By Kathy Sawyer
Washington Post StaffWriter
Between 1964 and 1975, the United States sent six spacecraft to Mars, including two that landed. These reconnaissance probes might as well have been firing ray guns, the way they shattered the visions of exotic big-brained Martian militants and mysterious artificial canals that had haunted human dreams since the 1800s.
Those first scouts instead sent back evidence of a disappointing reality: Mars is deader than Elvis; a chill and arid realm of red deserts and pink skies whose "Canals" were natural streambeds, but had been waterless for perhaps billions of years.
After a 17-year hiatus, the visitations from Earth are to resume with launch this week of NASA's Mars Observer spacecraft. Liftoff is scheduled for midday Friday.
Instead of the quick-look strategy of the early probes, this and future missions are designed to study the planet more broadly and deeply. Though not expecting any close encounters of the third (or any) kind, scientists do intend to investigate whether life forms may once have existed on Mars, and to lay the foundation of knowledge about climate, geology and good landing areas that will be needed for organisms of the future -- humans -- to land there in the 21st century.
The Mars Observer mission is to "provide the global database and the road maps that we will need for the missions that will follow. . . [Its instruments] will take the pulse of the planet every day, the surface and the atmosphere, to understand the processes of change going on on the planet," said Wesley Huntress, NASA's director of solar system exploration.
Such "comparative planetology," scientists said, will enhance understanding of why the four inner planets evolved so differently in their atmospheres, chemical composition, internal structure and other aspects, even though they all formed about 4.6 billion years ago out of the same raw materials, and why Earth is, as it seems, uniquely hospitable to life.
"Mars is an extreme example of what Earth could be or might have been," said Andrew P. Ingersoll of the California Institute of Technology, who will focus on the interaction of the Martian atmosphere with its polar regions.
The $511 million spacecraft will not land, as the two U.S. Viking craft did. Instead, it is to orbit the planet for 687 days-one Martian year. Among its seven instruments is a camera that is expected to return tens of thousands of pictures. Some are expected to reveal unprecedented detail-up to 40 times better than earlier Mars orbiters-including objects as small as a station wagon.
The mission, which is expected to cost $891 million including launch and operations at Mars, involves scientists from Russia, France and Germany.
Mars Observer is to be launched aboard a commercial Titan III rocket from Cape Canaveral Air Force Station in Florida. It is to travel for 11 months and about 450 million miles to rendezvous with Mars at a point 2 10 million miles from Earth.
Once "captured" by the Martian gravitational field, the craft is to phase itself into a polar orbit 204 nautical miles high so that the planet revolves beneath it. In December 1993, if all goes well, it is to begin sending data to the Jet Propulsion Laboratory in California-, which will disperse it electronically to team scientists at their universities and institutions.
The probe is expected to send back about a billion bits (binary digits) of data every day, for a mission total of about 600 billion-more than all previous planetary missions combined, excluding the current Magellan mission to Venus.
Scientists said they hope to find evidence that Mars might have supported life eons ago when its rivers flowed, its volcanoes erupted, its climate was warmer and it probably had a thicker carbon dioxide atmosphere.
Earth and Mars in their youth "weren't that different," said Mars scientist Michael Carr of the U.S. Geological Survey. "We want to go back in time" and study the ancient interaction of water with volcanic molten rock. The theory that Earth spawned its first life in a volcanic hot water vent might apply equally on Mars, he said. ''There's a lot of interest in water. Water clearly has implications for climate change and. . . the possibility of life."
The Mars of today is cold, with lows perhaps minus 190 degrees Fahrenheit and a sunny pink high of maybe minus 9 degrees. Its polar ice caps contain not only water ice, but dry ice of carbon dioxide crystallized from the thin atmosphere when seasons change. Scientists believe the missing Martian seas are permanently frozen beneath the planet's surface.
As for space monsters, scientists expect to find nothing more threatening than the great dust storms that, as the early robot scouts revealed, cloak the entire planet periodically, scouring its surface at speeds sometimes over 100 mph.
Mars Observer's seven instruments are designed to work in tandem, sometimes measuring the same things in different ways.
Among their goals is to map the entire Martian surface, monitor the great dust storms from birth to death, and provide daily weather maps of Mars good enough to make weatherman Willard Scott's mouth water.
They are to measure the heights of Mars's titanic volcanoes, mountains and canyons, study variations in the gravitational field, study the nature of the magnetic field (scientists have not been able to detect one), and determine the distribution, abundance and movements of materials such as dust, carbon dioxide and water ice as the seasons change.
In a sign of the increasingly international nature of Mars exploration, the spacecraft also carries a French radio system designed to receive and relay information from a Russian orbiter scheduled to arrive at the planet just as Mars Observer's primary mission is ending.
Huntress said NASA has informal plans for a series of about 16 small, relatively inexpensive Mars landers to begin launching as early as 1999. With Mars Observer, he said, "this great adventure really begins."