Medusa – Nuclear Explosive Propulsion For Interplanetary Travel
J. C. Solem. (1993), JBIS, 46, pp.21-26
The concept of rocket propulsion using a “disposable reactor” or “external nuclear motor” is nearly as old  as the concept of a nuclear bomb. Nuclear explosive propulsion was considered in the late 50s and early 60s under the ORION  program at Los Alamos  and General Atomics Corporation . ORION was a heavy-lift vehicle, launched from Earth or from a high altitude. The nuclear explosives, which ranged in yield from a few tons to several kilotons, were detonated behind a pusher plate fitted a two-stage shock absorber to mitigate the crew’s acceleration.