by Ben Bova
I don’t consider myself a hawk. Or a dove. Maybe an owl. The owl is the mascot of my alma mater, Temple University. The owl is also sacred to Athena, the one goddess in all the world’s religions who is worth worshiping. Originally a warrior-cult goddess, Athena grew into the patroness of wisdom and civilization, of arts and industries, of cities and democracy.
The arguments over SDI have been largely political debates. Although many prominent scientists (some of them friends and former colleagues of mine) have publicly claimed that SDI is technically impossible, no one really knows if “Star Wars” will be possible or not; that is why a multiyear research program is needed.
“Space Weapons” examines the heart of the controversy. Can weapons aboard satellites destroy ballistic missiles reliably enough to defend the world against nuclear-missile attack?
I try to give both sides of the technical debate, and show what the political consequences might be. I don’t feel terribly hawkish—but I can’t seem to escape the nagging memory that a dove is really a species of pigeon.
When President Reagan gave his “Star Wars” speech, March 23, 1983, he proposed to “counter the awesome Soviet missile threat with measures that are defensive,” measures that would “intercept and destroy strategic ballistic missiles before they reach our own soil or that of our allies.”
Although the President gave no hint in his speech of what these defensive measures might be, aides later revealed to the news media that the basic concept hinges on placing weapons in orbital space.
Satellites in orbit a few hundred miles above the Earth’s surface can be in a position to destroy hydrogen-bomb-carrying ballistic missiles within a few minutes after they are launched. While they are still rising above the Earth’s atmosphere, and their boosting-rocket engines are still working, the missiles are very vulnerable. If they can be hit then, they can be destroyed relatively easily.
But a defensive shield in space could destabilize the balance of terror that has been the cornerstone of U.S. and Soviet relations for more than twenty years. The policy of mutual assured destruction (MAD) assumes that no defense against missile attack is possible: if one superpower launches a nuclear attack, the other can retaliate in kind. When Reagan proposed a defensive system that would “save lives rather than avenge them,” the typical Russian response was, “Why do you want to attack us?” Soviet leaders see any attempt by the United States to defend itself against nuclear attack as a preparation for American nuclear attack on the Soviet Union.
Thus the arguments over “Star Wars” include questions of politics, policy, and technology. Is it necessary to put weapons in space? Should the Congress appropriate tens or hundreds of billions of dollars to build space-based defenses? Is it wise to shift American strategic policy away from MAD, a policy that —whatever its risks—has kept the superpowers from nuclear war for more than twenty years?
Before these questions can be gainfully addressed, the technology question must be considered. Will space-based weapons work? Will they be able to stop a nuclear missile attack?
Among the weapons being considered for the space-based ABM (antiballistic missile) role are high-power lasers, particle beam devices, small missiles, and electrically powered “rail guns” that fire small metal darts at very high velocities. Lasers and particle beam devices are often referred to as directed energy weapons (DEW) or, more simply, beam weapons.
Of these four types of weapons, lasers are the most commonly discussed and may well be the first type actually tested in space. The laser has distinct advantages as a space weapon. It fires a beam of light—pure energy. Nothing in the universe moves faster than light’s velocity of 186,000 miles per second. By comparison, a missile flying at 15,000 to 20,000 miles per hour seems like a turtle. In the vacuum of space, the laser’s beam moves in a perfectly straight line, undeflected by gravity, electric or magnetic fields, wind or weather. Not only is the laser “the fastest gun” in the universe; it can be the most accurate as well.
Small missiles are already being tested by the Air Force as an antisatellite (ASAT) weapon. Carried under the wing of a high-altitude F-15 jet fighter, the ASAT missile rockets into space, where it can seek out a satellite and destroy it by direct impact. Similar missiles could be used in the ABM role, carried aboard satellite “trucks” in orbit until they are needed to intercept enemy missiles. Their technology is well understood and highly developed. But missiles cannot give the speed and range that a powerful laser would. Laser beams could cross thousands of miles in a fraction of a second. This means that fewer defensive satellites would be needed, because each laser-armed satellite would have a “reach” that extends far beyond the limited range of small missiles.
Particle beam weapons are somewhat like lasers; they fire streams of subatomic particles such as protons and electrons instead of a beam of light. The particle beam can move at the speed of light. It must be an electrically neutral beam: negatively charged electrons or positively charged protons by themselves would be deflected by the Earth’s magnetic field. While some analysts such as retired Air Force Major General George J. Keegan insist that the Soviet Union is pushing development of particle beam weapons, most Western scientists feel that such devices are not yet as fully developed as lasers.
Rail guns, which can accelerate dartlike fléchettes to velocities of better than 11,000 miles per hour in less than a second, are even less developed than particle beam devices.
Lasers have reached power levels where they can be used as weapons, although they may not yet be powerful enough to destroy missiles in space.
In 1983 the Air Force released news that a 400-kilowatt laser flown aboard its Airborne Laser Laboratory (a specially outfitted Boeing cargo jet) had successfully shot down five Sidewinder missiles fired at it by a jet fighter plane. The test took place high above the Navy Weapons Center testing grounds at China Lake, California. Sidewinders are the missiles that U.S. fighters use to destroy other planes: air-to-air missiles. Although the laser did not destroy the Sidewinders, it damaged their heat-seeking sensors so severely that the missiles could not find their target and crashed into the desert.
TRW Corporation has built a laser of 2.2 megawatts (2.2 million watts) output for the U.S. Navy. Although it is not intended to fly, this laser is approaching the power range of interest for orbital ABM weaponry. It is called MIRACL, a somewhat whimsical acronym for mid-infrared advanced chemical laser. Installed at the White Sands Missile Range in New Mexico, it is used by all three armed services to study the mechanisms by which laser energy damages target, materials such as the metals and plastics of which aircraft and missiles are constructed.
Damage mechanisms are an important consideration in deciding which devices may be tested in space and eventually deployed. Missiles and rail-gun fléchettes use the “kinetic kill” approach: like supersophisticated shotgun pellets, they simply smash into the oncoming missile or bomb-carrying warhead. The target’s own forward velocity of more than 15,000 miles per hour merely adds more kinetic energy to the shattering collision.
The basic kill mechanism of a laser beam is to heat the target’s surface so quickly and intensely that the material is vaporized. A laser that can focus many kilowatts or megawatts of pure energy per square centimeter on its target will cause damage similar to the kind that Buck Rogers’s “disintegrator” gun did in the comic strips of fifty years ago. The skin of a missile can be boiled away by the searing finger of a laser beam, which can punch a hole in the missile’s skin in a second or less. If the missile’s rocket engines are still burning, and its tanks still contain volatile rocket propellants, rupturing the tankage will blow the missile apart in a spectacular explosion.
However, the metal boiled up by the laser beam creates a cloud that tends to absorb incoming laser energy. To counter this, the beam might be pulsed many times per second, so that the cloud created by the first pulse of laser energy dissipates before the next pulse arrives. The pulses could be thousandths of a second in duration, o
r even shorter. Very high-energy pulses could also damage a missile or warhead by mechanical shock, literally shaking its innards apart. A very energetic pulse would blast a small crater in the target’s surface and send a shock wave penetrating into its interior. A train of sufficiently energetic pulses could rattle a missile or hydrogen-bomb warhead to pieces.
A particle beam could also deliver a massive jolt of energy to its target. It would not be absorbed by clouds of gas, as a laser beam would be. Nor would it be reflected by a shiny surface or absorbed by an ablative coating. It could penetrate the metal skin of a missile or even the “hardened” heat shield of a reentry warhead within microseconds. The beam could shock-heat the inner workings of a nuclear bomb, destroying its electronic controls or damaging the triggering mechanism so badly that the bomb will not detonate.
There are many different kinds of lasers, but the type that appears to be closest to actual testing in space is the chemical laser, so called because its energy is derived from the chemical reaction of two or more “fuels,” such as hydrogen and fluorine. Chemical lasers emit infrared energy, at wavelengths of light that are invisible to the human eye.
Edward Teller, “father of the H-bomb,” is urging the development of a laser that produces X rays. It is powered by the explosion of a small nuclear bomb; thus the X-ray laser has been called a “third-generation nuclear device” (the first two generations being the fission-based atomic bomb and the hydrogen fusion bomb). Since the end product of Teller’s third-generation bomb is a laser beam of X rays, the system is also called a “directed nuclear device.”
The technical community is also excited by the more recent development of excimer lasers, which can emit energy at ultraviolet wavelengths.
But the basic question remains: Will lasers, or any of the proposed space weapons, actually be able to defend against a full-scale strategic missile attack? Many scientists and strategists believe that it will be impossible to destroy thousands of missiles and their multiple warheads with orbiting weaponry. Dr. Robert Bowman, former director of advanced space programs for the Air Force, says that “every dollar spent on defense can be neutralized by five cents of offense.”
Perhaps the strongest voice speaking against the concept of space-based defense belongs to Kosta Tsipis, associate director of the MIT Physics Department’s Program in Science and Technology for International Security.
“We are witnessing a tragedy … a cruel hoax,” he told me, “a repetition of the pattern that saw the government spend two billion dollars on a nuclear-powered airplane in the 1950s.”
Tsipis is convinced that neither lasers nor particle beams can be made to work well enough to serve as ABM weapons. Writing in Scientific American’s April 1979 and December 1981 issues (and later including much the same material in his book Arsenal: Understanding Weapons in the Nuclear Age), Tsipis concluded that “it is difficult to see how the development and deployment of such fragile, complex and expensive weapons would improve the military capability of a nation.”
He says quite firmly that the “dream” of orbiting energy weapons capable of destroying ballistic missiles is simply “not physically possible … . There are no weapons applications for existing lasers,” and even if much better lasers are developed, “the operational difficulties” will make orbital ABM systems impractical.
“The President has no sense of the physical reality” of such devices, Tsipis feels. He believes that Reagan is “trying to stampede the country” into pushing ahead with such a program because “it is good for the California industries, and good for negotiations” with the Soviets.
In his writings, Tsipis concludes that a laser ABM weapon cannot put enough energy on a missile to destroy it, especially within the few seconds after launch when the missile’s rocket engines are still burning and it is most vulnerable. He believes that a laser-armed satellite would itself be so vulnerable to attack and so expensive that it would have no real military value. “We have concluded that lasers have little or no chance of succeeding as practical, costeffective defensive weapons.”
Tsipis shows that an orbiting laser must be pointed at its target with extraordinary accuracy: “ … for a laser weapon to destroy its target, the position of the target must be known to within a distance equal to the shortest dimension of the target [the width of the ICBM booster rocket], and the laser must be pointed with the same precision.”
He sets up a scenario in which fifty laser-armed ABM satellites face an attacking force of one thousand missiles, which they must destroy within eight minutes of launching. Under these conditions, only a single satellite would be in a position to engage the attacking force; the other forty-nine satellites would be orbiting over different areas of the globe, too far away to deal with the attacking missiles within the first eight minutes of their flight.
“Therefore,” Tsipis writes, “the [lone] satellite could devote only about half a second to each missile.” He estimates that a hundred-megawatt chemical laser would need a pointing mirror four meters wide (slightly more than thirteen feet) to put enough energy on a missile at one thousand kilometers’ range to destroy it within a second. “Making such a mirror sufficiently rugged and of the necessary optical quality, however,” he states, “is beyond the technical capabilities of the U.S. or any other nation.”
Moreover, Tsipis calculates that the chemical laser would need nearly 1,500 pounds of fuel for each missile destroyed, which means that each satellite must be supplied with roughly 750 tons of laser fuel because one cannot tell in advance which satellite might face the entire attacking missile fleet. Since the space shuttle carries about 30 tons of payload, each satellite would require twenty-five shuttle flights just to “fill ’er up.” The entire system of fifty satellites would require 1,250 shuttle missions merely to fuel the lasers. Even if shuttles were launched once a week to do nothing except carry fuel to the orbiting lasers, it would take more than twenty-four years to bring each of the fifty orbiting lasers to a condition of readiness.
Tsipis believes that even these conditions are “unrealistically optimistic,” since a hundred-megawatt chemical laser does not exist “and there is no indication that such a device could be developed in the foreseeable future.” Moreover, his calculations were based on a 100 percent efficiency for the laser, whereas in reality the best that might be expected is 30 to 40 percent efficiency. Thus the fuel requirements would balloon “by a factor of at least 10 and more likely 30.”
Finally, Tsipis points out that laser-armed satellites would be vulnerable to countermeasures. They could be attacked while under construction in orbit, their sensors could be blinded by the attacker just before the ICBMs are launched, or their communications links to command centers could be jammed.
Bowman, Tsipis, and others have shown that the attacking missiles could be protected from laser beams by shiny, reflective coatings on their surfaces, or by blowing a stream of laser-absorbing fluid along the missiles’ length. The reentry warheads are already coated with heat-absorbing ablative materials; the entire length of the missile could be “painted” with an ablative plastic. An even simpler countermeasure would be to increase the number of attacking missiles until the defensive system is overwhelmed.
Daniel Deudney, senior researcher at the Washington-based Worldwatch Institute, brought out another cautionary point in his 1983 testimony to the Senate Subcommittee on Arms Control:
“Large-scale space weapons would be an example of what I call a destruction entrusted automatic device [DEAD]. Space weapons could never be commanded and controlled by humans. A space laser, for example, would have about five minutes to detect, target and engage an ICBM in the boost phase. One Department of Defense analyst put it this way, ‘We would have to delegate the decision-making to the weapon system itself and we have had no experience in that type of operational system.’ To start a nuclear war in the MAD era would have required a major political misjudgment; with space weapons, a machine malfunction would be sufficient.”
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bsp; Tsipis and other scientists in the academic community complain about their lack of access to the President. “We don’t have a voice in the Oval Office,” he claims. “The White House has cut itself off almost completely from the academic community.” He maintains that President Reagan relies on industrial scientists, especially those employed by the major aerospace corporations, for his scientific advice.
One of those “industrial scientists” is Edward T. Gerry, a youthful physicist who headed the effort at Avco Everett Research Laboratory, in Massachusetts, in the mid-1960s that produced the breakthrough to high-power lasers. A descendant of the Massachusetts politician from whom the word “gerrymander” arose, Gerry went into government service in the 1970s to become chief of all laser programs for the Defense Department’s Advanced Research Projects Agency. Today he is president of W. J. Schafer Associates, a Washington-area research and development firm.
When I asked Gerry about the criticisms voiced by Tsipis and others, he said flatly, “Tsipis is wrong. The articles he’s written are misleading. He sets up ‘straw man’ arguments that are based on false assumptions.” He took Tsipis’s example of a hundred-megawatt laser and analyzed the situation this way:
Such a laser is powerful enough to put at least ten to one hundred kilowatts per square centimeter of laser energy on the skin of a missile, over a range of more than one thousand miles. That much energy on the missile will boil away enough of the metal within one second to make the missile’s structure crumple and destroy the missile. While Tsipis makes the point that “shiny aluminum” will reflect all but 4 percent of the infrared energy from a chemical laser, Gerry maintains that 4 percent of the energy from a hundred-megawatt laser is quite sufficient to destroy the missile, even assuming that its metal skin is protected by an ablative coating.
Every pound of material used to protect the missile, Gerry points out, is a pound taken away from the payload. For purposes of calculation, he assumed that the protective ablative coating reduced the weight of the missile’s warhead by 20 percent. “The more protection you build into the missile, the smaller its payload [the warhead] becomes,” he says. Protecting the ballistic missile costs the attacker kilotons of explosive power.
