Apollo

Apollo 12 was struck by lightning twice during lift off

Apollo 12 was struck by lightning twice during lift off.

Apollo 12 launched on schedule from Kennedy Space Center, during a rainstorm. It was the first rocket launch attended by an incumbent US president, Richard Nixon. 36.5 seconds after lift-off, the vehicle triggered a lightning discharge through itself and down to the earth through the Saturn’s ionized plume. Protective circuits on the fuel cells in the Service Module (SM) falsely detected overloads and took all three fuel cells offline, along with much of the Command/Service Module (CSM) instrumentation. A second strike at 52 seconds after launch knocked out the “8-ball” attitude indicator. The telemetry stream at Mission Control was garbled. However, the vehicle continued to fly correctly; the strikes had not affected the Saturn V Instrument Unit.

The loss of all three fuel cells put the CSM entirely on batteries. They were unable to maintain normal 28 V DC bus voltages into the heavy 75-ampere launch loads. One of the AC inverters dropped offline. These power supply problems lit nearly every warning light on the control panel and caused much of the instrumentation to malfunction.

Apollo

Legendary EECOM John Aaron (the original NASA “steely-eyed missile man”) remembered the telemetry failure pattern from an earlier test when a power supply malfunctioned in the CSM Signal Conditioning Equipment (SCE). The SCE converts raw signals from instrumentation to standard voltages for the spacecraft instrument displays and telemetry encoders.

Aaron made a call, “Try SCE to aux.” This switched the SCE to a backup power supply. The switch was fairly obscure, and neither Flight Director Gerald Griffin, CAPCOM Gerald Carr, nor Commander Conrad immediately recognized it. Lunar Module Pilot Alan Bean, flying in the right seat as the CSM systems engineer, remembered the SCE switch from a training incident a year earlier when the same failure had been simulated. Aaron’s quick thinking and Bean’s memory saved what could have been an aborted mission. Bean put the fuel cells back on line, and with telemetry restored, the launch continued successfully. Once in earth parking orbit, the crew carefully checked out their spacecraft before re-igniting the S-IVB third stage for trans-lunar injection. The lightning strikes had caused no serious permanent damage.

Apollo

Initially, it was feared that the lightning strike could have caused the Command Module’s (CM) parachute mechanism to prematurely fire, disabling the explosive bolts that open the parachute compartment to deploy them. If they were indeed disabled, the Command Module would have crashed uncontrollably into the Pacific Ocean and killed the crew instantly. Since there was no way to figure out whether or not this was the case, ground controllers decided not to tell the astronauts about the possibility. The parachutes deployed and functioned normally at the end of the mission.

After Lunar Module (LM) separation, the S-IVB was intended to fly into solar orbit. The S-IVB auxiliary propulsion system was fired, and the remaining propellants vented to slow it down to fly past the Moon’s trailing edge (the Apollo spacecraft always approached the Moon’s leading edge). The Moon’s gravity would then slingshot the stage into solar orbit. However, a small error in the state vector in the Saturn’s guidance system caused the S-IVB to fly past the Moon at too high an altitude to achieve Earth escape velocity. It remained in a semi-stable Earth orbit after passing the Moon on November 18, 1969. It finally escaped Earth orbit in 1971 but was briefly recaptured in Earth orbit 31 years later. It was discovered by amateur astronomer Bill Yeung who gave it the temporary designation J002E3 before it was determined to be an artificial object

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