Apollo 13 accident question,?

Question

If a oxygen tank blew up did it catch fire being in the vacuum of space and why did this tank explode anyway?

Answer 1

The tank didn't catch fire per se, although there was some combustion involved in the tank's guts; it basically ruptured under too much pressure.  Because the rupture tore some of the piping open, the other (undamaged) tanks were vented too.

Why did it explode?  Because of a freak sequence of several unfortunate  events.  Working backwards:

The tank ruptured because some of the tank's inner components ignited from an electrical arc and burned rapidly in the oxygen, creating a lot of pressure.

The arc occurred because the electrical insulation had been burned off.

The insulation burned off because of a combination of an improperly rated thermostatic cutoff switch and an improvised detanking procedure.

The improvised detanking procedure arose because the tank did not empty properly during a test on the launch pad.  It didn't empty properly because its vent/purge assembly had been damaged during a disassembly at the factory, to rework it.  Because the vent/purge assembly is not a flight-critical component, it was not required to be requalified following the factory accident.

The thermostatic cutoff switch was meant to disconnect electrical power to the tank heater when the internal temperature reached 80 F.  It was originally rated for 28 VDC, one of the common voltages on the spacecraft.  It was decided during design that all components should be uprated to 60 VDC, the ground-support voltage.  The thermostatic cutoff switch was tested at 60 VDC, but not in its "trip" mode -- only the current-carrying capacity with the contacts closed.

Because of the factory damage, the tank did not vent properly after a launch-pad test.  The ground support people received approval to turn on the tank heater to vaporize the oxygen and allow it to vent faster.  It was believed that the thermostatic switch would prevent the heater from reaching dangerous temperatures, so the heater-assisted detanking procedure was allowed to proceed largely unattended.  The tank temperature was monitored sporadically, but the ground-support equipment (GSE) thermometer dial only went to 80 F, the maximum designed temperature for the tank.

When the thermostatic switch tripped under the heat load at 80 F, the contacts arced and fused under the higher voltage, allowing the heater to reach dangerous temperatures.  These high temperatures burned/melted off the insulation on the wires inside the tank, which led to the heater, the capacity transducer, and the circulation fan.  The high temperature was not noticed during any inspections because of the limits on the GSE thermometer.

The uninsulated wires then eventually arced when the stirring fans were turned on in flight.

Answer 2

  Zero degrees temperature caused the rubber insulators to crack and release hot gases from the solid boosters which burned a bracket holding the booster to the shuttle.

  The booster broke loose and rupture the main fuel tank and causing the explosion

Answer 3

The Apollo 13 malfunction was caused by an explosion and rupture of oxygen tank no. 2 in the service module. The explosion ruptured a line or damaged a valve in the no. 1 oxygen tank, causing it to lose oxygen rapidly. The service module bay no.4 cover was blown off. All oxygen stores were lost within about 3 hours, along with loss of water, electrical power, and use of the propulsion system.

The oxygen tanks were highly insulated spherical tanks which held a "slush" of liquid oxygen with a fill line and heater running down the center. The no. 2 oxygen tank used in Apollo 13 (North American Rockwell; serial number 10024X-TA0008) had originally been installed in Apollo 10. It was removed from Apollo 10 for modification and during the extraction was dropped 2 inches, slightly jarring an internal fill line. The tank was replaced with another for Apollo 10, and the exterior inspected. The internal fill line was not known to be damaged, and this tank was later installed in Apollo 13.

56 hours into the mission, at about 03:06 UT on 14 April 1970 (10:06 PM, April 13 EST), the power fans were turned on within the tank for the third "cryo-stir" of the mission, a procedure to stir the oxygen slush inside the tank which would tend to stratify. The exposed fan wires shorted and the teflon insulation caught fire in the pure oygen environment. This fire rapidly heated and increased the pressure of the oxygen inside the tank, and may have spread along the wires to the electrical conduit in the side of the tank, which weakened and ruptured under the pressure, causing the no. 2 oxygen tank to explode. This damaged the no. 1 tank and parts of the interior of the service module and blew off the bay no. 4 cover.

Answer 4

The vacuum of space bit is irrelevant, as there was plenty of oxygen, since this is what was in the tank.

However, there was not anything to burn around, so the oxygen just vented into space.

Post flight accident investigation proposed the following scenario: the oxygen tank was subjected to high heat for a long period of time during some ground test, and following a redesign, some components had not been upgraded and were not able to stand the heat, and were therefore damaged. During the flight, a routine operation to stir the content of the tank was commanded, and since some electrical wiring was damaged, this caused a short circuit that led to the explosion.

The real amazing thing is that records exist that allowed the whole sequence of operation to be deducted. But unfortunately, as is very often the case with space operations, the amount of data is so large, no one really looks at it unless they have a reason to, so accident happen instead of being prevented.

Wikipedia has a fairly good description of the sequence of event. Follow the link.