PSLV and GSLV Launch Vehicles

India’s Polar Satellite Launch Vehicle (PSLV) principally serves missions to low Earth orbits, especially polar and Sun-synchronous orbits. The Geosynchronous Satellite Launch Vehicle (GSLV) principally places heavier satellites into geosynchronous transfer orbit for onward movement to geosynchronous or geostationary orbit. Their central difference is therefore their main mission destination and payload requirement, not an absolute restriction on which orbits they can reach.

PSLV: principally for polar and Sun-synchronous missions

PSLV’s principal role is launching Earth-observation satellites into polar or Sun-synchronous low Earth orbits. These orbits suit repeated observation of the Earth’s surface rather than continuous observation from a fixed position above the equator.

• A polar orbit passes over or near the poles; as the Earth rotates beneath the satellite, successive passes cover different parts of the surface.
• A Sun-synchronous orbit allows a satellite to pass a location at approximately the same local solar time, providing comparable illumination for repeated imaging.
• These missions support applications such as resource mapping, agricultural monitoring and disaster assessment.
• PSLV has four stages, using solid and liquid propulsion alternately.

GSLV: principally for geosynchronous satellite missions

GSLV’s principal role is launching satellites into geosynchronous transfer orbit (GTO). Its propulsion system, including a cryogenic upper stage, supports the demanding task of delivering heavier payloads towards high-altitude orbits.

• GTO is an elliptical intermediate orbit; the satellite normally uses its own propulsion to reach its final geostationary orbit.
• A geostationary satellite follows a circular equatorial orbit with a period matching the Earth’s rotation, appearing stationary relative to the ground.
• This fixed apparent position is useful for communication, television broadcasting and sustained weather observation.
• GSLV has three stages: a solid first-stage core with liquid strap-on boosters, a liquid second stage and a cryogenic third stage.

Principal roles are not exclusive capabilities

The distinction is between principal mission profiles, not rigidly separate capabilities. Launcher selection depends on the satellite’s mass and the energy required to reach its target orbit.

• PSLV can also serve non-polar missions; it launched Chandrayaan-1 and the Mars Orbiter Mission into their initial Earth orbits.
• Thus, “PSLV for polar Earth observation; GSLV for heavier geosynchronous missions” is a useful revision rule, but not an exhaustive description of either vehicle.