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\h        Music

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\h        Zero and lift off the delta rocket with Mars Pathfinder

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\h        and the vehicle has cleared the tower.

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\h        It wasn't always this easy.

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\h        The Delta II has become a workhorse of NASA's Launch Services Program.

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\h        Thanks to a history of reliability and efficiency,

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\h        it has proven itself dozens of times.

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\h        Delta began as an improved version of the Thor,

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\h        and recorded its first successful mission August 12, 1960.

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\h        The payload then was the Echo I communications satellite,

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\h        which weighed about the same as an average adult male.

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\h        A gradual list of improvements gave the Delta I models better engines

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\h        and bigger fuel tanks.

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\h        With each change came a greater load the rocket could place into orbit.

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\h        That meant launching communications satellites that were more capable of

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\h        transmitting signals around the world, and a chance to launch probes

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\h        to nearby planets.

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\h        It didn't take long before engineers started attaching small booster rockets

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\h        to the side of the first stage to give an extra kick at liftoff.

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\h        It's a practice we still use today, although the booster rockets are considerably

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\h        stronger and somewhat larger than those early models.

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\h        By 1975, the Delta rocket could shoot a ton of cargo into high earth orbit.

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\h        That was about 11 times more than the first Delta could carry.

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\h        Delta production was temporarily halted when the space shuttle program began

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\h        in the early 1980s.

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\h        Manufacturing returned after 1986 as part of NASA’s mixed fleet manifest

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\h        and the changes began again.

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\h        Improved several times in recent years, the Delta II is still a reliable element

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\h        in NASA's launch fleet.