Source: nasa

09-18-2008 15:07

How do the outfits the astronauts wear feel?

Astronaut clothing is generally no different from outfits you wear on the ground, except that in their selection we have to observe special criteria of comfort and safety peculiar to life onboard a space vehicle. For example, they have to be made from fire retardant material. When you wear them in microgravity, you are actually "floating" inside you clothing, so you feel "dressed" only when and where it touches your skin.

How long can you stay in a spacesuit?

Nominal duration of excursions in a pressure suit usually runs between 5 and 7 hours. It depends, of course, on the consumables available to the suit, such as oxygen, battery power, cooling water, etc. (spacesuits really being rudimentary spacecraft), but working in a suit is also quite strenuous, and so its use is also limited by the comfort level and endurance of its wearer.

What are some of the special features of a spacesuit?

A spacesuit is really a small spacecraft, with all the features that are required to keep its occupant healthy and productive over many hours of extravehicular activity (EVA). Since there is no atmospheric pressure in space and no oxygen to sustain life, human beings must take their environment with them. And just like inside the Shuttle cabin, the atmosphere inside the suit can be controlled and regulated.

Thus, spacesuits must primarily supply oxygen (O2) for breathing while maintaining a pressure around the body to keep body fluids in the liquid state; in vacuum or at very low air pressures body fluids would boil just like warm water on top of a high mountain. Spacesuits for the Space Shuttle era are pressurized at 4.3 pounds per square inch (psi), which is only approximately a third of normal atmospheric pressure (14.7 psi, equal to one atmosphere). But because the gas in the suit is 100 percent oxygen instead of containing only 20 percent O2 as we are used to in the Earth's atmosphere, the suited person actually has more oxygen to breathe than is available at an altitude of 10,000 feet or even at sea level without the spacesuit. Before leaving the space shuttle to perform tasks in space, an astronaut has to spend several hours breathing pure oxygen before proceeding into space. This procedure is necessary to remove nitrogen dissolved in body fluids and thereby to prevent its release as gas bubbles when pressure is reduced, a condition commonly called decompression sickness or "the bends." On the other hand, if pure O2 is breathed at normal atmospheric pressure for an extended time, it becomes toxic for the human body. Since the pre-breathing requirement, with its lengthy, unproductive and boring waiting periods for the crewmembers, is a real nuisance, we are lowering it for the Space Station era by going to spacesuits designed for an internal pressure of 8.3 psi which require shorter prebreathing times.

Spacesuits must also shield the astronaut from deadly hazards. Besides providing protection from bombardment by micrometeoroids, the suit insulates the wearer from the temperature extremes of space. Without the Earth's atmosphere to filter the sunlight, the side of the suit facing the Sun may be heated to a temperature as high as 250 degrees Fahrenheit; the other side, exposed to darkness of deep space, may get as cold as -250 degrees Fahrenheit.

Some of the major features of a spacesuit, besides its multi-layered structure including boots and gloves, are: the primary life support system (PLSS) worn on the back, a display and control module on the chest, and a number of crew items designed for spacewalks and emergency life support, particularly a backup oxygen supply. These elements are combined in an aggregate called an EMU (extravehicular mobility unit) which accommodates a variety of interchangeable subsystems that interconnect easily and securely in single-handed operation for either normal or emergency use. They also include, typically: a urine-collection device that receives and stores urine for transfer later to the Shuttle or Space Station waste management system; the liquid cooling and ventilation garment which is a one-piece mesh suit made of spandex, zippered for front entry, and weighing about 6.5 pounds dry. This undergarment, which resembles long johns, has water-cooling tubes running through it to keep the wearer comfortable during active work periods because the suit's pure oxygen atmosphere cannot provide sufficient cooling like normal air could. There is also an in-suit drink bag containing 21 ounces of potable water, the "Snoopy Cap" or communications carrier assembly, with headphones and microphones for two-way communications and caution-and-warning tones, and a biomedical instrumentation subsystem.

For moving around in space, a suited astronaut straps into a manned maneuvering unit (MMU) weighing about 310 pounds on the ground, a one-person, nitrogen-jet-propelled backpack that latches to the 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 free-flying payloads or structures in the vicinity of the Shuttle or Station, and can reach many otherwise inaccessible external areas. Astronauts wearing MMU's, which some folks have called "space bikes", have deployed, serviced, repaired, and retrieved satellite payloads with great success.

What material are the spacesuits made of and how are they constructed?

Our current spacesuits/EMUs are a sandwich of 12 layers, each one for a specialized purpose. From the inside out, the first two layers are the liquid cooled undergarment, made from Spandex fabric with plastic tubing sewn in. Next comes the pressure bladder layer, of urethane-coated nylon, surrounded by a fabric layer of pressure-restraining Dacron. The next seven layers are for thermal and micrometeoid protection, consisting of aluminized Mylar, laminated with Dacron scrim. This seven-layer garment is topped by an outer single layer of fabric combining Gortex, Kevlar and Nomex (Kevlar being the material of bullet-proof vests).