Question map
"The experiment will employ a trio of spacecraft flying in formation in the shape of an equilateral triangle that has sides one million kilometres long, with lasers shining between the craft." The experiment in question refers to
Explanation
The correct answer is Option 4: Evolved LISA (eLISA). This mission, led by the European Space Agency (ESA), is designed to detect gravitational waves from space.
- Why Option 4 is correct: eLISA involves three spacecraft arranged in a massive equilateral triangle formation with sides approximately one million kilometers long. These craft will exchange laser beams to measure minute changes in distance caused by passing gravitational waves, acting as a giant space-based interferometer.
- Why other options are incorrect:
- Voyager-2 and New Horizons are deep-space probes designed for planetary exploration (outer planets and Pluto), not formation flying for wave detection.
- LISA Pathfinder was a successful technology demonstrator mission using a single spacecraft to test the feasibility of the instruments; it did not involve the three-craft triangular formation described.
Thus, the specific configuration of a million-kilometer triangle using laser interferometry uniquely identifies the Evolved LISA mission.
PROVENANCE & STUDY PATTERN
Full viewThis question rides the wave of the 2015 Gravitational Wave discovery (LIGO). It tests if you know the 'next big step' in that field. It is a classic 'Mission Architecture' question—UPSC didn't ask *what* it studies, but *how* it looks physically (triangle, lasers). Fair for anyone tracking major global science projects.
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: Is Voyager-2 the experiment that will employ a trio of spacecraft flying in formation as an equilateral triangle with sides one million kilometres long and lasers shining between the craft?
- Statement 2: Is New Horizons the experiment that will employ a trio of spacecraft flying in formation as an equilateral triangle with sides one million kilometres long and lasers shining between the craft?
- Statement 3: Is LISA Pathfinder the experiment that will employ a trio of spacecraft flying in formation as an equilateral triangle with sides one million kilometres long and lasers shining between the craft?
- Statement 4: Is Evolved LISA the experiment that will employ a trio of spacecraft flying in formation as an equilateral triangle with sides one million kilometres long and lasers shining between the craft?
- Describes the Laser Interferometer Space Antenna (LISA) as three spacecraft forming an equilateral triangle.
- Specifies side length in the passage as millions of kilometres (5 million km), showing the multi‑million‑km scale of the experiment the statement refers to.
- States the configuration uses interferometers operated with infrared laser beams — i.e., lasers shining between the spacecraft.
- Gives the inter-spacecraft distances as 5×10^9 m (5 million km), confirming the multi‑million‑kilometre baselines.
Describes Voyager probes as individual deep-space spacecraft that communicate with NASA's Deep Space Network, implying single-probe operations rather than a planned multi-spacecraft formation experiment.
A student could combine this with the basic fact that formation missions usually involve purpose-built, contemporary small spacecraft, to doubt that a 1977 probe like Voyager-2 is part of a new triangular laser-formation experiment.
Gives Voyager/other probe launch dates, mission objectives and current distances (AU), showing Voyager is a long-travel single probe with a decades-old mission profile.
Using a world/solar map and those distances, a student could judge the practicality and likelihood of re-tasking an ageing, solitary interstellar probe into a coordinated three‑craft laser formation with million-kilometre baselines.
Explains simple laboratory use of lasers and safety, showing lasers are terrestrial experimental tools and used under controlled supervision — not evidence of spaceborne million‑km laser links but establishes what 'laser experiment' entails.
A student can combine this with standard knowledge that space lasers for inter-spacecraft links require specialized hardware and planning, making it plausible to question whether Voyager-2 (a 1970s probe) would host such a system.
Contains a clear visual/example of a triangle used in a historical mathematical/diagrammatic context, providing a simple geometric reference for 'equilateral triangle formation' as a conceptual pattern.
A student could use basic geometry and maps to assess the scale (one million km sides) against known spacecraft separations and conclude whether Voyager‑2 could plausibly be part of such a formation.
- Explicitly states three spacecraft form an equilateral triangle with multi-million-kilometre sides (matching the 'trio' and 'equilateral triangle' parts of the claim).
- Identifies the configuration in the context of a laser interferometer mission (implying lasers between craft).
- Clearly describes 'The LISA mission consists of 3 spacecraft forming a laser interferometric antenna', tying the three-spacecraft triangle to laser interferometry.
- Gives the baseline as 5×10^9 m (5 million km), confirming the 'million-kilometre' scale.
- Specifies Michelson-type interferometers 'operated with infrared laser beams', directly supporting the 'lasers shining between the craft' element.
- States the distances between spacecraft as 5×10^9 m, again confirming the multi-million-kilometre separation.
This snippet identifies New Horizons as a single spacecraft launched in 2006 that flew past Pluto and is travelling through the Kuiper belt (~53 AU as of Jan 2022).
A student can extend this by noting New Horizons is described as one probe (not a trio) and, using basic mission-type knowledge and distances, judge whether a three-spacecraft, million-kilometre formation is consistent with a known single-probe mission.
This snippet lists 'major artificial objects that have achieved escape velocity' — a pattern of cataloguing individual distant spacecraft.
A student could compare examples of such distant missions (usually single probes) to the claim of a coordinated three-spacecraft experiment and infer whether multi-spacecraft million-km formations are typical for these distant-object missions.
This classroom snippet demonstrates the use and safety considerations of lasers and shows lasers produce visible straight beams in short-range lab setups.
A student can extend this by recalling basic optics and practical limits of lasers over large distances and ask whether lab-scale laser behavior and safety guidance make million-kilometre inter-spacecraft laser links plausible without additional technical evidence.
Gives a simple rule/example about lasers: they travel in straight paths and are used in controlled experiments.
A student could combine this with the idea that long-baseline space interferometers require lasers between craft to judge plausibility of lasers spanning large inter-spacecraft distances.
Mentions 'major artificial objects' that have achieved escape velocity, illustrating that spacecraft can travel and operate beyond Earth orbit.
A student could use this to infer that space missions have the capability to place multiple craft into distant heliocentric orbits where long baselines might be established.
Describes the Stardust project and asks about which agency launched it and what it collects — an example of a targeted scientific space mission.
A student could treat Stardust as an example that specialized science missions (not just satellites) are launched, supporting the plausibility of a dedicated experimental mission like LISA Pathfinder.
Lists multiple launch events and space missions, showing nations routinely launch complex spacecraft.
A student could extend this to note that repeated launches and mission diversity make multi-spacecraft experiments technically plausible.
Notes national space development and lunar probe planning, indicating development of advanced space programs.
A student might use this to argue that advanced space agencies could undertake coordinated formation-flying missions.
Mentions the Laser Interferometer Gravitational-Wave Observatory (LIGO), showing that laser interferometry is a known method to sense gravitational waves.
A student could extend this by noting that interferometric detection can be done with separated platforms (not just ground instruments) and therefore plausibly implemented by multiple spacecraft linked by lasers to create long baselines.
Gives a simple experimental note that lasers follow straight paths and are used in classroom/light experiments, illustrating lasers as practical tools for precise distance/beam measurements.
A student could combine this with the interferometry clue (snippet 8) to infer that lasers between distant spacecraft could serve as precise measurement links for a space-based interferometer.
- Bullet 1. [THE VERDICT]: Sitter for S&T enthusiasts; Trap for those who only read headlines. Source: Standard Science & Tech Current Affairs (The Hindu S&T page/NASA press releases).
- Bullet 2. [THE CONCEPTUAL TRIGGER]: Gravitational Wave Astronomy. The 2015 LIGO breakthrough made this a permanent high-yield theme. The logical progression is Ground (LIGO) → Space (LISA).
- Bullet 3. [THE HORIZONTAL EXPANSION]: Memorize architectures of other Mega-Science missions: James Webb (L2 point, honeycomb mirror), Euclid (Dark Energy, L2), Aditya-L1 (Halo orbit, coronagraph), and SKA (Square Kilometre Array - Radio astronomy).
- Bullet 4. [THE STRATEGIC METACOGNITION]: Don't just memorize the *objective* (e.g., 'detects gravity waves'). Memorize the *mechanism* (e.g., 'interferometry via three spacecraft'). Visualizing the mission profile is crucial for S&T questions.
Voyager-2 is a long-duration space probe launched in 1977 that has left the heliosphere and explores outer planets and interstellar space.
High-yield for UPSC: understanding flagship robotic missions clarifies India's and global space exploration context, technology progression, and policy implications. Links to topics on space policy, planetary science, and international cooperation in deep-space missions; enables answers comparing mission objectives and milestones.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > 2.8. Distant Artificial Objects Exploring the Solar System > p. 39
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > 2.8. Distant Artificial Objects Exploring the Solar System > p. 40
Deep Space Network is the global ground infrastructure used to communicate with distant probes like Voyager-2.
Important for questions on space infrastructure and mission operations: explains how distant spacecraft are tracked, commanded, and receive/return data. Connects to telecommunications, satellite ground segments, and disaster/resilience planning for critical infrastructure.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > 2.8. Distant Artificial Objects Exploring the Solar System > p. 39
Laser beams travel in straight paths and require safety precautions when used, as taught in simple classroom experiments.
Useful for optics and experimental-method questions: covers fundamental properties of coherent light, practical safety norms, and the limits of simple demonstrations versus large-scale laser applications. Helps frame answers on sensor technology and instrument design in space missions.
- Science-Class VII . NCERT(Revised ed 2025) > Chapter 11: Light: Shadows and Reflections > Activity 11.1: Let us investigate > p. 156
New Horizons is a Pluto/Kuiper Belt flyby probe whose purpose and current trajectory determine what kinds of experiments it can perform.
Understanding specific mission types (flyby vs. dedicated formation-flying mission) helps answer questions that conflate different spacecraft capabilities; space missions are frequent UPSC targets linking science & technology to policy and exploration strategy. Mastering mission objectives enables quick elimination of implausible claims about capabilities.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > 2.8. Distant Artificial Objects Exploring the Solar System > p. 40
Knowledge of which artificial objects achieve escape velocity clarifies which probes leave the Solar System and their possible operational regimes.
Questions often require distinguishing probes that remain in the Solar System from those that become interstellar; this concept ties orbital mechanics to space exploration history and helps reason about mission limits and design.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > 2.8. Distant Artificial Objects Exploring the Solar System > p. 39
Lasers propagate as narrow beams and have safety and operational constraints relevant to any proposal of laser links between distant spacecraft.
Optics basics (laser behaviour, safety, applicability) are useful for evaluating technological feasibility in exam scenarios linking science and technology; this enables reasoned critique of experimental claims involving lasers.
- Science-Class VII . NCERT(Revised ed 2025) > Chapter 11: Light: Shadows and Reflections > Activity 11.1: Let us investigate > p. 156
Lasers propagate in straight paths in transparent media and require caution because they can cause eye damage.
High-yield for questions on instrumentation and remote sensing: understanding laser behavior links optics fundamentals to practical uses in space technology and experimental design. Helps answer questions about measurement systems, communication links, and safety protocols in scientific missions.
- Science-Class VII . NCERT(Revised ed 2025) > Chapter 11: Light: Shadows and Reflections > Activity 11.1: Let us investigate > p. 156
LIGO-India (IndIGO): Since LISA is the space component, the next logical question is the Indian ground component. Fact: LIGO-India is being constructed in Hingoli, Maharashtra. It will be the third node in the global LIGO network to help triangulate the source of gravitational waves.
Use the 'Name vs. Function' logic.
1. Voyager & New Horizons are 'probes'—they fly *away* alone. A 'trio in formation' implies a fixed structure, impossible for a lone traveler. Eliminate A & B.
2. 'Pathfinder' implies a prototype/test (usually smaller/simpler). The description 'million km sides' sounds like the full-scale operational observatory. 'Evolved' fits the grand scale better than 'Pathfinder' (which was actually a single craft).
Mains GS-3 (Technology) ↔ GS-2 (International Relations): Mega-science projects like LISA, ITER, and TMT are vehicles for 'Science Diplomacy.' Participating in them (like India in LIGO) grants access to cutting-edge proprietary tech (cryogenics, lasers) that has dual-use applications in defense and industry.