Transient Effects
NASA had launched the Mars Polar Lander (MPL) spacecraft a month after MCO, so the MCO failure caused great consternation. The first phase of the MCO MIB Report included many recommendations for the MPL project intended to reveal problems hidden in the inevitable cracks between subsystems and teams. You can sense barely suppressed panic in the report's dry language.
As nearly as I can tell, the thruster unit conversion problem was fixed and the trajectory corrected during scheduled TCMs. MPL used the fifth contingency TCM skipped by MCO and was exactly on course for Entry, Descent, and Landing (EDL).
...the spacecraft slewed to entry attitude. At this attitude, the antenna pointed off-Earth, and the signal was lost as expected. Lander touchdown was expected to occur at 12:14 p.m. PST, with a 45-minute data transmission to Earth scheduled to begin 24 minutes later. ...However, no communications from MPL or the probes were received.
The 5.5 minute EDL phase consists of a precisely choreographed sequence of operations, each triggered by an external event, a calculation, or an elapsed time. Ensuring valid input data requires considerable attention to detail, because the lander can't pause to mull things over.
The touchdown sensors characteristically generate a false momentary signal at leg deployment. This behavior was understood and the flight software was required to ignore these events; however, the requirement did not specifically describe these events, and consequently, the software designers did not properly account for them.
The MIB determined the failure's probable cause happened after the legs were deployed, when the sensor data were enabled at an altitude of 40 meters, the engines would immediately shut down. The lander would free fall to the surface, impacting at a velocity of 22 meters per second (50 miles per hour), and be destroyed.
