BharatNotes Note: This chapter was removed from the NCERT curriculum in the 2022 rationalization. Retained here as gravitation underlies orbital mechanics, satellite technology, ocean tides (tidal energy), and geophysics — GS3 science & technology.
Gravitation is the force that holds planets in orbit, causes ocean tides, and determines whether a submarine sinks or floats. For UPSC, this chapter connects to India's tidal energy potential (Gulf of Khambhat, Gulf of Kutch), submarine technology (INS Arihant), space missions, and the geophysics behind gravity surveys for mineral exploration. GS3 tests energy sources, ocean energy, and science & technology — gravitation is the thread connecting all three.
PART 1 — Quick Reference Tables
Gravitation — Core Quantities
| Quantity | Value / Formula | Notes |
|---|---|---|
| Universal Gravitational Constant (G) | 6.674 × 10⁻¹¹ N⋅m²/kg² | Same everywhere in universe; discovered experimentally by Cavendish (1798) |
| g on Earth surface | 9.8 m/s² (≈ 10 m/s²) | Acceleration due to gravity; varies slightly by location |
| g on Moon | 1.62 m/s² (≈ g/6) | Astronaut weighs 1/6th on Moon; same mass |
| Gravitational Force (F) | F = G(m₁m₂)/r² | Inverse square law; doubles distance → force reduces to 1/4th |
| Weight (W) | W = mg | Force of gravity on mass; measured in Newtons; changes with location |
| Mass (m) | constant | Amount of matter; measured in kg; same everywhere in universe |
Tides — Types and Causes
| Tide Type | Cause | Effect | Timing |
|---|---|---|---|
| High Tide | Moon's gravity pulls ocean water toward it on near side | Sea level rises at coast | When coast faces Moon |
| Low Tide | Water drawn away from that coast toward Moon | Sea level falls | When coast is 90° from Moon |
| Inertial bulge | Water on far side left behind as Earth accelerates toward Moon | Second high tide | Opposite side of Earth from Moon |
| Spring Tide | Sun + Moon aligned (new/full moon) → gravitational forces add up | Highest high tides, lowest low tides | New and Full Moon |
| Neap Tide | Sun + Moon at right angles (quarter moon) → partially cancel | Weaker tides | Quarter Moon phases |
India's Ocean Energy Potential
| Source | Estimated Potential | Key Sites | Status |
|---|---|---|---|
| Tidal energy | ~9.6 GW total | Gulf of Khambhat (~8.5 GW), Gulf of Kutch (~1.1 GW), Sundarbans (~100 MW) | No commercial plant yet in India |
| Wave energy | ~40 GW (Indian coastline) | West coast (higher wave energy) | Pilot projects by NIOT |
| Ocean Thermal Energy Conversion (OTEC) | Large potential | Lakshadweep Islands, Andaman coast | NIOT pilot plant operational |
| Ocean current energy | Significant | Gulf of Mannar, Palk Strait | Research stage |
PART 2 — Detailed Notes
1. Newton's Universal Law of Gravitation
Every particle in the universe attracts every other particle with a gravitational force that is:
- Directly proportional to the product of their masses (more mass → stronger pull)
- Inversely proportional to the square of the distance between them (farther apart → much weaker pull)
F = G(m₁m₂)/r²
G = 6.674 × 10⁻¹¹ N⋅m²/kg² (universal gravitational constant — same everywhere).
This inverse square law is profound: double the distance → force becomes 1/4th; triple the distance → force becomes 1/9th. This is why gravity from distant stars, though real, is negligible.
The Universal Law of Gravitation is "universal" because it applies to ALL objects with mass — not just large bodies like planets. Two people sitting 1 metre apart exert gravitational force on each other, but the force is unimaginably small (G is extremely small). Gravity becomes significant only when at least one mass is very large (a planet, star, etc.).
2. Gravitational Acceleration (g)
The acceleration due to gravity near Earth's surface is derived from Newton's law:
g = GM/R² where M = Earth's mass (5.97 × 10²⁴ kg), R = Earth's radius (6.371 × 10⁶ m), G = 6.674 × 10⁻¹¹ N⋅m²/kg² → g ≈ 9.8 m/s²
Variations in g:
- With altitude: g decreases as you move away from Earth's surface (r increases in g = GM/r²). At very high altitudes (satellites), g is still non-zero — satellites are in continuous free fall.
- With depth: g also decreases as you go below Earth's surface.
- With latitude: g is slightly higher at poles than at the equator because (a) Earth is oblate (flattened at poles) — poles are closer to Earth's centre, and (b) Earth's rotation creates a centrifugal effect at the equator that slightly reduces effective g. g(poles) ≈ 9.83 m/s²; g(equator) ≈ 9.78 m/s².
3. Mass vs Weight
| Property | Mass | Weight |
|---|---|---|
| Definition | Amount of matter in a body | Gravitational force acting on a body |
| Formula | — (intrinsic property) | W = mg |
| Unit | kilogram (kg) | Newton (N); sometimes expressed in kgf |
| Type | Scalar | Vector |
| Varies with location? | No — same on Moon, Mars, ISS | Yes — less on Moon, zero in free fall |
An astronaut of mass 70 kg has mass = 70 kg everywhere. On Earth: weight = 70 × 9.8 = 686 N. On Moon: weight = 70 × 1.62 = 113.4 N (about 1/6th). On ISS in orbit: the astronaut is in free fall → apparent weight = 0 (weightlessness) → mass is still 70 kg. This is why mass is the fundamental measure of "how much matter," not weight.
4. Free Fall and Terminal Velocity
Free fall: Motion under gravity alone, with no air resistance. All objects fall with the same acceleration g, regardless of mass (Galileo's famous Leaning Tower of Pisa experiment — a 10 kg and a 1 kg ball dropped together hit the ground simultaneously in vacuum).
Terminal velocity: In reality, air resistance acts upward on a falling object. As speed increases, air resistance increases. Eventually, air resistance = gravitational force → net force = 0 → acceleration = 0 → object falls at constant speed (terminal velocity).
- Skydivers in free-fall position: terminal velocity ~195 km/h; with parachute deployed: ~18–20 km/h (parachute increases drag dramatically)
- Raindrops: terminal velocity depends on size; a large raindrop falls at ~9 m/s — without terminal velocity (if no air resistance), raindrops would reach ~200 km/h and be lethal
5. Tides — Gravitation at Planetary Scale
Tides are caused by the differential gravitational pull of the Moon (and to a lesser extent the Sun) on different parts of Earth.
The Moon's gravity is stronger on the side of Earth facing the Moon — it pulls ocean water toward it, creating a high tide. On the far side of Earth, the Moon's pull is weakest — Earth's centre is pulled toward the Moon more than the far side water → the far side water is "left behind" → another high tide (inertial bulge).
Between these two high tides, water is drawn away → two low tides per day (one between each pair of high tides). This gives most coastal regions two high tides and two low tides approximately every 24 hours and 50 minutes (slightly more than 24 hours because the Moon also orbits Earth).
UPSC GS3 — Tidal Energy and India's Ocean Energy Potential:
Tidal energy is a predictable, renewable, and non-intermittent energy source (unlike solar and wind). It harnesses the kinetic and potential energy of tidal flows.
India's tidal energy potential:
- Gulf of Khambhat (Cambay), Gujarat: ~8.5 GW potential — highest in India due to large tidal range (up to 11 metres — among the highest in the world) and funnel shape that amplifies tides
- Gulf of Kutch, Gujarat: ~1.1 GW potential; also large tidal ranges
- Sundarbans, West Bengal: ~100 MW potential; ecologically sensitive area — development challenging
Why no commercial tidal plant in India yet:
- High upfront capital cost; complex marine engineering
- Environmental concerns (barrages affect fish migration, estuarine ecology)
- Alternative: tidal stream generators (like underwater wind turbines) — less ecological impact but lower output
Globally operational tidal plants:
- La Rance Tidal Power Station, France (1966) — world's first and one of the largest; 240 MW capacity; barrage type
- Annapolis Royal, Canada — 20 MW; oldest tidal plant in North America
- Sihwa Lake Tidal Power Station, South Korea (2011) — 254 MW; currently world's largest tidal power plant
National Institute of Ocean Technology (NIOT), Chennai: India's nodal body for ocean energy R&D under the Ministry of Earth Sciences. Working on tidal current energy devices, wave energy converters, and OTEC (Ocean Thermal Energy Conversion) plants.
Ministry of New and Renewable Energy (MNRE): Responsible for promoting ocean energy in India. Ocean energy included under renewable energy for meeting RPO (Renewable Purchase Obligation) targets.
6. Archimedes' Principle and Buoyancy
Archimedes' Principle: Any object fully or partially submerged in a fluid (liquid or gas) experiences an upward buoyant force equal to the weight of the fluid displaced by the object.
Buoyant force = weight of displaced fluid = ρ_fluid × V_submerged × g
- If buoyant force > weight of object → object floats
- If buoyant force < weight of object → object sinks
- If buoyant force = weight of object → object is in neutral buoyancy (floats at that depth)
This is equivalent to saying: objects float if their average density is less than the fluid's density (a hollow steel ship floats because its average density — including the air inside — is less than water's density).
UPSC GS3 — Submarines and Buoyancy:
Submarines control their buoyancy using ballast tanks:
- To dive: Open valves to let seawater flood ballast tanks → average density of submarine increases → buoyant force < weight → submarine sinks
- To surface: Blow compressed air into ballast tanks, expelling seawater → average density decreases → buoyant force > weight → submarine rises
- Neutral buoyancy: Balance ballast precisely → submarine hovers at desired depth without using engine power
INS Arihant: India's first indigenous nuclear-powered ballistic missile submarine (SSBN — Ship Submersible Ballistic Nuclear). Displacement: ~6,000 tonnes when submerged. Nuclear reactor provides propulsion without need to surface for air (unlike conventional diesel-electric submarines). Commissioned 2016. Armed with K-15 Sagarika SLBMs (submarine-launched ballistic missiles, range ~750 km) and K-4 missiles (range ~3,500 km). Strategic importance: Completed India's nuclear triad (land, air, and sea-based nuclear capability) — critical for second-strike capability, which underpins India's No-First-Use (NFU) nuclear doctrine.
[Additional] INS Arighat: India's second SSBN, commissioned August 29, 2024 at Visakhapatnam in presence of Raksha Mantri Rajnath Singh. More advanced than INS Arihant — 70% indigenous content; can carry 12 K-15 missiles or 4 K-4 missiles. A third SSBN (INS Aridhaman) is also under construction — larger and more capable. India's expanding sea-based nuclear deterrent signals growing confidence in second-strike capability.
Scorpène-class submarines (Kalvari class): Six conventional (diesel-electric) submarines built under Project-75 at Mazagon Dock Shipbuilders Limited (MDSL), Mumbai, in collaboration with Naval Group (France). INS Kalvari (first of class) commissioned 2017. Quieter than nuclear submarines for shallow water operations.
Project-75 India (P-75I): Follow-on programme for 6 advanced conventional submarines with air-independent propulsion (AIP) — allows submerged operation without surfacing for air; longer endurance. Under strategic partnership model.
7. Gravity in Geophysics
Variations in Earth's gravitational field (measured by gravimeters) reveal subsurface geological structures:
- Gravity high: Dense rock (basalt, ore bodies) below surface → more mass → stronger g
- Gravity low: Less dense rock (salt domes, sedimentary basins — often associated with oil) → less mass → weaker g
Gravity surveys help locate oil and gas fields, groundwater aquifers, and mineral deposits. The National Geophysical Research Institute (NGRI), Hyderabad conducts gravity surveys across India.
India's GRACE (Gravity Recovery and Climate Experiment) satellite data: NASA-Germany mission; revealed groundwater depletion rates in India (Indo-Gangetic Plain — one of the fastest depleting aquifers in the world). This data informed India's groundwater policy and the National Aquifer Mapping Programme (NAQUIM).
[Additional] 10a. Kalpasar Project — India's Only Active Tidal Barrage Initiative
The chapter lists India's tidal energy potential (Gulf of Khambhat 8.5 GW) and notes "no commercial plant yet." What bridges potential and reality is the Kalpasar Project — the only government-level barrage initiative specifically targeting the Gulf of Khambhat.
[Additional] Kalpasar Project — GS3 (Energy / Water Resources / Infrastructure) + GS1 (Gujarat Geography):
What is Kalpasar? The Kalpasar Project proposes a 30 km sea dam (barrage) across the Gulf of Khambhat, enclosing a freshwater reservoir of ~2,000 sq km. It is a multipurpose project — not purely tidal:
- Primary objectives: Freshwater storage (irrigation for drought-prone Saurashtra/North Gujarat); flood control; road/rail link (connecting Saurashtra and South Gujarat)
- Secondary objective: Tidal power generation from the head difference created by the barrage
- Tourism and fisheries benefits also planned
Key project data:
| Parameter | Detail |
|---|---|
| Barrage length | 30 km (revised from original 64 km in 2017) |
| Reservoir area | ~2,000 sq km freshwater lake |
| Estimated cost | ₹85,000 crore (2022 estimate) |
| Projected duration | 20 years after feasibility approval |
| Status | No construction started; feasibility studies ongoing; Gujarat government has periodically revived the project |
India's actual tidal capacity (2024): Only 2.5 MW installed — the massive gap between 8,500+ MW potential and near-zero reality reflects the high costs, long project timelines, and ecological concerns with barrage designs.
Ecological concerns with Kalpasar:
- Closing the Gulf of Khambhat with a barrage would alter tidal flushing patterns, affect mangrove ecosystems, and impact flamingo breeding grounds (Gulf of Khambhat is a major flamingo habitat)
- Fisheries in the gulf — supporting hundreds of thousands of fisherfolk — would be significantly disrupted
- Similar concerns halted India's earlier proposed Sundarbans tidal barrage
Alternative approach — Tidal Stream Turbines: NIOT (Chennai) is testing underwater tidal current turbines (similar to submerged wind turbines) that do not require a barrage — smaller ecological footprint but lower output. India's first 10 kW tidal current turbine was tested at the Gulf of Kutch in 2019.
UPSC synthesis: Kalpasar is a textbook energy-versus-environment tradeoff question. The project spans GS1 (Gujarat coastal geography, freshwater geography), GS2 (Gujarat state politics — periodically revived before elections), and GS3 (tidal energy potential, ecological impacts of barrage). The gap between 8,500 MW potential and 2.5 MW actual is the UPSC hook.
[Additional] 10b. Project 75I — AIP Technology and the Submarine Deal's 2026 Status
The chapter mentions Project 75I (P-75I) for six advanced submarines with air-independent propulsion (AIP). What is missing is the conceptual explanation of why AIP matters and the live 2025-26 status of the contract negotiations.
Air-Independent Propulsion (AIP) — The Physics: Conventional diesel-electric submarines must surface (or use a snorkel) to run diesel engines (diesel needs atmospheric oxygen). This makes them detectable. AIP systems allow a submarine to operate submerged for weeks without surfacing — the engine does not need atmospheric oxygen.
How AIP works (Fuel Cell AIP — the most common technology):
- Liquid oxygen (LOX) + liquid hydrogen stored onboard in cryogenic tanks
- A polymer electrolyte membrane (PEM) fuel cell combines H₂ and O₂ electrochemically (no combustion) → produces electricity + water
- The electricity powers the propulsion motor
- No combustion → no heat or sound signature → extremely quiet → very difficult for sonar to detect
This connects directly to Archimedes' principle and buoyancy (the chapter's core physics) — an AIP submarine can maintain neutral buoyancy for days at optimal patrol depth without running engines or surfacing.
[Additional] Project 75I (P-75I) — GS3 (Defence Technology / Indigenisation):
Programme overview:
- 6 advanced conventional submarines with AIP (fuel cell type) + diesel-electric backup
- Displacement: ~3,000 tonnes; endurance: weeks without surfacing (with AIP)
- Estimated cost: ₹90,000–1,00,000 crore (making it one of India's largest defence procurement programmes)
- Built in India under the Strategic Partnership (SP) model — Indian private company (L) partners with a foreign OEM
2025-26 status:
- January 2025: L&T–Navantia (Spain's S-80 Plus design) was disqualified — leaving Mazagon Dock Shipbuilders Limited (MDSL) + TKMS (Germany, Type 216 design) as the sole remaining bidder
- July 2025: Commercial negotiations began
- April 2026: India's Defence Minister visited Germany for negotiations; contract expected within months — submarines to be delivered from the mid-2030s
- The AIP technology-transfer tension: India wants the option to eventually integrate DRDO's indigenous AIP (under development at DRDO's Research Centre Imarat, Hyderabad); TKMS wants India to accept its proprietary German AIP system. This is a technology-sovereignty vs. procurement-speed tradeoff — a classic Make in India vs. capability gap question.
Strategic significance:
- Conventional AIP submarines are more suited to shallow waters (Bay of Bengal, Arabian Sea coastal patrol) than nuclear submarines — complementary, not competing, with INS Arihant/Arighat class
- Pakistan is simultaneously expanding its submarine fleet with 8 Chinese Yuan-class AIP submarines (3 already delivered as of 2024) — P-75I is India's direct response
- AIP technology denial risk: If India depends on German AIP and Germany later restricts transfers (as Russia did with cryogenic engines in 1993), India's submarine capability is vulnerable — DRDO's indigenous AIP programme is the insurance policy
UPSC angle: P-75I appears in GS3 questions on Make in India in defence, AIP technology, India's maritime security, and comparison with Pakistan's growing submarine fleet. The technology-transfer dilemma (German AIP vs. DRDO AIP) is a direct "sovereignty vs capability" policy question.
[Additional] 10b. Gravity Assist Manoeuvres — ISRO's Mangalyaan and Interplanetary Physics
The chapter covers universal gravitation and escape velocity. It does not address how gravity assist manoeuvres exploit a planet's gravitational field to accelerate a spacecraft without burning fuel — the key technique that made ISRO's Mangalyaan (MOM) cost-effective and successful.
Key Terms — Gravity Assist and Interplanetary Orbits:
| Term | Meaning |
|---|---|
| Gravity assist (slingshot manoeuvre) | A spacecraft technique where the craft flies close to a planet, gains energy from the planet's gravitational field and orbital velocity around the Sun, and exits with higher speed — without expending propellant |
| Hohmann Transfer Orbit | The minimum-energy elliptical orbit connecting two circular orbits (e.g., Earth orbit to Mars orbit); the baseline fuel-efficient interplanetary transfer path |
| Trans-Mars Injection (TMI) | The engine burn that places a spacecraft from Earth orbit onto the transfer trajectory toward Mars; equivalent to exceeding Earth's gravitational pull toward Mars |
| Heliocentric orbit | An orbit around the Sun (as opposed to geocentric = around Earth); once TMI is complete, Mangalyaan was in a heliocentric orbit coasting to Mars |
| Mars Orbit Insertion (MOI) | The engine burn that slows the spacecraft to be captured into Mars orbit; if this fails, spacecraft flies past Mars and is lost |
| PSLV-C25 | The ISRO launch vehicle (Polar Satellite Launch Vehicle) that launched Mangalyaan from Sriharikota on November 5, 2013 |
[Additional] Gravity Assist and ISRO's Mangalyaan — Gravitational Physics in Space Exploration (GS3 — Science and Technology):
How gravity assist works — physics:
| Step | What happens | Gravitational physics |
|---|---|---|
| 1. Approach | Spacecraft approaches planet on a hyperbolic trajectory | Planet's gravity accelerates spacecraft (kinetic energy increases) |
| 2. Closest approach | Spacecraft reaches periapsis (closest point) at maximum speed | Gravitational potential energy at minimum, KE at maximum |
| 3. Departure | Spacecraft exits planet's gravitational sphere of influence | Planet's gravity decelerates spacecraft — BUT in the planet's reference frame, spacecraft exits at same speed it entered |
| 4. Net gain | In the Sun's reference frame, spacecraft has effectively "borrowed" momentum from the planet's orbital velocity | Planet slows down infinitesimally; spacecraft gains velocity |
| Conservation | Total momentum of spacecraft + planet is conserved; planet's mass is so large (~10²⁴ kg) that its velocity change is immeasurable | Newton's 3rd law + conservation of momentum |
Mangalyaan (MOM — Mars Orbiter Mission) key facts:
| Parameter | Detail |
|---|---|
| Mission name | Mangalyaan (Hindi: "Mars Craft"); formally Mars Orbiter Mission (MOM) |
| Launch date | November 5, 2013 from Sriharikota (Satish Dhawan Space Centre) |
| Launch vehicle | PSLV-C25 (XL configuration) |
| Mars arrival | September 24, 2014 — Mars Orbit Insertion (MOI) engine burn at 07:17 IST |
| First | Asia's first interplanetary mission; world's first to succeed on maiden attempt |
| Cost | ~₹450 crore (~USD 74 million) — cheaper than Hollywood film Gravity (USD 100 million) |
| Mass | ~1,350 kg at launch; payload ~15 kg |
| Payloads | 5 science instruments: LAP (Lyman Alpha Photometer), MSM (Methane Sensor for Mars), TIS (Thermal Infrared Imaging Spectrometer), MCC (Mars Colour Camera), MENCA (Mars Exospheric Neutral Composition Analyser) |
| Status | Mangalyaan lost contact in October 2022 after 8+ years in Mars orbit (fuel exhausted + long eclipse) |
How Mangalyaan used Earth gravity assist:
| Phase | Detail |
|---|---|
| Earth orbit phase | Nov 5–Dec 1, 2013: PSLV placed Mangalyaan in Earth orbit; 6 orbit-raising burns over 25 days progressively enlarged the elliptical orbit |
| Trans-Mars Injection | December 1, 2013: Final engine burn (TMI) placed Mangalyaan on Mars-bound trajectory using Earth's gravitational sphere as a "slingshot" — no mid-course correction needed |
| Why this approach? | PSLV (smaller rocket) couldn't directly inject Mangalyaan on interplanetary trajectory; Earth gravity-assist approach allowed the smaller, cheaper PSLV to do what normally requires a heavier rocket |
| Heliocentric coast | Dec 2013 – Sept 2014: ~9 months coasting in heliocentric orbit |
| Mars Orbit Insertion | Sept 24, 2014: 24-minute main engine burn to slow spacecraft into Mars orbit |
Chandrayaan-3 and Trans-Lunar Injection:
| Mission | Gravity technique used |
|---|---|
| Chandrayaan-3 (launched July 14, 2023) | Multiple Earth orbit raises → Trans-Lunar Injection (TLI) burn; lunar gravity used for final capture; soft landing August 23, 2023 — India = 4th country to soft-land on Moon |
| Future missions (Mangalyaan-2 / MOM-2) | Proposed; planned for late 2020s; will use more advanced gravity assist trajectories |
Escape velocity — chapter link:
| Concept | Value | Application |
|---|---|---|
| Earth escape velocity | 11.2 km/s | Spacecraft must exceed this to leave Earth permanently |
| Mars escape velocity | 5.03 km/s | Lower than Earth's — easier to escape Mars surface |
| Mangalyaan TMI | Delta-V (Δv) of ~648 m/s added by TMI burn on top of already-high Earth orbit velocity | Combined with Earth orbital speed (~7.7 km/s), total exceeded 11.2 km/s escape velocity |
UPSC synthesis: Key exam facts: Gravity assist = spacecraft gains velocity from planet's gravitational field = momentum borrowed from planet = no fuel burned = conservation of momentum; Mangalyaan (MOM) launched November 5, 2013 by PSLV-C25 from Sriharikota; Mars Orbit Insertion September 24, 2014; Asia's first interplanetary mission = world's first to succeed on maiden attempt; cost ~₹450 crore; payloads = 5 instruments including Mars Colour Camera (MCC); lost contact October 2022; Mangalyaan used Earth orbit raises → Trans-Mars Injection (TMI) on Dec 1, 2013; Chandrayaan-3 soft-landed August 23, 2023 = India = 4th country to soft-land on Moon. Prelims trap: Mangalyaan was Asia's first Mars mission (NOT the world's first — USSR launched Mars 1 in 1962); it succeeded on the first attempt (unlike USA, USSR, Europe which all failed first attempts); the launch vehicle was PSLV-C25 (NOT GSLV — GSLV was used for Chandrayaan-2); cost was ~₹450 crore (NOT ₹4,500 crore — the low cost is a key talking point); Earth escape velocity = 11.2 km/s (NOT 9.8 m/s² — that is gravitational acceleration 'g', not escape velocity).
Exam Strategy
Prelims traps:
- Mass is constant everywhere; weight varies — weight is zero in free fall but mass is NOT zero
- g on Moon ≈ 1/6th of Earth's g (1.62 m/s²) — not 1/4th or 1/8th
- Spring tides occur at new moon AND full moon (both, not just one); neap tides at quarter moon
- Gulf of Khambhat (not Kutch) has the higher tidal energy potential (~8.5 GW vs ~1.1 GW)
- La Rance (France) — world's first large tidal power station; Sihwa Lake (South Korea) — currently world's largest
- INS Arihant is an SSBN (nuclear ballistic missile submarine), not a fast-attack submarine
- India's nuclear triad: land (Agni missiles) + air (aircraft-delivered) + sea (INS Arihant Sagarika/K-4 SLBMs)
Mains linkages:
- Tidal energy → India's coastal geography (Gulf of Khambhat shape) → clean energy targets → challenges of cost and ecology
- Nuclear triad → INS Arihant → No-First-Use doctrine → credible minimum deterrence → maritime security
- Gravity surveys → oil/gas exploration → import dependency → energy security
Practice Questions
Prelims:
Which of the following pairs of locations in India is correctly matched with their tidal energy potential?
(a) Gulf of Kutch — 8.5 GW; Gulf of Khambhat — 1.1 GW
(b) Gulf of Khambhat — 8.5 GW; Gulf of Kutch — 1.1 GW
(c) Gulf of Mannar — 8.5 GW; Gulf of Kutch — 1.1 GW
(d) Gulf of Khambhat — 1.1 GW; Sundarbans — 8.5 GWWith reference to INS Arihant, consider the following statements: 1. It is India's first indigenous nuclear-powered submarine. 2. It completes India's nuclear triad. 3. It is classified as an SSBN. Which of the above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1, 2 and 3
(d) 1 only
Mains:
- India has significant ocean energy potential but has yet to harness it commercially. Examine the types of ocean energy available to India, their potential, and the challenges in their exploitation. (CSE Mains 2021, GS Paper 3, 15 marks)
