Posted on Saturday, 22 January, 2011 | 5 comments
Columnist: William B Stoecker
Getting into space is an incredibly difficult, expensive, and (for manned flights) dangerous operation. We are at the bottom of a deep gravity “well,” and merely getting into low Earth orbit requires accelerating a payload to a height of over one hundred miles and a speed of about 18,000 miles per hour. To escape Earth altogether we must exceed escape velocity, over 25,000 miles per hour. Up until now this has been accomplished by a particular type of reaction engine known as the chemical rocket. A reaction engine accelerates by propelling a reaction mass to the rear, and, literally, pushing off against that mass. A chemical rocket does this by burning chemical fuels like liquid oxygen and kerosene, or, for higher efficiency, liquid oxygen and liquid hydrogen. But even such powerful fuels as these have limited energy, and the rocket must burn fuel to lift the remaining fuel as well as the tanks, engine, pumps, etc., and fuel to lift fuel to lift fuel. The remaining payload is, proportionately, quite small. One way to overcome the difficulties is to resort to staging by piggybacking smaller rockets on top of larger ones, but, since it is next to impossible to recover the lower stages without their being destroyed or hopelessly damaged when they fall back to Earth, this, too, is a complex and difficult procedure. The Space Shuttle was supposed to overcome these difficulties by being reusable, but it is only partly reusable, and, absurdly, more expensive than the more conventional designs it replaced.
There are many ways to overcome at least some of these difficulties. Once low Earth orbit is achieved, an ion rocket could accelerate far beyond escape velocity by using solar or nuclear power to produce electricity to accelerate ions, or charged particles, to the rear at an incredibly high velocity but with a low thrust. Over days or weeks such a rocket could reach very high velocities. Or a light sail could be deployed, and use the pressure of sunlight and the solar wind (charged particles streaming out from the Sun) to do much the same thing, accelerating slowly but ultimately reaching sufficient velocity. It is even possible to deploy long tethers and use a photovoltaic array to produce electricity from sunlight and use that electricity to turn the tethers into electromagnets that would react with the Earth’s or the Sun’s magnetic field to slowly accelerate the spacecraft.
But getting into Earth orbit is still a chore. Since the spacecraft, before reaching the near vacuum of space, must accelerate up through Earth’s atmosphere and overcome its resistance, it makes sense to use that atmosphere for part of the thrust. A rocket, operating in airless space, must carry both its fuel and its oxygen, but, for the first part of the journey, a scramjet (supersonic combustion ramjet) could use atmospheric oxygen to begin the journey. Or a reusable turbojet might carry a rocket into the upper atmosphere, rather like our early space planes, which were carried aloft by conventional aircraft. And, incredibly, if strong enough materials can be developed, it is at least theoretically possible to build a “space elevator.” If you spin around while holding a weight on a rope, it will be pulled outward by “centrifugal force,” which, technically, is not a force but angular momentum. As the Earth turns on its axis every twenty four hours, a cable, perhaps made of carbon in its “Bucky tube” form (named after Buckminster Fuller) could extend to a weight placed well over 22,000 miles above the Earth, and angular momentum would hold it up. Needless to say, the difficulty, not to mention the expense, of fabricating and erecting such a structure is daunting, and there is the little detail of figuring out how to travel up and down it with reasonable speed.
At least as far back as the nineteenth century people speculated about gravity control, or antigravity. Might it be possible to create a field that would push against the Earth’s gravity just as like magnetic poles push against one another? Or could some kind of shield be produced that would free the spacecraft from the pull of our planet’s gravity? Since magnetic and electric fields, like gravity, produce an invisible force at a distance, and, in addition (and unlike gravity) can repel one another (like poles or charges) as well as attract (unlike poles or charges), it was only natural for inventors, guided perhaps more by intuition than logic, to attempt to use electromagnetism to overcome gravity. Thomas Townsend Brown, from the nineteen twenties through the nineteen fifties, experimented with “electrogravitics.” He discovered that a high voltage capacitor (two metal plates, one with a positive charge and one with a negative charge, separated by a dielectric, or insulator) seemed to generate a thrust toward the positive plate, and that certain shapes enhanced this effect. His devices actually levitated; I have myself witnessed this and examined the device. Critics say that the effect is merely a rocket effect caused by an ion wind, a movement of charged particles of the oxygen and nitrogen in the air, making the thruster merely another kind of reaction engine. Paul LaViolette and other enthusiasts claim that electrogravitic devices have been tested in vacuum chambers and actually worked better than ever, ruling out any possibility of an ion wind effect. Skeptics, like the people on the Myth Busters television show, claim that the device will produce little or no thrust in a vacuum, and have conducted their own tests. One Evgeny Podkletnov claims to have produced a slight reduction in the weight of objects placed over a spinning superconductor in a magnetic field; skeptics claim to have tested this and found no such effect. And there is nothing in modern physics, nothing in relativity theory or quantum mechanics, that seems to allow for any kind of gravity control.
But there is yet another exotic propulsion concept, not to be confused with gravity control, and that is the reactionless space drive. A reactionless space drive, if one could be made to work, would enable a spacecraft to dispense with the huge tanks of heavy and potentially explosive fuel. A relatively small engine and an energy source, perhaps solar power or beamed microwave power, is all that would be required. The problem is that the law of conservation of momentum, a well established, tried, tested, and proven law, does not permit this. In every case observed, a momentum in one direction is always balanced by an equal momentum (mass x velocity) in the opposite direction…which is why rocket engines work. Still, inventors have persisted, suspecting that there might be certain exceptions to this law, a kind of loophole. Various devices have been proposed and some of them even built; many of these attempt to produce an unbalanced centrifugal “force,” which, as we have seen, is not technically a force at all. So far as is known (and unlike gravity control) no one has demonstrated such a device that could actually lift itself straight up, and skeptics claim that the devices which have been able to move horizontally, or to appear to lose weight because of a thrust directed straight up were not really functioning as claimed. They have correctly pointed out that if a device produces a short but powerful force in one direction and a weaker one of longer duration in the opposite direction, the momentum may balance out, but the weaker force cannot overcome the friction of a machine rolling on wheels or sliding on even a smooth surface. So the device may move horizontally but prove nothing. For devices whose upward thrust seems to reduce their weight, skeptics claim that the effect is due to vibration and the harmonics of the scale used. Perhaps…but many of us are not so sure, and we continue to hope for that “loophole.”
One of the most famous purported space drives was the Dean Drive, named after its inventor, Norman L. Dean, who was able to secure a patent on it and another on a slightly modified version. The device was never able to levitate, but, placed on a scale, its weight would seemingly decrease when it was switched on. It was a fairly complicated machine, with spinning weights moving a larger component back and forth, and was powered by a small electric motor. Dean got his first patent in 1959, and John W. Campbell, a science fiction writer and the editor of Astounding Science Fiction magazine, became an enthusiastic supporter, writing at least one article about it, and proposing that a nuclear submarine be modified, equipped with Dean Drive propulsion units, and used as a spacecraft. Later, even Campbell admitted that this idea (a picture of the submarine in space was on the cover of the June, 1960 issue of his magazine) was a bit much. Even if the Dean Drive worked, and even if its thrust to weight ratio could be substantially improved, a submarine, with its heavy pressure hull and its reactor shielding, would be far too heavy to fly. An aerospace engineer named Jerry Pournelle who later became a successful science fiction author investigated the device for his company, but considered the demonstration to be inconclusive. The secretive Dean would not allow him to examine the inner workings of the device (even though the plans are in the patent, which is freely available) without a large cash advance. Understandably, Pournelle and his bosses were unwilling to shell out cash to someone claiming to have violated a law of physics. Yet they were open minded enough to investigate the matter and Pournelle travelled at company expense to visit Dean and see the device.
As a result of Dean’s obsession with secrecy, Pournelle became rather skeptical, and Dean never was able to sell the rights to any company, nor to make a machine that would actually levitate. The device is basically an oscillation thruster; such machines use rotating or linearly vibrating masses. One Steve Hampton claims to have built and tested a space drive inspired by Dean’s device, but simpler and basically different, using spinning weights and varying the axis length, causing them to move in an elliptical “orbit” and generate more centrifugal “force” in one direction than in the other. I once had a similar idea myself, but I suspect that as the weight moves outward from the center, its acceleration will produce a force to the rear, and that, some 180 degrees around, when it is pulled back toward the center its deceleration will do the same, and these forces will balance out the thrust, resulting in zero propulsive force.
One of the other inventors who have tried to create a space drive is David E. Coulishaw, with his Gyroscopic Inertial Thruster, or GIT. More recently, Roger Shawyer invented the “Em Drive,” which uses a conventional magnetron to produce microwaves within a closed “resonator cavity,” which tapers at one end. He claims that relativistic effects unbalance the radiation pressure inside (microwaves, like visible light, exert a weak force), producing a net thrust. Supposedly, the Chinese have shown interest, but most physicists who have examined the concept are skeptical. According to physicist Paul La Violette in 1990 NASA, via the Rand Corporation, invited inventors to submit innovative ideas for advanced propulsion systems, but then ignored Fred Nehen’s “gyro propulsion” and Roger Fritz’s “inertial engine,” and several other reactionless space drive concepts. La Violette, who is a proponent of an unconventional grand unified theory of physics, thinks such a drive might actually be possible.
I considered using energy transformations to create a thrust. If a weight (say, a permanent magnet) was accelerated to the rear of a tube or a set of rails by, say an electromagnet turned on long enough to repel it, and much of its kinetic energy was converted into another form, its net rearward momentum, plus the rearward momentum imparted to the engine during the process of energy conversion might be less than the forward momentum imparted to the electromagnet in front. Think of it as a rocket engine (the electromagnet) that recaptures and reuses its reaction mass (the permanent magnet) over and over, needing only an energy source. The conversion might be into electricity via a closed circuit coil surrounding the tube, turning it into a generator and recycling part of the waste energy. The permanent magnet would then be returned to the front by bouncing off a spring (or another, fixed permanent magnet) to be “fired” again. If even a little more than a specific amount of energy was converted, with the amount depending on the ratio of the mass of the moving permanent magnet to the mass of the entire spacecraft, there would be a net momentum gain in a forward direction. If a little less than this amount was converted, there would be a net momentum to the rear. In other words, for momentum to balance, in order not to violate the law of conservation of momentum, the amount of energy converted would have to be exactly right. So maybe at least a weak net thrust could be produced, but I’m not terribly optimistic.
But I have one more trick up my sleeve…a reactionless space drive with no moving parts. And it might actually work. Imagine two electromagnets facing one another, like pole to like pole, a “front” magnet and a “rear” magnet. We will have to dispense with any iron core (which greatly increases field strength) because they must be switched on and off with incredible speed, and an iron core cannot degauss fast enough. Obviously, if both are switched off, there are no magnetic fields and no forces in any direction. If both are switched on at the same time they will repel one another with equal force, and the spaceship will go nowhere. But suppose that they are switched on at different times. Suppose that they are about ten centimeters apart and the rear electromagnet switches on for one three billionths of a second, then turns off. At that point the front one switches on. The magnetic field of the rear electromagnet travels outward in all directions at light speed as a kind of magnetic wave, with the front end of the wave reaching the front magnet in one three billionths of a second. The front one stays on until most or all of the wave has passed it, then it switches off. After the magnetic wave generated by the front magnet has passed the rear one, the rear one switches on again. The front magnet will be repelled forward by the opposing field, but the rear one will not be repelled to the rear because it is not on, not generating a field, when the wave from the front one reaches it. This process is repeated over and over.
I can find no flaw in my reasoning, save for the fact that the device would seemingly have to violate the law of conservation of momentum. Perhaps we could think of it as a kind of rocket, propelled forward by a magnetic wave that goes rearward. Or perhaps, if the device could actually be made to work, the laws of physics may have to be revised just a bit.Article Copyright© William B Stoecker - reproduced with permission.