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Gas balloons

A man-carrying balloon using the light gas hydrogen for buoyancy was made by Professor Jacques Charles and flown less than a month after the Montgolfier flight, on 1 December 1783. Gas balloons have greater lift for a given volume, so they do not need to be so large, and they can also stay up for much longer than hot air, so gas balloons dominated ballooning for the next 200 years. In the 19th century, it was common to use manufactured town gas (coal gas) to fill balloons; this was not as light as pure hydrogen gas, having about half the lifting power, but it was much cheaper and readily available.

Light gas balloons are predominant in scientific applications, as they are capable of reaching much higher altitudes for much longer periods of time. They are generally filled with helium. Although hydrogen has more lifting power, it is explosive in an atmosphere rich in oxygen. With a few exceptions, scientific balloon missions are unmanned.

There are two types of light-gas balloons: zero-pressure and superpressure. Zero-pressure balloons are the traditional form of light-gas balloon. They are partially inflated with the light gas before launch, with the gas pressure the same both inside and outside the balloon. As the zero-pressure balloon rises, its gas expands to maintain the zero pressure difference, and the balloon's envelope swells.

At night, the gas in a zero-pressure balloon cools and contracts, causing the balloon to sink. A zero-pressure balloon can only maintain altitude by releasing gas when it goes too high, where the expanding gas can threaten to rupture the envelope, or releasing ballast when it sinks too low. Loss of gas and ballast limits the endurance of zero-pressure balloons to a few days.

A superpressure balloon, in contrast, has a tough and inelastic envelope that is filled with light gas to pressure higher than that of the external atmosphere, and then sealed. The superpressure balloon cannot change size greatly, and so maintains a generally constant volume. The superpressure balloon maintains an altitude of constant density in the atmosphere, and can maintain flight until gas leakage gradually brings it down.

Superpressure balloons offer flight endurance of months, rather than days. In fact, in typical operation an Earth-based superpressure balloon mission is ended by a command from ground control to open the envelope, rather than by natural leakage of gas.

High-altitude balloons are used as high flying vessels to carry scientific instruments (like weather balloons), or reach near-space altitudes to take footage or photos of the earth. These balloons can fly over 100,000 feet (30.5 km) into the air, and are designed to burst at a set altitude where the parachute will deploy to safely carry the payload back to earth.

Cluster ballooning uses many smaller gas-filled balloons for flight.