N.K. Chauhan 
In 2021, a high-level panel was established to examine the failed GSLV-F10/EOS-03 mission and recommended measures for making the Cryogenic Upper Stage (CUS) more robust.
The Geosynchronous Satellite Launch Vehicle (GSLV) with improvements added to its Cryogenic Upper Stage (CUS) is expected to be ready in the second half of 2022.
Augmented Satellite Launch Vehicle (ASLV)
The Augmented Satellite Launch Vehicle (ASLV) was a small-lift "five-stage" solid-fuel rocket developed by the ISRO to place 150 kg satellites into LEO (Low earth orbit).The ASLV made four launches, of which one was successful, two failed to achieve orbit, and a third achieved a lower than planned orbit which decayed quickly.
The type made its maiden flight on 24 March 1987, and its final flight on 4 May 1994.
Polar Satellite Launch Vehicle (PSLV)
The Polar Satellite Launch Vehicle (PSLV) is a third generationan expendable medium-lift launch vehicle.It was developed to allow India to launch its Remote Sensing (RS) satellites into sun-synchronous orbits.
After its first successful launch in October 1994, PSLV emerged as the reliable and versatile workhorse launch vehicle of India.
PSLV can take up to 1,750 kg of payload to Sun-Synchronous Polar Orbits of 600-800 km altitude.
PSLV has also been used to launch various satellites into Geosynchronous and Geostationary orbits, like satellites from the IRNSS constellation.
India's first lunar probe Chandrayaan-1 (2008), India's first interplanetary mission - Mars Orbiter Mission (Mangalyaan (2013)) and India's first space observatory, AstroSat (2015) are some notable payloads launched by PSLV.
On 15 February 2017, PSLV-C37 successfully deployed 104 satellites in sun-synchronous orbit making it the highest number of satellites sent to space on a single launch, the record was previously held by Russia.
Geosynchronous Satellite Launch Vehicle (GSLV)
GSLV is a space launch vehicle designed, developed, and operated by the Indian Space Research Organisation (ISRO) to launch satellites and other space objects into Geosynchronous Transfer Orbits.GSLV has been designed for launching communication satellites.
GSLV has the capability to put a heavier payload in orbit than the Polar Satellite Launch Vehicle (PSLV).
It is a "three-stage" launcher with strap-on motors.
GSLV follows a solid fuel first stage with another liquid fuel stage coming next, the second stage is followed by a third stage known as Cryogenic Upper Stage (CUS).
The cryogenic stage is technically a very complex system compared to solid or earth-storable liquid propellant stages due to its use of propellants at extremely low temperatures and the associated thermal and structural problems.
It was the rocket's crucial third stage, which failed to ignite and led to the failure of the GSLV-F10/Earth Observation Satellites (EOS)-03 mission in 2021.
GSLV MK-I
The first development flight of the GSLV (Mk I configuration), launched on 18 April 2001 was a failure as the payload failed to reach the intended orbit parameters.The launcher was declared operational after the second development flight successfully launched the GSAT-2 satellite.
GSLV MK-II
GSLV MK-II is meant to lift satellites in the weight category 2.5 tons to 5 tons.This is a three-stage launch vehicle with first stage using solid rocket motor, second stage using liquid fuel, and the third stage, called Cryogenic Upper Stage (CUS), using cryogenic engine.
GSLV MkIII
GSLV MkIII, chosen to launch Chandrayaan-2 spacecraft, is a three-stage heavy lift launch vehicle developed by ISRO.The 640-tonne rocket, equal to the weight of 200 fully-grown Asian elephants, is the country's heaviest but shortest rocket with a height of 43 metre.
GSLV Mk III is designed to carry 4 ton class of satellites into Geosynchronous Transfer Orbit (GTO) or about 10 tons to Low Earth Orbit (LEO), which is about twice the capability of the GSLV Mk II.
The first developmental flight of GSLV Mk III, the GSLV-Mk III-D1 successfully placed GSAT-19 satellite to a Geosynchronous Transfer Orbit (GTO) on June 05, 2017.
This is India's first fully functional rocket to be tested with a cryogenic engine that uses liquid propellants - liquid oxygen and liquid hydrogen.
Small Satellite Launch Vehicle (SSLV)
The SSLV is intended to cater to a market for the launch of small satellites into low earth orbits which has emerged in recent years on account of the need for developing countries, private corporations, and universities for small satellites.SSLV is a three-stage all solid vehicle and has a capability to launch up to 500 kg satellite mass into 500 km Low Earth Orbit (LEO) and 300 kg to Sun Synchronous Orbit (SSO).
The SSLV is the smallest vehicle at 110-ton mass at ISRO.
It will take only 72 hours to integrate, unlike the 70 days taken now for a launch vehicle.
Only six people will be required to do the job, instead of 60 people and the cost will be only around Rs 30 crore.
SSLV is perfectly suited for launching multiple microsatellites at a time and supports multiple orbital drop-offs.
ISRO's new chairman Dr Somanath is credited with designing and developing the SSLV during his tenure as director of the Vikram Sarabhai Space Centre in Thiruvananthapuram since 2018.
Geosynchronous orbit
A geosynchronous orbit is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, one sidereal day.For an observer on Earth's surface, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day.
Over the course of a day, the object's position in the sky may remain still or trace out a path, typically in a figure-8 form, whose precise characteristics depend on the orbit's inclination and eccentricity.
A circular geosynchronous orbit has a constant altitude of 35,786 km.
Geostationary orbit
While geosynchronous satellites can have any inclination, the key difference to geostationary orbit is the fact that they lie on the same plane as the equator.Geostationary orbits fall in the same category as geosynchronous orbits, but it's "parked over the equator".
An object in such an orbit has an orbital period equal to Earth's rotational period, one sidereal day, and so to ground observers it appears motionless, in a fixed position in the sky.
Communications satellites are often placed in a geostationary orbit so that Earth-based satellite antennas (located on Earth) do not have to rotate to track them but can be pointed permanently at the position in the sky where the satellites are located.
Weather satellites are also placed in this orbit for real-time monitoring and data collection, and navigation satellites to provide a known calibration point and enhance GPS accuracy.
Sun Synchronous Orbits
Sun Synchronous Orbits allows a satellite to pass over a section of the Earth at the same time of day.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.
These satellites orbit at an altitude between 700 to 800 km.
The Lagrange points
Other orbital "sweet spots", just beyond high Earth orbit, are the Lagrange points.At the Lagrange points, the pull of gravity from the Earth cancels out the pull of gravity from the Sun.
Anything placed at these points will feel equally pulled toward the Earth and the Sun and will revolve with the Earth around the Sun.
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