Complex sentence: Cooper was selected as backup Commander for the May 1969 Apollo 10 mission, and hoped this placed him in position as Commander of Apollo 13, according to the usual crew rotation procedure established by the Flight Crew Operations Director, grounded fellow Mercury astronaut Deke Slayton.
Split into simpler sentences: Cooper was selected as backup Commander for the May 1969 Apollo 10 mission. He hoped this placed him in position as Commander of Apollo 13, according to the usual crew rotation procedure established by the Flight Crew Operations Director-grounded fellow Mercury astronaut Deke Slayton.