ISRO Launch Vehicles: PSLV, GSLV, LVM3 and SSLV Notes

A launch vehicle is the rocket that carries a satellite from the ground to the speed and height an orbit needs. India has built four generations of them, and every general awareness paper takes questions from the family: how many stages a vehicle has, which stage is cryogenic, how much it can lift, and which mission it carried. This chapter arranges the vehicles in order of size and fixes those four answers for each.

How India built its rockets

The Indian National Committee for Space Research, INCOSPAR, was set up in 1962 under Vikram Sarabhai, who is called the father of the Indian space programme. The first sounding rocket went up from the Thumba Equatorial Rocket Launching Station near Thiruvananthapuram on 21 November 1963. ISRO itself was formed on 15 August 1969 and was brought under the Department of Space in 1972.

India's first launch vehicle was SLV-3, a four-stage all-solid rocket able to place about 40 kg in a low earth orbit. On 18 July 1980 it placed the Rohini RS-1 satellite in orbit and made India a space-launching nation; A. P. J. Abdul Kalam was its project director. The Augmented Satellite Launch Vehicle, ASLV, followed with two strap-on boosters and a 150 kg capacity; of its five flights the first two failed and the later ones carried the SROSS satellites.

Where the rockets are built and launched

All Indian orbital launches lift off from the Satish Dhawan Space Centre, SHAR, at Sriharikota on the coast of Andhra Pradesh, chosen because an eastward launch over the Bay of Bengal wastes nothing. Launch vehicles are designed at the Vikram Sarabhai Space Centre, Thiruvananthapuram; their liquid and cryogenic engines at the Liquid Propulsion Systems Centre; satellites at the U R Rao Satellite Centre, Bengaluru; payloads at the Space Applications Centre, Ahmedabad; and geostationary satellites are controlled from the Master Control Facility at Hassan in Karnataka.

PSLV, the workhorse

The Polar Satellite Launch Vehicle has four stages that alternate propellant: the first and third are solid, the second and fourth liquid, and the first stage of the larger versions carries six strap-on motors. It lifts about 1,750 kg into a 600 km sun-synchronous polar orbit and roughly 1,425 kg towards a geosynchronous transfer orbit. Its first flight in 1993 failed and PSLV-D2 succeeded in October 1994. It is called ISRO's workhorse because it has carried remote sensing satellites, the NavIC navigation satellites, Chandrayaan-1 in 2008 and the Mars Orbiter Mission in 2013. On 15 February 2017 the flight PSLV-C37 placed 104 satellites in orbit in a single launch. Its variants are PSLV-G, PSLV-CA, the core-alone version flown without strap-ons, and PSLV-XL with six extended strap-ons.

GSLV Mk II and the cryogenic step

A satellite bound for a geostationary slot needs more energy, which means a cryogenic upper stage burning liquid hydrogen with liquid oxygen at temperatures near minus 250 degrees Celsius. The Geosynchronous Satellite Launch Vehicle has three stages: a solid core with four liquid strap-ons, a liquid second stage and a cryogenic third stage. It carries about 2,250 kg to a geosynchronous transfer orbit. Its first flight was in April 2001 with a Russian cryogenic stage; the indigenous cryogenic upper stage flew successfully for the first time on GSLV-D5 in January 2014, making India the sixth country with the technology.

LVM3, the heavy lifter

LVM3, first called GSLV Mk III, is India's heaviest operational rocket. It has two S200 solid strap-on boosters, an L110 liquid core stage with twin Vikas engines and a C25 cryogenic upper stage, and it lifts about 4,000 kg to a geosynchronous transfer orbit or 8,000 kg to a low earth orbit. It launched Chandrayaan-2 in July 2019 and Chandrayaan-3 in July 2023, and it has flown commercial missions carrying batches of communication satellites. A human-rated version, HLVM3, is meant for the Gaganyaan crewed mission.

SSLV for small satellites

The Small Satellite Launch Vehicle answers the demand for cheap launches of small payloads. It has three solid stages and a liquid velocity trimming module, carries up to about 500 kg to a 500 km low earth orbit and can be readied in days by a small team. Its first developmental flight in 2022 failed to reach a usable orbit; SSLV-D2 in February 2023 placed EOS-07 correctly.

Words the question paper uses

• Strap-on booster: an extra motor tied to the first stage for thrust at lift-off.
• Cryogenic engine: one burning gases liquefied by extreme cooling, giving the highest efficiency per kilogram of propellant.
• GTO: geosynchronous transfer orbit, the long ellipse from which a satellite raises itself to a 36,000 km circular orbit.
• Sun-synchronous polar orbit: a near-polar orbit that crosses the equator at the same local time daily, which suits remote sensing.