Vega (space program) - astronomy.

Vega (space program) - astronomy. I INTRODUCTION Vega (space program), two robot spacecraft that the former Union of Soviet Socialist Republics (USSR) launched in 1984 toward the planet Venus and Halley's Comet. The twin Vega spacecraft were each designed to fly past Venus and drop off a lander and a balloon, then fly past Halley's Comet during the comet's passage through the inner solar system. Vega was an international effort--the spacecraft carried instruments from the USSR, Austria, Bulgaria, Hungary, the former East and West Germany, France, Poland, the former Czechoslovakia, and the United States. The Vega probes were the first of a fleet of Halley's Comet probes, including Giotto from the European Space Agency, Suisei and Sakigake from Japan, and International Comet Explorer (ICE) from the United States. II SPACECRAFT The Vega spacecraft used the same basic design as the earlier Venus-bound spacecraft Venera 9 through 14 (see Venera), with adjustments for the extended mission to Halley's Comet. The Vega probes started with three basic parts--the main spacecraft, the Venus lander, and the Venus balloon. The main spacecraft was hourglass shaped, with a pair of solar panels for generating electricity (see Solar Energy) and a dish-shaped radio antenna attached to the narrow middle section. The spacecraft body had more protective shielding than the Venera probes because of the dust that Vega would encounter near Halley's Comet. The lander and balloon rode on top of the main spacecraft inside a spherical descent module. At launch the Vega spacecraft weighed 4920 kg (10,850 lb). The 700-kg (1540-lb) Vega 1 and 2 landers had the same basic design as the Venera landers flown since 1975: a spherical instrument compartment with a ring below to cushion the probe's landing and an air brake, stabilizer, and cylindrical radio antenna above. In addition, the Vega landers carried a surface drill for collecting samples. The drill, located near the landing ring, bored into the ground after the probe landed. It passed the small sample of soil to a spectrometer inside the lander, which determined the sample's chemical composition. The lander communicated with the earth through its radio antenna. The French-built balloon inflated with helium after separating from the falling descent module. Measuring 3.5 m (11.5 ft) across when inflated, it carried a 7-kg (15-lb) gondola with instruments for studying winds and lightning in Venus's atmosphere. Twenty radio dish antennas in 10 countries tracked the balloon's weak radio signals. Instruments for the Halley's Comet flyby were attached to a platform on a boom, or arm, at the bottom of the main spacecraft. The spacecraft's underside carried dust shields to protect against collision with Halley's Comet dust particles, which travel at up to 78 km (47 mi) per second. III MISSIONS Vega 1 was launched on December 15, 1984. Its descent module separated on June 9, 1985, then the main spacecraft changed course to fly past Venus and head toward Halley's Comet. On June 11 the descent module entered Venus's atmosphere. The Vega 1 balloon detached and inflated 54 km (34 mi) above the surface. After touchdown the lander lasted for 56 minutes before the heat and high pressure on the surface of Venus caused it to fail. Its drill malfunctioned, so no soil sample was analyzed. The balloon's battery failed on June 13. Vega 2 launched on December 21, 1984. The descent module entered Venus's atmosphere on June 15, 1985, while the main spacecraft continued toward Halley's Comet. The lander lasted 57 minutes and successfully analyzed a soil sample, while the balloon's batteries failed on June 17. The main Vega 1 spacecraft came closest to Halley's Comet on March 6, 1986. Vega 1 came within about 10,000 km (about 6000 mi) of the comet's nucleus. Vega 2 made its closet approach to the comet--about 3000 km (about 1800 mi)--on March 9, 1986. IV SCIENCE RESULTS Vega contributed to knowledge about Venus's atmosphere and surface, as well as Halley's Comet. The Vega balloons confirmed the existence of high-speed winds in Venus's atmosphere, but did not return any data about the lightning that scientists expected to find in the atmosphere. The Vega 2 lander made new measurements of the composition of Venus's crust; Venus's surface composition is similar to that of the basalt that lines the ocean floors of Earth. At Halley's Comet, Vega 1 and Vega 2 helped pinpoint the nucleus's location for the Giotto spacecraft, which flew within 610 km (379 mi) of the comet on March 14, 1986. Spectrometers detected water and carbon dioxide ice mixed with organic molecules in the dust around the nucleus. The Vega spacecraft instruments revealed that the comet's nucleus was peanut-shaped and very dark. Contributed By: David S. F. Portree Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.