Watching Apollo 13 on TV today I looked it up on IMDB and found out some interesting facts.

The movie directed by Ron (Happy Days) Howard also stared his brother Clint Howard as Sy Liebergot - EECOM White, his mother Jean Speegle Howard who played grandma Lovell, his father Rance Howard who played the reverend and his wife Cheryl who played an onlooker at the launch site. Talk about keep it in the family...

Also the real life Astronaut Jim Lovell and wife Marilyn appeared in the movie, Jim playing the Captain of USS Iwo Jima and Marilyn as an onlooker at Launch Site. Jim Lovell wore his old navy captain's uniform in the scene where he greets the astronauts aboard the Iwo Jima. When Ron Howard asked Lovell if he'd like to be in the film as the ship's admiral, Lovell agreed but pointed out, "I retired as a captain; a captain I will be."

To get the 'real' weightless shots the cast and crew flew between 500 and 600 parabolic arcs in NASA's KC-135 airplane (nicknamed the "Vomit Comet"). Each of the arcs got them 23 seconds of zero gravity. All of these flights were completed in 13 days.