Apollo 13: The Moon Lander That Became a Lifeboat

Flight surgeons drew blood from the astronauts at their physical exams on Monday 6 April, five days before launch, to look for antibodies against rubella. Jim Lovell and Fred Haise were immune, as were the backups John Young and Jack Swigert. Ken Mattingly had no immunity. As command module pilot, Mattingly was due to orbit the Moon alone in Odyssey while Lovell and Haise explored the surface. Programme managers now had to decide who would fly.

NASA had a fallback: if the April launch slipped, May dates would be used for the same Fra Mauro mission. Jim Lovell argued to keep Ken Mattingly and fly in April, but NASA Administrator Thomas Paine said no. Jack Swigert, the backup command module pilot, was declared ready after refresher training and simulator runs with Lovell and Fred Haise. On 10 April, the day before liftoff, NASA made the final decision. It was the first time a member of an Apollo prime crew had been replaced so close to launch.

Apollo 13 lifted off from Launch Pad 39A at NASA’s Kennedy Space Center at 1:13 p.m. Houston time on 11 April 1970. About five and a half minutes into the flight, the centre engine of the Saturn V’s second stage shut down more than two minutes early. The other four engines burned longer to make up for it, and the third stage also fired longer than planned. The shutdown was later traced to severe vibrations known as pogo. Apollo 13 still reached Earth orbit, and the third stage then sent the spacecraft towards the Moon.

Apollo 13 left Earth on a free-return trajectory. On that path, if the service module’s main engine failed, the spacecraft would loop around the Moon and head back to Earth without major corrections. But the free-return path limited where a crew could land. To reach the Fra Mauro highlands, Apollo 13 had to leave the free-return path for a new one. About 30 hours and 40 minutes into the flight, the crew fired the main engine, the Service Propulsion System, and made the switch. The crew sent television pictures from the spacecraft around the time of the burn.

The oxygen tank at the centre of the accident had a troubled history. Oxygen tank 2 was first installed in the service module meant for Apollo 10. It was removed for modification in 1968 and dropped about 5 cm during the work, then later fitted to Apollo 13. During a countdown test at Kennedy Space Center in March 1970, tank 2 would not empty normally. Engineers boiled the remaining oxygen off with the tank’s heater, using ground power for about eight hours. On 13 April, the stir Houston requested was the third of the mission for the oxygen tanks.

The bang came about 55 hours and 55 minutes into the flight. Within seconds, a master alarm went off. A warning light showed low voltage on Main Bus B, one of the spacecraft’s two main power circuits. On the ground, data from the spacecraft dropped out for 1.8 seconds. The crew first suspected that something had struck the lunar module and tried to close the hatch between the two spacecraft. In Mission Control, Flight Director Gene Kranz and his team began sorting real failures from possible faulty readings.

Jim Lovell saw gas venting into space, which showed that the trouble was real, not a faulty gauge. Oxygen tank 2 already read empty. The explosion had also damaged a line or a valve on oxygen tank 1, which was now losing pressure. Two of the three fuel cells, which combined oxygen and hydrogen to make the spacecraft’s electricity, were off line. In Mission Control, Flight Director Gene Kranz told his team: “Let’s solve the problem but let’s not make it any worse by guessing.” NASA abandoned the Moon landing.

Jack Lousma was the Capcom, the astronaut in Mission Control who spoke directly with the crew. As oxygen tank 1 emptied, Lousma told the crew, “It’s slowly going to zero, and we’re starting to think about the LM lifeboat.” Jack Swigert replied, “Yes. That’s what we’re thinking about, too.” Aquarius was built to support two men for about two days. It now had to keep three men alive for about four. Flight Director Glynn Lunney’s team, which had taken over from Gene Kranz’s, directed the power-up of the lander. Odyssey was shut down to save what was left for re-entry.

Mission Control had two basic ways to bring the crew home. A direct return would have turned back without going around the Moon. It meant casting off the lunar module and making a very large burn with the service module’s main engine. That engine sat next to the damaged area, and controllers could not be sure it still worked. The other way was to loop around the Moon. The lunar module’s descent engine, built to slow the lander for a Moon landing, would adjust the path. Mission Control chose the loop around the Moon.

The burn came about 61 and a half hours into the flight, about five and a half hours after the explosion. Aquarius’s descent engine, normally used to land on the Moon, pushed the docked spacecraft back onto a free-return path. On that path alone, Apollo 13 would have splashed down in the Indian Ocean. Planners were already working on a second, longer burn after the Moon to bring the crew home sooner. Until then, the crew flew the joined spacecraft from the lander, conserving power and water.

Debris from the damaged service module drifted alongside the spacecraft and glittered in the sunlight. The particles looked like stars, and they made it impossible to sight real stars through the lunar module’s alignment telescope. Without star sightings, the crew could not confirm in the usual way that the guidance platform was aligned. Mission Control worked out a check that pointed the telescope at the Sun instead, as if it were a star. The check showed the platform was off by about half a degree, close enough for the long burn ahead.

Apollo 13 passed behind the Moon on 14 April 1970, on the far side from Earth. At the farthest point, the crew was 400,171 km from Earth, a record for human spaceflight. Jack Swigert and Fred Haise, on their first trip to the Moon, photographed the Moon’s surface. Around the same time, Mission Control told the crew that the spent third stage of their rocket had hit the Moon as planned. The seismometer left behind by the Apollo 12 crew recorded the impact.

The burn was called PC+2, because it came two hours after pericynthion, the spacecraft’s closest point to the Moon. Aquarius’s descent engine fired for 4 minutes and 24 seconds. The burn moved the planned splashdown from the Indian Ocean to the Pacific. After the burn, the crew powered Aquarius down to save its batteries. With the electronics switched off, the cabins lost an important source of heat, and the temperature dropped.

Aquarius carried lithium hydroxide canisters to remove carbon dioxide from the air, but not enough for three men all the way home. Odyssey had spare canisters, but they were square and did not fit the lander’s round openings. In Houston, a Crew Systems Division team including chief Ed Smylie worked out an adapter made only from items the crew had aboard. Joe Kerwin, the astronaut in Mission Control who spoke directly with the crew, read the instructions to them. After the crew installed the adapter, carbon dioxide levels fell.

Water was a critical supply. Aquarius used water to cool its electronics as well as for drinking, so the crew rationed it strictly. The cold also made sleep difficult. Jim Lovell lost about 6 kg. Fred Haise developed a urinary tract infection during the flight. Haise was treated for it in the recovery ship’s sick bay after splashdown. All three men were extremely tired when they reached the recovery ship.

The burn was needed to fine-tune the angle at which Apollo 13 would enter Earth’s atmosphere. The lander’s guidance computer did not steer the burn. Instead, the crew held the spacecraft’s angle by sighting Earth and the Sun through the windows, with Mission Control’s instructions. The descent engine fired about 105 hours and 18 minutes into the flight. It was the last firing of Aquarius’s descent engine; a final small correction before re-entry used the lander’s thrusters.

Charging Odyssey’s batteries from Aquarius reversed the usual flow of power. Normally, the command module supplied the lander when the lander was first switched on. The crew connected the two spacecraft with the power cables, called umbilicals, that ran between them. Jack Lousma, the astronaut in Mission Control who spoke directly with the crew, told them the charge would take about 15 hours. The power from Aquarius recharged Odyssey’s re-entry batteries. Odyssey needed those batteries to run on its own for the final hours of the flight, after the lander was gone.

Mission Control kept the service module attached until shortly before re-entry. Engineers feared that cold space could damage the command module’s heat shield if it were left exposed. When the service module drifted free, the crew photographed it. Jim Lovell said: “Right by the high gain antenna, the whole panel is blown out, almost from the base to the engine.” Fred Haise added, “It’s really a mess.” The Review Board later found that escaping oxygen had blown off the panel covering bay 4.

Ken Mattingly took over as Capcom, the astronaut in Mission Control who spoke directly with the crew. Mattingly read the crew the long, new procedures for bringing Odyssey back to life. The command module had been powered down and cold for days, and its systems had to be restarted in a careful sequence before re-entry. A coded radio exchange about whether the flowers were in bloom in Houston had confirmed that Mattingly still had no symptoms of German measles. Mattingly did not catch the disease.

The crew released Aquarius about 141 and a half hours into the flight, roughly an hour before Odyssey met the atmosphere. To push the lander away, the crew closed the hatches. The remaining air pressure in the tunnel between the two spacecraft drove it off. Aquarius then entered Earth’s atmosphere. The parts that survived re-entry, including the nuclear power source meant for its Moon experiments, fell into the Pacific Ocean.

During re-entry, ionised air around the capsule cut off radio contact for several minutes, a normal blackout. Two drogue parachutes and then three main parachutes slowed Odyssey. The capsule splashed down 142 hours, 54 minutes and 41 seconds after launch, about 7 km from the recovery ship USS Iwo Jima. Navy swimmers and a helicopter brought the crew aboard. President Richard Nixon telephoned the crew in the ship’s sick bay. Because Apollo 13 had not landed on the Moon, the crew did not go into quarantine.

NASA set up the Apollo 13 Review Board on 17 April 1970, the day of splashdown. Edgar Cortright of NASA’s Langley Research Center was its chair. Cortright released the report on 15 June 1970. He said the accident came from “an unusual combination of mistakes coupled with a somewhat deficient and unforgiving design.” For Apollo 14, engineers added a third oxygen tank in a separate bay. Engineers also removed the stirring fans from the tanks and sheathed the wiring in stainless steel. Apollo 14 later landed at Fra Mauro, Apollo 13’s planned site.