The USA planned to phase out all expendable launch vehicles (ELV) after the Space Shuttle entered service. However, the Challenger accident of 1986 changed all that, and the Delta program was restarted. Termed Delta II, these rockets achieved their 75th consecutive successful launch on 18 September 2007. To date, they have made 151 launches since 1989, and the type is recognized as the most reliable system in service. Originally built by McDonnell Douglas, production for both US government and commercial entities is now the responsibility of United Launch Alliance (ULA). As an ELV, each rocket can only be launched once. A Delta II rocket consists of Stage I tanks, solid rocket boosters, interstage, Stage II tanks, optional Stage III rocket motor, and finally the payload fairing (nose cone).