Responding to Mechanical Antigravity (2006): Millis and Thomas on Why Oscillation Thrusters Like the Dean Drive Only Appear to Produce Thrust

"Responding to Mechanical Antigravity" is a NASA technical memorandum (NASA/TM-2006-214390, also AIAA-2006-4913) by Marc G. Millis of Glenn Research Center and Nicholas E. Thomas of the University of Miami. It was prepared for the 42nd Joint Propulsion Conference in Sacramento, California, 9–12 July 2006, and issued in December 2006. It is not a test of any particular machine. It is a guide, drawn from the experience of NASA's Breakthrough Propulsion Physics (BPP) Project, to how reviewers should answer people who believe they have built a reactionless mechanical thruster, and it names the device in US Patent 2,886,976 (1959): Norman L. Dean's System for Converting Rotary Motion into Unidirectional Motion as one of the best-known examples of the type.

What is being claimed

The memorandum deals with two families of machine whose builders believe they push or lift themselves with nothing to push against.

The first is the family Dean's machine belongs to. Millis and Thomas call it the oscillation thruster, and note the alternative names sticktion drive, internal drive and slip-stick drive. Their examples are the 1959 Dean Drive (Patent 2,886,976), Richard E. Foster Sr.'s US Patent 5,685,196 (granted 1997) and, as a rotating-mass version, Brandson R. Thornson's US Patent 4,631,971 (granted 1986). Whatever the layout, the paper says, each is a chassis carrying masses that a powered conveyor drives through a lopsided cycle, faster one way than the other. Set on a bench, such a machine visibly travels, and the claim is that it does so by internal motion alone.

The second family uses gyroscopes. The paper's example is Eric Laithwaite's 1973 demonstration, in which a single 50 lb gyro rose as it was made to precess, and his later US Patent 5,860,317, which the authors describe as claiming a linear force from such torques.

Why does the box move at all?

Nobody in this argument disputes that an oscillation thruster shuffles along a floor. The question is what is pushing it, and the memorandum's answer is the floor. In its words, "The ground is the reaction mass".

The mechanism it gives is a gap between two kinds of friction. Surfaces resting on each other usually grip harder than the same surfaces drag once they are already sliding. A machine that throws its weights hard in one direction and eases them back in the other exploits that gap: the hard throw kicks the chassis with enough force to break its grip, so it skids a short way, while the gentle return pushes back too weakly to unstick it. An everyday comparison, which is not the paper's own, is a person hitching a wheel-less chair across a room by lurching sharply and then settling back slowly. The chair moves, but only because there is a floor under it.

A schematic figure in the paper restates this as impulse (I = F × t): both halves of the cycle deliver the same total, but only the brief, hard half rises above the critical static friction force, Fc. The authors flag the figure as a sketch, not a rigorous analysis.

Take the floor away and, on this account, the effect goes with it. The authors say established physics predicts that in orbit the frame and its masses would merely shake against each other while their common centre of mass kept to its freefall path, and that a unit dropped with its supposed thrust axis vertical would fall at the same rate switched on or off.

For the gyroscopic machines the diagnosis is different. The paper attributes the rising gyro to conservation of angular momentum and says builders mistake the resulting torque for a linear lifting force. Gyroscopic designs whose motion is confined to a single plane, such as Thornson's, it counts as oscillation thrusters.

What was tested, and what test the paper asks for

Nothing was tested for this memorandum. It reports no measurements on Dean's machine or on any of the patented devices it cites; its verdict on the class rests on conservation of momentum and the friction argument.

What it offers instead is a test for builders to run themselves, on the grounds that detailed analysis is slow and, the authors judge, unlikely to be followed by an amateur. The machine is hung on a level-platform pendulum and the platform's position is compared with the machine running and switched off. A lasting shift to one side would count as real thrust. A swing back and forth about the rest position would not, and the swing is what the authors expect.

They attach conditions meant to exclude false positives:

• The power supply should ride on the pendulum with the device, so that power cords cannot interfere.
• The pendulum should be as tall as possible, both to enlarge the sideways displacement for a given force and to push its natural frequency well below the device's operating frequency. Similar frequencies can give spurious results.
• A level platform is preferred to a simple pendulum because shifting internal masses can tilt the base and mimic a deflection.
• An air track is not recommended: tilting spills more air from the dipped end, and the device is pushed by that asymmetric airflow.

Two relations are given for small deflections: lateral force F = mg tan θ, and pendulum natural frequency f = (1/2π)√(g/l), with g taken as 9.8 m/s2.

Gyroscopic claims are harder to check, the paper says, because the supposed effect is vertical and a pendulum cannot show it. Its suggestion is two identical units on a balance beam, one with its stems locked, and it warns that even this is difficult to do cleanly.

What the evidence does not show

The memorandum is an argument from accepted physics plus a proposed experiment. It does not demonstrate by measurement that any named machine produces no thrust, and it does not claim to.

It also leaves some questions formally open. A "jerk" effect (the time rate of change of acceleration), which the authors reference to a 1962 Analog article, "The Fourth Law of Motion", has been put forward as a theoretical explanation; they say no experiments or physical evidence supporting it have been reported. A literal reading of Mach's principle is mentioned as a possible way to reconcile a real effect with momentum conservation, with the caveat that the idea has not been fully explored and would need a formalism that had passed peer review first. James F. Woodward's transient inertia work is set apart as a different category, described as neither independently confirmed nor refuted at the time of writing.

Why NASA wrote it, and the reply it recommends

The memorandum says NASA sponsored BPP research from 1996 to 2002 and that press coverage brought a flood of mail: 1000 unsolicited submissions per year in 2000 through 2001, roughly a third of them from amateurs wanting their own ideas reviewed. The project reviewed some submissions early on and then adopted a policy of reviewing none. The memorandum is offered as a substitute, a reusable explanation for the two commonly proposed mechanical schemes.

Its advice on correspondence is not to dismiss a submitter flatly for violating known physics, which the authors found provokes heated replies and teaches nothing. A reply should name the apparent conflict with momentum conservation, enclose the pendulum test and the known pitfalls, and make a successful result the condition for further contact, so that "the burden of proof" returns to the builder.

Bearing on the Dean patent

Read beside the patent, the memorandum supplies the mainstream explanation for why a Dean-type machine can visibly move while producing no net thrust, and a concrete criterion that a positive claim would have to meet. It establishes neither by measurement for Dean's own apparatus. One detail differs between the two documents. The memorandum's reference list gives the patent's filing date as Jul. 13, 1954, with the grant on May 19, 1959. The patent record, as summarised in US Patent 2,886,976 (1959): Norman L. Dean's System for Converting Rotary Motion into Unidirectional Motion, gives the filing date as 13 July 1956 (application US597805A) and the same grant date of 19 May 1959. The memorandum's 1954 date therefore conflicts with the patent record, and this dossier follows the patent record's 1956.

Further reading

The demonstrations Dean gave in the early 1960s, the pendulum test that William O. Davis and G. Harry Stine wanted and Dean refused, and the other later assessments are set out in The Dean Drive: Norman L. Dean's Reactionless-Drive Claim, Its Demonstrations, Its Publicity and How It Was Later Judged.

A pendulum criterion much like the one proposed here was already being applied to inventors' machines at Huyck Corporation in the early 1960s, according to G. Harry Stine's 1976 Analog article, which also describes the experiments made in support of the "Fourth Law of Motion" idea; see Detesters, Phasers and Dean Drives (1976): G. Harry Stine's Witness Account of the Dean Drive and the Huyck Corporation Tests.