Types of Satellite Orbits
How satellites move in space
- A satellite’s orbit works because of a balance between two forces viz.
- Satellite’s velocity – the speed it is travelling in a straight line
- Force of the Earth’s gravitational pull on the satellite
- An artificial satellite is always falling towards earth, but it has enough tangential velocity to continue fall indefinitely.
- Centripetal force on the satellite balances the gravitational attractive force of the earth.
- This balance does not depend upon the mass and size of the satellite.
Orbit of a Satellite
- Before designing a satellite, scientists choose an orbit that is appropriate to its function as a satellite as one in an orbit very high up will not be able to see objects on Earth in as much detail as orbits that are lower, and closer to the Earth’s surface.
- Similarly, the speed of the satellite moving in the orbit, the angle over the Earth the satellite takes, the areas which the satellite can observe, and the frequency with which the satellite passes over the same portions of the Earth are all important factors to consider when choosing an orbit.
- Finally, the place from which a satellite is launched is important in determining its orbit.
- A satellite launched from a place with higher latitude would have a higher angle of inclination, suitable to launch satellites into polar orbits
- To put a satellite into equatorial orbit, it would be best to launch it from somewhere close to the equator
International Space Station
- a space station / a habitable artificial satellite, in low Earth orbit
- the largest artificial body in orbit and can often be seen with the naked eye from Earth
- suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars
- serves as a space environment research laboratory in which crew members conduct experiments
Types of Satellite Orbits
- Majorly, there are two major divisions in orbit types; viz. circular orbits and elliptical orbits
- Circular orbits comprises of geostationary, polar, sun-synchronous, and equatorial orbits
- Though no orbit is perfectly circular, the general name for any orbit that is not highly elliptical is circular
- Circular orbits have an eccentricity of 0
- The orbital path of satellites in these circular orbits is also affected by the satellite’s altitude – its height above the Earth
- Satellites in geostationary orbit are always in a high orbit.
- If the satellite is in a polar, sun-synchronous, or equatorial orbit, its orbital altitude may be medium or it may be low
- Moves along the line of the Earth’s equator
- To get into equatorial orbit, a satellite must be launched from a place on Earth close to the equator
- Equatorial orbits can be useful for satellites observing tropical weather patterns, as they can monitor cloud conditions around the globe.
- Has a period of revolution is equal to period of rotation of earth, but its orbit is not equatorial with anorbital period of one sidereal day, matching the Earth’s sidereal rotation period
- synchronized with the Earth’s rotation, but the orbit is tilted with respect to the plane of the equator
- synchronization of rotation and orbital period means that, for an observer on the surface of the Earth, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day
- Not in equatorial plane i.e. directly above the equator, it’s in inclined orbit
- Angular velocity of the satellite is equal to angular velocity of earth
- Period of revolution is equal to period of rotation of earth.
- Nearly at an altitude of 36000 Km from earth surface
- There are many geosynchronous orbits used for communication, weather monitoring & surveillance
Geostationary orbit / Geosynchronous equatorial orbit
- A circular orbit above the Earth’s equator, following the direction of the Earth’s rotation; has an orbital period equal to the Earth’s rotational period (one sidereal day), and thus appears motionless, at a fixed position in the sky, to ground observers.
- Speed at which a satellite orbits the Earth coincides with the speed that the Earth turns and at the same latitude, however, this does not mean that the satellite and the Earth are traveling at the same speed, but rather that the satellite is traveling fast enough so that its orbit matches the Earth’s rotation.
- When a satellite is in geostationary orbit, its instruments are looking at a certain part of the Earth. That part of the Earth is called a footprint for ex. India
- Suitable for communication satellites, or meteorological (weather) satellites
- Circular orbit + in equatorial plane i.e. directly above the equator and thus inclination is zero
- Geostationary orbit, therefore, is really just a special type of equatorial orbit
- Angular velocity of the satellite is equal to angular velocity of earth
- Period of revolution is equal to period of rotation of earth
- Nearly at an altitude of 36000 Km from earth surface
- A subset of geosynchronous orbit
- There is ONLY one geostationary orbit
- A polar orbit usually has an inclination of 90 degrees to the equator
- On every pass around the Earth, it passes over both the north and south poles
- This allows the satellite to see virtually every part of the Earth as the Earth rotates underneath it
- Suitable for mapping or surveillance operations
Sun Synchronous Orbit
- This orbit is a special case of the polar orbit.
- Like a polar orbit, the satellite travels from the north to the south poles
- Since there are 365 days in a year and 360 degrees in a circle, it means that the satellite has to shift its orbit by approximately one degree per day.
- Hence, orbit changes slowly in time with the planet moving around the Sun, and in time with the planet’s rotation so that the spacecraft is always at the same angle to the Sun
- These orbits allow a satellite to pass over a section of the Earth at the same time every day
- An elliptical orbit, also called an eccentric orbit, is in the shape of an ellipse
- Elliptical orbits are varying in speed & have eccentricity between zero to one
- Satellite’s velocity changes & depends on where it is in its orbital path
- When the satellite is in the part of its orbit closest to the Earth, it moves faster because the Earth’s gravitational pull is stronger.
- The satellite is moving the fastest at the low point of an elliptical orbit viz. perigee
- The high point of the orbit, when the satellite is moving the slowest, is apogee
Launch Vehicles for Satellites & Space Probes
- Launch Vehicles are used to transport and put satellites & space probes into space
- Satellites Orbits Height Classification to under different types of launch vehicles
|Lower earth orbit||180 km – 2000 km||Sun synchronous orbit, Polar Orbit|
|Mid earth orbit||2000 km – 35780 km||GPS & Navigation|
|High earth orbit||> 35780 km||Geostationary orbit|
- The first Indian experimental Satellite Launch Vehicle (SLV-3) was developed in 1980
- An Augmented version of this, ASLV, was launched successfully in 1992
India has made tremendous progress in launch vehicle technology & has achieved self-reliance in satellite launch vehicle programme with the operationalisation of Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV)
Satellite Launch Vehicle (SLV)
- The Satellite Launch Vehicle (SLV) project was born out of the need for achieving indigenous satellite launch capability
- SLV3, India’s first experimental launch vehicle, was capable of placing 40 kg class payloads in Low Earth Orbit (LEO)
- It was a four-stage rocket with all solid-propellant motors – weighing 17 tonnes with a height of 22 m
- The launch on July 18, 1980 from Sriharikota Range, successfully placed Rohini satellite, into the orbit, thereby making India the sixth member of an exclusive club of space-faring
The successful culmination of the SLV-3 project showed the way to advanced launch vehicle projects such as the Augmented Satellite Launch Vehicle (ASLV), Polar Satellite Launch Vehicle (PSLV) and the Geosynchronous satellite Launch Vehicle (GSLV)
Augmented Satellite Launch Vehicle (ASLV)
- The Augmented Satellite Launch Vehicle (ASLV) Programme was designed to augment the payload capacity to 150 kg, thrice that of SLV-3, for Low Earth Orbits (LEO).
- With a lift off weight of 40 tonnes, the 23.8 m tall ASLV was configured as a five stage, all-solid propellant vehicle to Low Earth Orbit (LEO)
Polar Satellite Launch Vehicle (PSLV)
- PSLV is capable of launching 1750 kg satellites in sun-synchronous polar orbit and 1425 kg satellite in geo-synchronous transfer orbit.
- It measures 44.4 m tall, with a lift off weight of 320 tonnes & known as the Workhorse of ISRO
- PSLV has four stages using solid and liquid propulsion systems alternately
- PSLV has proved its multi-payload, multi-mission capability in a single launch and its geosynchronous launch capability
- Launched Missions → Chandrayaan-1, Mars Orbiter Mission, Space Capsule Recovery Experiment, IRNSS, Astrosat
Geosynchronous Satellite Launch Vehicle (GSLV)
- The Geosynchronous Satellite Launch Vehicle (GSLV) was primarily developed to launch INSAT class of satellites into Geosynchronous Transfer Orbits.
- Presently GSLV is being used for launching GSAT series of satellites.
- GSLV is capable of placing 2 ton class of satellites viz. INSAT and GSAT into Geosynchronous Transfer Orbit (GTO)
- Payload to LEO is 5,000 kg & Payload to GTO is 2500 kg
- GSLV is a 49 m tall, three stage vehicle with a lift-off mass of 415 ton.
- The first stage is solid propellant motor stage
- The second stage is liquid propellant stage
- Third one is cryogenic stage viz. uses liquid hydrogen as fuel & liquid oxygen as oxidizer
- Cryogenic rocket engine – Fuel or oxidizer (or both) is gases liquefied and stored at very low temperatures
Difference Between PSLV & GSLV
|PSLV (Polar satellite launch vehicle)
||GSLV (Geosynchronous satellite launch vehicle)
Geosynchronous Satellite Launch Vehicle MK3 (GSLV Mk 3) / LVM3
- LVM 3 is a heavy launch capability launcher being developed by ISRO
- Have Multi-mission launch capabilities, can be used to launch satellites into different orbits
- It will allow India to achieve complete self-reliance in launching satellites as –
- It will be capable of placing 4 tonne class Geosynchronous satellites into GTO
- It will be capable of placing 8 tonne class satellites into LEO
- LVM3 wll have same 3 stages as GSLV but it will have an India built cryogenic stage with higher capacity than GSLV
Difference Between GSLV & GSLV Mk3
||GSLV – Mark 3
LVM3-X/CARE Test Flight
- First experimental flight of LVM3, lifted off from Sriharikota on December 18, 2014
- Directed By – Human Crew module Atmospheric Reentry Experiment (CARE)
- To check its atmospheric stability with luggage of around 4 tonne
- To study re-entry characteristics of the crew module
- Did not use cryogenic engine in test stage & carried only a passive (non-functional) cryogenic engine in upper stage
GSLV MK III with cryogenic upper stage successfully tested
- The GSLV D-6 is the second successful consecutive launch (earlier launch GSLV D-5 in January) of the GSLV series with indigenous cryogenic upper stage.
- ISRO is planning to test GSLV Mk III capable of carrying payload up to four tonne by the end of next year.
Significance of GSLV MK3
- GSLV will cost just one third of money spent on foreign agencies, which will reduce satellite launch cost as well as will save Forex
- It will enhance India’s capability to be a competitive player in the multimillion dollar commercial launch market. It will help in earning foreign exchange.
- The GSLV will help ISRO put heavier communication satellites of GSAT class into orbit.
- Reduction of dependence on foreign agencies gives strategic boost in this high tech sector
Types of Launch Engines
Solid Fuel Engine
- Once fired continue to be in operation till their fuel burns off
- Can’t control its velocity or direction
Liquid Fuel Engine
- Can be shut off once the spacecraft achieves the desired velocity
- Can restart the engine several times if required, making it possible to change satellite’s orbit with precision
LAM – Liquid Apogee Motor
- A special device on liquid-fuel powered engines, which helps to move the satellite in a precise orbit
- Recently, ISRO used LAM on its Mars orbiter and on IRNSS satellites
ISRO indigenous cryogenic engine CE-20 with four-tonne capacity
- Enable scientists to put satellites of up to the capacity of four tones in geostationary orbit
- So far India’s GSLVs were being powered by cryogenic engines given by Russia
- Generally uses Hydrogen as fuel and liquid oxygen as oxidizer stored at very low temperature
- evelop the thrust needed in the final state of the rocket to put satellites into a geosynchronous orbit
The cryogenic stage is technically a very complex system, as compared to solid liquid propellant stages, due to its use of propellants at extremely low temperature (cryo) and the associated thermal and structural challenges. A cryogenic rocket stage is more efficient and provides more thrust for every kilogram of propellant it burns.
ISRO’s Reusable Launch vehicle
- This launch vehicle (1.5 tonne) will be mounted on the Polar Satellite Launch Vehicle (PSLV) rocket
- At an altitude of 70 km, the model would get separated and would glide back to earth
- The descent speed would be controlled through the fins on the machine
- It will bring down costs significantly of launching satellites by one-tenth
- ISRO’s Augmented Reality application designed for Android devices
- It consists of 3D models of rockets (PSLV, GSLV Mk-III); videos of INSAT 3D-predicting cyclones Mars Orbiter Mission (MOM) orbit insertion, launch video of MOM, Anaglyph of Mars surface.
- Augmented Reality is a live direct view of a physical, real-world environment whose elements are augmented by computer-generated 3D models, animations, videos etc.
- It enhances user’s current perception of reality
- AR requires three elements – Android device with back camera, AR application and AR markers
Types of Satellites
- Satellite refers to a machine that is launched into space and moves around Earth or another body in space.
- A satellite is an artificial object which has been intentionally placed into orbit.
- Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth’s Moon & Sun’s Earth
Why we need satellites?
- Satellites have allows us to see large areas of Earth at one time.
- This ability means satellites can collect more data, more quickly, than instruments on the ground.
- Satellites also can see into space better than telescopes at Earth’s surface.
- Reason being that satellites fly above the clouds, dust and molecules in the atmosphere that can block the view from ground level.
Parts of a Satellite
- All satellites have at least two parts in common – an antenna and a power source.
- The antenna sends and receives information, often to and from Earth
- The power source can be a solar panel or battery
- Many satellites carry cameras and scientific sensors.
- Sometimes these instruments point toward Earth to gather information about its land, air and water
- Other times they face toward space to collect data from the solar system and universe
How Do Satellites Orbit Earth?
- A satellite orbits Earth when its speed is balanced by the pull of Earth’s gravity.
- Without this balance, the satellite would fly in a straight line off into space or fall back to Earth.
- Satellites orbit Earth at different heights, different speeds and along different paths. The two most common types of orbit are Geostationary and Polar
- A geostationary satellite travels from west to east over the equator. It moves in the same direction and at the same rate Earth is spinning.
- From Earth, a geostationary satellite looks like it is standing still since it is always above the same location.
- Polar-orbiting satellites travel in a north-south direction from pole to pole. As Earth spins underneath, these satellites can scan the entire globe, one strip at a time
Types of Satellites
- Satellites can be classified by their function since they are launched into space to do a specific job.
- For ex. satellite that is launched to monitor cloud patterns for a weather station will be different than a satellite launched to send television signals.
- Below mentioned are few of the most regular types of satellites launched into space
- Communications satellites allow radio, television, and telephone transmissions to be sent live anywhere in the world.
- The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated points
- Communication Satellites use Microwaves and Radio waves for transmitting signals
Before communication satellites, transmissions were difficult or impossible at long distances. The signals, which travel in straight lines, could not bend around the round Earth to reach a destination far away. Now as communication satellites are in orbit, the signals can be sent instantaneously into space and then redirected to another satellite or directly to their destination.
- There are two major classes of communications satellites, passive and active
- Passive → bouncing signals from the Earth back to another location on the Earth
- Active → carry electronic devices called transponders for receiving, amplifying, and re-broadcasting signals to the Earth
Communications satellites India
- Indian National Satellite (INSAT) Series
- GSAT Satellites Series
- A system of satellites that provide autonomous geo-spatial positioning with global coverage
- Designed expressly to aid the navigation of sea and air traffic via. Radio waves
- It allows small electronic receivers to determine their location to high precision using time signals transmitted along a line of sight by radio from satellites
- A satellite navigation system with global coverage may be termed a global navigation satellite system (GNSS)
- Currently Global Positioning System (GPS) and the Russian GLONASS are only globaly operational GNSSs
- China is in the process of expanding its regional BeiDou Navigation Satellite System into the global Compass navigation system by 2020.
- European Union’s Galileo is a GNSS in initial deployment phase, scheduled to be fully operational by 2020
- Japan is developing a regional based navigation system viz. Quasi-Zenith Satellite System
India has a regional satellite-based augmentation system, GPS Aided GEO Augmented Navigation (GAGAN), which enhances the accuracy of NAVSTAR GPS and GLONASS positions, and is developing the Indian Regional Navigation Satellite System (IRNSS)
Remote Sensing Satellites
- Remote sensing is observing and measuring our environment from a distance viz. earth observation satellites
- The electromagnetic radiation is normally used as an information carrier in remote sensing.
- The output of a remote sensing system is usually an image representing the scene being observed.
The data from these satellites are used for several applications covering agriculture, water resources, urban planning, rural development, mineral prospecting, environment, forestry, ocean resources and disaster management.
Remote Sensing Satellites India
- Indian Remote sensing (IRS) satellite series
- Cartosat; Oceansat; & RISAT (Resource Sat) Satellites
- Bhaskara Satellites; Megha-Tropiques Satellites
- Satellite with ARgos and ALtiKa (SARAL)
Space Exploration Satellites
- Space exploration satellites are not really satellites at all; they are properly known as space probes.
- Space probes send back detailed pictures and atmospheric data of planets and other stellar phenomena
- Space exploration satellites must be built to last because it takes so long for the satellites to reach their destinations.
- Jupiter’s rings were discovered by a space exploration satellite
Space Exploration Satellites India
- Stretched Rohini Satellite Series (SROSS)
- Chandrayaan 1
- Mars Orbiter Mission – Mangalyaan