- Concept Led By: NASA, DARPA, U.S. Air Force
- Companies Involved: N/A
Project Orion is probably one of the most notable on this list and for good reason. It should be noted that this did not involve a single spacecraft but rather, a spacecraft concept. The study was conducted sometime between the 1950s and 1960s by DARPA, NASA, and the U.S. Air Force. The goal? To measure the efficacy of a starship that would be propelled by a series of atomic bomb explosions behind the craft. Known as nuclear pulse propulsion, looking back the idea seemed odd. Early versions of these spacecraft designs were proposed to, if you can believe it, take off from the ground. Later versions, however, only involved versions that took off only in space.
A total of 6 non-nuclear tests were conducted using these models, but the project would be abandoned. This was due to many reasons, but one of the biggest was the Partial Test Ban Treaty. This did not explicitly target spacecraft but rather, involved the treaty to stop doing random tests with nuclear technology. Yet it did involve not testing things in space because of the worry of nuclear fallout. The entire idea behind using nuclear energy to go to space was connected to a concept that came from Russian explosives expert, Nikolai Kibalchich, back in 1881. Later on, men like Robert A. Heinlein and Harmann Ganswidt independently came up with similar ideas.