The Apollo program, which twice landed humans successfully on the Moon in 1969, suffered near-disaster when the Apollo 13 module had to be powered off and immediately returned to Earth after the module had been seriously damaged by an onboard oxygen tank explosion and fire. The crew survived, and the U.S. space program made significant changes to the Apollo design.
A series of seemingly unrelated events during the manufacture and testing of the Apollo 13 spacecraft led to the first in-flight space mishap for the U.S. space program. James A. Lovell, veteran of three spaceflights, including the first orbital lunar mission (Apollo 8), led the third in the series of planned piloted lunar landings. He would join rookie astronaut Fred W. Haise, Jr., to explore Fra Mauro on the lunar surface and deploy a set of instruments to study the Moon. Orbiting above in the Command and Service Module (CSM) was Jack Swigert, another rookie astronaut. Swigert replaced Thomas K. Mattingly II, who had been exposed to rubella before the mission but never contracted the disease. While no member of the Apollo 13 crew again flew in space, Mattingly went on to be the Apollo 16 Command Module (CM) pilot and commander of two space shuttle flights.
The seeds of the accident were planted five years earlier, during the manufacture of one of the oxygen tanks in the Apollo 13 Service Module (SM). Flight crews spent their time inside the conical CM, which rode atop a 110-meter (360-foot) tall Saturn V rocket. The SM was situated beneath the CM and housed the main supply of oxygen, the electrical system, and the maneuvering engines and their propellants. In bay 4 of the SM, two tanks stored liquid oxygen for breathing and for combining with liquid hydrogen to produce electricity and potable water. The tank’s design included a heater to convert the liquid oxygen to a gas, a fan to stir the gas, a quantity probe, and a thermostat to control the temperature. Once assembled and welded, technicians inserted the electrical components into the tank and bolted them in place.
During assembly, a technician had dropped the structure carrying oxygen tank 2 about five centimeters (2 inches). The exterior of the tank was undamaged, but the pipes that directed flow within the tank became misaligned. Filled for ground testing, the tank’s piping problem was discovered when it came time to empty it. Technicians had to run the heater extensively using 65-volt ground equipment to evaporate the liquid left in the tank. Designed only to handle the spacecraft’s 28-volt supply, the thermostat fused, allowing the contents to heat continuously. Instead of taking several days to evaporate as expected, the gas evaporated in hours, which led to the interior of the tank reaching an estimated 430 degrees Celsius and burning off the insulation of the tank’s internal wiring.
From left: astronauts Fred W. Haise, Jr., Jack Swigert, and James A. Lovell smile and wave aboard the USS Iwo Jima after returning safely to Earth on April 17, 1970.
Apollo 13 lifted off from launch pad 39A at the Kennedy Space Center on April 11, 1970, at 19:13:00 Coordinated Universal Time (UTC). During the second-stage boost of the Saturn V, onboard computers triggered an automatic shutdown of the center engine because of pogo-stick-like oscillations, which might have torn the vehicle apart. Earth-orbital insertion occurred without further incident, and the Saturn V third-stage engine ignited, sending the spacecraft on a trajectory toward the Moon. The CSM, at this point referred to by its call sign, Odyssey,
Apollo 13 had an uneventful journey toward the Moon. At a ground-elapsed time (GET) of 46:40:02, ground control in Houston asked the crew to turn on the fans in oxygen tank 2. This routine “cryo stir” prevented the mixture of liquid oxygen and gaseous oxygen from becoming stratified. This procedure was repeated twice during the next five hours without incident. As power was applied to the tank for the fourth time (at 55:53:20 GET), the exposed wiring shorted and then sparked a fire.
The oxygen spread the fire rapidly and the tank exploded, damaging other parts of the SM, including the number 1 oxygen tank sitting next to it. About ninety seconds later, telemetry from the spacecraft was lost almost totally for 1.8 seconds. During the period of data loss, the caution and warning system alerted the crew to a low-voltage condition on one of the two main power-distribution circuits, or buses, that powered the spacecraft’s systems. At about the same time, the crew heard a loud “bang” and realized something was amiss.
“Okay, Houston, we’ve had a problem here,” reported Swigert as he surveyed Odyssey’s instruments from his CM pilot seat. “I believe we’ve had a problem here,” radioed Lovell from Odyssey’s lower equipment bay. “Houston, we’ve had a problem,” repeated Lovell a few seconds later, “We’ve had a main B bus undervolt.” Warning alarms sounded throughout the spacecraft. Engineers at Mission Control surveyed their instruments for an explanation. The loss of both oxygen tanks led to the inability of the CSM to generate electrical power. The CM had batteries for use during re-entry, after the SM was jettisoned, but these would last about ten hours. More important, they were needed for re-entry. With the help of ground controllers, the crew powered down Odyssey and began the transformation of Aquarius into a lifeboat.
The LM “lifeboat” procedure was worked out during a training simulation not long before the flight. A major issue was Aquarius itself, designed and equipped to sustain two people for two days while on the Moon, but not three people for four days. The critical problem was the lithium hydroxide canisters used to remove carbon dioxide. There were enough lithium hydroxide canisters, but the square canisters from Rockwell International’s Odyssey were not compatible with the round openings in Grumman Aerospace’s Aquarius environmental system. Eventually, the crew fabricated an adapter from materials in the spacecraft with the guidance of ground personnel.
The crew used the LM’s descent engine for course corrections. The initial maneuver to change to a free return trajectory was made within hours of the accident. The engine was fired again in order to accelerate the spacecraft’s return to Earth after going around the Moon, and later for a minor course correction.
Just prior to re-entry on April 17, the SM was jettisoned. The crew photographed the damage, reporting that the access panel covering bay 4 was missing and part of the large communications antenna was damaged. Later, they jettisoned Aquarius, and the CM reentered the atmosphere. The CM splashed down east of American Samoa and 6.5 kilometers (4 miles) from the recovery ship, USS Iwo Jima, completing a journey of 5 days, 22 hours, 54 minutes, and 41 seconds.
As a result of the Apollo 13 accident investigation, NASA implemented several changes to the spacecraft, including a redesign to include a third cryogenic oxygen tank installed in a heretofore-empty bay of the SM. The addition of an auxiliary battery in the SM, identical to the LM batteries, provided a backup in case of fuel cell failure. Oxygen tank fans and thermostat switches were removed, and stowage of an emergency five-gallon supply of drinking water was added to the command module.
The Apollo 13 accident brought NASA’s engineering and technological resources together to develop a rescue plan in real time. It also brought the U.S. piloted space program back into the public’s eye. Perhaps a morbid curiosity increased television coverage of the remaining four Apollo missions. It would be another fifteen years before complacency resulted in the loss of U.S. astronauts during the STS 51-L Challenger space shuttle mission. Another seventeen years would pass before the loss of the STS-107 Columbia space shuttle crew.
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Godwin, Robert, ed. Apollo 13: The NASA Mission Reports. Burlington, Ont.: Apogee Books, 2000. One in a series of collections of Apollo documents. This edition provides some preflight information and the Post-Flight Mission Operations Report, as well as the Report of the Apollo Accident Board. Includes many illustrations. -
Liebergot, Sy, and David Harland. Apollo EECOM: Journey of a Lifetime. Burlington, Ont.: Apogee Books, 2003. The story of one of the controllers who helped save the Apollo 13 crew. Liebergot gives an insider’s view of the workings of mission control and the non-Hollywood version of how they accomplished the nearly impossible. -
Murray, Charles, and Catherine Bly Cox. Apollo: The Race to the Moon. Burkittsville, Md.: South Mountain Books, 2004. An intriguing look at the people who worked on the Apollo program. Reference notes, black-and-white photographs. -
National Aeronautics and Space Administration. Apollo Mission Press Kits. http://www-lib.ksc.nasa.gov/lib/presskits.html. Official preflight information about Apollo 6 through Apollo 17. -
_______. Apollo 13 Mission Report. Available at http://history.nasa.gov/alsj/a13/A13_MissionReport.pdf/. This is the definitive, official report on the Apollo 13 mission. Covers all aspects of the mission from launch, through the accident, and on to the landing. Details the vehicle’s systems. -
_______. “Apollo 13 Technical Air-to-Ground Voice Transcription, April 1970.” Available at http://www .jsc.nasa.gov/history/mission_trans/AS13_TEC.pdf. A transcription of all communications between the Apollo 13 crew and ground control.
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