The Lockheed Martin P-791 is an experimental aerostatic/aerodynamic hybrid airship developed by Lockheed Martin corporation. The first flight of the P-791 was on 31 January 2006 at the company's flight test facility on the Palmdale Air Force Plant 42. It has a unique tri-hull shape, with disk-shaped cushions on the bottom for landing. As a hybrid airship, part of the weight of the craft and its payload are supported by aerostatic (buoyant) lift and the remainder is supported by aerodynamic lift. The combination of aerodynamic and aerostatic lift is an attempt to benefit from both the high speed of aerodynamic craft and the lifting capacity of aerostatic craft. The P-791 was originally part of the U.S. Army's LEMV program, but lost to Northrop Grumman's design. The P-791 is now being modified to be a civil cargo aircraft with a lift capability of 20 tons (40,000 pounds). An airship or dirigible is a type of aerostat or lighter-than-air aircraft that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms. Unlike aircraft that use aerodynamics, such as fixed-wing aircraft and helicopters that produce lift by moving an airfoil through the air, aerostatic aircraft stay aloft by having a large "envelope" filled with a lifting gas that is less dense than the surrounding air. In early dirigibles, the lifting gas used was hydrogen, despite widespread concern due to its flammability. The alternative, helium, is nonflammable, but rare in most parts of the world. Large amounts of it were discovered in the United States. Thus, for a while, helium was rarely used for airships outside the United States. [1] All modern airships, made since the 1960s, have used helium.[note 1] Lockheed Martin (NYSE: LMT) is an American global aerospace, defense, security, and advanced technology company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area. Lockheed Martin employs 123,000 people worldwide. Marillyn Hewson is the current president and Chief Executive Officer. Lockheed Martin is one of the world's largest defense contractors; In 2009, 74% of Lockheed Martin's revenues came from military sales.[2] It received 7.1% of the funds paid out by the Pentagon.[3] The United States Air Force (USAF) is the aerial warfare service branch of the United States Armed Forces and one of the seven American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on 18 September 1947 under the National Security Act of 1947.[5] It is the most recent branch of the U.S. military to be formed, and is the largest and one of the world's most technologically advanced air forces. The USAF articulates its core functions as Nuclear Deterrence Operations, Special Operations, Air Superiority, Global Integrated ISR, Space Superiority, Command and Control, Cyberspace Superiority, Personnel Recovery, Global Precision Attack, Building PartnershThe United States of America (USA or U.S.A.), commonly referred to as the United States (US or U.S.), America, or simply the States, is a federal republic[10][11] consisting of 50 states and a federal district. The 48 contiguous states and the federal district of Washington, D.C. are in central North America between Canada and Mexico. The state of Alaska is the northwestern part of North America, west of Canada and east of Russia which is across the Bering Strait in Asia, and the state of Hawaii is an archipelago in the mid-North Pacific. The country also has five populated and nine unpopulated territories in the Pacific and the Caribbean. At 3.79 million square miles (9.83 million km2) in total and with around 315 million people, the United States is the fourth-largest in total area, the fifth largest in the contiguous area and third in population. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries.[12] The geography and climate of the U.S. is also extremely diverse, with deserts, plains, forests, and mountains that are home to a wide variety of wildlife.ips, Rapid Global Mobility and Agile Combat Support.[6] Barack Hussein Obama II (Listeni/bəˈrɑːk huːˈseɪn oʊˈbɑːmə/; born August 4, 1961) is the 44th and current President of the United States, the first African American to hold the office. Born in Honolulu, Hawaii, Obama is a graduate of Columbia University and Harvard Law School, where he was president of the Harvard Law Review. He was a community organizer in Chicago before earning his law degree. He worked as a civil rights attorney in Chicago and taught constitutional law at the University of Chicago Law School from 1992 to 2004.

• published: 11 Sep 2013
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