If you have ten engines firing in pairs, you're even worse off than one engine firing quickly. You haven't changed the fact that one pound of your explosive propellant gives less energy (less speed) to your ship than would one pound of hydrogen/oxygen propellant, and now you've got the added weight of nine extra engines.<br /><br />Interestingly, a model rocket motor is exactly the opposite of what you're talking about here. Low-end model rocket motors are black powder, a substance traditinally known for going boom, put together in such a way that it burns at a controlled speed instead.<br /><br />In addition to the Orion test with the conventional explosvies, you might want to read into the experiments done with laser propulsion. If I understand it right, you have a huge high powered laser on the ground firing up at the underside of a disc-shaped craft with little bits of ice on it. The laser bursts vaporize the ice, creating thrust.