Overview
A satellite orbit is the path a satellite follows around the Earth, set by its altitude and its inclination to the equator; orbits are classified by altitude into low, medium and high (geostationary) Earth orbits, and the two most important are the geostationary orbit, used for communications and weather, and the sun-synchronous polar orbit, used for Earth observation.
How a satellite stays in orbit
Orbits, gravity and inclination
A satellite stays in space because it is constantly falling around the Earth. Its forward speed and the pull of gravity balance so that it curves around the planet instead of flying off or falling back, and that curved path is its orbit.
Orbits differ in two main ways: how high they are and how they are tilted. The tilt, measured against the equator, is the inclination; an orbit that passes over both poles has an inclination near 90 degrees and is called a polar orbit.
Orbits classified by altitude
Low, medium and high Earth orbits
The first way to sort orbits is by altitude. Low Earth Orbit (LEO) runs from about 160 to 2,000 kilometres up and carries space stations and many imaging satellites, where the view is close and launch is cheapest.
Above it, Medium Earth Orbit (MEO) reaches from 2,000 kilometres to about 35,786 kilometres and is the home of navigation satellites such as GPS. Higher still, at 35,786 kilometres, lies the geostationary orbit, the special case taken up next.
The two workhorse orbits
The geostationary orbit
The geostationary orbit sits at 35,786 kilometres directly above the equator. At that height a satellite takes one sidereal day, about 24 hours, to circle the Earth, exactly matching the planet's spin, so it appears to hang motionless over a single point.
That fixed position is ideal for two jobs. Communications satellites use it so that ground antennas can point at one spot in the sky, and weather satellites such as INSAT use it to watch the same region continuously.
The sun-synchronous polar orbit
The other workhorse is the sun-synchronous orbit, a low, near-polar orbit at about 600 to 800 kilometres with an inclination near 98 degrees. It is timed so that the satellite crosses any given place at the same local solar time on every pass.
Constant local time means constant lighting, which is exactly what an imaging satellite needs. This is why Earth-observation and remote-sensing satellites, such as India's Cartosat series, are placed in sun-synchronous orbits.
Transfer and highly elliptical orbits
GTO, HEO and the Molniya orbit
Not every orbit is circular. A Geostationary Transfer Orbit (GTO) is a stretched, elliptical path used as a stepping stone: a launcher first drops the satellite into the GTO, which then raises itself into the final geostationary orbit.
| Orbit | Altitude | Typical use |
|---|---|---|
| Low Earth Orbit (LEO) | 160 to 2,000 km | Space stations, imaging, small satellites |
| Medium Earth Orbit (MEO) | 2,000 to 35,786 km | Navigation (positioning) |
| Geostationary (GEO) | 35,786 km | Communications and weather |
| Sun-synchronous (polar) | about 600 to 800 km | Earth observation, remote sensing |
| Highly elliptical (HEO) | varies (high apogee) | High-latitude communications |
Other paths serve special needs. Highly elliptical orbits, including the Molniya type, swing far out over high latitudes and linger there, giving long coverage to polar regions that the equatorial geostationary orbit cannot easily reach.
Matching the orbit to the mission
Which orbit for which job
The orbit is never chosen at random; it follows the mission. A satellite's altitude and inclination are picked so that it can do its particular job, and a few pairings cover most of what satellites are built to do:
- Communications and weather: geostationary orbit (for example India’s INSAT and GSAT).
- Earth observation and remote sensing: sun-synchronous polar orbit (for example India’s Cartosat).
- Navigation and positioning: medium Earth orbit (for example GPS).
- Space stations and many small satellites: low Earth orbit.
The lesson is that orbit and mission are inseparable. Engineers begin with what a satellite must do, then choose the altitude and inclination that make it possible, which is why the same few orbits recur across the world's space programmes.
How this appears in the UPSC exam
What the exam tests on satellite orbits
In the exam this is a Prelims and science-and-technology favourite, often tucked into questions on ISRO missions. The high-yield facts are the geostationary altitude of 35,786 kilometres and why communications satellites use it.
Equally testable is the contrast between the two workhorse orbits. Knowing that geostationary orbits suit communications and weather while sun-synchronous orbits suit Earth observation, and pairing each Indian satellite with its orbit, answers most questions cleanly.
Prelims MCQ practice
Each question below tests one specific concept on the topic. Click to reveal the answer and a full option-wise explanation.
Q1. A geostationary orbit lies at an altitude of about:
- 360 km
- 2,000 km
- 35,786 km
- 384,000 km
Show answer and explanation
Answer: 35,786 km
Explanation.
A geostationary orbit lies at about 35,786 km above the equator. 360 km and 2,000 km are low Earth orbit; 384,000 km is roughly the distance to the Moon. Hence (c).
Q2. Why does a geostationary satellite appear to stay fixed over one point on the Earth?
- because it does not move at all
- because its orbital period matches the Earth's rotation period and it lies over the equator
- because it is held up by a cable
- because it orbits over the poles
Show answer and explanation
Answer: because its orbital period matches the Earth's rotation period and it lies over the equator
Explanation.
A geostationary satellite circles the Earth once per sidereal day, matching the planet's rotation, and lies in the equatorial plane, so it appears fixed over one point. It is in fact moving fast; it does not orbit over the poles. Hence (b).
Q3. With reference to the classification of Earth orbits by altitude, consider the following statements:
- Low Earth Orbit lies roughly between 160 and 2,000 km.
- Medium Earth Orbit lies between about 2,000 km and the geostationary altitude.
- Navigation satellites such as GPS are placed in Low Earth Orbit.
Which of the statements given above is/are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer and explanation
Answer: 1 and 2 only
Explanation.
Statements 1 and 2 are correct: LEO is about 160 to 2,000 km and MEO runs from 2,000 km to the geostationary altitude. Statement 3 is wrong: navigation satellites such as GPS use Medium Earth Orbit, not LEO. Hence 1 and 2 only.
Q4. A sun-synchronous orbit is best suited for:
- television broadcasting
- Earth observation and remote sensing
- manned space stations
- interplanetary missions
Show answer and explanation
Answer: Earth observation and remote sensing
Explanation.
A sun-synchronous orbit crosses each point at the same local solar time, giving consistent lighting, which makes it ideal for Earth observation and remote sensing. Broadcasting uses geostationary orbit. Hence (b).
Q5. With reference to a polar orbit, which one of the following is correct?
- it has an inclination of about 0 degrees
- it has an inclination of (or close to) 90 degrees and passes over both poles
- it lies only over the equator
- it is always geostationary
Show answer and explanation
Answer: it has an inclination of (or close to) 90 degrees and passes over both poles
Explanation.
A polar orbit has an inclination of (or very close to) 90 degrees, so the satellite passes over or near both poles on each revolution. An inclination near 0 degrees is equatorial. Hence (b).
Q6. A Geostationary Transfer Orbit (GTO) is:
- the final orbit of all weather satellites
- an elliptical orbit used as a stepping stone to reach the geostationary orbit
- a low orbit used by space stations
- an orbit over the poles
Show answer and explanation
Answer: an elliptical orbit used as a stepping stone to reach the geostationary orbit
Explanation.
A Geostationary Transfer Orbit is an elliptical orbit into which a satellite is first injected, from which it then raises itself into the final geostationary orbit. The other options are incorrect. Hence (b).
Sources and Further Reading
Editorial Disclaimer
This article explains the types of satellite orbits for UPSC preparation, drawing on standard space-science sources, ISRO and NASA. Altitudes and figures reflect the cited authorities.
