t is the most powerful railgun in the world, and it now lies in pieces in a New Jersey Army lab. Using bursts of electricity instead of gunpowder, it shoots plastic cubes so fast that they carry the wallop of a Mack truck traveling 60 miles an hour. Someday, its descendants might blast missiles and warheads from the sky as if they were shooting skeet. ``We're talking about something that's really quite revolutionary,'' says Dr. Ted Gora, chief of railgun research at the Army's weapon design facility here. Of the weapons the Pentagon is studying for use in ballistic-missile defense, lasers and other exotica have received the most public attention. But a ``star wars'' system, at least at first, would likely rely on railgun projectiles and warheads on fast rockets. They get their destructiveness from kinetic energy, the energy of motion.
This kinetic-energy firepower is in essence high-technology artillery. It could be based on Earth or on platforms in space. In theory, it could attack enemy missiles at every stage -- from the boost phase, when a missile is easiest to spot and all its warheads and decoys are in one neat package, to the terminal phase, when warheads are reentering the atmosphere. In practice, it might be difficult for projectiles to reach missiles during the all-crucial first few minutes of flight.
Some kinetic-energy weapons are technologically well developed. High-acceleration rockets, fired from the ground and intended to protect missile silos, are perhaps ready for deployment today.
Others are still experimental. Railguns and other electromagnetic launchers excite many weapons designers, but power supplies for these devices pose problems, and the projectiles they shoot move so fast they tend to rip up the inside of the barrel.
``All of our experiments have not been raging successes,'' concedes the Army's Ted Gora.
In Washington the Strategic Defense Initiative (SDI) is an abstraction, budget figures on a page. The program's nickname -- star wars -- emphasizes its futuristic aura. But to Dr. Gora and others working on its technology, it is as real as the metal and wire in their labs.
Dr. Gora has been working on railguns for seven years in a shed-like building of the Army's Armament Research and Development Center. The Army has not always been wild about the project, finding it hard to believe in something that had no trigger, didn't go boom, and shot plastic shells.
But Gora and cohorts -- among them physicist Harry Fair, and William Weldon, now at the University of Texas -- perservered. Now, with the coming of President Reagan's SDI program, railgun researchers are flush with money and respect. Enthusiasts say electric cannons could be the biggest jump in gun technology since the Chinese invented gunpowder in the ninth century.
This potential stems from the tremendous velocity reached by railgun projectiles. The destructive power of a bullet largely results from its mass and velocity: A small bullet traveling very fast can be the equal of a larger one that moves more slowly.
A bullet for an M-16 rifle travels just over 3,000 feet per second. In tests, the Army's New Jersey railgun has sent an 11-ounce plastic cubes winging along at 2.6 miles per second. Other labs have shot small, thimble-sized objects at greater velocities (more than 6 miles per second). But the Army's railgun has hurled the largest projectile at high velocities. SDI officials envision a railgun that would shoot yet larger objects to up to 12 miles per second.
The Army railgun, never before seen by reporters, does not look like something that might spawn a powerful space rifle. It looks instead like 12 feet of large drainpipe with a cement mixer on one end. Inside the gun's barrel stretch two parallel copper rails.
When the gun is fired, a powerful electric current surges up one rail, hits the projectile, leaps across it to the other rail, and surges back toward the gun's breech. Contained by its own magnetic field, the electric force explodes forward, pushing the projectile as it goes.
Such brute force may have applications more terrestrial than shooting down missiles. The Army is interested in high-speed railgun artillery, which might be able to blast apart tanks as if they were made of balsa wood.
Electromagnetic launchers are not a new idea. At the turn of the century electrical engineers theorized that such guns were possible. During World War II, German scientists toyed with the technology -- including using them to hurl cargo-laden gliders across battlefields. The Japanese tried to build an electric machine gun.
These efforts, say researchers, all foundered on the same problem: power. You could briefly light Buffalo, N.Y., with the pulse of electricity today's railgun experiments require. ``Power supplies right now are larger and heavier than we would like them to be,'' says Mr. Weldon, director of the University of Texas (UT) Center for Electromechanics.
But new advances hold hope that the problem of producing space-transportable, powerful generators can be solved, SDI officials say. For example, they point to a machine that Weldon perfected over the last decade. Called a compulsator, the device is capable of loosing huge surges of current in quick succession. This winter, UT researchers hope to fire a 10-shot burst with a compulsator-driven railgun. Last year, they successfully fired four projectiles in a row.
Such machine-gun capability is crucial if railguns are to become viable missile-defense weapons.
Projectiles are another railgun problem. Electromagnetic launchers would be firing at targets hundreds of miles away. At such distances, shells must have some sort of ability to guide themselves to be accurate. They must be, in an oft-quoted phrase, smart rocks.
But current guidance technology -- such as the heat-seeking sensors in air-to-air missiles -- would be turned into silicon junk by the acceleration forces that railgun shells experience.
Tough new metal alloys and other materials would be needed for missile-defense railguns as well. Currently, railguns can be so scarred after one shot that their interiors must be rebuilt.
If railguns are to be put in space, they must also be made a fraction of their current size. The Army's New Jersey railgun experiment, with its support equipment, takes up one-quarter of a room the size of a hangar. SDI officials ultimately envision a space-based weapon being something over 30 feet long and weighing around 40 tons.
``We need a jet aircraft to do the SDI job. We're at the propeller-plane stage now,'' says Gene McCall, a physicist at the Los Alamos National Laboratory in New Mexico.
While railguns and other electromagnetic launchers are still experiments, another type of kinetic-energy weapon is much more technologically mature: gazelle-quick rocket interceptors. The United States military now has a wide range of such rockets in its arsenal, from shoulder-fired, antiaircraft Stingers, to the Sidewinder, favored weapon of fighter pilots and the recently tested Air Force antisatellite missile.
This technology could be taken off the shelf, modified for higher performance, and used to attack ballistic missiles and warheads in space, according to one vision now gaining favor among SDI officials.
In this scenario, bundles of small rockets with explosive warheads would be mounted on satellites and sent into orbit. In times of political tension the satellite would be turned on alert and ordered to fire on ballistic missiles rising from the Soviet Union.
``The weapons could not kill people, because they would burn up before they got to the ground,'' claims Col. Malcolm O'Neill, head of SDI kinetic-energy weapon programs. ``But they could kill anything flying in space, including missiles, reentry vehicles, or satellites.''
This proposal for ``porcupine'' satellites mirrors a little-remembered 1960 Pentagon study named Project SPAD (Space Patrol Active Defense). SPAD recommended orbiting hundreds of small satellites, each studded with six small missiles, for defense against the burgeoning Soviet intercontinental ballistic missile (ICBM) force, according to John Bosma, editor of the newsletter Military Space. The technology of the times was not up to the task, however, and Pentagon interest passed to other forms of antimiss ile systems.
Small space rockets must be cheap to build and orbit, SDI officials say, since they are in essence ammunition that will be fired in quantity at Soviet missiles.
They must also be able to reach their targets. This will be particularly hard in the all-critical boost phase -- the 3- to 5- minute period between launch and the time when an ICBM's final booster stage burns out. Missiles are the most vulnerable during this phase: The engine exhaust is easy to spot and all the warheads are in one package.
If the Soviets adopted fast-burn boosters, which could take about 100 seconds to complete their work, the engines would burn out within the atmosphere. In either case, projectiles entering the atmosphere from the vacuum of space might break apart or generate enough heat to destroy their guidance systems.
Thus kinetic-energy weapons might not be quick enough to reach Soviet missile boosters before they burn out and release their warheads, a recent Congressional Office of Technology Assessment report points out.
Outside the atmosphere, rocket interceptors or railguns would have a relatively long time, 10 to 20 minutes, to reach targets. But these objects -- small, dark warheads coasting through cold, dark space -- would be extraordinarily difficult to find and track. SDI officials and critics alike rate this ``midcourse discrimination'' as one of the toughest technical problems the program faces.
The final option for kinetic-energy weapons would be to hit a warhead when it plunges back into the atmosphere and heads for its target. In this terminal phase, which lasts about a minute, kinetic weapons -- probably rockets -- would be based on the ground, and launched up to intercept intruders.
The US fielded such a defense in the 1970s. This system, which protected missile silos in North Dakota, was eventually scrapped as too costly and ineffective. The Soviet Union has a similar defensive screen in place around Moscow.
These early defense systems, however, used nuclear-tipped interceptors. What the Pentagon wants to do this time is use nonnuclear interceptor warheads.
``What makes the terminal engagement so difficult is that we are going to do it without a nuclear weapon,'' says Colonel O'Neill. ``My marching orders are that I have nothing nuclear.''
Without the brute force of a nuclear explosion, rocket interceptors will have to be incredibly accurate. They will either have to collide with a warhead or get close enough to take it out with an explosion of shrapnel.
Such accuracy has been demonstrated on a small scale. In a much-publicized experiment in June 1984, the Army used a rocket interceptor to catch a dummy warhead over the Pacific. Ground-based radar and the interceptor's sensors were used to zero in on the device. Then the interceptor unfurled a metal umbrella and destroyed the warhead in a grand collision.
In a nuclear war, however, there would likely be hundreds of warheads falling on the US that would have to be found and foiled. Exquisite radar and sensing systems will be needed -- systems that would also have to be resistant to blinding by nuclear explosions. Such blasts would result if an attacker sets warheads to explode when an interceptor comes too close.
Interceptor rockets, too, would have to be fast enough to stop warheads high in the atmosphere, so that if the warheads went off they wouldn't harm people on the ground. Colonel O`Neill says this will take ``incredibly hot rockets,'' perhaps capable of reaching their targets within 10 seconds.
It is clear that in the not-too-distant future kinetic-energy weapons will be capable of knocking down some targets during a nuclear attack. The question is: How expensive and effective would such a defense be?
A first-step missile defense deployed in this century, say SDI officials, would likely rely heavily on kinetic-energy weapons, with more exotic stuff such as lasers used for target tracking and communication. But to build a final shield highly effective against attack and all countermeasures, directed-energy weapons -- an even more difficult frontier -- are necessary.