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Orbital spaceflight
 
 
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An orbital spaceflight (or orbital flight) is a spaceflight
Spaceflight

Spaceflight is the use of space technology to achieve the flight of spacecraft into and through outer space.Spaceflight is used in space exploration, and also in commercial activities like space tourism and telecommunications satellite....
 in which a spacecraft
Spacecraft

A spacecraft is a Craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters outer space then returns to the Earth....
 is placed on a trajectory where it could remain in space
Outer space

Outer space comprises the relatively empty regions of the universe outside the atmospheres of celestial bodies. Outer space is used to distinguish it from airspace and terrestrial locations....
 for at least one orbit
ORBit

ORBit is a Common Object Request Broker Architecture 2.4 compliant Object Request Broker . It features mature C , C++ and Python bindings, and less developed bindings for Perl, Lisp , Pascal , Ruby , and Tcl....
. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee (altitude at closest approach) above (this is, by at least one convention, the boundary of space). To remain in orbit at this altitude requires an orbital speed
Orbital speed

The orbital speed of a body, generally a planet, a natural satellite, an satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body....
 of ~7.8 km/s.






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An orbital spaceflight (or orbital flight) is a spaceflight
Spaceflight

Spaceflight is the use of space technology to achieve the flight of spacecraft into and through outer space.Spaceflight is used in space exploration, and also in commercial activities like space tourism and telecommunications satellite....
 in which a spacecraft
Spacecraft

A spacecraft is a Craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters outer space then returns to the Earth....
 is placed on a trajectory where it could remain in space
Outer space

Outer space comprises the relatively empty regions of the universe outside the atmospheres of celestial bodies. Outer space is used to distinguish it from airspace and terrestrial locations....
 for at least one orbit
ORBit

ORBit is a Common Object Request Broker Architecture 2.4 compliant Object Request Broker . It features mature C , C++ and Python bindings, and less developed bindings for Perl, Lisp , Pascal , Ruby , and Tcl....
. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee (altitude at closest approach) above (this is, by at least one convention, the boundary of space). To remain in orbit at this altitude requires an orbital speed
Orbital speed

The orbital speed of a body, generally a planet, a natural satellite, an satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body....
 of ~7.8 km/s. Orbital speed is slower for higher orbits, but attaining them requires higher delta-v
Delta-v

In astrodynamics, the term delta-v, literally "change in velocity" , has a specific meaning: it is a scalar which takes units of speed that measures the amount of "effort" needed to carry out an orbital maneuver, i.e., to change from one trajectory to another....
.

The expression "orbital spaceflight" is mostly used to distinguish from sub-orbital spaceflight
Sub-orbital spaceflight

A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches Outer space, but its trajectory intersects the atmosphere or surface of the gravitating body from which it was launched, so that it does not complete one orbital revolution....
s, which are flights where apogee of a spacecraft reaches space but perigee is too low.

Orbital launch

Orbital spaceflight from Earth has only been achieved by launch vehicle
Launch vehicle

In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....
s that use rocket engine
Rocket engine

A rocket engine or simply rocket is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive Jet ....
s for propulsion. To reach orbit, the rocket must impart to the payload a delta-v
Delta-v

In astrodynamics, the term delta-v, literally "change in velocity" , has a specific meaning: it is a scalar which takes units of speed that measures the amount of "effort" needed to carry out an orbital maneuver, i.e., to change from one trajectory to another....
 of about 9.3-10 km/s. This figure allows for atmospheric drag (approximately 300 m/s with the ballistic coefficient
Ballistic coefficient

In ballistics the ballistic coefficient of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the deceleration—a high number indicates a low deceleration....
 of a 20 m long dense fuelled vehicle), gravity losses
Gravity drag

In astrodynamics and rocketry, gravity drag is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field....
 (depending on burn time and details of the trajectory and launch vehicle), gaining altitude, and the horizontal acceleration needed to reach orbital speed.

The main proven technique involves launching nearly vertically for a few kilometers while performing a gravity turn
Gravity turn

A gravity turn or zero-lift turn is a maneuver used in launching a spacecraft into, or descending from, an orbit around a celestial body such as a planet or a Natural satellite....
, and then progressively flattening the trajectory out at an altitude of 170+ km and accelerating on a horizontal trajectory (with the rocket angled upwards to fight gravity and maintain altitude) for a 5-8 minute burn until orbital velocity is achieved. Currently, 2-4 stages
Multistage rocket

A multistage rocket is a rocket that usestwo or more stages, each of which contains its own Rocket engine and Rocket propellant. A tandem or serial stage is mounted on top of another stage; a parallel stage is attached alongside another stage....
 are needed to achieve the required delta-v.

The Pegasus rocket
Pegasus rocket

Pegasus rockets are the winged space booster vehicles used in an expendable launch system developed by Orbital Sciences Corporation . Three main Staging burning Solid rocket provide most of the thrust....
 for small satellites instead launches from an aircraft at an altitude of 12 km.

Other techniques, such as use of a launch loop
Launch loop

A launch loop or Lofstrom loop is a design for a belt based maglev orbital launch system that would be around 2,000 km long and maintained at an altitude of up to 80 km ....
, have been proposed for non-rocket spacelaunch
Non-rocket spacelaunch

Non-rocket spacelaunch is the idea of space launch specifically from the Earth's surface predominately without the use of conventional chemical rockets, which today is the only method in use....
. These techniques are theoretical: no attempts have been made to orbit a vehicle using any of them.

Stability

An object in orbit at an altitude of less than roughly 200 km is considered unstable due to atmospheric drag. For a satellite to be in a stable orbit (i.e. sustainable for more than a few months), 350 km is a more standard altitude for low Earth orbit
Low Earth orbit

A Low Earth Orbit is generally defined as an orbit within the Locus extending from the Earth?s surface up to an altitude of 2,000 km. Given the rapid orbital decay of objects below approximately 200 km, the commonly accepted definition for LEO is between 160 - 2,000 km above the Earth surface....
. For example, on 1958-02-01 the Explorer 1 satellite was launched into an orbit with a perigee of . It remained in orbit for more than 12 years before its atmospheric reentry
Atmospheric reentry

Atmospheric reentry refers to the movement of human-made or natural objects as they enter the atmosphere of a planet from outer space, in the case of Earth from an altitude above the "edge of space." This article primarily addresses the process of controlled reentry of vehicles which are intended to reach the planetary surface intact, but th...
 over the Pacific Ocean on 1970-03-31.

However, the exact behaviour of objects in orbit depends on altitude
Altitude

Altitude has multiple uses depending on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object....
, their ballistic coefficient
Ballistic coefficient

In ballistics the ballistic coefficient of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the deceleration—a high number indicates a low deceleration....
, and details of space weather
Space weather

Space weather is the concept of changing environmental conditions in outer space. It is distinct from the concept of weather within a Celestial body atmosphere, and deals with phenomena involving ambient Plasma , magnetic fields, radiation and other matter in space....
 which can affect the height of the upper atmosphere.

Orbits

There are three main 'bands' of orbit around the Earth: low Earth orbit
Low Earth orbit

A Low Earth Orbit is generally defined as an orbit within the Locus extending from the Earth?s surface up to an altitude of 2,000 km. Given the rapid orbital decay of objects below approximately 200 km, the commonly accepted definition for LEO is between 160 - 2,000 km above the Earth surface....
 (LEO), medium Earth orbit
Medium Earth Orbit

Medium Earth Orbit , sometimes called Intermediate Circular Orbit , is the region of space around the Earth above Low Earth Orbit and below geostationary orbit ....
 (MEO) and geostationary orbit
Geostationary orbit

A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero....
 (GEO).

Due to Orbital mechanics orbits are in a particular, largely fixed plane around the Earth, which coincides with the center of the Earth, and may be tilted with respect to the equator. The Earth rotates about its axis within this orbit, and the relative motion of the spacecraft and the movement of the Earths surface determines the position that the spacecraft appears in the sky from the ground, and which parts of the Earth are visible from the spacecraft.

By dropping a vertical down to the Earth's surface it is possible to calculate a ground track
Ground track

A ground track or ground trace is the path on the surface of the Earth directly below an aircraft or satellite. In the case of a satellite, it is the 3D projection of the satellite's orbit onto the surface of the Earth ....
 which shows which part of the Earth a spacecraft is immediately above, and this is useful for helping to visualise the orbit.

NASA provides real-time tracking of the over 500 artificial satellites maintained in orbit around Earth. For the position of these satellites see .

Re-entry

Due to the high speeds of orbital spaceflight, atmospheric reentry
Atmospheric reentry

Atmospheric reentry refers to the movement of human-made or natural objects as they enter the atmosphere of a planet from outer space, in the case of Earth from an altitude above the "edge of space." This article primarily addresses the process of controlled reentry of vehicles which are intended to reach the planetary surface intact, but th...
 is much more difficult compared to sub-orbital flights.

Even if the vehicle is a satellite that is ultimately expendable, most space authorities are pushing towards controlled re-entry techniques to avoid issues of space debris
Space debris

Space debris or orbital debris, also called space junk and space waste, are the objects in orbit around Earth created by humans, and that no longer serve any useful purpose....
 reaching the ground and causing a hazard to lives and property. In addition, this minimises the creation of orbital space junk.

Returning craft though (including all potentially manned craft), have to find a way of slowing down as much as possible while still in higher atmospheric layers and avoid hitting the ground (lithobraking
Lithobraking

Lithobraking is a technique of descent by an unmanned space vehicle to the surface of a body by which the vehicle is slowed by impact with the body's surface....
) or burning up. The problem of deceleration from orbital speeds is solved through using atmospheric drag (aerobraking
Aerobraking

Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit by flying the vehicle through the atmosphere at the low point of the orbit , using Drag to slow the spacecraft....
) to lose nearly all of the speed. On an orbital space flight initial deceleration is provided by the retrofiring of the craft's rocket engines, perturbing the orbit (by lowering perigee down into the atmosphere) onto a suborbital trajectory.

Aerobraking is achieved by orienting the returning space craft to fly so as to present the heat shields forwards towards the atmosphere so as to protect against the high temperatures generated by atmospheric compression and friction caused by passing through the atmosphere at hypersonic
Hypersonic

In aerodynamics, hypersonic speeds are speeds that are highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach number and above....
 speeds. The thermal energy is dissipated mainly by compression heating the air in a shockwave ahead of the vehicle using a blunt heat shield shape, with the aim of minimising the heat entering the vehicle. Sub-orbital space flights, being at a much lower speed, do not generate anywhere near as much heat upon re-entry.

See also

  • Orbit
    ORBit

    ORBit is a Common Object Request Broker Architecture 2.4 compliant Object Request Broker . It features mature C , C++ and Python bindings, and less developed bindings for Perl, Lisp , Pascal , Ruby , and Tcl....
  • List of orbits
    List of orbits

    The following is a list of types of Orbit s:...
  • Ground track
    Ground track

    A ground track or ground trace is the path on the surface of the Earth directly below an aircraft or satellite. In the case of a satellite, it is the 3D projection of the satellite's orbit onto the surface of the Earth ....
  • Orbital mechanics
  • Project HARP
    Project HARP

    Project HARP, short for High Altitude Research Project, was a joint project of the United States Department of Defense and Canada's Department of National Defence created with the goal of studying ballistics of re-entry vehicles at low cost; whereas most such projects used expensive rockets, HARP used a non-rocket spacelaunch method ba...
     was a failed attempt, and a ram accelerator
    Ram accelerator

    A ram accelerator has the same function as a gun; i.e., it is a device for accelerating projectiles; however, it is entirely different in that jet-engine-like propulsion cycles utilizing ramjet and/or scramjet combustion processes are used to accelerate a projectile to extremely high speeds....
     is another design, to launch an object into orbit with a gun
    GUN

    Gun is a Revisionist Western-themed video game developed by Neversoft. It was published by Activision for the Xbox, Xbox 360, Nintendo GameCube, Microsoft Windows and PlayStation 2....
  • Rocket launch
    Rocket launch

    A rocket launch is the first phase of the flight of a rocket. For orbital spaceflights, or for launches into interplanetary space, which is usually a fixed location on the ground but may also be on a floating platform such as the San Marco platform, or the Sea Launch launch vessel....
  • Non-rocket spacelaunch
    Non-rocket spacelaunch

    Non-rocket spacelaunch is the idea of space launch specifically from the Earth's surface predominately without the use of conventional chemical rockets, which today is the only method in use....
  • Spacecraft
    Spacecraft

    A spacecraft is a Craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters outer space then returns to the Earth....
  • Spaceflight
    Spaceflight

    Spaceflight is the use of space technology to achieve the flight of spacecraft into and through outer space.Spaceflight is used in space exploration, and also in commercial activities like space tourism and telecommunications satellite....


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