Mission controllers believe that the orbiter may have dipped 60 miles closer to the Martian surface than expected -- just 38 miles (60 kilometers) high -- with friction from atmospheric entry tearing the craft apart.

An alternative explanation is that the orbiter ricocheted off the atmosphere and is now hurtling off in space.

In preliminary findings, the review board says that project teams in Colorado and California were using different measurement systems -- one in feet and pounds, and the other in metric units -- to measure "critical" information for the spacecraft's maneuvers.

Those units were not standardized, the team says, leading to errors that sent that craft on an incorrect path.

"People sometimes make errors," Dr. Edward Weiler, NASA's Associate Administrator for Space Science, said in a statement. "The problem here was not the error, it was the failure of NASA's systems engineering, and the checks and balances in our processes to detect the error. That's why we lost the spacecraft."

NASA set up two investigation teams after the loss of the craft, an internal review board and another board made up of experts from both inside and outside NASA. The space agency is also planning to form a third panel to review the accident.

While NASA is gazing back at the orbiter's accident, it is also looking forward to another Mars mission, the Mars Polar Lander, which is scheduled to land on the planet on December 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."