Orion: Nuclear Pulse Propulsion

This essay owes a debt of gratitude to Winchell Chung for his Atomic Rockets website, for the wealth of information to be found there. Aerospace engineer and space historian Scott Lowther's research into Project Orion published in Aerospace Projects Review (available at links at the bottom of this page) has been indispensable.

Nuclear Pulse Propulsion In The Orion's Arm Future History Setting: 1. Assumptions

Any entity, be it a nation, state, or coalition of private sector corporations acting in concert, possessing sufficient industrial infrastructure and funding to construct and fabricate nuclear pulse propulsion units in sufficient quantities to launch an Orion to a distant planetary target, by default possesses sufficient military might, in terms of raw firepower, to do so without significant effective opposition, undue interference, or hindrance.

Efforts to prevent the launch and use of spacecraft powered by such technology would be approached in the same manner, and with the same cautious diplomacy, nuclear powers exercise with one another.

Fabrication facilities and launch sites would be as vigilantly guarded as any strictly military nuclear weapons facility, in similar manner, and with sufficient on-site security to prevent any compromise, and repel or capture, any would-be intruder.

When it comes to lofting and transporting hundreds, or even thousands of tons, of payload to distant planetary targets there is no other propulsion method, within the capacity of present day technology, as capable as Orion.

Orion is so capable, that if your goal is to launch and propel payloads of hundreds or even thousands of tons to distant planetary targets, it is inevitable that one day it will be built and launched, and the nation, or group of nations, or coalition of private sector entities involved, will literally own the resources of the solar system.

2. Historical Background: Orion Nuclear Pulse Propulsion.

Project Orion was initiated in 1958 at General Atomics, primarily under auspices of the U.S. Air Force Special Weapons Center, and Los Alamos Scientific Laboratory, with later participation by the George C. Marshall Space Flight Center and NASA's Future Projects Office. Project Orion was funded under ARPA (Advanced Projects Research Agency (now DARPA)).

You can download and read the specifications for NASA's 10-meter nuclear pulse propulsion spacecraft 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.

Winchell Chung's Atomic Rockets site has an excellent page on Project Orion, here: Project Orion.

Stanislaw Ulam is credited with the idea of using nuclear explosives to propel spacecraft.

Orion is a refinement of this concept. Orion reacts small directional nuclear explosives against a large steel pusher plate attached to the spacecraft with shock absorbers. Efficient directional explosives maximize the momentum transfer, leading to specific impulses in the range of 6,000 seconds, or about thirteen times that of the Space Shuttle Main Engine. With refinements a theoretical maximum of 100,000 seconds (1 MN•s/kg) might be possible. Thrusts were in the millions of tons, allowing spacecraft larger than 8 × 10⁶ tons to be built with 1958 materials.

Orion works because the plasma is dynamically shaped (as the explosion happens) by the specially designed shaped charge nuclear explosive, X-rays are channeled by the radiation case in the instant before the weapon is vaporized, these exit a single aperture, striking and heating up a beryllium oxide channel filler and propellant disk (tungsten), resulting in a narrow conical jet of ionized tungsten plasma, traveling at high velocity (in excess of 1.5 × 10⁵ meters per second). This crashes into the pusher plate, accelerating the spacecraft. The jet is not physically contained by the pusher, and contact with the pusher is infinitesimally brief, so the pusher is not subject to extreme heating during thrust maneuvers.

Freeman Dyson theoretical physicist and mathematician, famous for his work in quantum electrodynamics, solid-state physics, astronomy and nuclear engineering was tasked with proving the workability of the system. He calculated the thermal fluid dynamic's of superheated plasma striking the steel pusher plate thousands of times per vehicle flight—his conclusion was that the system was viable. Orion works. Freeman set up the equations for the plasma jet generated by a pulse-unit and the numbers were run on General Atomics IBM 650 card-programmed calculator, one of the workhorse machines that had handled many of the early bomb and blast-wave calculations at Los Alamos.

Theoretical physicist and prominent nuclear weapon designer Ted Taylor managed the project for General Atomics.

The General Atomic reference design was to be constructed of steel using submarine-style construction techniques with a crew of more than 200 and a vehicle takeoff weight of several thousand tons. This low-tech single-stage reference design would reach Mars and back in four weeks from the Earth's surface (compared to 12 months for NASA's current chemically powered reference mission). The same craft could visit Saturn's moons in a seven-month mission (compared to chemically powered missions of about nine years).

The pulse-unit converts the energy released by a nuclear explosion into a well-focused cloud of high velocity propellant vapor.  Pulse-units are ejected via a gas-fired gun, passing through an aperture in the center of the pusher-plate and falling behind the vehicle to a safe stand-off distance, as they near the detonation point they are armed, at a carefully calculated distance behind the vehicle they detonate. With pulse rates of 1 to 4 units per second extremely high velocities can be imparted in a relatively short time.

Winchell Chung's Atomic Rocket's site has a detailed description of the Orion pulse-unit:

The device is basically a nuclear shaped charge. A pulse unit that was not a shaped charge would of course waste most of the energy of the explosion.

Each pulse unit is a tiny nuclear bomb, encased in a "radiation case" that is open on one end. A nuclear blast is initially mostly x-rays. The radiation case is composed of a material that is opaque to x-rays (depleted uranium). The open end thus "channels" the flood of x-rays in one direction (at least in the few milliseconds before the bomb vaporizes the radiation case). The channeled x-rays then strike "channel filler" material (beryllium oxide). This transforms the atomic fury of x-rays into an atomic fury of heat. Lying on top of the channel filler, forming the end-cap of the pulse-unit, is a disc of propellant (tungsten). The heat flashes the tungsten into a jet of ionized tungsten plasma, traveling at high velocity (in excess of 1.5 × 10⁵ meters per second). This crashes into the pusher plate, accelerating the spacecraft. The shock of impact is stepped down by a two-stage shock-absorber system. The jet is confined to a cone about 22.5 degrees. It is estimated that 85% of the energy of the nuclear explosion can be directed in the desired direction. The pulse units are popped off at rates between one and four per second.

Freeman Dyson describes the Orion 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 white light.

From Project Orion, the true story of the atomic spaceship
George Dyson, Henry Holt, 2002

Unlike conventional rockets which get more complex and less efficient the larger you build them, an Orion is quite the opposite.

The bigger the better. Efficiency just keeps going up.

The smallest Orion spacecraft were designed for NASA. According to Scott Lowther this was 32' diameter, 115' long interplanetary exploration vehicle massing about 210 metric tons.

NASA interplanetary exploration designs ranged from the minimum 4 man Mars exploration mission crew with alternate mission plans calling for a 6 man, 8 man, and a 24 man mission crew vehicle – the large mission crew proposals provided for a second heavier logistics Orion spacecraft to carry several hundred tons of supplies. Another NASA proposal called for a 24 man Callisto mission.

From there the scale went up.

USAF designs included an Orion Orbital Battleship. Scott Lowther has done some research into the proposal, which was to be armed with naval gun turrets, minuteman missiles with city-killing 20 megatons warheads, and Casaba-Howitzer. It appears that the Casaba-Howitzer charges would be from subkiloton to several kilotons in yield, be launched on pancake booster rockets until they were far enough from the battleship to prevent damage (several hundred yards), whereupon they would explode and skewer the hapless target with a spear of nuclear flame. Another design was intended to loft a hemisphere-killing Teller-Ulam fusion device.

Among what I refer to as the "Legacy" General Atomic proposals were a 50 man Lunar mission, a duel vehicle Mars exploration mission with more than a hundred personnel carried aboard two 4,000 ton Orion spacecraft, and the alternate 200 man Mars mission and/or Saturn Enceladus mission.

Other Orion vehicle concepts included the following:

            Vehicle mass and type                                                                                     Dimension's

880 ton ………….. Test vehicle.    82' diameter 118' height.
4,000 ton ……….. Interplanetary spacecraft. 101'diameter 196' height.
10,000 ton ……… Interplanetary spacecraft. 183' diameter 278' height.

My Orion Mars Settlement Transports

50,000 ton (structure + 10,000 ton payload).                                              328' diameter 600' height.

Freeman Dyson's theoretical deigns for 8 million ton "Energy Limited," and "Momentum Limited" interstellar spacecraft were exercises intended to explore the outer limits of Orion as a propulsion system—and even for these the validity of the system proves out.

There is no other real-world propulsion system capable of lofting payloads in the mass range of Orion—for perspective vehicles in the several thousand ton range are equivalent to the mass of Navel battleships and commercial ocean liners, the theoretical maximum mass for Orion is 8 million ton's—Dyson's theoretical starships, generational ark's, were of this scale, to be propelled by hydrogen bombs with pusher plates 2,000 feet across. No other system, grounded in real world physics, is capable of lofting vehicles and payloads massive as small ocean liners, or has the off-the-shelf technological capability to hurl these payloads across the solar system. Whether Orion can be built is not really a question—the question is when will it be built, and who will build it.

In an interview, speaking in regards to Orion, Arthur C. Clarke said:

"Even now the only way we could get large payloads around the solar system is by something like Orion, because atomic bombs contain thousands of times more energy, indeed millions of times more energy, than any of the chemical fuels used in existing rockets – hydrogen and oxygen are feeble compared to the energies released by an atomic bomb. So when you talk of sending hundreds of tons, or even thousands of tons of payload, including human beings, to Mars, say, that's the only way we could do it, even now. The space age hasn't even begun yet. I believe the day will come when very few members of the human race will even be able to point at the part of the sky where the earth is."

Freeman Dyson speaking on Orion:

"I am still very strongly interested in spreading life beyond the Earth. Humans of course should go along. The most important thing, to me, is just enlarging the domain of life. Life has this marvelous adaptability – it's able to adapt itself to almost anything. Life has hardly even begun yet adapting itself to the universe – this little planet doesn't give it so much scope."

Scott Lowther, on his Unwanted Blog, posted an essay on the utility of the Orion nuclear impulse device as a tool to deflect potential impactors such as the recent Chelyabinsk Meteor – staging Orion vehicles out at the Sol-Earth Lagrange points as deep space detection and "picket ships."

Link: Nuking The Chelyabinsk Meteor

Rare Flight test footage of Orion can be found here in an excerpt of the BBC documentary To Mars by A-Bomb. Orion Flight test footage

I also highly recommend the entire seven-part documentary, part one here: To Mars by A-Bomb

More information on Project Orion

Project Orion: The True Story of the Atomic Spaceship

In Aerospace Projects Review issue Volume 2, Number 2, available here aerospace engineer and space historian Scott Lowther offers a beautifully illustrated 56-page article on Project Orion. This is one of the most definitive articles on the subject, covering the large designs, 20 meters and diameter and larger. The 4,000 ton nuclear pulse propulsion orbital battleship design for the USAF is shown in never-before-published detail. Scott was able to interview one of the surviving members of the original General Atomics Orion team, this issue contains details unavailable elsewhere and is highly recommended.

Aerospace Projects Review issue Volume 1, Number 4 V1N4

The primary article in this issue is a 58-page article on the development of Project Orion. This article covers the initial development of Project Orion, from the earliest configurations through to the near-final designs, test facilities, safety and environmental issues, and subscale flight vehicles. Vehicle scaling relationships, operating principles, and, published for the first time, pulse unit physics and interactions.

Copiously illustrated with photos, film stills, presentation graphics, diagrams and original drawings.

Aerospace Projects Review issue Volume 1, Number 5 V1N5

The primary article in this issue is a 71-page article on the late 10-meter Project Orion vehicles designed for the USAF and NASA by General Atomic. This article is packed with diagrams taken from official reports, as well as data, performance graphs, all-new reconstruction drawings and artwork. The Orion vehicle is described and shown in greater detail here than ever before in publicly available articles. Also includes information on 8-meter and 12-meter concepts for military applications as well as the baseline 10-meter design that was to serve both military and Martian exploration purposes. Launch vehicles, both solid and liquid rockets, are also described.

Aerospace Projects Review issue Volume 1, Number 3 V1N3

The Helios program: contained nuclear-pulse propulsion program, run parallel with Orion, specifically the ideas of Dandridge Cole and Project Helios. This is the first part in a series on the Orion Project. Included are full-color reproductions of period artwork as well as all-new reconstructions of the designs.