Launched at 9:34:00 am EST on July 26, 1971, Apollo 15 took four days to reach the Moon. After spending two hours in orbit around the Earth, the S-IVB third stage of the Saturn V was reignited to send them to the Moon. During the retrieval of the Apollo Lunar Module (LM) from its stowed position below the command and service module (CSM), a light came on on the control panel that indicated the valves of the service propulsion system were open and the engine should be firing. A short was found in a switch that controlled the redundant valves for the engine. New procedures were developed to deal with this. During their first inspection of the LM, Scott and Irwin found that the glass cover of a tapemeter had broken forcing them to clean up the glass shards lest they breathe them in. On the fourth day they entered into lunar orbit and prepared for lunar descent.
Launch and trans-lunar injection
The crew were awakened at 4:19 am EST. After brief medical exams, they ate breakfast with the backup and support crews. They then put on their space suits and were taken by van to the launch site, where they arrived at 6:45 am. This was about two-and-a-half hours before launch. During the launch phase of the flight, Scott sat in the left-hand seat of the CSM, Worden in the center seat, and Irwin in the right-hand seat. Apollo 15 was launched at 9:34:00 am EST on July 26, 1971. One of the few problems encountered during the launch phase came at the separation of the first and second stages. Solid-fuel ullage rockets had been removed from the interstage between the first and second stages. These rockets were used to settle the fuel and oxidizer in the S-II. The first stage also carried only four retrorockets whereas previous missions had used eight. The first stage engines did not cutoff cleanly, taking over four seconds to drop from 2% thrust to zero. This meant that the S-IC was closer to the S-II than planned and the ignition of the second stage disabled the telemetry package on the first stage. Eleven minutes and 34 seconds after launch the crew were in their Earth parking orbit 92.5 by 91.5 nm (171.3 by 169.5 km). An orbit of this height is not sustainable for very long due to friction with the Earth's atmosphere, but the crew would only spend three hours before reigniting the S-IVB third stage to put them on a lunar-bound trajectory. About 485 lb (220 kg) of liquid oxygen (LOX) was lost through an open vent of the S-IVB after the rocket was pitched down too quickly after cutoff. One of the windows of the Apollo 15 CSM was specifically designed to transmit ultraviolet radiation, permitting the crew to acquire UV photographs of the Earth and the Moon. These photographs began as soon as they reached Earth orbit and would continue throughout the mission. During times when they were not using the window, Mission Control had them place a cover over the window that blocked the UV, in an effort to minimize their exposure. Two hours, 50 minutes and 2.6 seconds after launch the S-IVB reignited and burned for 5 minutes and 49 seconds. The burn increased the spacecraft's speed from 25,620 feet per second (7,809 m/s) to 35,522 feet per second (10,827 m/s). The altitude had been raised to 167.4 nautical miles (310.0 km).
Engine problems The next major task for the crew was transposition, docking, and extraction. The lunar module sat below the command and service module, head-to-tail. As such, it was required for the CSM to separate from the S-IVB, travel a short distance, turn 180 degrees and then dock with and extract the lunar module. First the CSM, Endeavour, separated, taking ten minutes to turn, come back and hard dock. About half an hour later, after pressurizing the lunar module and checking the integrity of the docking latches, the crew extracted Falcon from the S-IVB. The S-IVB would be put on a trajectory so that it would impact the lunar surface at 3°39'S, 7°35'W. It was sometime during the transposition and docking that the "SPS Thrust" light on the entry monitor system part of the control panel came on. The service propulsion system (SPS) was the rocket engine of the CSM and this particular light was used to indicate the valves in the engine were open and that the rocket should be firing, something that was not in fact happening. As a precaution the crew opened the circuit breakers that controlled the valves to stop them being opened by a short circuit and causing the engine to fire. After some period of troubleshooting it was determined that there was a short circuit in the "Delta-V Thrust" switch. This switch opened the valves in the SPS. With the cause being in the switch it meant that the engine itself was fine, but new procedures would have to be used when operating the engine to stop accidental ignition. One of the reasons for the success of the Apollo program was the redundancy of critical systems—in the case of the SPS, there were two independent valve systems for the engine. The short in the switch only affected one of these sets of valves and as such it was still possible to fire the engine. But instead of having both sets of valves open at the start of each ignition, only the trouble-free valves would be used. For long burns, the valves affected by the short would be opened only after ten seconds, and closed before the end of the burn. Mission Control decided to cancel the first midcourse correction (MCC-1). This would give them a chance to fire the SPS engine at the second planned correction. This cancellation meant that tasks that would have been done later could be brought forward and the crew could get to sleep sooner. These tasks included a water dump and putting the spacecraft into passive thermal control (PTC) or what was often called "barbecue mode", as the spacecraft was put into a slow roll so that there was even heat distribution. Nearly 15 hours after launch, the crew switched off the lights in the cabin and went to sleep.
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