In January 1965, unnoticed and unmourned by the general public, Project Orion died. The men who began the project in 1958 and worked on it through 7 strenuous years believe that if offers the best hope, in the long run, of a reasonable program for exploring space. By “a reasonable program” they mean a program comparable in cost with our existing space program and enormously superior in promise. They aimed to create a propulsion system commensurate with the real size of the task of exploring the solar system, at a cost which would be politically acceptable, and they believe they have demonstrated the way to do it.

The purpose of this article is neither to bury Orion nor to praise it. It is only to tell the public for the first time the facts of Orion’s life and death, and to explain as fairly as possible the political and philosophical issues which are involved in its fate.

…All alternative propulsion systems which we know how to build are either temperature-limited or power-limited. Conventional rocket systems, whether chemical or nuclear, are temperature-limited in that they eject gas at a velocity V limited by the temperature of chemical reactions or of solid structures. The upper limit for V appears to be about 4 kilometers per second for chemical rockets, 8 kilometers per second for nuclear rockets. For missions involving velocity changes many times V, multiple-staged rockets are required, and the initial vehicle size needed in order to carry a modest payload soon becomes preposterous. The initial weight is multiplied by about a factor of 3 whenever an amount V is added to the velocity change of a mission. [cf. Tsiolkovsky rocket equation] It is for this reason that programs based on conventional propulsion run into a law of heavily diminishing returns as soon as missions beyond the moon are contemplated.

The other class of propulsion systems at present under development is the so-called nuclear-electric class. These systems use a nuclear reactor to generate electricity, which then accelerates a jet of ions or plasma by means of electric or magnetic forces. The velocity of the jet is no longer limited by considerations of temperature, but the available thrust is limited to very low values by the power of the electric generator. Vehicles using nuclear-electric propulsion necessarily accelerate very slowly and require long times to achieve useful velocities. They have undoubtedly an important role to play in long-range missions, but they offer no hope of transporting men or machines rapidly around the solar system.

The Orion propulsion system is neither temperature-limited nor power-limited. It escapes temperature limitations because the contact between the vehicle and the hot debris from the explosions is so brief that the debris does no more than superficial damage. It escapes power limitations because the nuclear engine (bomb) is outside the vehicle and does not depend on coolants and radiators for its functioning. An Orion vehicle is unique in being able to take full advantage of the enormous energy content of nuclear fuel in order to achieve, simultaneously, high exhaust velocity and high thrust.

…The story of Orion is important, because this is the first time in modern history that a major expansion of human technology has been suppressed for political reasons. Many will feel that the precedent is a good one to have established. It is perhaps wise that radical advances in technology, which may be used both for good and for evil purposes, be delayed until the human species is better organized to cope with them. But those who have worked on Project Orion cannot share this view. They must continue to hope that they may see their work bear fruit in their own lifetimes. They cannot lose sight of the dream which fired their imaginations in 1958 and sustained them through the years of struggle afterward—the dream that the bombs which killed and maimed at Hiroshima and Nagasaki may one day open the skies to mankind.

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