President Obama's just canceled a Bush-backed missile defense shield destined to protect Europe from Iranian ICBMs. It's a whole new ball game compared to the original "Star Wars" SDI program. Remember that? Let us remind you.
President Reagan's famous Strategic Defense Initiative was conceived during the high tensions of the Cold War, and was designed to prevent incoming nuclear weapons from Russia or China from reaching U.S. soil. With such lofty goals, and an ever-present threat of annihilation by foreign nuclear missiles, the program had billions of dollars tossed at it, both officially and via "black program" undisclosed funding.
It was controversial, and its "Star Wars" pseudonym, invented by a former spokeswoman for Wehrner von Braun himself, was well-deserved. Check out three examples of the crazy technology that was dreamed up.
Nuclear-Bomb X-Ray Lasers
This is perhaps the most famous and most sci-fi Star Wars like component of the original SDI program. the basic premise is that normal optical-type lasers would've been too slow to intercept a myriad of incoming missiles or warheads in the event of an all-out Soviet attack. If you were to use a raygun-style anti-missile weapon, you'd need something faster.
Hence the X-ray laser was conceived. Essentially a curtain of space satellites would be deployed, each armed with a small nuclear warhead. When activated, these bombs would explode, and some of the fantastic amounts of energy released would be used to pump numerous on-board x-ray laser modules--each one directed towards an incoming warhead. Of course the satellite and the lasers would be vaporized by the explosion, but just after deadly beams of x-rays had been fired to destroy incoming ICBMs.
Sounds fantastical doesn't it? Well, it was--x-ray lasers powered like this are likely to remain the stuff of fiction for a while yet, because the early test detonation, dubbed Cabra, produced incredibly disappointing results. People were also wary about pre-deploying nuclear weapons and super-powerful lasers in space, and the systems would have contravened many arms-limitation treaties all by themselves.
Some say this catchily-named system was the pinnacle of the SDI. It too was a space-based satellite swarm system, but this time instead of rayguns, the satellites would have fired mini "kill missiles" at the incoming targets.
The principle is simple: Using a suite of sensors (dubbed Brilliant Eyes) the system would have identified and tracked the incoming threats with incredible accuracy. This data would've been sent to the satellite swarm, and then high-velocity missiles sent to intercept the targets. There would've been nothing particularly high tech about these kill vehicles--their pure, dumb, solid mass would do the job thanks to simple kinetic energy, hence the "pebble" bit of the title. It's absolutely like throwing a stone at something, whereas on the beach you'd get 10 meters per second of speed in the pebble, and in space the closing speeds would be more like 10 kilometers per second.
Brilliant Pebbles was cancelled in 1994.
Homing Overlay Experiment
Unlike the other two examples, HOE used a ground-based system--essentially a missile launched to intercept a bigger missile. Upon detection of incoming ICBMs, the HOE would've rocketed into space, and then fired off a kinetic kill vehicle. En route, the KKV would have unfurled a stiff umbrella-like device akin in purpose to a catcher's mitt: Its physical size boosts your chances of catching the incoming target. Using an advanced infrared sensor system, the KKV would've fired itself towards an incoming warhead. Upon collision with its umbrella the warhead would've been annihilated, partially destroyed or had its velocity upset so it would burn up in the atmosphere on re-entry.
Believe it or not, the Army actually built and tested the system, and after three failures the HOE successfully intercepted a dummy warhead that had been launched by a real Minuteman missile 4000km away, at an altitude of 160km in space.
It's a descendant of these latter two programs that President Bush had intended to be deployed in Poland and the Czech Republic--a ground-based anti-missile missile that would've lofted into space and destroyed ICBMs and nuclear warheads before they could re-enter the atmosphere and threaten Europe. You could consider these missiles as the children or grand-children of the SDI. And Obama's actions, along with the imminent nuclear arsenal cuts expected by the U.S. and Russia really do seem to indicate that the Star Wars program is winding down to a close. It hasn't been an entirely negative affair though--the innovations developed during the SDI have given us aerogels, enhanced sensors for detection of breast cancer, and even sensors used to image the Moon during the Clementine mission.