A Helios-propelled vehicle would make use of a containment vessel--perhaps 30 feet in diameter--in which small nuclear explosive charges would be placed, together with a few hundred pounds of hydrogen. Firing of a charge would result in bringing the mixture of charge residue and hydrogen to a high temperature--say 5000 or 6000/sup 0/K--and subsequent release through a nozzle would provide propulsive thrust. This process would be repeated several thousand times, at intervals likely to be 10 seconds or longer. High impulsive acceleration loads would be moderated by a system of shock absorbers between the engine and vehicle. The paper summarizes characteristic features of the concept, especially with reference to system optimization studies and analysis of heat transfer to the engine structure.