Excerpt from “Apollo 13 – Lost Moon” by Jim Lovell and Jeffrey Kluger ~~Thermostat~~

picture-lostmoon-lovellBut the wrong thermostat switch – the 28-volt switch – was in the tank, and, as it turned out, the heaters stayed on for a long, long time. On the evening of March 27, fifteen days before Apollo 13’s scheduled liftoff, the warming coils in Spacecraft 109’s second oxygen tank were flipped on. Given the huge load of O2 trapped in the tank, the engineers figured it would take up to eight hours before the last few wisps of gas would vent away. Eight hours was more than enough time for the temperature in the tank to climb above the 80-degree mark, but the technicians knew they could rely on the thermostat to take care of any problem. When this thermostat reached the critical temperature, however, and tried to open up, the 65-volt current surging through it fused it instantly shut.
The technicians on the Cape launch pad had no way of knowing that the tiny component that was supposed to protect the oxygen tank had welded closed. A single engineer was assigned to oversee the detanking procedure, but all his instruments told him about the cryogenic heater was that the contacts on the thermostat remained shut as they should be, indicating that the tank had not heated up too much. The only possible clue that the system was not functioning properly was provided by a gauge on the launch pad’s instrument panel that constantly monitored the temperature inside the oxygen tanks. If the readout climbed above 80 degrees, the technician would know that the thermostat had failed, and he would shut the heater off manually.
Unfortunately, the readout on the instrument panel wasn’t able to climb above 80 degrees. With so little chance that the temperature inside the tank would ever rise that far, and with 80 degrees representing the bottom of the danger zone, the men who designed the instrument panel saw no reason to peg the gauge any higher, designating 80 as its upper limit. What the engineer on duty that night didn’t know – couldn’t know – was that with the thermostat fused shut, the temperature inside this particular tank was climbing indeed, up to a kiln-like 1000 degrees.
For most of the evening the heater was left running, all the while the temperature needle registering a warm but safe 80. At the end of eight hours, the last of the troublesome liquid oxygen had cooked away as the engineers hoped it would – but so too had most of the Teflon insulation that protected the tank’s internal wiring. Coursing through the now empty tank was a web of raw, spark-prone copper, soon to be reimmersed in the one liquid likelier than any other to propagate a fire: pure oxygen.
Seventeen days later and nearly 200,000 miles out in space, Jack Swigert, responding to a routine daily request from the ground, switched on the cryogenic fan to stir up the contents of the oxygen tanks. The first two times Swigert had complied with the instruction, the fan had operated normally. This time, however, a spark flew from a naked wire, igniting the remains of the Teflon. The sudden build-up of heat and pressure in the pure-oxygen environment blew off the neck of the tank, the weakest part of the vessel. The 300 pounds of oxygen inside the tank flashed instantly into gas and filled bay four of the service module, blowing out the ship’s external panel and causing the bang that so startled the crew.


1 Comment

Filed under Literature, Non-Fiction

One response to “Excerpt from “Apollo 13 – Lost Moon” by Jim Lovell and Jeffrey Kluger ~~Thermostat~~

  1. The Apollo 13 mission was launched on 11 April 1970, and the crew returned safely to Earth on 17 April. “Lost Moon” was published in 1994 by astronaut James Lovell and journalist Jeffrey Kluger.
    Jim Lovell was born in Cleveland, Ohio, USA on 25 March 1928.
    Jack Swigert was born in Denver, Colorado, USA on 30 August 1931, and died on 27 December 1982, aged 51 years.
    Fred Haise was born in Biloxi, Mississippi, USA on 14 November 1933.

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