The mission had proceeded normally and was believed to be on track as the spacecraft went behind Mars causing a planned 20 minute loss of its signal as it was occulted by the planet (occult means to hide). The 20 minutes came and went with no resumption of contact with the spacecraft. NASA now believes that the Mars Climate Orbiter was destroyed because of a navigation error which caused a much lower angle of descent into the Martian atmosphere, an angle of descent outside the structural capabilities of the spacecraft. NASA's disappointment was understandable. What wasn't understandable was the reason that the target altitude of 80 to 90 kms was missed.
To quote NASA, '[t]he 'root cause' of the loss of the spacecraft was the failed translation of English units into metric units in a segment of ground-based, navigation-related mission software, as NASA has previously announced.' In plain English, spacecraft engineers failed to coordinate their numbers. It turns out that a team of engineers at NASA was using metric numbers to calculate the target altitude, while the company that built the spacecraft was using feet and inches. A trip of 35 million miles was destined to failure because of a few inches and millimeters. So next time you're doing some math problems, remember what your teacher told you -- check your work.
'The strength and weakness of physicists is that we believe in what we can measure. And if we can't measure it, then we say it probably doesn't exist. And that closes us off to an enormous amount of phenomena that we may not be able to measure because they only happened once. For example, the Big Bang. ... That's one reason why they scoffed at higher dimensions for so many years. Now we realize that there's no alternative... '