SCIENCE / SPACE EXPLORATION : Maneuver Gives Venus Probe New Life, Hints at Cost Savings
By skipping an aging satellite over the atmosphere of Venus like a flat stone on a rippling lake, NASA has demonstrated the feasibility of building cheaper planetary probes in the future--and made it possible to wring another year of science from an old craft already in space.
Researchers at the Jet Propulsion Laboratory in Pasadena said Tuesday that they had used gentle wind resistance from the uppermost fringe of the Venusian atmosphere to significantly slow the Magellan radar-mapping satellite, dragging it from a loose, elliptical equatorial orbit into a tight, nearly circular polar orbit.
Ann Tavormina of JPL, Magellan deputy mission director, said the aerodynamic repositioning of the probe would not have been possible using jet thrusters because of a lack of fuel. The maneuver shows that future satellites need not carry a lot of heavy fuel for navigation.
This, she said, means that space probes can be made smaller and launched for less money, or they can carry more scientific instruments without requiring bigger rockets to throw them into space.
“We think this will have a significant impact on lowering the costs of future missions,” said Magellan project manager Douglas Griffith. “Planned well and done properly, it can be a very effective way to alter a spacecraft’s orbit.”
Before the “aerobraking” maneuver began May 25, Magellan was traveling at 19,000 m.p.h. in an elliptical orbit from 5,282 to 105 miles above Venus. Controllers maneuvered the craft and its broad solar energy panels so that it dragged through the top of the Venusian atmosphere “like a badminton shuttlecock” when it drew closest to the planet.
The pressure was slight--equivalent to the breeze felt out the window of a car moving only 1 1/2 m.p.h.--but after nine weeks and 730 “drag passes,” it shaved 775 m.p.h. off the probe’s speed. That was enough to let it descend into an eccentric but roughly circular orbit from 122 to 335 miles high.
Scientists said the new orbit will afford them an opportunity to analyze the roiling molten interior of Earth’s “sister” and study the planet’s dense carbon dioxide atmosphere--but only if the project is included in the National Aeronautics and Space Administration budget next year.
Continued operation of Magellan, which scientists said can help them to understand geologic and atmospheric processes on Earth, would cost $7.4 million next year, Griffith said. NASA has not decided whether to add a fourth year to the $800-million Magellan mission.
The craft, which was launched from the space shuttle Atlantis in 1989 and reached Venus three years ago Tuesday, has used its radar mapper to pierce the planet’s opaque yellow atmosphere and make remarkably detailed three-dimensional images of the volcano-pocked surface.
But scientists said those images have raised about as many questions as they have answered because Venus appears in many ways to mimic Earth, yet in other ways remains distinct. Why, for example, are so many of its volcanoes concentrated in one area? What causes those volcanoes?
“We know a lot about what is going on down on the surface,” said project scientist Steve Saunders of JPL. “We just don’t know why.”
Saunders wants to continue mapping gravity on Venus. Unusually dense parts of the planet--such as mantle hot spots where molten rock rises from the core like a blob in a Lava Lamp--would tug on the satellite as it streaks overhead. This would cause a slight but measurable change in a radio signal the probe would transmit to Earth.
Meanwhile, Gerald Keating of NASA’s Langley Research Center in Virginia said the new orbit could let him better understand how the abundance of carbon dioxide cloaking Venus causes the upper atmosphere to radiate large amounts of heat into space. This unexpected effect may lead to changes in global warming theories on Earth, he said.
