Mars Orbiting Craft Presumed Destroyed By Navigation Error

New York Times - September 24, 1999

By JOHN NOBLE WILFORD

$125 million robotic spacecraft, the first ever dispatched especially to investigate weather on another world, was missing on Thursday and presumed destroyed just as it was supposed to go into an orbit around Mars.

As the slenderest hopes of re-establishing radio contact diminished with each passing hour, project officials announced that the spacecraft, the Mars Climate Orbiter, was "believed to be lost due to a suspected navigation error." It probably flew too close to the planet, within 37 miles of the surface, disintegrating or burning up in the atmosphere or, possibly but less likely, crashing into the surface.

The apparent navigation problem, officials said, was caused by human or software error, not mechanical failure on the spacecraft. The trouble was not detected by flight controllers until it was too late to be corrected.

Engineers were investigating the failure Thursday night, and tracking stations were still trying a wide range of radio frequencies in the hope of catching a signal, in the event all is not lost.

But if the spacecraft somehow drifted as far off course as the last tracking data indicated, engineers said, it could not have survived. At any altitude less than 53 miles, their studies showed, the vibrations and heat from atmospheric friction would have torn the vehicle apart.

At a news conference at Jet Propulsion Laboratory in Pasadena, Calif., Richard Cook, the project manager, said, "We believe the spacecraft came in at a lower altitude than we thought it would and that potentially resulted in the loss of the mission."

Scientists and officials of the National Aeronautics and Space Administration, putting the best face on the situation, said the apparent loss of the spacecraft was a bitter disappointment but not a devastating blow to the newly revived program of systematic Mars exploration with low-budget missions mounted every two years.

They emphasized that the failure was not expected to disrupt operations of a companion spacecraft, Mars Polar Lander, which is scheduled to reach the planet on Dec. 3. It is cruising on course for a landing at the edge of the south polar ice cap, where the frozen ground is thought to hold a record of the planet's climate history.

Though the ill-fated Climate Orbiter was supposed to relay communications between the lander and Earth, flight controllers said that the landing craft was capable of direct communications to Earth. Another alternative would be to transmit some radio traffic through Mars Global Surveyor, a spacecraft that has been orbiting and mapping the planet since 1997.

Referring to the polar lander, Dr. Carl Pilcher, science director for solar system exploration at NASA headquarters in Washington, said, "The science return of that mission won't be affected."

Even if the Climate Orbiter is indeed lost, Pilcher said, its science objectives -- observing weather over a full Martian year (687 days) and searching for the cold, arid planet's water resources -- could be met by missions already on the drawing board for the next decade.

"This is not necessarily science lost," he said. "It is science delayed."

Still, it was especially frustrating for scientists like Dr. Daniel McCleese, who built one of the two principal scientific instruments on the Climate Orbiter. It is an infrared radiometer for examining the temperatures and water content of the Martian atmosphere.

And it is identical to the instrument he designed for an earlier spacecraft, Mars Observer, which suffered an eerily similar fate as it approached Mars six years ago. For reasons still unknown, all signals from Observer suddenly stopped three days out from Mars, and it was never heard from again.

That was a devastating failure, McCleese recalled in an interview, because the mission cost nearly $1 billion and was all scientists had for exploring Mars.

In the new strategy of spreading risks by sending out several, low-cost spacecraft, he said, "Mars exploration is now designed to be tolerant of this kind of failure, and no one mission should make or break the program."

McCleese, who is also chief scientist for the Mars Exploration Directorate at Jet Propulsion Laboratory, said he was not sure he wanted to try again with a third radiometer. "I can do it," he said, "but will I?"

As far as flight controllers knew, all was well with the 1,387-pound Climate Orbiter when it approached the northern hemisphere of Mars and fired its main rocket engine at about 5 a.m. Eastern time to go into orbit. All data coming into the control rooms in Pasadena and at Lockheed Martin Astronautics in Denver appeared normal.

The rocket firing to slow down the craft was to last 16 minutes, but controllers could monitor only the first 5 minutes. As planned, the craft slipped behind the planet as seen from Earth and radio contact was lost.

If the spacecraft was safely in orbit, contact with it should have been restored by 5:30. But there was nothing but silence. Flight controllers waited anxiously. If it was some common malfunction on board, the spacecraft had instructions on how to call on backup systems to restore operations. But nothing happened.

More than three hours later, Dr. Richard W. Zurek, the project scientist, grew pessimistic. "The longer we don't hear from it, the worse off we are," he said.

After engineers examined tracking data from the spacecraft's approach to Mars, officials discovered the likely navigation problem. A trajectory-adjusting maneuver last Wednesday had put the spacecraft on course to come no closer to the surface of Mars than 93 miles. It appeared that the actual altitude would be 37 miles.

Cook, the project manager, said that there was a significant drop in the spacecraft's trajectory in the last few hours of the approach, but ground controllers had for some reason failed to detect the navigation deviation until it was too late.

Asked if human error, software problems or mechanical failures were to blame, Cook said, "We are essentially ruling out spacecraft (mechanical) error and we are looking at the other two."

The two spacecraft, Climate Orbiter and Polar Lander, are part of a $327.5 million mission to Mars primarily to study its climate for an understanding of conditions there in an earlier epoch that might have been conducive to the emergence of life.

Two years ago, Mars Pathfinder and its roving vehicle, Sojourner, explored the geology of the planet, and Global Surveyor is photographing the surface for evidence of the planet's warmer, wetter past.