Published by the MIT News Office at the Massachusetts Institute of Technology, Cambridge, Mass.
Published by the MIT News Office at the Massachusetts Institute of
Technology, Cambridge, Mass.
LIFTOFF TODAY? Shuttle Mission to Explore Space Motion Sickness by Eugene F. Mallove News Office The mysteries of space motion sickness are a major focus of the first space laboratory totally dedicated to experiments in the life sciences.The laboratory is nestled within Shuttle Columbia, awaiting its anticipated launch this week, possible today (Wed., May 22). Professor Laurence R. Young and his colleagues in the Department of Aeronautics and Astronautics are eagerly anticipating their role in this exciting mission, which will have eight astronauts aboard, three of whom are women. Three of the astronauts are physicians. In addition to the astronaut human subjects, who will be the focus of Professor Young's experiments, there will be many less illustrious crew members: several dozen rodents and thousands of jellyfish, each of which will play a role in neurophysiological experiments complementing the MIT investigations. These creatures will provide animal models for space adaptation. Dr. Young's experiments will study human adaptation to the novel environment of weightlessness and will seek to understand and learn how to deal with space motion sickness. For thirteen years, Professor Young, director of the MIT Man Vehicle Laboratory, and his MIT associates, including senior research engineer Dr. Charles M. Oman, have been planning for this opportunity to mount a major assault on the mysteries of space motion sickness. Also participating are co-investigators from Ontario, Quebec, and the University of Illinois. The mission is an extension of the 1983 and 1985 Spacelab flights that were key to refining some of the questions that may be answered aboard this or subsequent Spacelabs. Astronaut Byron K. Lichtenberg of Payload Systems, Inc., an MIT graduate who was a crew member aboard the 1983 Spacelab mission, is a co-investigator on this week's flight. For most of the previous Spacelab missions, experiments in diverse disciplines such as astronomy, life sciences, and materials science shared the reusable bus-sized modular laboratory that is carried in the Shuttle payload bay. By contrast, Spacelab Life Sciences-1 (SLS-1) will be fully dedicated to the important goal of learning how living and working in space affects the human body. Besides Professor Young's critical vestibular orientation experiments, the nine-day SLS-1 mission will investigate how the heart, lungs, blood vessels, kidneys, and hormone-secreting glands react to weightlessness of orbital flight. There will also be studies of changes in muscles, bones, and cells. Much of what is learned will have value in more prosaic terrestrial medicine, but the main goal is to study the physiological adaptation of humans to eventual missions of much longer duration--for example, trips to Mars, or assignments aboard a space station. Space motion sickness, which has symptoms similar to motion sickness on Earth--pallor, loss of appetite, nausea, and vomiting--has affected from 50 to 70 percent of all astronauts, says Professor Young. It usually occurs and subsides in the first few days of a mission, but it is still of concern in hypothetical emergency situations on flights. Professor Young is Principal Investigator on the Vestibular Experiments part of the mission, which will try to deepen understanding of this potentially hazardous affliction. As a practical matter, NASA would like to improve crew efficiency and comfort by eliminating space motion sickness. The experiments of Professor Young and his colleagues will study the interaction among the otolith sensors within the inner ear, the semicircular canals, vision, and spinal reflexes. The key objective is to determine how the body, which receives redundant information from several sensory sources, interprets that information in microgravity (weightlessness). Otoconia are microscopic calcium crystals that accumulate to form a dense mass deep within the inner ear. Acceleration of the body affects the way the crystals bend some 20,000 protruding fibers, called cilia, which are part of nerve cells in the inner ear. Under normal gravity, the cilia are bent by the weight of the crystals and this helps the brain determine which way is up. In the microgravity environment of spaceflight, the crystals aren't weighed down, so the brain receives signals that conflict with other messages that it receives, such as visual cues. On Earth, the vestibular organs and eyes tell people which way they are moving and how fast. However, visually induced feelings of self-motion are inhibited if vestibular signals fail to confirm the motion. It is hypothesized that with exposure to weightlessness, people suppress vestibular signals and become increasingly dependent on vision to perceive motion and orientation. On previous missions, a rotating dome with dot patterns into which a subject's head could be inserted, made subjects feel as though they were rotating in a direction opposite to that of the dome. As expected, in space subjects reported stronger visual effects and sensations of rotation than they did on the ground. The SLS-1 mission will feature an enhanced version of this experiment stressing the role of neck angle receptors. A subject looks into the dome and with a joy stick indicates the direction of perceived motion. Eye and body movements will be recorded on video tape, and a strain gauge will measure neck movements. Crew members may wear miniature acceleration-measuring sensors (accelerometers) and tape recorders that measure head movements. If the subjects experience symptoms, they will record them and note when they occurred. By correlating the accelerometer data and reports of symptoms, the investigators will be able to study the relationship between provocative head movements and periods of discomfort. Also to be studied will be the role of visual cues. The subjects might test a collar that restricts head movements to see if wearing it reduces the occurrence of space-sickness symptoms. Complementing flight data, crew members will participate in motion-sickness susceptibility tests before and after the mission. It is important to know whether tests on the ground and in aircraft, which can simulate low-gravity for several tens of seconds, can predict whether space sickness will occur. Another phenomenon to be investigated by Dr. Young's group: eye movements called nystagmus. When a person moves his head, the eyes rotate in the opposite direction to fix on an object long enough to form a clear image. After the eyes have rotated to one side, they suddenly jump back in the direction of the head rotation to fix on a new object; then they slowly rotate backward again. Otolith organs and the fluid- filled semi-circular canals of the inner ear are known to influence the reflex that causes nystagmus. If a crew member is rotated about a vertical axis and then stopped, this causes post-rotational nystagmus--eye movements opposite in direction from normal nystagmus, which suddenly decay (are lessened) when the head is tipped forward. Investigators have hypothesized that the nystagmus decay works differently in space. To test this theory, a crew member harnessed in a chair will rotate for one minute and then stop and nod forward. Head movements and eye movements will be recorded for different rotation levels. Planned for 1993 is a second Space Life Sciences Spacelab mission, which will run McGill University Professor Douglas Watt's "hop and drop" experiment in addition to the rest of the MIT experiments. A crew member will initiate a simulated fall using elastic cords that make him seem to "fall." Sensors will then measure muscle activity in the legs as the brain quickly adapts and takes into account what the otoliths are telling it. Professor Young and Dr. Oman say that they and other scientists are beginning to have a very good idea of how space motion sickness works. They anxiously await the additional data from the Columbia shuttle crew. Though Professor Young is only "halfway through" his proposed list of experiments, he has been "waiting 13 years for this and it's time to fly." Other scientist involved in the the mission are Dr. Daniel M. Merfeld of MIT and Dr. Serge Roy of Boston University. Also involved are: Center for Space Research staff members Sherry Modestino and Jim Costello and MIT graduate students Dave Balkiwill, Keoki Jackson, Jock Christie, Glenn Law, and Nick Groleau, as well as Anthony Rodrigues of BU. During the mission, the experiments will be supported at MIT by Bill Mayer, Bob Goeke, Pete Tappan, Dr. Alan Natapoff, Beverly Linton, and Kim Tseko of the Center for Space Research, and MIT undergraduates Victoria Mixon and Tom Brady. UROP students participating include Lilac Muller, Michelle Bakkila, Michele Zavada, Chris Pouliot, Roy Mendoza, and Shervin Limbert.