UPSC Prelims 2020 GS Paper I · Q43 of 99 General Science medium

"The experiment will employ a trio of spacecraft flying in formation in the shape of an equilateral triangle that has sides one million kilometres long, with lasers shining between the craft." The experiment in question refers to

  1. (a) Voyager-2
  2. (b) New Horizons
  3. (c) LISA Pathfinder
  4. (d) Evolved LISA ✓ UPSC's answer

Why the answer is (d)

• The description matches Evolved LISA (eLISA/LISA), the European Space Agency's planned space-based gravitational-wave observatory: three spacecraft in a triangle with million-kilometre arms, using laser interferometry to detect ripples in spacetime — option (d).

• LISA Pathfinder (c) was a single 2015–17 technology demonstrator that tested the free-falling test masses.

• Voyager-2 (a) and New Horizons (b) are single planetary probes.

• Ground detectors like LIGO have arms of only 4 km; LISA will sense low-frequency waves from merging supermassive black holes.

• Hence option (d).

Why the other options are wrong

(a) Voyager-2
Voyager-2 is a lone interstellar probe.
(b) New Horizons
New Horizons is a single Pluto/Kuiper Belt probe.
(c) LISA Pathfinder
LISA Pathfinder was a single test spacecraft, not the trio.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2020, held on 4 October 2020. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

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