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How to build railguns and coilguns, continued...
 
  Star Wars

The evening of March 23, 1983, President Ronald Reagan addressed the nation: "Let me share with you a vision of the future. I call upon the scientific community in our country, who gave us nuclear weapons… to give us the means of rendering these nuclear weapons impotent and obsolete."

By now Fair and his team were managers at DARPA’s Tactical Technology Office. They were all for Reagan’s Star Wars, and had opinions about how to do it. They had long argued that kinetic energy weapons would be better than laser weapons. The infrared lasers touted by Lockheed for shooting up ICBMs needed four meter diameter mirrors to make even a head fake at frying nuclear warheads. A fellow from Perkin Elmer told an audience of U.S. Senators that his employer could turn out these mirrors by the hundreds and get them into orbit before 1990, just sign the check.

This was before Perkin Elmer delivered an out of focus Hubble space telescope, which had a much smaller mirror, and went out of business.

Free electron laser advocates said their weapon could deliver ultraviolet wavelengths, which meant smaller, cheaper optics. Never mind that they had not yet produced anything more than “chirps” of infrared.

At Lawrence Livermore Laboratory, Lowell Wood and Rod Hyde were working on a nuclear pumped X-ray laser. News stories claimed that they could focus so much energy so tightly that just one shuttle launch could put enough of their lasers into orbit to take out the entire Soviet ICBM arsenal. It was hard for anyone to argue with their analysis because it was all classified.

During the summer of 1983, the Pentagon conducted a study of options for missile defense. Fair told them that ground-based EM guns might be able to kill ICBMs during midcourse flight or reentry. That fall the Pentagon formed the Strategic Defense Initiative Office (SDIO) and asked Fair to join them and manage an EML program. It was quite a temptation. He could control more funds, but in a risky new environment. If he were to stay at DARPA, he would lose control of much of the upcoming research. He chose to stay behind.

That’s how the SDIO EM gun program ended up under the Army’s Roger X. Lenard. Early on in his program, the Air Force ran a paper study of EM guns to launch of space assets for missile defense. The challenges appeared too great, so Lenard funded experiments focused upon kinetic weapons. This in itself was reasonable, but he funded hardware demonstrations to the detriment of test and analysis. Fabulous results soon materialized. Rail gun teams at Westinghouse and Vought each reported projectile velocities of 5.9 km/s. Then a railgun at Lawrence Livermore beat them all at 10 km/s, fast enough for an intercontinental gun or to launch payloads into space.

DARPA analysts wondered. How did they measure velocity? Lenard and the contractors hemmed and hawed and it turned out that they had taken the equation for kinetic energy, used the electrical energy that powered these guns as input, solved for v with a fudge factor or two, and let’s get on with phase III! Later, when projectile velocities were actually measured, none of these guns looked so great. Some of the energy went into muzzle flash; more was dissipated by the plasmas caused by current arcing. The plasmas, in turn, corroded everything they brushed. Kinetic energy from the projectile went into gouging the rails, and the same Lorenz force that propelled the armature also warped the rails. All this destructive wasted energy also meant the researchers kept on having to rebuild their guns.

Researchers made better progress on guided projectiles that could be fired from an EM gun, or, for that matter, any gun or fast burn rocket: the D-2 (endoatmospheric) and LEAP (Lightweight ExoAtmosperic Projectile).  Back then, researchers were just discovering one of the benefits of integrated circuits: they take kilogees just fine.

High Temperature Superconductors Discovered

The discovery in 1986 of high temperature superconductors briefly reenergized the EM gun community. In 1987 the Army conducted a study of the potential of the newly discovered high temperature superconductors for EM space launch. However, this new technology remained too immature to move beyond paper studies.

By 1988, SDIO analysts had discredited laser weapons. Even the X-ray laser turned out to be vaporware – literally. Sensors from two nuclear explosion tests that had suggested X-ray lasing had been vaporized an instant after sending data. Despite loss of the sensors, later analyses showed that it all had been instrumentation error.

Invention as a hostile act --->>

The remaining contender for SDIO was what its public relations people called “smart rocks”: systems based upon the D-2 and/or LEAP. And then, in came Wood and Hyde, yes, the leaders of Livermore’s X-ray laser project. Why work on smart rocks when SDIO could fund their Brilliant Pebbles? The idea was to orbit thousands of tiny rockets packed with integrated electronics. Then if any of their Brilliant Eyes (another Livermore project) saw something that wasn’t cleared for space travel, the nearest Brilliant Pebble would wipe it out. They promised their system would never shoot anything by accident.

Feb. 9, 1989, SDIO head Gen. James Abrahamson reported that Brilliant Pebbles could be ready in 5 years and would cost less than $25 billion. And that was the end of the D-2 and LEAP. On the plus side for EML, Brilliant Pebbles funded three studies of gun launch to space.

John Hunter at Lawrence Livermore evaluated light gas guns. These use an explosive charge to work a piston which compresses a light gas such as hydrogen, which has the highest speed of sound of any gas. Therefore, a light gas gun can accelerate a projectile to higher velocities than any gun that uses chemical reactions alone. Some light gas guns have been recorded at over 10 km/s. This is enough, even after losses from atmospheric drag, to require a rocket boost of less than 2 km/s at apogee to raise perigee (which otherwise would intersect the Earth) enough to achieve low Earth orbit. A problem with light gas guns, however, is that it is unclear how to scale them up to launch payloads of more than a few grams. Acceleration is another issue. A 10 km/s light gas gun typically fires Lexan projectiles because little else is able to survive the shock of the launch force.

Sandia National Laboratories studied coil guns for Brilliant Pebbles. These launchers should be able to spread acceleration over a long enough distance to accommodate any payload, up to and including human beings. Their disadvantages include instabilities in the bucket levitation system, control issues of feedback between the bucket and drive coils and timing of the switching of the drive coils.

The Air Force Armament Laboratory studied rail guns. They were (and still are) the only EML technology that has achieved hypervelocity.

But none of this looked gfood enough to compete with Brilliant Pebbles. Thus, in 1989, SDIO shut down EML reserch.

Next: The Rocket Empire Strikes Back --->>


Op. Cit. Broad, Teller’s War, chapter seven, “A Final Crusade.”

"Hypervelocity Gun Report: Electromagnetic Coilgun," by R.J. Lipinski and M. Cowan, Sandia National Lab Report SAND91-1600, Albuquerque, NM, October, 1991. DTIC AD-B158943, May 31, 1991.

"Hypervelocity Gun Report: Light Gas Gun," by John Hunter, Lawrence Livermore National Lab Report, Livermore Ca, 1992. DTIC AD-B158944, May 31, 1991.

"Earth-to-Orbit Hypervelocity Railgun Launcher for Deploying the Brilliant Pebbles System," 3 Vols., by P. Coutee, et al, Air Force Wright Labs Armament Division WL/MNSH, Eglin Air Force Base, Florida, 1992. DTIC AD-B158942, May 31, 1991.


"Electromagnetic Acceleration as an Alternative to Rockets for Rapid Launch of Large SDI Payloads"; U.S. Air Force Forecast 2000 white paper, July, 1985.

"Evaluation of the Utility of High Temperature Superconductors in Electromagnetic Accelerators for Earth to Space Launch," presented at an Army ARDEC Workshop on Superconductivity, Picatinny Arsenal, New Jersey; December 8, 1987.

For an in-depth dissection of the nuclear-pumped X-ray laser program, see Teller’s War, by William J. Broad (Simon & Schuster, 1992).

 

 
       © 2013 Carolyn Meinel