Previous Year UPSC Prelims Questions (With Explanations)

Theme: Satellite Technology, Earth Observation, and International Collaboration

✅ Q1. [UPSC Prelims 2022]

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

PSLV is mainly used to launch satellites into geosynchronous orbits.
GSLV Mk III is a four-stage launch vehicle.
PSLV-G and PSLV-XL are variants of PSLV.

Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

🟩 Correct Answer: (b) 2 and 3 only

📝 Explanation:

PSLV is mainly used for sun-synchronous polar orbits, not geosynchronous.
GSLV Mk III is a 4-stage launch vehicle (2 solid, 1 liquid, 1 cryogenic).
PSLV-G and PSLV-XL are real PSLV variants used for different payloads.
📌 Link to NISAR: NISAR was launched by GSLV-F16, so knowledge of launch vehicles is crucial.

✅ Q2. [UPSC Prelims 2020]

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

PSLVs launch satellites only into equatorial orbits.
Satellites launched by PSLV appear to move from west to east.

Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

🟩 Correct Answer: (b) 2 only

📝 Explanation:

PSLV launches satellites into polar, sun-synchronous, and sub-geostationary orbits — not only equatorial.
Satellites launched in the same direction as Earth’s rotation appear to move west to east.
📌 Link to NISAR: PSLVs/GSLVs form the backbone of India's satellite launches including dual-band radar satellites.

✅ Q3. [UPSC Prelims 2019]

Which of the following can be found as pollutants in the drinking water in some parts of India?

Arsenic
Sorbitol
Fluoride
Formaldehyde
Uranium

Select the correct answer using the code given below:
(a) 1 and 3 only
(b) 2, 4 and 5 only
(c) 1, 3 and 5 only
(d) 1, 2, 3, 4 and 5

🟩 Correct Answer: (c) 1, 3 and 5 only

📝 Explanation:

Arsenic, fluoride, and uranium have been reported in Indian groundwater.
Sorbitol and formaldehyde are not natural water pollutants.
📌 Link to NISAR: Earth observation and SAR data are critical for hydrology, water pollution mapping, and groundwater risk assessment.

✅ Q4. [UPSC Prelims 2020]

Enhanced Vegetation Index (EVI) is used in the context of:
(a) Tracking the spread of vector-borne diseases
(b) Estimating greenhouse gas emissions from agriculture
(c) Assessing land degradation and desertification
(d) Measuring vegetation health using satellite imagery

🟩 Correct Answer: (d) Measuring vegetation health using satellite imagery

📝 Explanation:

EVI is a satellite-based vegetation index used to quantify green biomass.
It improves over NDVI in areas with dense canopy cover.
📌 Link to NISAR: One of NISAR’s main applications is forest biomass estimation and vegetation analysis using dual-band SAR.

✅ Q5. [UPSC Prelims 2018]

With reference to the Earth’s atmosphere, which one of the following statements is correct?
(a) The total amount of insolation received at the equator is more than that received at the poles.
(b) The atmosphere is an important medium of mechanical energy.
(c) The movement of air and water vapor occurs in the thermosphere.
(d) Ozone layer lies in the mesosphere.

🟩 Correct Answer: (a)

📝 Explanation:

The equator receives more direct sunlight due to Earth's curvature.
The ozone layer lies in the stratosphere, not mesosphere.
Air movement is mainly in troposphere, not thermosphere.
📌 Link to NISAR: NISAR’s SAR technology helps track global heat distribution, cloud patterns, and vegetation cycles related to insolation.

✅ Q6. [UPSC Prelims 2020]

Which of the following phenomena might have influenced the evolution of organisms?

Continental drift
Glacial cycles

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

🟩 Correct Answer: (c) Both 1 and 2

📝 Explanation:

Continental drift and glacial cycles significantly impact habitat, climate, and evolution.
📌 Link to NISAR: NISAR will study ice sheet dynamics and tectonic motion, aiding understanding of long-term climate and habitat changes.

✅ Q7. [UPSC Prelims 2018]

In which of the following areas can GPS technology be used?

Mobile phone operations
Banking operations
Controlling power grids

Select the correct answer using the code below:
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

🟩 Correct Answer: (d) 1, 2 and 3

📝 Explanation:

GPS supports location services, time stamping in banking, and synchronisation in power grids.
📌 Link to NISAR: NISAR’s precise geolocation and timing abilities feed into infrastructure and logistics networks.

✅ Q8. [UPSC Prelims 2021]

Karman Line, often mentioned in news, refers to:
(a) The boundary between Earth's atmosphere and outer space
(b) An international agreement on climate change
(c) An oceanic fault line
(d) A disputed border region in space law

🟩 Correct Answer: (a)

📝 Explanation:

Karman Line is defined at 100 km above sea level, used as the legal boundary of space.
📌 Link to NISAR: Understanding orbital paths and space demarcations is essential for all space-based Earth observation missions.

✅ Q9. [UPSC Prelims 2021]

With reference to the history of India, consider the following pairs:

Famous place	Present State
Bhilsa	Madhya Pradesh
Dwarasamudra	Maharashtra
Girinagar	Gujarat

Which of the pairs given above is/are correctly matched?
(a) 1 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3

🟩 Correct Answer: (a) 1 only

📝 Explanation:

Bhilsa is in MP; Dwarasamudra (modern Halebidu) is in Karnataka; Girinagar is in Maharashtra, not Gujarat.
📌 Link to NISAR: Cultural sites can be mapped and preserved better using high-resolution Earth observation.

🧾 Summary Table

Year	Topic	Direct Link to NISAR
2022	Launch Vehicles	GSLV knowledge for NISAR launch
2020	PSLV orbits	Satellite utility understanding
2020	Vegetation Index	NISAR and forest biomass
2019	Water Pollution	NISAR in groundwater risk
2018	GPS Tech	Infrastructure, banking, and logistics
2021	Karman Line	Legal orbit boundaries

Suryavanshi IAS

Blog Archive

Sunday, August 3, 2025