Space Review comment:
A Nuclear Thermal Rocket, for fantastic expense, roughly doubles the Isp of chemical rockets…using a source of energy literally one million times more powerful. Stan Ulam, who is sometimes credited with being the real father of the hydrogen bomb, considered this problem and realized it is difficult just keeping a chemical rocket from melting and trying to contain nuclear energy in this manner was a fool’s errand. That is what NTR is.
Ulam, who was an Einstein level genius, called the concept of Nuclear Pulse Propulsion his greatest work. Ulam did not just think outside the box, he threw the box away. It is best characterized as the opposite of a jet aircraft being catapulted off the deck of an aircraft carrier. A device a fraction of the size of the jet (a repurposed nuclear weapon) being used to push the spaceship the size of an aircraft carrier to around a hundred miles an hour. Instead of a hundred jets on an aircraft carrier it is a couple thousand “pulse units” each about the size and weight of a fifty-gallon drum on a spaceship. Each pulse unit representing very roughly 7 pounds of plutonium and a hundred miles an hour or so of delta V. Global non-weapon inventories of separated plutonium, which is actually a security problem needing a solution, total 371 metric tons, enough for at least 46,000 nuclear weapons…or pulse units. 15 or 20 missions to the outer solar system would solve this “security problem.” There is also a couple thousand more tons of non-separated plutonium residing in spent fuel rods and other material available to be processed for more missions. And we can always make more plutonium. Breeder reactors on the Moon, a “Nuclear Moon”, being the best solution.
The most fascinating feature of Nuclear Pulse Propulsion is that it scales very poorly in the opposite direction of other systems. The smaller the bomb the lower the Isp. The bombs are not made more powerful by adding more plutonium but by boosting the yield with teaspoonfuls of deuterium or tritium. Spaceships massing hundreds of thousands of tons would thus likely have very high Isp’s in the tens of thousands. All the information on Star Wars directed energy research is classified so it is impossible to guess with any accuracy.
Many space enthusiasts find this information shocking and do not believe it. It is all true. Nuclear Pulse has always been shouted down and ridiculed mostly because nuclear weapons and deep space Human Space Flight propulsion are two completely different money holes and nobody wants to mix them together. Ironically, Kubrick was originally advised to make his spaceship in 2001 an Orion project pulse propelled type, but he was reportedly so burned out on nukes from Dr. Strangelove that he nixed it.
I have for many years suggested the nuclear deterrent be based months away in deep space on human-crewed “Space Boomers.” My entourage of fans have always reacted the same to these posts. The reasons to base all nuclear weapons Beyond Earth and Lunar Orbit (BELO) are logical and fact-based. And it would not cost any more than the present vast amounts being spent on new fleets of submarines, stealth bombers, ICBMs, and…..the “golden dome.”
I would suggest disbanding Space Force, which Biden should have done on his first day in office, and pursuing a true military branch with actual spaceships and service members who go in harm’s way, instead of a satellite money machine more likely to start a nuclear war than prevent one.
As I explained in other comments, Nuclear Pulse is by far the best solution to Human Space Flight Beyond Earth and Lunar Orbit (HSF-BELO). Interesting that the most difficult part of constructing such an atomic spaceship is a big dumb metal disc several hundred feet in diameter and massing several thousand tons. A flying saucer if you like. How would such a construct be placed well away from the Earth? Until we have lunar industry operating, sections might be lifted up by Super Heavy Lift Vehicles in “slices” and welded together in space. The best way to lift the “pulse unit” pits (bomb pits) would be on a human-rated launch vehicle in a human-rated capsule, packaged to survive an anomaly, with the most powerful escape tower system available. That would be Orion, which, as many are aware of, was also the name of the original nuclear pulse project.
The simplest method to allow the crew to tolerate the G-forces would be a several hundred-foot tower mounted on the “plate”, with the crew compartment inside suspended by cables. Upon lighting off a pulse unit, the crew compartment at the top of the tower would absorb the acceleration forces using the cable system and end up at the bottom of the tower. And that would be the basic design of a spaceship capable of traveling the solar system at tremendous speeds. Only Nuclear Pulse is going to provide the speed for human missions beyond the asteroid belt to Jupiter and the outer planets, which must necessarily be limited to two or three years.
The biggest misconception about Nuclear Pulse that it is like a nuclear explosion on Earth. The re-purposed nuclear weapon, re-branded a pulse unit, is a directional device that projects 80 percent or more (classified) of it’s energy in one direction, in a “beam.” In a vacuum this is a very short flash. This directed energy turns an attached slug of material into a hi-speed cloud of plasma and this is what is projected at the metal plate of the spacecraft and pushes it momentarily. Like a piston in a reciprocating engine, the metal is heated only fractions of a second and then cools and thus does not melt.
There is also the option of the Medusa concept, which uses a parachute-like “spinnaker” instead of a massive plate. This system would likely use much smaller yield devices and not be nearly as efficient. But it would work.
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