NASA's Galileo mission clears hurdles for Jupiter voyage. In flying past Venus, probe could learn much about `greenhouse effect'

Several loose ends on NASA's Galileo mission to Jupiter have finally been tied down, and this has given the space agency the confidence to launch a public education campaign about the project. In a press conference in Washington yesterday, and in interviews here, scientists say they are elated about the new information they'll be able to gather not only on the Jovian planet, but on Venus, the moon, the asteroids, and interplanetary space.

According to NASA, the Galileo spacecraft has received a green light from the White House and the Department of Energy. An environmental impact statement has been cleared, since Galileo will use a small amount of plutonium in its generator instead of solar panels for its power. And the spacecraft is on the shuttle's launch schedule for October 1989.

What makes the Galileo mission unique is that it will use the gravity and orbital motion of Venus and Earth to hurtle toward its ultimate objective - Jupiter. This path was devised in July 1986 after delays and other setbacks left the Galileo orbiter/atmospheric probe far short of the fuel needed to take a direct route to Jupiter.

In an interview at the Jet Propulsion Laboratory (JPL) here, William J. O'Neil, science and mission design manager for Galileo says that despite the project's troubled history, the outcome includes ``everything we ever hoped to do. The delays have been unfortunate, but they've allowed us to get smarter and smarter. The mission has been enriched.''

Three months after its prospective launch date in 1989, Galileo is scheduled to swing by Venus. ``Our main enthusiasm is for Venus,'' says JPL's Robert W. Carlson, talking about the mission's bonus targets. He heads a team using an infrared device that will map, track, and analyze the chemistry of Venus's cloud cover to altitudes unreachable by previous techniques. The device, called a near-infrared mapping spectrometer, opens a window on a new wavelength range for studying Venus.

The results are likely to have implications for Earth, where scientists are concerned about the ``greenhouse effect'' - a warming of global climate traced to a buildup of carbon dioxide in the atmosphere.

Venus's fiery climate has often been cited as the greenhouse effect run amok - temperatures at the surface are hot enough to melt lead. By studying the chemistry of Venus's atmosphere in greater detail and on a wider scale than previously possible, Carlson's team hopes to pin down more precisely the impact of the greenhouse effect on Venus's climate.

In addition, he says, past studies have uncovered evidence that suggest chlorine is destroying ozone on Venus - a phenomenon also of concern on Earth. Ozone in the Earth's upper atmosphere shields the planet from much of the Sun's ultraviolet radiation. Carlson and his team are looking to verify and then study in greater detail the ozone destruction process on Venus.

Scientists using other instruments on the orbiter are equally as enthusiastic about the scientific opportunities resulting from the new mission profile.

The Earth-Venus-Earth portion of the flight marks the first time that a probe will return from interplanetary space - even if briefly. But this part of the mission is costly. The spacecraft will undergo about $20 million to $30 million in changes to protect some of its instruments from the sun, says JPL's Dr. O'Neil.

Once Galileo swings back by Earth in December 1990, it will fly out to its first asteroid, arriving in October 1991. From there it returns to Earth again in December of 1992; and flies past its second asteroid in August of 1993 on its way toward a Dec. 7, 1995, arrival at Jupiter.

Dr. Greeley says his team will use the Earth flybys to look at poorly understood features on the far side of the moon. Some of Galileo's thermal imaging equipment may be used to look for evidence of water in permanently dark parts of the moon.

The extra science from the new mission profile is a bittersweet bonus.

The project was approved as a new start for the fiscal year beginning October 1977. Originally, Galileo was to lift off in January 1982, follow a direct path to Jupiter, and arrive during the summer of 1985. The combined cost of development and data collection and analysis for that mission would have run at roughly $450 million, says O'Neil. Because of the delays, changes, and inflation, the combined cost is now expected to run to about $1.4 billion. Keeping Galileo on the ground and ready runs some $40 million to $50 million a year.

``The program has been threatened many, many times, and we've had to scramble many, many times to save it,'' O'Neil says. He adds that orbiter designers shoulder some of the blame for the delays. Initially, he says, they weighed in ``with what was then a woefully underestimated spacecraft mass. In all fairness, the spacecraft grew in mass almost to the same degree that the shuttle's capability diminished.''

But delays in development and from the added flight time to Jupiter have taken their toll.

``Frustration is the working word now,'' says Dr. Greeley. ``When we were ready for a May 1986 launch, graduate students were really geared up.'' Now he says, several have had to take other projects to get their degrees.

O'Neil says that while JPL awaits the October '89 launch, ``We've had to ask people to find something else to do because we can't afford to keep them at current funding levels.''