Balloons and the exploration of the unknown
A balloon is a nonsteerable aircraft consisting of a thin envelope inflated with any gas lighter than the surrounding air. The balloon rises from the ground similar to a gas bubble in a glass of soda. The physical principle underlying this ability to ascend is Archimedes' law, according to which any immersed body is pushed upward by a force equal to the weight of the displaced fluid. If this force is greater than the weight of the body itself, the body rises. The lighter the balloon is in comparison with air of the same volume, the more load (envelope, people, instruments) it can lift. The approximate lifting capacity of some lighter-than-air gases in a 1000 cu m balloon at 32°F (0°C) is shown below (in pounds):
For example, a balloon filled with nitrogen possesses only about 1/30 of the lifting capacity of the same balloon filled with hydrogen. As a matter of fact, only hydrogen, helium, and hot air are of practical importance. Hydrogen, the lightest existing gas, would be ideal for the balloon inflation if it had not one serious demerit: inflammability. Helium is 7% less efficient than hydrogen. It is absolutely safe in usage, however, but it is not easily available and its production is not cheap. Hot air is safe and easy to obtain, making it the most often used for common manned flights. But to get from hot air a lifting power equal to at least 40% of that of helium it would be necessary to heat it to about 570°F (299°C). The ascensional force of a hot-air balloon is difficult to control, since it is very unstable, sharply reacting to any variations of the inside air temperature. There is always an element of uncertainty in the balloon flight. Once airborne, it floats freely in air currents, leaving a man the possibility to regulate only the vertical motion.
For 123 years, since the first flight of a bag filled with smoke publicly launched by the Montgolfier brothers in Paris in 1783 till the first flight of the practical powered airplane of the Wright brothers in 1905, a balloon and its later modification, an airship, remained the only means of aerial navigation. This period was full of exciting achievements of courageous aeronauts. The crossing of the English Channel (1785, by Blanchard, France and Jeffries, USA), the parachute descent from the balloon (1797, by Garnerin, France), the crossing of the Irish Sea (1817, by Windham Sadler, England), and the long-distance flight from London to Nassau (1836, by Green, England) are a few of the milestones in the balloons early history.
The suitability of balloons for making observations and for reaching inaccessible areas was soon generally recognized. The first air force in the world was created by France in 1794, and by the end of the nineteenth century balloon corps, whose main function was reconnaissance, were the common feature of European and American armies. With the introduction of a heavier-than-air craft military interest in balloons faded. However, the most challenging pioneering and scouting missions via balloons were yet to come.
In 1863, the first remarkable high-altitude ascent was made by Glaisher and Coxwell in England. The purpose of this flight was purely a scientific one: to observe and record the properties of the upper atmosphere. The explorers rose to over 33,000 ft (10,000 m). The attempt almost cost them their lives, but fortunately they survived to describe the unique experience. This outstanding attempt was followed by many others, and high-altitude scientific ascents continued until the early 1960s. A specific layer of the atmosphere between 35,000 and 130,000 ft (11,000 and 40,000 m), which is called stratosphere, for some time became a new challenge to human spirit and engineering art. The mark of 72,395 ft (22,066 m), achieved by Stevens and Anderson in 1935, was a tremendous success for that time and was surpassed only twenty years later, when the United States resumed the manned stratosphere ballooning. The last in the series was the flight of Ross and Prather, who attained the altitude of 113,740 ft (34,467 m) in 1961. The technology developed to secure man's survival in extreme conditions became a germ of future space life-support systems.
The introduction of new lightweight and very strong plastic materials made it possible to build extremely big balloons able to take aloft huge payloads. Loaded with sophisticated instruments, such balloons began to carry out complex studies of the atmosphere, biomedical and geographical research, and astronomical observations.
Each day, thousands of balloons measure all possible characteristics of the atmosphere around the entire globe, contributing to the worldwide meteorological database. This information is needed for understanding the laws of air-mass movement and for accurate weather forecasting.
Balloon astronomy takes advantage of making observations in the clarity of the upper air, away from dust, water vapor, and smoke. Telescopes with a diameter of up to 3.3 ft (1 m) are placed on platforms, which are supported by mammoth balloons, as high as an eight-story building, at elevations of up to 66,000-120,000 ft (20,000-35,000 m).
The Russian mission to Venus in 1985 used two helium balloons to examine the motion of the Venusian atmosphere. For 46 hours, they floated above Venus with an attached package of scientific equipment that analyzed the environment and transmitted the information directly to Earth. For comparison, a landing module in the mission functioned for only 21 minutes.
The success of balloons on Venus may be possibly continued on Mars. To carry a multipurpose research probe above the Martian surface, American scientists suggested an original device consisting of a big hot-air balloon and a much smaller helium-filled balloon connected together. During the day, the air-balloon, heated by the sun, would drift in the Martian atmosphere with a payload of instruments. At night, the air-balloon would cool and descend to the ground, where it would stay, supported in the upright position by the smaller gas-balloon. Thus, the same probe would perform the on-ground experiments at night and the atmospheric experiments during the day, travelling from one location to another.
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Elena V. Ryzhov