Science fiction is a film genre blessed by our streaming “golden age,” with bold concepts and adventurous futuristic evocations readily gambled upon by Netflix and others, and, from my point of view, that is entirely welcome. I came to “Stowaway,” with its premise of a three-astronaut flight to Mars jeopardized by an unwitting extra passenger, open to the splendiferous recent pleasure of wonderment and excitement that, for example, Proxima delivered. Alas, Stowaway is a pleasant, astronaut-centered spectacle but its early narrative promise soon fizzles out. The central plot conceit fails to generate tension beyond a wonderfully choreographed spacesuit scene and none of the four key characters feels at all carefully cast (although Daniel Dae Kim trumps his better known stars with seriousness and grace). Overall, there is nothing lamentable about Stowaway but it falls well short of its spectacular setting.