In Mission: Red Planet (the 2005/2015 board game by Bruno Cathala & Bruno Faidutti), you are NOT required to complete a mission in a single turn.
Plan your role selections (Captain, Pilot, Scientist, etc.) to efficiently advance multiple mission criteria across the 10-round game. Don't tunnel-vision one mission; diversify.
Note: If you meant the classic game Risk: Mission (secret mission variant), those missions are also completed over the entire game, not in one turn.