The propulsion technology the human characters conceive in the Netflix version of Liu Cixin’s novel The Three Body Problem clearly has roots in the ideas we’ve been kicking around lately. I should clarify that I’m talking about the American version of the novel, which Netflix titles ‘3 Body Problem,’ and not the Chinese 30-part series, which is also becoming available. In the last two posts, I’ve gone through various runway concepts, in which a spacecraft is driven forward by nuclear explosions along its route of flight. We’ve also looked at pellet options, where macroscopic pellets are fired to a departing starship to impart momentum and/or to serve as fusion fuel.
All this gets us around the problem of carrying propellant, and thus offers real benefits in terms of payload capabilities. Even so, it was startling to hear the name Stanislaw Ulam come up on a streaming TV series. Somebody was doing their homework, as Freeman Dyson liked to say. Ulam’s name will always be associated with nuclear pulse propulsion (along with the Monte Carlo method of computation and many other key developments in nuclear physics). It was in 1955 that he and Cornelius Everett performed the first full mathematical treatment of what would become Orion, but the concept goes back as far as Ulam’s initial Los Alamos calculations in 1947.
Image: Physicist and mathematician Stanislaw Ulam. Credit: Los Alamos National Laboratory.
Set off a nuclear charge behind a pusher plate and the craft attached to that plate moves forward. Set off enough devices and you begin to move at speeds unmatched by any other propulsion method, so the deep space concepts that Freeman Dyson, Ted Taylor and team discussed began to seem practicable, including human missions to distant targets like Enceladus. Dyson pushed the concept into the interstellar realm and envisioned an Orion variant reaching Alpha Centauri in just over a century. So detonating devices is a natural if you’re a writer looking for ways to take current technology to deep space in a hurry, as the characters in ‘3 Body Problem’ are.
Johndale Solem’s name didn’t pop up on ‘3 Body Problem,’ but his work is part of the lineage of the interstellar solution proposed there. Solem was familiar with Ted Cotter’s work at Los Alamos, which in the 1970s had explored ways of doing nuclear pulse propulsion without the pusher plate and huge shock absorbers that would be needed for the Orion design. Freeman Dyson explored the concept as well – both he and Cotter were thinking in terms of steel cables unreeled from a spacecraft as it spun on its axis. Dyson would liken the operation to “the arms of a giant squid,” as cables with flattened plates at each end would serve to absorb the momentum of the explosions set off behind the vehicle. Familiar with this work, Johndale Solem took the next step.
Image: Physicist Johndale Solem in 2014. Credit: Wikimedia Commons.
Solem worked at Los Alamos from 1969 to 2000, along the way authoring numerous scientific and technical papers. In the early 1990s, he discussed the design he called Medusa, noting in an internal report that his spacecraft would look something like a jellyfish as it moved through space. He had no interest in Orion’s pusher plate because examining the idea, he saw only problems. For one thing, you couldn’t build a pusher plate big enough to absorb anything more than a fraction of the momentum from the bombs being detonated behind the spacecraft. To protect the crew, the plate and shock absorbers had to be so massive as to degrade performance even more.
The solution: Replace the pusher plate with a sail deployed ahead of the vehicle. The nuclear detonations are now performed between the sail and the spacecraft, driving the vehicle forward. The sail would receive a much greater degree of momentum, and it would be equipped with tethers made so long and elastic that the acceleration would be smoothed out. I quoted Solem some years back on using a servo winch in the vehicle which would operate in combination with the tethers. Let’s look at that again, from the Los Alamos report:
When the explosive is detonated, a motorgenerator powered winch will pay out line to the spinnaker at a rate programmed to provide a constant acceleration of the space capsule. The motorgenerator will provide electrical power during this phase of the cycle, which will be conveniently stored. After the space capsule has reached the same speed as the spinnaker, the motorgenerator will draw in the line, again at a rate programmed to provide a constant acceleration of the space capsule. The acceleration during the draw-in phase will be less than during the pay-out phase, which will give a net electrical energy gain. The gain will provide power for ancillary equipment in the space capsule…
This is hard to visualize, so let’s look at it in two different ways. First, here is a diagram of the basic concept:
Image: Medusa in operation. Here we see the design 1) At the moment of bomb explosion; 2) As the explosion pulse reaches the parachute canopy; 3) Effect on the canopy, accelerating it away from the explosion, with the spacecraft playing out the main tether with its winch, braking as it extends, and accelerating the vehicle; 4) The tether being winched back in. Imagine all this in action and the jellyfish reference becomes clear. Credit: George William Herbert/Wikimedia.
Second, a video that Al Jackson pointed out to me, made by artist and CGI expert Nick Stevens, shows what Medusa would look like in flight. I recall Solem’s words when I watch this:
One can visualize the motion of this spacecraft by comparing it to a jellyfish. The repeated explosions will cause the canopy to pulsate, ripple, and throb. The tethers will be stretching and relaxing. The concept needed a name: its dynamics suggested MEDUSA.
Bear in mind as you watch, though, that Solem’s Los Alamos report speaks of a 500-meter canopy that would be spin-deployed along with 10,000 tethers. The biggest stress that suggested itself to readers when we’ve discussed Medusa in the past is in the tethers themselves, which is why Solem made them as long as he did. Even so, I became rather enthralled with Medusa early when I first encountered the idea, an interest reinforced by Greg Matloff’s statement (in Deep Space Probes): “Although much analysis remains to be carried out, the Medusa concept might allow great reduction in the mass of a nuclear-pulse starprobe.” With Dyson having given up on Orion, Medusa seemed a way to reinvigorate nuclear pulse propulsion, although to be sure, Dyson’s chief objection to Orion when I talked with him about it was the sheer impracticality of the concept, an issue which surely would apply to Medusa as well.
Like so much in the Netflix ‘3 Body Problem,’ the visuals of the bomb runway sequence are well crafted. In fact, I find Liu Cixin’s trilogy so stuffed with interesting ideas that my recent re-reading of The Three Body Problem and subsequent immersion in the following two novels have me wanting to explore his other work. I haven’t yet attempted the Chinese series, which is longer and presents the daunting prospect of dealing with a now familiar set of plot elements with wholly different actors. I’ll need to dip into it as Netflix ponders a second season for the American series.
Anyway, notice the interesting fact that what you have as a propulsion method on ‘3 Body Problem’ is essentially Medusa adapted to a nuclear bomb runway, with the sail-driven craft intercepting a series of nuclear weapons. As each explodes, the spacecraft is pushed to higher and higher velocities. I’m curious to know how the Chinese series handles this aspect of the story, and also curious about who introduced this propulsion concept, which I still haven’t located in the novels. I’m not aware of a fusion runway combined with a sail anywhere in the interstellar literature. Nice touch!
The Los Alamos report I refer to above is Solem’s “Some New Ideas for Nuclear Explosive Spacecraft Propulsion,” LA-12189-MS, October 1991 (available online). Solem also wrote up the Medusa concept in “Medusa: Nuclear Explosive Propulsion for Interplanetary Travel,” JBIS Vol. 46, No. 1 (1993), pp. 21-26. Two other JBIS papers also come into play for specific mission applications: “The Moon and the Medusa: Use of Lunar Assets in Nuclear-Pulse Propelled Space Travel,” JBIS Vol. 53 (2000), pp. 362-370 and “Deflection and Disruption of Asteroids on Collision Course with Earth,” JBIS Vol. 53 (2000), pp. 180-196. To my knowledge, Freeman Dyson’s ‘The Bolo and the Squid,’ a 1958 memo at Los Alamos treating these concepts, remains classified.
The show gets the correct originator of the ‘pulse’ idea … Stanislaw Ulam Los Alamos 1947. Project Orion originated from his idea.
( I can’t say I have ever seen a bomb runway suggested before, tho staged cannons are an old concept. The show has a technical adviser Dr.Matt Kenzie, at Cambridge, did he come up with this ‘runway’ nuclear pulse method? According to a plot summery it is in the novel (novels?) seemingly its Liu Cixin. I have not read the novel, so Paul; you can verify that Staircase is not in the novel, novels?)
In the Netflix version of the Three Body Problem a payload of 1000kg is to be sent at 1% the speed of light into interstellar space using a nuclear bomb ‘runway’ and a ‘sail’. Initially it is said there are 1000 pulse units (nuclear bombs), later this is stated as 300 units.
Orion was re-imagined as new concept by Johndale Solem in 1991 [1]. The pusher plate of Orion is replaced with a large sail or spinnaker whose canopy intercepts pulses from thermonuclear bomb units to give a final additive velocity, Solem called this pulse method Medusa. The show’s vehicle is a hybrid Medusa concept. Medusa, like Orion, is subject to the Rocket Equation mass ratio problem. The Three Body problem ‘Staircase’ concept is ‘runway’ idea like the ‘Fusion Pellet Track’ which also solves the mass ratio problem.
Watching the show had me thinking “the bomb runway is clever but can be improved”. Main element is to get rid of the tethers, just make a sail. With a bomb seeded track one does not have to pull a payload, with Medusa it is both a payload and a bomb propulsion supply. Just a sail will do. Here is a candidate ‘vehicle’. Make a 100 meter radius sail, make it out of Graphene, embed the payload in the ‘sail’ (Matloff had a vehicle like this, see [2].) From tactical nuclear weapon development one can extrapolate a 25 kiloton yield H bomb that weighs 100 kg. (Wikipedia has info on this.) What are the constraints? (1) Can’t melt the sail. (2) Can’t blow the sail to pieces. Using Solem’s modeling one calculates:
(1) Critical melt distance of explosion = 112 meters. (May seem surprising but Graphene melts at nearly 4000 K.)
(2) Critical stress distance = 1.7 km. Graphene’s tensile strength is about 2 gigapascals.
At nearly 2km the sail will not melt nor will it get busted. Assume the sail has a thickness of 5 microns.
Even in the late 50’s and early 60s Orion was designed to use ‘shaped’ nuclear devices , I am guessing that progress on focusing thermonuclear explosion plasmas has progressed… so that at 2km one has a nice ‘shaped’ impingement on the sail.
A 25 kt thermonuclear pulse unit at 2km (following Solem) gives a delta v to the ‘ship’ , each pulse, of about .0002 % the speed of light. For a final velocity of 1% c this would require approximately 57 pulse units (bombs). That also factors in the ‘sail’ mass of 282 kg, for a ‘ship’ mass of 1282 kg. (In the show it is 300 pulse units, to not sure of their unit yield.)
One would figure the whole mission is assembled quite a distance from the Earth , at least outside the Moon’s orbit. One would have to address a lot of technical issues such as the phasing of the pulses and especially the guidance, navigation and control of the ship and pulse units. One would guess that both the pulse units and the ‘ship’ would have a refined reaction control system, a quite robust and radiation hardened one. Currently technology needs not too much refinement for this, especially in this alternate universe story. All calculations by Solem are approximations but this should be in the ballpark.
Just for fun , how about a Star-Shot-Like scenario. Set the final speed to 20% the speed of light. The payload at 1kg, radius of sail 10m, and all the other GNC equipment is 9 kg. The ‘payload’ package could be an assembly of 1000 of gram mass nanocraft dispersed at the end of the first phase of the mission. That would require about 12 25kt pulse units. One wonders it would be cheaper than the laser system? (All this is back-of-the-envelope a more sophisticated analysis is needed.)
As Paul notes a ton of technical problems to solve , not to mention budget… modulo political considerations! Even the show mentioned use of nuclear weapons in space as a treaty violation.
[1] Johndale C. Solem. “Some New Ideas for Nuclear Explosive Spacecraft Propulsion,” LA-12189-MS, October 1991.
https://fas.org/sgp/othergov/doe/lanl/docs1/00189777.pdf.
[2] Graphene solar photon sails and interstellar arks. Journal of the British Interplanetary Society, vol. 67, p. 237-246
Correct, Alex. Or at least I can say that despite going back through all three, I can’t find the fusion runway concept to propel a sail. If I missed it, maybe one of the readers can give us a page reference.
The animation by Nick Stevens is interesting. There is a quasi-reefing system for the canopy. Solem does mention something like this at all. For parachutes reefing reduces shocks in the system. Not sure the physics for this set up … could be true.
I notice that Stevens canopy has no ‘gores’ , Solem (not explicitly) seemed to introduce these to reduce stress. He goes into this in detail in his paper.
I see not reason for the tethers , they just add mass to the ‘ship’.
Of course this makes the guidance-navigation-control of the ‘sail’ more complected but one already has that technological problem with Medusa. However this is an ‘advanced’ technological system , one that one supposes with advances in engineering physics one would be able to solve. Not new physics here.
After all this is a problem for Star Shot, have to get and keep those chip ships on course to Alpha Centauri within a reasonable error ellipsoid.
Have make a correction. I did not have a copy of “Medusa: Nuclear Explosive Propulsion for Interplanetary Travel,” JBIS Vol. 46, No. 1 (1993), pp. 21-26. , got one today.
Indeed there is a ‘reefing’ system, Solem calls it SERVO-WINCH. Nick Stevens does a good job with a schematic representation of this device. The cycling of this provides a higher ‘specific impulse’ and a smoother ride for a crew.
This needs to be a two-fer.
Laser detonation fusion seems better for propulsion than power.
The Medusa cap needs to focus on a spot behind a rod filled by NIF type fusion pellets fired like a BB gun.
You run out–the Medusa cap unfolds into the wider but more fragile laser pushed sail.
Very interesting — is it possible to provide a similar back-of-the-envelope calculation for the acceleration forces caused by each explosion in scenarios like these? I can see the total delta-v, and divide by the number of bombs, but how long is the acceleration provided by each detonation? Obviously very short, but how short?
One thing that (if I remember correctly) was incorrect in the Netflix series, was that they said the pre-positioned devices would be equally spaced. But surely you would want to spread them further and further apart to account for the accelerating vessel.
Glad you brought this up jonW. I should have looked at the acceleration. First order it is easy to calculate an approximate acceleration. For the Three Body Problem vehicle I put the pulse unit right at the safety margin for the stress, about 2 km. Then the acceleration about 10s of thousands of gs! Probably turn a brain into soup! Put it at 10 times that distance it’s only 50gs. Frogs recover from this kind of acceleration , don’t remember the reference.
The main problem becomes the focusing of the explosion. This was a big problem for Orion and a lot of effort put into it (see Dyson Project Orion). According to Dyson the shaped nuclear explosion problem was solved , alas the technical documents are still classified. Dyson went on about this in chapter 12 of his book. Lot of shaped thermonuclear bomb work was done after the 1960s , so I am guessing that ‘plasma’ focusing of the final plasma is a problem with a solution , after all it’s now 22 years after Dyson wrote his book.
As a reference see the Casaba Howitzer. (Boy! is this concept ever classified! Can find no technical documents at all.)
https://en.wikipedia.org/wiki/Casaba-Howitzer
Intriguing stuff. However, as in 3 Body Problem, we are still talking about low mass payloads and long flight times. Consequently the payload is electronic/robotic in nature. The main thing that occurred to me in reviewing this was to replace the payload container with two structures. The first could be described as the “Gun”. Tethered behind the Gun would be the “Ship” containing the science and payload elements of the mission. The workings are only modified from Medusa by the Gun firing the nuclear bombs under program control, allowing the Gun itself to be part of the radiation protection for the Ship and allowing the Ship to be tethered perhaps without need of “stretchy” tethers. Given the payload is electronic and robotic, the need for buffering the acceleration pulses is less than would be needed for a living payload. This may allow reduced complexity and reduced mass for the mission. In terms of deceleration at the destination, the whole rig could be rotated 180 degrees without need to change the configuration. I call this rig Helios and Selene. Or parsimoniously Helioselene.
This HelioSelene configuration could also be called tugboat because virtually anything could be connected behind the Gun.
In the Chinese 30-part tv series, Three-Body, I don’t recall any mention of the means to propel the head to the enemy fleet. IIRC, this is part of the 2nd novel. “The Dark Forest”.
I gather there is a fanbase in China that writes fanfic based on this universe, e.g. The Redemption of Time – The Three-Body Problem, Book 4 by Baoshu. I have the audiobook but I haven’t listened to it yet.
Just to add to what Alex said: I have watched the Chinese version–all 30 episodes of it–and it only covers the first book So, there’s no mention of the spacecraft to intercept the alien fleet.
The pacing is glacial; however, I did find it interesting from an anthropological perspective–seeing things from a modern Chinese perspective. The series focuses heavily on character and motivation. The CGI is excellent. This is a series on which a lot of money was spent. The alien society is hokey in some ways and deeply weird in others.
The series also elides the violent beating to death of the main character’s father, which makes her motivation murky. Actually, there’s a fair bit murky about this series, but if you don’t expect fast-paced entertainment, have patience and 30 hours to spare, it’s interesting.
Readers may find these links useful, especially the first one:
https://projectrho.com/public_html/rocket/enginelist3.php#id–Pulse–Medusa
https://beyondnerva.com/nuclear-pulse-propulsion/
Although the Valkyrie rocket uses antimatter propulsion note the design:
https://charlespellegrino.com/nuclear-propulsion/
https://web.archive.org/web/20100529041650/http://www.projectrho.com/rocket/rocket3aj.html#valkyrie
Regarding the Dark Forest idea:
https://projectrho.com/public_html/rocket/aliencontact.php#id–Lack_of_Aliens_To_Contact–The_Fermi_Paradox–The_Dark_Forest_Rule
In the Liu book series, the runway concept is called the “Staircase Project” and is part of the third book “Death’s End”. The Neflix series decided to pull it into the first season because it fits the overall chronology of events that humans undertake.
Thanks, Michael. The third volume was the one I went through the quickest as I was writing the piece (I hadn’t made allowances for all the jumps in chronology) and I clearly missed it. Much appreciated.
Perhaps a nuke is not needed.
Suppose you have a very long tether.
On one end, a weight…dead tankage, whatever.
This falls towards a gravity web…Jupiter’s or Planet Nine…especially if it is a black hole.
This pulls on the spacecraft far behind, which has the cable release it.
A small burn slingshot s the payload to its destination
My issue with this concept is the gamma, neutron and x-ray radiation which could negatively affect the sail and tethers. They may need to be reannealed or reconstituted every now and then.
Yes this is a problem that bothered the Orion designers. The solution , maybe not the only one, was to build the pulse units (bombs) such that the xray and gamma radiation was absorbed by a filler (in the pulse unit) and this radiation is stepped down to infrared. Actually converting Tungsten to a plasma propellant.
https://commons.wikimedia.org/wiki/File:Orion_pulse_unit.png
(I notice Wikipedia does not have the primary source of this figure which was from a General Atomic document , George Dyson has the correct atribution in his book Project Orion.)
Al, I believe this is the document you are looking for:
https://web.archive.org/web/20070704104944/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770085619_1977085619.pdf
Hello,
I ask myself a naive question about the ingenious Médusa project: when the habitable capsule “advances” by reaction to traction, would it not pose a problem on a biological organism (a human) in the sense or this one would suffer several series of accelerations/ decelerations quite violent? Certainly there is no or little rubbing in space but would this not imply a perfect sealing of the caspula in relation to its medium (magnetic fields? ) to avoid these problems? The question of the resistance of a human organism such as the flow of blood to the brain, as the pilots of fighter planes on earth and the “black veil”, has already arisen for the interstellar journeys at supraluminal speeds, if I am not mistaken… Of course we can also assume that the crew is in hibernation bathing in a box of Campells soup but it’s less fun :)
It is interesting to note that ideas of interstellar travel have evolved over the last 50 years and that we are now moving towards systems that use less “fuel” energy.
It is interesting to note that ideas of interstellar travel have evolved over the last 50 years and that we are now moving towards systems that use less “fuel” energy. In a way – and this is not a criticism – it shows that humanity has still not managed to master another source of energy, in other words that we do not manage to pass into civilization type I.
This brings us to the other question: what would happen if tomorrow we managed to master for example the energy of our star? Would all these beautiful projects be abandoned? What would become of our space exploration projects if tomorrow we could travel in the universe at 20; 30; 40 C? That would change the deal… ;)
Fred