The effects of weightlessness are not confined to humans. The roots of plant seedlings grown in space can sprout upwards; the flames of burning material spread in all directions; bubbles in boiling water do not float to the surface, and sand in a beaker of water does not sink to the bottom. Weightlessness produces intriguing phenomena: scientists are anxious to learn about the results of a series of low-gravity experiments that will end this week with the return to Earth of the Columbia space shuttle.
Columbia, due back on Wednesday, will have spent nearly 13 days in space, on the longest shuttle flight to date. Its crew of seven have spent the bulk of their time tending a variety of experiments designed to investigate 'microgravity' experienced in orbit around Earth. Gravity on the shuttle is never quite eliminated, which is why scientists prefer not to call it weightlessness. In microgravity, the gravitational pull on humans and other objects in the spacecraft is between a thousandth and a millionth of that on the ground.
Scientists at the US National Aeronautics and Space Administration (Nasa) are keen to investigate the effects of microgravity for two main reasons. First, they want to know how humans will cope with long periods in space - information necessary for the planning of a permanent space station, which Nasa hopes to launch around the turn of the century. Second, researchers believe that certain delicate industrial processes, such as the manufacture of computer chips and drugs, could be done better in the microgravity environment of space. Some believe that there could be factories in space within a few decades.
Any talk of long-term habitation of space requires a thorough understanding of what near weightlessness can do to the human body. From the earliest manned space flights, it was clear that microgravity could have serious effects on astronauts. A man standing on Earth has about 0.7 litres of blood and 1.5 litres of water in his legs. In microgravity, a substantial amount of this fluid is shifted to the lungs, heart and face. This increase in fluid in the upper parts of the body not only causes the kidneys to excrete more urine, but appears to upset the salt concentration in the body - which in turn decreases the ability of the muscles to work. And yet regular exercise of the muscles in space is important, otherwise they tend to waste away from underuse.
Overactive kidneys that excrete too much urine cause more problems for astronauts when they return to Earth. Gravity then pulls fluid back into the legs and leads to what doctors call 'orthostatic insufficiency'. The symptoms are a low heart rate, sweating and fainting, essentially caused by too little blood reaching the brain when the astronaut stands up. To try to offset such uncomfortable effects of microgravity, the astronauts on board the Columbia have spent some time standing in special inflatable cylinders enclosing their legs and lower bodies, sealed at the waist. As the pressure inside the cylinder is decreased, the suction created causes body fluids to return to the legs. What Nasa researchers want to know is how effective this is in the long term at offsetting microgravity, and how big the pressure decrease has to be to bring this about.
Professor Heinz Wolff, a microgravity researcher at Brunel University, says suprisingly little is known about the effects of near weightlessness despite nearly four decades of manned space flight. Russian scientists may know a lot more because of the very long time cosmonauts have spent on board the Mir space station, he adds, but little research has been published.
Apart from studying the effects on astronauts, Nasa is keen to discover whether it is possible to grow plants in space. The reason, Nasa says, is straightforward: 'Plants can reduce the cost of providing food, oxygen and pure water and lower the cost of removing carbon dioxide in human space habitats.' The shuttle Columbia is carrying an experiment designed to test a system of growing plants, not as easy as it sounds considering that roots grow all over the place and water and soil tend to float around. The experiment uses porous stainless steel tubes and pumps to test how easy it is to deliver nutrients and water to growing plants, and recover the water that escapes.
Another experiment involves setting fire to some combustible material in a sealed chamber. Nasa wants to know how flames tend to spread in microgravity to help devise safety procedures for future space stations. Hot air does not necessarily rise in space, says Mark Lee, senior scientist at Nasa's Microgravity Science and Applications Division. 'If you strike a match in space, the flame burns in a spherical shape. In space, material burns with flames coming out on all sides. Trying to understand burning in space is important for fire safety.'
Just as gravity influences the movements of hot air in a fire, it affects the microscopic movements in a fluid turning into a solid - the phenomenon of crystallization. Scientists have many uses for crystals; the more perfect the crystal, the better it is for their purposes. 'Crystals grown in space have a much more ordered structure,' says Robert Sokolowski, a programme scientist at Nasa. Growing crystals on Earth is like trying to arrange hundreds of ping-pong balls in a straight line on a windy day. In the microgravity environment of space, the 'wind' is a mere whisper.
Drug designers believe protein crystals grown in space will make it easier to unravel the precise atomic structure of these large, complex molecules. 'Since proteins play an important role in everyday life - from providing nourishment to fighting disease - research in this area is quickly becoming a viable commercial industry,' according to Nasa. 'Scientists need large, well-ordered crystals to study the structure of a protein and to learn how a protein's structure determines its functions. Structural information gained from these experiments may provide better understanding of the immune system, the function of individual genes and treatment of disease, and may ultimately aid in the design of a specific, effective and safe treatment of viral infections.'
The Columbia space shuttle is also carrying experiments designed to investigate the growth of other, non-protein crystals. One of these is a substance called zeolite which can be used in extremely fine filters. On Earth, zeolite crystals grow only to a certain size, then they sink to the bottom of a reaction chamber. Such settling should not occur in space: 'Zeolite crystals produced in space are expected to be larger and more perfect than their ground-produced counterparts, providing tremendous industrial potential for space-produced crystals.'
Nasa's future relies to a great extent on industry being induced to take up the challenge of factories in space. The question is whether the enormous costs of launching and maintaining space factories can be justified by the products that can be made in microgravity. 'It all comes down to cost,' Dr Sokolowksi says. 'If the benefits warrant the costs, then somebody will go ahead and do it.'-
What space does to humans
Short-term effects: Within minutes to hours, people can feel nauseous and strange, a phenomenon that has never been completely explained. Called 'space motion sickness', it is thought to result from neurophysiological changes similar to sea sickness.
Medium-term effects: Within hours or days, astronauts experience a shift in body fluids from their legs to the upper body, resulting in cardiovascular deconditioning and hormonal disruption.
Long-term effects: After weeks or months, muscles and bones begin to waste away. Prolonged weightlessness causes muscles to be underused; the lower stress on bones causes them be become weaker and demineralised. Astronauts have to exercise vigorously to counteract the effects.Reuse content