Not only was this the first launch of the Space Shuttle, but it marked the first time that solid-fuel rockets were used for a NASA crewed launch (although previous systems had used solid-fuel motors for their escape towers or retro rockets). STS-1 was also the first U.S. crewed space vehicle launched without an uncrewed powered test flight. The STS-1 orbiter, "Columbia", also holds the record for the amount of time spent in the Orbiter Processing Facility (OPF) before launch – 610 days, the time needed for the replacement of many of its heat shield tiles.