Brilliant Pebbles
Brilliant Pebbles was a space-based ballistic missile defense system proposed by Lowell Wood and Edward Teller of Lawrence Livermore National Laboratory in 1987, near the end of the Cold War. The system would consist of thousands of small satellites, each with missiles similar to conventional heat seeking missiles, placed in low Earth orbit constellations so that hundreds would be above the Soviet Union at all times. If the Soviets launched their ICBM fleet, the pebbles would detect their rocket motors using infrared seekers and collide with them. Because the pebble strikes the ICBM before the latter could release its warheads, each pebble could destroy several warheads with one shot.
Brilliant Pebbles is named as a play on "Smart Rocks," a concept promoted by Daniel O. Graham under the Strategic Defense Initiative. Smart Rocks envisioned at least 423 large orbital battle stations equipped with powerful sensors and carrying numerous small missiles. The Air Force states this was not possible due to limited space lift capabilities at the time. Edward Teller dismissed the idea as "outlandish" and vulnerable to anti-satellite attacks. But after their own Excalibur —an X-ray laser system powered by a nuclear warhead— failed critical tests, Teller and Lowell Wood risked losing out on the SDIO program. When SDIO realized the various directed energy weapons were nowhere near use, they revisited missile-based concepts akin to Smart Rocks. Wood introduced "Pebbles," proposing that advances in sensors and microprocessors allowed missiles to operate independently without central stations, solving many of the problems with Smart Rocks.
To intercept missiles promptly, the autonomous pebbles fly in low Earth orbit. Because of these orbit's high velocities, the pebbles are over their targets only for a brief period. Consequently, many thousands of pebbles evenly distributed around the Earth are necessary to ensure sufficient coverage. Critics contend that this global distribution renders the majority of satellites ineffective during a conflict, thereby making the system less efficient compared to localized or regional missile defense systems.
Pebbles replaced Rocks as the baseline SDI design and in 1991 it was ordered into production and became the "crowning achievement of the Strategic Defense Initiative". By this time the Soviet Union was collapsing and the perceived threat changed to shorter-range theatre ballistic missiles. Pebbles was modified, but doing so raised its weight and cost; the original design called for around 10,000 missiles and would cost $10 to $20 billion, but by 1990 the cost for 4,600 had ballooned to $55 billion. Fighting in Congress through the early 1990s led to Pebbles' cancellation in 1993, but elements of the concept re-emerged with the Space Development Agency in 2019, and later in 2025 with the Golden Dome.
History
Smart Rocks
There are a wide variety of stories about the origins of Ronald Reagan's Strategic Defense Initiative. According to one often repeated tale, it was Reagan's viewing of Alfred Hitchcock's Torn Curtain that did it. Edward Teller instead pointed to a talk he gave on the topic of BMD in 1967 that Reagan attended. Others point to Reagan's visit to the Cheyenne Mountain Complex in 1979; there he saw the systems that could detect a Soviet launch and then track their warheads. When he asked what they could do in that situation, the answer was "launch our own missiles". Whatever the source, Reagan was convinced that mutual assured destruction was ridiculous, dismissing it as the international equivalent of a suicide pact.Reagan asked Daniel O. Graham, his military advisor during the 1980 presidential campaign and former director of the Defense Intelligence Agency, to look for possible solutions. At first, Graham proposed a system of crewed space fighters, but the idea was quickly dismissed. Next, he revived the 1960s Project BAMBI to be the basis of a new system he referred to as Smart Rocks. This concept used "battle stations" in low Earth orbit, each carrying several dozen small missiles similar to a conventional heat-seeking air-to-air missile. The platforms would carry advanced sensors to detect and track Soviet ICBMs as they launched, and then launch its missiles and guide them until the missile's own infrared sensors picked up the ICBM. As the ICBM rocket engine was extremely bright in infrared, even a very simple interceptor missile could successfully track them.
As the interceptors were relatively small and carried a limited amount of rocket fuel, they could only attack ICBMs within a limited range of the stations. This meant the stations had to be in low orbit, to keep them close to their targets. At these altitudes, the stations moved at speeds around compared to the surface of the Earth. At that rate, any given station would spend only a few minutes over the Soviet Union. To ensure there were enough stations in the right locations at any given time, hundreds of stations were needed. The Air Force noted that there was nowhere near enough launch capacity to build such a system, and even if it could be launched, maintaining it would cost at least $30 billion a year in 1963 dollars. Additionally, it was noted that there was no effective way to protect the stations against attacks by anti-satellite weapons, and the Soviets could easily afford to launch one for each platform.
Although twenty years had elapsed since BAMBI had first been studied and the concept had been re-examined several times, no obvious solution to these problems had presented itself. The Smart Rocks proposal, now known officially as Global Ballistic Missile Defense, ignored all of these problems, presenting a bare minimum of information. One observer derided the concept as being "one view-graph deep" and "unencumbered by practical engineering considerations or the laws of physics". In spite of this, Graham soon found a group of like-minded Republicans who formed a group known as the High Frontier Panel to help develop and support his idea. The group was led by Karl Bendetsen and began meeting in a room provided by The Heritage Foundation.
Excalibur
Around the same time that Graham was formulating his Smart Rocks concept, studies into X-ray lasers at Lawrence Livermore National Laboratory made an apparent breakthrough. Nuclear explosions give off massive amounts of X-ray energy, and it appeared possible these could be focused down into narrow beams as the basis for a long-range laser weapon. Previous systems had used carbon-based lasing materials, but calculations showed that the energy could be greatly increased by using a metal rod instead. The idea had been largely theoretical until a key test of the new concept in November 1980.By surrounding a nuclear warhead with dozens of rods, each could be independently aimed to shoot down an enemy missile. A single such warhead might be able to destroy 50 missiles in a radius of around it. A small fleet of such warheads could seriously disrupt any Soviet attack. In February 1981, Teller and Wood traveled to Washington to pitch the idea of a Manhattan Project-level development effort to produce these weapons in what they called Project Excalibur.
Teller was also a member of the High Frontier group and began attacking Graham's Smart Rocks as "outlandish", and suggested his own Excalibur be used in its place. Graham countered by pointing out a serious flaw in Excalibur; he noted that it worked by blowing itself up, so in the event a Soviet anti-satellite weapon approached, it could either blow itself up to attack the ASAT, or allow itself to be blown up by the ASAT. In either case, the Excalibur would be destroyed. Teller soon returned with a solution. In this concept, the Excalibur weapons would be placed on missiles on submarines and launched when needed.
Seeing himself increasingly sidelined, Graham left the group in December 1981 to form High Frontier Inc. In March 1982, they published a glossy book on the topic. It claimed that the system could be "fully deployed within five or six years at a minimum cost of some $10–$15 billion". A pre-publication copy was sent to the Air Force, who dismissed it, saying that it "had no technical merit and should be rejected".
Early failures, APS report
On 23 March 1983, Reagan gave his famous "Star Wars" speech that called on the scientists of the United States to build defenses that would render nuclear weapons obsolete. Over the next year this was formalized as the Strategic Defense Initiative Office as a separate branch under the Department of Defense, and soon, many of the United States weapons laboratories and major defense contractors were exploring a variety of systems to meet this goal. Along with Excalibur and the space-based laser, new proposals included ground-based lasers, various particle-beam weapons and nuclear shaped charges.Through the early phases of SDI, the Smart Rocks concept was ignored by the SDIO. A study by research scientist Ashton Carter concluded that the system had "extremely limited capability for boost phase intercept of present Soviet ICBMs and no capability against future MX-like Soviet boosters, even with no Soviet effort to overcome the defense". Graham's connections in Washington's political circles meant the concept was well known in spite of any official indifference. This led to a constant stream of questions by politicians to the SDIO about the system and why they were not working on it. In 1985, Sam Nunn asked James A. Abrahamson, director of the SDIO, about it once again. Abrahamson stated that "he would not recommend that the United States proceed to deploy it".
By 1986, many of the systems being studied had run into difficulties. Among these was Teller's Excalibur, which failed several critical tests in 1986. A similar test carried out by skeptical physicists at Los Alamos National Laboratory suggested there was no lasing going on at all. Other concepts, like the neutral beam weapon which shot hydrogen atoms near the speed of light, demonstrated performance that was so poor it was unlikely it could ever work. The best among them all was the space-based laser, but it needed to improve its beam quality by at least 100 times before it would be able to disable an ICBM.
That same year, the American Physical Society published their review of the directed-energy weapon efforts. After a lengthy declassification procedure, it was released to the public in March 1987. Compiled by a number of notables in the laser and physics community, including Nobel laureate Charles H. Townes, the lengthy report stated in no uncertain terms that none of the concepts were remotely ready for use. In every case, performance had to be improved at least a hundred times, and for some of the concepts, as much as a million times. It concluded that at least another decade of work was required before they would even know if any of the systems could ever reach the necessary performance.