Rockets of Today

PSLV and GSLV — India, 1993


PSLV (Polar Satellite Launch Vehicle) is an odd one. It evolved from predecessors named SLV and ASLV, which were small solid-fuel rockets. It has a solid fuel first stage with a multisegment steel body, commonly augmented by six small strap-ons, then a hypergolic second stage, a solid fuel third stage which is narrower but has an enclosing ring to support the fairing, and finally, inside the fairing, a tiny twin-engined fourth burning hypergolics... but not the same hypergolic chemicals as the second stage: it uses monomethylhydrazine and mixed oxides of nitrogen, whereas the lower one works with the more usual combination of unsymmetrical dimethylhydrazine (UDMH) and dinitrogen tetroxide. (Lately they’ve started mixing some hydrazine hydrate into the UDMH to make it more stable.) It’s as if they tried to develop and master as many different technologies as they could, all with one rocket. Even the solid stages differ: the upper one steers with a flexing nozzle, but the core booster steers by injecting liquid oxidizer into the sides. The stages also separate by different means, using explosives in some cases and mechanical latches in others.

The six strap-ons come in two sizes: the PSLV-G has short ones and the later PSLV-XL uses stretched ones with more thrust. The PSLV-CA (for “core alone”) has neither. When they are used, four of them ignite at launch time, and the other two not until 25 seconds later. In 2019 they added variants DL and QL, which use two and four side boosters respectively. This may mean the G-size boosters are now retired.

Despite this very idiosyncratic and irregular design, which seems to have been chosen to produce the greatest possible number of different ways to fail, the PSLV has a pretty good reliability record. It also once held a record for the most separate satellites launched in a single flight, with 104 in early 2017. And it’s affordably priced.


The GSLV (for Geosynchronous) variant swaps out the solid third stage for a restartable hydrogen burner, adding another technology to the list. The little fourth stage is now optional, and I don’t think the option has yet been used. The GSLV uses much bigger strap-ons than the PSLV, and they burn liquid fuel — an inversion of the natural order for cores and strap-ons. These are loosely based on the hypergolic second stage, but longer and thinner. That stage uses an engine called the Vikas-4B, which started as a variant of the Viking engine used in older Ariane models. In the strap-ons, the engine is angled slightly away from vertical, and it has a sea-level sized bell; this variant is called the Vikas-2B. The four boosters don’t detach, but remain integrated with the first stage as it separates from the second... in fact, they carry the solid first stage for 40 seconds after it is exhausted.

The reliability record is not so good compared to the PSLV, despite the slightly less baroque design. It had to go through a major overhaul after a series of early failures. It went disused for several years, except for a single isolated flight in 2021 which was another failure, but in 2023 it returned to successful flight.

But the GSLV that’s based on the PSLV is old news. That’s the Mark II. Now here comes the GSLV Mark III, which has since been renamed as the LVM 3, but has up to now mainly been known by the former name. Despite the familiar-sounding designation, this is an all-new rocket with no stages in common, so it has its own article in the Revival Era section.

PSLV-CA (no added boosters): mass 230 t, diam 2.8 m, thrust 2700 kN?, imp 2.3 km/s, solid fuel, payload 2.5 t? (1.1%) [PSLV-XL 4.2t? (1.3%)], cost $6M/t?, record 57/0/3 through April 2024.
GSLV Mark II: mass 415 t, diam 2.8 m, thrust 4360 kN?, imp 2.6 km/s, solid fuel and gas generator (UDMH blend), payload 5 t (1.2%), cost $9M/t, record 11/0/5 through April 2024.
[Show stages] (both rockets)
Stage name PSOM (PSLV-G+) PSOM-XL (PSLV-XL) GS0/L40H (GSLV) PS1/GS1 PS2/GS2/L40 PS3 (PSLV) GS3/CUS15 (GSLV) * PS4/L2.6 *
Role (pos) count booster (S) ×0|6 booster (S) ×0|6 booster (S) ×4 core (1) upper (2) upper (3) upper (3) upper/kick (4) *
Diameter (m)   1.00   1.00   2.10   2.80   2.80   2.02   2.80   2.02
Liftoff mass (t) 11.1 14.7 48.2 161    42.8  8.4 17.6  3.6
Empty mass (t)  2.0  2.2  5.6 23    4.3  0.8  2.6  1.0
Fuel mass (t) ~2.7 ~3.8 ~15.7  ~41    ~14.2  ~2.3 ~2.5
Oxidizer mass (t) ~6.4 ~8.7 ~26.9  ~97    ~24.3  ~5.3 ~12.5 
Engine S9 S12 Vikas-2B S138 Vikas-4B S7 CE-7.5 L-2-5 ×2
Power cycle solid solid gas gen solid gas gen solid staged pressure-fed?
Chamber pres. (bar) 59   59   75    8.4
Ox./fuel ratio   2.3?   2.3?   1.71   2.3?   1.71   2.3?   5.05
Thrust, vac max (kN) 719    765    4860     805    240    93   14.6
Thrust, SL initial (kN) 450?   678    2700?   
Spec. imp, vac (km/s)   2.60   2.60   2.80   2.60   2.96   2.89   4.45   3.02
Total imp, vac (t·km/s) 133    183    121    365    124    22   117     7.7