It was early morning in Houston when the first hint of trouble came. Watching his instrument console, an engineer on duty in Mission Control noticed an unusual temperature drop in the fuel system of one of the clusters of little steering rockets on the Apollo command and service modules (CSM) that had carried the second Skylab crew to their orbital home on July 28 and is needed to ferry them back to earth. About fifteen minutes later, the astronauts themselves became aware of the problem when an alarm went off aboard the space station, jolting them out of their sleep. Later, as they looked out of the window, they saw sparkling particles streaming by the orbital workshop. Said Skylab Commander Alan Bean with the coolness of a lunar-landing veteran: "We thought that was unusual." So it was. The temperature drop and the particles signaled a crisis that could lead to the first rescue mission in the history of space flight.
Controllers quickly determined the cause of the symptoms: a line from the tank containing the oxidizer necessary to fire the thrusters had apparently sprung a leak. That mishap—coupled with the earlier loss of oxidizer from a unit in one of the other four-nozzle clusters when a valve jammed during rendezvous with Skylab—left the ferry craft with part of its attitude control system not working. For several nerve-racking hours last week, NASA officials contemplated bringing the second crew of Skylab astronauts home immediately, lest any further deterioration in the Apollo rocket control system jeopardize their chances of a safe splashdown. By week's end the space agency had settled on a different course. For the time being at least, the Skylab team would be allowed to continue its record-breaking 59-day mission. As a safeguard, however, round-the-clock work was ordered at Cape Kennedy to prepare another Apollo craft for a rescue mission.
Skylab's most recent problem came only a day or so after Bean and Space Rookies Jack Lousma and Owen Garriott had finally overcome a bad case of motion sickness brought on by their exposure to zero G. During the initial stages of their mission, the crewmen—especially Lousma, who vomited several times—were barely able to perform routine housekeeping and experimental chores. But their "stomach awareness," as NASA euphemistically called it, was quickly overshadowed by the oxidizer leak.
The loss of the thrusters on Apollo's service module was not in itself critical. Experience in NASA'S ground simulators has shown that an Apollo spacecraft can be steered with only one service-module rocket cluster—or even with only the thrusters on the command module. What worried space-agency engineers was the possibility of further deterioration in the propulsion system. The small thruster systems, as well as Apollo's big main engine at the rear of the service module, use the same type of oxidizer. What is more, the chemical had come from the same batch at Cape Kennedy. Thus, if it contained some contaminant, all of the spacecraft's engine systems might well be imperiled.