STRATEGIC DEFENSE INITIATIVE (SDI)
The Strategic Defense Initiative (SDI), derisively nicknamed the “Star Wars program“, was a proposed missile defense system intended to protect the United States from attack by ballistic strategic nuclear weapons (intercontinental ballistic missiles and submarine-launched ballistic missiles). The concept was announced on March 23, 1983, by President Ronald Reagan, a vocal critic of the doctrine of mutually assured destruction (MAD), which he described as a “suicide pact”. Reagan called upon American scientists and engineers to develop a system that would render nuclear weapons obsolete. Elements of the program reemerged in 2019 with the Space Development Agency (SDA).
The Strategic Defense Initiative Organization (SDIO) was set up in 1984 within the US Department of Defense to oversee development. A wide array of advanced weapon concepts, including lasers, particle beam weapons and ground- and space-based missile systems were studied, along with various sensor, command and control, and high-performance computer systems that would be needed to control a system consisting of hundreds of combat centers and satellites spanning the entire globe and involved in a very short battle. The United States holds a significant advantage in the field of comprehensive advanced missile defense systems through decades of extensive research and testing; a number of these concepts and obtained technologies and insights were transferred to subsequent programs.
Under the SDIO’s Innovative Sciences and Technology Office, headed by physicist and engineer Dr. James Ionson, the investment was predominantly made in basic research at national laboratories, universities, and in industry; these programs have continued to be key sources of funding for top research scientists in the fields of high-energy physics, supercomputing/computation, advanced materials, and many other critical science and engineering disciplines and funding which indirectly supports other research work by top scientists.
In 1987, the American Physical Society concluded that the technologies being considered were decades away from being ready for use, and at least another decade of research was required to know whether such a system was even possible. After the publication of the APS report, SDI’s budget was repeatedly cut. By the late 1980s, the effort had been re-focused on the “Brilliant Pebbles” concept using small orbiting missiles not unlike a conventional air-to-air missile, which was expected to be much less expensive to develop and deploy.
SDI was controversial in some sectors, and was criticized for threatening to destabilize the MAD-approach potentially rendering the Soviet nuclear arsenal useless and to possibly re-ignite “an offensive arms race”. Through declassified papers of American intelligence agencies the wider implications and effects of the program were examined and revealed that due to the potential neutralization of its arsenal and resulting loss of a balancing power factor, SDI was a cause of grave concern for the Soviet Union and her primary successor state Russia. By the early 1990s, with the Cold War ending and nuclear arsenals being rapidly reduced, political support for SDI collapsed. SDI officially ended in 1993, when the Clinton Administration redirected the efforts towards theatre ballistic missiles and renamed the agency the Ballistic Missile Defense Organization (BMDO).
In 2019, space-based interceptor development resumed for the first time in 25 years with President Trump’s signing of the National Defense Authorization Act. The program is currently managed by the Space Development Agency (SDA) as part of the new National Defense Space Architecture (NDSA) envisioned by Michael D. Griffin. Early development contracts were awarded to L3Harris and SpaceX. CIA Director Mike Pompeo called for additional funding to achieve a full-fledged “Strategic Defense Initiative for our time, the SDI II”.
SDI DIRECTED-ENERGY WEAPON (DEW)
PROGRAMS
X-ray laser
An early focus of the SDI effort was an X-ray lasers powered by nuclear explosions. Nuclear explosions give off a huge burst of X-rays, which the Excalibur concept intended to focus using a lasing medium consisting of metal rods. Many such rods would be placed around a warhead, each one aimed at a different ICBM, thus destroying many ICBMs in a single attack. It would cost much less for the US to build another Excalibur than the Soviets would need to build enough new ICBMs to counter it. The idea was first based on satellites, but when it was pointed out that these could be attacked in space, the concept moved to a “pop-up” concept, rapidly launched from a submarine off the Soviet northern coast.
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, however the test setup had the booster shell pressurized and under considerable compression loads. These test conditions were used to simulate the loads a booster would be under during launch. The system was later tested on target drones simulating cruise missiles for the US Navy, with some success. 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.
During the mid-to-late 1980s a number of panel discussions on lasers and SDI took place at various laser conferences. Proceedings of these conferences include papers on the status of chemical and other high power lasers at the time.
The Missile Defense Agency’s Airborne Laser program uses a chemical laser which has successfully intercepted a missile taking off, so an offshoot of SDI could be said to have successfully implemented one of the key goals of the program.
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 Ultraviolet 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 Railgun (CHECMATE)
Research out of hypervelocity railgun technology was done to build an information base about railguns so that SDI planners would know how to apply the technology to the proposed defense system. The SDI railgun investigation, called the Compact High Energy Capacitor Module Advanced Technology Experiment, 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 railguns 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.
A hypervelocity railgun works very much like a particle accelerator in so far as it converts electrical potential energy into kinetic energy imparted to the projectile. A conductive pellet (the projectile) is attracted down the rails by electric current flowing through a rail. Through the magnetic forces that this system achieves, a force is exerted on the projectile moving it down the rail. Railguns can generate muzzle-velocities in excess of 2.4 kilometers per second.
Railguns face a host of technical challenges before they will be ready for battlefield deployment. First, the rails guiding the projectile must carry very high power. 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 railgun system is projectile survivability. The projectiles experience acceleration force in excess of 100,000 g. To be effective, the fired projectile must first survive the mechanical stress of firing and the thermal effects of a trip through the atmosphere at many times the speed of sound before its subsequent impact with the target. In-flight guidance, if implemented, would require the onboard navigation system to be built to the same level of sturdiness as the main mass of the projectile.
In addition to being considered for destroying ballistic missile threats, railguns were also being planned for service in space platform (sensor and battle station) defense. This potential role reflected defense planner expectations that the railguns 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).
Source: Wikipedia
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