Nearly half a century after man first walked on the moon, traveling to the outer reaches of our solar system, let alone to other stars, remains a distant dream. In order to cross cosmic distances in a reasonable amount of time, a spaceship would have to travel at a significant fraction of the speed of light. This feat seems presently well out of reach for our civilization. Yet perhaps as early as the 1940's, scientists imagined ways in which an existing technology - namely, the nuclear bomb - might be repurposed as a means of powering interstellar travel.
Project Orion, which began in the 1950's at San Diego-based company General Atomics, was perhaps the first serious effort to develop spacecraft designs based on nuclear pulse propulsion.  Physicists Ted Taylor and Freeman Dyson were notably involved with Orion. In a nutshell, the concept behind the project was that periodic nuclear explosions could be used as thrust to power a spaceship. Each bomb would explode against an inertial plate, propelling the ship forward.  This process could accelerate the ship to incredible speeds, on the order of a tenth of the speed of light. At that speed, a passenger could rapidly visit any part of the solar system. In fact, he could even conceivably travel to another star within his lifetime. Such a machine would far surpass any existing space travel technology.
Naturally, the basic design suffers from a number of potential difficulties. For example, the ship would have to be properly shielded against radiation from the bombs. Furthermore, the Partial Test Ban Treaty restricts the use of nuclear technology in space. For these and perhaps also for budgetary reasons, Project Orion was rejected by NASA and eventually abandoned by its parent company.  Consequently, space travel today still relies on chemical propulsion.
Since Orion ended, nuclear pulse propulsion has been explored from time to time by other organizations, which have evolved and refined the original concept. For instance, NASA sponsored Project Longshot in the 1980's, which built off the results of an earlier project, Daedalus.  The Medusa design, which succeeded that work in the '90's, made use of a lightweight sail, rather than the heavy plate from the original Orion design.  To date, all of these projects have been fairly conceptual, suggesting that nuclear-powered spacecraft are far from an imminent reality. Still, it is encouraging to imagine that technology which today threatens our existence may one day provide us with a portal to new worlds.
© Andrea Klein. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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