Orbit Classification

An orbit is the curved path a satellite follows as it keeps falling around the Earth without ever hitting it. Satellites are grouped by how high they fly and what shape their path has. A satellite close to the Earth moves very fast and circles the planet many times a day. A satellite far away moves slower and takes longer to go around once. The height chosen for a satellite depends on its job: taking photos, sending TV signals or telling you your location.

Why does a satellite stay up?

Think of throwing a cricket ball. The harder you throw it, the farther it lands. If you could throw it fast enough, the ground would curve away under it as fast as it falls, and it would never land. That is an orbit. Near the Earth, this speed is about 7.8 km per second. To escape the Earth's pull completely, an object needs about 11.2 km per second, which is called escape velocity.

The higher the orbit, the weaker the Earth's pull, so a satellite there needs less speed and takes more time to complete one round.

Where did these ideas come from?

In the early 1600s, the astronomer Johannes Kepler worked out that planets move in oval paths called ellipses. His third law says the farther an object is from what it orbits, the longer its orbit takes. In 1945, the science writer Arthur C. Clarke suggested that three satellites placed about 36,000 km above the equator could cover almost the whole world with radio signals.

This is why the geostationary orbit is sometimes called the Clarke orbit. The first artificial satellite, the Soviet Union's Sputnik 1, reached low orbit in 1957.

Low Earth Orbit (LEO)

LEO is any orbit up to about 2,000 km above the Earth. A satellite here goes around the Earth in about 90 to 120 minutes. Examples:

• The International Space Station flies at about 400 km.
• Large internet constellations such as Starlink fly at about 550 km.
• India's Earth-watching satellites and its planned human spaceflight (Gaganyaan) use LEO.

LEO satellites are close, so photos are sharp and signals arrive quickly. But each satellite sees only a small patch of the Earth at a time, so many satellites are needed for constant coverage.

Sun-Synchronous and Polar Orbits

A polar orbit passes over or near the North and South Poles. As the Earth spins below, the satellite sees a new strip of land on each round, and in time it covers the whole planet. A special type, the Sun-Synchronous Orbit (SSO), is usually about 600 to 800 km high and tilted at about 98 degrees.

Its plane turns slowly, in step with the Earth's yearly journey around the Sun. So the satellite crosses any given place at the same local solar time every day. This gives the same lighting in every photo, which is ideal for comparing crops, forests or floods over time. ISRO's PSLV is famous for SSO launches.

Medium Earth Orbit (MEO)

MEO lies between about 2,000 km and 35,786 km. Global navigation systems use it. The American GPS satellites fly at about 20,200 km and go around the Earth twice a day. Russia's GLONASS, Europe's Galileo and most of China's BeiDou satellites are also in MEO.

Geosynchronous Orbit (GSO)

A satellite at a height of about 35,786 km takes exactly one sidereal day (23 hours, 56 minutes, 4 seconds) to go around the Earth. That is the time the Earth takes to spin once with respect to the stars. Any orbit with this period is called geosynchronous. If the orbit is tilted to the equator, the satellite does not stay at one point in the sky.

Seen from the ground, it moves north and south in a figure-of-eight pattern every day, but it comes back to the same place at the same time each day.

Geostationary Orbit (GEO)

A geostationary orbit is a special geosynchronous orbit that is circular and lies directly above the equator with almost no tilt. Here the satellite moves at about 3.07 km per second, exactly as fast as the Earth turns below. So from the ground it seems to stand still at one point in the sky. That is why your DTH dish can point in one fixed direction forever.

India's INSAT and GSAT communication and weather satellites sit in GEO. Each satellite is given a fixed orbital slot, named by its longitude, such as 83° East.

How does a satellite reach GEO? The Geosynchronous Transfer Orbit (GTO)

Rockets do not usually carry a satellite all the way to 36,000 km. Instead, they put it into a GTO, an oval orbit with:

• a low point (perigee) of a few hundred kilometres, often about 170 to 250 km, and
• a high point (apogee) close to 36,000 km.

The satellite then fires its own engine, usually a Liquid Apogee Motor (LAM), several times when it is at the high point. Each firing makes the oval rounder and raises the low point, until the orbit becomes a circle at about 36,000 km. This step-by-step climb is called orbit raising. A simple picture: the rocket throws the ball up a long staircase, and the satellite climbs the last flights itself.

Here is a real example. On 30 October 2026, India's GSLV-F18 rocket dropped the navigation satellite NVS-03 into a transfer orbit of about 170.3 km x 38,080 km. NVS-03 then fired its LAM four times, for about 6,164 seconds in total. By 4 November 2026, it had climbed to its final geosynchronous orbit of about 35,765 km x 36,196 km.

Sub-GTO and Super-GTO

If a rocket cannot lift a heavy satellite all the way to a full GTO, it may place it in a sub-GTO, where the high point is lower than about 36,000 km. The satellite must then burn more of its own fuel to climb, which can shorten its working life. A super-GTO is the opposite: the rocket throws the satellite higher than needed, with a high point above GEO height, so the satellite saves fuel. In general, the more work the rocket does, the longer the satellite can work in orbit.

Here is a real example. EOS-05 is a 2,367 kg satellite, and India's first imaging satellite built to work from geosynchronous orbit. Because it was heavy, the GSLV-F17 rocket placed it in a sub-GTO in September 2026, and the satellite climbed the rest of the way with its own engine. The high point reached about 31,000 km, about 2,000 km above plan, so the climb needed less work.

NVS-03 also got a bonus: its high point was about 1,000 km above plan, which slightly cut the fuel it had to use.

Other orbits worth knowing

• Highly Elliptical Orbit (HEO): a very stretched orbit, like Russia's Molniya orbit, which spends long hours over far northern areas that GEO satellites cannot see well.
• Lagrange points: five points between two large bodies (like the Sun and the Earth) where a spacecraft can stay in a fixed position relative to both. India's solar mission Aditya-L1 works near the Sun-Earth L1 point, about 1.5 million km from the Earth.
• Graveyard orbit: at the end of its life, a GEO satellite uses its last fuel to move about 300 km above GEO, so that it does not crowd or hit working satellites.

India's position and Indian examples

• PSLV: India's workhorse for LEO and SSO missions.
• GSLV: carries satellites of about 2 to 2.5 tonnes to GTO, such as the NVS navigation satellites.
• LVM3: India's heaviest rocket, for about 4 tonnes to GTO and for Gaganyaan to LEO.
• NavIC uses a mix of orbits: three satellites in GEO (at 32.5°E, 83°E and 129.5°E) and four in inclined geosynchronous orbits (tilted about 29 to 30 degrees) that cross the equator at 55°E and 111.75°E.
• NVS-03: as of November 2026, this second-generation NavIC satellite has reached its geosynchronous orbit, tilted 29.98 degrees, for the 111.75°E slot. It must still finish its in-orbit testing (commissioning) before it starts service.

Orbital slots and radio frequencies are scarce. They are coordinated worldwide by the International Telecommunication Union (ITU), a United Nations agency. Countries file for slots well in advance.

Commonly confused concepts

• Geosynchronous vs geostationary: both take one sidereal day per orbit. Every geostationary orbit is geosynchronous, but not every geosynchronous orbit is geostationary. Only GEO is circular, over the equator and fixed in the sky. For example, NVS-03 is geosynchronous but not geostationary, because its orbit is tilted by about 30 degrees.
• GTO vs GEO: GTO is the temporary oval "transfer" path; GEO is the final circular home. A satellite in GTO is not yet doing its job.
• Polar orbit vs sun-synchronous orbit: an SSO is a type of near-polar orbit, but its special feature is crossing places at the same local solar time.
• Perigee vs apogee: perigee is the point closest to the Earth; apogee is the farthest point.
• Sidereal day vs solar day: a sidereal day (about 23 h 56 min) is one spin of the Earth measured against the stars; a solar day (24 h) is measured against the Sun.
• LEO vs MEO for navigation: global navigation systems use MEO because each satellite then sees a large part of the Earth, so fewer satellites are needed than in LEO.

Issues, criticism and the way forward

• Space debris: LEO is getting crowded with broken satellites and rocket parts. Even a small fragment moving at about 7.8 km per second can destroy a satellite. Experts recommend removing dead satellites quickly and designing missions that leave no debris. In April 2024, ISRO announced its Debris Free Space Missions (DFSM) goal: all Indian space missions, government and private, should leave no debris by 2030.
• Crowding in GEO: there is only one geostationary ring, and good slots over busy regions are limited. Developing countries argue that early space powers took the best slots.
• Mega-constellations: thousands of internet satellites in LEO raise worries about collisions and about light pollution for astronomers.
• Orbit-raising risk: a satellite left in GTO depends fully on its own engine and valves. A single failed part can leave it stranded, as happened with NVS-02 in January 2025. Careful testing and backup paths for every critical part are the main remedies.

Concepts to Know

• Ellipse: a stretched circle, like the shape of an egg seen from the side. Most orbits are slightly or strongly elliptical.
• Sidereal day: the time the Earth takes to spin once with respect to far-away stars: about 23 hours, 56 minutes and 4 seconds.
• Orbital slot: a fixed position in the geostationary ring, named by its longitude (for example, 83° East), where a country's satellite is allowed to sit.
• Liquid Apogee Motor (LAM): the satellite's own main engine, fired at the high point of the transfer orbit to raise and round off the orbit.
• Inclination: how much an orbit is tilted compared with the equator. Zero degrees means exactly over the equator; 90 degrees means passing over the poles.
• Escape velocity: the speed needed to break free of the Earth's gravity completely, about 11.2 km per second.