"The Dean Drive and other Reactionless Drives" is a short essay by the science-fiction writer Jerry Pournelle, posted on his website, dated as created in 1990 and last revised in 2009. It began as a reply to a reader's letter and turned into a personal memoir. Pournelle had worked for an aerospace company in the 1950s and was sent to buy Norman L. Dean's machine if it proved to work. He never saw it. The essay says little about the device itself. Its interest lies in Pournelle's own recollection, written decades later and uncorroborated by any independent record it cites, of how his company tried to acquire the machine, why the deal collapsed, and how he explained the reports of weight loss.
Why an aerospace company wanted it
Pournelle frames the attraction around the rocket equation. A rocket gains speed only by throwing mass overboard, and he notes that a craft may have to discard up to 90% of its total mass to reach useful speeds. A machine that produced straight-line acceleration from rotary motion, without reacting against air or water and without shedding mass, would free spaceflight from that constraint. Even a tiny thrust would matter, he argues, because it could be applied continuously in free fall.
What prompted the interest was John W. Campbell, Jr., editor of Astounding Science Fiction, who said he had watched the device on a bathroom scale. Pournelle's illustration of what Campbell described is a machine, powered by a quarter-inch drill built into it, that weighs roughly nine pounds switched off and something like 8.5 pounds running. He works this out as a thrust of 1/18 g. He offers those numbers loosely, as an illustration rather than a record; they do not match the figures from Campbell's 1959 letter that G. Harry Stine reports in Detesters, Phasers and Dean Drives (1976): G. Harry Stine's Witness Account of the Dean Drive and the Huyck Corporation Tests, a scale reading falling from 135 lb to 50 lb.
The attempted purchase
Pournelle says he persuaded his employer, a retired general, that a low probability of success was worth a look given the size of the payoff. The company issued a letter of credit worth half a million, valid only if countersigned by Pournelle, a second company scientist and a finance officer in the Washington area who was told to sign if both scientists did.
By Pournelle's telling, the negotiation reached an impasse neither side would break. For the buyers, proof that the machine worked was the precondition of any payment; for Dean, money in hand was the precondition of any demonstration. Pournelle describes Dean as afraid, or claiming to be afraid, that the invention would be stolen. Dean also asked for a promise of a Nobel Prize, which Pournelle says he was willing to give, while having no idea how to deliver it.
Only later, Pournelle writes, did he learn that 3M had sent a team with almost the same instructions, and he mentions some evidence of a third bidder whom he could not identify. He speculates that Dean hoped competition would raise the price. Neither his team nor the 3M team saw the machine run. Pournelle adds that he would have recommended paying far more than half a million had it worked.
Who actually saw it
By Pournelle's account, the only two people he ever met who had seen the device were Campbell and Stine, and it was their reports that convinced him the trip was worthwhile. He says he does not know why Dean showed it to them and not to buyers. He also relays a story from a former Peenemünde rocket scientist he worked with: that a charlatan had earlier built a similar gadget that climbed a string and rocked like a pendulum, which impressed Hitler enough to order an investigation that came to nothing. That colleague never saw Dean's machine either, and the story is offered as hearsay.
Pournelle's judgement of Campbell is mixed: more enthusiast than scientist but "no fool", aware of earlier frauds, and possibly either deceived or deliberately encouraging scientists to believe such a drive could be built.
How Pournelle explains the weight loss
His conclusion is that the machine did not work. In his view the apparent lightness came from the machine's swinging interacting with the scale's own spring oscillation, and the same sort of machine can climb a string while not actually losing weight. He suspects Dean had independently rebuilt the gadget that interested Hitler.
He extends the point to a whole class of inventions that move several weights along non-circular paths, often out of phase with one another. Pournelle maintains that every claimed weight loss of this kind has proved to be a product of the measurement, not of the machine. Devices that creep through water are, on his account, exploiting unequal accelerations of the weights interacting with friction and with the inertia of the water, which he likens to bobbing a bobsled. This is an argument from physics and experience; the essay reports no measurement of Dean's or anyone else's machine.
The meeting that decided nothing
Because Stine remained convinced he had seen a real reactionless drive, Pournelle obtained a small grant from the Vaughn Foundation, about 3 grand as he recalls, to bring Possony (the essay gives only the surname), Stine, Robert Forward and others together. They concluded that nothing could be done: nobody knew how to build the device, it was lost, and the only evidence it had worked was Stine's impression, which Pournelle stresses rested on observation, not tests. Stine disagreed but had no proposal beyond keeping an open mind, and Pournelle says he died still convinced. Forward's summing-up, as quoted, was that what was needed was "A repeatable demonstration: a new data point."
Pournelle also records that the original device Campbell and Stine described was never found after Dean died, and that, according to Stine, the machine in Dean's patent (see US Patent 2,886,976 (1959): Norman L. Dean's System for Converting Rotary Motion into Unidirectional Motion) does not work and is not what Dean demonstrated.
The suspension test
Pournelle closes with the check he would want to see before taking any reactionless-drive claim seriously. With the device mounted on a two-wire swing, what would count is a sustained lean away from vertical in the direction of the claimed thrust, one that survives with air currents shut out by an enclosing bag, disappears when the power is cut, can be repeated at will, and comes with no loss of mass. Only a device passing all of that, he says, would merit a physicist's attention.
The idea of letting a hanging device show thrust as a lasting deflection is shared with the free-hanging test Stine applied at Huyck Corporation and the level-platform pendulum proposed in Responding to Mechanical Antigravity (2006): Millis and Thomas on Why Oscillation Thrusters Like the Dean Drive Only Appear to Produce Thrust. Pournelle's version is the most informal of the three, but it explicitly folds in two further controls: excluding air effects and confirming that nothing has been thrown off.
A closing section contrasts the Dean drive with ion drives, which Pournelle says do work: very low thrust at a specific impulse of up to 20,000 or so, against about 400 for the best chemical rockets.
What the essay does and does not establish
The commercial side of the story, including the letter of credit, the parallel 3M team, the Nobel Prize request and Dean's refusal to demonstrate before payment, rests on Pournelle's own recollection, and the essay offers no independent corroboration of any of those points. The essay is not evidence about the machine itself, which its author never saw. Its explanation of the scale readings is reasoned, not measured, and several details, including dates and Campbell's figures, come from memory decades later. The wider record is set out in The Dean Drive: Norman L. Dean's Reactionless-Drive Claim, Its Demonstrations, Its Publicity and How It Was Later Judged.
Source notes & attribution
- https://www.jerrypournelle.com/sciences/dean.html