Space


Charged Particle Beam [CPB]

Particle beam weapons differ from other instruments of war that carry destructive energy to the target in the form of explosive warheads in ponderous containers such as artillery shells or missile casings. Particle beam weapons, of which electron beams are just one possibility, increase the kinetic energy of a large number of individual atomic or subatomic particles and then direct them collectively against a target. Every particle in the beam that strikes the target will transfer a fraction of its kinetic energy to the target material. If enough particles hit the target in a short time, the deposited energy would be sufficient to burn a hole in the skin of the device, detonate the chemical explosives or disrupt the electronics inside including software. The most significant advantage of high-energy particle beam weapons over missiles is that, like lasers, they propagate at essentially the speed of light.

Early US efforts included a project called Seesaw, funded by the Advanced Research Projects Agency of the Department of Defense, to develop a Navy beam weapon. The project was discontinued because of insurmountable problems in physics. Some research continued, but the emphasis was on lasers rather than particle beam weapons. During the past few years, beam weapon research has been resumed by the Armed Services and is now being coordinated by the Department of Defense as a nationally directed program.

The Navy's Chair Heritage program was initiated in 1974 to develop a charged particle beam weapon for aircraft carriers and cruisers to defend against antiship cruise missiles. Because its particle accelerator is the best mechanism for testing beam propagation, the Chair Heritage program was given a higher priority than other beam weapon programs. The weapons would be located below deck, and the beams would be magnetically routed to small firing turrets located at strategic points on the hull and deck. The system would be capable of firing six shots per second and engaging targets at ranges out to 4.5 kilometers. Deployment of this system depends on beam propagation. Lethality tests in 1981 used two particle accelerators developed at the Lawrence Livermore Laboratories in California.

An Army beam ground-based, charged particle beam system was being funded at less than $10 million by 1980. It was based on an autoresonant particle accelerator being developed under contract from the Army Ballistic Missile Defense Command. The accelerator is a proof-of-principle device and is not intended for direct weapon application. The design has the potential of generating single pulses with 1 to 10 megajoules of beam energy.

The United States conducted beam weapon research for several years, but until the late 1970s it was a low priority effort. With the seeming risk of a Soviet technological breakthrough, the US program picked up momentum and direction. Parmentola and Tsipis presented a landmark paper on this subject in Scientific American in 1979 (J. Parmentola and K. Tsipis, "Particle-Beam Weapons," Scientific American, 240:54-65, 1979). The authors presented scientific reasons why such weapons would be highly useful, but also dramatized the fundamental reasons why these weapons could never work.

The authors presented many small but practical problems of particle-beam weapons such as how to generate sufficient power in space, how to deal with countermeasures, and how to find targets among decoys. They also discussed two problems that they considered unsolvable. That is, the smaller problems may be considered very difficult scientific and engineering problems that may challenge practical implementation.

However, even if all those could be dealt with, two significant problems remained that were unsolvable due to fundamental physical limitations that no amount of Herculean engineering could resolve. These fundamental problems are (1) that Coulomb repulsion of a particle beam spreads the energy over a large area at reasonable distances to targets, and (2) that the near-earth magnetic field deflects the beam and is somewhat variable. (The beam is steered electrically by magnetic fields or electric fields. Mechanical steering would not be fast enough.)

A practical electron beam weapon would need to hit a target that is 1,000 km away with a 1000 amp beam having an energy of 1 GeV for 0.1 msec. Furthermore, the beam needs to be 1 cm or so in diameter at the target in order for the deposited energy to be sufficiently intense. Parmentola and Tsipis indicate that a 1 GeV electron beam of 1000 amps would spread from an initial 1 cm diameter to a 5 meter diameter at 1,000 km due to Coulomb repulsion. They also indicate that a 1 GeV beam would be deflected by 1,000 km over a distance of 1,000 km due to the earth's magnetic field. It is well known that the earth's magnetic field is also not completely steady. Under such unstable conditions, it would be close to impossible to make a workable weapon that could reliably hit a target 1000 km away with enough energy to destroy it. Also, there are only 400 or so seconds to distinguish between multiple targets and decoys in the initial phase of a ballistic missile's trajectory and then destroy the targets. There is more time, however, near the apogee section of travel in which to detect and destroy the missile compared to its ascent and reentry phases.

SDIO spent $46 million to develop a ground-based charged particle beam before it canceled that program in fiscal year 1992. The charged particle beam program, also known as projects DELPHI and MINERVA, sought to develop a ground-based device to be launched upon an attack warning to engage targets at a range of 80 to 4500k ilometers. The mission was to interactively discriminate between reentry vehicles and decoys and then destroy the reentry vehicles. When the funding available for particle beam work (both charged and neutral) declined in fiscal year 1992, SDIO decided to cancel the charged particle beam work because the technical risk for the charged particle beam was greater than for the neutral particle beam.




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