The Galileo spaceship swooped past Venus early Saturday, and the cloud-shrouded planet acted as a gravity slingshot to help hurl the craft toward its 1995 rendezvous with Jupiter. Engineers at NASA's Jet Propulsion Laboratory received a radio signal confirming that the 2.8-ton spacecraft made its closest approach to Venus at 12:59 a.m. EST, cruising 10,028 miles above the planet's hellishly hot surface. ``We have just flown through our closest approach point to Venus,'' said Bill O'Neil, science and mission design manager. ``The greatest challenge of getting Galileo to Jupiter has been met.'' Four hours before the close encounter, radio signals received on Earth confirmed the spacecraft computer ordered Galileo's infrared light sensor to start observing Venus. The instrument was looking for the glow of the hot lower atmosphere backlighting cooler clouds overhead, O'Neil said. That started an eight-hour period of intensive photography and measurements, including a photographic search for lightning. Earlier Friday, Galileo studied dust particles and magnetic fields in space, and measured Venusian atmospheric temperatures. ``The Venus encounter is our first major milestone in the mission,'' said Galileo project scientist Torrence Johnson. ``After the encounter, we have gained enough energy out of this celestial billiard shot to get the energy we need to make it all the way to Jupiter.'' The power the spacecraft gains in the flyby is triple the energy of its propellant supply, said mission director Neal Ausman. The $1.35 billion mission will let Galileo examine Earth, its moon and one or two asteroids before the spacecraft separates into an orbiter and a small probe in July 1995. In December 1995, they arrive at Jupiter, the solar system's largest planet, after a 2.4-billion-mile trip, including 182 million miles to reach Venus. Galileo was deployed from the space shuttle Atlantis last Oct. 18. Venus circles the sun between the orbits of Earth and Mercury, the closest planet to the sun. Acid-laden clouds extend 40 miles above the surface, trapping heat in a runaway ``greenhouse effect'' that raised surface temperatures to 900 degrees Fahrenheit. Atmospheric pressure is 90 times that on Earth. Venus is about 95 percent as wide as Earth. Scientists suspect it may have active volcanoes and shifting plates on its crust. The Venus flyby was designed purely to give Galileo a boost for its trip to Jupiter by increasing its speed from 83,750 mph to 88,740 mph. In two other ``gravity assist'' maneuvers, the spacecraft will use the Earth as a slingshot next Dec. 8 and again on Dec. 8, 1992, so it will be properly aimed toward Jupiter, Ausman said. Scientists decided to take advantage of the Venus encounter by having Galileo's camera and instruments make photographs and measurements of Venus starting Thursday night and continuing for a week. But almost all the pictures and data _ stored on three tracks of Galileo's four-track tape recorder _ won't be sent back to Earth until October, when the spacecraft is close enough to transmit the material with its low-gain antenna. That antenna now can be used only for communications to keep Galileo operating. Galileo's main umbrella-shaped antenna must remain furled to protect it from sunlight until after the craft makes its first flight past Earth. Galileo was programmed to photograph Venus and study the planet with its ultraviolet, infrared and visible light sensors to look for lightning, study the makeup of the carbon dioxide atmosphere, examine cloud and wind patterns, map cloudtop temperatures and peer at the lower atmosphere. Sensors that detect particles and magnetic fields were programmed to study how solar wind interacts with Venus' atmosphere. At the same time, NASA arranged for the Pioneer Venus Orbiter, circling Venus since 1978, to make similar measurements closer to the planet, Johnson said. While nearly 20 other U.S. and Soviet spacecraft have visited Venus, ``we think we're going to get some real good stuff,'' he said. But scientists won't know for months unless engineers meet success next week when they try to have Galileo send back a small amount of data, Johnson added. Studies from Earth and previous spacecraft indicate Venus has continent-sized highlands with peaks dwarfing Mount Everest and hundreds of thousands of volcanoes stretching across lowland plains. NASA's Magellan spacecraft, launched from Atlantis last May 4, will go into orbit around Venus in August. It will use radar to peer through the clouds and map at least 70 percent of Venus' surface during a $550 million mission. When the Galileo probe and orbiter reach Jupiter, the probe will parachute into the atmosphere and make measurements until intense heat and pressure vaporize it. The orbiter will photograph and study Jupiter and its major moons until late 1997, circling the planet instead of flying past it like the Pioneer and Voyager spacecraft. The National Aeronautics and Space Administration originally planned to send Galileo on a two-year trip to Jupiter by launching it with a Centaur rocket after it was released from a shuttle. But the 1986 explosion that destroyed Challenger and killed seven crew members raised safety concerns. NASA decided against using the volatile, liquid-fueled Centaur. So Galileo was launched with a much weaker Inertial Upper Stage booster after it was deployed by Atlantis' crew. The weaker rocket required NASA to redesign Galileo's route so the craft could utilize gravity from Venus and Earth for a much longer, looping trip to Jupiter. Environmentalists failed in court to stop NASA from having a shuttle carry Galileo into space. They feared a Challenger-like explosion could contaminate Florida with plutonium in Galileo's nuclear batteries, which are not reactors but generate electricity using heat from the radioactive decay of plutonium. NASA said the risk was minimal. Galileo is named for the Italian Renaissance astronomer who discovered Jupiter's major moons.
