Explorers starred which American actor and activist?
Explorers (film):  The film stars Ethan Hawke, River Phoenix (in their film debuts), and Jason Presson as teenage schoolboys who build a spacecraft to explore outer space. River Phoenix: River Jude Phoenix (born River Jude Bottom; August 23, 1970 – October 31, 1993) was an American actor, musician, and activist.
River Jude Phoenix