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FOR IMMEDIATE RELEASE                                                April 4, 1991

       The Magellan Project at NASA's Jet Propulsion Laboratory claimed an early victory today and announced the spacecraft had achieved its objective for the primary phase of the Venus mission more than a month before the end of the first 243-day mapping cycle. That is one Venus rotation beneath the orbiting spacecraft.

       Project Manager Tony Spear said because of the quality of the radar images and the excitement they have generated in the scientific community, an extended mission for a second 243-day mapping cycle has been approved by NASA and will begin May 16.

       Magellan reached its goal of mapping 70 percent of the planet Wednesday, said Spear, adding that by the end of the first mapping cycle May 15, the spacecraft will have acquired 84 percent of the planet's surface.

       The radar imager used to penetrate the thick clouds of Venus and map the surface has worked flawlessly, Spear said. He added that the spacecraft is sufficiently healthy to continue mapping Venus well into this decade, "providing a windfall of additional, exciting science returns."

       The first objective of the extended mission is to collect the remaining 16 percent of the map, including the south pole which has never been imaged. Other surface features will be imaged from a different view angle to yield a new perspective, and image comparisons from one mapping cycle to the next will be made to look for surface activity, Spear said.

       Beginning in mid-November, every fourth orbit will be dedicated to acquiring gravity data. Instead of mapping the surface on those orbits, the high-gain antenna will point to Earth and slight changes in the radio signal resulting from variations in Venus' tug on the spacecraft will help scientists determine local gravity changes. That information will provide insight into the interior processes of the planet.

       Additionally, a number of experiments are under study which would use the radar in different modes to acquire higherresolution topography.

      Finally, near the end of the Magellan mission, the spacecraft may be dipped into the upper atmosphere of Venus to drag it into a circular orbit. That process called aerobraking would be a valuable engineering demonstration for future missions, Spear said.

       "More importantly," he said, "a circular orbit would greatly enhance science returns by permitting global, high resolution gravity and imaging data acquisition."

       Magellan is managed by JPL for NASA's Office of Space Science and Applications, NASA Headquarters, Washington, D.C. The Hughes Aircraft Co. developed and operates the radar instrument, and the Martin Marietta Corp. built and operates the spacecraft.


4/4/91 JJD