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The Evolved Expendable Launch Vehicle (EELV) program is a United States government, primarily a Department of Defense–sponsored effort to develop at least one family of space launch vehicles, that would meet the long term needs of the military and fulfill commercial and government need for cost-efficient and reliable access to earth orbit.

The U.S. Air Force assembled its initial blue print for the EELV in 1994, following many years of government funded studies into an improved system and architecture, which was intended to replace most if not all existing “legacy” spacelifters (e.g. Delta II, Atlas II/Centaur, Titan IV, etc.). The architecture called for the spacelifter to be based on standardized fairings, liquid core vehicles, upper stages, and solid rockets. The standard payload interface was also proposed as another way to save money and improve efficiency.

The initial bid from four major defense contractors Lockheed Martin, Boeing, McDonnell Douglas, and Alliant Techsystems. Each of the bids had a variety of different concepts. One of the contractors, Boeing, initially proposed utilizing the Space Shuttle Main Engines (SSME).^[1] McDonnell Douglas would merge with Boeing in 1997 and use its Delta IV spacelifter for the EELV.

Boeing and Lockheed Martin were both collectively awarded US$ 100 million for the final phase of the bid. Both companies built their designs around modularization, standardization and minimizing the amount of equipment and using proven, reliable and simplified systems. Boeing developed the Common Booster Core (CBC) that would be the center of the Delta IV. Lockheed Martin would do something similar with the Atlas V but call it a Common booster.

Boeing was found to be in possession of proprietary documents from Lockheed Martin. To end litigation both companies came to an agreement to join forces and form United Launch Alliance joint venture. Each will have a 50-50 stake in this venture.

• Delta IV rocket
• Atlas V
• Expendable launch system

• EELV on Global Security
• Lockheed Martin's Atlas V page
• Boeing's Delta IV page
• United Launch Alliance (ULA) page