Balloons in Planetary Research

Planetary astronomers have found balloons especially useful in several research areas. Balloons have allowed researchers to rise almost to the top of the Earth's atmosphere so they could focus on distant objects without atmospheric influences. Balloons also have been useful in planetary missions for testing systems that would be used later in space and for maneuvering close to a planet's surface during a planetary mission.

An early instance occurred on May 31, 1954, when Charles Dollfus, a French aeronaut, ascended to 22,966 feet (7,000 meters) to help his astronomer son, Audoin, search for the presence of water vapor in the Mars atmosphere. Later, on April 22, 1959, Audoin reached 42,000 feet (12,802 meters) under a string of weather bureau balloons to study Venus without atmospheric interference.

NASA has used high-altitude balloons as test vehicles for technology that would fly on missions to the planets. In 1972, NASA used balloons to test a parachute system that would lower NASA's Viking Lander to the surface of Mars in 1976. A zero-pressure helium balloon carried the test Lander to a height of 92,000 feet (28,042 meters). From this altitude, the spacecraft was allowed to free fall into the desired subsonic speed. For the final test, a 34.6 million-cubic-foot (979,763-cubic-meter) balloon carried the simulated Mars entry vehicle to 120,000 feet (36,576 meters). Then a rocket shot the entry vehicle to 147,000 feet (44,806 meters), where the parachute system deployed, dropping the vehicle safely to Earth. The tests indicated that the Viking parachute system could be used in the Mars mission. When the mission was underway, the parachute system landed two instrumented, unmanned spacecraft on the surface of Mars to search for evidence of past, present, and potential future life on the planet.

Balloons were also used to help simulate the conditions the entry vehicle would experience on the Voyager mission to Mars. NASA used a zero-pressure balloon system consisting of a main balloon and a small launch balloon. The main balloon was 815 feet (248 meters) tall, about mid-way between the 555-foot (169-meter) height of the Washington Monument and the 1,250 feet (381 meters) of the Empire State Building. The balloon took the test entry vehicle to approximately 130,000 feet (39,624 meters) and released while pointing slightly upward. Then twelve small rocket motors accelerated the test vehicle to Mach 1.2 in level flight. This velocity simulated the maximum anticipated speed for the capsule when it would enter the Martian atmosphere, as well as demonstrating the pressure to which the vehicle would be exposed.

NASA also developed plans to use balloons to explore Venus with the aid of balloons, but it was the Soviets and French who implemented the plan. In December 1984, France and the Soviet Union launched a project designed to place two balloons into the sulfuric-acid clouds that circled Venus. The project would use balloons to study Venus' atmosphere much in the same way that the United States used balloons to study the Earth's atmosphere. Jacques Blamont of France worked with the Soviets on the mission, which would examine the winds that seemed to be whipping up the clouds.

France constructed two 27-foot (8.2-meter)-high balloons that carried the instruments to examine the wind changes in the clouds. The balloons were made of five layers of plastic. The innermost and outermost layers were made of Teflon to resist corrosion in the acid clouds.

Two Russian spacecraft, Vega 1 and Vega 2, were launched on December 15 and December 21, 1984, respectively. Each had a descent module, which were metal spheres that contained a balloon package and a lander. The spacecraft reached Venus in June 1985. When the spacecraft dropped the metal spheres into the Venusian atmosphere, the descent modules separated and the balloons with their instruments were released. The balloon from Vega 1 entered the Venusian atmosphere on June 11, and the balloon from Vega 2 entered the atmosphere on June 15.

Released at an altitude of 37 miles (60 kilometers), the balloons started inflating with helium while they descended to the bottom of the Venusian sulfuric cloud layer. When they finished inflating, they climbed to 35 miles (56 kilometers). They drifted while they sampled horizontal and vertical wind changes in the clouds and measured the chemical makeup of the Venusian stratosphere and tops of clouds using an ultraviolet telescope. Vertical measurements showed the presence of wind vortices more powerful than those of hurricanes on Earth. The balloons transmitted data for 46.5 hours. Both landers reached the surface of Venus and returned valuable data about the atmosphere of Venus and its soil composition. The two Vega spacecraft continued on their voyage to observe Halley's comet.

--Linda Voss

Sources:

Kirschner, Edwin J. Aerospace Balloons – From Montgolfiere to Space. Fallbrook, Calif.: Aero Publishers, Inc. 1985.

Gatland, Kenneth. The Illustrated Encyclopedia of Space Technology. New York, NY: Crown Publishers, Inc. 1989.

On-Line Sources:

"Vega 1 and 2." Comets. http://stardust.jpl.nasa.gov/comets/vega.html.

"Vega 2." http://nssdc.gsfc.nasa.gov/nmc/tmp/1984-128A.html.