Homing Overlay Experiment

Strategic Defense Initiative

The Strategic Defense Initiative (SDI) was a proposal by U.S. President Ronald Reagan on March 23, 1983 to use ground and space-based systems to protect the United States from attack by strategic nuclear ballistic missiles. The initiative focused on strategic defense rather than the prior strategic offense doctrine of mutual assured destruction (MAD).

Though it was never fully developed or deployed, the research and technologies of SDI paved the way for some anti-ballistic missile systems of today. The Strategic Defense Initiative Organization (SDIO) was set up in 1984 within the United States Department of Defense to oversee the Strategic Defense Initiative. It gained the popular name Star Wars after the 1977 film by George Lucas. Under the administration of President Bill Clinton in 1993, its name was changed to the Ballistic Missile Defense Organization (BMDO) and its emphasis was shifted from national missile defense to theater missile defense; from global to regional coverage. BMDO was renamed to the Missile Defense Agency in 2002. This article covers defense efforts under the SDIO.

Strategic missile defense before SDI

SDI was not the first U.S. defensive system against nuclear ballistic missiles. In the 1960s, The Sentinel Program was designed and developed to provide a limited defensive capability, but was never deployed. Sentinel technology was later used in the Safeguard Program, briefly deployed to defend one U.S. location. In the 1970s the Soviet Union deployed a missile defense system, still operational today, which defends Moscow and nearby missile sites.

SDI is unique from the earlier U.S. and Soviet missile defense efforts. It envisioned using space-oriented basing of defensive systems as opposed to solely ground-launched interceptors. It also initially had the ambitious goal of providing a near total defense against a massive sophisticated ICBM attack, as opposed to previous systems, which were limited in defensive capacity and geographic coverage.

Initial impetus

In the fall of 1979, at Reagan's request, Lieutenant General Daniel O. Graham conceived a concept he called the High Frontier, an idea of strategic defense using ground- and space-based weapons theoretically possible because of emerging technologies. It was designed to replace the doctrine of Mutual Assured Destruction, a doctrine that Reagan and his aides described as a suicide pact.

The initial focus of the strategic defense initiative was a nuclear explosion-powered X-ray laser designed at Lawrence Livermore National Laboratory by a scientist named Peter L. Hagelstein who worked with a team called O Group, doing much of the work in the late 1970s and early 1980s. O Group was headed by physicist Lowell Wood, a protégé and friend of Edward Teller, the "father of the hydrogen bomb".

Ronald Reagan was told of Hagelstein's breakthrough by Teller in 1983, which prompted Reagan's March 23, 1983, "Star Wars" speech. Reagan announced, "I call upon the scientific community who gave us nuclear weapons to turn their great talents to the cause of mankind and world peace: to give us the means of rendering these nuclear weapons impotent and obsolete." This speech, along with Reagan's Evil Empire speech on March 8, 1983, in Florida, ushered in the last phase of the Cold War, bringing the nuclear standoff with the Soviet Union to its most critical point before the collapse of the Soviet Union later that decade.

The concept for the space-based portion was to use lasers to shoot down incoming Soviet intercontinental ballistic missiles (ICBMs) armed with nuclear warheads. Nobel Prize-winning physicist Hans Bethe went to Livermore in February 1983 for a two-day briefing on the X-ray laser, and "Although impressed with its scientific novelty, Bethe went away highly skeptical it would contribute anything to the nation's defense.

Project and proposals

In 1984, the Strategic Defense Initiative Organization (SDIO) was established to oversee the program, which was headed by Lt. General James Alan Abrahamson, USAF, a past Director of the NASA Space Shuttle program. Research and development initiated by the SDIO created significant technological advances in computer systems, component miniaturization, sensors and missile systems that form the basis for current systems.

Initially, the program focused on large scale systems designed to defeat a Soviet offensive strike. However, as the threat diminished, the program shifted towards smaller systems designed to defeat limited or accidental launches.

By 1987, the SDIO had developed a national missile defense concept called the Strategic Defense System Phase I Architecture. This concept consisted of ground and space based sensors and weapons, as well as a central battle management system. The ground-based systems operational today trace their roots back to this concept.

In his 1991 State of the Union Address George H. W. Bush shifted the focus of SDI from defense of North America against large scale strikes to a system focusing on theater missile defense called Global Protection Against Limited Strikes (GPALS).

In 1993, the Clinton administration further shifted the focus to ground-based interceptor missiles and theater scale systems, forming the Ballistic Missile Defense Organization (BMDO) and closing the SDIO. Ballistic missile defense has been revived by the George W. Bush administration as the National Missile Defense (since renamed "Ground-Based Midcourse Defense").

Ground-based programs

Extended Range Interceptor (ERINT)

The Extended Range Interceptor (ERINT) program was part of SDI's Theater Missile Defense Program and was an extension of the Flexible Lightweight Agile Guided Experiment (FLAGE), which included developing hit-to-kill technology and demonstrating the guidance accuracy of a small, agile, radar-homing vehicle.

FLAGE scored a direct hit against a MGM-52 Lance missile in flight, at White Sands Missile Range in 1987. ERINT was a prototype missile similar to the FLAGE, but it used a new solid-propellant rocket motor that allowed it to fly faster and higher than FLAGE.

Under BMDO, ERINT was later chosen as the Patriot Advanced Capability-3 (PAC-3) missile.

Homing Overlay Experiment (HOE)

The Homing Overlay Experiment (HOE) was the first system tested by the Army that employed hit-to-kill; four test launches were conducted in 1983 and 1984. The first three tests failed due to guidance and sensor problems. Although the fourth test succeeded, the New York Times charged in August 1993 that the test had been rigged. Investigations into this charge by the Department of Defense, headed John Deutch for Secretary of Defense Les Aspin, and the General Accounting Office concluded that the test was a valid, successful test.

The HOE technology was later used by the SDIO and expanded into the Exoatmospheric Reentry-vehicle Interception System (ERIS) program.

Exoatmospheric Reentry-vehicle Interception System (ERIS)

Developed by Lockheed as part of the ground-based interceptor portion of SDI, the Exoatmospheric Reentry-vehicle Interception System (ERIS) began in 1985, with at least two tests occurring in the early 1990s. This system was never deployed, but the technology of the system was used in the Terminal High Altitude Area Defense (THAAD) system and the Ground Based Interceptor currently deployed as part of the Ground-Based Midcourse Defense (GMD) system.

Directed-energy weapon (DEW) programs

X-ray laser

An early focus of the project was toward a curtain of X-ray lasers powered by nuclear explosions. The curtain was to be deployed using a series of missiles launched from submarines or, later on, satellites, during the critical seconds following a Soviet attack. The satellites would be powered by built-in nuclear warheads--in theory, the energy from the warhead detonation would be used to pump a series of laser emitters in the missiles or satellites in order to produce an impenetrable barrier to incoming warheads. However, on March 26, 1983, the first test, known as the Cabra event, was performed in an underground shaft and resulted in marginally positive readings that could be dismissed as being caused by a faulty detector. Since a nuclear explosion was used as the power source, the detector was destroyed during the experiment and the results therefore could not be confirmed. Technical criticism based upon unclassified calculations suggested that the X-ray laser would be of at best marginal use for missile defense. Such critics often cite the X-ray laser system as being the primary focus of SDI, with its apparent failure being a main reason to oppose the program. However, the laser was never more than one of the many systems being researched for ballistic missile defense.

Despite the apparent failure of the Cabra test, the long term legacy of the X-ray laser program is the knowledge gained while conducting the research. A parallel developmental program advanced laboratory X-ray lasers for biological imaging and the creation of 3D holograms of living organisms. Other spin-offs include research on advanced materials like SEAgel and Aerogel, the Electron-Beam Ion Trap facility for physics research, and enhanced techniques for early detection of breast cancer.

Chemical laser

Beginning in 1985, the Air Force tested an SDIO-funded deuterium fluoride laser known as Mid-Infrared Advanced Chemical Laser (MIRACL) at White Sands Missile Range. During a simulation, the laser successfully destroyed a Titan missile booster in 1985 and it was successfully tested on target drones simulating cruise missiles for the US Navy. After the SDIO closed, the MIRACL was tested on an old Air Force satellite for potential use as an Anti-satellite weapon, with mixed results. The technology was also used to develop the Tactical High Energy Laser, (THEL) which is being tested to shoot down artillery shells.

Neutral Particle Beam

In July 1989, the Beam Experiments Aboard a Rocket (BEAR) program launched a sounding rocket containing a neutral particle beam (NPB) accelerator. The experiment successfully demonstrated that a particle beam would operate and propagate as predicted outside the atmosphere and that there are no unexpected side-effects when firing the beam in space. After the rocket was recovered, the particle beam was still operational. According to the BMDO, the research on neutral particle beam accelerators, which was originally funded by the SDIO, could eventually be used to reduce the half-life of nuclear waste products using accelerator-driven transmutation technology.

Laser and mirror experiments

The High Precision Tracking Experiment (HPTE), launched with the Space Shuttle Discovery on STS-51-G, was tested June 21, 1985 when a Hawaii-based low-power laser successfully tracked the experiment and bounced the laser off of the HPTE mirror.

The Relay mirror experiment (RME), launched in February 1990, demonstrated critical technologies for space-based relay mirrors that would be used with an SDI directed-energy weapon system. The experiment validated stabilization, tracking, and pointing concepts and proved that a laser could be relayed from the ground to a 60 cm mirror on an orbiting satellite and back to another ground station with a high degree of accuracy and for extended durations.

Launched on the same rocket as the RME, the Low-power Atmospheric Compensation Experiment (LACE) satellite was built by the United States Naval Research Laboratory (NRL) to explore atmospheric distortion of lasers and real-time adaptive compensation for that distortion. The LACE satellite also included several other experiments to help develop and improve SDI sensors, including target discrimination using background radiation and tracking ballistic missiles using Ultra-Violet Plume Imaging (UVPI). LACE was also used to evaluate ground-based adaptive optics, a technique now used in civilian telescopes to remove atmospheric distortions.

Hypervelocity Rail Gun (CHECMATE)

Research into hypervelocity rail gun technology was done to build an information base about rail guns so that SDI planners would know how to apply the technology to the proposed defense system. The SDI rail gun investigation, called the Compact High Energy Capacitor Module Advanced Technology Experiment (CHECMATE), had been able to fire two projectiles per day during the initiative. This represented a significant improvement over previous efforts, which were only able to achieve about one shot per month. Hypervelocity rail guns are, at least conceptually, an attractive alternative to a space-based defense system because of their envisioned ability to quickly shoot at many targets. Also, since only the projectile leaves the gun, a railgun system can potentially fire many times before needing to be resupplied.


Rail guns face a host of technical challenges before they will be ready for battlefield deployment. First, the rails guiding the projectile must carry very high amperage and voltage. Each firing of the railgun produces tremendous current flow (almost half a million amperes) through the rails, causing rapid erosion of the rail's surfaces (through ohmic heating, and even vaporization of the rail-surface.) Early prototypes were essentially single-use weapons, requiring complete replacement of the rails after each firing. Another challenge with the rail gun system is projectile survivability. The projectiles experience acceleration force in excess of 100,000 gs. In order to be effective, the fired projectile must first survive the mechanical stress of firing, then the subsequent impact with the target. In-flight guidance, if implemented, would require the onboard guidance system to be built to the same standard of sturdiness as the main mass of the projectile.

In addition to being considered for destroying ballistic missile threats, rail guns were also being planned for service in space platform (sensor and battle station) defense. This potential role reflected defense planner expectations that the rail guns of the future would be capable of not only rapid fire, but also of multiple firings (on the order of tens to hundreds of shots).

Space-based programs

Space-Based Interceptor (SBI)

Groups of interceptors were to be housed in orbital modules. Successful hover testing was completed in 1988 and demonstrated successful integration of the sensor and propulsion systems in the prototype SBI. It also demonstrated the ability of the seeker to shift its aiming point from a rocket's hot plume to its cool body, a first for infrared ABM seekers. Final hover testing occurred in 1992 using miniaturized components similar to what would have actually been used in an operational interceptor. These prototypes eventually evolved into the Brilliant Pebbles program.

Brilliant Pebbles

Brilliant Pebbles was a non-nuclear system of satellite-based, watermelon-sized mini-missiles designed to use a high-velocity kinetic warhead. It was designed to operate in conjunction with the Brilliant Eyes sensor system and would have detected and destroyed missiles without any external guidance. The project was conceived in November 1986.

John H. Nuckolls, director of Lawrence Livermore National Laboratory from 1988 to 1994, described the system as “The crowning achievement of the Strategic Defense Initiative”. The technologies developed for SDI were used in numerous later projects. For example, the sensors and cameras that were developed for Brilliant Pebbles became components of the Clementine mission and SDI technologies may also have a role in future missile defense efforts.

Though regarded as one of the most capable SDI systems, the Brilliant Pebbles program was canceled in 1994 by the BMDO. However, it is being reevaluated for possible future use by the MDA.

Sensor programs

SDIO sensor research encompassed visible light, ultraviolet, infrared, and radar technologies, and eventually led to the Clementine mission though that mission occurred just after the program transitioned to the BMDO. Like other parts of SDI, the sensor system initially was very large-scale, but after the Soviet threat diminished it was cut back.

Boost Surveillance and Tracking System (BSTS)

BSTS was part of the SDIO in the late '80s, and was designed to assist detection of missile launches, especially during the boost phase. However, once the SDI program shifted toward theater missile defense in the early '90s, the system left SDIO control and was transferred to the Air Force.

Space Surveillance and Tracking System (SSTS)

SSTS was a system originally designed for tracking ballistic missiles during their mid-course phase. It was designed to work in conjunction with BSTS, but was later scaled down in favor of the Brilliant Eyes program.

Brilliant Eyes

Brilliant Eyes was a simpler derivative of the SSTS that focused on theater ballistic missiles rather than ICBMs and was meant to operate in conjunction with the Brilliant Pebbles system.

Brilliant Eyes was renamed Space and Missile Tracking System (SMTS) and scaled back further under BMDO, and in the late 1990s it became the low earth orbit component of the Air Force's Space Based Infrared System (SBIRS).

Other sensor experiments

The Delta 183 program used a satellite known as Delta Star to test several sensor related technologies. Delta Star carried an infrared imager, a long-wave infrared imager, an ensemble of imagers and photometers covering several visible and ultraviolet bands as well as a laser detector and ranging device. The satellite observed several ballistic missile launches including some releasing liquid propellant as a countermeasure to detection. Data from the experiments led to advances in sensor technologies.


In war-fighting, countermeasures can have a variety of meanings:

  1. The immediate tactical action to reduce vulnerability, such as chaff, decoys, and maneuvering.
  2. Counter strategies which exploit a weakness of an opposing system, such as adding more MIRV warheads which are less expensive than the interceptors fired against them.
  3. Defense suppression. That is, attacking elements of the defensive system.

Countermeasures of various types have long been a key part of warfighting strategy. However, with SDI they attained a special prominence due to the system cost, scenario of a massive sophisticated attack, strategic consequences of a less-than-perfect defense, outer spacebasing of many proposed weapons systems, and political debate.

Whereas the current U.S. NMD system is designed around a relatively limited and unsophisticated attack, SDI planned for a massive attack by a sophisticated opponent. This raised significant issues about economic and technical costs associated with defending against anti-ballistic missile defense countermeasures used by the attacking side.

For example, if it had been much cheaper to add attacking warheads than to add defenses, an attacker of similar economic power could have simply outproduced the defender. This requirement of being "cost effective at the margin" was first formulated by Paul Nitze in November, 1985.

In addition, SDI envisioned many space-based systems in fixed orbits, ground-based sensors, command, control and communications facilities, etc. In theory, an advanced opponent could have targeted those, in turn requiring self-defense capability or increased numbers to compensate for attrition.

A sophisticated attacker having the technology to use decoys, shielding, maneuvering warheads, defense suppression, or other countermeasures would have multiplied the difficulty and cost of intercepting the real warheads. SDI design and operational planning had to factor in these countermeasures and the associated cost.

Controversy and criticism

SDI may have been first dubbed "Star Wars" by opponent Dr. Carol Rosin, a consultant and former spokesperson for Wernher von Braun. However, Missile Defense Agency historians attribute the term to a Washington Post article published March 24, 1983, the day after the Star Wars speech, which quoted Democratic Senator Ted Kennedy describing the proposal as "reckless Star Wars schemes. Some critics used that term derisively, implying it was an impractical science fiction fantasy, but supporters have adopted the usage as well on the grounds that yesterday's science fiction is often tomorrow's engineering. In comments to the media on March 7, 1986, Acting Deputy Director of SDIO, Dr. Gerold Yonas, described the name "Star Wars" as an important tool for Soviet disinformation and asserted that the nickname gave an entirely wrong impression of SDI.

Ashton Carter, a board member at MIT, assessed SDI for Congress in 1984, saying there were a number of difficulties in creating an adequate missile defense shield, with or without lasers. Carter said X-rays have a limited scope because they become diffused through the atmosphere, much like the beam of a flashlight spreading outward in all directions. This means the X-rays needed to be close to the Soviet Union, especially during the critical few minutes of the booster phase, in order for the Soviet missiles to be both detectable to radar and targeted by the lasers themselves. Opponents disagreed, saying advances in technology, such as using very strong laser beams, and by "bleaching" the column of air surrounding the laser beam, could increase the distance that the X-ray would reach to successfully hit its target.

Physicist Hans Bethe, who worked with Edward Teller on both the nuclear bomb and the hydrogen bomb at Los Alamos, claimed a laser defense shield was unfeasible. He said that a defensive system was costly and difficult to build yet simple to destroy, and claimed that the Soviets could easily use thousands of decoys to overwhelm it during a nuclear attack. He believed that the only way to stop the threat of nuclear war was through diplomacy and dismissed the idea of a technical solution to the Cold War, saying that a defense shield could be viewed as threatening because it would limit or destroy Soviet offensive capabilities while leaving the American offense intact. In March 1984, Bethe coauthored a 106-page report for the Union of Concerned Scientists that concluded "the X-ray laser offers no prospect of being a useful component in a system for ballistic missile defense."

Teller countered that Bethe and the other anti-defense activists could not have it both ways. Bethe, who had helped him usher in the nuclear age, had become opposed to nuclear weapons and afraid of nuclear war. At the same time, Bethe was also opposed to stopping the threat of offensive capabilities through massive defensive programs. Teller testified before Congress that "instead of [Berthe] objecting on scientific and technical grounds, which he thoroughly understands, he now objects on the grounds of politics, on grounds of military feasibility of military deployment, on other grounds of difficult issues which are quite outside the range of his professional cognizance or mine."

On June 28, 1985, David Lorge Parnas resigned from SDIO's Panel on Computing in Support of Battle Management, arguing in 8 short papers that the software required by the Strategic Defense Initiative could never be made to be trustworthy and that such a system would inevitably be unreliable and constitute a menace to humanity in its own right.

Supporters of SDI hail it for contributing to or at least accelerating the fall of the Soviet Union by the strategy of technology, which was a prevalent doctrine at the time. At Reagan and Gorbachev's October 1986 meeting in Iceland, Gorbachev opposed this defensive shield, while Reagan wanted to keep it, and offered to give the technology to the Soviets. Gorbachev said he didn't believe the offer, saying "Excuse me, Mr. President, but I do not take your idea of sharing SDI seriously. You don't want to share even petroleum equipment, automatic machine tools or equipment for dairies, while sharing SDI would be a second American Revolution." Both Reagan and Gorbachev proposed total elimination of all nuclear-armed missiles, but SDI and intermediate-range missiles were sticking points. While SDI was a disagreement, the summit led to the Intermediate-Range Nuclear Forces Treaty, which some have claimed was an outgrowth of Gorbachev's fear of SDI. Opponents of the program say that Mikhail Gorbachev's reforms were the cause of the USSR's collapse and that SDI was an unrealistic and expensive program. Furthermore, some believed that Gorbachev's opposition to SDI was intended to encourage the United States to pursue ABM defense at great economic expense. To quote Gorbachev, "But I think that I am even helping the president [Reagan] with SDI. After all, your people say that if Gorbachev attacks SDI and space weapons so much, it means the idea deserves more respect. They even say that if it were not for me, no one would listen to the idea at all. And some even claim that I want to drag the United States into unnecessary expenditures with this."

Treaty obligations

Another criticism of SDI was that it would require the United States to modify, withdraw from, or violate previously ratified treaties. The Outer Space Treaty of 1967, which requires "States Parties to the Treaty undertake not to place in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner" and would forbid the US from pre-positioning in Earth orbit any devices powered by nuclear weapons and any devices capable of "mass destruction". Only the nuclear-pumped X-ray laser would have violated this treaty since other SDI systems would not utilize nuclear weapons. The Anti-Ballistic Missile Treaty and its subsequent protocol, which limited missile defenses to one location per country at 100 missiles each, would have been violated by SDI ground-based interceptors. The Nuclear Non-Proliferation Treaty requires "Each of the Parties to the Treaty undertakes to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control." Many viewed favoring deployment of ABM systems as an escalation rather than cessation of the nuclear arms race, and therefore a violation of this clause.


SDI was criticized for potentially disrupting the strategic doctrine of Mutual Assured Destruction. MAD postulated that intentional nuclear attack was inhibited by the certain ensuing mutual self-destruction. Even if a nuclear first strike destroyed many of the opponent's weapons, sufficient nuclear missiles would survive to render a devastating counter-strike against the attacker. The criticism was that SDI could have potentially allowed an attacker to survive the lighter counter-strike, thus encouraging a first strike by the side having SDI. Another destabilizing scenario was countries being tempted to strike first before SDI was deployed, thereby avoiding a disadvantaged nuclear posture.

Ronald Reagan responded that SDI would be given to the Soviet Union to prevent the imbalance from occurring. How and whether this massive technology transfer would have happened was often debated. A complication of the MAD argument was that MAD only covered intentional nuclear attacks by a rational opponent with similar values, not accidental launches, rogue launches, or launches by non-state entities.

Non-ICBM delivery

Another criticism of SDI was that it would not be effective against non-space faring weapons, namely cruise missiles, bombers, and non-conventional delivery methods.


Fiction and popular culture

Because of public awareness of the program and its controversial nature, SDI has been the subject of many fictional and pop culture references. This is not intended to be a complete list of those references.

  • Dale Brown's novel Silver Tower details the adventures on and around a space station that employs an anti-ICBM laser system called Skybolt against a Soviet invasion of Iran; it would reappear in the 2007 novel Strike Force and the 2008 novel Shadow Command.
  • Tom Clancy's novel The Cardinal of the Kremlin is based on part of a race between the USA and USSR to complete laser-based SDI systems.
  • Homer Hickam Jr's novel Back to the Moon used leftover SDI weapons, including the Homing Overlay Experiment, in an attempt to kill the crew of shuttle Columbia.
  • In the Civilization series, there are several references to ICBM defense systems similar to SDI.
  • The comedy movie Real Genius follows college physics prodigies who are unknowingly induced to develop a space-based laser weapon system for the Air Force.
  • In RoboCop, a brief satirical news story mentions how the Ronald Reagan memorial Strategic Defense platform in orbit malfunctioned, destroying a swathe of Southern California in the process.
  • Spies Like Us follows two duped 'spies' who are told to launch a single Soviet missile towards the USA as part of a black operation to demonstrate and justify the expense of SDI.
  • In the 1993 Larry Bond novel Cauldron the GPALS system is depicted as having been deployed with the Brilliant Pebbles weapons included. They are used to destroy all French and German military satellites covering an invasion of Poland in the then-future of 1998.

See also


  • Frances Fitzgerald (2001). Way Out There in the Blue: Reagan, Star Wars and the End of the Cold War. Simon & Schuster. ISBN 0-7432-0023-3.
  • Broad, William J. (1985). Star Warriors: A penetrating look into the lives of the young scientists behind our space age weaponry.. Simon & Schuster. ISBN 0-7881-5115-0. (Reprint edition 1993; Diane Pub. Co.)

External links

Search another word or see Homing Overlay Experimenton Dictionary | Thesaurus |Spanish
Copyright © 2014 Dictionary.com, LLC. All rights reserved.
  • Please Login or Sign Up to use the Recent Searches feature