Other Space Activities

Types of Earth Orbits and Their Applications

Last updated:Nov 28, 2025

Earth Observation

In planning a satellite mission, choosing the type of orbit is a critical part of the design process and is determined by the mission’s objectives and purpose. The orbital altitude, eccentricity, inclination, and orbital period can impact the drag experienced by the spacecraft, the viewing scene, how much of the Earth is visible to the satellite, and the revisit rate.

Overview

A principle of any orbit in space is governed by Newton’s first law of motion, which states that all objects will remain at rest or in uniform motion unless acted upon by another force. Satellites are launched upwards and accelerated tangentially, so that their forward velocity balances Earth’s gravitational pull, creating a stable, curved path around the planet. The balance between the gravitational force and the object’s forward momentum (velocity) therefore decides the characteristics of the orbit. 1) 2)

Figure 1: Balance between gravitational attraction and forward momentum results in an orbit (Image credit: NASA)

Factors affecting a satellite’s orbit around Earth are described in the table below alongside other relevant orbital parameters.

Table 1: Orbital parameters
Factor	Description	Effect
Altitude	The height of a satellite above the Earth’s surface.	Higher altitudes allow for a larger field of view, but also increases the period and hence lengthens the revisit rate.
Inclination	The angle of a satellite’s orbit relative to the equator, i.e. a 90° orbit passes over the North and South poles. Geostationary orbits are at inclination of 0°.	Inclination impacts coverage of different regions. Low inclination satellites provide greater coverage over the equator, while higher inclination satellites pass closer to the poles, allowing for closer to global coverage, but increasing the revisit rate
Prograde / Retrograde Orbits	Prograde orbits travel in the same direction as the rotation of the body that they orbit. Retrograde orbits travel in the opposite direction.	Placing satellites in retrograde orbit requires more energy, as the launch must work against the rotation of the planet. Satellites in prograde orbits definitionally have inclinations between 0° and 90°, while retrograde orbits have inclinations between 90° and 180°.
Eccentricity	The degree of circularity of an orbit. An eccentricity of 0 indicates a perfectly circular orbit. Eccentricities between 0 and 1 are elliptic orbits, while eccentricities greater than 1 are hyperbolic orbits and can be used for interplanetary missions.	High eccentricity orbits can be used to provide targeted observations over polar regions, however they are less stable in the long term, and altitude varies greatly over the course of an orbit. Lower eccentricity orbits (close to zero) are often used to provide continuous, consistent observations. Perfectly circular orbits (eccentricity = 0) are practically impossible to achieve and maintain.
Period	The time taken to complete one full orbit. For example, a satellite at 400km completes an orbit in about 92 minutes, while one in geostationary orbit takes 23h 56 minutes (one sidereal day).	A lower altitude increases the satellite’s velocity, and hence reduces the orbital period. A lower period correlates to a shorter revisit time. By orbital mechanics, the orbital period (T) is proportional to the square root of the cube of the orbital radius (r) (T ∝ √(r3)).
Revisit rate	The time between a satellite’s consecutive passes over the same spot on Earth, also known as temporal resolution.	A satellite’s revisit rate determines how frequently it can observe the same location and depends on several factors. Primarily the orbital altitude and inclination, but also the sensor’s swath width, the ground track repeat cycle, and whether the satellite operates as a constellation.
Longitude For Geostationary orbits only	The positioning of the satellite along the equator.	The longitude of Geostationary satellites determines their viewing scene.
Local Time on Ascending/ Descending Node (LTAN/LTDN) For Sun-synchronous orbits only	Also known as Local Solar Time (LST), LTDN refers to the local time when the satellite crosses the equator in the North to South direction. LTAN is the same parameter, but when the satellite crosses South to North.	This determines the lighting conditions of the viewing scene for a sun-synchronous satellite. For example, a 10:30 am LTDN will allow consistently well sunlit imagery, consistently viewing the same scene in the mornings.

Orbit Regimes

Figure 1: Types of Earth orbits (Image credit: ESA)

Low Earth Orbit

Low Earth Orbit (LEO) refers to orbits relatively close to the Earth’s surface, classified by altitudes lower than 2000 km. Satellites in LEO typically operate beneath most of the Van Allen belts - regions of charged particles created by Earth’s magnetic field that result in hostile environments for spacecraft. The inner Van Allen belt can extend from a few hundred kilometers above the Earth’s surface up to several thousand kilometers, depending on geomagnetic activity. The lower limit of LEO is typically 180 km, as orbits lower than this experience high drag from the Earth’s atmosphere, making them hard to sustain. An exception to this lower bound is Very Low Earth Orbit (VLEO), which includes orbits as low as 100 km above Earth’s surface. Due to its extremely low altitude, VLEO allows for very high resolution observation of the Earth and reduced communications latency. However, the effects of atmospheric drag, as well as the corrosive nature of atmospheric components like atomic oxygen, mean that satellites in this regime need additional protection and more complex orbit maintenance systems.

LEO is an excellent orbit for Earth observation, as its proximity allows higher resolution imaging. Furthermore, LEO satellites typically travel at about 7.8 km/s with respect to Earth, resulting in orbital periods around 90 minutes. This allows for a higher revisit rate, allowing imagery to be captured more frequently of the same area, making it useful in time series analyses and time-sensitive end user demands, such as disaster monitoring. 1)

Example LEO Satellites

Sentinel-2: This Copernicus mission consists of at least two optical imaging satellites operating at an altitude of 786 km. The two primary Sentinel-2 platforms are equally spaced and phased at 180° to reduce revisit times to 5 days at the equator. Since January 21, 2025, Sentinel-2 has consisted of three operational satellites, with Sentinel-2B and -2C the primary platforms. Sentinel-2A began operating in an extended campaign from March 13, 2025, operating from a position 36° away from Sentinel-2B.
ALOS-2 and ALOS-4: The Advanced Land Observing Satellite (ALOS) mission series is owned and operated by the Japanese Aerospace Exploration Agency (JAXA). ALOS-2 carries the PALSAR-2 L-band synthetic aperture radar, as well as the Compact InfraRed Camera (CIRC). ALOS-2 orbits at an altitude of 628 km with a 14 day revisit time and an inclination of 97.9°, allowing coverage of higher latitudes. ALOS-4 joined ALOS-2 in the same orbit in July 2024, enabling for interoperable observations and reduced revisit time across the series.
CYGNSS: The Cyclone Global Navigation Satellite System (CYGNSS) is a National Aeronautics and Space Administration (NASA) Earth Venture mission, consisting of eight microsatellites measuring ocean surface wind speeds in tropical cyclones. The National Oceanic and Atmospheric Administration (NOAA) cooperates as a key data user and research partner, applying CYGNSS observations to improve hurricane formation, evolution, and forecasting. Each satellite carries a Delay Doppler Mapping (DDM) instrument, and all eight satellites operate at an altitude of 520 km.
Iridium NEXT: This commercial satellite program is a constellation of 66 communications satellites. Each satellite carries an L-band communications radio array antenna. All of the Iridium satellites operate at an altitude of 780 km, with the selected LEO providing lower communications latency.
Hubble Space Telescope: NASA’s deep space observatory was the first major optical telescope to be placed in space. It was placed into LEO at an altitude of 547 km, above any atmospheric distortions.
ISS: The International Space Station (ISS) is a collaborative space station constructed by NASA, ROSKOSMOS, ESA, JAXA, and CSA. The space station operates in a nearly circular orbit maintained at an altitude of 400-420 km using visiting spacecraft and onboard thrusters to perform periodic reboosts, and an inclination of 51.6°. LEO was chosen for the space station to allow for easier access for resupply and crew missions. The ISS has thrusters onboard to help maintain the orbit, as it experiences significant atmospheric drag due to the low altitude.

Medium Earth Orbit

Medium Earth Orbit (MEO) covers a wide range of orbit altitudes, from the top of LEO, at 2000 km and usually outside of the Van Allen belts, to just below Geostationary orbit (GEO). This orbit is commonly used by navigation satellites, as it provides a balance of wide coverage at altitudes higher than LEO and lower latency than GEO satellites. 1)

Example MEO Satellites

Galileo: The European Space Agency’s satellite navigation program operates 30 MEO satellites, orbiting at 23,222 km. Galileo provides a high accuracy global navigation system with precise positioning and timing.
O3b mPOWER: This telecommunications constellation is owned by SES, a satellite communications company operating out of Luxembourg. O3b mPOWER consists of 13 high throughput MEO satellites, at an altitude of 8000 km. The constellation aims to provide high speed satellite internet to underserviced regions, such as cruise liners and offshore oil or gas rigs. 8)
LAGEOS I/II: The Laser Geodynamics Satellites (LAGEOS) I and II missions are passive research satellites stationed in MEO, designed by NASA. Both satellites consist of an aluminium sphere with a 60 cm diameter, with 426 corner cube reflectors attached. These satellites act as permanent reference points used to track the movement of the Earth through space. LAGEOS I is in MEO at an altitude of 5860 km, while LAGEOS II orbits at an altitude of 5620 km.

Geostationary Earth Orbit

Geostationary Earth Orbits (GEO) are west to east orbits above the Earth’s equator, exactly matching the Earth’s rotation. This results in satellites in GEO appearing to be stationary from Earth’s perspective, remaining above a fixed point on the equator. To achieve this, GEO satellites travel at 3 km/s at an altitude of 35,786 km. The relative fixed position of GEO satellites provides obvious advantages for missions that require continuous observation of a single scene. For this reason, GEO is most commonly used by telecommunications satellites, allowing antennas on Earth to remain in a constant position, and by weather satellites, for continuous monitoring of regional weather. However, its very high altitude results in slow communication (around 240 ms for a signal to be sent and returned), and low to medium resolution imagery (minimum around 500-1000 m). 1)

Example GEO Satellites

GOES-R: The Geostationary Operational Environmental Satellite R series (GOES-R) mission is a constellation of four GEO satellites. The constellation is jointly operated by NOAA and NASA, aiming to provide continuous weather monitoring. The use of GEO for these missions enables the same scene, continuous element of this program.
TDRS: The NASA operated Tracking and Data Relay Satellites are a constellation of 10 data relay satellites in GEO. TDRS satellites ensure near-continuous global communications coverage for LEO satellites. The use of a geostationary constellation allows LEO satellites to communicate with ground stations at any point in orbit, rather than being restricted by the relative speed of their orbits to the ground. 11)
EGNOS: The European Geostationary Navigation Overlay Service (EGNOS) is the precursor to the Galileo navigation and positioning system. EGNOS consists of three geostationary satellites that provide regional coverage across Europe and neighbouring regions, improving GPS positioning accuracy to about 1 meter offering integrity information for aviation and other safety-critical applications. 5)
Sky Muster: These commercial communication satellites provide internet services in regional Australia. The satellites are owned by the National Broadband Network (NBN), and operate in GEO at longitudes of 140° and 145° East. GEO allows continuous provision of communications services. 13)

Geosynchronous Orbit

Geosynchronous orbits are very similar to geostationary orbits, but are not necessarily placed above the equator, meaning they can appear to travel north and south over a constant longitude over the course of a day. A geostationary orbit is a special case of a geosynchronous orbit - one that is circular, zero-inclination, and lies directly above the equator, keeping the satellite fixed over a single point on Earth. Geosynchronous orbits allow coverage of higher latitudes, where standard geostationary satellites cannot, and are typically used by navigation and communications satellites. 3)

Figure 2: Geosynchronous vs Geostationary orbits (Image credit: GIS Geography)

Example Geosynchronous Satellites

QZSS: The Quasi Zenith Satellite System (QZSS) is a Japanese regional satellite navigation system. It is a constellation of at least four satellites in elliptical, geosynchronous orbits at a 40° inclination. This orbit maximises elevation angles in urban canyons and mountainous regions.
CNSS: The Compass, or Beidou, Navigation Satellite System (CNSS) is a Chinese navigation satellite constellation. The constellation uses a combination of MEO, GEO and inclined geosynchronous orbits (ISGO), with 12 ISGO satellites currently in orbit. Geosynchronous orbits improve regional coverage of navigation services.
DSCS-3 B7: The American Defence Satellite Communications System 3 (DSCS-3) B7 satellite was a military communications satellite operating in a geonsynchronous orbit. It was used to provide telecommunications to the Amundsen-Scott South Pole station. ISGO was necessary for this mission as the South Pole station was not visible from equatorial GEO satellites. 10)

Lagrange Points

Lagrange points are regions in a two body gravitational system where the gravitational force of the two objects balances the centripetal force for a smaller object to move between them. Objects at these points will remain in position if no other force is acting on them. There are five Lagrange points in a two body system, of which three, L1, L2, and L3 are unstable, meaning objects here tend to fall out of orbit. Satellites operating at Lagrange points typically orbit around them in halo or Lissajous orbits. Halo orbits take repeating, non-planar paths around a Lagrange point, while Lissajous orbits are quasi-periodic trajectories that do not follow a simple elliptical path, instead consisting of complex, non-repeating motions.

Lagrange points are useful for satellites that can’t operate too close to Earth, due to its natural emission of infrared radiation and reflection of visible sunlight, making it a great place from which to operate deep space observatories. Additionally, the specific positioning of L1, between the Earth and the Sun, means it can be used for Earth-directed solar phenomena (e.g. coronal mass ejection) detection and early warning systems. 1) 4)

Figure 3: Earth-Sun Lagrange Points (Image credit: NASA)

Example Lagrange Point Satellites

James Webb Space Telescope: NASA’s cutting-edge deep space observatory operates in an orbit around L2. The mission has been tasked with surveying the universe in infrared wavelengths, allowing insight into the early universe, exoplanets, stellar evolution and other cosmic phenomena. Due to the infrared observations of the observatory, any Earth orbit would result in too much background radiation for the highly sensitive measurements.
Gaia: This ESA astronomy mission, which operated in orbit around L2, was launched in 2013 with the aim of mapping the positions, motions and properties of over a billion Milky Way stars. Gaia studied approximately 500,000 quasars and discovered hundreds of thousands of new celestial objects, such as extra-solar planets and brown dwarfs.
DSCOVR: The Deep Space Climate Observatory (DSCOVR) is a jointly operated NOAA-NASA mission that aims to provide space weather monitoring from L1, the point in between Earth and the Sun.

Special Earth Orbits

Sun-Synchronous Orbit

Sun-synchronous orbits (SSO) are specific polar orbits that match the Earth’s rotation around the Sun, meaning they pass over the same spot on the Earth at the same local time each day. SSOs are slightly retrograde, with an inclination around 98°, causing the orbital plane to precess eastward at the same rate the Earth moves around the Sun, keeping the satellite’s overpass consistent in local solar time. These satellites typically operate in LEO at altitudes between 600 and 800 km. The consistent local time allows for more accurate monitoring of trends over time, as observations are more comparable in terms of light and shadow conditions. SSO satellites are often classified by their local time at descending node (LTDN), the local time at the point where the satellite crosses the equator travelling north to south. 1)

Example SSO Satellites

Landsat 9: Is a NASA/USGS joint mission providing calibrated optical and thermal imaging for land, water and disaster monitoring. The satellite’s 10:00 LTDN allows constant illumination, lower morning haze from water vapour, and stable geometry for time series collections of observations.
Sentinel-3: This Copernicus constellation carries optical radiometers (OLCI and SLSTR) and a radar altimeter (SRAL) to provide long term operational marine and land monitoring services. The satellites operate in SSO at an altitude of 807 km, and an LTDN of 10:00, keeping stable viewing angles for colour, temperature and altimetry products.
Terra: NASA’s atmospheric observation satellite uses an SSO at an altitude of 705 km and an LTDN of 10:30. This LTDN is selected to complement the 13:30 LTDN of Aqua, Terra’s counterpart.
Hinode: This JAXA mission aims to study the sun and its effects on terrestrial climate change and space weather. Hinode has been placed in terminator SSO, following the division between the daylit and dark sides of the Earth. This means that the satellite experiences near-constant sunlight, with no day-night cycling for nine months a year, enabling long uninterrupted periods of sun viewing.

Highly Elliptical Orbits, including Molniya

Highly elliptical orbits (HEO) are those that greatly vary their altitude across the course of their orbit, often with eccentricity between 0.5 and 0.9. They are characterised by their apogee (the greatest distance from the object of its orbit) and their perigee (the closest). HEO is useful for missions that need to observe the Earth or look into space from high altitudes, away from the Earth’s atmosphere and background radiation, for long periods of time. HEO can also be used as a transfer orbit for GEO satellites launched far from the equator.

A specific type of HEO, the Molniya orbit, has a period of about 12 hours and an inclination of about 63.4 degrees, allowing satellites to dwell for long durations over high-latitude regions such as the Arctic. The orbit is ideal for communications and weather observation in areas poorly served by geostationary satellites.

Orbits with eccentricity greater than 1 are hyperbolic, and can be used for launching interplanetary missions, accelerating the object out of orbit. 1) 6)

Figure 5: Molniya Orbit Diagram (Image credit: Byju’s)

Example HEO Satellites:

Arktika-M: This Russian Federal Space Agency (ROSKOSMOS) mission consists of two satellites, aiming to monitor the Earth’s surface and atmosphere in the Arctic, as well as making cosmic ray observations. An HEO orbit with an apogee of 39,750 km, a perigee of 1043 km and eccentricity of approximately 0.7 is used by both satellites as GEO satellites provide limited visibility at extreme latitudes.
CXO: The Chandra X-ray Observatory (CXO) is a NASA deep space observatory. It operates in HEO with a perigee of approximately 10,000 km, an apogee of approximately 140,000 km and eccentricity of around 0.8 - 0.9. This mission uses HEO as most of the selected orbit falls above the Van Allen Belts, reducing background radiation from the Earth for lower interference, continuous exposures.
TESS: The Transiting Exoplanet Survey Satellite (TESS) is a NASA space telescope that aims to search for transiting exoplanets. TESS operates in a HEO with a perigee of 108,000 km and an apogee of 373,000 km, giving it an eccentricity of 0.54. Its orbit is in 2:1 resonance with the lunar orbit, creating a highly stable environment for long term photometry.

Constellations

Satellite constellations, multiple satellites working in tandem to achieve a single goal, are highly valuable tools across a range of satellite services. The main benefits of constellations, as opposed to single satellite missions, is coverage. A constellation of satellites in identical, but out of phase orbits, can reduce the revisit time for global coverage, and with enough platforms, providing continuous service or consistent observations of the entire Earth. Many such systems use mixed Walker constellation geometry, where satellites are evenly distributed over multiple orbital planes, with phasing patterns ensuring uniform global coverage and consistent revisit intervals. The use of large numbers of smaller and more cost-effective satellites operating in a constellation can replace large, single satellite missions, reducing cost through scalability, as well as providing redundancy. In Earth observation, satellite constellations allow continuous observation of single scenes, and can produce greater resolution imagery from multiple observations. For communications and navigation systems, constellations provide uninterrupted coverage for vital services. 9)

Figure 6: Walker Constellation Geometries (Image credit: Leyva-Mayorga et al.)

Example Satellite Constellations

Starlink: This LEO commercial communications constellation is owned and operated by Starlink Services and SpaceX, consisting of thousands of satellites and is ultimately designed to deploy tens of thousands to provide global mobile broadband coverage, offering speeds up to 1 Gbit/s.
Planet Flock Imaging Constellation: This commercial nanosatellite constellation consists of hundreds of low-cost, rapidly deployable imaging satellites, aiming to maintain over 180 active flight units. The mission aims to achieve spatial resolution of 3 - 5 m, and can image the entire Earth’s surface daily.
GHGSat Constellation: This mission is a commercial constellation that provides high resolution measurements of methane and carbon dioxide. As of 2025, the constellation consists of 12 satellites in orbit, and aims to provide individual site level detection of greenhouse gases.
GPS: The Global Positioning System (GPS) is a constellation nominally consisting of 24 satellites, though typically 30 or more are operational at any given time. The satellites are owned and operated by the US Space Force, orbiting in six Earth-centred orbital planes at an altitude of approximately 20,000 km. GPS provides global coverage for location, velocity and time synchronisation services. 7)