HOW IT WORKS: Nuclear Propulsion

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why is the nuclear rocket so much better than the chemical rocket in rocket propulsion exhaust velocity determines propulsion efficiency at a given temperature the lighter the exhaust gas the higher the exhaust velocity and the higher the exhaust velocity the more thrust is generated for each pound of propellant consumed per second the nuclear rocket merely heats hydrogen the lightest element of all and expels it at tremendous velocity chemical rockets burn fuel to produce exhaust gases that contain heavier elements so at the same exhaust temperature the exhaust velocity is much lower and each pound consumed per second produces less thrust rocket efficiency is stated in seconds of specific impulse this refers to the time in seconds that one pound of propellant will deliver one pound of thrust the higher the seconds of specific impulse the greater the propellant economy our best chemical rockets of today are limited to a specific impulse of about 450 seconds and only slight improvement can be expected on the other hand full-scale nuclear reactor tests have achieved 800 seconds and laboratory tests promise even more perhaps as much as 900 seconds this means the nuclear rocket with its lightweight high-velocity exhaust will use propellant about twice as efficiently as chemical rockets this then is the principal advantage of nuclear propulsion it was at the AEC's Los Alamos scientific laboratory high in the mountains of New Mexico that the first steps were taken here in the mid-1950s scientists set about to determine if nuclear energy really could be used to provide rocket propulsion theoretical studies and early experimental work revealed many problems that would have to be solved problems in reactor design material radiation structures control to name but a few the nuclear rocket was found to be feasible a series of experimental reactors was planned to convert theory into workable hardware [Music] optimum reactor designs were worked out by analysis prototypes were built a comprehensive test program was started these reactors called key we were to be used to prove out design and operational concepts they will be built only for ground testing all Kiwi power tests took place at the nuclear rocket development station at jackass flats Nevada here in the desert scientists and engineers check the actual performance at various power levels and for various time periods each experimental Kiwi reactor was received in sections assembled and checked out in a special reactor maintenance assembly and disassembly building called simply are mad when the reactor was ready for testing it was placed nozzle upon a special railcar and delivered to the test stand a mile or so away this car could be controlled from a remote station liquid hydrogen from nearby storage tanks was pumped through the reactor first tests were begun in 1959 and were run to the 100 megawatt level about 1/10 of Kiwis ultimate goal of 1,000 megawatts later tests beginning in 1962 operated at the full 1,000 megawatts films of these early tests show the flaming torch on the test stand that burns off the hydrogen exhaust gas and prevents an explosion hazard to the test facilities upon completion of these tests each reactor by then radioactive was transported by remote control back to the arm at building for disassembly and inspection here men working behind shielded walls used remote-controlled manipulators to remove the components for careful checking and analysis each test firing added information that helped scientists to evaluate the reactors performance and enable them to make adjustments in corrections before the next reactor was assembled but not all tests showed perfect performance in this one for example the flashing and the exhaust gas indicated a structural breakup caused by excessive vibration extensive redesign and testing were needed to correct the flaw and in this test a hydrogen leak caused a fire on the test and again a correction was made each test brought the scientists a little closer to the performance they were seeking until finally in September 1964 the 8th Kiwi reactor was brought up to full power and held for 8 minutes and a few weeks later it was restarted and operated at full power for two and a half minutes specific impulse about 750 seconds this concluded the Kiwi Test series it had proved that a nuclear reactor could be built that would power a spacecraft the next step already underway was to develop complete engine technology this project was called Nerva nuclear engine for rocket vehicle applications it was to be a combined industry government effort headed by the space nuclear propulsion office a joint NASA and Atomic Energy Commission activity the principal contractors were to be Aerojet General Corporation and Westinghouse Astro nuclear laboratory the Nerva technology reactor given the letter designation nrx was essentially the same as kiwi but now the contractors had to extend its lifetime and put it into an engine configuration here is how the nuclear rocket engine will work the reactor is a solid core heat exchange type cylindrical in shape fishin of uranium atoms in the core is the source of heat a reflector made of beryllium surrounds the core the core consists of many graphite elements impregnated with the uranium-235 fuel the core contains a number of channels running down its length hydrogen passing through the channels picks up heat generated by the fission process the channels are coated with niobium carbide a material which resists the corrosion that would occur if the hot hydrogen were allowed to come into direct contact with the hot graphite the hydrogen is stored in a liquid state to achieve the lowest possible volume the flight model will use about a third of a million gallons for a 30-minute firing to start the engine the cold liquid hydrogen at minus 420 degrees Fahrenheit moves through a pump down to the nozzle through internal passages in the nozzle walls and back up inside the reactor Pressure shell and reflector this cools the nozzle the reactor shell and the reflector and at the same time warms the hydrogen the hydrogen then passes through the hot fuel elements where it is heated to about 4,000 degrees Fahrenheit from there it is expanded through the nozzle to provide thrust the bleed line carries some of the hot hydrogen back to drive the turbo pump the whole engine system is amazingly compact for a nuclear power source the reactor works through fission of uranium-235 which constantly emits nuclear particles called neutrons when reflected back toward the reactor these particles will set up a chain reaction generating terrific heat the heat is controlled by rotating rods installed in the beryllium reflector around the reactor the rods are also made of beryllium but one side is coated with boron which absorbs neutrons initially the rods are turned so the boron side is toward the fuel elements and sufficient neutrons are absorbed to prevent nuclear fission from starting beryllium reflects neutrons by turning the beryllium side toward the elements a point is reached where sufficient neutrons are reflected for fishin to begin the amount of heat produced depends upon the position of the rods heat increases as more of the beryllium side turns toward the core when the desired rate of heat production is reached the rods are turned back to stabilize it heat decreases as the rods are turned back when the boron side absorbs enough neutrons to halt the fission process heat is no longer generated these rods can be operated by remote control test facilities for engine components were built near Sacramento California the problem get adequate performance with minimum weight the pup must move huge quantities of liquid hydrogen under pressure at minus 420 degrees Fahrenheit while the hydrogen cooled nozzle must expand high-pressure gases hydrogen at 4,000 degrees to low pressure the reactor was designed to meet the structural requirements of ground handling launch and spaceflight in a late 1965 test it operated intermittently for an hour including 16 minutes at full power but in that test as in all reactor tests before it the hydrogen had been forced through the reactor by test and pumping facilities instead of its own turbine driven pump in early 1966 the new technology reactor and the chief engine components including the turbo pump were assembled for tests it was called a breadboard because they were not arranged as they would be in an actual engine it would be the first self-starting test and it was a vital step in the nuclear propulsion concept this engine test model started perfectly and increased to full power proving that a nuclear rocket could be started by its own pump during a two-month period it was started and stopped ten times and operated at different power levels for a total of 110 minutes twenty-eight minutes at full power technology had now advanced to the point where performance limits could be extended work was already underway to increase reactor power and operating time in February in 1967 this reactor the Phoebus 1b was operated at a power level roughly equivalent to 75,000 pounds of thrust and in December 1967 this reactor the nrx a6 was operated at full power for an hour also in 1967 a new test stand was completed that would permit a test engine to be fired nozzle down into a vacuum chamber below at least partially simulating the space environment in early 1968 the first ground test engine was mounted in the new stand its success was a new milestone along the long road leading to a flight engine heavy shielding was used in this test engine to protect some of the components from intense radiation in flight engines all components will be radiation hardened and less shielding will be needed these tests will complete the technology for a nuclear rocket engine or application to space missions at the late 1970s and Beyond it thrust will be approximately 75,000 pounds for missions that require higher thrust two or more of these engines may be used in a single stage or several engine stages may be assembled side-by-side this versatility will give us the capability to perform a variety of advanced missions someday a manned trip to Mars and return may become the mission assignment exactly how it would be carried out depends upon a number of factors but here is one way it might be done with nuclear rocket propulsion using the technology developed for earlier missions using several saturn v launch vehicles components of the huge spacecraft would be placed into Earth orbit and assembled separate nuclear stages might be provided for each major step of the mission the first stage might consist of three clustered Rockets for departure from Earth orbit two other nuclear stages consisting of one engine each would be used in the vicinity of Mars the first stage cluster fires to accelerate the spacecraft to the velocity needed to get to Mars in the time that was decided upon say 200 days at burnout the first stage cluster is jettison and goes into orbit around the Sun mid-course correction is made by chemical rockets [Music] about 200 days later the space vehicle approaches Mars there it is slowed down by a single nuclear rocket and enters an orbit around the planet the used second stage is put into a higher Mars orbit than the space vehicle a chemically powered module departs for the planet's surface for the first time men from Earth will set foot on another planet [Music] for the return trip the module is lifted by chemical power back into a Mars orbit where it ducks with the main space vehicle the men transfer to the main craft and jettison the module leading it in an orbit around Mars a third nuclear rocket accelerates the vehicle for the return trip [Music] and it is jettisoned [Music] again mid-course correction is made chemically just before reaching the vicinity of Earth the crew transfers to a re-entry vehicle and jettisons the large spacecraft [Music] chemical rockets slowed down the vehicle to re-entry speed and they are jettison after deceleration through the atmosphere the re-entry vehicle returns to the Earth's surface by parachute a trip to Mars and back for centuries a dream of earthbound men is now much closer to reality [Music] of course there are many many other problems to be solved before such advanced space missions can be attended life support systems for extended space journeys more accurate space navigation communication systems power supplies and so forth what any successful advanced mission must begin with propulsion the power to get there and back lure overall weight larger payloads shorter travel time these are the chief advantages of nuclear propulsion you
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Keywords: physics, speed, spaceship, aviation, future, engineering, energy, reactor, mechanics, spacex, aerospace, lecture, things, chemistry, learn, interesting, course, class, fiction, UFO, star, marvels, deep, systems, how, math, fuel, new, old, project, 101, degree, structured, MIT, NASA, light, made
Id: Zm7PNlK5Aco
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Length: 18min 4sec (1084 seconds)
Published: Wed Apr 11 2018
Reddit Comments

Interesting film ... clearly it was created not long after 1968; that's the last test they mention. The narrator goes into detail of how US nuclear rocket engine propulsion was designed, how a ring of rods on the perimeter of the reactor spin to regulate the reaction, etc.

I'm amazed they showed an Isp (specific impulse) of 800+ seconds, and even hoped for 900.

The last 1/3 or so spends time on a Mars mission architecture using such rockets. The more things change, the more they stay the same!

For my part I'm curious how this technology (from 50 years ago) compares with Russia's bleeding-edge nuclear-powered cruise missile.

You may recall a plume of radioactive Iodine-131 appeared above Europe about a year ago, and nobody could figure out where it came from. The Kola peninsula looked like a source, but Moscow insisted they were just as baffled as the rest of us. Later in 2017, a cloud of radioactive Ruthenium-106 came wafting over eastern Europe, with some agencies saying its source seemed to be near the Russian border with Ukraine.

CNN says Russia has been crashing flying reactors into the ground for some time, so it's hard to say.

👍︎︎ 62 👤︎︎ u/BrandonMarc 📅︎︎ Apr 25 2018 🗫︎ replies

I did a project on this in grad school. I was lucky enough to take the first course in nuclear engineering that Virginia Tech had offered in decades. Here is the NASA report on the ROVER program, which also includes overviews of KIWI and NERVA.

TL;DR People did wild stuff back in the 1960s. The big problem with nuclear rockets is that the core fractures. They had chunks of fissile material flying out the nozzle. Also, one time, they melted a nuclear rocket down, just for fun.

Follow-up comment: We've made a lot of progress in materials science in the decades since the ROVER program. We have much better embedding materials available, and the technology might be feasible now. That being said, Putin's claim that Russia has an operational nuclear rocket is absolute bullshit. We've got better embedding materials, but we haven't had them for that long.

👍︎︎ 47 👤︎︎ u/FA_in_PJ 📅︎︎ Apr 25 2018 🗫︎ replies

Given the opportunity, working on modern day nuclear thermal rocket engines would absolutely be one of my highest engineering aspirations.

👍︎︎ 13 👤︎︎ u/BPC1120 📅︎︎ Apr 26 2018 🗫︎ replies

Here's the full film, the original documentary, minus the youtube ads It's really shady to cut out all the credits at the end and put your own website.

👍︎︎ 27 👤︎︎ u/archlich 📅︎︎ Apr 25 2018 🗫︎ replies

Im surprised how simple this is

👍︎︎ 6 👤︎︎ u/Cronenburg_jerry 📅︎︎ Apr 25 2018 🗫︎ replies

Space is the one place where nuclear does make sense. It's comparatively light/compact and it cannot contaminate the environment. I never understood why it wasn't being used.

👍︎︎ 6 👤︎︎ u/ThreeEagles 📅︎︎ Apr 26 2018 🗫︎ replies

Those rotating control shafts are absolutely genius. I was wondering how the fuck they controlled it, from the very start - and then they show that. Amazing.

👍︎︎ 4 👤︎︎ u/ShitInMyCunt-2dollar 📅︎︎ Apr 26 2018 🗫︎ replies

Someone correct me if I'm wrong, but this only works in space because it would spew radioactive hydrogen freaking everywhere if it took off from ground?

👍︎︎ 1 👤︎︎ u/RiceIsBliss 📅︎︎ Apr 26 2018 🗫︎ replies
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