You might be interested in some previous threads on travel between the United States and the Soviet Union:

• Cold war travel from the West to the Soviet Union, possible? - 2 comments, over 6 months old.
• Very brief, but both comments give overviews of travel (and a travel agency!) between the USA and the USSR.
• How isolated was the Soviet Union? - 6 comments, over 2 years old.
• The commenters her go into travel between the West and Soviet satellite states.
• Did Soviet scientists attend international science conferences? - 6 comments, over 2 months old.
• One commenters gives a strong overview of how often and under what restrictions Soviet scientists were allowed to go to foreign countries and how that changed over the course of the Cold War.