in orbit. The launch vehicle for Apollo 10 was a Saturn V, designated AS-505, the fifth flight-ready Saturn V to be launched and the third to take astronauts to orbit. The Saturn V differed from that used on Apollo 9 in having a lower dry weight (without propellant) in its first two stages, with a significant reduction to the interstage joining them. Although the S-IVB third stage was slightly heavier, all three stages could carry a greater weight of propellant, and the S-II second stage generated more thrust than that of Apollo 9. The Apollo spacecraft for the Apollo 10 mission was composed of Command Module 106 (CM-106), Service Module 106 (SM-106, together with the CM known as CSM-106), Lunar Module 4 (LM-4), a spacecraft-lunar module adapter (SLA), numbered as SLA-13A, and a launch escape system. The SLA was a mating structure joining the Instrument Unit on the S-IVB stage of the Saturn V launch vehicle and the CSM, and acted as a housing for the LM, while the Launch Escape System (LES) contained rockets to propel the CM to safety if there was an aborted launch. At about 133.8 metric tons, Apollo 10 would be the heaviest spacecraft to reach orbit to that point. Mission highlights Launch and outbound trip Apollo 10 launched from KSC on May 18, 1969, at 12:49:00 EDT (16:49:00 UT), at the very start of a 4.5 hour launch window. The launch window was timed to secure optimal lighting conditions at Apollo Landing Site 2 at the time of the LM's closest approach to the site days later. The launch followed a countdown that had begun at 21:00:00 EDT on May 16 (01:00:00 UT on May 17). Apollo 10 launched from Pad 39B and was the only flight to launch from that pad during the Apollo program, and it was also the only flight to be controlled from Firing Room 3 there. Pad 39B was used because preparations for Apollo 11 had already begun at Pad 39A. Issues that arose during the countdown were dealt with during the built-in holds, and did not delay the mission. On the day prior to launch, however, Cernan had been stopped for speeding while returning from a final visit with his wife and child. Lacking identification and under orders to tell no one who he was, Cernan later attested in his autobiography that he had feared being arrested. Launch