Menu

Science and Technology

Image Aug 12, 2025, 08_58_17 AM

Atmospheric Optics – Iridescent Clouds

0

Iridescent clouds, also known as irisation, occur when thin parts of clouds display soft pastel colors. This phenomenon is caused by diffraction and interference of sunlight or moonlight by tiny, uniformly sized water droplets or ice crystals. The effect is most commonly observed near the edges of thin clouds, especially when they are newly formed.

Mechanism
When light encounters droplets or ice crystals of nearly uniform size, diffraction bends different wavelengths by slightly different amounts. These diffracted waves interfere with each other, producing visible colors. Smaller droplets produce a larger angular spread of colors, while larger droplets result in smaller, tighter patterns.

Favourable Conditions

  • Thin, optically transparent clouds with low optical depth.

  • Droplets or ice crystals with narrow size distribution.

  • Locations at cloud tops or edges, often in altocumulus, cirrocumulus, lenticular, or pileus clouds.

Related Optical Phenomena

  • Coronae: Concentric colored rings around the Sun or Moon caused by diffraction from tiny, uniformly sized droplets or ice crystals. The radius of the corona is inversely proportional to particle size.

  • Glory: Concentric colored rings opposite the Sun, surrounding the observer’s or an aircraft’s shadow, caused by backward diffraction from water droplets.

  • Halos and Sundogs (Parhelia): Formed by refraction through hexagonal ice crystals at fixed angles (commonly 22°), distinct from diffraction phenomena.

Key Distinctions

  • Iridescence and coronae are diffraction-based phenomena, while halos and sundogs are refraction-based.

  • Iridescence is usually irregular and patchy, while coronae appear as concentric rings.

  • Glories occur opposite the Sun; iridescence and coronae occur near it.

UPSC-Relevant Facts

  • Smaller droplets → larger corona radius.

  • Uniform droplet size → sharper, more vivid colors.

  • Thick clouds or wide droplet size range lead to muted or absent colors.

  • Common in mid- and high-level clouds during early stages of development.

Exam Tip
Identify the mechanism (diffraction vs. refraction) and location in the sky (near Sun/Moon vs. opposite) to distinguish between similar atmospheric optical phenomena.

ChatGPT Image Jul 29, 2025, 08_24_28 AM

Seeing Earth in All Weather: NISAR, SAR Basics, and the GSLV Launcher

0

What Exactly is Launching?

NISAR (NASA–ISRO Synthetic Aperture Radar) is a joint Earth-observation satellite developed by NASA and ISRO. It features two SAR instruments on a single platform:

  • NASA’s L-band SAR

  • ISRO’s S-band SAR

It will orbit in a Sun-synchronous, dawn-dusk orbit at ~747 km altitude, 98.4° inclination, with a 12-day repeat cycle. A 12-meter gold-mesh reflector on a 9-meter boom captures a ~242 km swath. All data from NISAR will be free and openly available.

The satellite will be launched by India using the GSLV Mk-II (GSLV-F16) with a 4-meter fairing from the Satish Dhawan Space Centre (SDSC), Sriharikota. The lift-off mass is ~2,400 kg based on ISRO’s I-3K satellite bus.

Mission Duration:
NASA outlines a baseline 3-year science mission with consumables for ~5 years. As of July 25, 2025, ISRO officially lists the mission life as 5 years, aiming for extended operations.

Workshare Details:

  • NASA: L-band radar, 12-m reflector, 9-m boom, GPS, solid-state recorder, high-rate telecom, payload data system

  • ISRO: S-band radar, spacecraft (I-3K), GSLV Mk-II launch, satellite operations

  • Both agencies will provide ground support and data distribution.

SAR Fundamentals (Static Core)

How SAR “Sees” (Active Microwave)

SAR is an active sensor: it sends microwave pulses and records echoes. It works day or night, in any weather, unlike passive optical sensors.

Synthetic Aperture: Instead of requiring a physically long antenna, SAR synthesizes one using the satellite’s motion to build high-resolution images.

Key Geometry Terms:

  • Along-track (Azimuth): Direction of satellite motion

  • Across-track (Range): Perpendicular to motion

  • Slant range vs Ground range: Important SAR image dimensions

L-band vs S-band

  • L-band: 1.257 GHz ±40 MHz (~24 cm wavelength)

  • S-band: 3.2 GHz ±37.5 MHz (~9 cm wavelength)

Penetration and Use:

  • L-band penetrates vegetation, dry soil, and snow, making it ideal for monitoring biomass, ground deformation, and ice sheets.

  • S-band interacts more with leaves and surface textures, useful for assessing crop structure, moisture, and sea-ice characteristics.

  • Dual-band SAR helps separate canopy and ground responses.

Polarimetry: NISAR supports various polarization modes (e.g., HH, HV, VH, VV). These enhance the ability to classify surfaces and estimate biomass.

Revisit and Repeat Cycles

  • Repeat cycle: 12 days (same ground track)

  • With both ascending and descending passes, average sampling = ~6 days

  • Sun-synchronous orbit ensures the satellite crosses the same area at ~6 a.m. and ~6 p.m., maintaining consistent lighting — crucial for change detection.

Interferometry (InSAR)

SAR captures the phase of radar waves. Comparing the phase from two different passes gives line-of-sight displacement — down to millimetre accuracy.

Interferograms: These visualize movement (e.g., tectonic shifts) with color fringes, each corresponding to half the radar wavelength of displacement. L-band is better for vegetated terrains due to longer wavelength and better coherence.

Orbit & Mission Profile

  • Altitude: ~747 km

  • Inclination: ~98.4°

  • Repeat: 12 days

  • Orbit Type: Sun-synchronous, 6 a.m./6 p.m. local time

  • Geometry: Left-looking

  • Orbit control: <500 m

Coverage Cadence: Entire Earth mapped every 12 days (ascending + descending = ~6-day average revisit).

Swath & Resolution:

  • Swath: ~242 km

  • Resolution: ~3–10 m (mode-dependent); ISRO cites 5–100 m

  • Achieved via SweepSAR: Transmits over full swath and “sweeps” receiving beams for wide, high-res coverage.

What Can NISAR Measure?

Biomass & Carbon:
L-band penetrates canopy, enabling estimation of woody biomass, forest degradation, and carbon stock changes — useful for climate goals like REDD+.

Ground Deformation:
Tracks earthquakes, volcanic activity, subsidence, and landslides using InSAR — valuable for disaster risk reduction.

Cryosphere:
Monitors ice-sheet flow, glacier movement, and sea-ice — vital for understanding sea-level rise.

Coasts & Wetlands:
Maps shoreline changes, mangrove extent, storm impacts — works well even in cloudy monsoon regions.

Agriculture & Water:
Tracks crop extent, health, soil moisture, and impacts of irrigation or groundwater withdrawal.

Disaster Response:
Plans to provide data within hours during emergencies. NASA’s Alaska hub and ISRO will distribute these datasets rapidly.

ISRO–NASA Cooperation & Open Data

Both agencies follow a free and open data policy.

  • NASA: Alaska Satellite Facility (ASF) DAAC is the main data hub.

  • ISRO: Will mirror and distribute data via its own portals.

This policy enhances scientific use, supports operational agencies, and aligns with India’s evolving data policy.

Launch Vehicle Family: GSLV vs LVM3

The Launcher Chosen

GSLV Mk-II:

  • Uses CE-7.5 cryogenic upper stage (LH₂/LOX, staged-combustion)

  • Fairing options: 3.4 m (metallic), 4.0 m (ogive); NISAR uses 4.0 m

  • Capacity: ~2.5 t to GTO, ~5 t to LEO

  • NISAR (~2.4–2.8 t) fits within GSLV Mk-II’s range

Differences from LVM3

LVM3 (formerly GSLV Mk-III):

  • Larger fairing: 5 m

  • CE-20 engine (~200 kN) on C25 cryogenic stage

  • Capacity: ~4 t to GTO, ~8 t to LEO

  • Used for Chandrayaan-2/3, OneWeb, and Gaganyaan

Key Comparison:

  • Engines: CE-7.5 (GSLV-II) vs CE-20 (LVM3)

  • Fairing: 4 m vs 5 m

  • Staging: GSLV Mk-II has three stages; LVM3 has two solid boosters, one liquid core, one cryo stage

Numbers at a Glance (Memorize for Exams)

  • Orbit: 747 km altitude, 98.4° inclination, 12-day repeat, SSO 6 a.m./6 p.m.

  • Antenna: 12 m reflector on 9 m boom

  • Swath: ~242 km

  • Resolution: 3–10 m typically, 5–100 m across modes

  • Frequencies: L-band 1.257 GHz (~24 cm), S-band 3.2 GHz (~9 cm)

  • Mission Duration: Baseline 3 years, goal 5 years

  • Launcher: GSLV Mk-II with CE-7.5 engine, 4 m fairing

  • Data Policy: Free and open via NASA and ISRO platforms

Likely UPSC Angles

  • Benefits of dual-band SAR over single-band (L penetrates canopy, S captures fine surface structure)

  • Concept of SweepSAR and how it resolves the swath–resolution trade-off

  • Differences between Sun-synchronous vs Geostationary orbits for Earth observation

  • Technical comparison between GSLV Mk-II and LVM3

  • InSAR applications: subsidence, faults, volcanoes, glaciers

  • Value of open data policy in supporting disaster management and scientific research

tribal genome

Decoding India’s Tribal Genome Project & the Genetic Essentials Behind It

0

What exactly is the Tribal Genome Project, Gujarat?

  • First state‑run tribal WGS initiative. Launched in July 2025 by the Gujarat Biotechnology Research Centre (GBRC) and the Tribal Development Department, the scheme will collect ≈4,158 blood samples from 20+ tribes across 17 districts and generate ~2,000 whole‑genome sequences (WGS). Sampling includes “genetic trios” (both parents + one child) to track inheritance.

  • Why?
    Fill the data gap: existing national efforts such as the 10,000‑genome GenomeIndia project pooled Indians in general, but tribal groups—8 % of India’s population—are still under‑represented.
    Precision public health: high rates of anaemia, sickle‑cell disease and infant mortality in tribal belts need variant‑specific diagnostics and drug dosing.
    Heritage science: unique lineages (e.g., the Sidi of African descent) can illuminate ancient migrations.

  • Ethics guard‑rails. The protocol follows ICMR’s National Ethical Guidelines—written consent in local languages, gender parity in sampling, and community briefings before data sharing or publication.

Static Foundations You Must Know

A. Human‑Genome Architecture

Chromosomes → Genes → DNA letters. Humans pack ~3 billion base‑pairs (A,T,G,C) into 23 chromosome pairs. A gene is a coding stretch that makes a functional RNA/protein. A single‑nucleotide polymorphism (SNP) is a single‑letter change that varies among people (≈1 in every 1,000 bases). A haplotype is a cluster of SNPs that tends to be inherited together—think of it as a “genetic sentence” you receive intact from one parent. These blocks help trace ancestry and disease risks.
 

B. Population Genetics – Founder Effect & Genetic Drift

Picture a few families founding an isolated village. The founder effect locks in whatever gene variants those few carried—rare alleles may become common just by chance. Genetic drift is this random fluctuation carried forward generation after generation, strongest in small, isolated groups (many tribal communities), gradually shaping their gene pool independent of natural selection.
 

C. Monogenic Disorders Spotlight

Sickle‑cell disease (SCD). A single A→T switch in the β‑globin gene swaps glutamic acid for valine, making haemoglobin molecules stick together when oxygen is low; red cells distort into “sickles”, causing pain crises, anaemia and organ damage. Thalassaemia. Here, whole sections of the α‑ or β‑globin genes are deleted or mutated, cutting haemoglobin production. The body tries to compensate with rapid but ineffective red‑cell turnover, leading to severe anaemia that often requires lifelong transfusions. Both disorders are common in Indian tribal belts—hence the project’s focus.
 

D. Next‑Generation Sequencing (NGS) & Reference Genomes

Workflow in four bites: 1. DNA extraction (blood sample → pure DNA). 2. Library prep (DNA chopped into small fragments and bar‑coded). 3. Sequencing (millions of fragments read in parallel on an Illumina or similar platform). 4. Data analysis (software aligns reads to the current human reference build GRCh38/hg38, flags variants, and stores them in secure databases). The Gujarat project will eventually create tribe‑specific reference panels—useful for more accurate variant calling in those populations.
 

E. Bio‑Ethics: Informed Consent, Privacy, Community Engagement

Informed consent means individuals (and often village councils) must understand purpose, risks, future data use, and their right to withdraw. Privacy & data security demand de‑identification, restricted access committees, and compliance with Biotech‑PRIDE & forthcoming Digital Personal Data Protection rules. Community engagement involves co‑designing study aims, sharing plain‑language results, capacity‑building and ensuring benefits (like anaemia screening camps) flow back. Frameworks from ICMR 2017 Guidelines and global Indigenous genomics literature emphasise these steps.
 

Why this matters for UPSC

  1. Prelims: expect factual MCQs—e.g., “What is a haplotype?” or “Which state launched the first tribal genome sequencing project?”

  2. Mains GS III (Science & Tech): link how NGS + population genetics can enable precision medicine in marginalised groups, while highlighting ethical safeguards.

  3. Essay / Interview: showcases the balance between scientific advancement and indigenous rights—excellent fodder for discussions on inclusive development.

ChatGPT Image Jun 26, 2025, 09_08_00 AM

Indian astronaut on the ISS / Gaganyaan progress

0

Historic ISS visit (June 2025)

  • Group Captain Shubhanshu Shukla became the first Indian citizen to reach the International Space Station, flying as pilot on Axiom Space’s Ax-4 mission aboard a SpaceX Crew Dragon.

  • The launch from Kennedy Space Center on 25 June 2025 ended a 41-year gap since Wing Cdr Rakesh Sharma’s 1984 Soyuz flight.

  • Besides 60 multinational experiments, India gained real-time experience with commercial crew operations—an important rehearsal for its own astronauts under Gaganyaan.

Where does Gaganyaan stand?

gaganyantab1

The human-rated LVM3/HLVM3 (adapted GSLV-Mk III) will carry three Indian astronauts for a 3-day low-Earth-orbit mission targeted for 2026, after two uncrewed dress-rehearsals.

Outer Space Treaty (1967), Moon Agreement (1979) & UN-COPUOS

Outer Space Treaty (OST), 1967

The OST is the ‘Magna Carta’ of space law. Key principles:

  1. Peaceful uses only—no stationing of WMDs in orbit or on celestial bodies.

  2. Non-appropriation—space and celestial bodies cannot be claimed by sovereignty or occupation.

  3. State responsibility & liability for all national (governmental or private) space activities.

  4. Astronauts as “envoys of mankind”; duty of rescue and return.

Moon Agreement, 1979

Extends OST principles specifically to the Moon and other bodies:

  • Declares them the “common heritage of mankind” and calls for an international regime to govern resource use.

  • Requires sharing of scientific results and notification of any station’s purpose.

  • Ratified by India in 1982, but not by major space powers—the reason exploitation rules are still debated.

UN Committee on the Peaceful Uses of Outer Space (COPUOS)

  • Set up in 1959 to frame space treaties, guidelines and capacity-building.

  • Works through two sub-committees (Scientific & Technical, Legal) that draft soft-law guidelines on space debris mitigation, long-term sustainability, planetary defence, etc.

Article 73 of the UN Charter – why is it mentioned?

Article 73 actually deals with the duties of states administering non-self-governing territories to act in the inhabitants’ interests. Although it does not speak of outer space, scholars draw an analogy: just as colonial powers had trusteeship duties, space-faring nations have fiduciary duties towards humankind when operating in the global commons of outer space. UPSC may test this conceptual link.

ISRO launch-vehicle evolution & cryogenic technology

gaganyantab2

Cryogenic propulsion (-253 °C liquid H₂/Lox) gives higher specific impulse, essential for heavy-lift and crew safety margins.

Institutional architecture: Dept. of Space, IN-SPACe & NSIL

  • Department of Space (DoS)—a direct portfolio of the Prime Minister; formulates policy and funds ISRO.

  • Indian National Space Promotion & Authorisation Centre (IN-SPACe) – autonomous single-window body (2020) that authorises, promotes and supervises private space activities, issues licences under the Indian Space Policy-2023.

  • NewSpace India Ltd. (NSIL) – DoS Public-Sector Unit (2019) that commercialises ISRO technology, markets launch services and coordinates full-vehicle production by industry consortia.
    Together, they separate regulator, promoter and operator roles, aligning with global best practice.

Draft Space Activities Bill (latest version under finalisation)

gaganyantab3

Human-factor challenges in crewed spaceflight

gaganyantab4

How to integrate in your study

  1. Prelims drill: Memorise treaty dates, firsts in launch-vehicle ladder, IN-SPACe vs NSIL roles, liability clauses.

  2. Mains angle: Use Shukla’s ISS flight as a contemporary example to evaluate India’s human-spaceflight roadmap, or to discuss private sector regulation under Space Activities Bill.

  3. Ethics paper: Trusteeship analogy from Article 73 can serve as a value-based intro on stewardship of global commons.