Over the end credits an epilogue plays that picks up with the characters several years after the events of the film as the Ares V mission prepares to launch. This immediately tells us a very important thing (which is one of the more subtle Apollo 13 parallels) - this disaster didn't stop the space program. In fact, it actually advanced it, turning exploration into an international effort. Earlier on in the film, the Chinese space agency wrestles with whether to reveal their secret jet propulsion system to NASA, knowing that it would allow them to save Mark Watney, but at the cost of their scientific advantage. They eventually offer their help (Starman FTW) because Mark's predicament is something bigger than one nation, similar to how the Moon Landings were far from just an American achievement. Far from a one-time deal, this leads to the Ares V mission being a joint effort, with an international crew and mission command. The conflict that has dominated galactic exploration since the Cold War is alluded to throughout The Martian, most pointedly (and, yes, humorously) in Mark's discussion of maritime law and how Mars is essentially international waters. The ending, however, suggests such archaic ideals should be put aside; in having the world's two biggest superpowers working together, we're seeing a future where Earth is functioning as one on the path to its future in the stars. Given the scientific accuracy throughout the film, this is clearly Scott pointing towards what he (and Weir) view as a realistic future.
