LOS ANGELES (AP) - A mixup over metric and English measurements likely caused the loss of the $125 million Mars Climate Orbiter as it started to circle the planet last week, officials said Thursday.

The error led the probe to fly too close to the red planet, causing the spacecraft to break up or burn up in the Martian atmosphere that it had been designed to study, mission controllers at NASA's Jet Propulsion Laboratory said.

English measurements are the familiar terms like inches, feet and pounds. Metric measurements such as meters and kilograms, however, are commonly used in space exploration and other scientific studies.

A spacecraft team at Lockheed Martin Astronautics in Colorado submitted acceleration data in pounds of force, but JPL navigators assumed the numbers were metric newtons. Error checkers failed to notice the discrepancy. ''Newtons'' are a metric measurement of the force needed to get something to accelerate.

''It was embedded in the system from the beginning,'' said Tom Gavin, deputy director of JPL's space and Earth science program. ''We're still looking at why it was not detected.''

Gavin said the erroneous numbers affected the trajectory of the probe in a way that was not immediately apparent to Earth-based navigators.

''People sometimes make errors,'' said Edward Weiler, the National Aeronautics and Space Administration's associate administrator for space science. ''The problem here was not the error, it was the failure of ... the checks and balances in our processes to detect the error. That's why we lost the spacecraft.''

Two separate review committees are investigating the incident at JPL; a third board will be formed shortly by NASA.

''Our inability to recognize and correct this simple error has had a major implications,'' said JPL director Edward Stone. ''We have under way a thorough investigation to understand the issue.''

The spacecraft, built in about four years on what for space exploration was a shoestring budget, was to have been a shining example of NASA's policy of faster, better and cheaper solar system missions.

Last week, NASA Administrator Daniel Goldin said the investigators will not be casting blame but making sure that whatever caused the loss does not happen again.
The orbiter's sibling spacecraft, Mars Polar Lander, is set to arrive Dec. 3.

''Our clear short-term goal is to maximize the likelihood of a successful landing of the Mars Polar Lander,'' Weiler said. ''The lessons from these reviews will be applied across the board in the future.''

The orbiter was to have acted as a relay for the lander. With the loss, mission controllers will rely on direct communications with Earth as well as relaying information via the Mars Global Surveyor, which has been orbiting Mars since 1997.

The lander is equipped with instruments to study Mars' climate history and weather with the goal of finding what happened to water on the red planet. It is equipped with a robotic arm that will collect samples for testing inside the spacecraft.

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