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Skydiver (submarine)
Parachuting, including also skydiving, is a method of transiting from a high point in the atmosphere to the surface of Earth with the aid of gravity, involving the control of speed during the descent using a parachute or parachutes. For human skydiving, it may involve a phase of more or less free-falling (the skydiving segment) which is a period when the parachute has not yet been deployed and the body gradually accelerates to terminal velocity. For cargo parachuting, the parachute descent may begin immediately, such as a parachute-airdrop in the lower atmosphere of Earth, or be significantly delayed, such as in a planetary atmosphere where an object is descending "under parachute" following atmospheric entry from space, and may begin only after the hypersonic entry phase and initial deceleration that occurs due to friction with the thin upper atmosphere. History Common uses Parachuting is performed as a recreational activity and a competitive sport, and is w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mars Lander
A Mars landing is a landing of a spacecraft on the surface of Mars. Of multiple attempted Mars landings by robotic, uncrewed spacecraft, ten have had successful soft landings. There have also been studies for a possible human mission to Mars, including a landing, but none have been attempted. Soviet Union’s Mars 3, which landed in 1971, was the first successful Mars landing. As of May 2021, the Soviet Union, United States, and China have conducted Mars landings successfully. Methods of descent and landing As of 2021, all methods of landing on Mars have used an aeroshell and parachute sequence for Mars atmospheric entry and descent, but after the parachute is detached, there are three options. A stationary lander can drop from the parachute back shell and ride retrorockets all the way down, but a rover cannot be burdened with rockets that serve no purpose after touchdown. One method for lighter rovers is to enclose the rover in a tetrahedral structure which in turn is e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aviators
An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are also considered aviators, because they are involved in operating the aircraft's navigation and engine systems. Other aircrew members, such as drone operators, flight attendants, mechanics and ground crew, are not classified as aviators. In recognition of the pilots' qualifications and responsibilities, most militaries and many airlines worldwide award aviator badges to their pilots. History The first recorded use of the term ''aviator'' (''aviateur'' in French) was in 1887, as a variation of ''aviation'', from the Latin ''avis'' (meaning ''bird''), coined in 1863 by in ''Aviation Ou Navigation Aérienne'' ("Aviation or Air Navigation"). The term ''aviatrix'' (''aviatrice'' in French), now archaic, was formerly used for a female aviator. These terms were used more in the ea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territories, nine Minor Outlying Islands, and 326 Indian reservations. The United States is also in free association with three Pacific Island sovereign states: the Federated States of Micronesia, the Marshall Islands, and the Republic of Palau. It is the world's third-largest country by both land and total area. It shares land borders with Canada to its north and with Mexico to its south and has maritime borders with the Bahamas, Cuba, Russia, and other nations. With a population of over 333 million, it is the most populous country in the Americas and the third most populous in the world. The national capital of the United States is Washington, D.C. and its most populous city and principal financial center is New York City. Paleo-Americ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Smokejumpers
Smokejumpers are specially trained wildland firefighters who provide an initial attack response on remote wildland fires. They are inserted at the site of the fire by parachute. In addition to performing the initial attack on wildfires, they may also provide leadership for extended attacks on wildland fires. Shortly after smokejumpers touch ground, they are supplied by parachute with food, water, and firefighting tools, making them self-sufficient for 48 hours. Smokejumpers are usually on duty from early spring through late fall. Smokejumpers worldwide Smokejumpers are employed by the Russian Federation, United States (namely the United States Forest Service and Bureau of Land Management), and Canada (in British Columbia). History Prior to the full establishment of smokejumping, experiments with parachute insertion of firefighters were conducted in 1934 in Utah and in the Soviet Union. Earlier, aviation firefighting experiments had been conducted with air delivery of equipm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Forest Firefighter
Wildfire suppression is a range of firefighting tactics used to suppress wildfires. Firefighting efforts in wild land areas require different techniques, equipment, and training from the more familiar structure fire fighting found in populated areas. Working in conjunction with specially designed aerial firefighting aircraft, these wildfire-trained crews suppress flames, construct fire lines, and extinguish flames and areas of heat to protect resources and natural wilderness. Wildfire suppression also addresses the issues of the wildland–urban interface, where populated areas border with wild land areas. In the United States and other countries, aggressive wildfire suppression aimed at minimizing fire has contributed to accumulation of fuel loads, increasing the risk of large, catastrophic fires. History Australia Wildland fire, known in Australia as bush fire, has played a major role in Australia due to arid conditions. Notable fire services tasked with wildfire suppressio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Special Operations
Special operations (S.O.) are military activities conducted, according to NATO, by "specially designated, organized, selected, trained, and equipped forces using unconventional techniques and modes of employment". Special operations may include reconnaissance, unconventional warfare, and counter-terrorism actions, and are typically conducted by small groups of highly-trained personnel, emphasizing sufficiency, stealth, speed, and tactical coordination, commonly known as " special forces". History Australia In World War II following advice from the British, Australia began raising special forces. The first units to be formed were independent companies, which began training at Wilson's Promontory in Victoria in early 1941 under the tutelage of British instructors. With an establishment of 17 officers and 256 men, the independent companies were trained as "stay behind" forces, a role that they were later employed in against the Japanese in the South West Pacific Area during 1942 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Airborne Forces
Airborne forces, airborne troops, or airborne infantry are ground combat units carried by aircraft and airdropped into battle zones, typically by parachute drop or air assault. Parachute-qualified infantry and support personnel serving in airborne units are also known as paratroopers. The main advantage of airborne forces is their ability to be deployed into combat zones without land passage, as long as the airspace is accessible. Formations of airborne forces are limited only by the number and size of their transport aircraft; a sizeable force can appear "out of the sky" behind enemy lines in merely hours if not minutes, an action known as ''vertical envelopment''. Airborne forces typically lack enough supplies for prolonged combat, so they are utilized for establishing an airhead to bring in larger forces before carrying out other combat objectives. Some infantry fighting vehicles have also been modified for paradropping with infantry to provide heavier firepower. Due ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
United States Parachute Association
The United States Parachute Association (USPA) is a private sports governing body for the sport of skydiving in the United States. Its headquarters are located in Fredericksburg, Virginia. The USPA's roots go back to the National Parachute Riggers-Jumpers, Inc., which was formed in the 1930s. Functions USPA performs the following functions: * Issues sport skydiving licenses * Publishes and maintains skydiving training manuals and course guidelines from which instructional ratings are issued * Serves as legal advocate and political lobbyist for skydiving * Provides third-party insurance for skydivers * Maintains the Basic Safety Requirements (BSRs) as a set of voluntarily followed safety guidelines * Coordinates skydiving competitions and awards * Issues awards for longevity, skill and achievement * Publishes ''Parachutist'', a monthly magazine for members In November 2020, USPA announced their plans for a National Skydiving Museum to be built in Central Florida, but didn't specif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extreme Sport
Action sports, adventure sports or extreme sports are activities perceived as involving a high degree of risk. These activities often involve speed, height, a high level of physical exertion and highly specialized gear. Extreme tourism overlaps with extreme sport. The two share the same main attraction, " adrenaline rush" caused by an element of risk, and differ mostly in the degree of engagement and professionalism. Definition The definition of extreme sports is not exact and the origin of the terms is unclear, but it gained popularity in the 1990s when it was picked up by marketing companies to promote the X Games and when the Extreme Sports Channel and Extreme International launched. More recently, the commonly used definition from research is "a competitive (comparison or self-evaluative) activity within which the participant is subjected to natural or unusual physical and mental challenges such as speed, height, depth or natural forces and where fast and accurate cogniti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Recreation
Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasure and are considered to be "fun". Etymology The term ''recreation'' appears to have been used in English first in the late 14th century, first in the sense of "refreshment or curing of a sick person", and derived turn from Latin (''re'': "again", ''creare'': "to create, bring forth, beget"). Prerequisites to leisure People spend their time on activities of daily living, work, sleep, social duties and leisure, the latter time being free from prior commitments to physiologic or social needs, a prerequisite of recreation. Leisure has increased with increased longevity and, for many, with decreased hours spent for physical and economic survival, yet others argue that time pressure has increased for modern people, as they are committed t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aerodynamic Drag
In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or between a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, the drag force depends on velocity. Drag force is proportional to the velocity for low-speed flow and the squared velocity for high speed flow, where the distinction between low and high speed is measured by the Reynolds number. Even though the ultimate cause of drag is viscous friction, turbulent drag is independent of viscosity. Drag forces always tend to decrease fluid velocity relative to the solid object in the fluid's path. Examples Examples of drag include the component of the net aerodynamic or hydrodynamic force acting opposite to t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
