George Mueller, the man who was at the forefront of NASA's human spaceflight efforts through the first moon landing and was credited as the "father of the space shuttle," died on Monday. He was 97.

Mueller also played an important role for initiating the Skylab and space shuttle programs. Announcing his death, NASA said the cause of death was congestive heart failure.

As head of NASA's Office of Manned Spaceflight, Mueller ensured that the Apollo program of NASA met the challenge Kennedy issued in a 1961 address: landing a man on the moon and bringing him back.

A NASA history read, "It is clear that without all-up testing, the first manned lunar landing could not have taken place as early as 1969," the last year that met Kennedy's schedule.

The same NASA history went on to say that Mueller's "bold telescoping of the overall plan bore magnificent fruit." Apollo 8 crew orbited the moon on Christmas 1968, and in the next year, the sixth Saturn V took Neil Armstrong's Apollo 11 to the first manned lunar landing.

In an interview for a Smithsonian Institution publication, Mueller had said: "Well, one thing that gave me the confidence is that there wasn't any other way we were going to get the program done on the schedule that we had."

Mueller, however, stressed that he was not being rash in sending Apollo 8 to circle the moon after the 6.5 million-pound rocket that was to lift it into space had flown only twice.

"It wouldn't have gone if I hadn't been comfortable," he said. "I spent about four months that summer looking at every possible way that it could fail, and convinced myself that it wasn't going to fail," he said. "So we went forward with it."