In Returnal, the astronaut is a noteworthy artifact you should collect at every opportunity. For the beginner or intermediate player, it is arguably the single most important artifact in the game.
Before the astronaut will appear for purchase at terminals or on certain pedestals throughout the biomes, you must unlock it by completing the first House segment. Each time you begin a new cycle, one of the areas you encounter in the first biome contains a 20th-century home.
Using the House Key item found in that biome, which remains in your inventory permanently after you acquire it, you can enter and explore a portion of the house before finally you must leave. The first time you leave, the astronaut artifact rests on the ground near the building’s front porch.
Once you obtain the astronaut artifact in a cycle, it has no immediate effect. When your integrity meter empties, however, it revives you a single time with full health before vanishing from your collection of artifacts. An on-screen notice advises you the astronaut has revived you.
Ideally, you will collect the astronaut after you have powered up Selene, but before you face stiffer challenges. That way, if a run is essentially doomed, the astronaut doesn’t merely delay the inevitable. If you manage to reach a boss encounter with a full integrity meter and the astronaut in your possession, your odds of surviving are essentially doubled. If you reach a boss encounter without first finding the astronaut, you may want to backtrack to see if you simply missed it.