This slow, often intriguing space drama from writer/director Joe Penna could have and should have been more tense. After a terribly dull opening sequence, “Stowaway” tries to convince you that you’re in for something special. No luck. Toni Collette leads a solid cast that features Anna Kendrick and Daniel Dae Kim. They’re all a part of a three-way crew on a mission to Mars (don’t bother with the details). The plot truly kicks in when an unplanned passenger (Shamier Anderson) shows up, threatening the safety of everyone on board. At first, you might think that this could turn into an old-fashioned space thriller. But the movie loses its momentum only halfway through and never truly recovers. The rest is tedious, to say the least. I don’t know what I was personally expecting from this movie, but all I know that it was a letdown. Considering the people behind it and the grade-A cast, you’d expect something better. Too bad.