[sterlind]

SDI freaked out the Russians because it was possible, if not feasible. A number of research projects (e.g. Brilliant Pebbles, Project Excalibur, Shiva Star) were spec'd and tested to various degrees. It would have cost many trillions, but we could have built a missile shield. SDI lives on as the Missile Defense Agency, which has had some modest successes (though nothing like taking down ICBMs during midcourse.)

Russia realized they couldn't afford to clone SDI, so they came up with an asymmetric tactic - MIRVs. A cat-and-mouse game on paper followed - the Soviets planned dummy warheads in MIRV payloads to confuse SDI, the Americans devised sensors to measure warhead density, etc.

AFAIK, Reagan really wanted SDI to work - if he'd been willing to compromise on it, we could have had denuclearization at the Rejkyavik summit. The myth that SDI was a misinformation campaign seems unsubstantiated by what I've read.

[scottlocklin]

MIRVs had been around since the 1960s, and were probably a response to the first gen ABM systems, which were to light off a giant nuke in the path of incoming missiles. I think SDI really did freak out the Soviets; the Russians are still mad every time we field a new kind of ABM, and have been developing numerous obvious countermeasures to them, like "use something that isn't a standard ballistic missile." It's all so tiresome. Everyone should stop.

Of course SDI looked plausible like you said, and ultimately did materialize various ABM systems. This stuff is just insane gorp. Dr Pais has a history of this sort of thing; a quick look at his patent trail on google scholar nets nonsense like "laser augmented jet engines"[1] which are obvious nonsense.

[1] https://patents.google.com/patent/US7080504B2/en