Orion was a study of a spacecraft intended to be directly propelled by a series
of explosions of atomic bombs behind the craft (nuclear pulse propulsion).
Early versions of this vehicle were proposed to take off from the ground with
significant associated nuclear fallout; later versions were presented for use
only in space.

The Orion
concept offered high thrust and high specific impulse, or propellant efficiency,
at the same time. The unprecedented extreme power requirements for doing so
would be met by nuclear explosions, of such power relative to the vehicle’s
mass as to be survived only by using external detonations without attempting to
contain them in internal structures. As a qualitative comparison, traditional
chemical rockets—such as the Saturn V that took the Apollo program to the
Moon—produce high thrust with low specific impulse, whereas electric ion
engines produce a small amount of thrust very efficiently. Orion would have
offered performance greater than the most advanced conventional or nuclear
rocket engines then under consideration. Supporters of Project Orion felt that
it had potential for cheap interplanetary travel, but it lost political
approval over concerns with fallout from its propulsion.

Partial Test Ban Treaty of 1963 is generally acknowledged to have ended the
project. However, from Project Longshot to Project Daedalus, Mini-Mag Orion,
and other proposals which reach engineering analysis at the level of
considering thermal power dissipation, the principle of external nuclear pulse
propulsion to maximize survivable power has remained common among serious
concepts for interstellar flight without external power beaming and for very
high-performance interplanetary flight. Such later proposals have tended to
modify the basic principle by envisioning equipment driving detonation of much
smaller fission or fusion pellets, although in contrast Project Orion’s larger
nuclear pulse units (nuclear bombs) were based on less speculative technology.

Currently, I
have multiple requests for documents relating to Project Orion. They will be
added when they become available.

Declassified Documents

Propulsion Concepts (4th Symposium) Palo Alto, California, April 26, 27, 28
1965. Orion Space Propulsion (Technical Status and Mission Potential). Parts 1,
2 and 3
[54 Pages, 6.9MB]