ISRO and Space — PPSC previous year questions

IRNSS is the Indian Regional Navigation Satellite System. It is ISRO's own regional navigation constellation, named NavIC (Navigation with Indian Constellation) in operation. It has 7 satellites. They cover India and about 1,500 km beyond it. It gives a Standard Positioning Service for civilians and a Restricted Service for authorised users. ISRO's Mars mission is Mangalyaan (MOM, 2013), and its Moon missions are the Chandrayaan series.

The 'L1' in Aditya-L1 stands for the first Lagrangian point of the Sun–Earth system. It lies about 1.5 million km from Earth, towards the Sun. There the gravity of the two bodies balances the centripetal force on a small object. So a spacecraft can stay in a halo orbit around the point. From L1 it views the Sun non-stop, with no occultation or eclipse. That is why ISRO placed Aditya-L1 (launched September 2023) there. LED, Low Earth Orbit and lithium-ion battery are unrelated expansions of 'L'.

NISAR stands for NASA-ISRO Synthetic Aperture Radar, a joint Earth-observation mission of NASA and ISRO, not ESA, so statement 1 is wrong. Its dual-frequency radar (NASA's L-band and ISRO's S-band) maps the whole globe every 12 days and tracks earthquakes, landslides, glacier movement, sea-level rise and changes in crops and forests, so statement 2 is correct. It was launched on 30 July 2025 aboard GSLV-F16 from Sriharikota.

Sounding rockets (research rockets) have one or two stages and use solid propellant. They carry instruments to about 50–500 km on a sub-orbital path. They give a few minutes of measurements of the upper atmosphere and ionosphere, then fall back. India's space programme began with a Nike-Apache sounding rocket from Thumba (TERLS) on 21 November 1963. ISRO's Rohini series (RH-200, RH-300, RH-560) continues the tradition. Cruise missiles and ASAT weapons are military systems. Plasma rockets are electric propulsion units, not research vehicles.

Comets are the icy planetesimals of the outer Solar System: small bodies of frozen water, carbon dioxide, ammonia and methane mixed with dust, left over from the formation of the planets. When a comet approaches the Sun its ices sublimate, forming the glowing coma and the tail that always points away from the Sun. Asteroids, by contrast, are rocky or metallic planetesimals concentrated between Mars and Jupiter, while black holes and planets are not planetesimals at all.

Chandrayaan-3's Vikram lander soft-landed near the Moon's south pole on 23 August 2023, and the Government of India declared 23 August as National Space Day to mark it. It was launched on an LVM3 rocket from Sriharikota, was India's second landing attempt, and made India the fourth country to soft-land on the Moon, so the other options are wrong.

Aditya-L1 carries seven payloads. PAPA (Plasma Analyser Package for Aditya) is the instrument that studies the composition of the solar wind and its energy distribution. ASPEX (Aditya Solar wind Particle Experiment) studies the variation of solar-wind particles and their spectral characteristics, SUIT images the Sun in ultraviolet, and VELC is the coronagraph that studies the corona.

The Aditya-L1 Support Cell is located at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. It is a community centre where any researcher in India can learn to use and analyse data from Aditya-L1, ISRO's solar observatory. Aditya-L1 was launched in September 2023 and orbits the Sun-Earth L1 point.

Chandrayaan-3's lander and rover are named Vikram and Pragyan, the same names used in Chandrayaan-2. The lander, named after Vikram Sarabhai, soft-landed near the Moon's south pole on 23 August 2023 and released the Pragyan rover on the surface.

ISRO launched Chandrayaan-3 on 14 July 2023 from Sriharikota, and its Vikram lander touched down near the Moon's south pole on 23 August 2023. India became the fourth country to soft-land on the Moon and the first near the south pole.