By Robert Zimmerman
The question always has been the same: Can human life survive in the alien environment of space? As Wernher von Braun wrote in 1952, “Some medical men are concerned at the prospect of permanent weightlessness, not because of any known danger, but because of the unknown possibilities.” There were even fears that the launch into space might itself be lethal. Dr. Heinz Haber of the U.S. Air Force’s Department of Space Medicine wrote in 1952, “Some pessimists maintain that the crew members of a rocket ship would not live to experience space, because they wouldn’t even survive the tremendous stresses placed upon them during the powered ascent.”
Following Sputnik and the advent of the space race, the United States and the Soviet Union fervently raced to find out the answer to these questions, sending dogs, monkeys, frogs and various other life forms into space. Very quickly both countries learned that the worst fears were unfounded, and that lower forms of life could readily survive both launch and weightlessness.
Could humans live in space, however, and for how long? Once again the space race provided the answer. Throughout the 1960s, NASA and its competitors in the Soviet Union flew increasingly complex manned missions to find out the limits of human endurance in space. In flights lasting anywhere from a few orbits to several days, astronauts and cosmonauts braved the unknown environment of space to find out if humans could withstand its effects, and if so, how it would change them.
At the time, the problem for scientists was as much figuring out how to monitor the life signs of their biological specimens, whether human or animal, as it was trying to understand the effects of weightlessness itself. NASA scientists developed a variety of remote sensing devices to monitor heart rate, breathing, temperature, blood pressure and other vital life signs. Today these esoteric medical devices are found everywhere in daily medical practice on Earth, where their use in intensive and cardiac care, for example, has helped reduce death rates by 30 to 60 percent. Other medical technologies that we now take for granted, such as pacemakers and other miniaturized systems, originated from the need to monitor astronauts in spacesuits from long distances.
In space, however, the initial reports from astronauts about the effects of microgravity were mixed. Russian cosmonauts reported space to be an uncomfortable place. Gherman Titov on Vostok 2, for example, felt like he was hanging upside down during his entire daylong mission, an experience that at one point made him feel so sick that he wanted the flight cut short.
In contrast, early American astronauts found space to be a generally benign place, though quite alien. During the entire Mercury and Gemini programs there were no reports of any astronaut feeling sick or nauseous. Instead, astronauts were surprised by how their perceptions of the universe around them changed. When Jim McDivitt tried to rendezvous with the spent third stage of the rocket that brought him into orbit, he found it almost impossible to judge distance and motion correctly. Meanwhile, Gordon Cooper was astonished at the minute details he could make out on Earth’s surface.
“I could detect individual houses and streets in the low humidity and cloudless areas such as the Himalayan mountain area,” he reported. “I saw what I took to be a vehicle along a road. I could see the dust blowing off the road, then could see the road clearly, and when the light was right, an object that was probably a vehicle.”
By the mid-1960s NASA had forged ahead in the space race, launching a series of longer missions in Gemini and Apollo capsules that demonstrated unequivocally that humans could survive in space for periods as long as two weeks. The medical data from these flights also suggested that extended weightlessness might have serious long-term consequences for the human body. On the four-day Gemini IV mission, for example, astronauts McDivitt and Ed White sustained bone loss of between 8 to 10 percent, a loss so significant that it could seriously threaten the health of an astronaut on a two-week lunar mission.
These longer missions provided conflicting data, however. For example, in 1965 the astronauts of Gemini VII, Frank Borman and Jim Lovell, spent 14 days in orbit and thus proved that manned missions to and from the moon were possible. In addition, despite being confined together in a space no larger than a compact car, both came through in excellent condition. Though the astronauts showed some bone loss, and there was evidence of change to their cardiovascular and muscular systems, none of the changes were as severe as McDivitt’s and White’s.
It wasn’t until NASA’s three Skylab missions in 1973-1974 that scientists were able to get their first in-depth and definitive knowledge of the long-term effects of weightlessness on the human body. Three crews of three men each stayed on Skylab a total of 171 days, with the longest mission lasting 84 days. Unlike the Mercury, Gemini and Apollo capsules, Skylab was big, and thus the second and third crews had to deal with nausea and space sickness as they adapted to weightlessness, while the first crew noticed how the fluids in their body became redistributed, with blood moving up from their legs toward their heads. Upon return all three crews experienced back pain, significant muscle soreness and weakness, balance issues and bone loss.
To mitigate the muscle loss, the daily exercise regimen for each crew was increased from 30 to 60 and finally to 90 minutes a day. Though these daily workouts did not stop muscle loss, they succeeded in reducing it enough that the third crew was able to recover almost entirely within 24 hours upon return. All subsequent long-term flights to every space station since have followed this regimen.
The bone loss discovered on Skylab was of greater concern. Overall the loss in the weight-bearing bones averaged between 0.3 to 0.4 percent per month, with the rate for some individuals being much higher. That some astronauts might lose as much as 1 percent per month during an 18-to-36 month Mars mission meant that such interplanetary journeys simply might not be possible. To conduct additional research was essential. With the end of Skylab, NASA’s human life sciences program in space shifted to a series of short duration shuttle missions, lasting two weeks or less. “In the early 1990s, we flew Spacelab life sciences missions on the shuttle that helped define the human response to short duration,” explained Dr. Chuck Sawin, a NASA consultant and former Johnson Space Center Life Sciences chief scientist. “Some other important Spacelab missions were flown by the Europeans, especially the German D-1 and D-2 missions.”
A multitude of experiments were performed on these shuttle flights. For example, in an effort to understand why two-thirds of all astronauts experienced back pain during and after their flights, astronauts kept careful measurements of any changes to their spines, confirming that the spine lengthened and straightened while in space. One astronaut, Richard Hieb, found that his height increased by 1 inch during his two-week flight. Other studies tracked the changes in the cardiovascular system and the shifting of fluids from the legs into the upper body. Various experiments found that increased salt intake combined with four-hour stints in a lower-body pressure device, which forces body liquids back into the legs, helps mitigate the effect of microgravity upon return to Earth. These NASA shuttle missions studied more than the human body. Experiments were conducted using rats, jellyfish, frogs, plants, shrimp and a host of other life forms. For example, on STS-58 in 1993, astronaut and veterinarian Martin Fettman did the first in-space dissections, preserving the spleen, bone marrow, whole blood and other tissues from six rats. The data from these samples showed no tissue damage, indicating that many of the harmful effects of spaceflight found previously in other samples after their return to Earth came not from weightlessness but from the violent stress of re-entry. Similarly, astronauts on STS-47 in 1992 studied the development of fertilized frog eggs in space. While the eggs fertilized in orbit developed normally, tadpoles that had been hatched on Earth behaved abnormally once in space, with more than half dying. This once again suggested that it was the strain of traveling to and from orbit that caused many of the problems.
Today, life sciences research at NASA moves forward on many fronts, both in space and on Earth. For example, bed rest, during which inactivity causes loss of muscle or bone mass, and casts, which cause muscle atrophy by immobilization, have been used for decades to mimic the absence of gravity.
“At the University of Texas-Galveston, we have about 10 people in bed, at 6-degree head down bed rest, as an analog for spaceflight,” noted Kenneth A. Souza, NASA consultant and former senior staff scientist in life sciences at Ames Research Center. “We previously determined that [this position] gives the physiological response closest to spaceflight.”
Such studies not only replicate the effects of microgravity, they also provide crucial information on the debilitating effects of bed rest on ill patients.
Centrifuges, which simulate high gravitational forces by spinning the subject at high rates of speed, and neutral buoyancy (suspension in water) also continue to play a role. Centrifuge studies with the Air Force, for example, demonstrated the need for a different kind of anti-g pressure suit for astronauts than those worn by jet pilots, who can be subjected to very high g forces for short durations while making high-speed maneuvers. In the space shuttle, those forces do not exceed 3 g, but can last up to 20 minutes. Because human blood volume can decrease by up to 15 percent during spaceflight, it was all the more important to develop a suit that would prevent blood from pooling in the lower extremities.
The NASA Extreme Environment Mission Operations (NEEMO) project provides one of the agency’s neutral buoyancy research capabilities. The National Oceanic and Atmospheric Administration (NOAA) Aquarius Underwater Laboratory, located about 60 feet below the surface some 3.5 miles off Key Largo in the Florida Keys National Marine Sanctuary, is a frequent destination for NEEMO astronauts, most recently testing lunar exploration concepts and a suite of long-duration spaceflight medical objectives.
Since the late 1970s, NASA’s life sciences program also has included joint research with the Russians, beginning with their recoverable unmanned Bion capsule, flying a menagerie of life forms -- including monkeys, rats, flies, newts, fish, ants and worms – on flights lasting from five to 14 days. While the results from these unmanned missions suggested that microgravity was harmful to life, the shuttle data mentioned above again indicated that these negative symptoms were caused not by the environment of space but by the stress of launch and landing.
The Bion program ended in 1996 with the accidental death of a monkey one day after its return during an operation to obtain tissue and bone samples. Yet even that event may save astronaut lives in the long run.
“We also learned that physiology is compromised by flight, creating a greater sensitivity to some anesthetics,” Sawin explained. “So it wasn’t a failure – it led to changes in procedures on things we allow to be done on astronauts.”
NASA’s partnership with Russia truly matured with their work together on Mir. After Skylab, the Russians took the lead in researching the long-term effects of microgravity on the human body with their Salyut and Mir space stations, sending cosmonauts on flights lasting from 10 to 14 months and proving that humans can survive in space for that long. For example, the Russian flights showed that with proper exercise the rate of bone loss could be stabilized consistently at about 0.5 percent per month.
In the 1990s, the United States joined the effort. From 1995 to 1997, NASA flew a series of extended manned missions to Mir, the longest being Shannon Lucid’s then-record-setting 179-day stay on the Russian facility. During these flights American astronauts not only studied the long-term effects of weightlessness on their bodies, they also attempted to grow the first crops in space. An attempt to produce wheat resulted in healthy looking plants but no seeds because of impurities in the atmosphere of Mir. A later effort by astronaut Michael Foale to grow mustard plants from seed to seed, however, was more successful. Foale’s effort produced the first viable seeds grown from seeds planted and nurtured in space, proving that plant reproduction is possible in weightlessness.
On the International Space Station, the cooperation with Russia has continued. “One thing we’ve been trying and been pretty successful with on the ISS, working with the flight surgeons and the Russians as a joint project, is what can be done with ultrasound remotely to support crew health,” Sawin said. “Some of that has had practical spinoffs, such as real-time support for injury analysis for athletes.”
This cooperation on the International Space Station expanded with the addition of the European Space Agency’s Columbus module on the STS-122 mission in February 2008, and will further progress with the addition of the Japanese Kibo module, thereby making the space station a full functioning laboratory, with life sciences as one of its primary focuses.
NASA’s life sciences research also has benefited from its long-standing collaborations with numerous other government agencies, particularly the National Institutes of Health and the Department of Energy. The results of those efforts have affected a far larger population than astronauts, with some of the equipment developed for those experiments finding terrestrial applications. For example, the bioreactor that was developed by NASA to enable cell cultures to be grown and studied in a microgravity environment, keeping cell cultures suspended rather than settling, has been adopted aggressively. “Six thousand of those units are now in research labs worldwide,” Sawin noted, “because they allow cells to be grown in ways that emulate the body, which helps cancer researchers study cells in ways they cannot in a human.”
Other examples of life sciences research at NASA now benefiting society include:
• special technologies for measuring human bone densities;
With the advent of NASA’s plan to return astronauts to the moon and eventually send humans to Mars, the focus of life sciences research has shifted even more to the study of human health on extended missions in space. For example, there is the issue of protecting astronauts from the harsh radiation in interplanetary space.
“We need more experiments in radiation studies to identify what the risks are and what we can do about them,” Souza noted. “[Rather than] take tons of shielding to the moon … there may be other ways to mitigate the effects of radiation, whether biological, chemical or physical.”
Similarly, the ongoing research of bone loss in weightlessness is of crucial importance. Not only is it essential to reduce the decline in bone density in order to make the two-to-three-year trips to Mars possible, any knowledge gained in this area could lead to improved treatments for osteoporosis on Earth.
To help bring together all that has been learned, what is being pursued and what is yet required, in 2006 NASA created the “Bioastronautics Roadmap: A Risk Reduction Strategy for Human Space Exploration.”
“The roadmap is the product of six or seven years' work by 50 to 60 contributors, compiling the current state of knowledge in the physiology of spaceflight and the questions needing answers to move ahead in support of future missions,” Sawin said. “It has helped clarify and prioritize our issues, especially the most important – radiological, muscle, bone.”
As the human race moves out into the solar system in the coming years to establish the first permanent settlements on other worlds, life sciences research will be crucial to enabling that exploration. And as it has done for the past 50 years, life sciences will not only teach us how to overcome the hostile environment of space and make it bloom with life, it will show us many new and wonderful techniques for making our lives better here on Earth.
Writer J.R. Wilson also contributed to this article.