THE NECESSARY COMPUTER POWER FOR SDI WAS AVAILABLE IN 1963

MANNED ORBITAL LABORATORY? MORE LIKE MANNED ORBITAL LASER. 

Russell Targ standing next to his megawatt laser in the 1960's.. 

The product announcement for the CDC 6600 was made in 1963. This computer had the necessary computing power to run the programs used to shoot down missiles ("CDC 6600"). The successor to the computer the CDC 7600 was actually used by the Air Force to track Soviet ICBM's. Megawatt lasers were built in 1963 (Targ 98). The SNAP family of reactors were being developed in the 1960's to power the manned satellites such as the MOL ( 88 AIR FORCE WEAPONS LABORATORY). These reactors were being developed to produce electrical power in the multi-megawatt range; the range needed to power the computers and lasers for a space based laser. So, all the pieces of the puzzle were there. 

BIBLIOGRAPHY/SOURCES:

1. AIR FORCE WEAPONS LABORATORY. SNAP REACTOR OVERVIEW. Air Force Systems Command, Kirtland Air Force Base, NM, 1984, pp. 82-89.
2. Biddle, Wayne. "'Star Wars' Technology: It's More Than A Fantasy". The New York Times, 1985, p.
3. "CDC 6600". En.Wikipedia.Org, 2018, https://en.wikipedia.org/wiki/CDC_6600. Accessed 19 June 2018.
4. "CDC 7600". En.Wikipedia.Org, 2018, https://en.wikipedia.org/wiki/CDC_7600. Accessed 19 June 2018. A1. 
5. Targ, Russell. Do You See What I See?. Hampton Roads Pub. Co., 2008

Notes: 

1. The successor to the CDC 6600, the CDC 7600 were used for  missile launch and inbound tracking of Soviet ICBM's. https://en.wikipedia.org/wiki/CDC_7600
2. "CDC also manufactured two multi-processor computers based on the 7600, with the model number 7700.[22] They consisted of two 7600 machines in an asymmetric configuration: a central and an adjunct machine. They were used for missile launch and inbound tracking of USSR ICBMs. The radar simulator was a real-time simulator with a CDC 6400 for input/output front-end. These systems were to be used in the Pacific Missile Range. One computer was installed at TRW in Redondo Beach CA (later moved to Kwajalein Atoll, South Pacific), and the second one was installed at McDonnell Douglas in Huntington Beach CA. They were actual 7600s connected by chassis 25 to make them a 7600 MP. The operating system was TOS/BOS (Tactical Operating System/Basic Operating System).[23]"