section_path: Capabilities/Engine-out capability
section_name: Engine-out capability
paragraph_text: Engine-out capability
  
  Like the Saturn family of rockets, multiple engines allow for mission completion even if one fails. Detailed descriptions of destructive engine failure modes and designed-in engine-out capabilities were made public.
  
  SpaceX emphasized that the first stage is designed for "engine-out" capability. CRS-1 in October 2012 was a partial success after engine number 1 lost pressure at 79 seconds, and then shut down. To compensate for the resulting loss of acceleration, the first stage had to burn 28 seconds longer than planned, and the second stage had to burn an extra 15 seconds. That extra burn time reduced fuel reserves so that the likelihood that there was sufficient fuel to execute the mission dropped from 99% to 95%. Because NASA had purchased the launch and therefore contractually controlled several mission decision points, NASA declined SpaceX's request to restart the second stage and attempt to deliver the secondary payload into the correct orbit. As a result, the secondary payload reentered the atmosphere.
  
  Merlin 1D engines have suffered two premature shutdowns on ascent. Neither has affected the primary mission, but both landing attempts failed. On an March 18, 2020, Starlink mission, one of the first stage engines failed 3 seconds before cut-off due to the ignition of some isopropyl alcohol that was not properly purged after cleaning. On another Starlink mission on February 15, 2021, hot exhaust gasses entered an engine due to a fatigue-related hole in its cover. SpaceX stated the failed cover had the "highest... number of flights that this particular boot design had seen."