An Interstellar Reminiscence

by Paul Gilster on March 28, 2012

by A. A. Jackson

Although it was probably science fiction that got Al Jackson into interstellar flight, he remembers discovering the work of Eugen Sänger back around 1960 and becoming energized to seek out the few scientific papers on relativistic rocket designs that were then available. With a firm background in engineering, he turned to physics in 1975, receiving a PhD from the University of Texas at Austin, a natural move for a man who had worked for NASA during the heyday of Apollo as astronaut trainer on the Lunar Module Simulator. Going through Al’s papers is a fascinating exercise in its own right, but I was reminded because of our recent articles on Robert Bussard’s ramjet ideas that Al had worked with Daniel Whitmire.

Bussard spoke about fusing protons in his ramscoop engine, but subsequent analysis showed that the power needed to compress protons to fusion densities far outweighed the power that would be produced. It was Daniel Whitmire who developed the ‘catalytic ramjet’ idea we looked at yesterday, in which the starship draws its power through the much more energetic CNO cycle, a catalytic cycle that is the dominant energy source in stars more than 1.3 times the mass of the Sun. Thus the ‘catalytic ramjet’ was born, and Al would go on to collaborate with Whitmire on a laser ramjet in a paper the two published in 1977. I asked Al if he had any reminiscences of Whitmire and this period and he was kind enough to send the following.

I was looking at Bussard’s original paper the other day and I noticed he does mention without elaborating too much the idea of using a magnetic scoop and the attendant problems with synchrotron and bremsstrahlung radiation. He just did not do a quantitative calculation of these things. Seems to me it was Sagan who gave a long discussion, in print, of using a mag scoop, though that was not quantitative either, so I think Bussard and Sagan originated that idea.

Rather than making any technical comments, let me tell you a story. When I was at the University of Texas from 1970 to 1975 I used to go to the physics library a lot. I am a real library haunter… I noticed there was another grad student there as much as me, which got me curious. He noticed me too. Well I introduced myself to the guy, who turned out to be Dan Whitmire. We became boon friends, have been now for, lord, nearly 40 years. (Have not really seen much of Dan in the last 10 years).

Dan was in nuclear physics, at the nuclear studies center there, working on his dissertation, but he was interested in all sorts of things, especially relativity. So we got together a lot, schmoozing at lunch, families got together for picnics on weekends, saw a lot of him. He was not much interested in science fiction, which got me into interstellar flight…. He did not know much about the subject of starflight, but when I
brought it up, he really thought it was a neat problem.

We talked about fusion and fission propulsion and he noticed the mass ratio problem. I told him a Robert Bussard had solved that problem, and gave him a copy of Bussard’s paper. Dan read it very carefully, noticed the problem with the smallness of the proton-proton reaction (in fact that was kind of Dan’s dissertation work, the main work on that had been done by Willy Fowler — Dan worked on some variant on it, so Dan really knew the physics).

He told me he had a solution for the proton-proton problem. It took Dan a month or so of calculating, but one weekend he wrote up the paper, showed it to me and asked where to send it. I thought the same place Bussard had published his, Astronautica Acta (which , for some reason, later swapped its name around to Acta Astronautica). I could have suggested JBIS but AA seemed more to the point. I kind of understood that paper better then than I do now.

A funny story. Dan’s adviser let him use his secretary to type up the manuscript, thinking it was an interesting exercise. Dan sent it to Astronautica Acta, where there was some minor revision and they accepted and published it. Dan did not get much reaction… but about a few months later Dan got a bill for page charges. Dan had thought publication was free! He showed this to his supervisor, who had no money for extracurricular papers so he told Dan to throw it away. Dan never heard anything about it, but he never published there again.

Dan graduated the same year as me and went to Southwest Louisiana in Lafayette (I think it’s called U of Louisiana now, it was and still is a pretty large school). In 1976 or so Dan got a call from Bob Bussard saying he would be in Lafayette and would like to meet him. Bob really loved Dan’s paper and they had a great day of it, wish I had been there.

Bob and Dan corresponded for many years. Enclosed is one of Bussard’s early letters that Dan copied to me. (Dan had some idea about detecting XT civilizations by the radioactive waste they dumped into their local star). You can kind of see what Bob thought about interstellar flight in the letter, he was really interested but never wrote another ‘really technical’ paper on it. (I can’t find my letter from Bob, but that did not say much except that he would accept our invitation to come to an AIAA meeting in San Francisco).

A few clips from Bussard’s letter to Whitmire (dated November 19, 1976) follow. We learn, for example, that Bussard became a champion of the catalytic ramjet idea that so significantly extended his concept:

Of course, your paper on the catalyzed ISR [interstellar ramjet] is a milestone contribution, as it offers a solution to the dominant n2 (σ V) problem of the p,p chain invoked (hypothetically) in my own 1960-ish note on the ISR. Your paper will become an enduring classic in this field.

We also learn that Bussard, at least as of late 1976, was not at all taken with many of the ramjet’s alternatives, especially those with a laser component:

Not so, I fear, for the proliferating array of alternative interstellar propulsion means. From experience and intuition (no physics) I am suspect of all schemes which solve the problem by putting it somewhere else, e.g., in the external-laser-driven ships, whether of photon-reflective, scoop-collecting, or on-board-fuel-mass variety. The problems of the driving laser(s) seem to me so overwhelming as to make those of the ISR, which is (in principle) self-contained, seem tractable.

And finally, Bussard’s thoughts on Whitmire’s interest in detecting extraterrestrial civilizations through unusual stellar signatures, a form of SETI we’ve described in these pages as ‘interstellar archaeology’:

No, I have not yet written the book in my mind on this topic (implications of diffusion theory) – sheer procrastination – but may get to it in 1977. Meanwhile, I still think it would be fascinating to do the ‘observables’ problem for the ISR galactic community, and seek NASA funds to go and look for signatures.

Thanks to Al Jackson for his reminiscences and the above letter. It’s fascinating that both Bussard and Whitmire were already thinking (in the 1970s!) along the lines of those who today would like to look for the signatures of advanced civilizations as revealed in astro-engineering or other large scale modifications to their environment. We’ve written a good deal here about people like Milan Ćirković and Richard Carrigan, who have urged hunting, among other things, for interesting infrared signatures that might reveal Dyson spheres. But the possibilities are numerous (see Eternal Monuments Among the Stars for more, or search the archives). What would a galactic community look like if interstellar ramjets were in use? Where would we look, and using what tools, to observe their signatures?

tzf_img_post

{ 2 comments }

Adam March 28, 2012 at 16:01

Sagan’s “Direct Contact” paper from 1963 might give an idea of a Galactic community using ISRs. He assumed they’d launch 1/yr and thus explore the Galaxy, touching on every habitable system, contacting each other (Sagan estimated 1 million civilisations) and so on. Thus non-technological planets with life might get a visit every 10,000 years. The ETIs operating their Star-Fleets might also leave monitoring bases (this paper was before Bracewell’s probe paper) and thus our first contact might be in our own Solar System.

What has changed? In the 1970s ISRs became disfavoured, while slower star flight seemed more plausible thanks to O’Neill’s cylinder-city designs. But crawling between the stars for centuries made colonisation seem more compelling than merely studying other systems, thus the Fermi Paradox seemed even more paradoxical.

And since? We know exoplanets exist. We haven’t seen O’Neill colonies fill the sky. We argue over the singularity. And we’re revisiting the Ramjet…

ljk March 29, 2012 at 9:04

Mr. Jackson, if you have not already, I sincerely suggest that you write your autobiography.

Comments on this entry are closed.