Venus Probe’s Grand Finale: a Fiery Fall Into Planet : Science: A final lesson is sought in Magellan’s destruction. Four-year trek called profoundly revealing.
Behind three locked security doors in a windowless operations room at the Jet Propulsion Laboratory, James M. Stewart patiently is arranging the destruction of a $900-million spacecraft.
The NASA craft, called Magellan, is orbiting Venus. Since its arrival at the evening star in 1990, the probe has overcome repeated misfortunes and transmitted to Earth a revealing portrait of a seared planet pockmarked by towering volcanoes and etched by sinuous canyons longer than the River Nile. Because of Magellan, scientists have come to know the planet in more detail than they do parts of Earth.
Now the spacecraft has faltered. Its solar power sails, alternately frozen and broiled every day for four years, are coming apart. Power is falling to dangerous lows. Money to carry on the mission has diminished steadily.
Rather than turn off its transmitters and abandon the craft, the mission team decided that there could be one last thing to learn about Venus from a spacecraft’s fiery fall from grace.
On Tuesday the craft will be ordered to begin a fatal plunge into the planet’s dense, acidic atmosphere. Scientists hope that they can learn more about aerodynamics in the superheated sulfuric mist enveloping the planet, as the thick gases pull at the spacecraft.
Presiding over a planning meeting this week, mission director Stewart listened stolidly as, amplified on a speaker phone, a disembodied voice from Denver argued with a voice from Washington about how best to nurse the damaged spacecraft until then.
There was no joy in the debate. Project manager Douglas G. Griffith interrupted the technical discussion. “We are trying to live long enough to get to our funeral,” he said sardonically.
The impending destruction of Magellan is a bittersweet ending to what scientists say is one of the most successful missions in the history of space exploration.
“Magellan was responsible for a very profound revelation of the planet,” said Clark Chapman, a senior scientist at the Planetary Science Institute in Tucson, Ariz. “It showed a wealth of surprising features, toppled a bunch of hypotheses and showed us more detailed geological mapping than for any other planet, including our own.”
The Magellan mission has returned more information than all other U.S. planetary missions combined. And, because they have been recorded on small computer CD-ROM disks instead of bulky computer tapes, its images have been more widely distributed.
Many high school science teachers have a set for their students. The images are even on the Internet.
Yet surprisingly few scientists will be able to analyze the data in detail because funding for planetary studies has dwindled, scientists said.
Last week, the Venus data analysis program was canceled. Next week, a special panel of NASA officials and their science advisers plan to meet to consider funding cuts of up to 20% in the agency’s entire space research and analysis program, to free up money for other projects, agency officials said.
In all, NASA allocates about $90 million a year for the study of all the data gathered from 25 years of planetary missions--barely a quarter of the cost of a single space shuttle flight.
Some space scientists are dismayed that the funding for studying the data Magellan gathered at Venus is vanishing just when they are beginning to understand the fundamental features of the planet.
“A lot of really interesting discoveries about Venus now are only beginning to come home, especially in the question of how Venus works in comparison to Earth,” said Victor Baker, a professor of geosciences and planetary science at the University of Arizona who has been involved in NASA’s exploration of the solar system since the early 1970s.
Since its inception more than a decade ago, the Magellan mission has taxed the ingenuity of JPL engineers and scientists to the limit.
Magellan began as an act of recovery when the Ronald Reagan Administration canceled a more ambitious Venus mission to save money. JPL mission planners then created Magellan as a replacement from spare parts and leftover antennas. Delays caused by the space shuttle, which launched the probe in 1989, swelled the program’s cost.
When the spacecraft arrived at Venus in 1990 after a perilous 15-month flight, it vanished--just as the space agency’s $900-million Mars Observer space probe would do during its approach to the red planet last year.
Unlike the Observer, Magellan resurfaced. Fourteen hours after Magellan disappeared from their screens, JPL operations engineers re-established contact. Griffith remembers the loss of Magellan’s signal as the single worst moment in a mission filled with emergencies. Four more times, the spacecraft vanished during the mission, only to be recovered by imaginative acts of engineering millions of miles away in Pasadena.
Eventually, two of the craft’s four gyroscopes failed, one of its two data recorders broke and persistent static jeopardized its transmissions. Overheating threatened to end the mission prematurely. Nonetheless, the spacecraft and its distant controllers persisted and prevailed.
To extract an additional useful year from the mission--and a unique gravity map of the entire planet--the JPL team coaxed the craft through an unplanned and risky maneuver called aerobraking, to slow Magellan down and lower its orbit by skimming it across the planet’s atmosphere like a stone skipping across a pond.
The mission’s annual funding was $45 million in 1991 but was canceled by the George Bush Administration in 1992. The mission managed to survive on a meager surplus until funding at a much lower level--about $6 million--was restored last year. Staff dropped from 220 in 1991 to about 27 people today.
Many of the Magellan team have joined the ranks of those preparing the agency’s next mission to Mars, the Mars Environmental Surveyor Pathfinder, in 1996. There are no plans to return to Venus in the foreseeable future. Griffith and Stewart are not certain what they will be doing next year.
In the meantime, they are eager to ensure that Magellan has something new to teach with its finale.
“We are not destroying it,” Griffith said. “We are trying to get the last bit of good out of it before it destroys itself.”
On Tuesday, Magellan will fire its thrusters four times to lower itself progressively deeper into the planet’s atmosphere.
Scientists on Earth will measure the more powerful atmospheric flow from the thicker gas by noting how hard Magellan’s stabilizing system must work to keep the speeding craft from twisting off course.
JPL planners suspect that the craft may not last any longer than a day at lower altitude before burning up from the friction generated by the dense gases, or losing its electrical power as the clouds obscure the sun.
“We would not survive too long down there, but it is going to be good science,” Stewart said.
Venus Unveiled
NASA engineers at the Jet Propulsion Laboratory plan to send the Magellan spaceprobe on a fatal plunge into the atmosphere of Venus next week, culminating one of the most successful planetary missions in the history of spaceflight.
Magellan revealed that Venus:
* Has about 30 times more volcanos than Earth.
* Has a surface barely 500 millions years old, with craters showing almost no erosion.
* Is etched by sinuous channels, some more than a mile wide and longer than the River Nile.
* Does not have shifting tectonic plates like Earth’s.
Source: JPL, NASA
A Tale of Two Planets
Venus is Earth’s closest planetary neighbor, forming at about the same time and from the same gaseous nebula. They both were shaped by planetary bombardment and volcanism.
CHARACTERISTIC VENUS EARTH Atmosphere carbon dioxide, oxygen, nitrogen nitrogen Air Pressure 1,288 lbs. per square inch 14 lbs. per square inch* Distance From Sun 67.1 million miles 93.2 million miles Rotation Period 243 Earth days 24 hours Rotation Type East to West West to East Surface Temperature 890 degrees F. 80 degrees F.
* at sea level
