Reflight
Prior to launch, and continuing through the early part of the mission, flight controllers on the ground were monitoring an anomaly within the electrical power generating Fuel Cell #2 (of three), making it appear that oxygen and hydrogen might be starting to uncontrollably mix, which could lead to detonation. Despite troubleshooting, the anomaly persisted and appeared to worsen. Mission Flight Rules required that the fuel cell be shut down once a certain voltage threshold had been crossed, and with only two of three fuel cells working, that invoked another Flight Rule which required the mission be terminated early (loss of a second fuel cell would require severe and dangerous powerdowns, though the shuttle operates normally on two). Payload Specialist Dr. Linteris described the mission as "an exercise in crisis management. The main buss alarm was going off continually."
Upon landing, mission managers decided that Columbia did not need to be processed per a typical end of mission maintenance flow. Instead, they called for an unprecedented reflight of the same mission, once the normal processing could be completed (refill the propellant tanks and other consumables like oxygen, hydrogen, nitrogen, and water, change out the main engines, etc.). The same crew flew the reflight, which was designated STS-94 (the next available unused shuttle mission number at the time), three months later, in July 1997. The crew patch was updated with the reflight, changing the outer border from red to blue and changing the flight number from 83 to 94.
Read more about this topic: STS-83