University of Florida Introduction to Lasers
Laser Safety by Laser Professionals
Beam Propulsion Technologies
This page is to go over various beam propulsion technologies, such as the recently controversial microwave thruster featured on EMDrive.com We’ll start with a history of beam propulsion research, by both military and private corporations. Then talk a bit about where that technology is at today and where it may be going tomorrow.
In his Book “Secrets of Antigravity Propulsion” Dr. Paul LaViolette discusses Project SkyVault which was started at Rocketdyne (Present Day North American Rockwell) Laboratories as early as the 1940’s when it was discovered that microwave beams could move objects if the object happened to be made out of the right kind of material. The effect was extremely frequency sensitive and the effect would only occur within the certain bands which were specific to each type of material.
However, If the frequency was slightly off the object could suddenly vaporize! The researchers discovered this was due to the strong electromagnetic resonance that metamaterials have at a specific frequency. Such materials respond to incident microwaves in an unusual way. Take as an example a material that exhibits a resonant response to the electric component of an electromagnetic wave. Over most frequencies the material’s permittivity will have a positive value and as a result the applied electric field will induce a polarization in the same direction of it’s own field vector. Near a resonant frequency however, the induced polarization will become very large, the metamaterial’s large response being due to its accumulation of energy from the microwave beam over many wave cycles. The energy stored in the resonating medium can then greatly exceed that delivered by the incident-driving field. It can be so large that even changing the phase or sign of the incident wave would have little effect on the polarization oscillation.
As a result, when the frequency of the incident wave is increased slightly above this resonant frequency, the applied electric field will be out of phase with respect to the induced polarization oscillation, and as a result, the material will respond by exhibiting a negative permittivity, the induced polarization now being out of phase with the applied electric field, and as a result, the electromagnetic wave will exert a repulsive force on the material.
Physicists John Pendry and David Smtih illustrate this repulsive force in an article from Scientific American where they wrote: “Think of a swing: apply a slow, steady push, and the swing obediently moves in the direction of the push-although it does not swing very high. Once set in motion, the swing tends to oscillate back and forth at a particular rate, known technically as its resonant frequency. Push the swing periodically, in time with this swinging and it starts arcing higher. Now try to push at a faster rate, and the push goes out of phase with respect to the motion of the swing- at some point, your arms might be outstretched with the swing rushing back. If you have been pushing for a while the swing might have enough momentum to knock you over-It is then pushing back on you.” In the same way, electrons in a material with a negative permittivity, go out of phase and resist the “push” of the electromagnetic field. Such materials include silver, gold, and aluminum, whose resonances usually occur at optical frequencies.
The same repulsive force occurs in materials that resonate with the MAGNETIC components of an incoming electromagnetic wave as well. The Magnetic Permeability u, becomes negative at frequencies slightly above the material’s resonant frequency. The material’s response then is to magnetically resist the magnetic component of the applied ElectroMagnetic Wave. Materials that naturally exhibit negative u domains include ferromagnetic or anti-ferromagnetic materials that exhibit resonances. Such resonances usually occur in frequencies in the gigahertz range and tail off at higher frequencies approaching infra-red.
The original Project SkyVault set up used cavity magnetron vacuum tubes to generate the microwave source beam, which operated on frequencies ranging from 7 to upwards of 1,000 gigahertz. By comparison the magnetron tubes used in microwave ovens are 2.54 gigahertz . The original set-up used a metamaterial target made of Barium Titanate placed in line with the source beam. Further experiments discovered that using sawtooth wave patterns were ideal for maximizing the effect, so specially shaped cavity magnetrons were designed that would generate more perfect sawtooth waves. It was also discovered that waveforms exhibiting a sharper rise and more gradual fall would produce an attractive force, while waveforms exhibiting a gradual rise and a sharp fall would exhibit a repulsive force. To understand the reason for this we must go back to the swing analogy and think about the timing and mechanics for how you would generate the largest reaction force from the oscillating swing and then apply that concept to the resonating atoms inside the metamaterial.
Eventually various experiments were performed using a test craft made of Barium Titanate mounted on a rig resting above a microwave emitting source beam. The beam being supplied a more efficient diode based emitter rather than a cavity magnetron. The craft was then made to ride on the microwave beam, which could actually supply enough force to overcome gravity and achieve lift. However, they could only get the craft to go about 100 feet high or so because the instabilities such as wind would blow it out of alignment with the source beam causing it to fall back to earth.
Another interesting point brought up by Dr. LaViollete in his book “Secrets of Antigravity Propulsion”, which I believe should be further investigated, is why the original TV Series for Mr. and Mrs. Smith, a show about two top secret Government agents who are married to one another, each without the other one’s knowledge, was cancelled seemingly for no reason after they aired an episode featuring a top secret microwave beam project taking place in the Arizona desert. It seems the experiments in the plot of the episode drew a striking resemblance to actual experiments that had taken place at top secret test facilities. But it’s not like we didn’t already know the media was controlled or anything. It’s just funny when their direct efforts of censorship backfire against them by directly showing us what they censor and leaving us to ask why. They may control TV but the world wide web is in the hands of the people and we have the best hackers on our side.
so it was back to the drawing board. A unidirectional remote source propulsion beam has a limited range of applications. They needed a self contained system, something on board the craft. The invention of the Gunn Diode helped immensely to cut down the weight of the beam emIssion technology, and it was fairly easy to find a range of microwave frequencies that would bounce nicely off of the Earth’s surface, however there was the puzzle of how to get this system to actually produce thrust. Finally someone figured out that if you added the waves using phase conjugation, by splitting the source beam sending half to the ground and the other half through a metamaterial. While inside the metamaterial the second beam, known as the “pump beam” travels faster than the speed of light due to the structural and electromagnetic properties of the metamaterial. It bounces around inside the metamaterial before being sent to the ground to bounce off the same atom that the original source beam just bounced off of, only it does this slightly out of phase in order to exert a force on the ground in a similar manner to the swing analogy mention before.
The first beam travels back to the metamaterial along the same path as the second beam only in the opposite direction, the same goes for the second beam which travels back along the track of the first beam, back into the emitter to be merged with the returning beam 1 which just passed back through the metamaterial to converge in phase with the second beam on return.
Now what happens here is that while inside the metamaterial the beam travels a further distance in a shorter amount of time, it also bounces off the walls and transfers a portion of its momentum back into the craft. This provides a net force on the craft equal and opposite the net force applied to the earth. Then hopefully with a little luck and a really smart engineer, we can figure out how big we need to make it to get that force to be larger than the force of gravity… But in order to build a craft we would need omnidirectional thrust, which means there needs to be three of these Microwave Phase Conjugators and they needed to be vectorable as well. The craft would also need to be extremely light weight, because microwave beam propulsion cannot generate sufficient force to lift a heavy craft. Nevertheless it is still a viable option for antigravity propulsion, even if used as a backup system to provide additional maneuverability to a craft. It is also useful for moving satellites from Low Earth Orbit to Geostationary Orbit without having to carry all that extra rocket fuel. This was the reason a small UK company called, Satellite Propulsion Research Ltd was able to get funding to build the prototype EMDrive in the first place. Their technology is very similar to the microwave phase conjugator’s only they use semiconductor materials which retard the speed of light, rather than propagate it faster like the metamaterial.
Unfortunately this is all YouTube lets me have time for, so I hope we’ve come full circle with this and answered a lot of questions people had about how the EM Drive works, whether it was real or not, and what other beam propulsion technologies might exist that they’re not telling us about. I will be posting more of the theory and the math on my website. For those of you who haven’t checked out the EMDrive site, please do so. They have a short page and a pdf on the theory behind their model.. For everyone else, just keep learning everything you can about physics and know that a future, where these craft will be as common as automobiles, is not far away.
Direct Energy Weapons (DEWs)
One major problem with laser weapons (and directed-energy weapons in general) is their high electric energy requirements. Existing methods of storing, conducting, transforming, and directing energy are inadequate to produce a convenient hand-held weapon. Existing lasers waste much energy as heat, requiring still-bulky cooling equipment to avoid overheating damage. Air cooling could yield an unacceptable delay between shots. These problems, which severely limit laser weapon practicality at present, might be offset by:
1. Cheap high-temperature superconductors to make the weapon more efficient.
2. More convenient high volume electricity storage/generation. Part of the energy could be used to cool the device.
Chemical lasers use energy from a suitable chemical reaction instead. Chemical oxygen iodine laser (hydrogen peroxide with iodine) and deuterium fluoride laser (atomic fluorine reacting with deuterium) are two laser types capable of megawatt-range continuous beam output. Managing chemical fuel presents other problems, so the problems of cooling and overall inefficiency remain. This problem could also be lessened if the weapon were mounted either at a defensive position near a power plant, or on board a large, possibly nuclear powered, water-going ship. A ship would have the advantage of water for cooling.
The new weapon was the result of a 1977 development by George Chapline, Jr. of Lawrence Livermore’s “O-Group”. Livermore had been working on x-ray lasers for some time, but Chapline found a new solution that used the massive release of x-rays from a nuclear warhead as the source of light for a small baseball-bat sized lasing crystal in the form of a metal rod. The concept was first tried out in 1978s underground nuclear test “Diablo Hawk” but had failed. Peter Hagelstein, new to O Group, set about creating computer simulations of the system in order to understand why. At first he demonstrated that Chapline’s original calculations were simply wrong and the Diablo Hawk system could not possibly work. But as he continued his efforts, he found, to his dismay, that using heavier metals appeared to make a machine that would work. Through 1979 a new test was planned to take advantage of his work. The follow-up test in November 1980s “Dauphin” appeared to be a success, and plans were made for a major series of experiments in the early 1980s under “Excalibur”.
Since the lasing medium was fairly small, a single bomb could host a number of them and attack multiple ICBMs in a single burst. The Soviet ICBM fleet had tens of thousands of warheads, but only about 1,400 missiles. If each satellite had two dozen lasers, two dozen satellites on-station would significantly blunt any attack. In Molniya orbits, where the satellites would spend much of their time over the USSR, only a few dozen satellites would be needed, in total. An article in Aviation Week and Space Technology described how the devices “… are so small that a single payload bay on the space shuttle could carry to orbit a number sufficient to stop a Soviet nuclear weapons attack”. Some time later Teller used similar language in a letter to Paul Nitze, who was preparing a new round of strategic limitations talks, stating that “A single x-ray laser module the size of an executive desk… could potentially shoot down the entire Soviet land-based missile force…”
Livermore is just one of several major US weapons labs. Other labs had been working on ideas of their own, from new space or ground-based missiles, to chemical lasers, to particle beam weapons. Angelo Codevilla argued for similar funding for powerful chemical lasers as well. None of these efforts were taken very seriously by members of the Carter administration. In a meeting with Teller and Lowell Wood, a critic noted that the Soviets could easily defeat the system by attacking the satellite, whose only defense was to destroy itself. They also pointed out that the US public would be unlikely to accept nuclear bombs in space, regardless of the potential benefits. At the time Teller was stymied by these arguments; the concept was later adapted to be popped-up from submarines based off the Russian coast.
Star Wars Defense Program and DEW Capabilities
Image Credit: http://www.globalsecurity.org/space/systems/images/sdi-image02.jpg
(From Wikipedia article on SDI) – Here is a list of technologies that were developed by the Star Wars SDI Program, and some comments on their capabilities.