ISRO Missions and Discoveries



From UPSC perspective, the following things are important :

Prelims level : SSLV, PSLV, GSLV

Mains level : Read the attached story

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 this year.

What is GSLV?

  • GSLV is an expendable space launch vehicle designed, developed, and operated by the ISRO to launch satellites and other space objects into Geosynchronous Transfer Orbits.
  • GSLV is 49.13 m tall and tallest among all other vehicles of ISRO.
  • It is a three-stage vehicle with a lift-off mass of 420 tonnes.
  • ISRO first launched GSLV on April 18, 2001 and has made 13 launches since then.

Stages in GSLV

  • The first stage comprises S139 solid booster with 138-tonne propellant and four liquid strap-on motors, with 40-tonne propellant.
  • The second stage is a liquid engine carrying 40-tonne of liquid propellant.
  • The third stage is the indigenously built Cryogenic Upper Stage (CUS) carrying 15-tonne of cryogenic propellants.

Variants in GSLV

  • GSLV rockets using the Russian Cryogenic Stage (CS) are designated as the GSLV Mk I while versions using the indigenous Cryogenic Upper Stage (CUS) are designated the GSLV Mk II.
  • All GSLV launches have been conducted from the Satish Dhawan Space Centre in Sriharikota.

Difference between PSLV and GSLV

  • GSLV has the capability to put a heavier payload in the orbit than the Polar Satellite Launch Vehicle (PSLV).
  • PSLV can carry satellites up to a total weight of 2000 kg into space and reach up to an altitude of 600-900 km.
  • GSLV can carry weight up to 5,000 kg and reach up to 36,000 km.
  • PSLV is designed mainly to deliver earth observation or remote sensing satellites, whereas, GSLV has been designed for launching communication satellites.
  • GSLV delivers satellites into a higher elliptical orbit, Geosynchronous Transfer Orbit (GTO) and Geosynchronous Earth Orbit (GEO).

Back2Basics: ISRO’s transportation modules

(1) SLV

  • In the space transportation domain, the commissioning of the Satellite Launch Vehicle-3 (SLV-3) project in the early 1970s was the first indigenous experimental satellite launch vehicle.
  • As a four stage, all solid, launch vehicle, SLV-3 had its successful launch in July 1980, thrusting India into the select league of six countries with the capability to launch satellites on their own.
  • The ASLV- Augmented Satellite Launch Vehicle project, in the early 1980s, was the next step of evolution in launch vehicle technology.

(2) PSLV

  • In mid 80s came the Polar Satellite Launch Vehicle (PSLV) project. PSLV was successfully launched in 1994.
  • The vehicle has proven to be a workhorse of ISRO, logging over 50 successful missions, launching national as well as foreign satellites.
  • On 15 February 2017, PSLV created a world record by successfully placing 104 satellites.
  • The nation embarked upon a highly challenging quest to master the complex cryogenic technology.

(3) GSLV

Discussed above.

(4) SSLV

  • The Small Satellites Launching Vehicles (SSLVs) used for commercial launching of small satellites is under incubation.
  • It is a small-lift launch vehicle being developed by the ISRO with payload capacity to deliver:
  1. 600 kg to Low Earth Orbit (500 km) or
  2. 300 kg to Sun-synchronous Orbit (500 km)
  • It would help launching small satellites, with the capability to support multiple orbital drop-offs.
  • In future a dedicated launch pad in Sriharikota called Small Satellite Launch Complex (SSLC) will be set up.


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