Depending upon the detail method chosen, this kind of revolutionary propulsion could be in flight test within 5 years, and flying in its initial form in 10 years. That would be the 1950’s fission technology. The other versions might perform better, but lack the materials, and the necessary detonation or containment technologies, that are required even to build test devices. They still might not be ready to fly in 50 to 100 years, if fusion is involved, according to some experts.
This article is based upon a NASA paper and two Wikipedia
writeups about pulse propulsion, plus
George Dyson’s book “Project Orion” about his father’s work on the Orion
project at General Atomics in San Diego,
CA, in the 1950’s and early
1960’s. That last begins with company
R&D work leading up to their first government contract.
Between those four sources,
a pretty good picture of the propulsion is available, particularly the technologically-ready
fission charge version originally pursued in the 1950’s and early 1960’s. For readers wishing to pursue this
further, those references are:
AIAA paper 2000-3856 “Nuclear Pulse Propulsion - Orion and
Beyond”, by G. R. Schmidt, J. A. Bonometti, and P. J. Morton, then from the NASA Marshall Space Flight
Center, Huntsville, AL.
Wikipedia article “Nuclear Pulse Propulsion”, as retrieved 2-26-2025, and last edited January 2025.
Wikipedia article “Project Orion (nuclear propulsion), as retrieved 2-26-2025, and last edited February 2025.
George Dyson, “Project
Orion – the True Story of the Atomic Spaceship”, published 2002 by Henry Holt and
Company, New York City. (A second edition is forthcoming very soon, if not already available.)
The basic external detonation concept is depicted in the
Figure 1 sketch below. All
figures are at the end of this article.
The idea is to explode a fission bomb at a safe distance
behind the vehicle, which vaporizes a
reaction mass, and blows that reaction
mass into the pusher plate at the rear of the vehicle. This requires a sort of “shaped charge”
technology for the fission device, in
order to increase the amount of reaction mass intercepted by the pusher
plate. There are shock absorbers between
the pusher plate and the rest of the vehicle,
to smooth-out the high-gee “hits” into a nearly-continuous and almost-steady
acceleration.
Figure 2 gives some indication of the effects of
vehicle size on this process. Bigger
mass is inherently a larger pusher plate dimension, which then intercepts a larger fraction of
the plasma blast created by vaporizing the reaction mass. The bigger mass also reduces the high-gee
“hit” from the explosion, making the
shock absorber design easier.
At the time this technique was pursued in the 1950’s and
early 1960’s, it was thought that the
main environmental concern would be the radiation fallout in the atmosphere
from a surface launch. Being fractional-kiloton
(KT) devices, leading to low-KT devices
once out of the atmosphere, there is
less fallout than one might otherwise suspect,
more or less comparable to one atmospheric test of a low-range megaton
(MT) thermonuclear device. See Figure
3.
The risk of electromagnetic pulse (EMP) effects was not
really recognized until after the “Starfish Prime” megaton-range nuclear test, that was conducted in space in 1962. Some data about that are given in Figure 4.
This really restricts where and how one
might surface-launch such a vehicle. These
vary inversely with the square of the distance,
and directly with yield. Bear in
mind that we simply do not have the necessary technological capabilities
yet, to build such vehicles out in space, so surface launch is still the only means
available in the short term.
Based on the data in the four references, a rough approximation to the performance
values one might expect are given in Figure 5. These are quite remarkably high, sufficient for sending crews pretty much
anywhere within the solar system, on
relatively short trips. Some of the
fusion concepts, if they can really be
made to work, might even be suitable for
interstellar missions.
It is this author’s opinion that we need to get over our
fears about “nuclear things in near-Earth space”, modify the Space Treaty to allow this kind of
propulsion, and simply “get on with the
war”. However, finding massive new fissionable material resources
is inherent to support the quantities of fissionable material that will be
necessary. If not on Earth, then “out there” somewhere.
As a conceptual example,
the one-way velocity requirement to go from low Earth orbit to
rendezvous with asteroid 2024YR4 is about 5.9 km/s as depicted in Figure 6. Back to low Earth orbit, about 4 years later, the same velocity requirement can decelerate
one back to low orbit, excluding all
rendezvous and course correction requirements.
If one wanted to send a large expedition to explore mining this asteroid
(to include bringing significant mass home),
using a pulse propulsion vehicle already based in low orbit, the rough sizing of such a vehicle’s weight
statement might look like the numbers given in Figure 7. The contrast with a chemically-powered
vehicle is quite stark. But with pulse
propulsion, the basic message is to
build it big!
Figure 1 – The Basic Concept of Nuclear Pulse Propulsion As
It Was Originally Pursued
Figure 3 – About the Risks From Surface-Launching a Nuclear
Pulse Propulsion Vehicle
Figure 4 – About the “Starfish Prime” Nuclear Test That
Revealed the Risks of EMP
Figure 5 – Assessment of Achievable Performance Vs. Size
With Fission Pulse Propulsion
Figure 6 – Getting to Asteroid 2024YR4 At Its 2028 Close
Approach
Figure 7 – How a Large Round-Trip 4-Year Mission Might Be
Mounted to Asteroid 2024YR4
