On Nasa using russian rockets , I assumed it could have some to do with using the rockets for better purposes . and there is is "It should be noted that utilization of Russian engines was not a strictly technical
decision, but was also tied into US government policy in the aftermath of the
collapse of the Soviet Union. Namely to engage the Russian aerospace ind" http://www.spacefoundation.org/programs/research-and-analysis/whitepapers-and-analysis/fact-sheet-russian-rocket-engines-used