If you stand in an elevator and drop a coin, the coin will fall to the floor. But if he elevator cable breaks and it beings to fall, the coin will float relative to you and the elevator, since the elevator and everything in it will be in a state of ‘free fall’ and experience weightlessness. The free-fall environment can be experienced for about 30 sec in an air-plane zooming down in a parabolic trajectory at high speed or inside a spacecraft (such as the shuttle) orbiting at 27,740 km at an altitude of 320 km. the effect of the spacecraft’s speed in countering gravity. Without gravity, the spacecraft would not be in a circular orbit.
Isaac Newton has explained the concept cannon ball fired from a tall mountain above the atmosphere with enough energy would fall continuously around the Earth, if only no other force than gravity acted upon it. A shuttle orbits at the required speed in a path parallel to the curvature of the Earth, where the upper atmospheric friction is very low, though some atmospheric drag is still present. At the height the shuttle orbits, the pull of the Earth’s gravity is still almost as strong as it is at ground level. But the greatly reduced gravitational environment experienced by the astronauts and the cosmonauts, described as micro-gravity, makes them float inside. The force that pulls an apple to the ground virtually prevails outside the shuttle but inside, under the influence of the shuttle’s speed, its effect is ‘isolated’ and a falling apple floats in microgravity.
Astronauts on the moon found its one-sixth gravity (compared with the ground level on the Earth) a pleasant experience. It is calculated that only at a distance of 6.37 million kilometers from the Earth (almost 17 times farther away than the moon) can one find the Earth’s gravitational pull reduced to one-millionth of that at its surface.
Life and gravity have been together for the last two billion years! Does life need gravity? We wonder at the influence of gravity: Is it the apparent reason for the difference between up and down and between the horizontal and vertical? We are just beginning to answer these questions.
Orbital space stations are ideal laboratories for microgravity research. The prolonged stay (several months at a time) by space travelers has opened a new frontier of research on the role of gravity in life on Earth. The free-fall environment unveils subtle and complex phenomena, normally hidden by the strong force of gravity. For example, the abnormally condition affects the human heart, bones and muscles, blood circulation and the behavior of metals, liquid and fires as well as plant growth and animal life. By studying the impact of microgravity on living organisms and materials, scientists hope to provide a better understanding of life on Earth.
More than 400 human beings have ventured into space since the world’s first cosmonaut orbited the Earth in 1961. a broad range of human physiology experiments have been conducted during various manned missions. The investigations include studies on bone tissue loss, muscle performance and adaptation, pulmonary function, sleep and biological (circadian) rhythms and neuron-vestibular adjustment and behavior. Studies are also designed to collect data on the adaptation of other living systems, such as fish, rats and monkeys as well as plants and seeds.
US senator John Glenn, Jr., who was the first American to orbit the Earth in Project Mercury in 1963 returned to space flight to be a member of a shuttle crew (STS-95) in November 1999. The 77-year old Senator participated in many age-related tests, such as understanding of the physiological aging process, control of balance and blood pressure, muscle atrophy caused by the release of stress-related proteins, bone mineral loss, sleep disruptions and immune system changes. A transmitter in a pil taken by Glenn recorded his core body temperatures accurately. The payload of the shuttle also included 1,500 commercial protein crystal growth samples of research drugs for multiple diseases, e.g. cancer or heart treatments or production of cells and tissues as synthetic bone or haemoglobin.
Several questions can only be answered in long-term missions. For example, does bone demineralization in astronauts induce kidney-stone formation? Is the loss of postural muscle irreversible? Does the unexpectedly high deposit of mall aerosol particles in the lungs increase the risk of chest infections? It appears that during certain critical periods of growth in living beings, gravity is essential for normal development of the vestibular-motor reflexes in both frogs and rats. Again, without gravity, oxygen and water uptake by plant roots may be affected.
Loss of Calcium
The most puzzling and disappointing feature is the loss of calcium in the bones. Surprisingly, as experienced by the Russian cosmonauts who stayed up for 175 days, the loss of bone mass was minimal. The trouble comes with change of bone’s composition. The calcium content of the urine goes up by 50 percent. The cardiovascular system is flooded with excess calcium. It is similar to osteoporosis, generally suffered by elderly people. The result is dangerous. Bones fracture easily.
According to the world’s first physician-cosmonaut, Dr Boris G. Yegorov, blood from the lower part of the body rushes up in space and one feels as if one is hanging upside down. The body adapts itself remarkably, but only after five or seven days. In an interview with the author in Moscow, he said that the more one stayed in space, the better one would feel. His prescription still holds good (Box 23)!
In space, there is no need for a strong bone structure and muscles to resist any pressure. Muscles therefore get reduced who want to slim have a good chance! The normal amount of body fluid seems unnecessary. The pulse rate drops and remains low. The weight decreases as in the case of patients confined to bed for a long time. Dr Yegorov was of the view that there were no really effective medicines to stabilized calcium. The rapid displacement of body fluids (mainly blood) influences the control of circulation and changes in pattern of salt and water excretion by the kidneys. These mechanisms are still poorly understood.
Physical exercises give the heart and blood system a chance to feel some pressure. Regular exercises on a stationary bicycle would give the rider the feeling of pedaling up a steep hill. A device is used to apply negative pressure to the lower half of the body. The blood would be sucked down to the legs and the heart would get some extra work. The penguin-like suits donned by cosmonauts were reported to have brought about near-normal blood circulation. Repeated experiments have revealed that the best way to face normal gravity on return s to prepare for it onboard the spacecraft by experiencing it a little. Cosmonauts returning after prolonged space missions need help to walk steadily. The exercises done in space improved their ability enormously. As Dr Yegorov points out, “It is not god to alternate between zero gravity and artificial gravity. It is better to use gravity devices from the beginning of the flight.”