Vocabulary that will help you understand this section

• circadian
• orthostatic intolerance
• physiological
• vestibular

Life on Earth evolved under the unique conditions of Earth's environment. This environment includes a narrow range of temperature and pressures, daily and seasonal cycles, partial protection from space radiation by the Earth's atmosphere and magnetic field, and the cues provided by the of Earth's gravity. When we fly into space, even to relatively short distances up from Earth, most of these conditions disappear. For example, space presents the unique microgravity environment that scientists can exploit to conduct research on basic biological processes by manipulating gravity as an experimental variable. Space life science research has developed, therefore, as an area of life sciences research that is concerned with the interactions between living systems and any of the characteristics of the space environment. Space life sciences contribute to biomedical knowledge here on Earth by improving our understanding of physiological systems and how they can be altered by disease and other factors.

Doing experiments in space is a very complex process. Skylab and Spacelab programs, as well as the Russians' Salyut and Mir programs, have established that humans can survive in space for more than a year, but questions about how long humans can remain in space, conduct effective science, explore space, and return to Earth's gravitational environment in good health, still abound. The answers to some of these questions require greater understanding about the ways in which one of the main characteristics of space, microgravity, affects organisms at the single cell level, and at the level of the whole organism.

For example, previous research on Earth has shown that sensory stimulation plays a crucial role in the normal development of nervous system structures that sense, respond, or use special sensory modalities. Scientists are interested in knowing how microgravity affects the sensory systems that detect gravity, the regions of the brain that process this kind of information, and other nervous system structures that use information to define complex actions such as movement and coordination. They are also interested in knowing whether gravity influences the development of non-gravity related processes, such as the early development, migration, and proliferation of cells.

We know that our bones and muscles have evolved in response to gravity-induced mechanical stresses, and that in the microgravity environment of space, our muscles lose mass, and our bones lose minerals thereby making it easier for them to fracture or break. Also, in space, our perception of our location interacts with our physiological systems to create motion sickness and balance disorders when we return to Earth. Radiation in space also has the potential to damage cells that are needed for the various body organs and tissue to function properly, and can initiate mutations in our genes or cause cancers. Studying how these space characteristics affect all forms of life, from single cells to whole organisms, including the human body, is, therefore, an important feature of space life sciences.

Other basic research questions that space life scientists are seeking answers to are: How do living organisms sense gravity? What levels of exposure to gravity are required for normal biological functioning? How does gravity influence the evolution of life? How does gravity affect circadian rhythms when the human body is separated from the periodic cycles that govern life on Earth?

Space life sciences research is also of vital important for the health and performance of crews that conduct research, live in space for long periods of time, and perform extravehicular walks on other planets. Over the past ten years scientists have focused on these problems and have used the Spacelab on several missions to study these issues. The Neurolab Shuttle mission will further improve our understanding of why astronauts experience space motion sickness when they enter space, and have balance and motor control problems when they return to Earth. Some crew members experience "orthostatic intolerance," dizziness, and fainting when they return from space. This condition could endanger crews if they were required to exit their spacecraft during an emergency.

Astronauts also report sleeping difficulties in space. Many factors, such as launch and mission work scheduled, loss of normal Earth cues, effects of microgravity on respiration and circadian rhythm, and fatigue could be contributing factors. Neurolab experiments will study some of the factors that affect sleep, and the effects of the space environment on circadian rhythms.

Space life science research holds possibilities of clinical application on Earth. Neurolab experiments could provide information that could be of help to people suffering from insomnia, hypotension, and heart problems. It is estimated that at least half of the overall USA population experience a balance or vestibular disorder at sometime during their lives. Space life science research will provide valuable information about some of these conditions, and will contribute to our further understanding of normal and abnormal nervous system development and function.