My notional spacecraft is essentially a metal cube holding a number of nukes in front of it to shield them from detonations behind it. It has a nuke-launching mechanism which projects a nuke a certain distance behind it before detonation.
Questions:
i) What force F would a large H-bomb exert per square metre of my cube in space at, say, 1 km proximity? Assuming that radiation falls off exponentially, how much radiative energy E would be incident per square metre?
ii) What would my cube comprise (eg. a titanium cube with reflective shielding) in order to offer the best low-weight/high durability solution?
iii) Given that the cube of (ii) has a density of D kg per square metre exposed to the force F of part (i), how many nukes would be required to accelerate the structure to, say, 0.1c? Also, what temperature would each cubic metre attain given its specific heat capacity and E?
Further feasibility/modification questions to follow, perhaps. (I would research all this myself if I had time - go on, indulge me.)
A nuke in space would produce very little force due to the tiny number of atoms involved in the explosion. A great deal of energy is produced but very little propulsion - essentially it would just be a huge fireball. From Caltech Q&A:
So, the energy must be transferred to some kind of propellant which pushes on, say, a concave push plate. From the best source I found:
(Expletive mine)
Apologies for the long quote, but it appears that all of the engineering difficulties were solved long ago, and the only remaining barriers to genuine space travel of this kind stem from International Treaty violation and environmental risk inherent in the transportation of fissile materials into space.
Of course, you could just use the nukes on the surface to lift you into orbit, thus negating the use of unreliable and expensive chemical rockets to get the vehical into orbit, as well as allowing you to build one huge-ass spaceship here on earth, with no need for special construction materials- you could probably build it in a shipyard. Of course, a ground lauch would put some extra fallout into the atmosphere, and really piss off various enviroment groups, but I consider the second part a bonus.
The Orion book mentioned that they calculated how high they’d have to turn on the nuke pulses to avoid blinding any observers. it was ~50 miles up. Unless you can put your launch site in the center of an uninhabited desert, the very sight of the “exhaust” is dangerous. (Imagine desert animals with hundreds of little dead spots burned into their retinas.)
Project Orion was a foolish project. No-one would ever actually go for a launch. The only point that Orion served was as a Think-Tank for better projects. Consider using a laser to super heat the air underneath a space-craft. This is a more modern variant of the orion project, and it has much more potential and better likelyhood of becoming a reality.
I’m thinking that this method of propulsion isn’t too useful on a “space-craft.” Perhaps for a launch vehicle, at least to get it into LEO.
Using fusion bombs to accelerate a vessel obviously has the problem of extreme impulse to over-come, but isn’t an inherently flawed idea (assuming you only use the drive for extra-atmospheric propulsion). Of course, using a reactor to provide power some form of high-thrust ion drive would be a much better use of nuclear technology for space travel. (Current ion drives have a very high exhaust velocity, but very low impulse. That makes them desirable for very long trips, where the constant acceleration can eventually overcome their slow start.)
Finally found a number. From here, Dyson predicted an acceleration of 30 m/s/s for each nuke for a medium or large craft capable of storing thousands of nukes. (This being well within human tolerance).
0.1c (30 million m/s) would therefore require one million nukes, and at one nuke release every ten seconds it would attain this speed in 10 million seconds (3.8 months). Unfortunately, the mass of a million nukes would presumably lower this acceleration figure, thus requiring more nukes.
However, a craft weighing one tonne per nuke appears entirely possible. So, as the nukes gradually become depleted as the journey progresses, it seems entirely feasible to build a craft capable of accelerating to 0.1c within a matter of months, thus reaching Alpha Centauri in 44 years.
(How you stop is a whole new problem, even if a tiny capsule is ejected. You’d best hope someone os expecting you!)
Actaully, erratum for my last post: Dyson predicted an increasein velocity of 30 m/s for each nuke, but this acceleration would occur over less than a second, perhaps much less, possibly resulting in a brief but fatal acceleration.