EETimes - Apollo - July 20, 2009 - 21

P o w e r Bu dg e t e r Luck and an EECOM’s curious mindset helped Aaron during the crisis. The young EECOM remembered a simulation he had observed the previous year. Apollo 12’s telemetry after the lightning strike matched the strange, nonsensical patterns of the earlier simulations, where Aaron had engaged in some “schematic walkthroughs with colleague Dick Brown” to figure out what was going on. As Apollo 12 rocketed into space with no electrical power, Aaron knew what might get things back online. He made an arcane call: “Flight, [this is] EECOM. Try SCE to AUX,” meaning the crew should throw the command module switch “signal conditioning electronics to auxiliary.” Aaron’s suggestion was relayed to the puzzled crew, the switch was set and the electrical systems came back online. A bus undervoltage had tripped critical telemetry electronics (SCE), which Aaron knew would still 21 EE Times | Apollo | July 20, 2009 work when powered with a lower-voltage backup power rail (AUX) that bypassed the voltage monitor. Aaron’s curiosity about every Apollo system, along with his detailed systems and circuit knowledge, allowed the second moon landing mission to continue. For his actions, Aaron’s colleagues at Mission Control honored him with the sobriquet “steelyeyed missile man.” The oxygen tank explosion that crippled Apollo 13 in April 1970 presented EECOM with perhaps the biggest challenge in the history of manned space flight. In the namesake film, the use of an ammeter for critical CSM power-up negotiations didn’t seem quite right. Aaron had served as “power broker” in the rescue mission; if anyone is in a position to set the record straight, he is. Unlike the peak-current limit approach portrayed in the movie, powering up the dead Apollo 13 command module came down to a watt-hours-delivered-when set of decisions, according to Aaron. By devising the right set of power-on timings and integrating them under power consumption curves, the scarce remaining watt-hours could be stretched long enough to get the crew back home. Aaron orchestrated the sequence planning and carefully negotiated among various flight controllers in allocating power during restart. He wondered early in the crisis whether lunar module specialists might be persuaded to “spare some power for the CSM power-up.” LM controllers declined, since they were dealing with their own energy crisis on the Apollo 13 lifeboat. In the search for some spare power, Aaron said, he had sent along his engineer, hat in hand, but “he wasn’t gone long.” Still, once CSM power-up was completed and the LM was ready to be Aaron made an arcane call: ‘Try SCE to AUX’

EETimes - Apollo - July 20, 2009

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