Nasa plans to launch a ''flying saucer'' into Earth's atmosphere to test technology that could be used to land on Mars.
After several weather delays, the attempt off the coast of the Hawaiian island of Kauai will test the disc-shaped vehicle and a giant parachute.
Since the 1970s, Nasa has used the same parachute design to slow landers and rovers as they streak through the thin Martian atmosphere.
With plans to send heavier spacecraft and eventually astronauts, the space agency needs a much stronger parachute.
NASA is testing the technology high in Earth's atmosphere because conditions there are similar to that of Mars.
High winds at the Kauai military range forced Nasa to miss its original two-week launch window in June.
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