Data and Expressions - Java Software Solutions: Foundations of Program Design - page 112

The cause of the lander's communication problem is unresolved but is not
believed to be related to the orbiter's problem. The investigation concluded that
the most likely cause was a software error that mistook the vibration caused by
the deployment of the lander's legs for the vibration caused by actually landing on
the planet's surface. That mistake would have caused the lander's descent engines
to cut off while it was still 40 meters above the ground. Other problem scenarios
are possible, however.
Lessons Learned
The mismatch of units in the Mars Climate Orbiter shows that seemingly obvious
problems can be overlooked in a highly complex system. Mistakes are inevitable,
but processes must be in place to catch them before they become critical. The
investigation concluded that, in this case, the system for tracking and double-
checking interconnected elements between subsystems was not robust enough.
There was also inconsistent training of and communication with new members of
the team, and some communication lines were too informal. In short, the mission
lacked a rigorous total-system view that would have led to the discovery of the
mismatched units problem before it was too late.
It's difficult to draw strong conclusions from the lander's problem given that the
cause is not clearly understood. The fact that it remains an open question under-
scores the need for more evaluation, simulation, and testing in situations where
critical resources are at stake.
Source: nasa.gov