a baseline, allowing for subtraction of rays from the CM or from cosmic radiation to gain better data from the earlier results. In addition, the S-band transponders in the CSM and LM were pointed at the Moon to gain data on its gravitational field. Results from the Lunar Orbiter probes had revealed that lunar gravity varies slightly due to the presence of mass concentrations, or "mascons". Data from the missions, and from the lunar subsatellites left by Apollo 15 and 16, were used to map such variations in lunar gravity. Mission events Launch and outbound trip Originally planned to launch on December 6, 1972, at 9:53 p.m. EST (2:53 a.m. on December 7 UTC), Apollo 17 was the final crewed SaturnV launch, and the only one to occur at night. The launch was delayed by two hours and forty minutes due to an automatic cutoff in the launch sequencer at the T-30 second mark in the countdown. The cause of the problem was quickly determined to be the launch sequencer's failure to automatically pressurize the liquid oxygen tank in the third stage of the rocket; although launch control noticed this and manually caused the tank to pressurize, the sequencer did not recognize the fix and therefore paused the countdown. The clock was reset and held at the T-22 minute mark while technicians worked around the malfunction in order to continue with the launch. This pause was the only launch delay in the Apollo program caused by a hardware problem. The countdown then resumed, and the liftoff occurred at 12:33 a.m. EST on December 7, 1972. The launch window, which had begun at the originally planned launch time of 9:53 p.m. on December 6, remained open until 1:31 a.m., the latest time at which a launch could have occurred during the December 6–7 window. Approximately 500,000 people observed the launch in the immediate vicinity of Kennedy Space Center, despite the early-morning hour. The launch was visible as far away as , and observers in Miami, Florida, reported a "red streak" crossing the northern sky. Among those in attendance at the program's final launch were astronauts Neil Armstrong and Dick Gordon, as well as centenarian Charlie Smith, who alleged he was 130 years old at the time of Apollo 17. The ascent resulted in an orbit with an altitude and velocity almost exactly that which had been planned. In the hours following