With less than two weeks remaining until the July 26, 1971 launch of the Apollo 15 lunar mission, engineers at NASA’s Kennedy Space Center (KSC) in Florida completed the Countdown Demonstration Test (CDDT) on July 14. The CDDT, a full dress rehearsal for the actual countdown to launch, consisted of two parts. The “wet” test included fueling the rocket as if for flight, with the countdown ending just prior to first stage engine ignition, and did not involve the flight crew. The “dry” test followed, an abbreviated countdown without fueling the rocket but with astronauts David R. Scott, Alfred M. Worden, and James B. Irwin boarding their spacecraft as if on launch day. Successful completion of the CDDT cleared the way for the start of the actual countdown to launch.
Left: The Apollo 15 Saturn V rocket on Launch Pad 39A during the Countdown Demonstration Test (CDDT), with the vapor clouds indicating the rocket was fueled for the test. Right: A view from the Launch Umbilical Tower of the Apollo 15 spacecraft atop the Saturn V rocket during the CDDT.
Controllers in Firing Room 1 of the Launch Control Center at KSC’s Launch Complex 39 monitored all aspects of the CDDT as they would during the actual countdown for launch. They completed the wet countdown test on July 13. The next day, Scott, Worden, and Irwin, already in their preflight medical isolation, suited up and climbed aboard their spacecraft, remaining there until the countdown test reached T-0. The test was a complete success, clearing the way for the start of the actual countdown on July 20. The astronauts continued with final preparations for their 12-day mission to explore the Hadley-Apennine landing site on the Moon, including preflight medical examinations and training for the lunar surface excursions.
Left: Engineers in Firing Room 1 of the Launch Control Center at NASA’s Kennedy Space Center’s Launch Complex 39 monitor the Countdown Demonstration Test (CDDT) for Apollo 15. Middle: Apollo 15 astronauts David R. Scott, left, Alfred M. Worden, and James B. Irwin put on their pressure suits in preparation for the dry portion of the CDDT. Right: Scott, left, Irwin, and Worden arrive at Launch Pad 39A for the CDDT.
John Uri
NASA Johnson Space Center