Spaceflight
For other uses, see Spaceflight (disambiguation).
Spaceflight is used in space exploration, and also in commercial activities like space tourism and satellite telecommunications. Additional non-commercial uses of spaceflight include space observatories, reconnaissance satellites and other earth observation satellites.
A spaceflight typically begins with a rocket launch, which provides the initial thrust to overcome the force of gravity and propels the spacecraft from the surface of the Earth. Once in space, the motion of a spacecraft—both when unpropelled and when under propulsion—is covered by the area of study called astrodynamics. Some spacecraft remain in space indefinitely, some disintegrate during atmospheric reentry, and others reach a planetary or lunar surface for landing or impact.
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History
Main articles: History of spaceflight and Timeline of spaceflight
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| History |
| Space Race · Timeline of spaceflight |
| Applications |
| Earth observation satellites · Spy satellites · Communications satellites · Satellite navigation · Space observatory · Space exploration · Space colonization · Space tourism |
| Spacecraft |
| Robotic spacecraft (Satellite · Space probe · Unmanned resupply spacecraft) · Human spaceflight (Space capsule · Space station · Spaceplane) |
| Launch |
| Spaceport · Launch pad · Expendable and Reusable systems · Escape velocity · Non-rocket spacelaunch · |
| Destinations |
| Sub-orbital · Orbital · Interplanetary spaceflight · Interstellar travel · Intergalactic travel |
| Space agencies |
| ESA · NASA · RKA · CNES · DLR · CNSA · ISRO · JAXA |
 Spaceflight portal |
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 fuel rockets gave sufficient power that interplanetary travel became possible. He also proved in the laboratory that rockets would work in the vacuum of space; not all scientists of that day believed they would. This paper was highly influential on Hermann Oberth and Wernher Von Braun, later key players in spaceflight.
The first rocket to reach space, an altitude of 100 km, was the German V-2 Rocket, on a test flight in June, 1944. On the 4th of October, 1957, the Soviet Union launched Sputnik 1, which became the first artificial satellite to orbit the Earth. The first human spaceflight was Vostok 1 on April 12, 1961, aboard which Soviet cosmonaut Yuri Gagarin made one orbit around the Earth. The lead architects behind the Soviet space program's Vostok 1 mission were the rocket scientists Sergey Korolyov and Kerim Kerimov.
Rockets remain the only currently practical means of reaching space. Other non-rocket spacelaunch technologies such as scramjets still fall far short of orbital speed.
Phases of spaceflight
Launch
Main article: Rocket launch
A rocket launch for a spaceflight usually starts from a spaceport (cosmodrome), which may be equipped with launch complexes and launch pads
for vertical rocket launches, and runways for takeoff and landing of
carrier airplanes and winged spacecraft. Spaceports are situated well
away from human habitation for noise and safety reasons. ICBMs have various special launching facilities.A launch is often restricted to certain launch windows. These windows depend upon 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 angle to the axis of the Earth, and the Earth rotates within this orbit.
A launch pad is a fixed structure designed to dispatch airborne vehicles. It generally consists of a launch tower and flame trench. It is surrounded by equipment used to erect, fuel, and maintain launch vehicles.
Reaching space
The most commonly used definition of outer space is everything beyond the Kármán line, which is 100 kilometers (62 mi) above the Earth's surface. (The United States sometimes defines outer space as everything beyond 50 miles (80 km) in altitude.)Rockets are the only currently practical means of reaching space. Conventional airplane engines cannot reach space due to the lack of oxygen. Rocket engines expel propellant to provide forward thrust that generates enough delta-v (change in velocity) to reach orbit. Propulsion systems for different applications include:
- Expendable launch system
- Single stage to orbit
Other ways of reaching space
Main article: Non-rocket spacelaunch
Many ways other than rockets to reach space have been proposed. Ideas such as the space elevator and rotovators require new materials much stronger than any currently known.Electromagnetic launchers such as launch loops might be feasible with current technology. Other ideas include rocket assisted jet planes such as Reaction Engines Skylon or the trickier scramjets. Gun launch has been proposed for cargo.Leaving orbit
Main articles: Escape velocity and Direct injection (disambiguation)
However, the parking orbit approach greatly simplified Apollo mission planning in several important ways. It substantially widened the allowable launch windows, increasing the chance of a successful launch despite minor technical problems during the countdown. The parking orbit was a stable "mission plateau" that gave the crew and controllers several hours to thoroughly check out the spacecraft after the stresses of launch before committing it to a long lunar flight; the crew could quickly return to earth, if necessary, or an alternate earth-orbital mission could be conducted. The parking orbit also enabled translunar trajectories that avoided the densest parts of the Van Allen radiation belts.
Apollo missions minimized the performance penalty of the parking orbit by keeping its altitude as low as possible. For example, Apollo 15 used an unusually low parking orbit (even for Apollo) of 92.5 by 91.5 nautical miles (171x169 km) where there was significant atmospheric drag. But it was partially overcome by continuous venting of hydrogen from the third stage of the Saturn V, and was in any event tolerable for the short stay.
Robotic missions do not require an abort capability or radiation minimization, and because modern launchers routinely meet "instantaneous" launch windows, space probes to the moon and other planets generally use direct injection to maximize performance. Although some might coast briefly during the launch sequence, they do not complete one or more full parking orbits before the burn that injects them onto an earth escape trajectory.
Note that the escape velocity from a celestial body decreases with altitude above that body. However, it is more fuel-efficient for a craft to burn its fuel as close to the ground as possible; see Oberth effect and reference.This is another way to explain the performance penalty associated with establishing the safe perigee of a parking orbit.
Plans for future crewed interplanetary spaceflight missions often include final vehicle assembly in Earth orbit, such as NASA's Project Orion and Russia's Kliper/Parom tandem.
Astrodynamics
Main article: Astrodynamics
Astrodynamics is the study of spacecraft trajectories, particularly
as they relate to gravitational and propulsion effects. Astrodynamics
allows for a spacecraft to arrive at its destination at the correct time
without excessive propellant use. An orbital maneuvering system may be needed to maintain or change orbits.Non-rocket orbital propulsion methods include solar sails, magnetic sails, plasma-bubble magnetic systems, and using gravitational slingshot effects.
Reentry
Main article: Atmospheric reentry
Landing
The Mercury, Gemini, and Apollo capsules all splashed down in the sea. These capsules were designed to land at relatively slow speeds. Russian capsules for Soyuz make use of braking rockets as were designed to touch down on land. The Space Shuttle and Buran glide to a touchdown at high speed.Recovery
Types of spaceflight
Human spaceflight
Main article: Human spaceflight
The first human spaceflight was Vostok 1 on April 12, 1961, on which cosmonaut Yuri Gagarin of the USSR
made one orbit around the Earth. In official Soviet documents, there is
no mention of the fact that Gagarin parachuted the final seven miles.
The international rules for aviation records stated that "The pilot
remains in his craft from launch to landing". This rule, if applied,
would have "disqualified" Gagarin's spaceflight. Currently the only
spacecraft regularly used for human spaceflight is the Russian Soyuz spacecraft. The U.S. Space Shuttle fleet has been retired. Each of those space programs have used other craft in the past. Recently, the Chinese Shenzhou spacecraft has been used three times for human spaceflight, and SpaceShipOne twice.
Sub-orbital spaceflight
Main article: Sub-orbital spaceflight
On a sub-orbital spaceflight
the spacecraft reaches space and then returns to the atmosphere after
following a (primarily) ballistic trajectory. This is usually because of
insufficient specific orbital energy,
in which case a suborbital flight will last only a few minutes, but it
is also possible for an object with enough energy for an orbit to have a
trajectory that intersects the Earth's atmosphere, sometimes after many
hours. Pioneer 1 was NASA's first space probe
intended to reach the Moon. A partial failure caused it to instead
follow a suborbital trajectory to an altitude of 113,854 kilometers
(70,746 mi) before reentering the Earth's atmosphere 43 hours after
launch.The most generally recognized boundary of space is the Kármán line (actually a sphere) 100 km above sea level. (NASA alternatively defines an astronaut as someone who has flown more than 50 miles (80 km) or 80 km above sea level.) It is not generally recognized by the public that the increase in potential energy required to pass the Kármán line is only about 3% of the orbital energy (potential plus kinetic energy) required by the lowest possible earth orbit (a circular orbit just above the Kármán line.) In other words, it is far easier to reach space than to stay there.
On May 17, 2004, Civilian Space eXploration Team launched the GoFast Rocket on a suborbital flight, the first amateur spaceflight. On June 21, 2004, SpaceShipOne was used for the first privately-funded human spaceflight.
Orbital spaceflight
Main article: Orbital spaceflight
A minimal orbital spaceflight
requires much higher velocities than a minimal sub-orbital flight, and
so it is technologically much more challenging to achieve. To achieve
orbital spaceflight, the tangential velocity around the Earth is as
important as altitude. In order to perform a stable and lasting flight
in space, the spacecraft must reach the minimal orbital speed required for a closed orbit.Interplanetary spaceflight
Main article: Interplanetary spaceflight
Interplanetary travel is travel between planets within a single planetary system. In practice, the use of the term is confined to travel between the planets of the Solar System.Interstellar spaceflight
Main article: Interstellar travel
Five spacecraft are currently leaving the Solar System on escape trajectories. The one farthest from the Sun is Voyager 1, which is more than 100 AU distant and is moving at 3.6 AU per year. In comparison Proxima Centauri,
the closest star other than the Sun, is 267,000 AU distant. It will
take Voyager 1 over 74,000 years to reach this distance. Vehicle designs
using other techniques, such as nuclear pulse propulsion are likely to be able to reach the nearest star significantly faster.
Intergalactic spaceflight
Main article: Intergalactic travel
Intergalactic travel involves spaceflight between galaxies, and is
considered much more technologically demanding than even interstellar
travel and, by current engineering terms, is considered science fiction.Point-to-point sub-orbital spaceflight
Point-to-point sub-orbital spaceflight is a category of spaceflight in which a spacecraft uses a sub-orbital flight for transportation. This can provide a two-hour trip from London to Sydney. Today, no company offers this type of spaceflight for transportation. However, Virgin Galactic is planning to build a spaceplane called SpaceShipThree, which will offer this service in the future.Spacecraft and launch systems
Main article: Spacecraft
The first 'true spacecraft' is sometimes said to be Apollo Lunar Module,since this was the only manned vehicle to have been designed for, and operated only in space; and is notable for its non aerodynamic shape.
Spacecraft propulsion
Main article: Spacecraft propulsion
Spacecraft today predominantly 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.Expendable launch systems
Main article: Expendable launch system
All current spaceflight except NASA's Space Shuttle and the SpaceX Falcon 1 use multi-stage expendable launch systems to reach space.Reusable launch systems
Main article: Reusable launch system
The first (and so far only) automatic partially 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 2011 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 planned to begin reusable private spaceflight carrying paying passengers (space tourists) in 2008, but this was delayed due to an accident in the propulsion development.
Challenges associated with spaceflight
Space disasters
Main article: Space accidents and incidents
All launch vehicles contain a huge amount of energy that is needed
for some part of it to reach orbit. There is therefore some risk that
this energy can be released prematurely and suddenly, with significant
effects. When a Delta II
rocket exploded 13 seconds after launch on January 17, 1997, there were
reports of store windows 10 miles (16 km) away being broken by the
blast.Space is a fairly predictable environment, but there are still risks of accidental depressurisation and the potential failure of equipment, some of which may be very newly developed.
In 2004 the International Association for the Advancement of Space Safety was established in the Netherlands to further international cooperation and scientific advancement in space systems safety.
Weightlessness
Main article: Weightlessness
Radiation
Once above the atmosphere, radiation due to the Van Allen belts, solar radiation and cosmic radiation issues occur and increase.Further away from the Earth, solar flares can give a fatal radiation dose in minutes, and the health threat from cosmic radiation significantly increases the chances of cancer over a decade exposure or more.
Life support
Main article: Life support system
In human spaceflight, the life support system is a group of devices that allow a human being to survive in outer space. NASA often uses the phrase Environmental Control and Life Support System or the acronym ECLSS when describing these systems for its human spaceflight missions. The life support system may supply: air, water and food.
It must also maintain the correct body temperature, an acceptable
pressure on the body and deal with the body's waste products. Shielding
against harmful external influences such as radiation and
micro-meteorites may also be necessary. Components of the life support
system are life-critical, and are designed and constructed using safety engineering techniques.Space weather
Main article: Space weather
Space weather exerts a profound influence in several areas related to space exploration and development. Changing geomagnetic conditions can induce changes in atmospheric density causing the rapid degradation of spacecraft altitude in Low Earth orbit. Geomagnetic storms due to increased solar activity can potentially blind sensors aboard spacecraft, or interfere with on-board electronics. An understanding of space environmental conditions is also important in designing shielding and life support systems for manned spacecraft.
Environmental considerations
Rockets as a class are not inherently grossly polluting. However, some rockets use toxic propellants, and most vehicles use propellants that are not carbon neutral. Many solid rockets have chlorine in the form of perchlorate or other chemicals, and this can cause temporary local holes in the ozone layer. Re-entering spacecraft generate nitrates which also can temporarily impact the ozone layer. Most rockets are made of metals that can have an environmental impact during their construction.In addition to the atmospheric effects there are effects on the near-Earth space environment. There is the possibility that orbit could become inaccessible for generations due to exponentially increasing space debris caused by spalling of satellites and vehicles (Kessler syndrome). Many launched vehicles today are therefore designed to be re-entered after use.
Applications of spaceflight
Main article: List of private spaceflight companies
Uses for spaceflight include:
- Earth observation satellites such as Spy satellites, weather satellites
- Space exploration
- Space tourism is a small market at present
- Communication satellites
- Satellite navigation
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