Space Technology: ISRO, orbits, launchers and navigation

ISRO, space reforms and orbits

The Government of India unleashed reforms in the space domain in 2020, opening the doors for non-government entities (NGEs) to carry out end-to-end activities in the space domain on a level playing field. The Indian Space Policy 2023 is the overarching framework for these reforms. Under it, ISRO focuses on applied research and development of newer systems (space infrastructure, space transportation, applications, capacity building and human spaceflight), shares technologies with NGEs and enables open data access from remote sensing satellites; NewSpace India Limited (NSIL) is the Government company named in the policy (Indian Space Policy 2023, Department of Space).

IN-SPACe (Indian National Space Promotion and Authorisation Centre) is an autonomous Government organisation mandated to promote, hand-hold, guide and authorise space activities, and to act as the single window agency for authorising space activities (Indian Space Policy 2023). ISRO describes it as a single-window, independent, nodal agency in the Department of Space (ISRO, IN-SPACe page). So UPSC accepted that IN-SPACe is an autonomous agency formed to facilitate participation of private entities; the key also accepts the Agnikul Cosmos 3D-printed engine statement and rejects the claim about Skyroot and GSLV fuel (Prelims 2026: answer (c), 1 and 2 only; answer key provisional).

A geostationary orbit lies above the Earth’s equator; the satellite moves from west to east, once every 23 hours 56 minutes 4 seconds, matching the Earth’s rotation, so it seems fixed in the sky. It is circular and sits 35,786 km above the surface, which is why it is used for telecommunication and weather satellites (European Space Agency, Types of orbits). So the orbit is geosynchronous, circular and The orbit lies in the plane of the equator; 22,236 is the height in miles, not km (Prelims 2011: answer (a), 1, 2 and 3 only).

Low orbits serve other jobs. Polar orbits run roughly north-south, usually 200 to 1,000 km up; a sun-synchronous orbit (SSO) is a polar orbit timed so a satellite passes over each place at the same local solar time, which suits Earth observation. A geostationary transfer orbit (GTO) is the elliptical orbit into which rockets drop satellites bound for geostationary orbit (European Space Agency).

Heights are design or reference values from the sources named.

Mains 2016 asked: Discuss India’s achievements in the field of Space Science and Technology and how they helped socio-economic development. Points: reliable launchers (PSLV, GSLV, LVM3), NavIC and GAGAN for navigation and aviation, remote sensing for crops and water, the Mars Orbiter Mission, Chandrayaan-3’s landing near the lunar south pole, Aditya-L1 and NISAR (all covered on later pages), and the 2020 reforms that opened the sector to private firms.

Launch vehicles: PSLV, GSLV, LVM3 and SSLV

PSLV, the Polar Satellite Launch Vehicle, has four stages: the solid PS1 (S139, HTPB), the liquid PS2 with the Vikas engine, the solid PS3, and a PS4 with two liquid engines. It first flew on 20 September 1993 and had its first successful launch in October 1994. ISRO calls it its workhorse: it can carry 1,750 kg to a 600 km sun-synchronous polar orbit and 1,425 kg to a sub-geosynchronous transfer orbit, and it launched the IRNSS navigation satellites. PSLV-C37 carried 104 satellites in one flight (ISRO, PSLV page).

GSLV Mk II has three stages and four liquid strap-ons. Its upper stage is the Cryogenic Upper Stage, powered by the CE-7.5, India’s first cryogenic engine, burning liquid oxygen and liquid hydrogen; the indigenous stage flew from GSLV-D5 in January 2014. It lifts 2,250 kg to GTO and is meant for INSAT-class communication satellites (ISRO, GSLV page). LVM3 (Geosynchronous Satellite Launch Vehicle Mk III) has three stages: two S200 solid strap-ons, the L110 liquid core stage and the C25 cryogenic stage; it lifts 4,000 kg to GTO and 8,000 kg to low Earth orbit (ISRO, LVM3 page).

So PSLVs launch the satellites useful for Earth resources monitoring whereas GSLVs are designed mainly to launch communication satellites (true). Satellites launched by PSLV go mainly to polar orbits, so they do not stay fixed in the sky, and GSLV Mk III has three stages, not four (Prelims 2018: answer (a), 1 only).

SSLV, the Small Satellite Launch Vehicle, made its third developmental flight on 16 August 2024, placing EOS-08 (about 175.5 kg) in a 475 km low Earth orbit at 37.4 degrees. This completed the SSLV

Development Project and opens the way for operational missions by Indian industry and NSIL (ISRO, SSLV-D3; PIB, PRID 2045802).

Source: ISRO vehicle pages; SSLV row from PIB, PRID 2045802. Payloads are rated capacities, not a single flight, except SSLV.

Navigation satellites: NavIC and GAGAN

IRNSS, renamed NavIC in 2016, is India’s regional navigation system; it covers India and a region extending about 1,500 km around it, and was designed with 7 satellites (ISRO IRNSS page; GPS.gov). It offers a Standard Positioning Service for all users and an encrypted Restricted Service, with position accuracy better than 20 m in the primary service area (ISRO). The constellation combines geostationary and inclined geosynchronous satellites; UPSC’s key rejects the statement that IRNSS covers entire India and about 5500 sq. km beyond (its range is 1,500 km), and India never planned global coverage by 2019 (Prelims 2018: answer (a), 1 only).

Status in 2026: eleven NavIC satellites have been launched, eight are functional, three broadcast navigation signals and five can broadcast one-way messaging signals (PIB, 25 Mar 2026). A receiver needs at least four satellites for a standalone position, so standalone positioning is not available with three, though the timing service works (Lok Sabha reply, 2026).

NavIC status as reported to Parliament in 2026.

Other countries run regional systems too: QZSS is a regional GNSS owned by the Government of Japan that complements GPS in East Asia and Oceania; the global systems are GPS (USA), GLONASS (Russia), BeiDou (China) and Galileo (EU) (GPS.gov, Other GNSS). So Japan is the one with its own Satellite Navigation System (Prelims 2023: answer (d)).

GAGAN is a satellite-based augmentation system built jointly by the Airports Authority of India and ISRO. Certified by DGCA in 2015, it is one of only four such systems, with WAAS (USA), EGNOS (Europe) and

MSAS (Japan) (PIB, PRID 1820947). It augments GPS for accuracy, integrity and continuity, with benefits in aviation and non-aviation sectors (PIB, 8 Dec 2022). So it provides additional accuracy and integrity and better air traffic management, but statement III (aviation only) is wrong (Prelims 2025: answer (d), I and II only).

GPS also gives time: it provides precise synchronisation of communications systems, power grids, financial networks and other critical infrastructure, and helps wireless networks use radio spectrum efficiently (GPS.gov, GPS and Telling Time). So mobile phone operations, banking and Controlling the power grids all use GPS (Prelims 2018: answer (d), 1, 2 and 3).

Mains 2018 asked: Why is Indian Regional Navigational Satellite System (IRNSS) needed? Mains 2018 Mains 2015 asked about Standard Positioning Systems and Precision Positioning Systems and the advantages of IRNSS with just seven satellites. Points: SPS is open to all; the precise, encrypted service (RS) is for authorised users; a regional system under national control avoids dependence on foreign systems in a crisis, and only a few satellites are needed because the coverage area is regional (ISRO; GPS.gov).