2018 GS Paper I, all questions

UPSC Prelims 2018 · GS Paper I

Question 95: Science and Technology

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

  1. 1.PSLVs launch the satellites useful for Earth resources monitoring whereas GSLVs are designed mainly to launch communication satellites.
  2. 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. 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 ?

a1 only
b2 and 3
c1 and 2
d3 only

AnswerUPSC’s answer is (a).

PSLV puts satellites into polar sun-synchronous orbits, which suit Earth observation and resource monitoring, while GSLV was designed to place heavier communication satellites in geosynchronous transfer orbits, so statement 1 is accepted as correct. Satellites that appear fixed in the sky are geostationary, the GSLV-type orbit, not PSLV's polar orbit. GSLV Mk III has three stages (two solid strap-on boosters, a liquid core and a cryogenic upper stage), not four.

  • 1. PSLV serves Earth observation; GSLV serves communication satellites.
  • 2. Satellites that look fixed are geostationary, not in PSLV's polar orbits.
  • 3. Mk III has three stages: solid boosters, a liquid core and a cryogenic upper stage.

How you could have got this

  1. If you were sure statement 1 is correct, (b) and (d) go: each of them leaves 1 out.

    What you needed to know: PSLV serves Earth observation; GSLV serves communication satellites.

  2. Then, if you were sure statement 2 is not correct, (c) goes: it includes 2.

    What you needed to know: Satellites that look fixed are geostationary, not in PSLV's polar orbits.

Only (a) is left. You didn’t need statement 3.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong
  • (a) Right: only statement 1 is correct.
  • (b) Wrong: statements 2 and 3 are both false.
  • (c) Wrong: statement 2 is false.
  • (d) Wrong: Mk III is a three-stage vehicle.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2018, General Studies Paper I, Series A. The paper on upsc.gov.in.