PATHFINDER ZEROS IN ON RED PLANET : NASA PROBE'S LANDING TO BE 1ST ON MARS SINCE '70S.

Byline: Tony Knight Daily News Staff Writer

NASA's Mars Pathfinder space probe is scheduled to make a historic landing on the Red Planet today, and if all goes well live images of Earth's neighbor that hold surprises even for scientists will be broadcast nationally by around 6 p.m.

The spacecraft will end its seven-month cruise to Mars with a fiery, Independence Day plunge into the thin Martian atmosphere just after 10 a.m. Pacific Daylight Time.

NASA Administrator Daniel Goldin acknowledged that the July Fourth landing was chosen for publicity purposes since it fit within the mission's launch window.

``We are in America, and I think it's very, very appropriate to celebrate this country's independence and say that we are still a pioneering nation,'' Goldin said at a news briefing at Pasadena's Jet Propulsion Laboratory.

This is the first National Aeronautics and Space Administration mission to attempt a direct planetary landing without orbiting first, and the first to deploy a rover vehicle to the surface of another planet.

The spacecraft is headed for a broad sandy Martian plain thought to have been once submerged by a great flood.

Mission scientists said they expect the pictures to be similar to those returned by the twin Viking landers in 1976, but acknowledged they won't really know what's there until they see the images themselves.

``We're going to be surprised,'' said mission manager Richard Cook. ``That's why we're going there. It's going to be pretty flat, lots of rocks. What we're hoping is that we're going to be able to see something interesting on the horizon.''

The landing marks the beginning of a 10-year NASA program to explore Mars, the most Earth-like of the solar system's other planets, a place that many scientist's theorize could once have harbored life.

Pathfinder, and its little rover named Sojourner, won't be able to search directly for life, but its ability to analyze rocks could help scientists learn whether the planet could have supported life in its distant past.

This is the second of NASA's smaller, faster, cheaper missions. The first is the Near Earth Asteroid Rendezvous, which is currently flying into the asteroid belt between Earth and Mars.

At $171 million, Pathfinder is a sharp contrast to the $1 billion Mars Observer, which was lost just before it entered Mars orbit in 1993 probably because of a fuel explosion.

NASA's new way of doing business will allow for more missions, and less downside if one should fail, Goldin said. But it means being willing to take more risks.

``This is not the last ship out of port,'' Goldin said. ``Clearly, if we have 10 missions and eight failures, this is not a very successful program. But the program is tolerant of failure and the success of the program is not riding on this mission.

``We are at the space frontier,'' he said. ``We have to take some risks.''

This series of Mars missions envisions two launches every two years through 2005, culminating with a mission to bring a load of Mars rocks back to Earth.

Such a mission, which will require a blastoff from the Martian surface, would be the precursor to a manned Mars mission.

No manned mission will be proposed, Goldin said, until scientists can guarantee a mission that costs less than $25 billion, takes eight years from go-ahead to launch and resolves the human safety issue. He also said NASA and JPL must define the scientific payoffs and get other countries involved.

``It will not be brought into the political domain until we answer these questions,'' he said. ``We owe it to the American people to do it right.''

Anticipation of the first Mars landing in nearly 21 years was high at JPL, where the spacecraft was designed and built.

``The entire science community is rooting for us,'' said project scientist Matthew Golombek. ``Everyone is very excited about the prospect of what we are about to do.''

Launched from Kennedy Space Center on Dec. 4, the spacecraft has had a near-perfect cruise and as of 7:45 p.m. Thursday was only 250,000 miles from Mars, roughly the distance from Earth to its moon.

It was traveling at 12,000 miles per hour, but was expected to accelerate to more than 16,000 mph as it was captured by Mars gravity.

Mission scientists said it was right on target for its planned landing in the Ares Vallis region of Mars, a broad sanding plain at the end of a deep valley thought to have been carved by a great flood.

The latest Mars images from the Hubble Space Telescope show a large dust storm is raging within Valles Marinaris, the vast, 2,500-mile-long canyon near the planet's equator, about 600 miles from the landing site.

But mission scientists said they didn't expect the storm to grow into one of the monster storms that periodically envelop much of the planet.

This is because the air near the landing site is clear and very cold, according to the latest information from Earth observatories.

``That dust is staying down in the canyon,'' said scientist Golombek. ``There's no way that that dust storm could rise up and become a major dust storm.''

Even if a dust storm were to envelop the landing site during Pathfinder's 30-day mission it is unlikely to drastically affect mission operations. The air on Mars is 100 times thinner than on Earth, and like everything else on Mars, the dust is 62 percent lighter than dust on Earth.

``A 100 mph wind on Mars would be like 10 mph on Earth,'' said Brian Muirhead, flight systems manager.

The two Viking landers, which arrived at Mars in the summer of 1976, and operated for years, were often deluged with dust storms to little effect, the scientists said.

Unlike the Viking landers, which were launched from orbiters that were circling Mars, Pathfinder will plunge directly into the atmosphere, eased into its landing by an air-cushion.

Its heat shield glowing at 2,000 degrees, it will streak across the Martian night sky like a meteor.

In a precisely timed sequence of events, it will descend to the surface in about five minutes, essentially going from 16,600 mph at entry to a retro-rocket-assisted complete stop just 100 feet above the surface.

With its air bags inflated to form a 17-foot diameter cocoon, it will drop to the surface and bounce, probably as high as a 10-story building.

``The air bags make very good Super Balls,'' said Rob Manning, flight systems chief engineer. ``It could actually bounce a football field in length. It will be quite dramatic. I wish I was going to be there to see it.''

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