Spaceflight
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Spaceflight is the transportation of manned or unmanned spacecraft into and through space. The first man-made object to achieve spaceflight was the German V-2 Rocket during test flights in 1942. The next major milestone was the Russian satellite Sputnik 1 in 1957 which became the first man-made object to orbit the Earth. A key component of spaceflight is the launch, which is the initial thrust to overcome the force of gravity from the surface of the Earth. Once in space, astrodynamics is used to determine the motion of a spacecraft, and spacecraft propulsion is used to control the motion.
Spaceflight is a necessary component of space exploration, but also supports activities such launching of telecommunications satellites and space tourism.
[edit] History of spaceflight
The realistic dream of spaceflight dated back to Konstantin Tsiolkovsky, however Tsiolkovsky wrote in Russian, and this was not widely influential outside Russia.
Spaceflight became an engineering possibility with the work of Robert H. Goddard's publication in 1919 of his paper 'A Method of Reaching Extreme Altitudes'; where his application of the de Laval nozzle to liquid fuelled rockets gave sufficient power that interplanetary travel became possible. This paper was highly influential on Hermann Oberth and Wernher Von Braun, later key players in spaceflight.
[edit] Earth launched spaceflight
[edit] Reaching space
The most commonly used definition of space, at least from the perspective of spacecraft, is everything more than 100km (60 mi) above the Earth's surface. The United States sometimes uses a 50 mile definition. (See Karman line.)
One can distinguish between sub-orbital spaceflight and the orbital spaceflight (cf. Difference between sub-orbital and orbital spaceflights). For sub-orbital flights, on October 3, 1942 a German A4 rocket (a prototype for the V2 rocket used to bomb London), became the first successful launch of an object into space. The first organisms launched into space were bacteria trapped aboard the same flight. Another milestone was achieved on May 17, 2004 when Civilian Space eXploration Team launched the GoFast Rocket on a suborbital flight, the first amateur space flight. On June 21, 2004, SpaceShipOne became the first privately-funded manned spacecraft.
Achieving a closed orbit is not essential for manned or unmanned interplanetary voyages, where an escape orbit needs to be reached. Early Russian space vehicles successfully achieved very high altitudes without going into orbit. The USA, in its early Apollo mission planning considered using a direct ascent to the moon, but abandoned that idea later due to weight considerations. Many unmanned space probes to the outer planets use direct ascent -- they do not orbit the earth before departing.
However, plans for future manned flight often include final vehicle assembly in earth orbit.
Because suborbital space flights are by definition short (less than 1.7 hours) any longer mission requires orbital flight (with elliptical or circular trajectory), or superorbital flight (over parabolic or hyperbolic trajectory). However, orbital flight requires much higher velocities than suborbital making it technologically challenging to achieve.
[edit] Launch pads and Spaceports, takeoff
A launch pad is a fixed structure, for the launch of launch vehicles.
It generally consists of a launch tower and flame trench, and there is equipment used to erect, fill and launch vehicles.
A spaceport, by way of contrast, is typically for winged launch vehicles and consists of a long runway.
Both spaceport and launch pads are situated well away from human habitation for noise and safety reasons.
Rockets run though a countdown sequence prior to Rocket launch.
Launch is often restricted to certain launch windows. These windows occur due to the position of celestial bodies and orbits relative to the launch site. The biggest influence is often the rotation of the Earth itself. Once launched, orbits are normally located within relatively constant flat planes at a fixed angled to the axis of the Earth, and the Earth rotates within this orbit.
[edit] Reentry and landing/splashdown
Orbital vehicles have enough kinetic energy to vapourise the vehicle many times over. This energy must be lost if the vehicle is to land.
The theory behind reentry is due to Harry Julian Allen. Based on this theory, reentry vehicles present blunt shapes to the atmosphere for reentry. Blunt shapes mean that less than 1% of the kinetic energy ends up as heat that reaches the vehicle and the heat energy instead ends up in the atmosphere.
The Apollo and Mercury capsules landed in the sea. The capsule was designed to land at relatively slow speeds.
Russian capsules for Soyuz land on land and use braking rockets.
The Space Shuttle glides into a touchdown at high speed.
[edit] Expendable Launch Systems
All current spaceflight except NASA's Space Shuttle use multi-stage expendable launch systems to reach space.
[edit] Reusable launch systems
Image:Space Shuttle Columbia launching.jpg
The first partially reusable spacecraft, the X-15, was air-launched on a suborbital trajectory on July 19, 1963. The first partially reusable orbital spacecraft, the Space Shuttle, was launched by the USA on the 20th anniversary of Yuri Gagarin's flight, on April 12, 1981. During the Shuttle era, six orbiters were built, all of which have flown in the atmosphere and five of which have flown in space. The Enterprise was used only for approach and landing tests, launching from the back of a Boeing 747 and gliding to deadstick landings at Edwards AFB, California. The first Space Shuttle to fly into space was the Columbia, followed by the Challenger, Discovery, Atlantis, and Endeavour. The Endeavour was built to replace the Challenger when it was lost in January 1986. The Columbia broke up during reentry in February 2003.
The first (and so far only) automatic reusable spacecraft was the Buran (Snowstorm), launched by the USSR on November 15, 1988, although it made only one flight. This spaceplane was designed for a crew and strongly resembled the U.S. Space Shuttle, although its drop-off boosters used liquid propellants and its main engines were located at the base of what would be the external tank in the American Shuttle. Lack of funding, complicated by the dissolution of the USSR, prevented any further flights of Buran.
Per the Vision for Space Exploration, the Space Shuttle is due to be retired in 2010 due mainly to its old age and high cost of the program reaching over a billion dollars per flight. The Shuttle's human transport role is to be replaced by the partially reusable Crew Exploration Vehicle (CEV) no later than 2014. The Shuttle's heavy cargo transport role is to be replaced by expendable rockets such as the Evolved Expendable Launch Vehicle (EELV) or a Shuttle Derived Launch Vehicle.
Scaled Composites SpaceShipOne was a reusable suborbital spaceplane that carried pilots Mike Melvill and Brian Binnie on consecutive flights in 2004 to win the Ansari X Prize. The Spaceship Company will build its successor SpaceShipTwo. A fleet of SpaceShipTwos operated by Virgin Galactic should begin reusable private spaceflight carrying paying passengers in 2008.
[edit] Spacecraft
Spacecraft are vehicles capable of controlling their trajectory through space.
The first 'true spacecraft' is sometimes said to be Apollo Lunar Module since this was the only vehicle to have been designed for, and operated only in space; and is notable for its non aerodynamic shape.
[edit] Private versus Governmental spaceflight
There is growing interest in spacecraft and flights paid for by commercial companies and even private individuals. It is thought that some of the high cost of access to space is due to governmental inefficiencies; and certainly the costs of the governmental paperwork surrounding NASA is legendary. If a commercial company were able to be more efficient costs could come down significantly. Space launch vehicles such as Falcon I have been wholly developed with private finance, and the quoted costs for launch are lower.
[edit] Human spaceflight
[edit] Zero-gravity
Long term zero gravity exposure causes multiple health issues; most significantly bone loss, some of which is permanent, but also significant deconditioning of muscular and cardiovascular tissues.
Short term zero gravity causes space adaptation syndrome, a self-limiting nausea due to lack of gravity causing derangement of the vestibular system.
[edit] Life support
[edit] Space disasters
[edit] Orbital and Sub-orbital spaceflight
[edit] Interplanetary spaceflight
[edit] Interstellar spaceflight
Travel between the stars in any reasonable time is extremely difficult due to the enormous distances involved. Vehicle designs using nuclear pulse propulsion might be able to reach the nearest star in a few decades.
[edit] Astrodynamics
Astrodynamics is the study of spacecraft trajectories, particularly as they relate to gravitational and propulsion effects. Astrodynamics allows for the spacecraft to arrive at their destination at the correct time; without excessive propellant use.
[edit] Spacecraft propulsion
Spacecraft today predominately use rockets for propulsion, but other propulsion techniques such as ion drives are becoming more common, particularly for unmanned vehicles, and this can significantly reduce the vehicle's mass and increase its delta-v.
[edit] List of spaceflights
See: List of spaceflights by year.
Also:
[edit] See also
</div>[edit] External links
[edit] References
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