by S. Prasad Ganti

By 1970, man had been to the moon twice on successful Apollo 11 and 12 missions.  Jim Lovell the commander had dreamt for a long time to set his foot on the moon. Midway to the moon, a loud explosion destroyed an oxygen tank powering the fuel cells. Leaving the crippled spacecraft with much less power to the extent that landing on the moon was ruled out completely. Even getting the astronauts safely back to Earth was considered a slim chance.

Apollo 13 Crew: Commander, James A. Lovell Jr., Command Module pilot, John L. Swigert Jr.and Lunar Module pilot, Fred W. Haise Jr. Photo Credit: NASA

Since the near space disaster in 1970, a lot has been written about it: articles, a book, a documentary and a full-length feature film with Tom Hanks playing the role of Jim Lovell. The salvaging of the mission, returning the astronauts safely back to Earth and finding out the root cause of the loud explosion is considered a shining moment for NASA and its contractors who did all kinds of thinking on the steps to be taken for a safe return of the astronauts. The mission was later termed the most successful failure !

At the time of the launch, the whole rocket and the spacecraft looks like a huge tall metallic monster. The Saturn V rocket which pushed the spacecraft into the space along with the massive fuel tanks makes up bulk of the structure. Once in space, most of that structure was jettisoned. What went to the moon is just three compact pieces joined together like blocks of Lego: the Command Module, Service Module and the Lunar Module. The Command Module was used by astronauts to pilot the spacecraft to the moon. After reaching the moon, the Command Module along with Service Module orbitted the moon while the Lunar Module landed on the moon. Once the mission on the moon’s surface was over, the Lunar Module took off and joined with the orbiting Command Module and Service Module combination.

The Service Module contained all the support systems for the astronauts to live and work in the Command Module including generating power using the fuel cells that combine oxygen and hydrogen. With the explosion in the oxygen tanks, the power generation was almost lost. There was no chance of landing on the moon and no way to turn back either because in space a spacecraft keeps going in the same direction at the same speed. Any change in direction or speed requires burning fuel. The rescue plan was to reach the moon and use its gravity to sling back towards Earth.

The circumlunar trajectory followed by Apollo 13, drawn to scale; the accident occurred about 5½ hours from entry into the Moon’s sphere of gravitational influence. Credit: NASA

The Command Module was shut down to conserve power. It was required to reenter the Earth’s atmosphere. The Lunar Module then became the astronauts’ home for the remainder of the journey. The Lunar Module was not built to support three astronauts for four days. Only essential systems were switched.  The astronauts lay in the cold Lunar Module hanging on to a very slim hope of making it back home, while hundreds of engineers on the ground were figuring out power conserving strategies and the steps required to restart the Command Module, which was never shut down in space before.

As the spacecraft swung around the moon and headed home, the astronauts were in constant conversation with Mission Control trying to understand and review the checklists for the different maneuvers. As it neared the Earth, the Service Module was first jettisoned and then the Lunar Module, which provided hope and shelter for the astronauts on their long journey home. The Command Module was restarted and it reentered the Earth’s atmosphere. There is usually a radio silence of a few minutes during reentry due to interference to the radio waves. This time it was longer thereby extending the anxiety and suspense in the Mission Control. Finally the Command Module appeared in the sky and the astronauts were deposited on to the surface of the Pacific Ocean. The nation heaved a sigh of relief. The astronauts were honored by President Nixon.

For those who are technically inclined, here is the root cause of the explosion in the oxygen tank. There are thermostats in the tank which control the heat or cooling  in the tank. The thermostats were not redesigned when the specification for the electrical system changed from 28 to 65 volts. As a result, one of them malfunctioned  and caused heat to build up and destroy the insulation on the wiring. When the astronauts switched on a system to stir up the oxygen in the tanks on the way to moon, the wires short circuited and caused the damage.

But why did heat build up inside the tank in the first place? While on the ground, the tank was dropped accidentally. As a result, a drain pipe that is used to drain all the oxygen went out of alignment. This damage was not noticed. During the dress rehearsal, oxygen is filled and drained to check the different systems. The draining was not complete due to the problem with the pipe. The electric heater was switched on to boil off the liquid oxygen to drain completely. The heater stayed on due to the malfunctioning thermostat. Like the proverbial nail in the horseshoe which caused a battle to be lost, an inexpensive thermostat brought an expensive space mission to its knees.

Odyssey was the name of the Command module, and Aquarius was the name of the Lunar module. They proved to be apt names which came in handy during the nearly doomed mission !