slow down and the missing piece of the puzzle; a freeze and revive procedure for the crew. The only other option is a truly gigantic generation ship to support a crew and their descendants.

The Small Black Hole engine is the most probable successful technology for galactic colonizations and even intergalactic travel. It is really the only candidate right now that does not require some new law of physics or unobtanium.

So, I have to disagree and hold to fusion pulse Starships as the only direct way to another system- until a tremendous amount of space solar energy is avialable for manufacturing SBH engines. As I said, right now the only technology missing is a freeze and revive procedure.

GaryChurch November 18, 2012 at 19:27

Darn…forgot to mention anti-matter catalyzed fusion. As a way to ignite deuterium the use of a small amount of anti-matter would be ideal for a pulse propulsion system. But this technology is more speculative than probable at present.

Eniac November 18, 2012 at 23:47

As I pointed out to Shawn Westmoreland and Louis Crane, the black hole starship needs a gamma-ray reflector to concentrate the energy sufficiently.

On the other hand, an absorptive shield instead of a reflector might do. It is less efficient, but has the advantage that it can actually be done. It should still be a lot better than fusion or fission.

Adam Crowl November 19, 2012 at 17:08

Hi Eniac

The reflector is to concentrate the gamma-rays to make the black-hole. Or a huge gamma-ray generating implosion device. Louis is naturally a bit vague on details.

FrankH November 19, 2012 at 17:50

@Gregory Benford – Laser fusion may be a huge waste of money, but it’s no worse than ITER. Their goal is to maybe, possibly think about break-even in 2020. February 30, 2020 sounds like as good a date as any.

If we ever develop viable fusion power, it’ll probably be via smaller magnetic confinement systems like Polywell and similar designs.

Ron S November 19, 2012 at 19:58

Adam: “Louis is naturally a bit vague on details.”

That’s exceptionally generous of you. ;-)

Eniac November 20, 2012 at 2:26

If we ever develop viable fusion power, it’ll probably be via smaller magnetic confinement systems like Polywell and similar designs.

Not likely. A big, complicated, expensive project that might succeed is still better than a nice and small one that won’t.

Eniac November 20, 2012 at 2:45

Thanks, Adam, I misunderstood that. A ship would require some kind of directing device, also. Brett’s observation about the welding arc indicates that it must indeed be a very highly reflective gamma mirror, or else it will likely vaporize in nanoseconds….

I put my hopes in magnetizing the black hole. Even a very modest induced magnetic dipole would create immense fields at the hole’s surface, enough hopefully to create tightly focussed relativistic jets at the poles, like the ones from the bigger brethren in AGNs. Maybe you could even tweak the fields so a jet would only emerge from just one of the poles. Then we’d be in business.

Just don’t point it at something you’d like to keep, like Earth.

One problem I see is feeding the hole. If it is really attometers in size, it would be a real problem to feed it just a single nucleus. It seems that the density of ordinary matter (mostly vacuum) might starve any black hole this small.

Brett Bellmore November 20, 2012 at 8:05

“If we ever develop viable fusion power, it’ll probably be via smaller magnetic confinement systems like Polywell and similar designs.”

The physics and history of the thing suggest to me that, if we ever develop viable fusion power, it will probably be by admitting that fusion doesn’t “want” to happen small scale, and building a plant that can use relatively small fusion bombs as “fuel pellets”. Which is, after all, feasible. It would just have to be a fairly *large* powerplant.

The thing is, while fusion has an obvious appeal for interstellar propulsion, (Where energy density is everything.) and for the outer solar system, (Where heavy elements are in short supply.) it makes very little sense on a planet where fission fuels are sufficiently common to power industrial civilization for longer than we’ve been walking around upright.

Fission is just too much easier than fusion, for fusion to be viable for terrestrial purposes any time soon.

Brett Bellmore November 20, 2012 at 19:40

“One problem I see is feeding the hole. If it is really attometers in size, it would be a real problem to feed it just a single nucleus. It seems that the density of ordinary matter (mostly vacuum) might starve any black hole this small.”

I think you have to enclose the hole in a sphere of ordinary matter. At the center that should be compressed to neutron star density by the intense local gravitation. The surface is absurdly hot, but not enough to have problems with pair formation from high energy radiation messing things up.

Some quick figuring indicates that as the sphere gets larger, the black hole’s grip on particles on the surface, (Escape velocity) drops faster than the expected thermal velocity of the particles based on the temperature needed to radiate the black hole Hawking radiation. On the positive side, this suggests that with a constant feed rate, the sphere will be stable in size. On the minus side, I don’t know enough of the physics to determine whether that stable size isn’t zero…

ljk November 26, 2012 at 13:14

If we are honest, the real problem with interstellar travel and exploration is not so much with the technology or the ability to accomplish this, but with the human species’ incredibly short life spans and our rather limited success at maintaining long-term collective memories and stable societies.

Technically it is not our fault, of course. Terrestrial nature made us to handle various environments on Earth and to last just long enough to mature enough to reproduce and ensure that our offspring live long and successfully enough to keep the gene pool train moving along. On Earth.

If anything regarding colonizing space here in the Sol system and beyond, our minds and bodies are still responding to this basic, primal need to seek our new lands and places to breed, only now we are just aware enough that our home planet cannot sustain so many people, especially as we have exceeded our capacity to successfully reproduce over death and its varied methods.

When the Arecibo Message was radioed out to Messier 13 in 1974, the transmission included the number of humans on Earth at the time: Three billion. Just 38 years later, four billion more people are now occupying our world. From the time humans first appeared 4 to 7 million years ago, depending on what you consider to be our true ancestors, we did not reach the first billion until around 1800. Then we became more urban than rural, our medical knowledge improved (we figured out what causes disease and how to combat it), and boom!

The point is, on the one hand it is seemingly amazing that a group of beings who could barely live together and know how to plant seeds to make food ahead of time just a cosmic blink of an eye ago can now seriously contemplate sending ships to another star. However, that same short temporal distance between the savannahs and now also means and shows how limited we are when it comes to not just what we know about interstellar engineering, but more importantly how different our makeup is compared to the rest of the Universe. By that I mean how small and fragile we are compared to, say, a typical star.

Even more to the point, we are incredibly short-lived creatures in a reality that is roughly 13.7 billion years old. A few thousand years to get to another star should, on the cosmic scale, not be a problem. But we want our answers NOW (and yes, I am just as guilty of that intellectual desire as anyone) and thinking really long-term for our descendants is still a novel idea that we have yet to master only recently have begun to practice sincerely.

I am not saying we should ever stop trying to reach the stars, literally, as that is one of the much more noble aspects and aspirations of our species – not to mention it is a refreshing change from our culture’s usual short-sighted and instant gratification. Because we probably will figure out a means to reach Alpha Centauri in a relatively short time period – and by figure out I mean build an actual ship to do the job.

What I am saying is that unless a nearly miraculous means of fast galactic transportation comes along soon, we should rather focus on starships which can be built based on known physics and available resources so that our not terribly distant children can reap the benefits of our efforts. And do this deliberately with a system and setup that preserves the information about the fact that a ship sent to our stellar neighbors is on its way there and they should be ready and able to receive its precious data.

I know there will be the usual response of “If we wait a while, someone will come along with something better and faster and we will get to Alpha Centauri in decades or maybe even 4.3 years, thus there will be no need for a slower starship.” Whether that is ultimately true or not, I think it is foolhardy to wait and hope for that to happen, because history routinely shows how often such plans fail due to societies collapsing and breeding generations of people who don’t know how to build and operate technology and even worse, don’t care about even general science and technology.

This may be a bit of a pipe dream, but that claim about needing a stable civilization in order to send ships to the stars might come from the need to maintain a strong and long-lasting system of support for our slow starships.

It doesn’t have to be every member of the human race, but a large and stable enough society that keeps things together might be enough to not only ensure our survival but eventually achieve that goal of reaching the other points of light in years and decades – and maybe even faster.

Eniac November 28, 2012 at 0:24

@ljk

to last just long enough to mature enough to reproduce and ensure that our offspring live long and successfully enough to keep the gene pool train moving along. On Earth.

There is nothing keeping that principle from working in space, as well. Civilization has to be stable just long enough to send colonies to neighboring stars and ensure that our offspring can settle there and keep the gene pool train moving along.

This may be a bit of a pipe dream, but that claim about needing a stable civilization in order to send ships to the stars might come from the need to maintain a strong and long-lasting system of support for our slow starships.

Last I checked, slow starships were required to be self-sufficient and independent of any support from back home, which it would not be feasible to provide, anyway. It would require a civilization long-lived enough only to design, build, and launch the ships. A few hundred years, perhaps, well within the range of historic precedent. After that, the gene pool train has left the station, and Earth-bound civilization is free to collapse and replaced by something completely different. Something that will likely start the process over again, sooner or later. Only this time there will be competition from the former colonies.

The other thing it takes is a much smaller organization able to keep the crew and ship functioning during transit and settlement. This is somewhat less obviously feasible than the above, but there are several avenues that could work by themselves or together: Lasting organizations, faster travel, suspended animation, and advanced robotics, to name a few.

ljk November 28, 2012 at 13:20

Eniac said on November 28, 2012 at 0:24:

“After that, the gene pool train has left the station, and Earth-bound civilization is free to collapse and replaced by something completely different. Something that will likely start the process over again, sooner or later. Only this time there will be competition from the former colonies.”

While I know what you are getting at here, I think an attitude that is in some ways detrimental to the whole concept of interstellar travel and especially concepts of galactic colonization is that we need to get to another star system because something is going to go drastically wrong with Earth and/or humanity if we don’t.

While that is true to some degree (one example is Sol expanding into a red giant sun and frying Earth, but that is several billion years from now), we should rather focus on the more positive reasons for interstellar exploration and colonization. If the general public and purse string holders see starships as primarily escape vessels, they will miss the larger and more important reasons why our species needs to expand beyond Earth. This will result in decades of symposiums on the subject but no actual ships.

It is also detrimental to assume that Earth and human civilization are just going to collapse anyway, so let’s get some of us out of here while we can. Of course this will only spread out the problem, which may make your idea of colonies spreading the gene pool moot if we just keep assuming humans are flawed and eventually self-imploding.

The very thing that gets put on the back burner and derided today, space utilization, can solve this cultural self-defeating attitude, which is why we need to focus on the positive aspects of reaching Alpha Centauri. And yes, we can do it without becoming terribly pollyannish about it.

To go back to the primary point of my initial post on this thread, we have to “fix” the human element or all our calculations and technological ideas and physics will be, again, moot.

Eniac November 28, 2012 at 23:18

@LJK: You are, of course, right about that. I did not mean to convey the impression that I think civilization will collapse. I was more reacting to your earlier pessimism on the subject, meaning to express an hypothetical “even if it were this bad, it would not prevent us” point of view.

Friedwardt Winterberg December 6, 2012 at 1:51

When writing his paper with Wood and Nuckolls, Rod Hyde must have not seen my earlier papers: 1. In the Conference Proceeding of Enrico School of Physics ” Physics of High Energy Density” 1969 Varenna, Italy, published by Academic Press 1971, and 2. “Rocket Propulsion By Thermonuclear Microbombs Ignited With Intense Relativistic Electron Beams” , Raumfahrtforschung 5, 208 (1971). Both papers propose to use the large magnetic beam field to entrap the DT fusion reaction alpha particles, and the British Interplanetary Society had based their Daedalus study on my 1971 paper. Had Hyde run beam magnetic field supported pellets through the LASNEX code he would have obtained a different result. I admit that relativistic electron beams may be not “stiff” enough, but that would certainly be true for GeV -10^6 Ampere proton beams. For them cylindrical targets would be ideal, with axially moving burn waves, as they have been suggested in all of my more recent publications. As it was shown by Kidder in the 1998 SPIE Proceedings, implosion driven spherical targets pose a serious problem in particular for laser fusion, because the input energy required for ignition is inversely depending on the 6th root of the convergence ratio. Since the NIF facility could not achieve ignition even with two Megajoule, ignition with these energies would require order of magnitude larger convergence ratios. This problem does not occur for magnetic beam field supported cylindrical targets. Regarding the 80% of the DT fusion energy going into neutrons, and to a lesser degree for the DD reaction but even for a D-He3 burn, this poses only a problem for interstellar missions, because for missions in the solar system on can place the fusion target inside a thick (30 cm radius) liquid hydrogen shell, heatet to 10^5 K by the neutrons stopped in the shell, and as a fully ionized plasma repelled by a magnetic mirror. Also this idea was contained in my 1971 paper. In this case one does not need a large radiator, because the proton beam can be efficiently produced with a magnetically insulated gigavolt capacitor by electrostatic means in space. Because of their low efficiency this is not possible for lasers which require an onboard fission reactor power plant, and with it a large radiator.

ljk December 6, 2012 at 16:21

Friedwardt Winterberg said on December 6, 2012 at 1:51:

“Since the NIF facility could not achieve ignition even with two Megajoule, ignition with these energies would require order of magnitude larger convergence ratios.”

Maybe we need to check cold fusion one more time….

Friedwardt Winterberg December 27, 2012 at 2:00

Dear Mr. ljk: The Rossi hydrogen cold fusion reactor, for example, can only work via the weak interaction, but there one would have to wait a billion years to get some energy out. The same applies to the Bussard ramjet. For this reason cold fusion is too nice to be true. I remember an International Astronautical meeting around 1956 in Zurich where von Karman said the same in German about a lukewarm, not cold, fusion idea, citing Goethe: “Es ist zu schoen um wahr zu sein”.

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