A smaller ”boom” I'm currently writing a science fiction novel, and while I'm certainly no physicist, I still aim to minimize the use of handwave devices built from unobtainium. It appears that the only propulsion system realizable with technology in use today or in the near future which combines high specific impulse with high thrust is nuclear pulse propulsion as proposed in the Orion project of the 1960s. The problem of course is, as it utilizes nuclear bombs, and each has a yield of several kilotons, the spacecraft would have to be humongous. The only way to adapt nuclear pulse propulsion to smaller scale craft seems to be to either reduce the yield of the individual bombs, or detonate said bomb farther away from the ship. Both methods would mean that most of the expensive fissile material goes to waste. The critical mass as I understand it can only at best be reduced to about a half, using compression by high explosives and a mantle of neutron reflectors, and if anything this seems to increase the efficiency of the bomb. So, how can the amount of fissile material needed for each nuclear explosion be reduced without reducing the energy output per unit weight of fissile material? These all have in common that they require substantial “infrastructure” to be present in order to detonate the charge, which makes such a setup utterly useless as a weapon. This is NOT a “help me build a bomb” thread, which I know is prohibited. As I've researched, I have come across the following schemes to solve this problem: A. Using lasers to ablate an outer mantle, much like the explosive lenses surrounding an implosion type bomb, but by higher energies causing much greater pressures, reducing the critical mass by increased density. B. Using railguns or some similar setup to collide two subcritical masses, thereby achieving immense pressures by relative velocities of 10-20km/s. C. Using a small amount of antiprotons to cause nucleus to release a massive burst of neutrons, causing the device to go supercritical. As in the ICAN-II study by Penn state university. D. Surrounding a fusion target, such as those used by the national ignition facility (NIF) with a blanket of U-238, which would be split by the fast neutrons released by the fusion reaction, greatly increasing the energy output. As theoretical concepts I find them understandable, but how can these parameters be calculated? I feel I'm in way, way over my head here! How does pressure affect density in solids? How can the peak pressure of colliding bodies at a given velocity be calculated? How will a sudden flux of “x” neutrons affect criticality? I am in dire need of your help!