Magellan Probe on Track for Date With Mysterious, Alluring Venus

A $500-million robot probe built with spare parts and set for launch aboard a space shuttle in 1989 promises to strip away the veil of mystery surrounding the cloud-shrouded surface of Venus.

Named after the 16th-Century explorer, Magellan is scheduled for launch on April 29, 1989, aboard the shuttle Atlantis to begin a 500-day voyage to Venus, the second planet from the sun.

Because of the alignment of the two planets and the trajectory required by Magellan’s solid-fuel rocket, Atlantis must blast off by May 23, 1989. If a delay pushes liftoff beyond that point, the probe would have to wait 19 months for another launch opportunity.

Magellan’s primary instrument is a “synthetic aperture radar,” a device that will be able to produce a photograph-like map of the hidden surface of Venus showing objects as small as 900 feet across, a significant improvement over earlier efforts and one that may show signs of ancient seabeds and other features.

Project manager John Gerpheide of the Jet Propulsion Laboratory near Pasadena, Calif., said a recent test of the interface between the radar and the probe’s electronics assembly was a success. He said the spacecraft is on track for delivery to the Kennedy Space Center next year for launch processing.

Venus, one of the most brilliant “stars” in Earth’s sky, has long been a target of science fiction writers because of its general similarity to Earth. The two planets have similar diameters and densities, and on the scale of the solar system, they both orbit the sun at roughly similar distances.

But with the advent of the space age Venus’ mysteries have been slowly stripped away, and along with them was the fiction writer’s dream of a sister planet friendly to life.

Instruments aboard American and Soviet spacecraft have found a hellish environment beneath the clouds that perpetually shield the surface from view.

The atmosphere is composed mostly of carbon dioxide and its clouds are laced with acid. Ground-level pressure is about 90 times that of Earth’s, and temperatures are in the 900-degree range.

Scientists believe that Venus is a victim of the “greenhouse effect,” in which a carbon dioxide atmosphere inhibits the reflection of solar radiation into space. By studying the effect on Venus, researchers may one day help prevent a similar catastrophe on Earth.

Four Soviet spacecraft successfully landed on Venus in 1975 and 1982 and beamed back half a dozen pictures of a barren, rocky landscape. Crude radar maps of the surface have been collected from both spacecraft and Earth-based instruments.

Those maps show what may be the largest volcano in the solar system and a highland region called Ishtar Terra that is about the size of Australia and features towering mountain chains. Recent studies also indicate that Venus may once have had oceans.

But such maps are unable to show details less than several kilometers across, which is why scientists so eagerly await the launching of Magellan.

Magellan, assembled from spare parts left over from previous planetary missions, is to glide into a looping elliptical orbit around Venus in August, 1990.

By April, 1991, 70% to 90% of the planet is to have been mapped and the mission’s primary goals met. But the probe should continue to fill in the blanks in the picture for as long as its instruments--and NASA’s budget--can hold out.