Mars Climate Oribiter
Type of Bug: Bad specification
Description: The flight system software on the Mars Climate Orbiter was written to calculate thruster performance using the metric unit Newtons (N), while the ground crew was entering course correction and thruster data using the Imperial measure Pound-force (lbf).
Outcome: The cost of the mission was $327.6 million total for both orbiter and lander, $193.1 million for spacecraft development, $91.7 million for launching it, and $42.8 million for mission operations.
The Ariane V88 exploded 40 seconds after its start.
Type of Bug: The software was written for another type of hardware.
Description: A 64 Bit floating point number was converted into a 16 bit integer in the "inertial reference system" → Overflow → the rocket got into a tilted position and destroyed itself for security reasons. The interesting part is, that this program wasn't even needed for the flight! It had been developed for the Ariane 4.
Outcome: 290 Million Euro destroyed
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