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Space launches Oct 1957- May 1961
Total orbital attempts 109
USSR attempts 14 out of 25 successful (+1 failed in parking orbit) which is 56 percent (or 60 percent)
US attempts 41 of 84 successful, or 49 percent
Marginal case: USSR Apr 1960 moon launch counted, had 200000 km apogee, better than Pioneer 1 and 3
If these probes are excluded rates are 52 percent to 46 percent
Within root-n Poisson standard deviation, both countries had 50 percent success rate
Note the small number of early USSR launches despite large number of “firsts”