A suit adapted, not invented
The Mercury program flew the first American astronauts, beginning with suborbital flights in 1961 and orbital flights in 1962. For clothing, the program chose to adapt an existing garment rather than design a new one. The starting point was a full-pressure suit used by the U.S. Navy for high-altitude flight, the Mark IV, whose history is covered in the story of pressure suits for pilots. Engineers modified it for the capsule, and the result is the well-known silver Mercury suit.
The Soviet Union flew Yuri Gagarin in April 1961, soon after the Sputnik launch of 1957 had opened the space age, a few weeks before Alan Shepard’s first flight on May 5, 1961. Mercury was therefore the American answer to an existing lead, and the suit was designed in a hurry by comparison with later programs.
What it looked like and what it was made of
The suit’s most striking feature was its metallic appearance. The outer layer was a nylon fabric with an aluminized coating, which reflected heat. Underneath was an inner layer of rubber-coated fabric that held the gas, with a layer of restraining fabric between them. The visible hardware included:
- a helmet with a hinged visor
- gloves that locked to the suit sleeves with rings
- boots built into the garment
- hoses for oxygen, carried from the capsule’s supply
The suit used the same chemistry of synthetic fibers and coated fabrics that was behind earlier aviation suits. It was made in several sizes and then adjusted for each astronaut.
A backup, not a spacewalk suit
The suit’s role is often misunderstood. In normal flight the capsule cabin was kept at a pressure of roughly 5 psi in pure oxygen, and the suit was worn unpressurized, with oxygen flowing through it. It would inflate only if the cabin lost pressure. In other words, it was an emergency protection layer, similar in purpose to the earlier suits for pilots.
The suit was also never used for spacewalking. It had no independent backpack and no way to shed heat in a vacuum. Walking outside the spacecraft was a problem that later suits, ending with the lunar spacesuits, had to address.
Air moved through the suit and across the body helped with cooling, though crews did report being warm during certain parts of flights. Shepard’s first flight had no urine collection arrangement, and delays on the pad meant he had to relieve himself inside the suit. Later flights added a collection device. These are small details that show how early the design was.
Fitting each astronaut
Each of the seven Mercury astronauts was measured, and suits were individually fitted. Measurements for arm length, torso length and glove sizes were taken, and the suits were then tailored or adjusted. Fit mattered: the suit had to be comfortable lying down in the capsule couch, which is quite different from standing, and loose or tight areas could cause pain over several hours.
Astronauts took part in fitting sessions and adjustments throughout training. The close working relationship between astronauts and suit technicians became a pattern for later programs.
Testing
Suits were tested in several ways before flight:
- Pressure checks. Suits were inflated on the ground to check seals and joints.
- Altitude chamber runs. Test subjects and astronauts wore suits in chambers where air was removed to simulate high altitude, to confirm they would hold pressure.
- Heat and cooling tests. Engineers tested how well the airflow handled the heat produced by the wearer.
- Training. Astronauts practiced in the suits in simulators, on centrifuge rides, and in capsule mockups to learn what the suit would be like during acceleration and weightlessness.
John Glenn wore the suit on the first American orbital flight, on February 20, 1962. By the end of the program in 1963, the suits had been used on all flights, and the design had been improved over the series.
What came next
Mercury showed that a suit adapted from aviation could protect a person in a capsule. The next program, Gemini, introduced a suit with more mobility and, for some flights, the ability to leave the spacecraft for short periods. After that came the lunar spacesuits for Apollo. Early station crews on Skylab also depended on this lineage when they began carrying out spacewalks to repair their spacecraft, discussed in the history of space stations.