Near Earth Orbit

Information about Near Earth Orbit

An orbiting cannon ball showing various sub-orbital and orbital possibilities.

A Low Earth Orbit (LEO) 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 200 - 2000 km (124 - 1240 miles)^[1]^[2] above the Earth's surface.

Orbital Characteristics

Objects in LEO encounter atmospheric drag in the form of gases in the thermosphere (approximately 80-500 km up) or exosphere (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. 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 requirement of any orbit. Orbits with a high inclination angle are usually called polar orbits.

Higher orbits include medium Earth orbit (MEO), sometimes called intermediate circular orbit (ICO), and further above, Geostationary orbit (GEO). Orbits higher than low orbit can lead to earlier failure of electronic components due to intense radiation and charge accumulation, while commercial devices such as laptops have been used successfully in LEO during manned flight.

Human use

International Space Station photographed from space shuttle Atlantis on 19 June 2007.

Upgrading the International Space Station.

The International Space Station is in a LEO that varies from 319.6 km to 346.9 km above the Earth's surface. With the exeception of the Project Apollo missions to the Moon and suborbital test flights such as the early Project Mercury missions and the flights of the X-15 rocket plane, most manned spaceflights have been in LEO, including all Space Shuttle and various space station missions.

While a majority of artificial satellites are placed in LEO, where they travel at about 27,400 km/h (8 km/s), 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 rotates. 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") of satellites is required to provide continuous coverage. Lower orbits also aid remote sensing satellites because of the added detail that can be gained. Remote sensing satellites can also take advantage of sun-synchronous LEO orbits at an altitude of about 800km and near polar inclination. ENVISAT 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 due to the effects of freefall.

Atmospheric and gravity drag associated with launch typically add 1,500-2,000 m/s to the $\text{[math]}$ (delta-V) required to reach normal LEO orbital velocity of around 7,800 m/s.

Space debris

The LEO environment is becoming congested with space debris 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. The Space Control Center, part of United States Strategic Command (formerly the United States Space Command), currently tracks more than 8,500 objects larger than 10cm in LEO.^[3]

References

1. ^ IADC Space Debris Mitigation Guidelines. Inter-Agency Space Debris Coordination Committee (15 Oct 2002).
2. ^ NASA Safety Standard 1740.14, Guidelines and Assessment Procedures for Limiting Orbital Debris. Office of Safety and Mission Assurance (1 Aug 1995).
3. ^ USSTRATCOM Space Control Fact Sheet

• • [ e] Orbits
Orbit types	Box orbit • Circular orbit • Ecliptic orbit • Elliptic orbit • Highly Elliptical Orbit • Graveyard orbit • Hyperbolic trajectory • Inclined orbit • Osculating orbit • Parabolic trajectory • Capture orbit • Escape orbit • Semi-synchronous orbit • Subsynchronous orbit • Synchronous orbit • Parking orbit
Earth-centered orbits	Geosynchronous orbit • Geostationary orbit • Sun-synchronous orbit • Low Earth orbit • Medium Earth Orbit • Molniya orbit • Near equatorial orbit • Orbit of the Moon • Polar orbit • Tundra orbit
Other orbits	Areosynchronous orbit • Areostationary orbit • Halo orbit • Lissajous orbit • Lunar orbit • Heliocentric orbit • Heliosynchronous orbit
Orbital elements	Inclination ( $\text{[math]}$ ) • Longitude of the ascending node ( $\text{[math]}$ ) • Eccentricity ( $\text{[math]}$ ) • Argument of periapsis ( $\text{[math]}$ ) • Semi-major axis ( $\text{[math]}$ ) • Mean anomaly at epoch ( $\text{[math]}$ )
Other orbital parameters	True anomaly ( $\text{[math]}$ ) • Semi-minor axis ( $\text{[math]}$ ) • Linear eccentricity ( $\text{[math]}$ ) • Eccentric anomaly ( $\text{[math]}$ ) • Mean longitude ( $\text{[math]}$ ) • True longitude ( $\text{[math]}$ ) • Orbital period ( $\text{[math]}$ )
Orbital maneuvers	Bi-elliptic transfer • Geostationary transfer orbit • Gravitational slingshot • Hohmann transfer orbit • Orbital inclination change • Orbit phasing • Space rendezvous
Other orbital mechanics topics	Apsis • Celestial coordinate system • Delta-v budget • Epoch • Ephemeris • Equatorial coordinate system • Gravity turn • Ground track • Interplanetary Transport Network • Kepler's laws of planetary motion • Lagrangian point • List of orbits • n-body problem • Orbit equation • Orbital state vectors • Perturbation • Retrograde and direct motion • Specific orbital energy • Specific relative angular momentum • The Oberth effect

ORBit is a CORBA compliant Object Request Broker (ORB). The current version is called ORBit2 and is compliant with CORBA version 2.4. It is developed under the GPL license and is used as middleware for the GNOME project.
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EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001. Their greatest hit, their debut single "time after time", peaked at #13 in the Oricon singles chart.
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Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape. Compared to the solid and liquid states of matter a gas has lower density and a lower viscosity.
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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. (see also: ionosphere). It is the fourth atmospheric layer from earth.
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exosphere is the uppermost layer of the atmosphere. On Earth, its lower boundary at the edge of the thermosphere is estimated to be 500 km to 1000 km above the Earth's surface, and its upper boundary at about 10,000 km.
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The Van Allen Radiation Belt is a torus of energetic charged particles (plasma) around Earth, held in place by Earth's magnetic field. The Van Allen belts are closely related to the polar aurora where particles strike the upper atmosphere and fluoresce.
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In general physics, delta-v is simply the change in velocity.

Depending on the situation, delta-v can be referred to as a spatial vector () or scalar (). In both cases it is equal to the acceleration (vector or scalar) integrated over time:

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A polar orbit is an orbit in which a satellite passes above or nearly above both poles of the planet (or other celestial body) it is orbiting on each revolution. It therefore has an inclination of (or very close to) 90 degrees to the equator.
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For other uses, see Meos (disambiguation).

Meo (Hindi: मेव, Urdu: میو) is a prominent Muslim Rajput tribe from Northern India and Pakistan.
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Medium Earth Orbit (MEO), sometimes called Intermediate Circular Orbit (ICO), is the region of space around the Earth above low Earth orbit (2,000 kilometres (1243 mi)
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A geostationary orbit (GEO) is a geosynchronous orbit directly above the Earth's equator (0° latitude), with orbital eccentricity of zero. From the ground, a geostationary object appears motionless in the sky and is therefore the orbit of most interest to operators
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International Space Station (ISS) is a research facility currently being assembled in space. The building of ISS started in 1998. The station is in a low Earth orbit and can be seen from Earth with the naked eye: its altitude varies from 319.6 km to 346.
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Apollo program was a human spaceflight program undertaken by NASA during the years 1961 – 1975 with the goal of conducting manned moon landing missions. John F. Kennedy announced this goal in 1961, and it was accomplished on July 20 1969 by Neil Armstrong and Buzz Aldrin
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Moon

The Moon as seen by an observer on Earth
Orbital characteristics
Periapsis: 363,104 km
0.0024 AU
Apoapsis: 405,696 km
0.0027 AU
Semi-major axis: 384,399 km
0.
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Project Mercury was the first human spaceflight program of the United States. It ran from 1959 through 1963 with the goal of putting a man in orbit around the Earth. The Mercury-Atlas 6 flight on February 20, 1962 was the first Mercury flight to achieve this goal.
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Type Rocket plane
Manufacturer North American Aviation
Maiden flight 8 June 1959
Introduced 17 September 1959
Retired December 1968
Status Museum piece
Primary users U.S.
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human spaceflight is a spaceflight with a human crew, and possibly passengers. This makes it unlike robotic space probes or remotely-controlled satellites. Human spaceflight is sometimes called manned spaceflight
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Space Shuttle

Space Shuttle Atlantis on the launch pad prior to the STS-115 mission.
Fact sheet
Function Manned partially re-usable launch and reentry system
Manufacturer United Space Alliance:
Thiokol/Boeing (SRBs)
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space station is an artificial structure designed for humans to live in outer space. So far only low earth orbit (LEO) stations are implemented, also known as orbital stations.
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satellite is an object 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.
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communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, other elliptical orbits
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remote sensing is the short or large-scale acquisition of information of an object or phenomenon, by the use of either recording or real-time sensing device(s) that is not in physical or intimate contact with the object (such as by way of aircraft, spacecraft, satellite, buoy, or
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sun-synchronous orbit (sometimes incorrectly called a heliosynchronous 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.
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The Envisat (Environmental Satellite) satellite is an Earth-observing satellite built by the European Space Agency. It was launched on March 1, 2002 aboard an Ariane 5 into a Sun synchronous polar orbit at a height of 790 km (±10 km).
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Gravitation is a natural phenomenon by which all objects with mass attract each other. In everyday life, gravitation is most familiar as the agency that endows objects with weight.
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Weightlessness is 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 gravity itself being eliminated or even reduced significantly (in fact, the acceleration towards earth due to gravity
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Free fall is motion with no acceleration other than that provided by gravity. This also applies to objects in orbit, even though these objects are not "falling" in the usual sense of the word.
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In astrodynamics, gravity drag (or gravity losses) is inefficiency encountered by a spacecraft thrusting while moving against a gravitational field. It describes an inefficient use of thrust, not some magical effect on the efficiency of the operation of the engines.
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