Update at 9:35 a.m. ET

NASA's Orion spacecraft, which could one day send astronauts to Mars, is stuck on terra firma for at least another day after the space agency's mission control was unable to satisfactorily resolve a number of issues before a 9:45 a.m. ET launch window closed.

The unmanned vehicle is awaiting its first test in Earth orbit. But after multiple delays for high winds and a stuck liquid-oxygen drain valve on one or more of the Delta IV Heavy rocket's booster engines, NASA didn't have time to get the rocket off the pad. It will try again Friday morning.

The vehicle perched atop the Delta rocket, known officially as Orion Multi-Purpose Crew Vehicle, or MPCV, is designed to carry up to four astronauts.

As NPR's Geoff Brumfiel reported earlier this week, Orion is expected to make two orbits at a distance of 3,600 miles from the Earth's surface on its second lap, before conducting a re-entry burn and splashing down in the Pacific Ocean.

The flight is meant to validate the vehicle's basic systems, including avionics, heat shielding and parachutes.

According to Geoff: "It's designed for deep space, but Orion's first mission will be back to the neighborhood of the moon. The plan is to have a robot capture a small asteroid and drag it back to lunar orbit. Then Orion will carry up to four astronauts to meet it. It's all supposed to happen in the 2020s, though some say the mission is too complicated and not much of an advance."

Although unmanned, Orion is a high-stakes project for the space agency, which sees this test flight as a first step toward the exploration of deep space.

NASA hopes that by the year 2040, Orion will be a key piece of a manned mission to Mars — considered the next logical, if not extremely ambitious, target following the Apollo moon shots of the 1960s and 1970s.

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