https://en.wikipedia.org/wiki/Mars_Climate_Orbiter
> The spacecraft encountered Mars on a trajectory that brought it too close to the planet, and it was either destroyed in the atmosphere or escaped the planet's vicinity and entered an orbit around the sun. An investigation attributed the failure to a measurement mismatch between two software systems: metric units by NASA and non-metric ("English") units by spacecraft builder Lockheed Martin.
https://en.wikipedia.org/wiki/Mars_Polar_Lander#Landing_atte...
> Communication was expected to be reestablished with the spacecraft at 20:39:00 UTC after having landed. However, no communication was possible with the spacecraft, and the lander was declared lost.