My predecessors have already captured the nuances in the movie so well that I have nothing more add. But there is one thing in the movie which kept me glued to it ( apart from the performances, of course) and that was the hidden message that is subtly delivered.
In todays world where the immigration laws by different nations are becoming more and more stringent because of the claims of limited resources by each country- this movie is the real test of this world dilemma as to how do you define human existence. How do you define as being human. Even in a limited resources spaceship with much lesser options to survive, the technical worker ( like most immigrants who come to developed nations with a work permit), inadvertently stays ( however most of the immigrants come with an intention to stay). His life value does not compare much as pitted against the life of knowledgeable and experienced astronauts ( whose life has a lot to offer to people and the nation). There is a moral dilemma here- should he be killed for no fault of his ( which is the most logical thing to do) just for being there or work it out till the last breath and explore all options, even with life risks, so that he lives...So that an OUTSIDER lives...