You may be thinking of Cassini; it is powered by an RTG and flew back by the Earth for part of its gravity assist, which caused some controversy about if it som

You may be thinking of Cassini; it is powered by an RTG and flew back by the Earth for part of its gravity assist, which caused some controversy about if it somehow went off course and re-entered Earth's atmosphere. More info here: http://www.motherjones.com/politics/1997/09/cassini-controversy http://www.motherjones.com/politics/1997/09/cassini-controve...