Space technology: previous-year questions
71 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 28 of them came in the last five papers.
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Questions per year, counted from the official papers.
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In which of the following activities are Indian Remote Sensing (IRS) satellites used?
- 1. Assessment of crop productivity
- 2. Locating groundwater resources
- 3. Mineral exploration
- 4. Telecommunications
- 5. Traffic studies
Select the correct answer using the code given below.
Answer (a) & explanation
IRS satellites, such as Resourcesat, Cartosat and Oceansat, image the earth for crop production forecasts (1), groundwater prospect maps (2) and mineral and geological mapping (3). So the answer is (a). Telecommunication (4) is the job of the GSAT/INSAT series, and UPSC's key does not count traffic studies (5).
IRS data also supports forest mapping, urban planning, disaster monitoring and the FASAL crop forecasting programme. Bhuvan is ISRO's geoportal that shares this data. Notice how India built its space programme around development needs.
Answer as per the official UPSC answer key.
With reference to ‘Near Field Communication (NFC) Technology’, which of the following statements is/are correct?
- 1. It is a contactless communication technology that uses electromagnetic radio fields.
- 2. NFC is designed for use by devices which can be at a distance of even a metre from each other.
- 3. NFC can use encryption when sending sensitive information.
Select the correct answer using the code given below.
Answer (c) & explanation
Statements 1 and 3 are correct (c). NFC is a contactless technology using electromagnetic radio fields at 13.56 MHz (1). It supports encryption for sensitive data such as tap-to-pay transactions (3). Statement 2 is wrong: NFC works only within about 4 cm, which is part of its security. A one-metre range is closer to some RFID or Bluetooth uses.
NFC powers contactless cards, phone wallets, metro cards and FASTag-like systems, though FASTag itself uses RFID. Notice how short range is a design choice for safety: a device must be held close on purpose.
Answer as per the official UPSC answer key.
The term ‘Goldilocks Zone’ is often seen in the news in the context of
Answer (c) & explanation
The Goldilocks zone, or habitable zone, is the band of orbits around a star where a planet is neither too hot nor too cold, so liquid water can exist. It is used in the search for Earth-like planets in outer space (c). It does not refer to habitable limits above Earth's surface (a), shale gas regions (b) or meteorites with precious metals (d).
The name comes from the fairy tale in which Goldilocks picks porridge that is "just right". Missions such as Kepler, TESS and the James Webb Space Telescope study such planets. Notice how astronomy meets biology in the search for life.
Answer as per the official UPSC answer key.
In addition to fingerprint scanning, which of the following can be used in the biometric identification of a person?
- 1. Iris scanning
- 2. Retinal scanning
- 3. Voice recognition
Select the correct answer using the code given below.
Answer (d) & explanation
All three are used (d). Biometrics identifies people by unique physical or behavioural features. Iris scanning reads the coloured ring's patterns (1). Retinal scanning maps blood vessels at the back of the eye (2). Voice recognition analyses the pitch and features of speech (3). Options that leave any of these out are incomplete.
Aadhaar collects fingerprints, iris scans and a face photograph, and face authentication is now widely used too, including in DigiYatra at airports. Notice how biometrics links technology to welfare delivery, while also raising privacy concerns addressed in the Puttaswamy judgment (2017).
Answer as per the official UPSC answer key.
Which of the following pairs is/are correctly matched?
| Spacecraft | Purpose
| 1. Cassini-Huygens | Orbiting the Venus and transmitting data to the Earth
| 2. Messenger | Mapping and investigating the Mercury
| 3. Voyager 1 and 2 | Exploring the outer solar system
Select the correct answer using the code given below.
Answer (b) & explanation
Pairs 2 and 3 are correct (b). Cassini–Huygens studied Saturn, not Venus, and its Huygens probe landed on the moon Titan in 2005, so pair 1 is wrong. NASA's MESSENGER orbited and mapped Mercury from 2011 to 2015. Voyager 1 and 2, launched in 1977, explored the outer planets and have since entered interstellar space.
Venus missions include Magellan, ESA's Venus Express and Japan's Akatsuki; India plans its Venus Orbiter Mission. Notice how UPSC likes pairing spacecraft with their targets: a short table of missions saves marks.
Answer as per the official UPSC answer key.
Which of the following is/are cited by the scientists as evidence/evidences for the continued expansion of universe?
- 1. Detection of microwaves in space
- 2. Observation of redshift phenomenon in space
- 3. Movement of asteroids in space
- 4. Occurrence of supernova explosions in space
Select the correct answer using the codes given below :
Answer (a) & explanation
Microwaves and redshift are correct (a). Light from distant galaxies is red-shifted: its wavelength is stretched because the galaxies are moving away, faster the farther they are (Hubble's law) (2). The cosmic microwave background radiation, found in 1965, is the cooled afterglow of the Big Bang, spread evenly across the sky (1). Statement 3 is wrong: asteroids move within our solar system and say nothing about expansion. Statement 4 is wrong: supernovae alone are not evidence, though Type Ia supernovae used as distance markers showed in 1998 that expansion is accelerating. So (b), (c) and (d) fail.
Notice the puzzle: this acceleration is blamed on dark energy, and the 'Hubble tension' is a mismatch in measured expansion rates. Trap: (4) hides a partial truth.
Answer as per the official UPSC answer key.
Satellites used for telecommunication relay are kept in a geostationary orbit. A satellite is said to be in such an orbit when :
- 1. The orbit is geosynchronous.
- 2. The orbit is circular.
- 3. The orbit lies in the plane of the Earth’s equator.
- 4. The orbit is at an altitude of 22,236 km.
Select the correct answer using the codes given below :
Answer (a) & explanation
Statements 1, 2 and 3 are correct (a). A geostationary orbit is a special geosynchronous orbit: the satellite completes one revolution in one sidereal day (about 23 h 56 min) (1). It must be circular (2) and lie in the plane of the equator (3), moving west to east, so it appears fixed above one spot. Statement 4 is wrong: the altitude is about 35,786 km, which is 22,236 miles, not 22,236 km. So options (b), (c) and (d) fail.
Notice the difference: every geostationary orbit is geosynchronous, but a geosynchronous orbit can be inclined or elliptical and then traces a figure-of-eight. India's GSAT and INSAT satellites use GEO, launched on the GSLV and LVM3. The NavIC system uses both geostationary and inclined geosynchronous satellites. Trap: the number 22,236 is right only in miles.
Answer as per the official UPSC answer key.
What is the difference between Bluetooth and Wi-Fi devices ?
Answer (a) & explanation
Option (a) is correct. Bluetooth works in the 2.4 GHz band for short-range personal area networks (PAN), linking devices a few metres apart. Wi-Fi uses 2.4 GHz or 5 GHz (and newer 6 GHz in Wi-Fi 6E/7) for wireless local area networks. (b) is wrong: Bluetooth is not a WLAN technology, and Wi-Fi is a LAN, not a wide-area, technology. (c) is wrong: neither needs line of sight; radio waves pass through walls, unlike infrared remotes. (d) fails because (b) is wrong.
Notice the wider idea: India delicensed the lower 6 GHz band (5925–6425 MHz) for Wi-Fi in 2025. Bluetooth is named after the Danish king Harald Bluetooth. Trap: line of sight belongs to infrared, not Bluetooth.
Answer as per the official UPSC answer key.
A new optical disc format known as the Blu-ray Disc (BD) is becoming popular. In what way is it different from the traditional DVD ?
- 1. DVD supports Standard Definition video while BD supports High Definition video.
- 2. Compared to a DVD, the BD format has several times more storage capacity.
- 3. Thickness of BD is 2.4 mm while that of DVD is 1.2 mm.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Statements 1 and 2 are correct (b). A Blu-ray disc is read by a blue-violet laser (405 nm) with a shorter wavelength than a DVD's red laser, so data packs more tightly: about 25 GB per layer against 4.7 GB on a DVD. That gives several times more storage (2) and room for High Definition video, while DVD is mainly standard definition (1). Statement 3 is wrong: both discs are 1.2 mm thick; Blu-ray's data layer just sits nearer the surface. So (a), (c) and (d) fail.
Notice the trend: Ultra HD Blu-ray stores up to 100 GB for 4K video, but streaming has largely replaced discs. Trap: '2.4 mm' doubles the real thickness.
Answer as per the official UPSC answer key.
What is the difference between asteroids and comets ?
- 1. Asteroids are small rocky planetoids, while comets are formed of frozen gases held together by rocky and metallic material.
- 2. Asteroids are found mostly between the orbits of Jupiter and Mars, while comets are found mostly between Venus and Mercury.
- 3. Comets show a perceptible glowing tail, while asteroids do not.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Statements 1 and 3 are correct (b). Asteroids are small rocky or metallic bodies, while comets are 'dirty snowballs' of frozen gases, ice and dust held with rock (1). Near the Sun, a comet's ice vaporises and forms a glowing coma and tail pointing away from the Sun, while asteroids show no tail (3). Statement 2 is wrong: asteroids are mostly in the belt between Mars and Jupiter, but comets come from the distant Kuiper Belt and Oort Cloud, not between Venus and Mercury. So (a), (c) and (d) fail.
Notice the missions: NASA's DART (2022) changed an asteroid's orbit, OSIRIS-REx returned Bennu samples (2023), and the interstellar comet 3I/ATLAS was seen in 2025. Trap: statement 2 puts comets in the inner solar system.
Answer as per the official UPSC answer key.
What is “Virtual Private Network” ?
Answer (b) & explanation
Option (b) is correct. A Virtual Private Network builds a secure, encrypted 'tunnel' over the public internet, so a remote user can reach the office network as if sitting inside it, while the data stay private. (a) is wrong: a VPN does not need a private network; its point is to use the public internet safely. (c) is wrong: it describes cloud computing, where users share computing resources from a provider. (d) fails because (b) is correct.
Notice the policy angle: CERT-In's 2022 directions require VPN providers in India to keep user records for five years, which led some foreign providers to remove Indian servers. VPNs also let users hide their location. Trap: (a) sounds similar but misses the 'public internet' part.
Answer as per the official UPSC answer key.