For NASA, balloons are of considerable interest as a means of lowering spacecraft to a planet's surface, delivering instruments to various altitudes and performing aerial photography and other forms of remote-sensing science. Balloons can also potentially conduct explorations faster and cover greater distances than conventional ground-based planetary explorers.

"Solar-heated balloons can descend more slowly than heavier parachutes to drop off a payload, and yet they can rise again after the drop-off. They offer us bonus science because they can take off repeatedly during daylight hours, and land in hard-to- reach terrain," said Jack Jones, technical monitor for balloon activities at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Our inspiration comes from the centuries-old Montgolfiere balloons named after the two French Montgolfier brothers who flew the first hot-air balloon by burning a pile of wool and old shoes in 1783."

Other balloons use ammonia, which evaporates with solar heat, and causes inflation of the balloon. Helium balloons can also potentially be used and can fly for several weeks, which is much longer than the one-day flights of the solar heated balloons. The helium balloons tend to be heavier and more complicated since they must be stronger and carry their own high- pressure compressed gas cylinders for in-flight filling. All of these balloons can be used to explore the atmosphere and large areas of a planet's surface. "Thus far, most of our work has concentrated on balloon deployment testing in Earth's upper atmosphere, which simulates deployment in the cold, thin atmosphere like that of Mars," said Jones.

Engineers in JPL's Mechanical Systems Engineering and Research Division are also developing a variety of aerovehicles to explore other solar system bodies, such as Venus, Saturn's moon Titan, and the outer planets (Jupiter, Saturn, Uranus and Neptune). The aerovehicles include balloons designed to enable scientific exploration by either hovering over or soft landing on planetary bodies. Another class of inflatable drag devices, called ballutes, may someday be used to decelerate a spacecraft's speed to allow insertion into orbit.

In addition to solar-heated balloons, hot-gas balloons also look promising for Jupiter and Saturn, while balloons on Uranus and Neptune can capture light, high-altitude gas to float in the heavier atmosphere below the methane clouds. These balloons may be able to study the gas planets' internal energy sources and atmosphere.

On Venus, a combination helium-and-water or steam balloon may be used to make repeated descents to the hot, scalding surface with re-ascents to the upper, cooler clouds and perhaps help define what caused Earth's twin to have such a hot, greenhouse atmosphere. And on Titan, a helium-filled "aerover" may be able to fly like a blimp and then land as an amphibious rover to explore that moon's strange frozen surface and liquid hydrocarbon lakes or seas.

More information on JPL's balloon activities is available at: http://www.jpl.nasa.gov/adv_tech/balloons/summary.htm

JPL's planetary balloon activities are funded by the NASA Mars Exploration Office and the NASA Cross Enterprise Program. Managed for NASA by the California Institute of Technology in Pasadena, JPL is the lead U.S. center for robotic exploration of the solar system.

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