Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in 1989. There were two main variants, the Delta 6000 and Delta 7000, with the latter also having "Light" and "Heavy" subvariants. During its career, Delta II flew several notable payloads, including 24 Global Positioning System (GPS) Block II satellites, several dozen NASA payloads, and 60 Iridium communication satellites. The rocket flew its final mission, ICESat-2, on 15 September 2018, earning the launch vehicle a streak of 100 successful missions in a row, with the last failure being GPS IIR-1 in 1997. In the late 1990s, Delta II was developed further into the unsuccessful Delta III, which was in turn developed into the more capable and successful Delta IV, though the latter shares little heritage with the original Thor and Delta rockets.

McDonnell Douglas Corporation was a major American aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own merger with Boeing in 1997, it produced well-known commercial and military aircraft, such as the DC-10 and the MD-80 airliners, the F-15 Eagle air superiority fighter, and the F/A-18 Hornet multirole fighter.