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John Ford Fishback and the Leonora Christine

Like the Marie Celeste, the Leonora Christine is a storied vessel, at least among science fiction readers. In his 1967 story “To Outlive Eternity,” expanded into the novel Tau Zero in 1970, Poul Anderson described the starship Leonora Christine’s stunning journey as, unable to shut down its runaway engines, it moved ever closer to the speed of light. Just how a real Leonora Christine might cope with the stresses of a ramjet’s flight into the interstellar deep is the subject of Al Jackson’s latest, which draws on memories not only of Robert Bussard, who invented the interstellar ramscoop concept, but a young scientist named John Ford Fishback.

by A. A. Jackson

Project Pluto – a program to develop nuclear-powered ramjet engines – must have been on Robert Bussard’s mind one morning at breakfast at Los Alamos. Bussard was a project scientist-engineer on the nuclear thermal rocket program Rover — Bussard and his coauthor DeLauer have the two definitive monographs on nuclear propulsion [1,2]. He said many times that the idea of the hydrogen scooping fusion ramjet came to him that morning. This was sometime in 1958 or 1959 and the SLAM (Supersonic Low Altitude Missile) would have been well known to him. SLAM was an nuclear ramjet, a fearsome thing, sometimes called the Flying Crowbar. Finding a solution to the mass ratio problem for interstellar flight was also something on Bussard’s mind. Thus was born the Interstellar Ramjet, published in 1960 [3].


Image: Al Jackson delivering a plenary talk at the recent Tennessee Valley Interstellar Workshop. Credit: Joey O’Loughlin.

Most here at Centauri Dreams know that the interstellar ramjet scoops hydrogen from the interstellar medium and uses this as both a fuel and energy source by way of fusion reactor. The sun does proton fusion using gravity as the agent of confinement and compressional heating. However, doing fusion in a ‘non-gravitational’ magnetic fusion reactor makes the process very difficult [3,4]. That is, the proton and Deuterium burning is quite severe to realize on a ‘small scale’. Dan Whitmire attacked this problem by proposing the use of a carbon catalyst using the CNO cycle [4]. The CNO cycle is about 9 orders of magnitude faster than proton-proton fusion. It would still require temperatures and number densities way beyond any technology known at this time.


Bussard noted a number of problems such as losses from bremsstrahlung and synchrotron radiation. He also noted scooping with a material scoop would create a problem with erosion, hinting that magnetic fields might be used, and noting that drag would have to be accounted for.

About 8 years after Bussard’s paper, an undergraduate at MIT, John Ford Fishback, took up the problems Bussard had mentioned. He wrote this up for his Bachelor’s thesis under the supervision of Philip Morrison. The thesis was published in Astronautica Acta [5] in 1969.

Image: Physicist Robert W. Bussard.

Fishback did three remarkable things in his only journal paper: finding an expression for the ‘scoop’ magnetic field, computing the stress on the magnetic scoop sources, and working out the equations of motion of the ramjet with radiation losses. These calculations were done using a special relativistic formulation.

Fishback’s most important finding is noticing that when capturing ionized hydrogen to funnel into the fusion reactor, there is a large momentum flow of the interstellar medium which must be balanced by the scooping and confining magnetic fields. Using very general arguments, Fishback showed that sources (magnetic coils and their support) of the magnetic field determine an upper limit on how fast a ramjet can travel. The convenient measure of starship speed is the Lorentz factor


where v is the starship velocity and c the speed of light. It comes from the physical properties of the field sources, in particular the shear stress.

At the time, Fishback modeled the upper limit using diamond, because of its shear stress properties, and found that one could only accelerate until the Lorentz factor reaches about 2000 [5,6]. Tony Martin expanded on Fishback’s study [6, 7] in 1971, correcting some numbers and elaborating on Fishback’s modeling. Since that time, Graphene has been discovered and it has a shear stress that allows a limiting Lorentz factor of about 6000. This in turn implies a range of over 6000 light years when under 1 g acceleration. It does not mean the final range is 6000 light years, but one must travel at a reduced acceleration and then constant speed, which means a longer ship proper time.

This is bad news for the Leonora Christine of Poul Anderson’s Tau Zero [8].The range can probably be pushed to 10,000 light years, but accelerating at 1 g for 50 years would bust the Lenora Christine’s coils! That is, unless some magic material is found to take the stress loading at a Lorentz factor 1019, there is no way to circumnavigate the universe. And with the new accelerating universe, the story of Tau Zero becomes still more complicated.


Image: The interstellar ramscoop as envisioned by artist Adrian Mann.

What became of John Ford Fishback? I went to a lecture in California at Stanford in 1979 by Phillip Morrison. After the lecture I asked Morrison what had happened to Fishback. Morrison sadly told me that Fishback had gone to the University of California at Berkeley to work on his doctorate, but had committed suicide.

1. Bussard, R. W.; DeLauer, R.D. (1958). Nuclear Rocket Propulsion. McGraw-Hill.

2. Bussard, R.W.; DeLauer, R. D. (1965). Fundamentals of Nuclear Flight. McGraw-Hill.

3. Bussard, R.W., “Galactic Matter and Interstellar Flight”, Acta Astronatica, VI, pp. 179-195, 1960.

4. Whitmire, Daniel P. , “Relativistic Spaceflight and the Catalytic Nuclear Ramjet”, Acta Astronautica, 2 (5-6): 497–509, 1975.

5. Fishback, J. F., “Relativistic interstellar spaceflight,” Astronautica Acta, 15 25–35, 1969.

6. Anthony R. Martin; “Structural limitations on interstellar spaceflight,” Astronautica Acta, 16, 353-357 , 1971.

7. Anthony R. Martin, “Magnetic intake limitations on interstellar ramjets,” Astronautica Acta, 18, 1-10 , 1973

8. Anderson, Poul (2006), Tau Zero, Gollancz. ISBN 1407239139.

Table 1. Cut-Offs and Range for Ramjet accelerating at 1g. Interstellar medium 1/cm-3 using the p-p fusion reaction.

Structural Material𝛔/𝛒
dyn cm-2/gcm-3
Stainless Steel.26136.27.5

Addendum: While he was working on this article and corresponding with me, Al shared the story with Greg Benford, who had further thoughts on John Ford Fishback, as below:


Good article. I can add a touch: I was interested in this, after Edward Teller pointed out to me Fishback’s 1969 paper in Astronaut. Acta. I discussed it with Teller and did some calculations (just exploratory, never published). The idea seemed extreme but enlivened my discussions of the paper with Poul Anderson, who lived in Orinda near my Walnut Creek home and whom I saw often.

Someone told me Fishback was at Berkeley and I called him, agreed to meet. I had a one-day-per-week agreement with the Livermore Lab, where I was just turning from being a postdoc for Teller into a staff physicist — I spent Wednesdays at the Lab in Berkeley. So I met him at an Indian restaurant–a rail-thin smoker, nervous, ascerbic. “I wanted to show that we could reach the stars, really do it, with the right engineering,” he said, approximately. His anxiety was clear, but not its cause.

I found him an odd duck but was shocked when a bit later I heard he had killed himself.

When I mentioned it to Poul, he found it contrasting that a man who wanted the stars would cut off his own personal hopes. We often discussed Tau Zero, Poul once remarking that he wished he had taken more time to polish and expand the novel, since it already looked as though it might be the most remembered of his works–and indeed, seems so. He said he had written it in a few months and needed the money–its 1967 serialization in Galaxy helped, but it was tough going as a full-time pro writer then. Plus he had a word limit on the hardcover.

Poul used his Nordic background in the novel, as he liked to do. From Wikipedia:

“Incidental to the main themes is the political situation on the Earth from which the protagonists set out: a future where the nations of the world entrusted Sweden with overseeing disarmament and found themselves living under the rule of the Swedish Empire. This sub-theme reflects the great interest which Anderson, an American of Danish origin, took in Scandinavian history and culture. In later parts of the book, characters compare their desperate situation to that of semi-mythical characters of Scandinavian legend, with the relevant poetry occasionally quoted.”


Comments on this entry are closed.

  • Greg Matloff April 1, 2016, 9:36

    I discussed the work of Fishback with Al and Greg during the recent Tennessee Valley Interstellar Workshop. Fishback’s paper was brilliant, It inspired a host of researchers, including me. What a paradox that such an original thinker would take his life! If he had only hung on a few more years, he would have seen his work cited in designs of ramscoops and possibly feasible ramjet derivatives in the early Interstellar Studies issues of JBIS.

    • Michael April 2, 2016, 12:03

      Hi Greg, Al

      Its always great when you post here,

      I was thinking the stress issue may be alleviated somewhat by deflection and great acceleration of some on coming particles (maybe waste He ions) to the sides to cause a compressive force to oppose the tensile build up in the structure.

  • James Stilwell April 1, 2016, 11:08

    Got it…
    No more talk about plodding along at one million miles an hour to alpha centauri…still need several smallish artilect guided scout ramjets to map the best course from here to there…wouldn’t want to find myself plowing through a nasty dusty rocky debris field along the way…mid-course changes would seem a bit difficult if even possible were a rogue planet encountered…counting on luck would be ill advised…
    A great post…

  • Al Jackson April 1, 2016, 11:12

    A small correction.
    I notice I labeled column 3 in Table 1, gamma*beta*c , that should read simply gamma. Fishback and Martin used gamma*beta but when gamma is big beta is essentially 1.
    Also ‘proton’ means the proton-proton chain fusion reaction. Actually this could be CNO for the CNO cycle but the energy production is almost the same.

  • Charlie April 1, 2016, 13:49

    “At the time, Fishback modeled the upper limit using diamond, because of its shear stress properties, and found that one could only accelerate until the Lorentz factor reaches about 2000 [5,6]. Tony Martin expanded on Fishback’s study [6, 7] in 1971, correcting some numbers and elaborating on Fishback’s modeling. Since that time, Graphene has been discovered and it has a shear stress that allows a limiting Lorentz factor of about 6000. This in turn implies a range of over 6000 light years when under 1 g acceleration. It does not mean the final range is 6000 light years, but one must travel at a reduced acceleration and then constant speed, which means a longer ship proper time.”

    What does it mean that the ” …shear stress that allows a limiting Lorentz factor of about 6000.” ??
    I don’t understand the relationship between acceleration and shear stress; I would assume that if you accelerate at a rate which is unchanging that the stress on the coils would be a manageable factor.
    I mean if you accelerate at a reasonable rate in a car, for example, and you don’t push the acceleration into such a region that it stresses the car engine beyond its engineering tolerance, you can reach any desired speed you want – you just have to keep feeding the gas to the car until you reach the top speed you want. Nothing magical here. Why is this thing with regards to the coils of this magnetic scoop any different ??
    Could someone please explain this to me ??

    • Michael April 1, 2016, 18:46

      The shear ‘weight’ of material ahead.

    • Harold April 2, 2016, 10:15

      As the ramjet accelerates, its mass will increase and its space time will vary along its…length and time; it will become “heavier” and be stretched and compressed, putting tremendous stress on the structure. Your car experiences the same effects but because it is traveling so slowly, they are barely noticeable.

      • Michael April 2, 2016, 16:14

        The inertial frame of the moving craft will have the same properties as the stationary inertial frame, its is the velocity difference that gives the illusion of the change in length, there is no physical change in length.

        If it were the case that the density increased as it got faster then particularly fast protons from cosmic rays which have high energies, 1 x 10^20 eV’s would have collapsed to form black holes as the nucleus is relatively near the BH density already, they clearly have not.

        Not to worry, I made that mistake before, I should have stayed awake during lectures!

        • djlactin April 3, 2016, 11:51

          Another perspective is that the spacetime (that contains the moving object) itself contracts, (from the perspective of an external observer); but an object in the contracted spacetime it does not ‘notice’ the change, so dimensions like lattice constants do not change: shear stress does not happen. Just like a moving observer measures c = 3 x 108 m/s in any direction regardless of how fast he is moving.

    • Eniac April 3, 2016, 9:56

      If you keep accelerating your car, eventually your rear view mirrors will be blown off for lack of shear strength in their supports. This is the same, just replace wind by oncoming protons and mirror by ramscoop.

      This whole thing about shear strength is somewhat irrelevant, because the same “proton wind” that might blow the diamond ramscoop to pieces at gamma 2000 will also stop the craft in its track. At much, much, lower velocities.

    • Al Jackson April 3, 2016, 12:53

      I should have mentioned, earlier than I did, that the limit is for a constant 1g acceleration. One can still accelerate beyond the gamma cutoff but the acceleration has to tail off.
      The reason for the gamma cutoff is at base the conservation laws of physics. Conservation of momentum and energy. The rate of momentum flow into the scoop field must be balanced by the capacity of the structure to absorb it. If the configuration is to be in equilibrium the magnetic forces will everywhere be balanced by mechanical forces.
      The calculation gets a little involved and Fishback uses conservation laws and a thing called Kash’s [1] minimum mass theorem to calculate the gamma limit as a function of a material’s tensile strength.
      [1] Kash,S.W., Magnetic space shields, Advances in Plasma Dynamics, pp.135-166. Northwester Univ. Press (1964).

  • Dana Andrews April 1, 2016, 15:36

    The stress limits mentioned are within the scoop area. As Robert Zubrin and I showed back in 1988, the magnetic dipole field extends way beyond the scoop area, and acts to deflect the protons beyond the scoop resulting in far more drag than thrust. Hence, the magnetic scoop interstellar ramjet is really an effective braking device.

    • Al Jackson April 1, 2016, 21:59

      I have just started looking at Fishback’s paper again. Is the field he derives in the section under The Magnetic Field a dipole? It does not look like one.
      Also in the section Equations of Motion Fishback seems to account for the momentum balance of the ram jet. This is done in a kind of plasma physics way, with a Boltzman distribution of scooped particles. He seems to establish some physical constrains on the factors F and N that allow acceleration. Tony Martin does the same thing in his ” Magnetic Intake Limitations on Interstellar Ramjet” paper. Is the analysis in the papers wrong? I mean they seem to conclude that the field can be configured both for acceleration and deceleration (thought they don’t talk much about the ‘braking’ part).

  • Sanford Zane Meschkow April 1, 2016, 16:34

    Does this translate to mean that fusion ramscoop drives with reasonable safety factors could be used to reach exoplanets within 50 light years with some limited time contraction to shorten subjective trip times? It would be more realistic to expect success if the crew were young married couples and their kids were to be the actual colonists. My descendants in 2100 don’t really need to visit the Core or any globular clusters, but I would like them to be able to check out some nice real estate on planets circling Zeta Tucanae, Chi Ceti, or 82 Eridani if they want to.

  • evan April 1, 2016, 18:00

    @Charlie I am no engineer (well I am a software engineer) but I would guess that as the ship accelerates and it’s velocity increases the ship’s magnetic field would encounter more and more material (interstellar gas) per second and encounter it with greater force. Thus the faster the ship travels, the more force applied to the field coils. Since we are traveling at a constant acceleration we can then calculate how many ly we can travel before a given material can no longer withstand the additional force.

    Like I said I am just guessing so if anyone out there can explain this for real that would be great!

  • Joe G April 1, 2016, 18:44

    I always wondered if a “magnetic scoop” traveling incredibly fast through albeit very thin hydrogen gas would induce a massively dangerous electric charge… Maybe one of the engineer/physicists out there could answer that…

    • Michael April 2, 2016, 11:53

      If the ramjet’s magnetic field cuts any neutral gas the gas will become ionised if fast enough, fractions of c are more than enough. Locally the charged particles will want to recombine as they are oppositely charged so there is no net charge. However electrons are much lighter than nucleus’s and if they gain extra energy they could flow away from the collection area at a greater rate. There would be a glow in the front of the scoop due to recombination events and friction, how detectable it would be I am not sure about.

      Here is an image of a stars bow shock, I would think it would be the same but the other way around to the stars, and much flatter due to the starships velocity.


  • Joe G April 1, 2016, 19:13

    An afterthought, would a bussard ramjet produce any kind of effect that would be observable? Would a magnetic scoop create a glow in the gas in front of the ship? Might there be any kind of radio emissions?

    • Al Jackson April 2, 2016, 15:23

      This has been looked at:
      D. R. J. Viewing, C. Horswell, E. W. Palmer, “Detection of Starships,” JBIS, 30, 99-104 (1977),
      R. Zubrin “Detection of Extraterrestrial Civilizations via the Spectral Signature of Advanced Interstellar Spacecraft,” Progress in the Search for Extraterrestrial Life, ASP Conference Series Vol. 74 (1995)
      Unfortunately even large energetic ships are very very dim compared to astronomical objects , at least at the distances that would make the detection statistics tractable. Still it is worth study, lord knows what advanced civilizations might deploy.

  • Brett Bellmore April 1, 2016, 21:50

    Back to what Dana said: later, more complete calculations show the scoop creates more drag than fusing the hydrogen collected can thrust. It’s a break, not a drive. Even assuming you can fuse protons at a worthwhile rate.

    Well, fine, for half of any mission, a brake is what’s needed.

    It’s also a great sail if you’re using mass beam propulsion, while also protecting the ship from interstellar gasses.

    Just not a ramjet, which really is a pity.

  • Charlie April 2, 2016, 16:28

    In revisiting what was said @Evan, where the statement was made that the faster the ship travels, the more interstellar material it encounters and therefore the drag increases.
    That got me to wondering about the magnetic scoop that is being used as the collector for interstellar hydrogen.

    As presumably this magnetic scoop would encounter greater and greater quantities of material to be gathered and this would cause a back reaction on the generating coils for the magnetic field would it be possible to permit a certain amount of “leakage” of interstellar hydrogen through the magnetic scoop, such that it would lessen the force on the scoop, and ultimately the coils that generate this magnetic scoop ??

    The advantage here of allowing some of the interstellar hydrogen to escape would be twofold. First off, it would lessen the amount of drag that the ship would encounter, but at the same time. Secondly, it would still allow collection of some hydrogen to be ultimately fed into the engine and still permit the ship to accelerate. Has anyone ever considered this particular arrangement of geometry and approach ?

  • Charlie April 2, 2016, 16:47

    @Al Jackson

    would you be kind enough to post a link to Fishback’s paper here on this website ?

    • Paul Gilster April 3, 2016, 8:59

      Charlie, the article is under copyright by the IAF — no direct link available.

  • Gregory Benford April 2, 2016, 18:17

    Joe G: Yes, I wrote a story ‘Bow Shock’ about detecting GHz emission from a starship. It’s in my Best Of.
    On the ship field: as Michael said, at greater distances the mag field is always dipolar, & Fishback’s solution is only for the inner portions (which one could get with extra magnetic coils; it’s not just a single dipolar field). The major braking effect comes from the distant dipolar form (which drops off as r^-3).

    I like also Michael’s remark:
    “I was thinking the stress issue may be alleviated somewhat by deflection and great acceleration of some on coming particles (maybe waste He ions) to the sides to cause a compressive force to oppose the tensile build up in the structure.”
    Yes, blend in higher mass atoms, ionize, and accelerate them by passing them through the fusion core, spew out the back in a mag nozzle. An offset to the drag. Should calculate that…

    • Michael April 3, 2016, 14:51

      If we matched the magnetic field to the hydrogen which has a lower ionisation energy need, the fuel, and allowed the heavier He (harder to ionise) to pass a little through. We then accelerate the He ions that go through the scoop to act as counter active force on the structure reducing the shear forces which want to turn the scoop into poop.

      We may have to let some gases to leak through and be accelerated to prevent the collapse of the structure, a compromise. But the brake concept has a lot of advantages as well in space, we could be in a win-win no mater what we do.

      This design just does not want to give up, if it worked we would be laughing.

  • Sean robert meaney April 2, 2016, 18:36

    I wonder what structural rating we can get from solid proton mass. I envision solar proton collectors feeding protons into three dee printers in space to print O’Neil cylinders. If graphene is six rated above six thousand, what of pure protons?

    • Eniac April 3, 2016, 10:37

      Proton will be rated at 0, because that is the shear strength of hydrogen gas.

  • Simon Kaufmann April 3, 2016, 5:58

    Dears Sirs;
    I would like to ask some questions
    Would it be possible to use proton-bore laser inertial fusion for starting the engine and latter a laser ignition scheme for the proton-proton reactions? Cross-sections are less of a problem when you think fast ignition and laser accelerated protons. (see http://spie.org/newsroom/technical-articles/5965-clean-boron-fusion-using-extreme-laser-pulses and http://www.fusenet.eu/node/575 )
    Could we can think of a laser scoop also or a magnetic-laser scoop arrangement integrating the new powerful scalable technologies as fiber lasers? Maybe some new beam forming techniques could induce new forces on the ionized protons? And New supraconductors magnets?

  • Eniac April 3, 2016, 10:29

    Another issue with ramscoops and magnetic sails is that surprisingly often people simply assume the magnetic field be constant (dipole or whatever) and determined by the coil alone, ignoring the contribution of plasma currents. Long before the material of the generating coil would break from shear, the magnetic field would be dragged away by the plasma, just like the magnetic field of the Earth is blown into a shell of limited extent around the Earth with a long downwind tail. When there is moving plasma, there is no “dipole field”. The field gets shaped by the plasma, more than by its source. This is not going to work in favor of ramscoops or magnetic sails of any kind.

    • Michael April 3, 2016, 15:42

      The large hadron collider does pretty well holding the path of those proton and lead bunches without falling apart, granted it needs a seriously strong support structure.

      I do feel, in the back of my mind that this concept looks good on paper but will never work in practice, nothing wrong with dreaming though.

      (BTW all, don’t misspell hadron in google images)

    • Dana Andrews April 3, 2016, 20:14

      Agreed. We always integrated the plasma pressure versus the dipole field to get the boundary shape to calculate drag for the MagSail.

  • Erik Landahl April 3, 2016, 13:14

    I’d never heard of John Ford Fishback until I read Centauri Dreams today. Thanks Al and Greg B. for bringing his work to us and to Greg M. for stating how much Fishback’s work inspired you. How influential his work turned out to be, considering his extremely brief career. It sounds like, and I assume that, he was severly depressed.

    Depression is a medical disease, caused by brain chemical imbalances and other medical factors. Depression is far and away the leading cause of suicide. Depression is not a choice. Yet society still quietly teaches us that if you have depression you should keep it to yourself, because it is a sign of unfitness, of weakness. So goes the unspoken diktat.

    Almost 41,000 people per year die of breast cancer in the U.S., but almost 43,000 people per year die from suicide. If you know someone with depression, please treat them the same way you would someone with breast cancer. Never laugh behind their back, marginalize them, or trivialize their disease. Have sympathy for their suffering, respect their struggle, and offer help if you can.

    John Ford Fishback, rest in peace. We’ll never know what else you might have conceived to help us realize our Centauri Dreams. But thanks for what you did while you were here.

  • Charlie April 4, 2016, 1:35

    @Al Jackson

    in regards to your most recent comment, as follows, “The reason for the gamma cutoff is at base the conservation laws of physics. Conservation of momentum and energy. The rate of momentum flow into the scoop field must be balanced by the capacity of the structure to absorb it. If the configuration is to be in equilibrium the magnetic forces will everywhere be balanced by mechanical forces.”

    I started to ask some questions to another poster, which had a very similar comment to what you yourself had said. I posted a reply by way of a question as to whether or not generating coil stress can be lessened by interstellar hydrogen leakage (please see my last comment). Does that speculation of mine in any way change your conclusions ? I certainly see where you’re coming from that, the lessening of the acceleration would probably be an necessity to prevent overtaxing of the field coils (allowing the acceleration, for example, to fall below 1 G).

    I would like to further add my hearty ascension to what the author of tau zero had to say concerning his story; I agree that is probably one of the best science fiction stories EVER, even if he had been given more time to actually work it up in finer detail. It’s just so engaging just the way it is; I’m still amazed that no one is ever produced a film based upon his book. Perhaps, though no film could ever do it any real justice.

    • Al Jackson April 4, 2016, 11:35

      Hi Charlie,
      I will have to study what you have said. I am 40 years past my grad student days and plasma physics was not my PhD field of study, tho I know a little.
      Fishback’s paper takes a bit of attention and I am still trying to go through it. He leaves some steps for the reader to fill in but his analysis looks sound. He derives the most complicated equation of motion for the ramjet I have ever seen! I note that Fishback remarks several times about problems with each area he studies, especially stability , nonlinear effects always bedevils real engineering physics. He says he was working on a second paper, and he may have been, but that, alas, was never realized.

      Modern science fiction as visual media is a real bee in my bonnet. Like you say Anderson’s Tau Zero is a good story with really good physics (except for one piece of poetic license). People seem, now, to like good science in their films and TV (even if they don’t understand it), but the scattering cross section is still small. Still the Martian did well last year and it is good! (I grew up having to watch Cat Women of the Moon and Plan from Outer Space!) It is a big big mystery as to why Hollywood has not used more of the source material in the best of modern science fiction. Sy Fy did Childhood’s End when they could have done Rendezvous with Rama.

  • kzb April 4, 2016, 12:39

    According to “Bell’s spaceship paradox” there are indeed stresses set up in the accelerated frame. Seems a bit odd to me but all I can say is check out the Wikipedia page on it:


    • Eniac April 4, 2016, 22:14

      The “paradox” postulates that all points of an object (or the two rockets in the example) accelerate equally and simultaneously in the observer’s resting frame S. However, an accelerating object actually accelerates equally and simultaneously in its own resting frame, which means that the accelerations are NOT simultaneous and equal in the external rest frame, at relativistic velocities. I think this solves the so-called “paradox”.

    • Michael April 5, 2016, 6:40

      It is an optical illusion, much like what happens with water distorting an image, the string only appears to get longer but does not. If we had a massive string and it shrank in the moving frame to almost zero it would form a BH and then on slowing down the BH would ‘reverse’ with the string getting longer and longer which would reverse time which contradicts entropy increases with time.

  • kzb April 6, 2016, 8:14

    Michael: the point of the solution to the paradox is that it is not simply an optical illusion. The string really has to get longer or break. Also, relativistic mass is held to be not real mass -its gravity does not increase and it does not form black holes. Otherwise, this would really happen with the highest energy cosmic rays -but BH formation is not observed.

    Eniac: yes I am sure the explanation is along those lines, and it is not a real “paradox”. The point I was making is that relativistic acceleration must put additional stress on extended structures, due simply to relativistic effects.

    Relativity seems to get very complicated when you have to consider real objects rather than “points”. The relativistic rotating cylinder is another problem which seems still under debate by the experts.

    • Michael April 10, 2016, 15:08

      You see here is the issue, the proton is made up of quarks and their field particles, the fastest recorded proton was at 99.99999999999999999999951 % the speed of light, that’s gamma 300418. This is so near the speed of light that if a photon were travelling with the particle, it would take 220,000 years for the photon to gain a 1 centimeter lead!

      If we traveled at the that velocity we would not have to worry about gravitational bone loss because it would be occurring at 1/300418 of the normal rate.

      It had 3×10^20 eV of energy in such a small region and such a high velocity but the quarks did not fall apart or become weakened. It appears that space-time is made of something special that must be very, very small indeed and does not interact with mater to any degree other than telling mater where to go.

  • John Herlosky April 14, 2016, 2:54

    The talk has been about the drag factor in ISRs and in the concept of air-breathing ramjets it is the same. Ramjets are only good up to about Mach 4-5 as they have stall problems as the airflow decelerates. What you need is the interstellar equivalent of a scramjet, with some sort of MHD field effects that replicate an air-breathing scramjet that solves the drag problem in the engine. As for the drag experienced by the scoop itself, as the vehicle’s speed increases the cross-section of oncoming protons would also increase then could not the ramscoop also be tuned down since the cross section would increase as the vehicle’s speed increases, thereby reducing drag. I’m not a plasma physicist but the ISR is such an elegant idea I think it is too early to give up on the idea. Dr. Benford and others in plasma and computational physics might find a saving grace!.

  • Michael April 14, 2016, 10:01

    The way I see to resolve the shear issue is to allow some particles (He), that are not to undergo fusion, to be accelerated through the scoops surface area using energy from the main drive. The reaction to the acceleration of the waste particles will be transmitted into a compressive manner on the scoop where materials are much stronger. There is even the potential possibility of using the magnetic field as the support and remove a lot of stress to the structure altogether but I would not know how to calculate it, magnetic fields under compression would be very complex indeed.