Somewhere spacious, and safe. Portable, but comfy. Lightweight, but robust to the dangers of space. Something like a big bouncy castle for kids, but built to house astronauts and solar system colonists and tourists looking for an out-of-this-world vacation.

It sounds like a sci-fi fever dream, but it's becoming reality. On Friday, SpaceX will launch a so-called "expandable"—a prototype called the Bigelow Expandable Activity Module—to the International Space Station. It will remain there, attached to the Tranquility module, for two years. Bigelow Aerospace hopes its time in orbit will prove the technology worthy of inhabitants.

Robert Bigelow didn't start his career with visions of astronaut hotels. No, the company's eponymous founder made his fortune on the hotel chain Budget Suites—extended-stay hotels with a stove in every room.