PATHFINDER FIRST STEP IN 10-YEAR PLAN.

Byline: Tony Knight Daily News Staff Writer

The Mars Pathfinder mission is only the beginning of a decadelong exploration of the Red Planet by robotic rovers and landers as NASA lays the groundwork for a manned mission.

Nine new unmanned missions are being designed and executed at Pasadena's Jet Propulsion Laboratory to take armchair astronauts into Martian orbit with high-resolution cameras, to the planet's south pole with a lander, and over the rocky terrain in robust rovers that will last up to two years and go for miles.

``We're trying to do the kind of things you might think of as preparation for a human mission,'' said Dan McCleese, chief of the JPL's Mars science program. ``The robotic program is a steppingstone to human exploration - the things the Pathfinder is doing right now.''

The National Aeronautics and Space Administration and the JPL intend to take the public with them every step of the way. So there will be cameras on all missions, more efforts to build virtual-reality programs and 3-D images to create the feeling of being there, and continued instant access to images and data through the Internet.

Why Mars? It's relatively close, it has an atmosphere, there is plenty of evidence that there was once water there, so it might once have supported life, and therefore presents humanity with the best opportunity to search for evidence of extraterrestrial life.

``The big goal is to understand Mars,'' said Norm Haynes, the JPL's director of Mars exploration. ``If you bring samples back, fairly large samples, you might have a chance of determining whether there was ever life on Mars.''

The Viking landers in 1976 looked for evidence of Martian life but found none in the few scoopfuls of dirt they examined. But interest in the prospect of life on the Red Planet was reignited last year when NASA scientists announced they might have found evidence of ancient life in a meteorite from Mars that landed in Antarctica.

Some critics have said it's not worth spending hundreds of millions to bring back a bag of rocks or even billions to send a human there. But the public's reaction to Pathfinder, with 100 million hits on the mission Web sites in one day, proves that the average American is fascinated with Mars, said Donna Shirley, manager of the JPL's Mars program.

The new frontier

``I think it's because it's the frontier,'' Shirley said. ``Here is a generation that's been raised on computer games and `Star Wars,' and all of a sudden they can participate in the real thing on the Internet.''

Indeed, the baby boomers were the last generation of schoolchildren to be taught that Venus is our sister planet and that Mars is a desolate place probably like the moon.

The Mariner 4 flyby of Mars in 1965 sent back images of a red world of valleys and mountains. And the Mariner 9 orbiter in 1971 returned pictures of an atmosphere with clouds and polar caps.

NASA spacecraft traveling to Venus found an inhospitable planet wrapped in seemingly impenetrable layers of clouds, with a runaway greenhouse condition that had pushed surface temperatures high enough to melt lead.

Mars, on the other hand, has a 3,000-mile-long valley that's a mile and a half deep. It has a mountain three times as tall as Mount Everest. Its surface was carved by great floods. It has winter, summer, spring and fall. It has an atmosphere and weather, and although it's cold, it's not any colder than the Arctic, and on summer days it's a lot warmer.

In short, it's a place we could go.

``I think human exploration of Mars is inevitable,'' McCleese said. ``The guess is, when is it going to happen?''

He said the reason why Pathfinder has generated so much more interest than the Viking landers in 1976 is the mobility provided by the rover Sojourner.

``I think this time is more exciting because we have the ability to reach out and experience what we are observing from the lander,'' McCleese said. ``We are a participant in the environment now.''

Haynes said he thinks a manned mission will fly sometime after 2020, but in the meantime the robotic program is moving into full swing with its 2005 goal of returning with a sample of the Martian landscape.

A decade of missions

The current program will launch a lander and an orbiter every two years through 2003. The orbiters will look for the likeliest places that evidence of primordial life might be found. The landers in 2001 and 2003 will release rovers at two of those sites to collect piles of rocks and cache them for the 2005 sample return mission.

The next mission is Mars Global Surveyor, which actually was launched in November 1996, before Pathfinder. But the Global Surveyor has taken a longer route to Mars so it can get into a polar orbit to begin a two-year mapping mission. The craft will arrive at the Red Planet in early September.

The orbiter is carrying two imagers, a wide-angle version that will study regions of the planet throughout the seasons and a high-resolution camera that can see objects on the surface as small as a desktop.

``It's much higher resolution than we've ever gotten before,'' Haynes said. ``But it's a huge amount of data, so you can't map the whole planet at that resolution.''

Nonetheless, Global Surveyor will vastly improve our image data of Mars. Data from the imagers and a laser altimeter will be combined with the data from Mariner 9 and the Viking orbiters to yield a highly detailed map of the Red Planet.

Global Surveyor also is carrying three other instruments to measure thermal emissions and atmospheric conditions.

The orbiter won't start mapping until March 1998 because it will take it that long to get into a close polar orbit using a technique called aerobraking. It starts in a highly elliptical orbit, dipping into the atmosphere on each pass close to the planet to gradually slow itself and reach a close-in circular orbit.

Global Surveyor's mission will be just winding up when the 1998 launches arrive with an orbiter equipped with an infrared sensor and a lander that will set down near the southern polar ice cap.

Descent cameras

There will be no air bags in this landing. The lander will settle to a touchdown on struts, just as the moon landers and the Viking landers did. Since the air bags won't be in the way, this lander will have a descent camera so viewers can watch the landing from the Martian high atmosphere all the way to the ground.

``I think personally we always have to have a camera for the public interest,'' Haynes said. ``We plan to have a descent camera on all future landers.''

Mars' south pole is composed of carbon-dioxide ice, but scientists think the carbon dioxide is covering a vast amount of water ice.

``What we will be looking for is volatile and climate history,'' Haynes said. ``And being close to the polar cap, perhaps you're close to water.''

One of the great mysteries of Mars is where all the water went. There are vast surface features that are clearly carved by great floods, but today liquid water couldn't exist on Mars' surface because the atmospheric pressure is too low. It can only be frozen as ice, or in the air as a gas.

The orbiter in 2001 will have a very high-resolution camera and will be looking for evidence of past or present oases, places where underground water warmed by geothermal energy was vented to the top.

``If you could find something like that, that would be of very high interest,'' McCleese said. ``The device will look for certain concentrations of minerals.''

New rovers

The new rovers will be twice the size of Pathfinder's little Sojourner, perhaps larger, said Jacob Matijevic, the Pathfinder rover manager.

Matijevic said JPL engineers continue to improve on rover designs, with each new generation called a ``Rocky.''

``Sojourner is Rocky IV,'' he said. ``We're up to Rocky VII now.''

The rovers in 2001 and 2003 will be able to travel about 12-1/2 miles and last a whole Martian year - two Earth years.

Only one mission will fly in 2005 because it is so expensive. On that mission, a lander will split off from the mother ship before reaching Mars' orbit. The mother ship will go into orbit while the lander carries a rover to the site where one of the earlier rovers stored a cache of rocks.

The rover will collect the rocks and return to the lander, which will blast off and dock with the mother ship. The mother ship will have enough fuel to power the return to Earth.

The same process is expected to be used in the manned mission, except that 100 tons of cargo will be placed on the Martian surface by earlier robotic missions ahead of the arrival of the crew.

A major component of the cargo will be a miniature plant that can manufacture and store the fuel for the return trip out of Mars' carbon-dioxide atmosphere.