Encyclopedia Astronautica - Everything you wanted to know about the space race

"What did the US know about Soviet missile and space plans and when did they know it? Fifty years of declassified American National Intelligence Estimates, compared to what we now know was really happening in Soviet programs, make a fascinating study. In some cases, the CIA reports provide additional authoritative information on programs that the Russians are still secretive about. In other cases, we can see where the Americans had quite good inside or deduced information, and where they did not.

Throughout the space race, even when faced with a lack of detailed information, the Americans generally made more realistic assessments of Soviet future accomplishments than the Soviets did themselves. The Americans quite clearly knew that the Soviets were not going to win the moon race (that was the reason Kennedy selected that objective in the first place).In general, they seem to have had little information on the inside details and workings of Soviet programs until the late 1970's, when suddenly such information becomes available. It may be conjectured whether this was due to the availability of crucial human spies, the advent of improved communications intercepts, or just the accumulation of small details until the picture became clear. Whereas they did not know the true configuration of the first Soviet ICBM's and space boosters until several years after they were in service, they had full information on the Buran shuttle and Energia booster before they were even rolled out. Perhaps this last knowledge was derived from debriefings of Jewish space industry workers, who were allowed to leave the Soviet Union in substantial numbers in the 1980's." (full text)

What did the CIA know and when did they know it?