Satellite Orbits and GNSS Constellations

A technical guide to where navigation satellites fly, why, and how augmentation systems sharpen the result.

1. Introduction

Every position fix a GNSS receiver produces relies on signals from satellites more than 20,000 km away, each travelling at close to 4 km/s. The receiver can only turn those signals into an accurate position fix if it knows exactly where each satellite was when it transmitted. The design of GNSS orbits, and how precisely they are known, therefore has a direct effect on the accuracy, availability and integrity that users see on the ground.

2. What is a GNSS orbit?

A GNSS orbit is the specific path that a Global Navigation Satellite System (GNSS) satellite follows as it travels around the Earth while broadcasting precise positioning and timing signals.

GNSS satellites provide the reference position and time needed for positioning measurements. A receiver estimates its position by measuring the propagation time of signals from multiple satellites whose positions are known or precisely modelled. Errors in the estimated satellite positions therefore contribute directly to the user’s positioning error. For this reason, GNSS satellite orbits are designed to be stable and predictable, and they are continuously monitored and determined by ground control networks.

Most GNSS satellites operate in medium Earth orbit (MEO), at altitudes of approximately 19,000-23,500 km. Examples include GPS at around 20,200 km, GLONASS at around 19,100 km, Galileo at approximately 23,222 km, and BeiDou’s MEO satellites at approximately 21,528 km. At these altitudes, a satellite completes one revolution in roughly 11-14 hours.

At MEO altitudes, each satellite can be visible over a large portion of the Earth’s surface. By deploying multiple satellites in carefully designed orbital planes, GNSS constellations provide continuous or near-continuous satellite visibility over most of the globe, with sufficient satellite geometry to support positioning. In open-sky conditions, users can typically observe several satellites simultaneously.

Some systems also use geostationary (GEO) or inclined geosynchronous (IGSO) orbits to enhance regional coverage. BeiDou uses GEO, IGSO and MEO satellites, while QZSS and NavIC use combinations of MEO and geosynchronous orbits, including IGSO, to improve coverage over their target regions.

2.1 Describing a GNSS orbit

Six parameters, known as the Keplerian elements, fully define a GNSS orbit:

1. Semi-major axis – sets the orbit’s size and therefore its period. For GPS, this gives a period of half a sidereal day (about 11 h 58 min), so the same satellite geometry repeats over a given location every day, roughly four minutes earlier each time.
2. Eccentricity – GNSS orbits are designed to be near-circular (e < 0.02), keeping altitude, signal power and Doppler behaviour predictable.
3. Inclination – around 55-56° for GPS, Galileo and BeiDou MEO, and 64.8° for GLONASS, which improves visibility at high latitudes.
4. RAAN (right ascension of the ascending node) – orients each orbital plane in space. Spreading satellites across several planes (six for GPS, three for GLONASS, Galileo and BeiDou MEO) is what gives global coverage.
5. Argument of perigee and mean anomaly – fix the satellite’s position within its plane at a reference time.

These elements, plus perturbation corrections, are broadcast in the navigation message as the ephemeris. From them, a receiver computes each satellite’s position to about 1 m, and that accuracy feeds directly into every range measurement.

3. The main orbit families

The orbit chosen for a satellite depends on its mission: the required coverage, visibility, revisit time, orbital period, and distance from Earth.

Figure 1 – the main orbit families: LEO, MEO, GEO/IGSO, the polar/Sun-synchronous orbit shown edge-on, and the GTO transfer ellipse between LEO and GEO.

Figure 2 — Representative altitudes on a logarithmic scale. GNSS constellations cluster in MEO between about 19,000 and 23,500 km.

GNSS constellations cluster in MEO, between about 19,000 and 23,500 km, well above LEO and well below the geostationary belt at 35,786 km.

3.1 Low Earth orbit (LEO)

LEO covers altitudes from roughly 160 km up to about 2,000 km, although most LEO missions operate below 1,000 km. Satellites in LEO travel at around 7.8 km/s and typically complete an orbit in about 90 minutes. The International Space Station, at an altitude of roughly 420 km, orbits Earth about 16 times per day. For comparison, commercial airliners typically cruise at around 11-12 km, so even the lowest operational orbits are more than ten times higher.

The proximity to Earth makes LEO particularly attractive for high-resolution Earth observation and crewed missions. LEO satellites can operate at a wide range of orbital inclinations, depending on the mission requirements. The trade-off is a relatively small coverage area and short visibility periods: a single LEO satellite passes across the sky in minutes, so continuous or near-continuous services generally require large constellations.

LEO is also attracting growing interest for positioning, navigation and timing (PNT), both through dedicated augmentation signals and as a complementary layer to traditional MEO GNSS. The lower altitude can provide stronger received signals and faster-changing geometry, potentially offering benefits for positioning performance and resilience.

3.2 Medium Earth orbit (MEO)

MEO occupies the region between LEO and geostationary orbit, generally from about 2,000 km to 35,786 km above Earth’s surface. It is the primary orbital regime used by the global navigation constellations – GPS, Galileo, GLONASS and the MEO component of BeiDou – because it offers a good balance between coverage, signal strength and constellation size.

MEO satellites typically have orbital periods of roughly 11 to 14 hours, depending on their altitude. Their movement across the sky provides continuously changing satellite geometry, which is important for accurate positioning. Because each satellite covers a relatively large area of Earth, global or near-global coverage can be achieved with constellations of roughly 24 or more satellites when they are distributed across suitable orbital planes. The exact number and orbital geometry depend on the design of each GNSS constellation.

BeiDou is somewhat different from the other global GNSS because, in addition to its MEO satellites, it also uses satellites in geostationary (GEO) and inclined geosynchronous (IGSO) orbits to provide additional regional coverage and system capabilities.

3.3 Geostationary orbit (GEO)

A geostationary satellite orbits at an altitude of approximately 35,786 km above the equator and travels eastward at about 3.07 km/s. It completes one orbit in one sidereal day (23 h 56 min 4 s), matching the rotation period of Earth relative to the stars. As a result, it remains above approximately the same point on the equator and appears fixed in the sky to an observer on the ground. Ground antennas can therefore be pointed at a fixed position without needing to track the satellite.

This makes GEO particularly valuable for broadcasting, telecommunications, continuous weather monitoring and certain satellite-based augmentation system (SBAS) services. Because of its great altitude, a single GEO satellite can see roughly one-third of Earth’s surface, although the exact coverage depends on the satellite’s field of view and the minimum elevation angle required by the service. A small number of suitably positioned GEO satellites can therefore provide coverage over most of the populated regions of the world, but coverage becomes increasingly limited at high latitudes and near the poles.

The main disadvantages of GEO are the long signal propagation delay, low elevation angles at high latitudes, and the limited number of usable orbital positions along the equatorial geostationary belt. The large distance also results in higher free-space path loss and weaker received signals compared with satellites in lower orbits.

3.4 Inclined geosynchronous orbit (IGSO)

An IGSO is a geosynchronous orbit whose orbital plane is inclined relative to the equator. For a circular IGSO, the satellite’s ground track forms a characteristic north-south figure-of-eight pattern as seen from Earth. The inclination determines the north-south extent of the ground track, while orbital eccentricity can further modify its shape and the amount of time the satellite spends over particular regions.

IGSO satellites are used by navigation systems such as BeiDou and NavIC, while Japan’s QZSS uses geosynchronous and other specially designed orbits to maintain high-elevation coverage over Japan and the Asia-Pacific region. These orbits can provide satellites that remain visible at relatively high elevation angles for extended periods, which is particularly valuable in environments where surrounding buildings or terrain obstruct lower-elevation signals, such as urban canyons and mountainous areas.

3.5 Polar and Sun-synchronous orbits (SSO)

Polar orbits are highly inclined orbits that pass over or near the polar regions, with an inclination close to 90°. They can operate at a wide range of altitudes, although many Earth-observation satellites operate in LEO, typically at altitudes of around 500-800 km. As the satellite orbits Earth while the Earth rotates beneath it, successive passes follow different ground tracks, allowing the satellite to build up coverage of much of the planet.

A Sun-synchronous orbit (SSO) is a special type of near-polar orbit, typically used at altitudes of several hundred kilometres, whose orbital plane slowly precesses at approximately the same rate as the Sun’s apparent annual motion. This means that the satellite crosses a given latitude at approximately the same local solar time on successive passes. The resulting consistency in solar illumination makes images acquired on different days, seasons and years more directly comparable. SSOs are therefore widely used for Earth observation, including applications such as crop monitoring, land-use mapping and flood assessment.

Dawn-dusk Sun-synchronous orbits are designed so that the satellite remains close to the day-night terminator. This can keep the spacecraft in sunlight for most or all its orbit, providing favourable conditions for solar-power generation and reducing the time spent in Earth’s shadow.

3.6 Orbit comparison at a glance

Orbit	Typical altitude	Period	Typical uses
LEO	160-2,000 km	~90-120 min	Imaging, crewed stations, broadband constellations, LEO-PNT
SSO (LEO subset)	600-800 km	~100 min	Earth observation with constant lighting
MEO	2,000-35,786 km	~2-24 h	GNSS (GPS, Galileo, GLONASS, BeiDou)
GEO	35,786 km (equatorial)	23 h 56 min	Communications, weather, SBAS, BeiDou GEO
IGSO	35,786 km (inclined)	23 h 56 min	Regional navigation (BeiDou, QZSS, NavIC)
GTO	~200 x 35,786 km	~10.5 h	Transfer to GEO
L1 / L2	~1.5 million km	Halo orbit	Solar and deep-space observatories

4. GNSS constellations

A receiver needs signals from at least four satellites to solve for its three-dimensional position and its receiver clock offset. Constellation designers therefore distribute satellites across multiple orbital planes and carefully chosen orbital positions so that, from almost anywhere on Earth, sufficient satellites are visible above the receiver’s elevation mask with good geometric distribution across the sky.

Using multiple GNSS constellations together increases the number and diversity of visible satellites. This can improve satellite geometry and positioning robustness, accelerate convergence for high-precision techniques such as RTK and PPP, and maintain service availability when buildings, terrain or other obstructions block part of the sky.

4.1 GPS (United States)

GPS satellites operate in MEO at an altitude of approximately 20,200 km. Each satellite completes an orbit in about 11 hours 58 minutes, or roughly two orbits per sidereal day. The GPS baseline constellation consists of 24 slots arranged in six equally spaced orbital planes, with four slots in each plane and an inclination of 55°. This geometry is designed to provide at least four satellites in view from virtually any point on Earth.

In practice, the U.S. Space Force operates more than the 24-satellite baseline. These additional satellites provide redundancy, helping maintain coverage when satellites are unavailable for maintenance or are retired, and can also improve constellation geometry and positioning performance. They are generally referred to as auxiliary or additional satellites rather than part of the baseline 24-slot constellation.

4.2 Galileo (European Union)

Galileo satellites operate in MEO at an altitude of approximately 23,222 km, in three orbital planes inclined at 56° to the equator. Each satellite takes about 14 hours to complete an orbit. The nominal constellation is a 24/3/1 Walker configuration, with 24 nominal satellites distributed across the three planes; additional satellites can serve as in-orbit spares and be repositioned to replace satellites that are unavailable.

Galileo provides the Open Service (OS) for free positioning and timing, the High Accuracy Service (HAS), which is freely available and provides PPP corrections for improved real-time positioning, and Open Service Navigation Message Authentication (OSNMA), which allows receivers to authenticate Galileo navigation data and helps protect against spoofing. OSNMA was declared operational on 24 July 2025.

4.3 GLONASS (Russia)

GLONASS satellites operate in MEO at an altitude of approximately 19,100 km, in three orbital planes inclined at 64.8° to the equator. Each satellite completes an orbit in roughly 11 hours 15 minutes. The relatively high orbital inclination gives GLONASS good satellite visibility at high northern and southern latitudes, making it particularly well suited to users in regions where lower-inclination constellations provide less favourable satellite geometry.

The GLONASS constellation is designed around 24 operational satellite slots, with eight satellites nominally distributed in each of the three orbital planes.

4.4 BeiDou (China)

BeiDou-3 uses a hybrid constellation of three orbit types: 24 MEO satellites at approximately 21,528 km, inclined at 55°; 3 IGSO satellites at 35,786 km, also inclined at 55°; and 3 GEO satellites at 35,786 km, positioned at 80°E, 110.5°E and 140°E. Spare satellites can also be deployed in orbit as required.

The MEO satellites provide the global backbone of the constellation, while the GEO and IGSO satellites provide additional high-elevation visibility and service capability over the Asia-Pacific region. This hybrid architecture is one of the defining characteristics of BeiDou and allows it to combine global MEO coverage with enhanced regional coverage and services.

4.5 Regional systems

Two regional systems complement the global constellations. Japan’s QZSS uses quasi-zenith and geostationary orbits to keep at least one satellite close to overhead in Japan, improving availability in dense cities and supporting augmentation services. India’s NavIC uses GEO and IGSO satellites to provide positioning over India and the surrounding region; the nominal constellation design and current operational satellite status can differ.

4.6 Constellation comparison

System	Orbit(s)	Altitude	Inclination	Planes / slots	Period (MEO)
GPS	MEO	20,200 km	55°	6 planes, 24 baseline slots	11 h 58 min
Galileo	MEO	23,222 km	56°	3 planes, 24 operational + 3 spares	14 h 05 min
GLONASS	MEO	19,100 km	64.8°	3 planes, 24 satellites	11 h 15 min
BeiDou-3	MEO + IGSO + GEO	21,528 km (MEO); 35,786 km (IGSO/GEO)	55° (MEO/IGSO), 0° (GEO)	24 MEO + 3 IGSO + 3 GEO	~12 h 53 min
QZSS	IGSO + GEO	~35,786 km*	~40° (IGSO), 0° (GEO)	Regional	–
NavIC	GEO + IGSO	~35,786 km	29° (IGSO), 0° (GEO)	Regional	–

*QZSS note: the inclined QZSS satellites are in elliptical geosynchronous orbits, so their altitude varies during each orbit. ~35,786 km is the reference altitude of a circular geostationary orbit, not the constant altitude of the inclined QZSS satellites.

Values are nominal constellation/design parameters; the number and operational status of satellites can change over time.

5. Satellite-based augmentation systems (SBAS)

GNSS augmentation improves the performance of standalone GNSS by providing additional information that allows the receiver to correct or bound errors in the positioning solution. This information can include estimates of satellite clock and orbit (ephemeris) errors, ionospheric delays, and integrity information indicating how large the remaining errors could be. Augmentation can also take the form of local corrections or external aiding, depending on the system. Augmentation systems are commonly classified according to how the additional information is delivered to the user.

SBAS provides wide-area corrections and integrity information, typically broadcast through geostationary satellites. A network of precisely surveyed reference stations continuously monitors the GNSS signals across a region. The measurements are sent to central processing facilities, which estimate satellite and atmospheric errors, generate corrections and integrity information, and send the resulting messages to uplink stations. These stations transmit the messages to geostationary satellites, which broadcast them over the service area on standardised GNSS-compatible signals. An SBAS-capable receiver within the coverage area can use the augmentation data without a separate subscription.

Beyond accuracy, SBAS supplies integrity: timely warnings when a satellite or correction should not be trusted, together with protection levels that bound the position error. This is why SBAS is certified for aircraft approach guidance and is widely used in agriculture, maritime, surveying and road applications.

Operational and developing SBAS include:

• WAAS – United States
• EGNOS – Europe
• MSAS – Japan
• GAGAN – India
• SDCM – Russia
• BDSBAS – China
• KASS – South Korea
• SouthPAN – Australia and New Zealand

6. Why this matters for GNSS users

For anyone designing or deploying a positioning solution, the space segment has direct, practical consequences:

• More constellations, more satellites. Tracking GPS, Galileo, GLONASS and BeiDou together typically puts several dozen satellites in view, improving geometry, availability and redundancy, and increasing resilience in obstructed environments.
• Orbit design drives local performance. High-inclination GLONASS helps at northern latitudes; IGSO satellites from BeiDou and QZSS add high-elevation signals in the Asia-Pacific region.
• Augmentation closes the gap. SBAS can improve accuracy and provide integrity information, while PPP and RTK services can deliver sub-metre to centimetre-level positioning depending on the service, receiver and operating conditions.
• New layers are coming. LEO-based positioning and correction services promise faster convergence and additional robustness alongside traditional MEO GNSS.

Linfinity GNSS works with customers to match receivers, antennas and correction services to the constellations and orbits that best serve their application. For further information, contact admin@linfinitygnss.com.