The Apollo 13 mission, which launched on April 11, 1970, was NASA’s third attempt to land humans on the Moon. It was NASA’s third moon-landing mission, but the astronauts never made it to the lunar surface. What began as a routine lunar mission quickly transformed into a life-threatening ordeal that captivated the world and showcased the resilience, ingenuity, and teamwork of NASA’s engineers, scientists, and astronauts. This “successful failure” is remembered not for achieving its original goal, but for overcoming extraordinary obstacles to return its crew safely to Earth. Apollo 13 was part of NASA’s Apollo program, which aimed to explore the Moon and advance human spaceflight capabilities. The mission’s primary objectives were to land on the Moon’s Fra Mauro highlands to collect geological samples to deploy scientific instruments to study the Moon’s surface and environment; and testing the spacecraft’s systems for extended lunar operations. The crew consisted of:
James A. Lovell Jr. (Commander): A veteran astronaut and the first person to fly into space four times.
Fred W. Haise Jr. (Lunar Module Pilot): Tasked with exploring the Moon’s surface.
John L. Swigert Jr. (Command Module Pilot): A last-minute replacement for Ken Mattingly, who was exposed to German measles.
The mission began smoothly, but a combination of technical issues, procedural oversights, and unforeseen circumstances led to a near-catastrophic failure. On April 13, 1970, two days into the mission, the crew was instructed to “stir” the oxygen tanks to ensure proper mixing and prevent stratification of the liquid oxygen. This routine procedure involved activating fans inside the tanks. However, when the stir was initiated, the damaged wiring inside Oxygen Tank 2 sparked, igniting the Teflon insulation and causing a catastrophic explosion. The explosion destroyed Oxygen Tank 2 and damaged Oxygen Tank 1, causing a rapid loss of oxygen in the Service Module. The oxygen tanks supplied not only breathable air but also fuel for the spacecraft’s fuel cells, which generated electricity and water. As a result, the spacecraft’s electrical power dwindled, water reserves became critically low and the Command Module (Odyssey) systems had to be shut down to conserve power for reentry. The blast also damaged adjacent systems, including the Service Module’s exterior. Debris from the explosion struck other components, exacerbating the spacecraft’s problems. The explosion altered Apollo 13’s trajectory. The crew needed to perform precise manual course corrections to ensure the spacecraft remained on a “free-return trajectory,” a path that would loop them around the Moon and back to Earth using the Moon’s gravity.
The disaster’s root cause
The disaster’s root cause lay in a series of events that began long before Apollo 13’s launch:
Damaged Teflon Insulation: During manufacturing, the oxygen tank’s Teflon insulation around internal wiring was inadvertently damaged when the tank was dropped about two inches. While the tank passed initial inspections, this flaw would prove critical.
Electrical System Mismatch: The tank’s heaters were designed to operate on 28 volts, the standard voltage for Apollo spacecraft. However, ground testing equipment supplied 65 volts, which damaged the wiring over time. All components were upgraded to accept 65 volts except the heater thermostatic switches, which were overlooked. These switches were designed to open and turn off the heater when the tank temperature reached 80 degrees F. (Normal temperatures in the tank were -300 to -100 F.)
Insufficient Testing: A procedural oversight during testing meant the tank’s wiring damage went undetected. Engineers did not realize the extent of the degradation caused by prolonged exposure to high voltage.
The Lunar Module (LM), Aquarius, was designed to support two astronauts for approximately 45 hours during lunar surface operations. Following the explosion, it became the crew’s lifeboat, supporting three astronauts for nearly 90 hours. The Lunar Module’s limited battery capacity required the crew to conserve power by shutting down non-essential systems. This led to minimal lighting and heat, resulting in extremely cold cabin conditions and restricted use of communication systems. With three astronauts in a confined space, carbon dioxide (CO₂) levels began to rise dangerously. The Lunar Module’s lithium hydroxide canisters, used to scrub CO₂ from the air, were insufficient for the extended duration. Engineers on Earth devised an improvised solution using materials onboard, including duct tape, plastic bags, and a flight manual cover. Adaptation of Command Module canisters to fit the Lunar Module system was done. The crew performed critical burns to adjust their trajectory manually, relying on basic tools like a sextant and Earth’s position in the spacecraft’s windows for alignment. Despite the challenges, these maneuvers ensured Apollo 13 remained on a safe return path.
“Square peg in a round hole” CO₂ filter
The “square peg in a round hole” CO₂ filter was a creative and critical fix devised by NASA engineers during the Apollo 13 mission to address a life-threatening problem: the rising levels of carbon dioxide (CO₂) in the spacecraft. As alrsady stated, after the oxygen tank explosion disabled the Command Module (Odyssey), the crew moved into the Lunar Module (Aquarius), which had a functional life-support system. However, the Lunar Module was designed to support two astronauts for two days, not three astronauts for four days. The CO₂ removal system in the Lunar Module used lithium hydroxide (LiOH) canisters to scrub carbon dioxide from the air. However, the Lunar Module ran out of its rectangular LiOH canisters. The Command Module, which had a supply of canisters, used square-shaped filters that were incompatible with the Lunar Module’s round system. Without a way to remove CO₂, the buildup of carbon dioxide in the Lunar Module could have quickly reached toxic levels, endangering the crew’s lives. Engineers on the ground at NASA Mission Control devised a workaround to fit a square Command Module CO₂ filter into the round Lunar Module system– hence the phrase “square peg in a round hole.” Using materials readily available to the crew onboard the spacecraft, the fix required a plastic bag, cardboard from a flight manual cover, duct tape (a staple onboard every spacecraft) and hoses from the spacesuits. The solution involved creating an improvised air duct to funnel air through the square LiOH canisters, securing the canister and hoses with duct tape and plastic to ensure a tight seal and using the Lunar Module’s airflow system to pull air through the makeshift filter. NASA engineers relayed step-by-step instructions to the Apollo 13 crew on how to build the improvised filter. The crew successfully assembled and installed the device, allowing the CO₂ levels to drop to safe levels. The “square peg in a round hole” fix became one of the most famous examples of NASA’s ingenuity and problem-solving under pressure. It is often cited as a testament to human creativity and teamwork in crisis situations.
Ground Control: NASA’s Ingenious Problem-Solving
The mission control team at NASA’s Johnson Space Center, led by Flight Director Gene Kranz, worked tirelessly to devise solutions to Apollo 13’s cascading failures. About an hour after the accident, mission control announced that “we are now looking toward an alternate mission, swinging around the Moon and using the lunar module power systems because of the situation that has developed here this evening.” The astronauts were to move into Aquarius, which would serve as a lifeboat, while the disabled Apollo 13 swung around the Moon and headed homeward. All thoughts of a lunar landing had long since been abandoned. NASA’s efforts included:
Conserving Resources: Calculating the minimum power and water requirements for the crew’s survival.
Testing Solutions: Simulating and validating procedures in real time using ground-based simulators before relaying instructions to the crew.
Boosting Morale: Maintaining clear and calm communication to keep the astronauts focused and reassured.
Re-entry and splashdown
The re-entry and splashdown of Apollo 13 marked the dramatic conclusion of one of NASA’s most perilous missions. As already stated, NASA engineers devised and implemented innovative procedures to correct Apollo 13’s trajectory, ensuring the spacecraft would re-enter Earth’s atmosphere at the correct angle. Any deviation could have caused the capsule to skip off the atmosphere or burn up. The astronauts endured harsh conditions, including extreme cold, water rationing, and rising carbon dioxide levels, which were mitigated with creative solutions like the “square peg in a round hole” CO₂ filter fix. On April 17, 1970, Apollo 13 began its re-entry into Earth’s atmosphere. Re-entry was particularly tense because spacecraft had sustained severe damage, raising doubts about the integrity of the heat shield. Also, the angle of re-entry needed to be precise- too shallow, and the spacecraft would skip off the atmosphere; too steep, and it would burn up. Furthermore, communications were expected to be lost for about 4 minutes during the ionization blackout as the spacecraft traveled through the atmosphere. Apollo 13 experienced a communication blackout longer than expected (about 6 minutes), causing extreme anxiety among mission control and the public. At 1:07 PM EST on April 17, 1970, the Command Module (Odyssey) splashed down safely in the Pacific Ocean near Samoa, approximately 4 miles (6.5 km) from the recovery ship, USS Iwo Jima. Recovery teams quickly reached the crew and ensured their safe return. The successful return of the Apollo 13 crew is considered one of NASA’s greatest achievements under pressure. It demonstrated extraordinary teamwork, problem-solving, and perseverance. The mission was famously described by Jim Lovell as a “successful failure” because, although the Moon landing was aborted, the safe return of the astronauts turned the near-tragedy into a triumph of ingenuity and human spirit.
Apollo 13’s failure to land on the Moon was a setback for NASA’s Apollo program, but its successful recovery transformed it into a triumph of human ingenuity. The mission demonstrated that even in the face of near-certain disaster, determination, resourcefulness, and teamwork could achieve the extraordinary. The lessons learned from Apollo 13 have continued to influence space exploration and remain a testament to the resilience of the human spirit.
