PORTABLE LIFE-SUPPORT SYSTEM

On 15 October 1962 Hamilton Standard of Windsor Locks, Connecticut, initiated development of the Portable Life-Support System (PLSS) for use by an astronaut on the lunar surface. It had to be able to accommodate the metabolic heat liberated by a man doing the equivalent of shovelling sand and, for short periods, sawing wood without overheating or fogging the visor. An attempt to use the oxygen circulation system of the space suit proved to be inadequate, and in September 1964 it was decided to develop an undergarment incorporating a network of fine tubes through which cool water could be pumped. In 1965, with the PLSS growing in size and complexity, consideration was given to cancelling it in favour of just providing the astronauts with 50-foot umbilicals that would snake out of the hatch, even though this would have restricted lunar surface activity to the immediate vicinity of the LM. Fortunately, the pace of development promptly improved. The backpack was 26 inches high, 18 inches wide and 10 inches deep, and contained: (a) a primary oxygen system to regulate the suit at 3.7 pounds per square inch; (b) a ventilator to circulate oxygen, both for breathing and to cool, dehumidify, and cleanse the suit of carbon dioxide and other contaminants; (c) a loop to circulate 4 pounds of water per minute through the liquid-coolant garment; (d) a sublimator to shed waste heat to vacuum; and (e) a communications system to provide primary and backup voice relay via the LM. Each internal system was covered by a thermal insulator of fire-resistant beta cloth, and the entire pack was covered with aluminised kapton to minimise heat transfer and fibre-glass as protection against incidental damage. It had sufficient water and oxygen for 4 hours of nominal operation, but this would begin at the time of disconnecting from the LM’s life-support system, prior to egress, and run on after ingress until switching back to the LM. However, as no one could be certain of the metabolic rate of a man on the lunar surface, and therefore of the rate at which oxygen and coolant would be consumed, it was decided to limit the first moonwalk to half of this time. If a second moonwalk were to be scheduled then the PLSS would be replenished as necessary from the LM’s resources.

When Apollo 9 lifted off on 3 March 1969 with LM-3, mission commander Jim McDivitt thought that if they achieved only 50 per cent of their demanding program they would still be able to declare the mission a success. Rusty Schweickart was to test the PLSS by emerging from the forward hatch of the LM, translating along a

Nevertheless, if it had been decided that Aldrin should egress first, it would have been possible for them to switch places prior to donning their bulky backpacks.

handrail onto the roof of the vehicle, grasping a shorter rail on the CSM and entering the command module through its side hatch, so rehearsing the external transfer that would be used in the event of a returning lunar crew being unable to employ the tunnel in the docking system. However, when Schweickart suffered ‘space sickness’ early in the flight his spacewalk was limited to the ‘porch’ of the LM. Nevertheless, the 38-minute excursion was sufficient to demonstrate the PLSS in the space environment, and no one seriously doubted that an external transfer between vehicles was feasible.