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 have made nearly 150 successful launches since 1989, making it 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). Among the Delta II?s missions are the launching of GPS Block II satellites, Iridium satellites, and several Mars missions for NASA. The latter includes the Mars Phoenix lander in 2007. The future of the Delta II space rocket is uncertain beyond 2011 once the Medium Launch Vehicle 3 contract with the US Air Force expires, but despite this it has proved a hugely successful design to date.
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