Meeting the Personal Needs of the Human in Space

The human being has certain personal needs, whether on Earth or in space, and the space shuttle has been designed to meet the most important of those needs. Special systems provide necessities that include cooked food (even snacks), water and other beverages, sleeping facilities, personal hygiene facilities, and the all-important waste management system. Providing these facilities in space is no small task. You see, not only does the human body function differently in space, but basic engineering principles also change in space due to the nearly complete absence of gravity. That means that equipment built for use on Earth is probably not appropriate for use in space.

Special equipment must be built for space use taking into consideration the lack of gravity as well as the lack of something called convection, which depends on gravity for its existence. Convection is the process that causes a flame on Earth to be shaped like a teardrop and to burn upward and is the process responsible for causing hot air to rise. It is a flow of heat (in gases and in liquids) that transfers energy upward and creates a motion to spread or radiate the heat. Some equipment here on Earth uses the principle of convection to perform its function. For instance, a regular oven heats food using convection. In space, we use an oven with a built-in fan to duplicate convective flow of heat and with very hot metal shelves that directly conduct heat to the food containers.

Other equipment depends directly on gravity to operate. For instance, a refrigerator/freezer compressor transforms freon gas into liquid freon to be circulated through the cooling system. The heavier liquid freon is normally pulled downward by gravity to flow into an evaporator. Without gravity, the freon gas and liquid would not separate, which would cause many freon bubbles to flow through the system. This, in turn, would cause the refrigerator/freezer to break down. Designing a space refrigeration system has been one of the biggest space engineering challenges for us to solve. It is such an important problem to overcome because of the need for low-temperature preservation of biological specimens. New systems are being looked that do not depend on gravity, and this new technology will hopefully provide us with a reliable and efficient refrigerator/freezer in space. /tr

Figure 6. The shuttle waste management system.

Another major challenge for space engineers is the development of acceptable methods of inflight collection of urine and feces under microgravity conditions. We all know that a toilet system works under the principles of gravity. The toilet system used on Earth had to be replaced by the "waste management system" in space to account for the lack of gravity (Figure 6). The shuttle system was designed to incorporate air pressure and flow for pneumatic collection and transport of wastes. This airflow system replaces gravity, causing separation and transportation of wastes from the body into waste processing equipment. Intimate contact with the collection system is not required. Disposal of urine is accomplished by dumping most of it to the space vacuum where it is vaporized (some urine is returned to Earth for special chemical analysis). Feces are collected in a container, vacuum dried, and returned to Earth for final disposal or testing.

Figure 8. The shuttle hand washer also serves as the "sponge bath" facility for astronauts.

Figure 7. The Skylab shower in use.

Personal hygiene requirements in space are similar to those on Earth, but most shuttle missions are short enough to allow certain shortcuts in terms of personal cleanliness. For instance, the shuttle does not have a shower, but a sprayable hand washer (Figure 8) where the astronauts can take a "sponge bath." Water droplets can float about in weightlessness, creating a potential hazard for electrical equipment, so the sprayed water is absorbed in a sponge that is then squeezed into an airflow system and moved to the shuttle's waste collection tank. A shower was developed for Skylab (Figure 7), but it required so much crew time to set up and operate that it was judged to be too much trouble to include it in the shuttle. The provision of water for personal hygiene, as well as for drinking and rehydrating food, is supplied as a by-product of the shuttle fuel cells.

The overall sanitation control of the surroundings is probably more important within the confines of a spacecraft than on Earth. Studies have shown that the population of some microbes can increase extraordinarily in microgravity and confined spaces. This would have the potential for the spread of infectious diseases. The eating equipment, dining area, waste deposit area, and sleeping facilities in the shuttle are regularly cleaned to prevent the growth of microorganisms. Illness in space is not well understood and it is very important to avoid any on-orbit medical emergencies.

Figure 9. Eating in space.

To meet the nutritional needs of shuttle crews, a new food system was developed. The primary objectives in designing a food system for the shuttle were to provide food that is safe and nutritious, light in weight and compact, and to package it in a convenient form that allows easy manipulation in the weightless environment of an orbiting spacecraft. The astronauts participate actively in choosing the shuttle menus, and new and better foods are being added all the time.

Figure 10. Sleeping in space

Sleeping accommodations onboard the shuttle vary, depending on the requirements of the particular mission. On the first flight, astronauts Young and Crippen slept in the commander and pilot seats. They wanted to be instantly available if needed during this maiden flight of the shuttle system. Later crews have slept in their seats, in sleeping bags, in bunks, or by simply tethering themselves to the walls of the spacecraft. The bunkbed system comes complete with an individual light, communications station, fan, sound suppression blanket, and sheets with microgravity restraints. The bunks even have pillows. Since there is no up or down in microgravity, the astronauts can sleep as comfortably in the vertical position as the horizontal. Because of the amount of work the astronauts perform during shuttle missions, going to sleep does not seem to be much of a problem!

Many of the problems that arise from living and working in space have been resolved. However, the physiological affects of weightlessness are still not completely understood. For the remainder of this Focus, we will look at how a scientific program was put together for the accomplishment of two dedicated life sciences shuttle flights, where the studies done on one mission complemented and enhanced the studies done on the other mission. Each of the studies looks at one piece of the physiological puzzle. When put together, the studies present a clearer picture of how the body responds to this new environment of space. We will examine the scientific payload of the Spacelab Life Sciences-1 (SLS-1) mission that flew in June 1991 as well as the payload for the Spacelab Life Sciences-2 (SLS-2) mission, a sequel to SLS-1 that flew in October 1993. /table