Apollo 13: The Successful Failure
The Accident
The injury to the Service Module was caused by damaged Teflon insulation on the fans inside the second cryogenic oxygen tank. When Jack Swigert stirred the tank 55 hours into the flight, the damaged Teflon caused the wires on the fan to short-circuit and ignite the insulation and vaporizing the liquid oxygen in the tank.
At 55 hours and 53 minutes the crew reported hearing a "loud bang" and minutes later they saw oxygen leaking out of the ship. This was the oxygen pressure finally becoming too much and the tank bursting, injuring the other oxygen tank and the fuel cell bay damaging fuel cells 1 and 3, which left emergency batteries as their only power.
By 58 hours and 40 minutes the crew had powered down the Command Module and powered up the Lunar Module. This procedure usually takes 3 hours but the crew did it in 2 hours and 33 minutes. Their quick action to conserve power ultimately saved their lives.
At 55 hours and 53 minutes the crew reported hearing a "loud bang" and minutes later they saw oxygen leaking out of the ship. This was the oxygen pressure finally becoming too much and the tank bursting, injuring the other oxygen tank and the fuel cell bay damaging fuel cells 1 and 3, which left emergency batteries as their only power.
By 58 hours and 40 minutes the crew had powered down the Command Module and powered up the Lunar Module. This procedure usually takes 3 hours but the crew did it in 2 hours and 33 minutes. Their quick action to conserve power ultimately saved their lives.
Oxygen tank technical pieces that were involved:
- quantity sensor
- stirring fan
- heater to vaporize liquid oxygen
- thermostat to protect heater
- temperature sensor
- fill and drain valves
Before Flight
The heater and thermostat were originally designed for a 28 volt DC bus but when the DC bus was changed to 65 volts the heater and thermostat were not upgraded and could not handle the higher voltage. During a testing prior to take off, engineers found that the tank was not draining properly. Replacing the tank would delay the mission for several days so instead the oxygen was boiled off with the heater. Lovell signed off on the procedure.
During this process the heater did not shut off automatically as it should have. Instead, the temperature in the tank rose to over 1,000 ° F. The temperature sensor was not designed to read over 100° F so it did not register. A thermometer malfunction had happened during Apollo 12, so no one thought anything was actually wrong. The heat melted the Teflon insulation which in turn caused the exposed wires to spark.
During this process the heater did not shut off automatically as it should have. Instead, the temperature in the tank rose to over 1,000 ° F. The temperature sensor was not designed to read over 100° F so it did not register. A thermometer malfunction had happened during Apollo 12, so no one thought anything was actually wrong. The heat melted the Teflon insulation which in turn caused the exposed wires to spark.
The master alarm had been turned off due to slightly low pressure in the hydrogen tank, and did not trigger for the oxygen tank as it should have.
Carbon Dioxide Poisoning
After the accident, all three members of the crew were living in the Lunar Module which was designed for only two people and was meant to hold two astronauts for two days, not three for four days. Consequently there was not enough lithium hydroxide to filter out the extra carbon dioxide the crew was producing. Once the carbon dioxide pressure reaches 15 millimeters it starts to become poisonous. The Command Module had extra LiOH canisters but they were cube shaped and the Lunar Module's sockets were circular.
Mission Control solved the problem by building what has since been nicknamed "the mailbox" to connect the canister to the socket. It works by using a hose from the astronauts' suits to draw air between the socket and the canisters.
Mission Control solved the problem by building what has since been nicknamed "the mailbox" to connect the canister to the socket. It works by using a hose from the astronauts' suits to draw air between the socket and the canisters.
