Electro-mechanical thruster
 

Hello All,

I wanted to pass along a concept for an electro-mechanical thruster. While I haven't built a prototype unit and am not 100% certain that it would work, I think it's worth looking into (it's based on another, purely mechanical device that passed a "ballistic pendulum" test--please see below). If any of you might wish to try building it and want to patent it, you have my blessing. I am not in a position to build one or promote the concept, and if it does work I would like to see it used for space travel instead of remaining an un-manifested idea.

This *very* simple device is the mechanical equivalent of an ion thruster--it is a low-thrust device that runs on electricity. Unlike an ion engine, however, it would never run out of reaction mass (propellant) because it reuses its reaction mass. Powered by solar cells or RTGs (Radioisotope Thermoelectric Generators), it could produce thrust indefinitely. First, a little background information:

In the early 1980s I ordered an information packet from Rex Research (which ran ads in "Popular Science" magazine) about alleged anti-gravity devices. Along with material on the infamous "Dean Drive" (about which Rex Research was ambivalent due to Dean's extreme secrecy regarding it) and "ion wind" devices such as those built by T. Townsend Brown (the packet included plans for one), there was a booklet that discussed all of the various supposed space drives. It also described a simple "ballistic pendulum" test setup (just a fancy term for a carpenter's plumb-bob) that could be used to test them--a space drive prototype hanging from the ballistic pendulum would, if it worked, cause the pendulum to be deflected away from the vertical in the direction of the space drive's thrust. (The old ion rocket ["ion wind"] experiment plan in the 1950s editions of "World Book" Encyclopedia also had the rocket hanging by its power supply wire, on which the rocket swung forward when the power supply [a Model-T spark coil] was turned on using a ham radio telegraph key.)

The Rex Research booklet also contained information on a simple mechanical thruster device (from which my concept is derived) that passed the ballistic pendulum test. It consisted of a metal rod with a disc affixed to each end. These discs were used to stop the travel of two doughnut-shaped masses, which moved along the rod in opposite directions. To make the device produce thrust, the two masses were placed in the middle of the rod, with a (compressed) coiled spring between them. When released, the spring propelled the masses toward the ends of the rod (one forward and one backward), where they would strike the discs and be brought to a stop. A second spring was mounted along the rod adjacent to the disc at the forward end of the device. It absorbed the energy of the mass that ran into it more efficiently than the "spring-less" disc at the other end of the rod absorbed the energy of the other mass simply smacking into it. This resulted in a net thrust in the direction of the forward end of the device.

My concept is similar but simpler. Imagine a spacecraft (similar to NASA's Dawn asteroid mission space probe) with a powerful electromagnet mounted at its rear end. Extending behind the electromagnet is a hollow tube a few feet long, closed at its far end. Inside the far end of this tube is a heavy solid cylinder of iron or steel, with a coiled spring mounted on its forward end (the end facing the electromagnet). This iron or steel cylinder is free to move within the tube.

To produce thrust the electromagnet is energized, pulling the metal cylinder rapidly up the tube toward it. When the cylinder strikes the end of the electromagnet, the cylinder's coiled spring is compressed, transmitting the energy of the impact to the electromagnet and thus to the spacecraft as a whole. The cylinder is prevented from rebounding away from the electromagnet either by means of a latching mechanism or by making the electromagnet powerful enough to simply hold the cylinder against the pressure of its compressed spring. Slowly, the spring is allowed to de-compress, leaving just enough impulse in it to cause the cylinder to drift gently back down to the far end of the tube. When the cylinder reaches the far end of the tube, the thrust cycle can begin again.

If desired, this electro-mechanical space drive could be built as a clustered system, in which several electromagnet/tube/cylinder/spring units could be operated in staggered fashion to produce a more uniform thrust instead of the pulsed thrust that a single unit would produce. The unit or units could also be used for spacecraft attitude control by affixing it/them to a gimbaled mount on the spacecraft (the same way that a gimbaled rocket engine is affixed to a satellite launch vehicle so that the engine can tilt its thrust vector to steer the vehicle). Also, smaller versions of these electro-mechanical thrusters could be mounted on a spacecraft in opposing pairs to provide translation (rotation) of the spacecraft about its pitch, roll, and yaw axes.

I hope this information will be useful.

I remember as a kid finding plans for making a small ion propulsion device as an experiment. It was supposed to give enough propulsion to make the device swing back and forth at the end of the wires it hung from. Of course it didn't work. ;) I believe part of it involved a high voltage coil from a car, you know, back when they still used points and condensors.

Your description sounds like the ion rocket experiment plan that was published in the "World Book" Encyclopedia in the 1950s. It was similar to Dr. Robert Goddard's glass-and-metal ion engines ("ion wind" engines) that he tested in the 1920s and/or the 1930s, but it used different materials than his. The "World Book" design used three clustered plastic tubes with a copper rod centered inside each tube. A copper ball was soldered to the forward end of each copper rod, and each rod was sharpened at its rear end (to more easily bleed off its charge there to ionize the surrounding air). Pressing the telegraph key allowed the Model-T spark coil to give the copper rods a strong negative charge, which ionized the air in the tubes and ejected the ionized air by electrostatic repulsion, producing thrust.

T. Townsend Brown's "thrusting capacitor" ion wind devices (often called "lifters" or "ionocraft" today) consist of two oppositely-charged grid screens held apart by dielectric supports (insulators). Ionized air molecules flowing from the top grid down to (and through) the bottom grid also entrain neutral air molecules to flow downward, which produces thrust. Brown believed that his devices also produced some kind of anti-gravity force that would allow them to produce thrust in a vacuum, but tests of his "lifters" in vacuum chambers showed that when all of the air was evacuated, their thrust output always dropped to zero.

That was it! You're right, it was a Model-T coil. I remember I got one from my grandpa along with his Morse Code key. He'd use that for practicing morse code. The coil would create a noise burst on the AM band whenever the key was pressed. I still have both, somewhere in my mess. The failed experiment was tossed.

Ion wind generator kits are now available from many sources (see: http://scientificsonline.com/product.asp_Q_pn_E_3082120 ). If memory serves, the ion rocket in the "World Book" Encyclopedia plan couldn't move very far under thrust (just a few millimeters each time the telegraph key was pressed). In the photograph, the rocket hung on its power supply wire in front of a large protractor that was drawn on a sheet of cardboard or poster board. The idea was to make the rocket swing higher and higher by applying thrust every time it swung back, which illustrated how even a low-thrust engine could accelerate a spacecraft to huge velocities in frictionless outer space if the low thrust was applied for long periods.

Those Model-T spark coils were also nice for making damped-wave ("spark gap") oscillators for spark gap AM morse code transmitters (now illegal because they emit radio noise all across the RF spectrum!).

They did one of the smaller versions on Mythbusters. Just used stiff wire and aluminum foil. It did produce enough lift to get the thing off the table (about an inch).

Since it doesn't do much, I thought it would make a nifty "blade-less" ceiling fan...

Indeed--those ion wind "lifters" share the same problem with their "siblings" (the ion thruster, hall effect thruster, arcjet thruster, and electrothermal thruster)--they can't produce enough thrust to lift themselves *and* their electrical power sources off the ground (these other electrical thrusters can't even lift themselves and are useful only in space). The ion wind "lifters" could propel lighter-than-air craft, but propellers would probably be more efficient for that application.

Blades are more efficient. Just seemed like a neet idea.

And, being 6' 2", I hit my head on those blades from time to time. Making it an even better idea...