A typical extravehicular activity (EVA) lasts about seven hours. During that time, an astronaut performs a number of activities, some of which are very strenuous. To make it possible to accomplish the mission, the spacesuit has to provide a steady and reliable oxygen supply for breathing and suit pressurization. The oxygen supply in the primary life-support system (PLSS) is contained in four oxygen tanks. Two of the tanks are used as the primary oxygen supply and two for an emergency secondary supply. The two primary tanks each have a volume of 3,980 cm3. They contain a total of 0.55 kilograms of oxygen at a pressure of 5,860.5 kilopascals. As this oxygen circulates through the suit, it passes through a recycling system that removes carbon dioxide, odors, and humidity. The two secondary oxygen tanks have a volume of 1,460 cm3 and contain a total of 1.19 kilograms of oxygen at a pressure of 41,368.5 kilopascals. This supplies only enough oxygen for about 30 minutes because this oxygen is not conserved and recycled.
Although the Shuttle spacesuit is used in Earth orbit where the suit is in effect, weightless, the oxygen tanks still have to be constructed from lightweight materials. Weight is not a problem in orbit, but it is a problem for Shuttle liftoff. The Space Shuttle can carry only so much mass to orbit. Lighter tanks means that additional payload can be carried.
Step 1. Obtain the materials in the material list and begin by calibrating the two liter soft drink bottle. Stand the bottle upright and pour measured amounts of water into the bottle with a beaker. Add 100 ml and mark the side of the bottle at the top surface of the water. Repeat this procedure until the bottle is filled.
Step 2. Make paper mouthpieces by rolling a strip of paper around one end of the tube. Use a small strip of tape to hold the mouthpiece together. Make a new mouthpiece each time a different person uses the apparatus.
Step 3. Partially fill a large pot or aquarium with water. Fill the bottle with water and invert it in the aquarium. Support the bottle by holding it with one hand around the neck. Insert the air hose into the bottle neck. Attach a mouthpiece to the other end of the tube and have a student fully exhale a normal breath of air through the tube. Water will be driven out of the bottle. Read the volume of air trapped inside the bottle from the calibration marks placed on the bottle's side in step 1.