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Antares vs. Falcon 9: How the two rockets ferrying NASA's cargo differ

SpaceX's Falcon 9 rocket has already proved itself able to get a cargo payload to the International Space Station. Orbital Sciences' Antares rocket, set for its first test launch Wednesday evening, is a very different animal.

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Last month, the propulsion system on a four-legged test frame lofted the frame and a dummy rocket 263 feet in the air, held that height for just over 30 seconds, then gradually eased back to Earth for a landing. At launch, a full-size manikin dressed to look like Johnny Cash stood on the frame and survived the round trip standing up.

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Orbital Sciences, on the other hand, has built its Antares rocket largely from hardware that already has been space tested, explains Lennard Fisk, a professor of space science at the University of Michigan at Ann Arbor and a member of Orbital Sciences' board of directors.

The company turned to Ukraine's Yuzhnoye Design Bureau to help with the tanks, pumps, and plumbing needed to support Antares's two liquid-fuel motors – themselves built in the former Soviet Union but modified for Antares by a US rocket-motor company. Yuzhnoye builds Russia's Zenit rockets.

The second stage is powered by a solid-fuel motor built by the company that produced the solid-fuel boosters for the space shuttle.

Orbital Sciences' progress has not been without hiccups.

During launches for NASA in 2009 and 2011, the sleek shell, or faring, that the company uses to protect a payload while the rocket rises through the atmosphere failed to split open, preventing the satellites from reaching orbit. It has since modified the faring, which encase a dummy payload perched atop Antares.

In addition, during a test in 2011, one of the engines caught fire during a test. The US company that modified them for Orbital Sciences, Aerojet, repaired the defect. The motor has passed subsequent "hot fire" tests in January and February.

The program also experienced delays as technicians coped with the challenges of installing and testing new hardware designed to handle frigid liquid fuel at the Mid Atlantic Regional Spaceport on Wallops Island in Virginia. Up to this point, the spaceport and the adjacent Wallops Island Fight Center, which NASA runs, had lofted solid-fuel rockets.

Today, NASA and Orbital will test the fruits of their labor.

"When we first started this program six years ago, there was no launch pad and no rocket" at the spaceport, said Phil McAlister, NASA's commercial-spaceflight development director during a prelaunch briefing. "I'm very much looking forward to the day where we have regular cargo resupply runs to the International Space Station. Hopefully we'll see that very soon."

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