Strategic Defense Initiative

History

After World War II, the US Army studied ballistic missile defense (BMD), finding that attacking a V-2 rocket was difficult due to short flight times. Bell Labs noted that longer-range missiles, though faster, had longer flight times and were easier to detect at high altitudes. Successive programs—Nike Zeus, Nike-X, Sentinel, and Safeguard—sought to defend against Soviet ICBMs, but the changing threat, including Soviet claims of producing missiles "like sausages" and the introduction of MIRV, shifted the cost-exchange ratio heavily in favor of offensive systems.

President Dwight D. Eisenhower asked DARPA to consider alternatives, leading to Project Defender and Project BAMBI, which used satellites to intercept ICBMs during boost phase. BAMBI was cancelled in 1963 due to prohibitive projected operational costs. By the late 1960s, BMD had become highly controversial, with public protests against the Sentinel system. Only one Safeguard base became operational in April 1975 and was closed in February 1976.

The Soviet A-35 anti-ballistic missile system, deployed around Moscow, was the only Soviet ABM system allowed under the 1972 Anti-Ballistic Missile Treaty.

Project and proposals

On March 23, 1983, Reagan announced SDI in a nationally televised speech, calling on the scientific community to render nuclear weapons impotent and obsolete. In 1984, the SDIO was established, headed by Lt. General James Alan Abrahamson, a past Director of the Space Shuttle program. Concepts considered included particle-beam weapons, updated nuclear shaped charges, and plasma weapons. SDIO invested in computer systems, component miniaturization, and sensors.

Initially focused on defeating a massive Soviet offensive strike, the program concentrated on "high tech" solutions like lasers. By 1986, many promising ideas were failing: Teller's X-ray laser failed key tests and was redirected to the anti-satellite role, the particle beam concept was demonstrated to not work, and only the Space-Based Laser seemed promising but grew in size due to fuel consumption. The American Physical Society (APS) was asked by SDIO to review the concepts.

Their report, presented in 1986 and released in redacted form in early 1987, concluded that none of the systems were near deployment, requiring energy output improvements of at least 100 times, and in some cases a million.

Directed-energy weapon (DEW) programs

An early SDI focus was the Excalibur X-ray laser, powered by nuclear explosions. The concept used metal rods as a lasing medium to focus X-rays from a nuclear burst, aiming to destroy many ICBMs in a single attack. The device was initially satellite-based but later moved to a "pop-up" concept launched from a submarine off the northern Soviet coast. On March 26, 1983, the first test (the Cabra event) was performed in an underground shaft, yielding marginally positive readings possibly from a faulty detector; the detector was destroyed during the experiment, so results could not be confirmed.

Technical criticism suggested the X-ray laser would be of at best marginal use. Despite the apparent failure, the program yielded knowledge used in laboratory X-ray lasers for biological imaging, advanced materials like SEAgel and Aerogel, the Electron-Beam Ion Trap facility, and techniques for early breast cancer detection. Beginning in 1985, the Air Force tested the SDIO-funded Mid-Infrared Advanced Chemical Laser (MIRACL) at White Sands Missile Range.

In a simulation, it destroyed a Titan missile booster in 1985, though the booster shell was pressurized and under compression loads simulating launch conditions. MIRACL was later tested on target drones and an old Air Force satellite, with mixed results, and its technology was used to develop the Tactical High Energy Laser (THEL).

Controversy and criticism

Jessica Savitch reported on SDI technology in a November 1983 episode of Frontline, demonstrating a laser destroying a model communication satellite, possibly the first televised use of a weapons-grade laser. Ashton Carter assessed SDI for Congress in 1984, noting difficulties in creating an adequate missile defense shield; he said X-rays become diffused by the atmosphere, requiring sources close to the Soviet Union during boost phase. Opponents argued that stronger beams and "bleaching" the air column could increase X-ray range.

Physicists Hans Bethe and Richard Garwin, who worked with Teller on the atomic and hydrogen bombs, claimed a laser defense shield was unfeasible, costly, and simple to destroy, and that the Soviets could use thousands of decoys to overwhelm it. They dismissed a technical solution to the Cold War, saying a defense shield could be viewed as threatening. In March 1984, Bethe coauthored a report for the Union of Concerned Scientists concluding that the X-ray laser offered no prospect of being useful in ballistic missile defense.

In response, Teller testified before Congress that Bethe was objecting on political and military grounds outside his professional cognizance.

Did You Know?

• The Strategic Defense Initiative was nicknamed the 'Star Wars program' after Senator Ted Kennedy derided it as 'reckless Star Wars schemes'.
• The American Physical Society concluded in 1987 that SDI technologies were decades away from readiness and at least another decade of research was required to know if such a system was even possible.
• A Soviet revolver cannon (Rikhter R-23) was mounted on the 1974 Salyut 3 space station, which successfully test-fired its cannon in orbit.
• Declassified intelligence material revealed that SDI was a cause of grave concern for the Soviet Union and its successor state Russia due to the potential neutralization of its arsenal.
• On May 20, 2025, President Donald Trump announced the Golden Dome, a project broadly similar to SDI, which he referenced in the announcement.