ROVER ON THE GO; SOJOURNER BEGINS SURVEY OF MARS.

Byline: Tony Knight Daily News Staff Writer

Mars Pathfinder's companion rover, Sojourner, was rolled down a metal ramp to the Martian surface Saturday and began its historic mission exploring the Red Planet.

Mission engineers at Pasadena-based Jet Propulsion Laboratory said the rover's deployment went off without a hitch after a glitch in communications between the rover and lander was solved earlier in the day.

``I'd like to present to you the first images of a rover on the surface of Mars as we open a new era of exploration,'' said a beaming Jacob Matijevic, manager of the rover team.

Images beamed to Earth late Saturday night showed the six-wheeled rover, which is about the size of a small microwave oven, on the deployment ramp and finally out on the surface, its wheel marks visible in the Martian soil.

``This is a beautiful set of images,'' said Matijevic, whose team has fretted over communications problems between the lander and its rover sidekick earlier in the day.

But the problems were cleared up as the sun rose on the Martian site Saturday at about 1 p.m. PDT, although the delay postponed the downloading of many new color images.

With the rover off on its voyage on the surface of Mars, the main imaging camera on the Pathfinder lander was to be deployed to its full height early this morning and new color images from the higher perspective were expected to be returned by midafternoon.

New images also were expected from the rover's two black-and-white cameras and one color camera as it picks its way through the boulder field, deploying an X-ray spectrometer to determine the composition of the rocks and soil.

Almost all the problems seemed to be cleared up, but mission engineers remained puzzled that the lander computer had automatically reset itself late Friday night as Earth communications were lost.

``The lander is fine, the rover is fine,'' said mission manager Richard Cook. ``It's essentially operating as it's supposed to. But we are a little perplexed. We're going to try to get some more diagnostic data down to analyze what's going on.''

Mission scientists were brimming with excitement at the variety of geological formations shown in the panoramic pictures. The primary science objective of the mission is to study the planet's geology.

``We landed in the most spectacular place we've ever seen on Mars,'' said Matt Golombek, chief mission scientist. ``It's gorgeous. We have a variety of rocks and soils to look at. It couldn't have been better.''

A stunning, 12-foot-long panorama of Pathfinder's landing site on Mars was displayed by the mission's imaging team Saturday clearly showing a crater rim to the south, sand dunes to the east and a curious dark outcropping on the northwest horizon that has been nicknamed ``The Couch.''

The black-and-white panorama, a mosaic of all the images downloaded Friday, was displayed on a long piece of paper held by six members of the imager team.

It took five hours to print out, said Peter Smith, the image team's principal investigator.

``It looks like Tucson,'' said the University of Arizona professor as he surveyed the panorama of sand and boulders.

``You see ridges and valleys like you see in the arroyos of Arizona,'' Smith said of the rocky Ares Vallis flood plain where pathfinder made its near-perfect landing Friday. ``The atmosphere seems to have a lot of dust in it. If we get some clear days, we may be able to see some distant mountains.''

Mission scientists said they think they have pinpointed their location on the Martian surface by comparing the landmarks that Pathfinder can see with images taken from space by the Viking orbiters in the 1970s.

A large crater to the south on the Viking image can be seen as a crater rim on the Pathfinder images.

The scientists also think Pathfinder can see the tip of a large hill peaking above the horizon to the southeast.

Already, scientists and reporters are giving nicknames to the Martian features.

A gnarled rock near the lander's northwest side has been dubbed ``Barnacle Bill.'' The double rise to the west is ``Twin Peaks.''

The Couch appears to be two dark boulders leaning against each other.

To the north and very close to the lander lies a huge boulder perhaps six feet high. Scientists haven't named it but some reporters encamped at JPL were referring to it as ``The Big Guy.''

``We're going to put this picture up in our science room, and as we come up with names for these features, we're going to put little Post-Its on it with the names so we know what to call them,'' Smith said.

Mission engineers on Saturday solved what could have been a crippling communication breakdown between the Pathfinder lander and its little rover.

Early data on the first day indicated that the two were communicating, but only barely.

``We're not getting full sentences,'' said Brian Muirhead, flight systems manager. ``We're only getting a few words across.''

Solving the problem was crucial because any data the rover gathers must be transferred to the lander to be beamed to Earth.

The lander and rover are communicating through commercially built radio modems each about the size of a pack of cards.

Late Friday, engineers commanded both the rover and lander to turn their modems off and on repeatedly. With the first down-link of data at 3:20 p.m. Saturday, they learned that the plan had worked.

``We have rover data,'' said flight director Jennifer Harris over the cheers and applause in mission control.

Rover team engineers said they aren't sure what went wrong and were analyzing the data.

But they were clearly relieved that the data were being transferred and the process of deploying the rover was begun late Saturday afternoon.

``We feel like somebody just invited us back to the party,'' said Matt Wallace, rover coordinator.

Mission scientists refer to the stereoscopic camera on the lander as the IMP, as in Imager for Mars Pathfinder.

The images taken by the camera on the first day were taken from its stowed position about three feet above the Martian surface.

Today, the imager team planned to raise the camera on a mast to its operational height 5 feet 7 inches above the lander base so that subsequent images are taken from the perspective of a human standing on the surface.

The mission engineers are using a duplicate of a Pathfinder lander and its rover sidekick in a special ``Mars room'' at JPL where they practice every move before it is made at the landing site.

The room is filled with sand and rocks similar to the Martian landscape. In practice sessions, mission engineers operate blind without being able to see in the room, just as if they were communicating with the distant Martian surface.

``We use the room to be our Mars, in a sense,'' said mission manager Richard Cook. ``We're acting like we're actually operating the spacecraft remotely and what happens in this room is what happens on Mars.''

Later in the week, mission engineers using JPL's big processing computers hope to be able to create a videotape simulation using hundreds of stereo images from the landing site.

``We have the ability to simulate flying around in the terrain,' Cook said. ``You'll really feel like you're at the landing site, flying around and looking at stuff.''

The Pathfinder probe had no camera to record its dramatic descent and bouncing landing on air bags. But the Discovery mission in 1998 will have a camera that will record its descent to the Red Planet's south polar ice cap.

CAPTION(S):

5 Photos

Photo: (1--color) Panoramic view from Pathfinder: A JPL composite shows a 360-degree view of the Martian surface from the probe.

(2--color) Pathrider's rover, Sojourner, rolls off its ramp into Martian soil late Saturday to begin its study of Mars geology.

(3--color) University of Arizona scientist Peter Smith describes a panoramic view of Mars during a news conference Saturday at JPL in Pasadena.

(4-5--color) A red arrow points to the area of Mars where scientists believe the Pathfinder landed, left, based on views from the surface, above, transmitted back to Earth. The lander's air bags are visible in the front of the image, while hills are visible on the Martian horizon about 20 miles away.

Associated Press