UPSC CSE Prelims
Basics of Space Science Previous Year Questions (PYQs)

Detailed Explanation:

Correct Answer: ✅ Option 2 (Statements 2 and 3 only)

Radioisotope Thermoelectric Generators (RTGs) generate electricity from the heat released during the natural radioactive decay of isotopes. They are widely used in deep-space missions where solar power is insufficient.

❌ Statement I is Incorrect: RTGs are not miniature fission reactors. They do not use nuclear fission; instead, they generate power from the natural decay of radioactive isotopes.

✅ Statement II is Correct: RTGs are used to power spacecraft, satellites, and planetary rovers, especially in deep-space missions where sunlight is weak.

✅ Statement III is Correct: RTGs commonly use Plutonium-238, which can be produced during nuclear weapons-related processes and is specifically manufactured for civilian space applications.

Short Notes: Radioisotope Thermoelectric Generators (RTGs)

• Convert heat from radioactive decay directly into electricity using thermocouples.

• Do not involve a nuclear chain reaction or fission process.

• Common fuel: Plutonium-238 (Pu-238).

• Pu-238 has a half-life of about 87.7 years, providing long-term power.

• Ideal for missions far from the Sun where solar panels are ineffective.

• Used in missions such as Voyager 1, Voyager 2, and Curiosity Rover.

• Reliable, maintenance-free power source for decades.

• Important for deep-space exploration and planetary missions.

Detailed Explanation:

Answer: Option 1 — Only one

This question tests the knowledge of celestial objects and their correct definitions. Out of the three pairs given, only the third pair (Pulsars) is correctly matched, while the first two pairs have their descriptions reversed.

❌ Pair 1 – Incorrect: Cepheids are not giant clouds of dust and gas; they are actually pulsating stars that brighten and dim periodically, making them important distance markers in astronomy.

❌ Pair 2 – Incorrect: Nebulae are not stars that brighten and dim periodically; they are giant clouds of dust and gas in space where stars are born or remnants of dead stars.

✅ Pair 3 – Correct: Pulsars are indeed rapidly rotating neutron stars formed when massive stars exhaust their nuclear fuel and collapse in supernova explosions, emitting regular pulses of radiation.

📝 Short Notes: Celestial Objects

Detailed Explanation:

Answer: Option 3 — 1, 3, 4, 6 and 7 only

Solar storms (solar flares and coronal mass ejections) release charged particles and electromagnetic radiation that interact with Earth's magnetosphere and ionosphere, causing various technological and atmospheric disturbances. The correct effects include disruption to satellite-based navigation, power grid damage, enhanced auroral displays, satellite orbital changes, and radio communication interference.

✅ Statement 1 – Correct: Solar storms disrupt the ionosphere, causing GPS signal delays and navigation system failures.
❌ Statement 2 – Incorrect: Tsunamis are caused by seismic or volcanic activity underwater, not by solar storms which affect electromagnetic and particle environments.
✅ Statement 3 – Correct: Geomagnetically induced currents (GICs) from solar storms can overload transformers and damage power grids, causing blackouts.
✅ Statement 4 – Correct: Enhanced solar wind energizes particles in the magnetosphere, creating intense auroras visible at lower latitudes than normal.
❌ Statement 5 – Incorrect: Solar storms do not directly cause widespread forest fires; they affect electromagnetic systems, not ignition sources on such a scale.
✅ Statement 6 – Correct: Increased atmospheric drag from heating during solar storms can alter satellite orbits, especially in low Earth orbit.
✅ Statement 7 – Correct: Ionospheric disturbances disrupt shortwave (HF) radio communications, particularly affecting polar routes where ionospheric effects are strongest.

📝 Short Notes: Solar Storms and Earth Effects

• Solar Storm Components: Solar flares (electromagnetic radiation) and Coronal Mass Ejections (CME - charged particles) that reach Earth in 1-3 days.
• Magnetosphere Interaction: Charged particles compress Earth's magnetosphere, inducing geomagnetic storms.
• Ionospheric Disruption: Solar radiation alters ionosphere density, affecting radio wave propagation and satellite communications.
• Geomagnetically Induced Currents (GICs): Magnetic field fluctuations induce currents in long conductors like power lines and pipelines.
• Aurora Formation: Charged particles collide with atmospheric gases (oxygen, nitrogen), producing light displays typically at 60-70° latitude, but extending to lower latitudes during major storms.
• Space Weather Monitoring: Organizations like NOAA's Space Weather Prediction Center track solar activity to issue warnings for critical infrastructure protection.
• Historical Events: Carrington Event (1859) caused widespread telegraph failures; Quebec blackout (1989) affected 6 million people for 9 hours.

Detailed Explanation:

Answer: Option 3 — A missile is put into a stable orbit around the Earth and deorbits over a target on the Earth.

The Fractional Orbital Bombardment System (FOBS) is a nuclear weapons delivery system that launches a warhead into a low Earth orbit trajectory instead of a traditional high-arc ballistic path. The key characteristic is that the missile completes only a fraction of an orbit before deorbiting to strike its target, making it harder to detect by early warning systems designed for conventional ballistic missiles. This orbital approach allows the weapon to approach from unexpected directions and reduces warning time significantly.

❌ Option 1 – Incorrect: FOBS is not designed for asteroid defense but for delivering weapons to Earth-based targets via orbital trajectory.
❌ Option 2 – Incorrect: This describes planetary landing maneuvers, not FOBS which is specifically about weapon delivery systems orbiting Earth.
✅ Option 3 – Correct: Accurately describes FOBS as a missile placed in orbit that deorbits over a terrestrial target.
❌ Option 4 – Incorrect: This describes a comet rendezvous mission, unrelated to FOBS weapons systems.

📝 Short Notes: Fractional Orbital Bombardment System (FOBS)

• Concept: A weapons delivery system developed during the Cold War era, primarily by the Soviet Union in the 1960s
• Trajectory: Uses a low Earth orbit (LEO) path rather than a high ballistic arc, completing only a fraction of an orbit before deorbiting
• Strategic Advantage: Can approach targets from unexpected directions (including over the South Pole), bypassing radar systems oriented toward traditional ballistic missile trajectories
• Detection Challenge: Early warning systems designed to detect high-arc ballistic missiles may fail to identify low-orbit FOBS until late in the attack sequence
• Reduced Warning Time: The orbital path and lower altitude mean less time between detection and impact compared to intercontinental ballistic missiles (ICBMs)
• Modern Context: Recent reports suggest renewed interest in FOBS technology by certain nations, making it relevant to contemporary strategic discussions
• Treaty Status: The Outer Space Treaty (1967) prohibits placing weapons of mass destruction in orbit, though FOBS occupies a grey area as it doesn't complete a full orbit

Detailed Explanation:

Answer: Option 2 — 'Gravitational waves' were detected.

The merger of black holes is expected to generate powerful gravitational waves, which are ripples in spacetime caused by accelerating massive objects. Detecting these waves with instruments like LIGO (Laser Interferometer Gravitational-Wave Observatory) allows scientists to study these cosmic events even when they are too far away or obscured to observe directly with traditional telescopes. This observation opened a revolutionary new window for astronomical observations and confirmed a major prediction of Einstein's General Theory of Relativity.

❌ Option 1 – Incorrect: Higgs boson particles are detected in particle accelerators like the Large Hadron Collider (LHC), not through astronomical observations of black hole mergers.

❌ Option 3 – Incorrect: While wormholes are theoretical concepts in physics, no observation of black hole mergers has confirmed the possibility of intergalactic space travel through wormholes.

❌ Option 4 – Incorrect: While black hole mergers provide insights into extreme gravity, understanding the singularity (the point of infinite density at the center of a black hole) remains beyond current observational capabilities.

📝 Short Notes: Gravitational Waves

• Definition: Gravitational waves are ripples in the fabric of spacetime caused by violent cosmic events involving massive accelerating objects.
• Prediction: First predicted by Albert Einstein in 1916 as part of his General Theory of Relativity.
• First Detection: Directly detected for the first time in 2015 by LIGO (Laser Interferometer Gravitational-Wave Observatory).
• Sources: Merging black holes, colliding neutron stars, supernovae, and rotating neutron stars with asymmetries.
• Speed: Travel at the speed of light through spacetime.
• Significance: Opens a new field of gravitational wave astronomy, allowing observation of events invisible to electromagnetic telescopes.
• Nobel Prize: The 2017 Nobel Prize in Physics was awarded to Rainer Weiss, Barry Barish, and Kip Thorne for the LIGO detector and observation of gravitational waves.

Detailed Explanation:

✅ Statement 1 – Correct: IceCube is the world's largest neutrino detector, encompassing a cubic kilometre of ice at the South Pole.

✅ Statement 2 – Correct: It functions as a powerful telescope to search for dark matter and investigates high-energy cosmic phenomena involving black holes and neutron stars.

✅ Statement 3 – Correct: The detector is buried deep in the ice, extending from 1,450 to 2,450 meters below the surface to shield it from atmospheric interference and enhance precision.

Detailed Explanation:

Goldilocks Zone (also called habitable zone) is the region around a star where conditions are just right for liquid water to exist on a planet's surface.

Astronomers use this concept to search for Earth-like exoplanets that could potentially harbor life, making option 3 correct.

Detailed Explanation:

✅ Statement 1 – Correct: Cosmic Microwave Background (CMB) radiation is relic radiation from the Big Bang, discovered by Penzias and Wilson, providing strong evidence for the expanding universe model.

✅ Statement 2 – Correct: Redshift phenomenon shows that light from distant galaxies is stretched as they move away, demonstrating universal expansion as per Hubble's Law.

❌ Statement 3 – Incorrect: Asteroid movement is governed by local gravitational forces within solar systems and has no relevance to large-scale cosmic expansion.

✅ Statement 4 – Correct: Type Ia supernovae serve as standard candles for measuring cosmic distances, providing evidence for the universe's accelerated expansion and leading to the discovery of dark energy.