The Spacesuit - A Primer on Spacesuits

An electrical harness inside the suit connects the communications carrier assembly and the biomedical instrumentation equipment to the hard upper torso where internal connections are routed to the extravehicular communicator by means of a pass-through.

The extravehicular communicator attaches to the upper portion of the life support system at the back of the hard upper torso. The controls are located on the display and control module mounted on the chest at the front of the upper torso. The extravehicular communicator provides radio communication between the suited crew member and the orbiter. In addition, electrocardiographic (EKG) information is telemetered through the extravehicular communicator to the orbiter and to flight surgeons in the Mission Control Center at Houston, Texas.

The radios for spacewalk communications have two single UHF channel transmitters, three single-channel receivers, and a switching mechanism. These backpack radios have a "low profile" antenna--a foot long rectangular block fitted to the top of the PLSS. The radios weigh 8.7 pounds and are 12 inches long, 4.3 inches high, and 3.5 inches wide.

Primary life support system

The PLSS consists of a backpack unit permanently mounted to the hard upper torso of the suit and a control-and-display unit mounted on the suit chest. The backpack unit supplies oxygen for breathing, suit pressurization and ventilation. The unit also cools and circulates water used in the liquid cooling ventilation garment controls ventilation gas temperature, absorbs carbon dioxide, and removes odors from the suit atmosphere. The secondary oxygen pack attaches to the bottom of the PLSS and supplies oxygen if the primary oxygen fails. The control-and-display unit allows the crew member to control and monitor the PLSS, the secondary oxygen pack, and, when attached, the manned maneuvering unit.

Maneuvering in space

The manned maneuvering unit (MMU) is a one-man, nitrogen-propelled backpack that latches to the EMU spacesuit's PLSS. Using rotational and translational hand controllers, the crew member can fly with precision in or around the orbiter cargo bay or to nearby free-flying payloads or structures, and can reach many otherwise inaccessible areas outside the orbiter. Astronauts wearing MMU's have deployed, serviced, repaired, and retrieved satellite payloads.

The MMU propellant-non-contaminating gaseous nitrogen stored under high pressure--can be recharged from the orbiter. The reliability of the unit is guaranteed with a dual parallel system rather than a backup redundant system. In the event of a failure in one parallel system, the system would be shut down and the remaining system would be used to return the MMU to the orbiter cargo bay The MMU, which weighs 310 pounds, includes a 35-mm still photo camera that is operated by the astronaut while working in space.

History Of Spacesuits

The Mercury spacesuit was a modified version of a U.S. Navy high altitude jet aircraft pressure suit. It consisted of an inner layer of Neoprene-coated nylon fabric and a restraint outer layer of aluminized nylon. Joint mobility at the elbow and knees was provided by simple fabric break lines sewn into the suit; but even with these break lines, it was difficult for a pilot to bend his arms or legs against the force of a pressurized suit. As an elbow or knee joint was bent, the suit joints folded in on themselves reducing suit internal volume and increasing pressure. The Mercury suit was worn "soft" or unpressurized and served only as a backup for possible spacecraft cabin pressure loss--an event that never happened. Limited pressurized mobility would have been a minor inconvenience in the small Mercury spacecraft cabin. Spacesuit designers followed the U.S. Air Force approach toward greater suit mobility when they began to develop the spacesuit for the two-man Gemini spacecraft. Instead of the fabric-type joints used in the Mercury suit, the Gemini spacesuit had a combination of a pressure bladder and a link-net restraint layer that made the whole suit flexible when pressurized. The gas-tight, man-shaped pressure bladder was made of Neoprene-coated nylon and covered by load bearing link-net woven from Dacron and Teflon cords. The net layer, being slightly smaller than the pressure bladder, reduced the stiffness of the suit when pressurized and served as a sort of structural shell, much like a tire contained the pressure load of the innertube in the era before tubeless tires. Improved arm and shoulder mobility resulted from the multilayer design of the Gemini suit.