Yes and no--how's that for an ambiguous answer? Really, though, here's why the story is credible. As science and technology allow humans to move past long-established boundaries, we often don't have time to consider the moral implications that breeching those boundaries might produce. In a future world, where the impossible is possible, teens such as Madeline will be used to being able to go wherever they want to go and space travel might seem like an everyday occurrence. When Madeline boards the ETS, she does not consider that because humans are not made for space travel, certain rules and regulations must be enforced in order to assure safety.
Likewise, the story's theme of a person having to make a difficult life-or-death decisions is a universal one and one that seems even more plausible in a futuristic setting.
In spite of those realistic elements, readers must question how a society that is so advanced that it has humans living on many different planets cannot design an efficient spacecraft that could carry a fuel reserve and another passenger. Also, it seems unlikely that Madeline just happens to stowaway on the one spacecraft that is on a desperate mission to deliver medicine and cannot be diverted.