Apollo 13: The Greatest Feat of Improvised Engineering
Andrew Wheeler posted on April 15, 2020 |
A detailed look into the legendary Apollo mission 50 years later.

The legendary Apollo Program ran from 1961 to 1972. During a launch rehearsal exercise of the first mission of the program in February of 1967 (originally named AS-204), all three members of the crew (Command Pilot Virgil I. "Gus" Grissom, Senior Pilot Ed White, and Pilot Roger B. Chaffee) were killed when an electrical fire spread quickly through the cabin. The astronauts perished because the electrical fire rapidly spread through the nylon material lining the cabin and highly pressurized oxygen atmosphere. The high internal pressure of the cabin also prevented the door plug hatch from opening. The name of the mission was later changed to Apollo I at the request of the crew’s family members.

Despite this initial failure and horrible loss of life, the program continued. In October of 1968, the Apollo 7 is known as the first manned mission from the United States into space. The three-man crew orbited Earth for 11 days and returned successfully to Earth. In December of 1968, Apollo 8 carried the first American astronauts past low Earth orbit to the Moon. They orbited the moon and returned to Earth safely. On Apollo 8, the first humans (Frank Borman, James Lovell, and William Anders) bore witness toA the first Earthrise on their journey. Apollo 9 followed in March of 1969. It was the first test of the Saturn V rocket and served as a qualification mission to test the viability of the lunar module and the command service module for the future Moon landing. In May of 1969, Apollo 10 saw astronauts once again orbit the Moon in a full rehearsal for the lunar landing of Apollo 11.

Neil Armstrong. (Image courtesy of NASA.)
Neil Armstrong. (Image courtesy of NASA.)

In July of 1969 on the Sea of Tranquility, Neil Armstrong and Buzz Aldrin walked on the Moon while Michael Collins flew the command module Columbia above them. Apollo 12 launched the following November, and saw NASA complete its second successful landing of astronauts on the Moon. Two members of the team landed at the Ocean of Storms on the Moon near the Surveyor 3 probe, completed two moonwalks, and rejoined the third in the command module and made it back to Earth safely.

Apollo 13 and the Short Circuit from Hell

50 years ago, Apollo 13 completed its launch on April 11th, 1970. Astronauts Jim Lovell, Fred Haise and Jack Swigert (who replaced Ken Mattingly after the prime crew was exposed to rubella) spent 56 hours in space after enduring an early burnout of their center engine due to pogo oscillations interacting with turbopump cavitation. After finishing a TV broadcast, CAPCOM (capsule communicator) Jack Lousma began sending Jack Swigert directions which included a request from EECOM Sy Libergot (responsible for monitoring the command system module) to stir the oxygen tanks. Swigert obliged, and a little more than 90 seconds later, all hell broke loose. The astronauts heard a large bang, and communications with mission control cut out and thrusters went off as electrical power fluctuated wildly.

Stirring the fans in the tanks in the command module was generally done once daily, but the instrumentation on the oxygen tanks had been malfunctioning, so Libergot thought that by doing an addition stir would destratify the tanks, the readings would improve. “Okay, Houston, we've had a problem here," Swigert reported about 30 seconds later.

Diagram of the Apollo 13 Odyssey spacecraft. From left to right are the lunar module, command module and service module. (Image courtesy of NASA.)
Diagram of the Apollo 13 Odyssey spacecraft. From left to right are the lunar module, command module and service module. (Image courtesy of NASA.)

The service module’s oxygen tanks vented into space and two of its fuel cells died completely. The mission changed from a lunar landing to a rescue mission with one objective: to get the astronauts back to Earth safely. This was accomplished by transforming the lunar module, which was meant to support two astronauts for 45 hours, into a lifeboat that could support three astronauts for three days.

The improvised ingenuity and decision making by flight engineers at mission control was extraordinary:

·        From a hybrid trajectory destined for the moon, a new software procedure had to be written in order to correct the path of the Apollo 13 spacecraft to a free return trajectory (after deciding against a direct abort) using the less powerful descent propulsion system of the lunar module for fears that a burn by the command module’s propulsion system would cause a fatal explosion.

·        Jim Lovell performed calculations by hand to transfer the command module's guidance system to the lunar module’s guidance system.

·        The first burn to bring the Apollo 13 craft back to a free return trajectory lasted 34 seconds and was a success.

·        A second burn was performed without the guidance computer, using only the sun and the moon as reference points to correct trajectory for re-entry to Earth’s atmosphere.

·        A third burn was performed for Earth’s entry without the guidance computer, and at this time the astronauts used the line between night and day on Earth as a reference point.

·        Mission control came up with a series of procedures to create a device known as “the mailbox” to scrub more CO2 from the lunar module to support three astronauts for alonger period of time required to get them back to Earth.

·        A fourth burn was needed prior to re-entry, and was performed using the lunar module’s reaction control systems.

·        Prior to re-entry, mission control had to figure out how much air pressure to use when separating the lunar module from the command module.

How did a routine procedure cause an explosion?

The insulating material on the wires to oxygen tank 2 was at fault. It was wrapped around the wires with enough room for a short-circuit, which ignited the insulating (and combustible) Teflon material. The fire caused a massive increase of pressure inside the tank and its dome was unable to prevent oxygen and other combustible material to fill a fuel cell bay.

Scan of the Odyssey’s service module explosion from Apollo 13. (Image courtesy of NASA.)
Scan of the Odyssey’s service module explosion from Apollo 13. (Image courtesy of NASA.)

Teflon insulation on the wires to the stirring fan inside Oxygen Tank 2 allowed the wires to short-circuit and ignite this insulation. The resulting fire quickly increased pressure inside the tank and the tank dome failed, filling the fuel cell bay (SM Sector 4) with rapidly expanding gaseous oxygen and combustion products. The resulting pressure exploded an exterior aluminum panel from the service module. A resulting mechanical shock cut oxygen from two fuel cells, rendering them useless.

Bottom Line

The Apollo program continued for several years until budget cuts forced several missions to be canceled. The successful return of the Apollo 13 astronauts was perhaps one of the greatest feats of improvised engineering in human history. The crew remained completely calm (the portrayal of infighting in the Hollywood film is inaccurate) and level-headed despite the mortal danger. Training is absolutely grueling for manned-space missions, and the astronauts previous experience as experimental test pilots helped them remain calm during the perilous circumstances that they faced fifty years ago.

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