Artist's concept of Magellan spacecraft

NASA's Magellan mission to Venus has received additional funding in fiscal year 1994 to complete gravity studies of Earth's sister planet through September.

Magellan has exceeded its original mission goals, and NASA plans to cease operations at the completion of gravity mapping.

The money will allow the flight team to acquire high resolution gravity data over 90 percent of the planet as well as to conduct atmospheric and radio science experiments, said Doug Griffith, Magellan project manager at NASA's Jet Propulsion Laboratory.

Deputy Project Scientist Dr. Ellen Stofan told an American Association for the Advancement of Science meeting in San Francisco that the funding would provide for continued gravity mapping.

She also described possible future new steps in Venus exploration -- possibly with rovers, landers and high-tech devices capable of operating in the forbidding Venus environment.

Griffith said the project team hopes to reduce ongoing operational costs to enable spacecraft operations to continue through October, thereby obtaining high-resolution gravity coverage of 97 percent of Venus.

The high-resolution gravity data were made possible as a result of a daring maneuver, called aerobraking, which placed the spacecraft into a near-circular orbit last summer.

Magellan was the first orbiting planetary spacecraft to use atmospheric drag, or aerobraking, to change its orbit. The aerobraking technique pioneered by Magellan will be used by the NASA/JPL Mars Surveyor orbiter -- planned for launch in 1996 -to lower its orbit when it arrives at Mars in November 1997.

Mars Surveyor is a new mission included in President Clinton's budget for fiscal year 1995, which begins next October.

Launched in May 1989 from the space shuttle Atlantis, the Magellan spacecraft arrived 15 months later at Venus. It was placed in a highly elliptical orbit from which it used imaging radar to map 98 percent of the planet's surface.

Starting in May 1993, thruster firings were used to lower Magellan's periapsis -- the point in its orbit closest to Venus -- from 300 kilometers (185 miles) to 140 kilometers (87 miles), just skimming the planet's thin upper atmosphere.

Carefully controlled atmospheric drag over the next 70 days was then used to lower Magellan's apoapsis -- the outermost point in its orbit -- from 8,340 kilometers (5,170 miles) to 540 kilometers (335 miles).

With the near-circular orbit, Magellan was positioned to make gravity measurements at the planet's mid- and higher latitudes as well as at equatorial regions.

Magellan completed its original primary mission between August 1990 and May 1991 by returning radar images covering at least 70 percent of Venus's surface. The mission exceeded that goal and went on to map 98 percent of the planet. Magellan ended the radar mapping portion of its operation in September 1992.

Gravity mapping began in the planet's equatorial band for a full 243-day orbital cycle, or one Venus day. Gravity mapping in the near-circular orbit began August 16, 1993.

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