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Remembering ‘Saturn by 1970’

One day in the late summer of 1958, at a time when the Jet Propulsion Laboratory was still in the hands of the U.S. Army (the transfer to NASA wouldn’t happen until the end of that year), Freeman Dyson and Ted Taylor showed up at the facility outside Pasadena. Try to imagine the scene: At the time, JPL was busy building the Explorer 6 satellite, all 65 kilograms of it. And here came two Project Orion scientists talking about not just satellites but auxiliary vehicles, additional payload to fly aboard their proposed 4000 ton spacecraft that they hoped would explore the outer planets.


“The reception there was rather cool,” Dyson would later say. “The lady at the front office decided Taylor and I were a pair of crackpots and tried to get rid of us. After about half an hour of arguing we got inside and then it all went very well.”

Image: Freeman Dyson, whose payload ideas must have confounded the team working on early Earth satellites. Credit: Courtesy of Princeton University Archives. Princeton University Library.

The entertaining tale is told in George Dyson’s Project Orion: The True Story of the Atomic Spaceship (Henry Holt, 2002), and it’s easy to see why even hardened rocket scientists would be confounded by what the duo proposed. By mid-1958, the largest payload ever lifted into orbit was Sputnik III, weighing in at 1325 kilograms. Project Orion was intended to loft 1600 tons to low-Earth orbit, or in its advanced version, 1300 tons to a landing on one of Saturn’s moons. The moon that most drew Dyson’s eye in 1958 was tiny Enceladus.

When I wrote about this in connection with the recent findings of an ocean within the distant moon, I was delighted to receive the diagram below from George Dyson, which shows the numbers as tabulated by Freeman Dyson in 1958, when details about the outer planets’ moons were sketchy at best. I want to run this as a bit of deep space history, the working figures that would later turn into Freeman Dyson’s document “Trips to Satellites of the Outer Planets, which was declassified in 1987.


Image: Thinking about deep space destinations in 1958, as the Orion team pondered their best options for a trip that might take place as early as 1970. Credit: Freeman Dyson, courtesy of George Dyson.

With reference to the figures, George Dyson comments:

“Note that the .618 density for Enceladus was not a transcription or arithmetic error, it is due to the mass and radius of the outer planet satellites being known only approximately at that time. (I believe Thomas “Tommy” Gold was brought in as a consultant on the question of selecting landing sites.) These calculations were made to determine the best destination both in terms of an optimum velocity match and highest probability of being able to obtain water ice or hydrocarbons on the surface to replenish the vehicle’s propellant mass.”

Below is the title page of the “Trips to Satellites of the Outer Planets’ report.


Image credit: Freeman Dyson, courtesy of George Dyson.

We’ve discussed Orion many times in these pages, though it’s been long enough that it may be time for a general review in the near future. Most Centauri Dreams readers will be familiar with George Dyson’s definitive book on the project’s history, and with the overall concept of detonating nuclear devices behind the craft, with a system of pusher plates and shock absorbers to cushion the crew, and the capability of launching payloads that were mind-boggling in the days of Sputnik. Interestingly, Mars was the first destination the team had in mind, though a landing on the Moon along the way would have been part of that mission. A four or five year mission seemed a possibility, one that Freeman Dyson would liken to the voyage of Darwin’s Beagle.

But the allure of the outer planets and their satellites was hard to resist, particularly when you threw in two ways to make the mission lighter and more efficient. For one thing, it was possible to use atmospheric braking (‘aerobraking’) to reduce propellant mass. I’ll quote from George Dyson’s book on the other:

The second part of the strategy is to gather propellant for the return trip at the destination, thereby reducing the average takeoff weight of the bombs. “We assume that we can use as propellant either ice, ammonia, or hydrocarbons,” wrote Freeman, explaining why Enceladus was such a good place to stop. “We suppose that each propulsion unit contains one-third of its mass in the form of the bomb and other fabricated parts, and two-thirds of its mass in the form of propellant. This means that, when propellant refueling is possible, only one-third of the mass required for the homeward trip need be carried out from Earth.” When you put these numbers together, the end results were astonishing. “With the use of atmospheric drag a round-trip to satellites of either Jupiter or Saturn could be made with a total velocity increment of the order of 40 km/sec. With refueling and braking, all the satellites become accessible with a round-trip mass-ratio less than 2.”

The Mars ship can thus become an outer planet ship that refuels along the way. And given the document shown above, I have to close with this last quote from the book:

Forty years later, Freeman and I review a two-page handwritten General Atomic calculation sheet, “Outer Planet Satellites,” dating from 1958 or 1959. It lists, for nine different satellites, ten different parameters such as orbital velocity, escape velocity, density, and gravity that determine the suitability of the satellites as places to land. Freeman smiles as he carefully studies the numbers.

“Enceladus still looks good,” he says.


Comments on this entry are closed.

  • Kari Lanigan April 14, 2014, 12:08

    I have nothing but nostalgia to add here, Paul, but I just can’t help it!

    In 1986, my dad bought a ’71 MG Midget convertible, which would be my very first automobile and an icon of my freedom as a super fortunate American teenager. One sunny day after a lot of days spent tinkering and polishing, Dad took me on a short drive and parked the car on an incline near the Jet Propulsion Laboratory at the entrance to Angeles Crest Forest. He turned off the engine, set the emergency brake and looked over at me and said, “This is your first driving lesson.” And so that’s where my adventures in ‘space’ travel began. I had to get the vehicle to move from that position pointing up the hill, which wasn’t easy! That car had a very short clutch made for swift shifting on mountain roads with sharp turns, (equal to zero tolerance for my lack of experience). But with only a few fumbles, I was able to get it moving, and soon we were flying through the hills with the wind in our hair and the sun on our faces. Dad pointed out the entrance to JPL on more than one drive. He talked about the ‘stuff’ that goes on there, (scientists, space, rockets, secret military…), igniting in me a sense of wonder and mystery I carry with me to this day. While people like Freeman Dyson were inside the JPL lab expanding the possibilities of space travel, a 16 year old Monkey was outside learning to drive. Funny how the memory of driving that MG Midget for the very first time through Angeles Crest with my Dad is, for me, synonymous with thoughts of great minds like Richard Feynman and Freeman Dyson, as well as an odd sense of familiarity connected to JPL.

    BTW- my dad’s birthday was April 6th. He would have turned 100 if he were still alive!! This makes me a real life time traveler, since I’m only 43! Ha! Ha! (I should really be like 70 or 80 right now!!!)

    Which brings me back to the topic of CONNECTIONS, PEOPLE and real world MAGIC: Like the piece of history you posted here today from a time and place far removed from present, yet so personal and relevant to current feelings of adventure about the future, which already feels like the ancient past in the context of traveling to the nearest star…

    And so we continue to dream of all the places we might travel to and what we might find/do there~*

  • railmeat April 14, 2014, 13:38

    Yes indeed “Enceladus still looks good,” lets go.

    I am not persuaded that Project Orion was the right way to go, but if we had at least tried we would be a lot smarter now.

  • Paul Gilster April 14, 2014, 17:30

    Kari, a very cool place indeed to learn how to drive! Congratulations to your father on what would have been his 100th year.

  • Jim Early April 14, 2014, 22:12

    I met Ted Taylor at a conference about twenty years ago. He was trying to communicate the sense of adventure during the fifties when they were seriously projecting possible flights as far as Saturn. I believe they were considering a crew of 20 for the trip. Since we were in the hotel bar at the time, I cannot guarantee the accuracy of that number.

  • John Frazer April 15, 2014, 3:17

    Orion still looks good.
    I can’t understand those who say that a SHLV (80-140 t-LEO isn’t needed without a government mandated fully funded politically popular “mission”.
    All things open up with it’s possible to get up there, and nothing is possible if we can’t.
    Seems simple.
    Relevance to this is the idea of the 10 meter ship, lifted in 100 ton segments. Sea Dragon could have lifted the entire 500 ton ship to LEO in one shot, ready to go.

  • david street April 15, 2014, 6:06

    surely youre joking mr feynman – almost picked up the book during the eclipse, but i have the graphic novel *note to scan it, asap.. & have the lectures, that i believe i am going to echo via video or tape, also *post asap, like the boardgame upon boardgame that is so exciting to put together, quickly or slowly, its the version of model train, we have, those 99 years & younger, that do not yet own comprehensive locomotive dioramas with cattle & convenience stores beside the ravine under the craggy chasms with frozen cascading rapids & falls, made of some kind of epoxy, because its terrible stuff to work with. we need a-gravity

  • Alex Tolley April 15, 2014, 13:43

    While I can admire the gung-ho spirit of teh time, Orion represents a very cavalier attitude to consequences. Launching a massive vehicle from the ground with a-bombs would have been very dirty, and a vehicle failure could have spread a lot of fissile material around the globe. The risks might have made sense before the test ban treaty, but after that, venerating such a machine seems somewhat unconscionable to me.

    The bravery of taking the trip into the unknown is either impressive or foolhardy. The conditions of the destination virtually unknown. Von Braun’s “Project Mars: A Technical Tale” is similar, assumptions about mars are made, the ships designed to meet those assumptions. Yet those assumptions were way off and would have do0omed the mission.

    Finally, the sheer size of the vehicle is staggering – the size of a small oceanic ship, 10x the mass of the ISS, all the more impressive for a mass ratio of just 2. The expedition to Saturn would not be unlike ship exploration of the globe, large vehicles with large crews and bringing along all supplies.

  • Rob Henry April 15, 2014, 19:42

    Alex Tolley is probably reflecting the views of many when he says “Orion represents a very cavalier attitude to consequences” then. In his next paragraph “…The bravery of taking the trip into the unknown is either impressive or foolhardy”. In my opinion, both are only the product of a confusing the current world view with that prevalent at the time of project Orion.

    Then it seemed obvious that nuclear was the way of the future, and the faster we got there, the more lives would be saved – even if it was as a mere side product. Today we live in an era of nuclear scares, were deaths due to that cause are highlighted above all others. For prospective, here are is an article in Forbes, where they quote findings of coal generating 2000 times more deaths per unit energy produced than.
    Okay, I admit that the conclusions in scientific literature on this topic are all over the place, but, in general, coal works out by far the worst. By contrast with estimates that the coal industry had caused 300,00 excess deaths last year in China alone, they had calculated an excess of radiation induced deaths one liftoff of ten (note, they were no so intoxicated by their idea as not to do that calculation). This would be spread over all America.

    Today we may compare their plans with the first assent of Everest, or the Apollo missions. They were mostly flag carrying missions, Apollo with only a faint hope of greatly accelerating the opening the high frontier to the benefit of all mankind. That cannot have been said of Orion, had it gone ahead. No Alex Tolley, to me, you really are confusing the mindsets of two very different times.

  • Alex Tolley April 16, 2014, 11:31

    @Rob Henry – It just goes to show how poor my writing is, that you got the impression you did. I am well aware that one mustn’t confuse historical mindsets (my historian wife reminds me of this if I stray). I also read accounts of aerospace work from this era and even the pilots and technicians reminiscing about the 1950’s note that they took risks and did things that would be unacceptable today. I think it is also clear that we take risks today that will be thought foolhardy 50 years from now. Even a cursory knowledge of Hollywood movies will expose these different mindsets.

    My comment was targeted at those who, today, venerate Orion and think we should resurrect it in some form. I think that they were either brave or foolhardy, I didn’t mean that the Orion team would feel that way. Having said that, Robert Falcon Scott didn’t think he was foolhardy trying to reach the South Pole with the approach he took, but with hindsight he probably should have, and most accounts today do not present him in a flattering light. My guess is that some of the sociopaths who govern us today, or their financial masters, will also be judged harshly both by historical standards, and by the mindsets of those in the future.

  • Andrew Palfreyman April 17, 2014, 0:24

    If we remove the pollution factor by lofting Orion piecewise into LEO and assembling it there, do we have something useful and viable?

  • Alex Tolley April 17, 2014, 9:28

    The test ban treaty applies to space as well. So technically such a vehicle cannot be legal unless the treaty is altered. This may happen, or conceivably a nation could just ignore the treaty and go ahead anyway.
    The sheer size should give one pause. It took a long time for the ISS to be built, this vehicle is 10x more massive. It would be 50x more massive than Skylab. It would take about 40 launches of the SLS to loft all the pieces, let alone crews to build it.
    The potential for an accident at a launch of the bombs resulting in potential atmospheric contamination has to be considered. Finally the issue of nuclear proliferation and potential bomb theft must be considered, especially in this age.
    We’ve argued in previous posts about how to launch a nuclear thermal rocket safely, with differing views. Supply chain security requirements and launch risks just don’t seem like a rational choice to me. If Orion was a good idea and viable, then we wouldn’t stop with one, but eventually a whole fleet would result, each requiring launches of bombs until they could be made off planet.

  • Marshall Eubanks April 17, 2014, 9:43

    The real trouble with Orion is the notion of giving a spaceship captain a complete nuclear arsenal.

    However, I have to wonder if the massive Orion ships would have been big enough to keep the crew from being killed from the Jupiter radiation belts, had they decided to go to one of the Galilean satellites. (I have been told that if an otherwise unprotected person was placed in a spacesuit on the surface of Europa, their life expectancy would be a few minutes. The radiation is so bad that the weight of a vault to put the electronics in is a major part of the Europa orbiter budget, and one reason why Europa clipper will not be a Europa orbiter.)

  • Brett Bellmore April 17, 2014, 12:30

    I count the cancelation of Orion as the day the West officially lost it’s nerve. Alex merely demonstrates the process is ongoing.

  • Michael April 17, 2014, 13:56

    @Andrew Palfreyman April 17, 2014 at 0:24

    ‘If we remove the pollution factor by lofting Orion piecewise into LEO and assembling it there, do we have something useful and viable?’

    Even if it is above the atmosphere (LEO) there will always be radioactive material that returns to earth via entrapment within the earths magnetic field or directional pointing of the exhaust. It would have to be pushed out further so neither could happen. Now days the nuclear bomb size could be reduced significantly by the use of an ion/electron or laser implosion. They thought about this 40 years ago!


  • Rob Henry April 17, 2014, 17:27

    @ Alex – Just from memory, I thought that intellectual theft of the process to make nuclear devices cheaply and quickly, was potentially an even greater danger than the bombs themselves. I believe that the Orion work on that problem has never been declassified.

    @Brett Bellmore – yes, we lost our nerve then but Alex (at least from his second comment on) is right. Resurrecting the project now would bring more costs than benefits UNLESS we transformed our whole society. Orion has great costs beyond the dollars spent. Only if we let it open up the high frontier at such pace that it ignites economic expansion, could those be justified.We are currently too cautious for that to happen in this era.

  • ljk April 18, 2014, 8:56

    China and Russia may not have the issues with building an Orion that the USA or at least some of its members do.

    They both have established space and nuclear programs, plenty of room to test and launch the rocket in away from major population centers, and centralized governments that tend not to wait for public opinion to decide things.

    Most importantly, they have definite ambitions towards settling the Sol system, whereas I expect NASA to have its mind changed for it again by the next presidential election.

  • Alex Tolley April 18, 2014, 10:48

    @Rob – yes and no. It depends on what you want to do. A nation, say N. Korea, wants information. But even with Pakistan’s help, they are, so far, unable to build a successful a-bomb. Iran, whatever its real nuclear intentions, has experienced disruption of its nuclear program, e.g. U235 enrichment.

    OTOH, if you are a terrorist, with the intention of detonating it at a target, acquiring a device through purchase or theft is the likeliest way to go.

    @Bret – one person’s “loss of nerve” may be another’s “we avoided a big mistake”. Did the US lose its nerve in not following MacArthur’s desire to use a-bombs in the Korean War? Did England lose its nerve in not bombing Moscow after WWII as Churchill suggested. Did the USSR lose its nerve when Kruschev backed down. Does Putin believe that Kruschev’s decision was a loss of nerve, resulting in the eventual loss of the Cold War, a mistake not to be repeated? Historic counterfactuals are fun, but we cannot know their outcomes, good or bad.

  • ljk May 21, 2014, 13:33

    Apparently Orion is a “bizarre” idea. Even if it could actually work and get us to the stars before just about any other plan?