Between life and death
Apollo 13 is a name that epitomizes a very special chapter in the history of astronautics and space travel: The mission symbolizes all the risks lurking in a technical discipline that was still young at the time, the courage and coolness of the astronauts, engineers, and mission control people, and the fact that minor human and technical inadequacies which mostly do not entail any consequences on Earth may quickly develop fatal or at least life-threatening effects in space.
At the end of the Apollo 13 mission, three astronauts had survived a terrible accident 328,300 kilometers away from Earth, had been saved in a nerve-wracking mental, technical, and physical tour de force, and had landed safely on Earth in the end. While many interpreted the mission‘s number ‘13’ as the writing on the wall that brought bad luck, it may well be that the figure ‘13’ ultimately symbolizes the good luck of the three rescued astronauts. The scientific destination of Apollo 13 was highly interesting. After no fewer than two superbly executed lunar landings followed by a safe return from the Moon, it appeared not only to the public that the Apollo program had become routine to a certain extent. While the first two landing sites had been chosen almost exclusively under safety aspects, the destination envisaged for the third lunar landing absolutely required a pinpoint landing. Moreover, it fulfilled a wish that was dear to the scientists’ heart: researchers were looking ahead with keen anticipation to the landing among the hills of the Fra Mauro formation.
The Commander of the mission was James Lovell, one of NASA‘s most experienced astronauts: the Apollo 13 mission was his fourth flight into space. He had already flown on Gemini VII and Gemini XII, and he also ‘knew’ the Moon because he had been on the crew of Apollo 8, which orbited the Moon for the first time at Christmas 1968. Fred Haise, who had no space experience, was assigned as Lunar Module Pilot. The man originally selected as the Command Module Pilot was Ken Mattingly. However, a few days before lift-off, the back-up Lunar Module Pilot, Charles Duke, was apparently taken ill with rubella, and as it turned out, Mattingly, who had naturally been frequently near Duke during the launch preparations, was not immune to the disease. Accordingly, NASA decided to replace Ken Mattingly with Jack Swigert, the back-up pilot.
Unlike the stormy launch of Apollo 12, the lift-off of Apollo 13 on April 11, 1970, at 14:13 local time was almost picture-perfect. During the ascent, engine number 5 in the second stage cut-off far too early, after no more than two minutes’ burn time. However, the launch sequence automatically compensated this by extending the burn time of the other four engines by 30 seconds. Having orbited the Earth as usual, Apollo 13, with the ‘Odyssey’ command module and the ‘Aquarius’ docked-on lunar module, entered a routine flight path to the Moon. The landing was scheduled for April 15.
328,300 kilometers away from Earth, with three quarters of the distance to the Moon travelled and 55 hours and 55 minutes of flight time behind them – it was, of course, April 13… – the three astronauts were startled by a loud bang in their spacecraft. They noticed immediately that two of the three fuel cells in the service module had ceased to function. This was the moment when Jack Swigert radioed to Earth, “OK Houston, we‘ve had a problem here”. Both the crew and the control center immediately realized that the astronauts’ lives were at stake. Looking out of the window of the command module, the astronauts saw that they were losing some kind of gas – it was oxygen. However, the worst part was the destruction of the fuel cells in which hydrogen and oxygen were combined to produce water and electricity. As the pressure in the service module’s oxygen tanks was falling quickly, it was obvious that the fuel cells would go on functioning only for a few hours more. The supply of electricity, water, and – most importantly – oxygen to the astronauts in ‘Odyssey’ was acutely threatened. The lunar landing had to be abandoned immediately to save the astronauts’ lives.
It was, however, decided not to turn back to Earth right away because it was doubtful whether the main engine was still functional. Led by the hard-boiled flight director Eugene ‘Gene’ Kranz (“Failure is not an option!”), Mission Control decided to take a daring step: Apollo 13 was to follow a path which would take it halfway around the Moon, whose attraction would correct its trajectory and bring it back on a flight path to Earth like a slingshot, after which Apollo 13 would be accelerated by the thrust of the engine of the lunar module. The maneuver was a success, but Apollo 13 was racing against time.
Because of the damage the service module had suffered, the crew had to move from the command module to the lunar module that now took on the function of a lifeboat. While there was enough oxygen on board, the life support systems of the lunar module had not been designed to keep three persons alive, particularly not for such a long period. For this reason, the astronauts’ lives were acutely threatened even in the lunar module because the proportion of exhaled carbon dioxide would rise to hazardous and ultimately fatal concentrations compared to the proportion of oxygen in the air.
To keep the air clean, both the command module and the lunar module were equipped with lithium hydroxide filters, which were used to operate the air purification system. However, the command module filter could not be used in the lunar module as the canisters differed in size and shape. At the same time, the quantity of lithium hydroxide available in the lunar module was only enough to purify the air for two astronauts, and for no more than about 30 hours. Now, however, it was supposed to clean the air for three astronauts during the four days, or 96 hours, of their return to Earth. Therefore, the filters had to be connected somehow. This problem was solved by engineers in Houston who experimented with the resources available on Apollo 13. They succeeded in cobbling together an adapter from tubes, plastic sample bags and duct tape. The crew imitated this improvisation, called ‘mailbox’ – and the filter worked. Electricity was another acute problem. At least, it proved feasible to string a cable from one of the lunar module’s batteries to feed electricity to the nearly-flat batteries of the command module.
The crux was the need to have enough power to ignite the engines before entering the Earth’s atmosphere. Consequently, all systems in the command module were switched off. Without the heat emanating from the electrical systems, the interior of the command capsule cooled down to 0°C. Moreover, the astronauts restricted their water ration to half a glass per person and day. To manage the entry into the Earth’s atmosphere, it was possible to use the systems of the command module, as the electrical installations had not been damaged by condensation or ice. After the separation of the service module and the lunar module, Apollo 13 entered the Earth’s atmosphere, coming down in the Pacific Ocean on April 17, 1970. Three astronauts emerged from the capsule, exhausted, emaciated, and marked – but alive and happy.
The rescue was one of NASA’s biggest-ever achievements. Despite the incredible relief at having saved the lives of the astronauts, NASA began to search for reasons immediately and uncompromisingly. After two months, the results were summarized in a tentative report. The accident had not had a single cause. It was the result of a concatenation and accumulation of human errors and technical defects.
Problems began as early as 1965, when engineers with the Apollo program decided to increase the voltage of the power supply system from 28 to 65 volts. However, the ‘chain reaction’ of necessary changes to the systems and components affected was not followed through, or else the need for downstream changes was not appreciated. Thus, it happened that the manufacturers of the oxygen tanks were not told of the voltage change. The equipment of these tanks included a propeller for stirring the cold semi-liquid ‘cryogenic’ oxygen, a heating element, and a thermostat designed to switch off the system if it should warm up beyond 25°C.
These three components were never adapted to the voltage increase. Even this would probably not have developed into a serious problem for Apollo 13 if an oxygen tank that had been originally installed in Apollo 10 had not been mechanically damaged as early as 1968. The damage was never properly investigated, and when this ‘tank number 2’ was experimentally drained a few days before the launch of Apollo 13, a residue of the cryogenic oxygen remained in the tank. The tank was heated for eight hours to expel the remaining oxygen. Originally designed for 28 volts, the thermostat was now exposed to 65 volts and a current of 6 amps, which heated up the cables so that they finally fused. Consequently, the thermostat was incapable of interrupting the flow of current under normal operating conditions, in particular during the flight of Apollo 13 to the Moon.
Therefore, ‘tank number 2’, which was designed for an operating temperature of 27°C, steadily heated up after lift-off, reaching a temperature of 370°C. After 55 hours and 54 minutes, Jack Swigert activated the propeller in the oxygen tank, which necessarily caused a short circuit. The heat of the tank ignited a mist of pure oxygen, pressure soared, and one minute later the tank exploded, damaging the neighboring ‘tank number 1’.
The texts presented here were created by the DLR Institute of Planetary Research and space expert Gerhard Daum for the exhibition ‘Apollo and Beyond’ at the Technik Museum Speyer. Among other things, the history of the Apollo programme is showcased in detail using both text and images. In addition, full-scale models of the Apollo 11 Lunar Module ‘Eagle’, the Apollo 15 Lunar Roving Vehicle and an Apollo space suit for visiting the Moon’s surface, as well as a 3.4-billion-year-old rock collected from the Apollo 15 landing site can be seen in a lunar landscape.