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Apollo-13: The successful failure

Anatoly Zak, Spaceflight Correspondent
Apr 18, 2015, 2:31 UTC

Sen—Apollo-13, the only space mission to warrant a Hollywood thriller, lifted off on April 11, 1970, at 2:13 p.m. EST without much media fanfare. Being the third expedition to the Moon after the pioneering landing of Apollo-11 less than a year earlier, it blasted off into Florida skies over Cape Canaveral, as the public interest in the Apollo program was withering away.

Onboard were Commander James Lovell, veteran of three previous space missions, and rookie astronauts Jack Swigert, Command Module pilot, and Fred Haise, the Lunar Module pilot, set out on an expedition to rugged highlands near the ancient lunar crater Fra Mauro.

Minutes into the flight, during the second-stage firing of the giant Saturn-5 rocket, the central engine of a five-engine propulsion cluster cut off two minutes prematurely, but the smart flight control system kept the remaining four engines operating 34 seconds longer and also added an extra nine seconds to the third-stage burn, resulting in a normal parking orbit around the Earth. The third S-IVB stage then fired again, sending Apollo-13 to its rendezvous with the Moon.

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Mission Operations Control Room in Houston, during the fourth television transmission from the Apollo 13 mission on April 13, 1970. Eugene F. Kranz (foreground, back to camera), one of four flight directors watches astronaut Fred W. Haise Jr. on the screen. Image credit: NASA

For the next two days, Apollo-13 sailed uneventfully toward the Moon. When, on the evening of April 13, the crew conducted a live TV tour of the spacecraft, its viewers were mostly ground controllers, because no network was interested in broadcasting the live grainy pictures of the mission. Most reporters then left mission control for the night.

Then nine minutes later the real drama began when, during a routine test of a cryogenic oxygen tank, astronauts suddenly heard a bang, vibration and saw ominous warning lights on their control panels. With their professional calm, they radioed to mission control what would become perhaps the world's most famous understatement: "Houston, we've had a problem." In fact Apollo-13 had experienced a real catastrophe and was about to embark on a perilous mission of survival.

It took the mission control and the crew around a dozen minutes to understand the gravity of the situation based on a cascade of worrisome data: power batteries detected low voltage, the two out of three fuel cells, which supplied Apollo spacecraft with electricity, water and oxygen, appeared to be dying, followed by an apparent loss of pressure in a second and last oxygen tank. Finally, a fountain of gas behind the window blew away the last hopes that all the warning lights could've resulted from some faulty sensors or some electric phenomenon. The astronauts' initial regrets about a missed opportunity to walk on the Moon quickly changed to thoughts about the possibility of surviving the ordeal.

As it transpired later, a botched ground test damaged electric wiring inside one of the liquid oxygen tanks. A short circuit during the testing of the same tank in flight triggered an explosion that blew off an exterior panel of the service module, but let the vacuum of space extinguish the fire. However, by that time, the service module was essentially out of commission. 

With key resources onboard the command module heading toward depletion, the crew quickly powered down its systems and moved to the lunar lander, which was now converted into an improvised lifeboat. Unfortunately, the lifeboat metaphor was not really accurate, because the Lunar Module could not land on Earth. If the stranded astronauts ever had a chance to approach the home planet, they would have no choice but to attempt to revive their crippled capsule with whatever resources left in it for the ultimate fiery descent through the Earth atmosphere. However, first they had to make a four-day journey through space in a slowly freezing spacecraft.

A day before the accident, the Apollo-13 left a free-return trajectory, which could take it back to Earth without any rocket thrust. After some discussion during the night, mission control decided not to attempt a sharp U-turn, but let the Apollo-13 gently swing around the Moon and then head back home along a carefully choreographed trajectory propelled by the engines of the Lunar Module.

On the morning of April 14, the crew conducted the first trajectory correction maneuver, which increased its closest pass near the Moon from 69 to 164 miles and put it roughly on the way toward Earth. Although a cloud of debris surrounding the damaged ship made navigation by the faint stars impossible, Houston quickly provided the crew with a backup method relying on the Sun, which allowed them to put the ship into the right orientation for all the crucial maneuvers.

The same night, after a short disappearance behind the Moon's far side, the Apollo-13 fired its engine one more time to cut the travel time to Earth. A day later, another maneuver adjusted the trajectory for a more accurate rendezvous with the home planet and Apollo-13 then sailed passively toward Earth.

In the meantime, the crew faced another potentially deadly problem: the life-support system onboard the Lunar Module designed for only two astronauts struggled to scrub carbon dioxide produced by three people. As a result, astronauts faced the risk of suffocation in the air contaminated with the exhaust from their own lungs. But, yet again, uncelebrated engineers on the ground improvised an ingenious solution. Using cardboard, tape, plastic bags and hoses from lunar spacesuits, astronauts assembled an improvised air-filtering system dubbed the 'mail box' from extra canisters "imported" from the command module. Amazingly, it worked.

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Interior view of the Apollo 13 Lunar Module (LM) showing the "mail box," a made on the fly solution to use the Command Module (CM) lithium hydroxide canisters to purge carbon dioxide from the LM. Image credit: NASA

On April 17, after more than three days of travel in their crippled ship, tired, cold, hungry and dehydrated astronauts approached the Earth.

At 8:15 a.m., the service module was jettisoned from the rest of the stack and, as it was floating away, the enormous extent of damage to the spacecraft had finally become apparent. Mission officials insisted on keeping the Service Module attached for all that time as extra protection for the critical heat shield on the Command Module. Fortunately, astronauts were able to revive their frozen capsule and at 11:43 a.m. it separated from the now empty Lunar Module.

Despite a mini-rain shower inside the cabin from all the moisture during the descent, no electrical system experienced a short-circuit and Apollo-13 splashed down safely in the South Pacific at 1:08 p.m.

Less than an hour later, Lovell, Haise and Swigert were safely onboard the aircraft carrier Iwo Jima, concluding the mission, which became known as the "successful failure".

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The Apollo 13 crew (from L to R: Fred Haise, James Lovell and John Swigert), step aboard the USS Iwo Jima, after splashdown and recovery operations in the South Pacific Ocean. Image credit: NASA