Q. With reference to India's satellite launch vehicles, consider the following statements:
- PSLVs launch the satellites useful for Earth resources monitoring whereas GSLVs are designed mainly to launch communication satellites.
- Satellites launched by PSLV appear to remain permanently fixed in the same position in the sky, as viewed from a particular location on Earth.
- GSLV Mk III is a four-staged launch vehicle with the first and third stages using solid rocket motors; and the second and fourth stages using liquid rocket engines.
Which of the statements given above is/are correct? (UPSC Prelims 2018)
Answer:
1 only
Notes: The correct answer is
[A] 1 only. This question requires a clear distinction between India’s two workhorse rockets: the Polar Satellite Launch Vehicle (PSLV) and the Geosynchronous Satellite Launch Vehicle (GSLV).
- Primary Roles (Statement 1 – Correct):
- PSLV is designed to place "Remote Sensing" or Earth observation satellites into Sun-Synchronous Polar Orbits (SSPO). These satellites are used for monitoring Earth's resources (agriculture, water, forestry).
- GSLV is a much heavier rocket designed to carry heavy communication satellites (like the GSAT series) into the much higher Geosynchronous Transfer Orbit (GTO).
- Stationary Appearance (Statement 2 – Incorrect): Satellites that appear "fixed" in the sky are in Geostationary Orbit (GEO), which is reached using GSLV (or similar heavy launchers). PSLV satellites usually move across the sky in low Earth orbits. A satellite in a polar orbit (PSLV's specialty) passes over the Earth's poles and circles the globe many times a day.
- Launch Vehicle Stages (Statement 3 – Incorrect):
- The GSLV Mk III (now known as LVM3) is a three-stage launch vehicle, not four.
- It consists of two large solid strap-on motors (S200), a core liquid stage (L110), and a high-thrust cryogenic upper stage (C25).
- The PSLV, on the other hand, is a four-stage vehicle alternating between solid and liquid fuels.
Historically, the development of the
Indigenous Cryogenic Engine for the third stage of the GSLV was a major technological hurdle for ISRO, eventually achieved to give India self-reliance in launching heavy communication satellites.