PSLV: ISRO's four-stage workhorse that alternates solid and liquid stages

Background

The Polar Satellite Launch Vehicle is India's third-generation launch vehicle and the first Indian one equipped with liquid stages.
It has four stages: PS1 is the S139 solid motor with 139 tonnes of HTPB, PS2 is powered by the Vikas liquid engine, PS3 is a solid motor, and PS4 uses two liquid engines.
Strap-on boosters vary by variant: PSLV-XL uses 6, PSLV-QL uses 4, PSLV-DL uses 2, and the core-alone PSLV-CA uses none.
It can lift up to 1,750 kg to a Sun-Synchronous Polar Orbit at 600 km altitude and 1,425 kg to Sub-GTO.
Its reliability has earned it the title 'the Workhorse of ISRO'.