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<\/p>\nMedusa: Deep Space via Nuclear Pulse
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The propulsion technology the human characters conceive in the Netflix version of Liu Cixin\u2019s novel The Three Body Problem<\/em> clearly has roots in the ideas we\u2019ve been kicking around lately. I should clarify that I\u2019m talking about the American version of the novel, which Netflix titles \u20183 Body Problem,\u2019 and not the Chinese 30-part series, which is also becoming available. In the last two posts, I\u2019ve gone through various runway concepts, in which a spacecraft is driven forward by nuclear explosions along its route of flight. We\u2019ve also looked at pellet options, where macroscopic pellets are fired to a departing starship to impart momentum and\/or to serve as fusion fuel.<\/p>\n 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\u2019s 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\u2019s initial Los Alamos calculations in 1947.<\/p>\n Image:<\/strong> Physicist and mathematician Stanislaw Ulam. Credit: Los Alamos National Laboratory.<\/p>\n 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\u2019re a writer looking for ways to take current technology to deep space in a hurry, as the characters in \u20183 Body Problem\u2019 are.<\/p>\n Johndale Solem\u2019s name didn\u2019t pop up on \u20183 Body Problem,\u2019 but his work is part of the lineage of the interstellar solution proposed there. Solem was familiar with Ted Cotter\u2019s 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 \u2013 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 \u201cthe arms of a giant squid,\u201d 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.<\/p>\n Image:<\/strong> Physicist Johndale Solem in 2014. Credit: Wikimedia Commons. <\/p>\n 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\u2019s pusher plate because examining the idea, he saw only problems. For one thing, you couldn\u2019t 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.<\/p>\n 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\u2019s look at that again, from the Los Alamos report:<\/p>\n 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\u2026<\/p>\n<\/blockquote>\n This is hard to visualize, so let\u2019s look at it in two different ways. First, here is a diagram of the basic concept:<\/p>\n Image:<\/strong> 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.<\/p>\n Second, a video that Al Jackson pointed out to me, made by artist and CGI expert Nick Stevens<\/a>, shows what Medusa would look like in flight. I recall Solem\u2019s words when I watch this:<\/p>\n 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.<\/p>\n<\/blockquote>\n<\/p>\n![\"\"](\"https:\/\/mycbh.com\/Games\/spaceperium\/wp-content\/uploads\/sites\/2\/2024\/04\/solem.jpg\")
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