September 23, 2021
Today in 1999, the Mars Climate Orbiter began a planned orbital insertion maneuver around Mars. The orbiter went out of radio contact when the spacecraft passed behind Mars and communication was never reestablished. It is believed the spacecraft encountered the planet at a lower than anticipated altitude and was either destroyed in the atmosphere or re-entered heliocentric space after leaving Mars’ atmosphere.
Diagram of Delta II launch vehicle with Mars Climate Orbiter. Credit: NASA, JPL/Caltech, Lockheed Martin