The Apollo program used four types of launch vehicles. The first was the Little Joe II, which was used for uncrewed suborbital launch escape system development. The second was the Saturn I, which was used for uncrewed suborbital and orbital hardware development. The third was the Saturn IB which was used for preparatory uncrewed missions and Apollo 7. Last, the Saturn V which was used for uncrewed and crewed Earth orbit and lunar missions. The Marshall Space Flight Center, which designed the Saturn rockets, referred to the flights as Saturn-Apollo (SA), while Kennedy Space Center referred to the flights as Apollo-Saturn (AS). This is why the uncrewed Saturn I flights are referred to as SA and the uncrewed Saturn IB are referred to as AS.