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The Forefront of Space Science

Aiming for a Much Higher Sky
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It was the time of 1783 when Humankind flew in the sky for the first time. It was balloons made by the Montgolfier brothers and Charles in France about 230 years ago. The ambition for the higher altitude has continued throughout, and our thin-film, high-altitude balloon currently holds the topmost position.

Balloons float in the sky because they are filled with gas lighter than air. The Montgolfier brothers filled their balloon with heated air while Charles used hydrogen for his balloon. Currently, helium gas is used for scientific balloons. Buoyancy generated in balloons can be explained by Archimedes' principle, “an object in fluid gains buoyancy equivalent to the weight of the fluid displaced by the object.EIf you fill a 1m-cubed bag with helium gas, the gas displaces air weight of 1.2 kg. Thus, you can float 1kg of matter with the bag, which is the difference between the filled helium balloon weight of 0.2 kg and the displaced air weight.

One problem with efforts to float balloons even higher is the thinning of the air higher up. Specifically, the air at an altitude of 16 km is 1/10th compared to that on the ground, similarly 1/100th at an altitude of 32 km and 1/1,000th at an altitude of 48 km. Thus, 1 kg buoyancy on the ground shrinks to only 1 g at an altitude of 48 km. Therefore, in order to fabricate a balloon to fly even higher, it is very important to obtain more buoyancy by increasing balloon size and reducing its weight.

The history of balloon-altitude records overlaps with the history of balloon-size increases and balloon-material weight reductions. From the age of the Montgolfier brothers and Charles to around 1940, thin cloth with airtightness reinforced by gum was most likely to be used for balloon film material. During that time, the highest altitude record was 22 km set in 1935 by the US Navy’s 100,000 m3 volume balloon. The quest for altitude was driven not only by simple ambition but also by curiosity about the upper atmosphere. Starting with CharlesEdiscovery that temperature lowers with altitude, later scientific results include discoveries of the stratosphere, cosmic rays, etc. The scientific balloons that we operate have evolved from this tradition. Balloons are used for various purposes including observation of earth and the universe, engineering experiments, etc.

In the 1940s, technical innovation for the balloon arose. The industrial manufacture of polyethylene film began and was soon incorporated for balloons. Because polyethylene was light, inexpensive and easily welded by heat, these advantages instantly drove increases in balloon size and reductions in total weight. New altitude records for balloons were set one after the other from the 1950s. It was the era before the birth of the artificial satellites and balloons set altitude records among all flying vehicles. In 1972, NASA launched a balloon of 1,500,000 m3 to reach an altitude of 51.8 km, a record that remained unbroken for 30 years.

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