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A Brief Window: The Bussard Ramjet in the 1960s

It’s fascinating to watch how expansive ideas take hold in the public imagination. The idea of a starship that could scoop up particles from the interstellar medium came to Robert Bussard while he was at Los Alamos Scientific Laboratory and, as we saw recently in our articles on slowing down a starship, became the basis for subsequent magsail concepts because Bussard’s design evidently generates far more drag than effective thrust. But before the problems of the design became widely known, Walter Sullivan, a writer for the New York Times, had brought the ramjet into play for future human journeys to the stars in a book called We Are Not Alone (definitely not the same book as the 2011 title by Dirk Schulze-Makuch).

Subtitled ‘The Continuing Search for Extraterrestrial Intelligence’ in its latest revision, the original 1964 book was written at a time when SETI was an infant discipline (although the later revision goes through the Drake equation and places SETI in the context of developing theories of astrobiology). In 1964, Drake’s Project Ozma forays were only four years old and, for all we knew, SETI might make a breakthrough any time. When one pondered the possibilities of human journeys to the stars, perhaps encountering one of those extraterrestrial civilizations that SETI might reveal, Sullivan turned to the Bussard ramjet as a potential enabling technology.

This was the same year that Stephen Dole’s RAND Corporation study Habitable Planets for Man was released as a popular title called, simply, Planets for Man, co-written with Isaac Asimov. Dole and Asimov would have known about Bussard’s ideas, although they don’t mention them by name in the book. But in a brief chapter called ‘Star Hopping,’ the authors describe a program of exploration through robotic probes leading to human missions, noting the useful effects of time dilation at extreme velocities:

At velocities approaching the speed of light…, relativistic time-contractions become quite evident, so that for a particular round trip considerably less time would seem to have elapsed for the traveler himself than for an Earthbound observer. Thus, enormous distances (from the viewpoint of the Earthbound observer) could be traversed in 20 years (from the standpoint of the traveler) if velocities very close to the speed of light are attainable.

Published by Random House and with the eye-catching Asimov’s name on the cover, Planets for Man brought the concept of interstellar migration front and center and, coupled with Sullivan’s curiosity about extraterrestrial life, kept the public engaged with ideas of extreme technologies enabling star journeys. The other key title of the era was the 1966 book Intelligent Life in the Universe, by Russian astronomer and astrophysicist Iosif S. Shklovskii and Carl Sagan. Like Planets for Man, this title has an extended history. Shklovskii had written the original in Russian, a volume whose title translates as ‘Universe, Life, Intelligence’ in 1962. Sagan came in as co-author for the 1966 release, adding new material that Shklovskii then commented on.

The book is a classic, fascinating in large measure because of the way it was assembled, with a core text enriched by a series of annotations, clarifications and new material, with later additions by the original author — we see two keen minds pushing back the frontiers of thinking on extraterrestrial life and our place in the universe. Along the way, Shklovskii and Sagan developed the idea of time dilation in terms of a spacecraft that moves at a constant acceleration as far as the mid point of its journey, then decelerates at the same rate all the way to its destination. Although it was not as widely marketed as the Sullivan or Dole/Asimov titles, Intelligent Life in the Universe showed to those who were paying attention that such accelerations allowed trips to the stars. In fact, in terms of ship-time, reaching the galactic core became a matter of just 21 years, while the Andromeda galaxy became accessible within a mere 28.

There is, of course, no going home after such journeys, unless the travelers want to return to the Earth of a remote futurity. But the idea that a human might make such a journey — or the far more likely one to a nearby star — was spreading beyond science fiction. The Bussard ramjet now enters the Shklovskii/Sagan discussion, in the context of other problematic starship ideas:

A way out of these difficulties which approaches elegance in its conception has been provided by the American physicist Robert W. Bussard, of the TRW Corporation, Los Angeles. Bussard describes an interstellar ramjet which uses the atoms of the interstellar medium both as a working fluid (to provide reaction mass) and as an energy source (through thermonuclear fusion). There is no complete conversion of matter into energy. Such a fusion reactor is certainly not available today, but it violates no physical principles. Its construction is currently being very actively pursued in research on controlled thermonuclear reactions, and there is no reason to expect it to be more than a century away from realization on this planet.

Despite their enthusiasm, Shklovskii and Sagan go on to look at the huge problems involved in creating the interstellar ramscoop and shielding its crew, even assuming the necessary proton-proton fusion reaction could be ignited and sustained. As we saw recently, follow-up work would put the entire ramjet concept into doubt while raising the prospects of using a related technology — the magsail — for deceleration. And as we’ll see tomorrow, other ideas about the key fusion reaction involved in the ramjet would soon come forward. But for a brief time in the 1960s, the idea of relativistic interstellar flight became something other than an idle fancy, firing the imagination of writers and in some cases launching careers in science and astronautics.


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  • Reverend Richard Prichard March 26, 2012, 10:51

    Paul, any chance that we might see an article on the work being done at the Eagleworks Laboratory? It would be interesting to see if any of the advanced propulsion work they are pursuing is getting validated. From what I have read some make or break research is being done there this spring. Also Woodward should be authoring a book on Mach propulsion this spring.

  • Paul Gilster March 26, 2012, 14:10

    Rev. Prichard, I’m not familiar with the Eagleworks Laboratory work other than through the one link I’ve seen, which I believed Adam Crowl noted on his Crowlspace site (www.crowlspace.com). I’ll keep an ear out on anything of interest. I’ll also be interested in that Woodward book and will give it a look in these pages.

  • FrankH March 26, 2012, 15:31

    The Stephen H. Dole books are still available from RAND, either as physical copies or PDFs. They’re worth getting and reading – not only are they of historical interest, many of the approaches and conclusions are still fairly applicable:

    Habitable Planets for Man:

    Planets for Man:

    Stephen Dole also wrote a few other articles of interest. Here’s his list of publications:

    Of interest: “Life in the Universe” (1967) and “The Search for a Rationale for Interstellar Communications” (1966).

  • Joy March 26, 2012, 17:24

    It is not a coincidence that the “Irrational Exuberance” of the 1960s occurred in an era when population growth was 3% and growth in energy use was an amazing 7%. Even in moribund East Germany, where prices were frozen, worker wages rose 4% annually. At the time, the steep rising slope of a parabolic curve is easily mistaken for a hyperbolic curve. To Infinity and Beyond!

    In the go-go quarter century post WWII, world per capita energy use doubled from circa 36 gigajoules per capita per year to circa 72. The following quarter century showed no per capita energy growth at all. The first decade of the 21st century did goose the per capita energy consumption up to 80 gigajoules per capita per year, but only by burning nearly 4 gigatons of coal annually in China. Well, China is planning to “cap” their coal use by 2015 (probably a face saving gesture to conceal reaching a limiting extraction rate). Yet people keep having babies. And there is a net loss of nuclear capacity. In a few short years, world per capita energy consumption (and standard of living, freedom, and the ability to fund engineering megaprojects) will begin a long downward slide.

    I recall the intellectual environment of the 1960s very well, all of the above (past) futurists would have been very confident that 21st century economic growth would have been driven by fusion, not a last gasp 19th century coal driven economy on steroids. We were young, knew it all, thought we were invincible. We were about as cautious as teens driving a Pontiac GTO home from the kegger after several hits on the bong. Reality would not get in the way of our egos or ambitions. Alas, we crashed our V8 into the ditch, and are still trying to sober up and recover from the concussion.

    The reality check graph, view it and weep:

  • Joy March 26, 2012, 17:38

    PS: In the news, Sandia is now asserting (after many years of a low public profile) that they (Stephen Slutz and Roger Vesey) have a computer model suggesting that they (might) be able to achieve sustainable fusion with a more powerful Z-pinch machine. I have my doubts, high energy plasmas in the real world don’t behave nearly as nicely as they do in computer models. But if I were planetary ruler, I would default on all the sovereign debts (sorry bankers) and fund this project. A slim chance is better than none.

  • dad2059 March 26, 2012, 18:02

    On the fiction side Larry Niven in his “Known Space” works during the mid- 1960s used a variation of the Bussard Ramjet called “ram-robots” which were precursor probes for interstellar exploration. The probes were unmanned because in Niven’s premise, the interstellar ram produced excessive amounts of radiation (the drag effect wasn’t known then).
    The follow-up colonization vessels were called “slow boats” and obviously didn’t use the ram-drive.
    Too bad the ramjet idea wouldn’t work, it would solve a lot of mass/fuel issues.

  • David March 26, 2012, 21:38

    I was a little kid in the 60s and I have found the future a real disappointment .
    Joy hit on an issue we have a political economic system problem. The buggy Whip industry was not as powerful as the fossil fuel/bankster combo….

  • Mike March 26, 2012, 22:54

    To Joy. Do you think Dr. Bussard’s Polywell fusion design will be a net producer of energy? Or is it just a less expensive long shot then the big fusion experiments. I’ve read a number of pro and con reports about the Polywell. It seems the U.S. Navy is being very slow to release any up to date results so it’s hard to know what if any success they’ve had.

  • Ole Burde March 27, 2012, 5:17

    “People keep having babies
    Yes , but WHO does , and who doesnt ? What happen is basicly that the population is still exploding in exactly the wrong places where they cant feed themselves , while the welleducated populations in the developped countries are declining leeding to a financial burden of supporting too many pensioners . The lack of ability to get your V8 out of the ditch , after being stuck there for more than a generation , comes from ecactly the same reason that welleducated parents DONT have enough babies , a strange lack of collective selfconfidence somehow connected to massproduced guiltfeelings about the western worlds past sinns of selfconfident expansion , the ultimate SINN of colonial” racism” ( who was basicly an early vertion of todays globalisation)
    Psycological profile studies have shown that good , decent people are prone to horrible guilt feeligs about close to nothing , while egoistic , brutal and violent people , who SHOULD be suffering from exactly those same horrible guiltfeelings ,mostly lack them completely .

  • A. A. Jackson March 27, 2012, 5:48

    I will have to do this off the top of my head, but I remember in 1979 talking to Bob Bussard about the limitations of the ramjet. He knew about Fishback and even Heppenheimer paper (which had come out a year before I talked to him).
    I am guessing that copies of the Robert Zubrin and Dana Andrews paper were sent to him, but don’t know what he thought of them.
    As I have noted before Bussard had noted the radiation loss problem in his original paper , he just did not delve into the quantitative details.
    His feelings about the limitations were that these constituted engineering physics problems to be solved. They might be show stoppers, but he felt some next generation of engineers would be clever in finding solutions.
    After all as a concept steam power started out 2000 years ago with Hero of Alexandria, even da Vinci wrote of the concept.
    Then it took 200 years from Thomas Savery to improve the later Watt engine to a truly useful powerful engine. Bob felt , though he was not 100% sure, that once the engineering physics problems were solved someone clever would work on their solution.
    I seem to see absolute statements made that the ramjet is dead in the water, well…. I am not so sure, but fixing them won’t be easy.
    He really did not have the inclination to work on this since he had bigger fish to fry in the area of earth based fusion power, a problem than he devoted his technical talents to the rest of his life.

  • Eniac March 27, 2012, 6:31

    Besides the problems with the ramscoop itself, there are also plenty of other reasons why relativistic flight with appreciable time dilation is not in the cards. ISM erosion and blue-shifted cosmic background radiation are two examples.

  • Eniac March 27, 2012, 6:54

    “Habitable Planets for Man” is a great read, but it suffers from the rather casual assumption that all Earth-like planets develop life and oxygen atmospheres.

  • Eniac March 27, 2012, 7:30


    In the go-go quarter century post WWII, world per capita energy use doubled from circa 36 gigajoules per capita per year to circa 72. The following quarter century showed no per capita energy growth at all. The first decade of the 21st century did goose the per capita energy consumption up to 80 gigajoules per capita per year, but only by burning nearly 4 gigatons of coal annually in China.

    Enough of the Oil Drum Drivel already. What do you think is the amount of energy a person really needs? Do you believe that it is possible to increase your living standard without increasing energy consumption? What is so special about energy? Why not talk about real-estate, education, health-care, access to information, entertainment, and all the other factors that have become much more important to our standard of living than SUVs and barrels of oil?

    A Toyota Prius is a much nicer drive than a Ford LTD, and uses a third of the gas. That is real progress, and energy use is a really bad measure for it. Not only don’t we really need more energy, there is a multitude of ways of obtaining it, some of which are already economical at current prices and have the potential to replace fossil fuels entirely. Lastly, new technologies have greatly increased our ability to extract fossil fuels to the point where we are now looking at a glut of natural gas and a significant reduction of our energy dependence on foreign sources over the last decade. And that old fallback, coal, is not going anywhere, either. It is good for centuries, more than enough time to move on to better ways.

  • ljk March 27, 2012, 9:14

    Here is the original Sandia Labs News Release on their fusion energy simulation:


    And more news here:


  • Daniel Highmountain March 27, 2012, 16:34

    I grew up in the 80’s and 90’s and read box after box of Illustrated Science and New Scientist and other science magazines ( both serious and less serious magazines ) that my much older brother had saved.. I was full of excitement and was really looking forward to my future life filled with AI-humanoid robots, space-elevators, flying cars, and a manned mission to Mars.. But somehow none of these things never happened. Humanity lost faith in it self and I lost faith in humanity. I really believe that its money and that our society is build around money, money and more money that is the problem. Yes I am naive, but I believe that until we find à way to rebuild our society on à totally new foundation, WITHOUT money, we Will not see the kind of progress many of us science/astronomy freaks want.. I have actually gone so far, that I dont believe “the singularity” Will happen in my lifetime, and Im just in My early 30’s. Neither Will I see any space-elevator nor a manned mission to Mars. It Will all continue to go downhill as it has the last 20 years.

  • Rob Henry March 27, 2012, 18:28

    Joy, that fist quarter century of post war growth that you mentioned also showed a tight coupling of gdp to energy usage. I put it to you that the uncoupling of first world gdp from energy usage in the next quarter century shows that disaster is not necessary, even if possible. Also good news is that first world population growth is all currently due to increasing longevity and immigration. We can cut back immigration whenever we want.

    We tend to exhibit bias from the experience of our upbringing. If Joy’s 60’s formative period was in New Zealand it would explain her unusual reluctance to sympathise with the current wisdom that the state must subsidy those who claim they can never find work and their large families. In 1959 and 1960 New Zealand had zero unemployment – and those were not faked figures. By the late sixties this had grown, but was still only about one sixth of one percent. We also measured as one of the most egalitarian countries in the world, and had one of the smallest pay gaps between skilled and unskilled workers. So you can see how a sufficiently old New Zealander can envision the welfare state as a machine that creates inequalities and social divisions. A monster of our own creation.

  • ljk March 28, 2012, 9:31

    Newt Gingrich says in 2012 that we should put a manned base on the Moon by 2020 and the general response is ridicule from most quarters.

    When I was a kid in the early 1960s, if you told the Average Joe that we would have lunar bases – even Mars bases – by the 21st Century, the likely response would have been not only positive, but they would have looked at you funny to even think otherwise.

    If the private sector can get a real foothold on space – and I am talking about staying up there, not those suborbital joyrides for the really rich – they will find riches beyond anything on Earth. And humans really do need new frontiers to conquer.

    Today’s generation seems to think between Star Trek and Star Wars and our space probes and the Hubble Space Telescope that somehow we have explored and know all of the Universe. The truth is we haven’t even gotten our ankles wet as Carl Sagan once said in Cosmos about our ventures into the Cosmic Ocean. It is up to folks like us to make the public aware of this so we can have that shiny future full of spaceships and robots and bases. Yes, us.

  • Joe Strout April 1, 2012, 23:05

    ljk, don’t knock the suborbital joyrides for the rich. Those are how it begins, and they will lead to higher launch rates, which are the single biggest factor in driving down launch costs. Falling costs will open up new uses of space, as well as making space travel available to slightly less rich folks, which will increase launch rate further, in a positive feedback loop that will ultimately bust open the frontier.