Orion: In Flight

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Nuclear pulse propulsion Mars mission spacecraft in powered flight.

Image featured: on Winchell Chung’s Atomic Rockets site, Project Orion page, under William Black's 3D Orions.

Circa 1964 Nuclear Pulse Propulsion Mars mission spacecraft modeled in high detail from specifications in Nuclear Pulse Space Vehicle Study GA-5009, Vol. III – Conceptual Vehicle Designs and Operational Systems, PDF here: GA-5009 vol III (PDF), prepared at General Atomics John Jay Hopkins Laboratory for Pure and Applied Science for George C. Marshall Space Flight Center’s Future Projects Office.

The energy for the propulsion of the nuclear pulse vehicle is provided by the nuclear pulse unit; it converts the energy released by a nuclear explosion into a well focused cloud of high velocity propellant vapor.  

The pulse-units are ejected via a gas-fired gun, passing through an aperture in the center of the pusher-plate, as they near the detonation point they are armed, at a carefully calculated distance behind the pusher they detonate –  

Few might think of a nuclear bomb as a complex machine – but that is precisely what it is. A nuclear bomb is a complex machine that performs a series of precise predetermined actions at very high rate of speed in a very short interval of time – as it detonates.

The pulse-unit consists of the propellant, the channel filler, the radiation-case, the nuclear explosive device, the delivery case, and the fusing and firing mechanism.

In Project Orion: The True Story of The Atomic Spaceship Freeman Dyson describes the operation of the pulse-unit:

"When the nuclear device is exploded, the channel filler absorbs radiation emitted and rises to a high temperature. The radiation case serves to contain the energy released by the explosion so that more energy is absorbed by the channel filler. The high pressure achieved in the heated channel filler then drives a strong shock into the propellant, which vaporizes the propellant and drives it toward the pusher-plate."

"The expansion of the bomb and the subsequent compression of the tungsten pancake take a few millionths of a second. During this time, the channel filler and the propellant absorb neutrons and X-rays emitted by the bomb. This reduces the shielding required to protect the Orion crew, and transforms much of the bombs output into kinetic energy that can be intercepted by the pusher-plate and used to propel the ship.

The propellant slab, after being compressed to about one-quarter of its original thickness, expands as a jet of plasma, moving at some 150 km/sec (300,000 mph) toward the ship. It takes 300 microseconds to complete the trip. During this time the propellant cools to about 10,000 degrees. Within another few hundred milliseconds the propellant cloud hits the pusher plate (or the advancing front of the reflected shockwave produced by the initial collision) and is suddenly recompressed. For less than a millisecond the stagnating propellant reaches a temperature of between 100,000 and 120,000 degrees – about ten times the temperature of the visible surface of the sun, as all of the kinetic energy is converted into heat."

In space, without an atmosphere to produce a fireball, when the bomb detonates, you get about a millisecond of intense light.

– firing pulse-units off at rates between one and four per second the system can impart extremely high velocities to the spacecraft in a very short period of time.


Photo credits: Earth and Moon images courtesy NASA/JPL.

Related Image:

On Orbit