From io9's roundup of science fiction movies where a director was fired before the movie was finished, here's part of the description of Supernova:
Then after Hill finished shooting, he and the studio both agreed that reshoots were needed — but they couldn't agree what needed to be reshot. So Hill was replaced with a new director, Jack Sholder, who did some reshoots. And then Sholder was out, and Francis Ford Coppola came in and recut the movie. It was Coppola, reportedly, who chose to insert some zero-G sex between James Spader and Angela Bassett — which he accomplished by taking unused nude footage of Peter Facinelli and Robin Tunney and digitally darkening Tunney's skin so she could look like Bassett.