UPSC Prelims 2018 · Question 95 of 99

UPSC Prelims 2018 question on PSLV vs GSLV Launch Vehicles

With reference to India's satellite launch vehicles, consider the following statements:

1. PSLVs launch the satellites useful for Earth resources monitoring whereas GSLVs are designed mainly to launch communication satellites.

2. Satellites launched by PSLV appear to remain permanently fixed in the same position in the sky, as viewed from a particular location on Earth.

3. 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?

  1. 1 only
  2. 2 and 3
  3. 1 and 2
  4. 3 only
Show answer

Answer: A. 1 only

Verdict

Only statement 1 is correct, so the answer is (a) 1 only.

Statement by statement

Statement 1 is CORRECT. The PSLV is designed mainly to deliver earth observation or remote sensing satellites of up to about 1750 kg to sun-synchronous circular polar orbits at 600 to 900 km altitude, while the GSLV is designed mainly to deliver communication satellites to the highly elliptical Geosynchronous Transfer Orbit.

Statement 2 is INCORRECT. Appearing permanently fixed in the sky describes a geostationary satellite. PSLV payloads go chiefly to polar sun-synchronous and lower earth orbits, so they do not appear fixed.

Statement 3 is INCORRECT. GSLV Mk III is a three-stage heavy lift vehicle with two solid strap-ons, a core liquid booster and a cryogenic upper stage, not a four-staged vehicle in the configuration described.

Source

The Hindu explainer on the difference between GSLV and PSLV; ISRO launch vehicle pages.

How to crack it

The reasoning chain runs from orbit to function. A satellite appears fixed only if it orbits at the same rate the Earth rotates, which requires geosynchronous altitude, and that is the GSLV's job. Fixing the vehicle to the orbit, and the orbit to the mission, resolves statements 1 and 2 together and leaves only the stage count to check.

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