18

The reaction mass is included in the bomb a.k.a. "pulse unit" The original project designed bombs with a reaction mass made of tungsten. The bomb's geometry and materials focused the X-rays and plasma from the core of nuclear explosive to hit the reaction mass. In effect each bomb would be a nuclear shaped charge. A preliminary design for a ...


12

The material of the bomb is the reaction mass. When a nuclear explosive is detonated in vacuum, the material of the bomb, and anything immediately adjacent to it, gets vaporized and accelerated at high velocity in every direction away from the center of the explosion. Organic Marble's answer describes how this can be optimized to make most of the vaporized ...


11

Using nuclear power, for any reason whatsoever, is looked upon with great suspicion by the existing nations with nuclear capabilities. There are a lot of countries, including the US, that are skeptical of Iran's nuclear program, that they are currently just building reactors, not bombs. Project Orion included nuclear pulse units that are in practice small ...


8

3 g's is about 30 meters/sec^2 or about .03/km/sec^2. Light speed is about 300,000 km/s. .01 c is 3000 km/s. So it would take about 100,000 seconds to reach .01 c. That's about 28 hours. With constant acceleration along the same direction, distance traveled is .5at^2. this works out to about 150,000,000 km or about 1 A.U. Distance between earth and Jupiter ...


8

3-5% of the speed of light would only be achievable for a really long duration mission. It just isn't efficient enough to do that kind of acceleration, and it takes a really long time to achieve. Okay, so how long would it take? The math is pretty easy, it's just speed/ acceleration. c=300,000,000 m/s, g= 9.8 m/s^2, so just find the speed, divide by 9.8, and ...


8

Let's start from the misconceptions in your question: "Unlimited reaction mass" - there's no unlimited reaction mass in pulsed nuclear propulsion - you can go as far as your bomb supply lasts, but no further. Specifically, you cannot manufacture nuclear devices on board. "Military advantage of getting an ice-teroid" - there's no advantage to be gained by ...


7

First consider what fallout actually is: basically any material blown into the upper atmosphere during a nuclear blast -- which eventually falls out of the sky. Essentially fallout is a bunch of ejecta flying outwards from the epicentre of the explosion. (In fact, fallout in space is kind of a contradiction, but let's ignore that!) So, what happens to a ...


7

The Outer Space Treaty (https://en.wikipedia.org/wiki/Outer_Space_Treaty) bars "weapons of mass destruction" from being placed or used in space. As the propulsion capsules of a nuclear-pulse spaceship are basically atomic bombs, I suspect the OST would apply.


6

How feasible was Project Orion and how feasible would it be if started today? In general, the only limitation on space flight has been political capital. Project Orion would thrive in an environment in which there was substantial interest (~500B USD range) in interstellar but not enough resources (~3-5T USD) or time (requiring space based solar) for ...


6

One of the countries that hasn't signed the treaty would make things quite difficult. So far as I can tell, it seems likely that a launch of Orion would be acceptable with the Treaty, but any testing relating to the treaty would be forbidden. It's hard to do without testing, so it seems unlikely to be of much help. Wikipedia states that the test ban treaty ...


5

George Dyson (son of Freeman Dyson) wrote a rather nice book on Project Orion, which amongst other things will disabuse you of the notion that this was a well funded and well received project (also it was not a NASA project, and I think it predates NASA. As Dyson tells it, a steel man cover was accidentally blown into space during an underground nuclear bomb ...


5

"How feasible" is a very large question. Technically feasible? They had found no show-stoppers by the time the project was cancelled, but acknowledged that it could only be proven by taking the next step and testing hardware. Testing might have (or probably would have, depending on who you ask) reveal that the pusher plate would be destroyed, even with the ...


4

Is that possible at all? Given the relatively low accuracy of all estimates, 1% or 10% of the speed of light would experience only minor relativistic effects. I will therefore treat them as 3.000.000 m/s and 30.000.000 m/srespectively. Given those extreme velocities, the fact that you start in lunar orbit is not important. Also, the exact number of pulse ...


3

Depleted uranium cannot sustain fission on its own, so there is no runaway possible and no negative feedback is needed to control it. As soon as the neutrons from the fusion stop, the fission stops. However once you start this thing, you will have highly radioactive fission products mixed in with your depleted uranium, so it is probably not something you ...


3

Bringing propellent rich asteroids to the earth moon neighborhood is an interesting idea. There are a number of entities pursuing this. However most proposals suggest solar powered ion rocket engines for asteroid retrieval rather than a vehicle driven by a series of nuclear blasts against a pusher plate. The U. S. is thinking of developing a solar powered ...


2

The amount of fusionable material isn't a problem: you can initiate fusion inside a tiny pellet containing milligrams of fusionable material if you compress it enough. But you need a facility the size of the National Ignition Facility to ignite it. The only place where we have working fusion at a small scale is inside thermonuclear weapons. These use a ...


2

For a nuclear pulse rocket, the peak acceleration is due to the shock of the push provided by each pulse unit. I struggled a bit trying to find a reference for the G-limit of what shocks electronic equipment can tolerate, but finally found it here. The paper mentions a spaceborne computer system that must tolerate shock levels of up to 450 G's


2

Roughly speaking, you want to maximise your pusher plate size, but without making it bigger than is needed for your propulsion units. The idea is that you chuck a propulsion unit out the back of your ship, it travels to some standoff distance and goes bang in such a way that it projects a cloud of energetic plasma towards your pusher plate. You want as much ...


1

Orion drives want to be large, including large in diameter. In general, bullet shaped Orions are ambitious military designs (including the one bristling with nuclear missiles, autocannon, and dropships that freaked out JFK) or the earlier, less developed designs, and narrower Orions with stuff strapped all over the outside are NASA or NASA-USAF modular ...


1

Have a read here. 'Evidence of this obtained from nuclear tests was the foundation for further research into the feasibility of a pusher plate. It was discovered that ablation (erosion) of the surface of a pusher plate could also be reduced by coating it with graphite. Coating the launch pad in similar fashion would minimize ablation of the surface and ...


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