Navy Mark IV - Project Mercury

Project Mercury

When NASA began the Mercury Project in 1958, one of the first needs was a "spacesuit" -- a pressure suit to protect the astronaut in the event of a sudden depressurization of the cabin in the vacuum of space. NASA tested both the Navy Mark IV suit and the X-15 high-altitude suit, and chose the Mark IV, because it was less bulky than the David Clark suit, and could be easily modified for the new space role.

The Mercury suit incorporated several changes from the Navy Mark IV:

• Replacement of the "open loop" breathing system with a "closed loop" system, eliminating the rubber diaphragm around the wearer's face. Oxygen entered the suit through a hose connected at the wearer's waist, circulated through the suit to provide cooling, and exited through a hose on the right side of the helmet, or through the face opening depending on whether the faceplate was closed or open. A small pressure bottle connected by a small hose to a connector next to the astronaut's left jaw was used to pressurize a pneumatic seal when the faceplate was closed.
• Replacement of the dark gray nylon outer shell with one made of aluminum-coated nylon, for thermal control purposes
• Replacement of the black leather safety boots with ones made first from white coated leather, later aluminumized nylon-coated leather, again for thermal control.
• Introduction of straps and zippers to provide a snug fit, along with refinements in the shoulder, elbow, and knee retaining cords
• Special gloves with four curved fingers for grasping the controls, with the middle finger made straight for pushing buttons and flipping toggle switches. (In the book We Seven, the astronauts pointed out that the special design of the gloves allowed them to avoid the use of a "swizzle stick" for the buttons and switches.)
• A "biomed" flap on the right thigh for the connection of biomedical connections to the spacecraft's telemetry systems.

Each astronaut had three pressure suits: one for training, one for flight, and one for a backup. All three suits cost $20,000 USD total and unlike the military Mark IV suits, had to be individually tailored to each astronaut.

No Mercury pressure suit ever failed during launch. No Mercury capsule ever lost pressure during a mission, so the suits never needed to be inflated after launch. The only suit-related incident was an uncapped ventilation inlet valve which almost led to the drowning of astronaut Gus Grissom: at the end of the MR-4 mission the hatch cover blew off while in the Atlantic Ocean and the capsule began to fill with water, forcing Grissom to make an emergency exit without securing his suit for the recovery operations. The most frequent suit complaints of the astronauts were discomfort due to poor temperature control, and inability to turn the head within the pressurized suit.