Maarg Manthan · Topic 12.1

Types of Orbits (LEO, MEO, GEO, Polar, Sun-Synchronous)

Science & Technology › Space Technology and ISRO · Topic 12.1

An orbit is the curved path that a satellite follows around the Earth under the pull of gravity, and its height, shape and tilt decide what the satellite can do. The main types by height are low Earth orbit, from about 160 to 2,000 kilometres, medium Earth orbit, from 2,000 to about 35,786 kilometres, and geostationary orbit at 35,786 kilometres above the equator, where a satellite takes 24 hours to go round and so appears fixed over one spot. By shape and tilt there are polar orbits that pass over both poles, and sun-synchronous orbits at about 600 to 800 kilometres that pass over a place at the same local time every day. A satellite in low Earth orbit travels at about 7.8 kilometres per second.

6 min read · UPSC Prelims · Science & Technology · Space Technology and ISRO

At a Glance

LEO 160 to 2,000 km
MEO 2,000 to 35,786 km
GEO 35,786 km, period 24 hours
Polar and SSO High inclination, near poles
Speed in LEO About 7.8 km per second
Exam link UPSC Prelims, Science & Technology: Space Technology and ISRO

Where Does It Fit?

This is the first topic of the macro on space technology and ISRO. Orbit types are the base for every later topic, from launch vehicles to navigation and remote sensing satellites. Previous topic: Designer Babies/Three-Parent Babies. Next topic: Categories of Launch Vehicles and Their Uses.

What Are the Main Types of Orbits?

Orbit	Features and uses
Low Earth Orbit (LEO)	About 160 to 2,000 km. Period about 90 to 120 minutes. Used by the International Space Station, Earth observation, many communication constellations such as Starlink and cubesats
Medium Earth Orbit (MEO)	About 2,000 to 35,786 km. Navigation satellites such as GPS (about 20,200 km), Galileo and GLONASS
Geostationary Orbit (GEO)	35,786 km above the equator, circular, zero inclination, period equal to Earth’s rotation. Communication and weather satellites such as INSAT and GSAT
Geosynchronous Orbit (GSO)	Same 24-hour period but may be inclined, so the satellite traces a figure of eight. NavIC uses a mix of geostationary and inclined geosynchronous satellites
Polar Orbit	Inclination near 90 degrees, passing over the poles. As the Earth turns beneath, the satellite scans the whole globe over time
Sun-Synchronous Orbit (SSO)	A near polar, slightly retrograde orbit, about 600 to 800 km, with inclination about 98 degrees. The satellite crosses each latitude at the same local solar time
Highly elliptical orbit	Molniya type orbits give long coverage of high latitudes

How Are Satellites Placed in Orbit and What Terms Matter?

Transfer orbit: a satellite for geostationary orbit is first placed in an elliptical geosynchronous transfer orbit, with a low perigee and an apogee near 36,000 km, then fires its engine at apogee to circularise
Inclination: the angle between the orbital plane and the equator. Zero for equatorial, near 90 for polar
Apogee and perigee: the farthest and nearest points of the orbit from the Earth
Orbital period: increases with height, according to Kepler’s third law
Prograde and retrograde: prograde moves in the direction of Earth’s rotation, which saves fuel. Sun-synchronous orbits are slightly retrograde
Launch site latitude: a site near the equator, such as Sriharikota at about 13.7 degrees north, gains from Earth’s rotation speed for launches to the east
Escape velocity: about 11.2 km per second from Earth’s surface, needed to leave Earth’s gravity
Station keeping: small engine burns that keep a satellite in its slot against drifts caused by the Moon, Sun and Earth’s shape

What Else Should You Remember?

Why geostationary orbit: a dish on the ground can point at it once, so it suits television, telephone and weather watch over a fixed area. One satellite covers about a third of the Earth
Clarke belt: geostationary orbit is also called the Clarke belt, after the writer Arthur C. Clarke who described the idea in 1945
Signal delay: the long distance causes a delay of about a quarter of a second, which low orbit constellations avoid
Why sun-synchronous: constant sun angle gives similar shadows in repeated images, which helps in comparing changes over time. Most Earth observation satellites and Indian IRS satellites use it
Polar Satellite Launch Vehicle: the PSLV was designed to reach sun-synchronous orbit, as in Launch Vehicle Technology: PSLV, GSLV and Cryogenic Engines
Lagrange points: positions where the pull of two bodies balances, such as L1 used by Aditya-L1, as in Solar Mission Aditya-L1
Graveyard orbit: old geostationary satellites are moved a few hundred kilometres higher to free the slot, as in Space Junk and Graveyard Orbits
Van Allen belts: radiation zones that influence the choice of orbits for satellites and crews
Constellations: many LEO satellites working together can give global internet, as in Space Technology Innovations: Nanosatellites, Electric Propulsion, Satellite-Based Internet
Indian examples: INSAT and GSAT in GEO, Cartosat and Resourcesat in SSO, NavIC in GEO and inclined GSO, and Astrosat in a low inclination LEO
Orbit and cost: higher orbits need more powerful rockets, and low orbits need more satellites to cover the same area
International coordination: slots in geostationary orbit and radio frequencies are coordinated by the International Telecommunication Union

Why Does It Matter for the Exam?

Heights and periods: GEO at 35,786 km with period of 24 hours
Differences: geostationary versus geosynchronous, polar versus sun-synchronous
Uses: which satellite uses which orbit
Current affairs link: LEO internet constellations and NavIC
Common errors: saying that all geosynchronous satellites are stationary or that GPS is in GEO

As an analytical point, orbit choice is a trade between coverage, delay, cost and lifetime. Understanding it explains why India uses different launch vehicles and satellite series for communication, imaging and navigation.

Why Is This Topic Important?

Heights Often asked as numbers
Types GEO versus GSO
Uses Satellite series

What Came Next?

The next topic covers the categories of launch vehicles and their uses. Next topic: Categories of Launch Vehicles and Their Uses.

Key People and Terms

Orbit Path around a body
Perigee Nearest point to Earth
Apogee Farthest point
Inclination Tilt to the equator
Period Time for one orbit
Transfer orbit Stepping stone orbit

Exam Corner

Points to Remember

GEO height: 35,786 km, period 24 hours.
GPS height: about 20,200 km, MEO.
SSO inclination: about 98 degrees.
Geostationary orbit lies over the equator.
Sriharikota latitude: about 13.7 degrees north.

Do Not Confuse With

Geostationary and geosynchronous Fixed over equator versus same period but possibly inclined
Polar and sun-synchronous Over the poles versus constant local time
Transfer orbit and final orbit Elliptical stepping orbit versus working orbit

Memory Hook

Low for eyes, medium for maps, high for broadcasting; sun-synced shadows stay the same.

Mains Angle

Questions ask for numbers and for matching orbit with use. These points help.

Choice Coverage versus delay
India Series and orbits
Trends LEO constellations

A Question You May Face

An original practice question, not a past paper question.

“Explain the different types of satellite orbits and the reasons for choosing a particular orbit for communication, remote sensing and navigation satellites.”

How to Answer

Types LEO to GEO.
Reasons Coverage, delay.
Examples INSAT, IRS, GPS.
Trend LEO constellations.

GS Relevance

Prelims: orbit heights, periods, uses, GEO versus GSO, sun-synchronous. GS Paper 3: science and technology, space technology.

Frequently Asked Questions

What is a geostationary orbit?

A geostationary orbit is a circular orbit 35,786 kilometres above the equator in which a satellite takes 24 hours to go round the Earth, the same as the Earth's rotation. The satellite therefore appears fixed in the sky over one place, which makes it ideal for communication and weather satellites such as INSAT and GSAT.

What is the difference between geostationary and geosynchronous orbit?

Both have an orbital period of 24 hours, but a geostationary orbit is circular and lies exactly over the equator, so the satellite stays fixed over one spot. A geosynchronous orbit may be inclined, so the satellite appears to move north and south in a figure of eight when seen from the ground.

What is a sun-synchronous orbit?

A sun-synchronous orbit is a near polar orbit, usually 600 to 800 kilometres high with an inclination of about 98 degrees, in which the satellite passes over any place at the same local solar time every day. This gives constant lighting for comparing images, so many Earth observation satellites use it.

Why are navigation satellites placed in medium Earth orbit?

Navigation satellites such as GPS, Galileo and GLONASS orbit at about 20,000 kilometres in medium Earth orbit. This height lets a few dozen satellites cover the whole globe, so that a receiver anywhere can see at least four of them, which is the minimum needed to calculate a position.

Why does the launch site matter for orbits?

A launch site near the equator, such as Sriharikota in India, benefits from the Earth's rotation speed, which helps rockets launched eastward to reach orbit with less fuel. Polar launches go south from Sriharikota, and the launch azimuth is chosen so that rocket stages do not fall on land.

PYQ Practice — Statement Analysis

1 A geostationary satellite orbits at about 35,786 km above the equator.

True

With a period of 24 hours.

2 GPS satellites are placed in geostationary orbit.

False

They are in medium Earth orbit.

3 A sun-synchronous satellite passes over a place at the same local time each day.