Long-Duration Spaceflight

Imagine this scenario: You have been chosen as one of seven astronauts on the first human mission to Mars. You are four months into the three-year, round-trip mission. You share a small spacecraft with six people of different cultures who you do not know very well; one of them does not like you, and there is no place to escape from this person. The spacecraft is noisy and the lighting is poor. You have not been sleeping well because your internal clock has been thrown off by the lack of a normal day/night cycle. The last time you spoke to your loved ones on Earth was a month ago. Though you cannot feel it, your bones are becoming weaker due to calcium loss. Your heart is shrinking too. You have a toothache, but there is no dentist onboard—one of your crewmates will have to drill and fill the tooth. There is no way to turn this spacecraft around and head back to Earth; you must endure these conditions for another thirty-two months.

Inviting? Maybe not, but this is a very real description of the challenges an astronaut would face on a long-duration spaceflight. Before accepting such an assignment, you may want to know about all the dangers you could encounter.

Dangers: The Big Three

"Space travel is severely debilitating to humans in many ways," stated a team of fourteen doctors and psychologists in a report titled Safe Passage: Astronaut Care for Exploration Missions issued in 2001 by the National Academy of Sciences Institute of Medicine. After reviewing the medical data available from U.S. and Russian piloted space missions, the panel noted three main areas of concern:

1. Loss of bone mineral density . Astronauts have lost an average of 1 percent of bone mineral density—mostly calcium loss—for every month in space, making their bones brittle and more susceptible to fracture. Medical scientists do not know why this happens. The prescribed treadmill and bicycle exercise regimens have had very little effect in preventing bone mineral loss. Questions remain: Does the loss stabilize at some value, say 50 percent, or does it keep getting worse? How well do broken bones heal in space? If bone mineral density loss cannot be prevented, the report stated, "interplanetary missions will be impossible."
2. Radiation dangers. Earth's magnetic field and atmosphere protect us from most of the charged particles coming from the solar wind , and from other forms of high energy cosmic radiation . But on interplanetary missions, astronauts will experience this damaging radiation full force. Electrons, protons, neutrons, atomic nuclei , X rays , and gamma rays will strike the spacecraft in a steady stream, and there is currently no way to stop them all. What is more, when a particle such as an electron slams into a metal barrier, it releases its energy in the form of X rays; a spacecraft hull that stops the electrons would still have to deal with the secondary X rays produced in the collision. Astronauts subjected to heavy doses of radiation may develop radiation poisoning and cancer.
3. Behavioral issues. For a space mission to be successful, all members of the crew must cooperate to reach common goals. Social compatibility and psychological health are therefore prime concerns in long-duration spaceflights. What if a dispute breaks out between two astronauts that leads to physical violence? Or what happens if an astronaut becomes claustrophobic in the cramped living quarters? Perhaps a crewmember will become severely depressed due to the isolation of outer space and separation from loved ones. While psychologists on Earth might be able to help, any social or psychological problems that could threaten the success of the mission must ultimately be resolved by the crewmembers.

Other Dangers

Muscles deteriorate in microgravity conditions; significant muscle atrophy has been seen in humans after only five days in space. The most important muscle—the heart—is no exception. Two-thirds of astronauts returning from long missions have experienced dizziness, lightheadedness, and disorientation when standing up. Recent studies have shown that this is due to shrinking and stiffening of the heart. Since the heart does not have to work as hard to pump blood throughout the body in microgravity conditions, it becomes weaker, and shrinks. Back on Earth, it is unable to pump enough blood up to the head, resulting in dizziness. Fortunately, this appears to be a temporary change that reverses itself in time after a return to Earth's gravity.

Problems with the nervous system show up in the form of motion sickness, loss of coordination, and altered sleep patterns. Without the daily signals of sunrise and sunset to tell astronauts when to wake up and when to fall asleep, they tend to sleep for shorter periods and get less deep sleep, making them tired and less clearheaded during their work shifts.

Medical emergencies could cause big trouble. While some, like the toothache described in the opening scenario, may be relatively minor, other more serious conditions could prove to be deadly. An astronaut may have a heart attack, or a diseased appendix might require surgery before it bursts. Without a doctor or a surgeon onboard, these illnesses could be fatal.

Possible Solutions

As scientists collect more medical data from astronauts aboard the International Space Station and conduct experiments to determine the causes of bone mineral density loss, muscle deterioration, and heart shrinkage, they will likely discover new exercise, nutrition, and pharmaceutical solutions to these problems. Alternatively, designing a spacecraft that rotates to create artificial gravity could eliminate problems caused by microgravity entirely. But such spinning spacecraft are much more costly to design, build, and operate. For the radiation problems, engineers may develop new materials that would provide proper shielding . Behavioral problems might be avoided by studying the interactions of small groups of people in cramped living spaces, and deliberately choosing astronauts who will be likely to remain compatible in stressful situations. Drugs to treat depression, anxiety, and other psychological conditions will no doubt be included in the space-craft's medicine chest.

So there are many challenges to be met before long-duration spaceflight is safe for humans. Is there a "point of no return"—a period of time in microgravity conditions after which it is impossible for the human body to readapt to Earth's gravity? We do not know, and the astronauts on the first flight to Mars may not know either. Like all pioneers before them, they must accept the fact that they are taking major risks, that they do not have solutions to all possible problems, and that their lives are at risk in space.

see also Career Astronauts (volume 1); Human Factors (volume 3); Human Missions to Mars (volume 3); Living in Space (volume 3); Mars Missions (volume 4); Medicine (volume 3); Mir (volume 3).

Tim Palucka

Bibliography

Ball, John R., and Charles H. Evans Jr., eds. Safe Passage: Astronaut Care for Exploration Missions. Washington, DC: National Academy Press, 2001.

Nicogossian, Arnauld E., and James F. Parker. Space Physiology and Medicine. Washington, DC: National Aeronautics and Space Administration, 1982.

Pitts, John A. The Human Factor: Biomedicine in the Manned Space Program to 1980. Washington, DC: National Aeronautics and Space Administration, 1985.

Stine, G. Harry. Handbook for Space Colonists. New York: Holt, Rinehart and Winston, 1985.