Space adaptation syndrome

• 1. Introduction

  ›

  Space adaptation syndrome struck Senator Jake Garn so severely during Space Shuttle flight STS-51-D in 1985. NASA's astronaut corps informally named a scale of measurement after him. As many as half of all people who reach orbit experience some version of the same condition. Nothing in a traveler's earthly history reliably predicts who will suffer. An elite aviator with a perfect stomach may be incapacitated within hours of reaching weightlessness. What triggers this reversal, and why does the human body turn against itself the moment gravity disappears?

• 2. An Inverted Mechanism

  ›

  'Your body just isn't built to deal with zero-gravity,' one account of the syndrome notes. That captures in plain terms what researchers have spent decades trying to explain. The explanation begins with two systems that are normally in agreement: the vestibular system, which governs balance and spatial orientation, and the visual system, which tells the brain what the body is seeing. On Earth, they report the same reality. In orbit, they stop.

  Contemporary sensory conflict theory holds that motion sickness arises when the vestibular and visual systems fail to agree. They must present a unified account of the body's position. When they cannot, nausea follows. In a more refined version of this framework, called neural mismatch, the problem is not only between the two sensory systems in the moment. The conflict arises because incoming sensory experience no longer matches the long-term memory of how movement has always felt. Scientists have identified the limbic system as the neural mismatch center of the brain. It is the structure where motion sickness symptoms are expressed and where anti-motion-sickness drugs and stress hormones have their effect.

  Space sickness is, in a precise sense, the mirror image of terrestrial motion sickness. Carsickness or seasickness occurs when the surroundings look stationary while the body is in motion. Space sickness is the reverse: the environment appears to shift while the vestibular system reports no movement at all. Sleep deprivation compounds this disorientation, making symptoms more intense and longer-lasting. As scientists have acknowledged, a fully adequate theory of motion sickness is not presently available, but sensory conflict remains the most useful working explanation. Only those without a functioning vestibular system are fully immune. For everyone else, the first days in orbit have always been a test.

• 3. From Vostok to Skylab

  ›

  Gherman Titov, a Soviet cosmonaut, became the first human to experience space sickness in August 1961 during the Vostok 2 mission. He was also the first person to vomit in space. Despite that extreme beginning, the condition was largely unknown during the earliest years of American spaceflight. Mercury and Gemini missions were conducted in extremely cramped spacecraft that allowed almost no room for head movement. Space sickness appears to be aggravated by freedom of movement, particularly in the head. The tight quarters of those early capsules seem to have suppressed its onset.

  The Skylab program, with its comparatively spacious interior, told a different story. All three astronauts on Skylab 3 suffered from nausea during their first days aboard, while their three counterparts on Skylab 2 had experienced none. Whether the Skylab 3 crew recovered by switching to six smaller meals instead of three larger ones, or simply by adapting, was never definitively resolved. NASA doctors watched with concern as the Skylab 3 crew's illness affected their work during the first few days. As shuttle missions grew in complexity, the stakes of managing that condition would only increase.

• 4. The Measure of a Garn

  ›

  Jake Garn had been piloting aircraft since the age of 16. By the time he launched into orbit, he had logged 17,000 hours flying military planes. That figure exceeded the flight time of every other NASA astronaut. He had also ridden the vomit comet, the zero-gravity parabolic training aircraft, without becoming sick. Garn was aboard the mission in part to serve as a subject for space motion sickness experiments.

  Robert E. Stevenson, when asked about the origins of the scale that bears Garn's name, described what happened: 'Jake Garn was sick, was pretty sick. I don't know whether we should tell stories like that. But anyway, Jake Garn, he has made a mark in the Astronaut Corps because he represents the maximum level of space sickness that anyone can ever attain, and so the mark of being totally sick and totally incompetent is one Garn. Most guys will get maybe to a tenth Garn if that high. And within the Astronaut Corps, he forever will be remembered by that.'

  Charles D. Walker flew on the same mission and also became ill, despite having already flown on the shuttle. Steven Smith estimated that across four separate shuttle missions he vomited 100 times. Symptoms in most cases last two to four days. Across that window, managing a crew still adapting to orbit required both medical and scheduling decisions.

• 5. Managing the Symptoms

  ›

  One to seven days is the natural window for adaptation. NASA generally considers it preferable to let that process run its course rather than rely on medication for extended periods. Contemporary anti-motion-sickness drugs work by temporarily suppressing the vestibular system. They can counter space sickness, but they carry side effects, primarily drowsiness, that are problematic during a working mission.

  Transdermal dimenhydrinate anti-nausea patches are the standard exception, used whenever space suits are worn. Vomiting inside a pressurized suit can be fatal: the material could obscure vision or block the flow of air. Space suits are worn by NASA crew members during launch and landing, and always during extra-vehicular activities. For that reason, EVAs are not usually scheduled during the first days of a mission. The crew is given time to reach a stable state before any outside work is required.

  Terrestrial motion sickness typically responds to looking out of a window, which re-synchronizes what the eyes see with what the body feels. Space sickness calls for the opposite: restricting one's vision to a small area, such as a book or screen, can reduce the nausea. Ignoring the broader surroundings, or simply closing one's eyes, offers similar relief during the adjustment period. Research indicates, however, that blindness itself does not provide complete relief. The patch protocol and the hold on early EVAs manage the most immediate effects. What they cannot address are the deeper physiological changes that begin from the first moment of microgravity exposure.

• 6. The Wider Health Toll

  ›

  Loss of muscle mass in microgravity makes movement difficult, particularly when astronauts return to Earth. An astronaut weakened by muscle loss may be unable to climb through an emergency egress hatch. Creating an unconventional exit in the event of a crash landing can become extremely difficult, or impossible. These are not theoretical risks. Emergency egress following a rough landing demands physical capability that prolonged weightlessness can significantly reduce.

  Bone resorption and inadequate hydration in space can lead to the formation of kidney stones. A sudden onset of kidney stone pain during a critical phase of flight could incapacitate a crew member at the worst possible moment. The cardiovascular system also undergoes changes in microgravity. Short-term and long-term effects have been documented. These changes can limit what an astronaut is able to do after returning to a regular gravity environment.

  Orthostatic intolerance is one specific consequence of cardiovascular adaptation to weightlessness. A body adapted to the absence of gravitational pressure may respond to standing upright with a temporary loss of consciousness. That loss of consciousness is not merely uncomfortable. It can endanger the individual and any crew depending on them during critical operations. Space sickness itself can persist for days after landing, as the vestibular system once again adapts to the pull of gravity.