NASA has been subjecting its Orion space capsule to a battery of tests designed to tell whether the spacecraft is ready to ferry humans into orbit and beyond. So far, the capsule seems to be on track—in a series of maneuvers this week, a joint team of NASA and U.S. Navy specialists successfully recovered the spaceship from the sea off the coast of San Diego, simulating what would happen when a deep-space mission splashed back to Earth.

If all goes to plan, Orion will become NASA’s flagship technology for launching astronauts to orbit and even to deep space, including to the lunar surface and maybe Mars. Here’s what’s at stake with Orion, and what still needs to be done before it can blast off.

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