Gerard Kitchen O'Neill -LRB- February 6 , 1927 -- April 27 , 1992 -RRB- was an American physicist and space activist .
He invented a machine for holding subatomic particles .
He invented a machine for holding subatomic particles .
Rewrite this sentence in a simpler manner: Gerard Kitchen O'Neill -LRB- February 6 , 1927 -- April 27 , 1992 -RRB- was an American physicist and space activist . Output: