The Saturn I and IB series of rockets fulfilled plans developed in the late 1950s to build a rocket which could triple the existing thrust levels of US rockets and equal the lifting capacity of the Soviet Union, launching satellites and spacecraft weighing more than 10 tonnes into Earth orbit and do it by the early 1960s. Three times more powerful than anything launched by America to that date, with a cluster of eight rocket motors for the first stage, the first Saturn I flew on 27 October 1961 and propelled America into the heavy-lift business. It was the Saturn I, and its successor the Saturn IB, with a more powerful second stage, that did all the preparatory work getting NASA ready to put men on the Moon. The Saturn I and IB was used on 19 launches, including the first manned Apollo spacecraft, Apollo 7 in 1968, all three Skylab flights in 1973 and the last Apollo spacecraft, flown in support of the Apollo-Soyuz Test Project in 1975.