The SIM and rover were the newest, but not necessarily the biggest, problems on Apollo 15; February and March 1971 were difficult months for the lunar module team. A combined systems test ran for ten days in February as test engineers attempted to resolve a series of discrepancies. Problem areas included the rendezvous radar, a frequent source of trouble in the past. The NASA-Grumman team discovered a malfunction in the radar's rangefinding circuitry and called Bethpage for a replacement on the 24th. It arrived on the 26th and went immediately to the boresight range. Weekend tests disclosed another deficiency: the radar would not slew from its normal straight-ahead position to directly overhead, which would be needed for tracking the command-service module from the lunar surface. The fault was apparently in the mode position switch. On 1 March KSC asked Bethpage to send another radar. It arrived the following day and passed inspection at the boresight range; the self-tests (internal checks of electrical circuits), range determinations, and angle readout checks were all satisfactory. The angle readouts told what direction the radar was pointing and therefore the azimuth and elevation of the target. After installation, tests of the third radar looked all right except for some ambiguous range sensings. Then a technician reported an unusual grinding sound in the gyroscope assembly. The noise increased; a bearing had gone bad. With its fourth radar installed on 13 March, the launch team had a satisfactory rendezvous system.13
Herman Widick's test team uncovered more problems when the lunar module began altitude chamber runs in late March. During an unmanned run on the 26th, engineers noted unsatisfactory conditions in the communications system and the environmental control system. The radio problem involved extraneous noise from the transceiver. With no crew on board, the radios operated in a relay mode, i.e., signals went to the lunar module on the VHF uplink and came back immediately over the S-Band downlink. Harold Cockran's engineering team traced the problem to an improper setting on the VHF receiver squelch circuit.14
The possible malfunction in the environmental control system concerned a relief valve on the suit circuit assembly. Two demand regulators controlled the oxygen pressure to the assembly.* The relief valves protected the suit circuit from overpressurization. On the test of the 26th, the regulator's maximum pressure and the relief valve's minimum line were closer than the prescribed tolerance. It was realized, however, that the regulator pressure would drop somewhat during the manned runs. On the 29th, as the backup crew prepared for an altitude run, a technician inadvertently applied too much pressure to the commander's oxygen umbilical, damaging the hose. The rescheduled test failed when both demand regulators continued to pressurize the suit circuit after reaching the acceptable limit. Technicians removed the regulators the following day. Finally, on 6-7 April, the test team managed successful altitude runs with the prime and backup crews.15
The problems prompted James Irwin, Apollo 15's lunar module pilot, to speak out publicly. At a press conference in Houston, Irwin singled out the difficulties with the lunar module's environmental control system, the landing radar, and the rendezvous radar. Irwin attributed some of the problems to the extended shelf life of the Apollo equipment. Due to the stretchout of Apollo flights, equipment was remaining in storage longer than manufacturers had expected. Irwin also noted that a lot of trained people were leaving the Cape and said, "I think maybe morale is slipping perhaps." Apollo 15's other two astronauts, David Scott and Alfred Worden, disagreed. Worden remarked: "I think the people there are more fired up about 15 than they have been before."16 Concern about the lunar module lessened after the successful altitude runs.
Lightning strikes were the most significant events after the Saturn V was moved to the pad in early May. During the flight readiness test on 14-15 June, lightning struck the mobile service structure and mobile launcher. Although there was no apparent harm to the space vehicle, some ground support equipment was damaged. Schedules were revised to permit retesting of all spacecraft systems. On 25 June, the day following the flight readiness review, lightning struck again with the same results. Damaged electrical components were replaced and the spacecraft systems checked once more. Pad A experienced a third strike on the evening of 2 July during hypergolic loading. While there was no apparent damage, some tests were repeated during the countdown demonstration test. Minor problems during the countdown demonstration test, 7-14 July, were corrected before the start of the countdown on 20 July. When more lightning struck LC-39A during countdown week, Kapryan delayed moving the service structure from the pad until the evening of the 25th.17 Apollo 15 lifted off the next morning at 9:34 a.m. Commander Scott radioed back from space: "As we watch the S-IVB drift away here, how about passing along to Jim Harrington [Apollo 15 space vehicle test conductor] at the Cape congratulations from the crew to the launch team for a superior job."18
* The suit circuit assembly included fans, a heat exchanger (cooling water), and lithium hydroxide to remove CO2 from the air. The suit circuit provided an environmental control system for the cabin and life support for the astronauts' spacesuits. When the mission called for cabin depressurization, e.g., prior to an extravehicular activity, the astronauts hooked up to the suit circuit assembly. The portable life support system provided the same support on the lunar surface.