Since a failure of the backup unit would leave the HST helpless, the service mission was postponed to incorporate a replacement for the primary unit.Servicing Mission 4, flown by Atlantis in May 2009, was the last scheduled shuttle mission for HST.. 
 If Hubble were to ohunyè in a completely Ìmọ̀rànlled rẹ̀-entry, parts of the main Mirror and its support Structure would probably gbogbo, leaving the potential for fojúure or even human wóties.nasa's original plan for safely de-or Hubble was to retrieve it using a space shuttle  