Getting the Right Fit
In spite of many decades of experience in developing and evaluating spacesuits, they are still fatiguing to wear. The internal pressure of the suit creates resistance to movements of the arms, hands, or legs. Consequently, astronauts training for a spacewalk are encouraged to stay in excellent physical condition by training on the ground for endurance and strength. After a spacewalk, crew members are allowed a day of rest before going out again. That is why missions, such as the multi-day servicing of the Hubble Space Telescope, have two EVA crews that alternate spacewalk days.
The exhaustion factor of spacesuits can be mitigated somewhat by insuring that the suit the crew member will wear in space fits properly. It is essential that the position of suit joints precisely match the position of shoulders, elbows, wrists, knuckles, knees, and ankles. A misalignment of a mere centimeter in the arm length, for example, can lead to aching fingers after a several-hours spacewalking.
Getting the right fit is complicated by a number of factors. It is important that the suit fits when it is pressurized. An unpressurized suit is slightly smaller than when it is pressurized. The suit must fit right when the crew member is in space. The microgravity environment experienced in Earth orbit affects the human body in many ways. One effect is spine lengthening. In one G (gravity), the vertebrae of the spine are close together but are kept separate by rubbery disks that act as shock absorbers. In space, without the perceived directional force of gravity, the disks expand slightly, causing the vertebrae to move slightly farther apart than they are when the crew member is standing upright on Earth. This spine-lengthening causes the astronaut to get taller, resulting in arm joint misalignment. Spine lengthening in microgravity has to be accounted for when astronauts are measured for their suits. The typical astronaut will gain between two and three centimeters in height while in space.
To avoid the expensive and time-consuming process of creating custom-made suits for astronauts, as NASA did during the Apollo missions, suits with interchangeable parts are used. Different-sized upper and lower torsos are available, but arm and leg lengths are still difficult to match. NASA has solved this problem for the Shuttle EMU by creating sizing inserts that are added or removed from the restraint layer in the arms and legs to achieve the right fit. The inserts are fabric rings of different lengths that are laced into the arms and legs. Selecting the right combination of inserts insures the best fit possible.
Step 1. Construct a variety of spacesuit arm segments by sawing off measured lengths of PVC plastic thin wall sewer pipe. (See the tip section for information on where the sewer pipe and other needed materials can be obtained.) Cut the pipe into segments 25, 50, 75, and 100 mm long. Cut two of each size. Cut three additional segments of the 50 mm length.
Step 2. Create a suit elbow joint by connecting two of the 50 mm segments with a 25 cm piece of vinyl clothes dryer hose. Slip the hose ends over one end of each of the segments. It will be necessary to the hose a small amount to accomplish this task. Fasten the hose to the segments with duct tape.
Step 3. Slip the cuff of one of the gloves over a 50 mm pipe segment. The fit may be tight but try to slide the ring in so that it just reaches the position of the wrist. Trim off the excess of the cuff so that the glove can be affixed to the ring with duct tape.
Body Size Range Measurements
Based on 1989 Man-Systems Intergration Standards, NASA-STD-3000
* Stature increases approximately three percent over the first three to four days in microgravity. Because almost all the change appears in the spinal column, other dimensions such as vertical trunk dimension increase proportionately.
Ý Thigh circumference will significantly decrease during the first
day in orbit due to the shift of fluid to the upper torso.