I’ve been aware of this concept for some time, but a key factor only just occurred to me, and I was hoping someone might know if it’s ever been addressed. It has to do with the shock absorbing system. Basically, tremendous amounts of energy are going to be cycling through the shock absorbers; if they’re anything less than absolutely 100% efficient- if even a tiny percentage of that energy becomes waste heat- they’ll end up melting. I have trouble imaging any mechanical system that could work that efficiently. How was it proposed to solve this?
I expect that the answer is simply that you keep your burns short, and allow the shocks time to shed their heat in between. Even doing that, you can probably still get a lot more oomph than from chemical rockets.
Why would you think they’d melt unless perfectly efficient? They can just radiate heat away as long as it doesn’t build up too quickly.
Note that while radiation isn’t a terribly efficient way to lose heat, it does get a lot more efficient the hotter the object gets. The rate at which heat is lost to radiation scales as the temperature (in Kelvin) to the fourth power. This means that an object that’s just starting to glow red-hot, at about 770 Kelvin, will be radiating its heat energy almost 50 times faster than an object at “room temperature” (290 Kelvin.)
While this is true, most structural mechanisms won’t function and will likely fail at the point that they are “white hot”. The answer to the o.p. is that the shock absorber system (which is strictly a spring system with no damper, as the purpose is to moderate the impulse from the bomblet) would very likely require an active cooling system which would help mediate the absorbed heat. One simple way of dong this is to use a compressible fluid as the pneumatic “spring” and then exchange some of the fluid with cooled fluid as part of the compression and extension cycle. The slight loss energy (from having to heat up the injected fluid) is likely minimal. The bigger problem is gamma rays and slow neutrons which are absorbed by the pusher plate, heating it. The proposed solution was to spray the plate with oil between shots which would evaporate, carrying away heat, but this brings into play a number of potential failure modes.
However, by virtue of having the ‘reaction’ (in this case, the nuclear detonation) occur external to the vehicle, the amount of energy absorbed (either by conversion of radiation to heat or mechanical work) can be controlled largely by vehicle configuration and the rate of impulse. The same is not true for existing and proposed systems in which the propulsion power source is located onboard the craft. In this case, whether the power source is nuclear electric, fission fragment, some form of nuclear fusion, et cetera, some means will need to be provided to radiate away the enormous amount of waste heat which will be produced in excess of that which can be utilized by conversion to propellant momentum. In fact, the more energetic the source, the worse the problem is likely to be, a fact glossed over by both space exploration enthusiasts and science fiction authors, but well understood by people who design actual spacecraft. If you actually had a propulsion system capable of propelling a craft to measurable percentages of c in a reasonable period, you would likely have huge problems with heat accumulation.
Stranger