All Topics  
Low Earth orbit

 

 
   Email Print
   Bookmark   Link
 

 

Low Earth orbit
 
 
  Topics Low Earth orbit Topic Home

A Low Earth Orbit (LEO) is generally defined as an 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....
 within the locus
Locus (mathematics)

In mathematics, a locus is a collection of point which share a property. The term locus is usually used of a condition which defines a continuous figure or figures, that is, a curve....
 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 (100 - 1,240 miles) above the Earth's
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
 surface.

With the exception of the lunar flights of the Apollo program, and the sub-orbital
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....
 flights of the Mercury program
Mercury program

Mercury Program might refer to:*the first successful American manned spaceflight program, Project Mercury*an American post-rock band, The Mercury Program...
 and the X-15
North American X-15

The North American Aviation X-15 rocket-powered aircraft was part of the X-plane of experimental aircraft, initiated with the Bell X-1, that were made for the USAF, the NASA, and the USN....
 and SpaceShipOne rocket planes, all human spaceflight
Human spaceflight

A human spaceflight is a spaceflight with a Astronaut, and possibly passengers. This makes it unlike Robotic spacecraft space probes or remotely-controlled satellites....
s have been in LEO, including all Space Shuttle
Space Shuttle

NASA's Space Shuttle, officially called the Space Transportation System , is the spacecraft currently used by the United States government for its human spaceflight missions....
 and space station
Space station

A space station is an artificial structure designed for humans to live in outer space. So far only low earth orbit stations are implemented, also known as orbital stations....
 missions.






Discussion
Ask a question about 'Low Earth orbit'
Start a new discussion about 'Low Earth orbit'
Answer questions from other users
Full Discussion Forum



Encyclopedia


A Low Earth Orbit (LEO) is generally defined as an 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....
 within the locus
Locus (mathematics)

In mathematics, a locus is a collection of point which share a property. The term locus is usually used of a condition which defines a continuous figure or figures, that is, a curve....
 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 (100 - 1,240 miles) above the Earth's
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
 surface.

With the exception of the lunar flights of the Apollo program, and the sub-orbital
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....
 flights of the Mercury program
Mercury program

Mercury Program might refer to:*the first successful American manned spaceflight program, Project Mercury*an American post-rock band, The Mercury Program...
 and the X-15
North American X-15

The North American Aviation X-15 rocket-powered aircraft was part of the X-plane of experimental aircraft, initiated with the Bell X-1, that were made for the USAF, the NASA, and the USN....
 and SpaceShipOne rocket planes, all human spaceflight
Human spaceflight

A human spaceflight is a spaceflight with a Astronaut, and possibly passengers. This makes it unlike Robotic spacecraft space probes or remotely-controlled satellites....
s have been in LEO, including all Space Shuttle
Space Shuttle

NASA's Space Shuttle, officially called the Space Transportation System , is the spacecraft currently used by the United States government for its human spaceflight missions....
 and space station
Space station

A space station is an artificial structure designed for humans to live in outer space. So far only low earth orbit stations are implemented, also known as orbital stations....
 missions. The altitude record for a human spaceflight in LEO was Gemini 11
Gemini 11

Gemini 11 was a 1966 manned spaceflight in NASA's Gemini program. It was the 9th manned Gemini flight, the 17th manned American flight and the 25th spaceflight of all time ....
 with an apogee
Apsis

In celestial mechanics, an apsis, plural apsides is the point of greatest or least distance of the elliptical orbit of an object from its center of attraction, which is generally the center of mass of the system....
 of 1,374.1 km.

Orbital Characteristics

Objects in LEO encounter atmospheric drag in the form of gases in the thermosphere
Thermosphere

The thermosphere is the layer of the earth's atmosphere directly above the mesosphere and directly below the exosphere. Within this layer, ultraviolet radiation causes ionization....
 (approximately 80-500 km up) or exosphere
Exosphere

The exosphere is the uppermost layer of an atmosphere. In the exosphere, an upward travelling molecule can escape to space or be pulled back to the celestial body by gravity with little probability of colliding with another molecule....
 (approximately 500 km and up), depending on orbit height. LEO is an orbit around Earth between the atmosphere and below the inner Van Allen radiation belt
Van Allen radiation belt

The Van Allen radiation belt is a torus of energy charged particles around Earth, held in place by Earth's magnetic field. Earth's geomagnetic field is not uniformly distributed around its surface....
. The altitude is usually not less than 300 km because that would be impractical due to the larger atmospheric drag.

Equatorial Low Earth Orbits (ELEO) are a subset of LEO. These orbits, with low inclination to the Equator, allow rapid revisit times and have the lowest 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....
 requirement of any orbit. Orbits with a high inclination angle are usually called polar orbit
Polar orbit

A polar orbit is an orbit in which a satellite passes above or nearly above both Geographical poles of the body being orbited on each revolution....
s.

Higher orbits include medium Earth orbit
Meo

Meo is a prominent Muslim Rajput tribe from North-Western India some of whom migrated to Pakistan after the partition of India....
 (MEO), sometimes called intermediate circular orbit (ICO), and further above, 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). Orbits higher than low orbit can lead to earlier failure of electronic components due to intense radiation and charge accumulation.

Human use

The International Space Station
International Space Station

The International Space Station is a research facility Assembly of the International Space Station in outer space. On-orbit construction of the station began in 1998, and is scheduled to be complete by 2011, with operations continuing until around 2015....
 is in a LEO that varies from to above the Earth's surface.

While a majority of artificial satellite
Satellite

In the context of spaceflight, a satellite is an Physical body which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
s are placed in LEO, where they travel at about , making one complete revolution around the Earth in about 90 minutes, many communication satellites require geostationary orbits, and move at the same angular velocity as the Earth. Since it requires less energy to place a satellite into a LEO and the LEO satellite needs less powerful amplifiers for successful transmission, LEO is still used for many communication applications. Because these LEO orbits are not geostationary, a network (or "constellation
Satellite constellation

A group of Electronics satellites working in concert is known as a satellite constellation. Such a constellation can be considered to be a number of satellites with coordinated ground coverage, operating together under shared control, synchronised so that they overlap well in coverage and complement rather than interfere with other satelli...
") of satellites is required to provide continuous coverage. Lower orbits also aid remote sensing
Remote sensing

Remote sensing is the small or large-scale acquisition of information of an object or phenomenon, by the use of either recording or real-time sensing device that is not in physical or intimate contact with the object ....
 satellites because of the added detail that can be gained. Remote sensing satellites can also take advantage of sun-synchronous LEO orbits
Sun-synchronous orbit

A sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit passes over any given point of the Earth's surface at the same local solar time....
 at an altitude of about and near polar inclination. ENVISAT
Envisat

Envisat is an Earth observation satellite built by the European Space Agency. It was launched on the 1st March 2002 aboard an Ariane 5 into a Sun synchronous polar orbit at a height of 790 km ....
 is one example of an Earth observation satellite that makes use of this particular type of LEO.

Although the Earth's pull due to gravity in LEO is not much less than on the surface of the Earth, people and objects in orbit experience weightlessness
Weightlessness

Weightlessness is a phenomenon experienced by people during free-fall. Although the term #Zero gravity is often used as a synonym, weightlessness in orbit is not the result of the force of gravity being eliminated or even significantly reduced ....
 due to the effects of freefall.

Atmospheric and gravity drag
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....
 associated with launch typically add 1,500-2,000 m/s to the (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....
 required to reach normal LEO orbital velocity of around .

Space debris

The LEO environment is becoming congested with 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....
 which has caused a growing concern in recent years, since collisions at orbital velocities can be highly damaging or dangerous and can produce even more space debris in the process, called the Kessler Syndrome
Kessler Syndrome

The Kessler Syndrome is a scenario, proposed by NASA scientist Donald J. Kessler in a 1978 publication, where the volume of space debris in Low Earth orbit is so high that objects in orbit are frequently struck by debris, creating even more debris and a greater risk of further impacts....
. The Space Control Center, part of United States Strategic Command
United States Strategic Command

United States Strategic Command is one of the ten Unified Combatant Commands of the United States Department of Defense. The Joint Chiefs of Staff created it in 1992 as a successor to the Strategic Air Command ....
 (formerly the United States Space Command), currently tracks more than 8,500 objects larger than 10cm in LEO.

See also

  • List of orbits
    List of orbits

    The following is a list of types of Orbit s:...
  • Escape velocity
    Escape velocity

    In physics, escape velocity is the speed where the kinetic energy of an object is equal to the magnitude of its gravitational potential energy, as calculated by the equation,...
  • 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)
  • Highly Elliptical Orbit
    Highly Elliptical Orbit

    Highly Elliptical Orbit is an elliptic orbit characterized by a relatively low-altitude perigee and an extremely high-altitude apogee. These extremely elongated orbits can have the advantage of long dwell times at a point in the sky during the approach to and descent from apogee....
     (HEO)
  • Specific orbital energy examples
    Specific orbital energy

    In astrodynamics the specific orbital energy of an orbiting body traveling through space under standard assumptions in astrodynamics is the sum of its potential energy and kinetic energy per unit mass....
  • International Space Station
    International Space Station

    The International Space Station is a research facility Assembly of the International Space Station in outer space. On-orbit construction of the station began in 1998, and is scheduled to be complete by 2011, with operations continuing until around 2015....
  • 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...
  • Satellite phone
    Satellite phone

    A satellite telephone, satellite phone, or satphone is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites....