The True Story of Apollo 13

The mission began with a little-known smaller incident: during the second-stage boost, the center (inboard) engine shut down two minutes early. The four outboard engines burned longer to compensate, and the vehicle continued to a successful orbit. The shutdown was determined to be due to dangerous pogo oscillations that threatened to tear the second stage apart. The engine experienced 68g vibrations at 16 hertz, flexing the thrust frame by 3 inches (76 mm).[7] The engine shutdown was triggered by sensed thrust chamber pressure fluctuations.[8] Smaller pogo oscillations had been seen on previous Titan and Saturn flights (notably Apollo 6), but on Apollo 13 they were amplified by an unexpected interaction with turbopump cavitation.[9] Later missions implemented anti-pogo modifications that had been under development. These included addition of a helium gas reservoir to the center engine liquid oxygen line to dampen pressure oscillations, an automatic cutoff as a backup, and simplification of the propellant valves of all five second-stage engines.

Oxygen tank incidentExplosion "Houston, we've had a problem."

Swigert and Lovell reporting the incident on April 14, 1970

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En route to the Moon, approximately 200,000 miles (320,000 km) from Earth, Mission Control asked Swigert to turn on the hydrogen and oxygen tank stirring fans, which were designed to destratify the cryogenic contents and increase the accuracy of their quantity readings. Approximately 93 seconds later the astronauts heard a "loud bang", accompanied by fluctuations in electrical power and firing of the attitude control thrusters.[6] The crew initially thought that a meteoroid might have struck the Lunar Module (LM).


Overall view of the Mission Operations Control Room during Apollo 13's fourth television transmission, on the evening of April 13, 1970....