To what extent was the Soviet Union successful in maintaining control over its satellite states in the period 1945-1980?
During the time period in question, Soviet control of its satellite nations was not complete, but it was quite effective.
Other countries in the Soviet bloc did not remain quietly and happily under Soviet domination for the whole time period that you are asking about. For example, there were major pushes to get out from Soviet control by the Hungarians in 1956 and the Czechs in 1968. In both cases, however, military force was used by the Soviets to crush the rebellions and reassert control over the satellites.
At the end of the time period you mention, the Solidarity movement was launched in Poland. This would be a major challenge to communist domination, but it had yet to really affect Soviet control in 1980.