Introduction
Space motion sickness (SMS) is experienced by 50 percent or more of astronauts during the first few days of exposure to the microgravity environment of space. SMS is similar to motion sickness on Earth, with symptoms including loss of appetite, malaise, nausea, vomiting, gastrointestinal disturbances and fatigue. SMS not only disrupts the well-being of crew members, but it also can impair their performance during critical stages of spaceflight.
The precise cause of space motion sickness is not fully understood. Scientists generally agree, however, that the problem originates in the vestibular system, or balance organs, of the inner ear. Crew members have reported that head movements and visual disorientation provoke space motion sickness.
The overall impact of SMS on mission operations in the U.S. space program has so far been minimal. Its effects on crew performance, however, have the potential to interfere with scheduling of extravehicular activities and to jeopardize the safety of space shuttle landings. Therefore, NASA has undertaken a vigorous research program to define the physiological and behavioral mechanisms underlying this phenomenon, find reliable predictors of susceptibility and develop preventive measures. Scientists at NASA's Ames Research Center are an important part of this effort.
History
During the first two space flight programs, Mercury and Gemini, astronauts did not experience space motion sickness. Scientists attribute this to the design of the capsules, which restricted the mobility of crew members, as well as their ability to see outside. Mercury and Gemini astronauts thus did not encounter spatial disorientation during space flight.
Space motion sickness was first reported by American crew members in the Apollo era. In the larger Apollo and Skylab spacecraft, crew members could move around freely and therefore experienced vestibular and other sensory problems in the microgravity environment. As a result of the unexpected incidence of space motion sickness during the Apollo and Skylab flights, the need to develop countermeasures became increasingly apparent. The Skylab program enabled NASA scientists to investigate early mission space motion sickness in a systematic way. Building on knowledge gained from Skylab and other research efforts, scientists in the space shuttle era use the term "space motion sickness" to describe the full range of symptoms encountered in adapting to microgravity, including those resembling motion sickness.
Ground-based Testing and In-flight Testing
Because of its complexity and uniqueness, this biomedical problem cannot be resolved solely with ground-based research. Data collected from astronauts during space shuttle missions is essential in finding valid solutions.
As part of the effort to find predictors of space motion sickness, crew members of early space shuttle flights were tested for susceptibility to motion sickness on the ground. Each crew member also was tested for sensitivity to experimentally-induced motion sickness.
Most crew members had some experience with motion sickness on Earth. This did not predict, however, who would experience motion sickness in space, or to what extent. Scientists at NASA Ames and Johnson Space Center in Houston, Texas, are continuing to work on ground-based methods for prediction of individual susceptibility.
Countermeasures
While research on predictors of SMS has been inconclusive, some progress has been made in the development of counter-measures. Current areas of investigation include anti-motion sickness drugs, autogenic feedback training and techniques for minimizing head and body movements,
Drugs that diminish the symptoms of space motion sickness are being used and studied. At present, the drug promethazine is available to crew members as a treatment for SMS. To date, the use of medication has been only partially successful, decreasing the symptoms of space motion sickness in most, but not all, crew members. Recent research indicates, however, that this medication can cause deleterious side-effects that further degrade human performance (e.g., reaction time, grammatical reasoning ability, pattern recognition) and negatively impacts "mood" and sleep.
Another preventive technique, developed at Ames, is Autogenic-Feedback Training Exercise (AFTE). This combined application of biofeedback and autogenic therapy (a learned self-regulation technique) controls some symptoms of SMS associated with the autonomic nervous system, such as nausea and vomiting.
In the course of 24 years of research at Ames, more than 350 individuals have been trained in autogenic feedback, with significant improvement in motion tolerance observed in 85 percent of them. The procedures also have been adopted as a treatment for air sickness in military flight crews.
Autogenic feedback has proven to be a superior method of physiological control because a) it produces relief with as little as six hours of training; b) it is effective in a wide population of individuals; c) it reduces the behavioral and physiological reactions to even the most provocative motion sickness stimuli; d) it is remembered over a long time. Further, the ambulatory monitoring system developed in support of this research (the Autogenic-Feedback System-2 or AFS-2), when used in conjunction with a computer-based battery of human performance tasks, can be used to document the effects of microgravity on crewmembers' functional state (operational efficiency). It also can be used to evaluate the effectiveness of other countermeasures such as exercise or medication.
Because crew members have reported that rapid head movements worsen the nausea and spatial disorientation associated with SMS, scientists also are testing head and neck restraints that restrict such movements.
Future Directions
Although past research has yielded a great deal of information applicable to space motion sickness, a definitive solution to this vexing problem is urgent. Among the objectives of current SMS research are:
• more precise predictive indices
• more effective drug treatments
• more efficient pre-flight adaptation procedures
• methods to evaluate performance impairment induced by SMS and anti-motion sickness drugs
• early detection of incipient symptoms
• mechanical restraints such as neck fixating devices
Of primary importance in developing methods for the prevention and treatment of space motion sickness are the health and efficiency of crew members. The countermeasures, whether used alone or in combination, must be relatively fast-acting, but they cannot inhibit the ability of a crew member to perform tasks.
FS-ARC-006
Revised: May, 1997
