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Evolved Expendable Launch Vehicle (EELV) is an expendable launch system program of the United States Air Force (USAF), intended to assure access to space for Department of Defense and other United States government payloads. The program, which began in the 1990s with the goal of making government space launches more affordable and reliable, resulted in the development of two launch systems, Delta IV and Atlas V. These two launch systems are the primary methods for launching U.S. military satellites. The USAF plans to use the EELV family of launch vehicles until at least 2030. Follow-on technologies are being considered, one of which was originally the Reusable Booster System until its discontinuation. == History == United States’ liquid rocket propulsion technology has evolved over the past five decades to meet the changing needs of the commercial community, agree with Department of Defense (DoD) diminishing budgets, and ensure national access to space. The importance of the United States having assured access to space is best laid out by the National Presidential Directive Number 40 which states: Access to space through U.S. space transportation capabilities is essential to: (1) place critical United States Government assets and capabilities into space; (2) augment space-based capabilities in a timely manner in the event of increased operational needs or minimize disruptions due to on-orbit satellite failures, launch failures, or deliberate actions against U.S. space assets; and (3) support government and commercial human space flight. The United States, therefore, must maintain robust, responsive, and resilient U.S. space transportation capabilities to assure access to space. The United States’ current solution to assure space access for operational space assets is to maintain two families of launch vehicles under the EELV program. The EELV program was initiated in 1995 as the Air Force’s premium space lift modernization program. The purpose of this program was to reduce the cost of operational space launch by 25–50% and to improve reliability over the heritage launch systems (Atlas II, Delta II, and Titan IV). Procurement of EELV boosters for military space launch was to evolve into a “commercial like” nature. The EELV program eventually produced two families of launch vehicles as the solution to US space lift needs. These two families are the Delta IV launch system, developed by McDonnell Douglas (now The Boeing Company), and the Atlas V launch system, developed by Lockheed Martin. The Atlas V and Delta IV Space Launch Boosters Make Up EELV. The United States Air Force (USAF) oversaw the development of the two new launch systems in just five years.〔 Boeing’s Delta IV and Lockheed Martin’s Atlas V programs eventually merged to form the United Launch Alliance (ULA). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Evolved Expendable Launch Vehicle」の詳細全文を読む スポンサード リンク
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