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Zero and lift off the delta rocket with Mars Pathfinder

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and the vehicle has cleared the tower.

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It wasn't always this easy.

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

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Thanks to a history of reliability and efficiency,

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it has proven itself dozens of times.

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Delta began as an improved version of the Thor,

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and recorded its first successful mission August 12, 1960.

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The payload then was the Echo I communications satellite,

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which weighed about the same as an average adult male.

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

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and bigger fuel tanks.

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

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That meant launching communications satellites that were more capable of

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

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to nearby planets.

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

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

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

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stronger and somewhat larger than those early models.

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

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

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Delta production was temporarily halted when the space shuttle program began

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in the early 1980s.

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

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and the changes began again.

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

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in NASA's launch fleet.

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The rocket regularly dispatches planetary probes, GPS satellites

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and groundbreaking missions that have proven new technologies.

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