NASA PINS HOPES ON LIFE ON MARS.

Byline: Mark Carreau Houston Chronicle

The United States begins a $1 billion, decadelong program this month to broaden the search for life on Mars, launching the first in a series of probes to Earth's neighboring planet.

If successful, the first three missions, blasting off before the end of the year, will place spacecraft on the surface of the Red Planet and in orbit for the first time since the National Aeronautics and Space Administration's highly successful Viking missions of the late 1970s.

The initial snooping will include reams of close-up snapshots, a sharp-eyed, creeping robot and earnest poking at the Martian soil.

The opening salvo includes NASA's Mars Global Surveyor, to launch Wednesday, and the Mars Pathfinder mission, launching Dec. 2. Sandwiched between those is launch of Mars 96, a Russian-led international mission equipped with two U.S. instruments.

``The most exciting thing about Mars is the prospect that life may have started there,'' said Michael Carr of the U.S. Geological Survey, an expert on the planet. ``The reason for optimism about life starting on Mars is really two things: evidence of abundant water on the planet and climate change.''

Water is vital for life as humans know it and, not inconsequentially, a natural resource that could be broken down to produce breathing air and rocket propellants for human explorers.

Larger than the moon but smaller than Earth, Mars would be the first stop on a journey into the outer reaches of the solar system. Past U.S. robotic missions reveal a desertlike world with a thin, cold atmosphere of carbon dioxide, a rocky, reddish surface, towering inactive volcanoes and an ugly gash that dwarfs Earth's Grand Canyon.

Ice caps come and go from the polar regions as the seasons change.

Embossed on the landscape of Mars' northern hemisphere are tracings of ancient shorelines and long river valleys, suggesting that water in the form of lakes or oceans and flowing streams once was plentiful.

``So where is the water now?'' Carr pondered. ``The fact is, we don't know.''

Experts believe its disappearance accompanied a puzzling climate change.

Surface geology appears as if it underwent a period of intense erosion followed by a long quiescent period.

It is possible, Carr believes, that Mars retains water, either frozen on the surface but camouflaged by rock and dust, or still liquid but channeled into subterranean lakes by long-ago meteor hits.

``Our scientists will act as lawyers to prosecute the questions: What did Mars know about water? When did it know it? And what did Mars do with it?'' said NASA's Wes Huntress, chief of the agency's space science division. He believes the answers can be coaxed from the Red Planet with the 10 missions envisioned by NASA, Russia and Japan over the next decade.

``Each mission learns from its predecessors, so we can systematically pry loose the secrets of Mars, its origins and its history,'' Huntress said.

The exploration program took on new significance in early August, when space agency researchers offered possible fossil evidence of ancient bacterial life buried within a meteorite suspected of being of Martian origin. The 4.5 billion-year-old rock was recovered from the Antarctic a dozen years ago and archived at NASA's Johnson Space Center in Houston.

Last week, British researchers announced similar findings in a considerably younger Martian meteorite also recovered from Earth's South Pole.

The U.S. exploration program will feature the launchings of an orbiting probe as well as a small surface probe each time Mars and Earth are favorably aligned - in 1998, 2001, 2003 and 2005 as well as during the waning weeks of this year.

The orbiters will extensively photograph the surface and analyze the atmosphere much as a weather satellite would. The surface craft will study the mineral content of the rocks and soil and attempt to dig below the surface in search of moisture.

The campaign will begin Wednesday, which will open a 20-day launching period for the Mars Global Surveyor. It is to be lofted from Cape Canaveral Air Force Station, Fla., aboard a Delta II expendable rocket.

Its 430-million mile journey will require 300 days. When it approaches Mars on Sept. 11, 1997, a braking rocket will maneuver the small spacecraft into a large elliptical orbit around the Martian poles. Over the next three months, the probe's ground control team on Earth will gradually lower the altitude of the probe through a technique called aerobraking.

The looping elliptical orbits will expose the spacecraft to the drag of the Martian atmosphere. Gradually, the slowing spacecraft will drop low enough for sharp photography of the surface.

For one Martian year, or 687 Earth days, the Mars Global Surveyor will turn its wide-angle and telephoto cameras toward the planet. Other instruments will document changes in the atmosphere and measure the surface topography as well as search for ice and the presence of a magnetic field that would reveal something of Mars' inner core.

NASA has scheduled the Mars Pathfinder for a Dec. 2 liftoff, the opening of a 25-day launching period, also from Cape Canaveral on a Delta II rocket. Dispatched on a much faster trajectory, Mars Pathfinder will pass the global surveyor mission, reaching its destination July 4.

After piercing the Martian atmosphere, the egg-shaped probe will descend by parachute. Three braking rockets will stop its descent at just more than 60 feet from the surface. Six large air bags will then deploy to cushion its fall.

The Pathfinder's destination is Ares Valles, which appears to be an ancient watershed in the equatorial belt of Mars' northern hemisphere.

Scientists calculate that long ago, the equivalent of all the water in the Great Lakes rushed through the 60-mile-wide watershed in a two-week period, likely depositing an assortment of scientifically valuable rocks collected from a much wider region.

``It was truly a catastrophic event,'' said NASA's Matt Golombeck, the Pathfinder chief scientist. ``No one on Earth has ever witnessed such a thing.''

Once safely at rest on the Martian surface, the Pathfinder probe is designed to open up like the petals of a flower, deploying a 22-pound, six-wheel robot dubbed Sojourner.

The camera-equipped Pathfinder will function much like a weather station and as the eyes of the Earth-based control team. Pathfinder was designed to function for at least 30 days and perhaps as long as a year.

Sojourner was developed primarily as a prototype for much more sophisticated future rovers. It was made robust enough for at least seven days of exploration and to range the length of a football field from Pathfinder.

Relying on three-dimensional television views flashed back to Earth, ground control teams will issue commands that direct Sojourner, at speeds of just over one foot per minute, toward the rocks they find most intriguing.

On Nov. 16, the Russians plan to launch their more massive Mars 96 probe from the Baikonur Cosmodrome in Central Asia. It includes an orbiter, two stationary landers with cameras and other instruments and a pair of surface penetrators to test the soil. U.S. instruments will measure cosmic radiation levels during the probe's journey to Mars, information that could be crucial to the design of manned spacecraft.

A NASA-furnished instrument attached to the spearlike penetrators will perform soil analysis.

Mars is neither a new nor an easy target for U.S. and Russian probes. Only a third of the 26 launched to the Red Planet since 1960 have scored successes.

The costs and the odds have prompted NASA, with its budgets in decline, to change strategy. Though $1 billion sounds like a hefty investment for 10 missions, it's quite low by previous standards.

NASA's enormously successful but much larger Viking 1 and 2 missions of the mid- and late 1970s also teamed orbiters with landers to produce thousands of photographs of the Martian landscape. They would cost $3.7 billion to duplicate today, the space agency estimates.

Most responsible for NASA's change of strategy was the 1993 loss of the Mars Observer, a probe that took nearly a decade and $1 billion to prepare. Ground control teams lost radio contact with the probe just as it was preparing to maneuver into orbit around the planet.

In contrast, Mars Global Surveyor will cost $235 million to develop, launch and operate. Yet, space agency scientists say, it is equipped to achieve 80 percent of the Mars Observer objectives. Mars Pathfinder carries a $262 million price tag, including the $25 million for its remotely operated rover.

``Instead of having one very large spacecraft in which we must succeed, we're giving ourselves some opportunity to fail and still get an enormous amount of data,'' said NASA Administrator Dan Goldin, who championed the change in approach.

The space agency has no mandate to send humans to Mars, though the prospect has sustained public interest. However, there is mounting interest in developing a robot that could collect Martian rocks and return them to Earth, a mission that would likely inflate the $1 billion cost of the current plan.

Goldin estimates a sample-return mission could be mounted in 2003, about two years earlier than thought just a few months ago, if taxpayers were willing.

If the United States did elect to send human explorers, he believes, the mission could be under way in eight years or less.

``We have to show the American people there is real scientific merit in going,'' he said. ``We have to show the American people we are not going to dim the lights on the gross national product to do it.''