The last remaining Delta II rocket lifted off from Vandenberg on September 15, 2018, marking the true end of an era. The Delta II had one of the most successful track records of any launch vehicle in history, with 154 successful launches out of 155 attempts. The Delta rocket was developed by placing an upper stage on the Thor ballistic missile—in fact, its original name was Thor Delta, which was later shortened to just Delta. Following the Challenger disaster in 1986, the Air Force revamped the Delta rocket to produce the Delta II; it became the rocket of choice for launching GPS, ultimately lifting 48 of the navigation satellites. The medium-lift rocket could haul more than 4000 lb to geosynchronous transfer orbit and sent several missions off to Mars, including the Spirit and Opportunity rovers. The first Delta II launched on February 14, 1989, from Cape Canaveral, carrying the initial GPS Block II satellite. The last one carried a NASA payload along with a number of secondary CubeSats. The final launch marked 100 consecutive launch successes—truly an impressive feat!