About old Project "Orion" - the nuclear explosion drive

The following data came from a book written by George Dyson, titled "Project Orion - the True Story of the Atomic Spaceship", published by Henry Holt, and copyrighted 2002. George Dyson is the son of physicist Freeman Dyson, who actually worked on this project. He interviewed many project participants, including his father.

Project "Orion" was a funded Air Force project in the 1959-1965 time frame. The Air Force had no application for a deep space ship, which restricted the funding and how far the project could go. The Air Force then had to turn its entire space program over to NASA in 1965. NASA saw "Orion" as a competitor to its Project "Rover" nuclear thermal rocket efforts, and so killed "Orion" by lack of funding.

"Orion" never flew or tested with nuclear devices. However, a 1-meter scale model flew just fine with pulses of high explosives. This verified the viability of the concept. The results would have been remarkable, had such a technology been pursued. Note that the following design data is based on surface launch of nuclear explosion-drive ships:

Design "name"..............test veh......orb.test.....interplan.....adv. I.P.

Gross weight, tons.........50-100........880..........4000..........10,000
Empty weight, tons..........45............370..........1700...........3250
Effective Isp, sec.......var, to 3000....3-6000........4000..........12,000
Dia, feet...................40.............80...........135............185
Length, feet................50............120...........200............280
Avg. gees...................2-4.............2.....var, to 2......var, to 4
Vacuum charge, KT.......0.1-0.5.........0.8-3.......about 5.......about 15
Sea level charge, KT.......0.003..........0.03.........0.15...........0.35
# charges to 125,000 feet...1-200..........200..........200............200
Total KT to 125,000 feet.. about 2.....about 20....about 100......about 250
# charges to 300 mile orbit..NA............800...........800............800
Total MT to 300 mile orbit...NA........0.45-1.8............3.............9

The name "test veh" was a sub-orbital test vehicle. The name "orb.veh" was to be a test vehicle capable of reaching a 300 mile orbit about the Earth. The name "interplan" was a smaller interplanetary transport ship, capable of reaching the moon or Mars. The name "adv.I.P" refers to a much larger interplanetary transport ship capable of touring the inner solar system in a single trip, or reaching Saturn and returning. Weight are shown in US customary units of the 2000 pound ("short") ton. The metric ton is a 10.25% larger unit. NA means "not applicable".

These are short, fat, bullet or projectile-shaped designs, of a heavy, strong type of construction resembling marine engineering more than any flight vehicles ever known. That means the heavy ship's hull provides a lot of radiation shielding against cosmic rays and solar flares. These ships are big enough to provide one full gee's artificial gravity by spinning at an acceptably slow rate. For example, the "adv.I.P." design needs to spin at only 20 degrees/sec (3.3 rpm) to provide one full gee at the outer hull.

Every one of them is a single stage device: nothing is jettisoned or lost, everything returns for re-use. Dimensions are in feet (one meter = 3.280833 feet). There is a large pusher plate mounted on resonant shocks at the rear. These pusher plates receive the impulse from the nuclear detonations and spread it over time.

The following data lists mission performance projected for these very same designs:

Design name.................test veh......orb.test.....interplan........adv.I.P
Payloads delivered, ton..................(3000 sec)............................
300 mile orbit (10 km/s)........NA..........300...........1600...........6100
Soft lunar landing (15.5 km/s)..NA..........170...........1200...........5700
Mars orbit & return (21 km/s)...NA...........80............800...........5300
(orb)Ven.-Mar.-ret. (30 km/s)...NA...........NA............200...........4500
To Saturn & back (100 km/s).....NA...........NA.............NA...........1300

Between the listed specific impulse data and the payload-to-Saturn data, bigger is clearly better with this pulsed-explosion propulsion approach. The mission data shown assume a return to Earth orbit for re-use of the ship. The speeds are the total velocity requirements based on Hohman transfer orbits. These ships do not make landings on Mars or the moons of Saturn, landing craft that are part of the cargo weight would be used for that.

The nuclear devices were "optimized" as shaped charges with a preferred "blast" axis. A "propellant" mass was included in each charge, to be vaporized into hypervelocity plasma and bounced off the pusher plate. Devices optimized in that way do not make very good weapons, but they are a very promising source of propulsion! This also raises a very interesting question: could this approach be scaled up further, and use higher-efficiency thermonuclear charges, for even higher effective specific impulse? Old Project "Orion" never looked at that.

Note that if Saturn could be reached, so also could Jupiter and the asteroid belt be reached. Round trip flight time on the Hohman-transfer Saturn mission would be 3 years. However, you could fly faster with this technology, if more of the vehicle were its nuclear "fuel" and less of it were cargo. That means even the outer solar system could be reached with this type of vehicle. Manned missions to the Kuiper Belt are possible!

Based on what they were able to achieve back then, we could build and operate such spacecraft right now. The atmospheric yields incurred to launch such things into space are not all that large, in terms of the fallout produced. Once a few of them are up there, we incur no further fallout risks. We could re-supply them with conventional launchers, and re-use them as space-based interplanetary transport vehicles for years, even decades. Or even longer.

Why not?