Global positioning system (GPS) is associated with 1. determining latitude and longitude 2. constellation of satellites 3. US system of GPS and Russian system of GLONASS 4. navigation Select the correct answer using the code given below : Code :

1. Basics of Earth Orbits: LEO, MEO, and GEO (basic)

To understand how Global Navigation Satellite Systems (GNSS) work, we must first understand the 'parking spots' in space where satellites reside. An orbit is a curved path that a satellite follows around Earth, maintained by a delicate balance between the satellite’s forward velocity and Earth's gravitational pull. While many satellites orbit just about 800 km above the surface and take roughly 100 minutes to circle the planet Science ,Class VIII . NCERT(Revised ed 2025), Keeping Time with the Skies, p.185, we categorize these paths into three primary layers based on their altitude. At the highest levels, specifically in Medium Earth Orbit (MEO) and High Earth Orbit (including GEO), satellites travel through the exosphere. This is crucial because the air is incredibly thin there, ensuring almost no atmospheric drag to slow the satellites down Physical Geography by PMF IAS, Earths Atmosphere, p.280. These orbits are chosen based on the job the satellite needs to do — whether it is taking high-resolution photos of the ground or providing a constant signal for your mobile GPS.

Orbit Type	Altitude Range	Key Characteristics & Use Cases
Low Earth Orbit (LEO)	160 km – 2,000 km	Satellites move very fast. Used for Remote Sensing (like India's IRS-1A) and the International Space Station Geography of India ,Majid Husain, Transport, Communications and Trade, p.56.
Medium Earth Orbit (MEO)	2,000 km – 35,786 km	The "sweet spot" for Navigation. Almost all GNSS constellations (GPS, GLONASS) reside here because it offers a wide coverage area with manageable signal delay.
Geostationary Orbit (GEO)	~35,786 km	Satellites match Earth's rotation, appearing "fixed" over one spot on the equator. Essential for Communication (like the INSAT series) and weather monitoring Geography of India ,Majid Husain, Transport, Communications and Trade, p.57.

Sources: Science ,Class VIII . NCERT(Revised ed 2025), Keeping Time with the Skies, p.185; Physical Geography by PMF IAS, Earths Atmosphere, p.280; Geography of India ,Majid Husain, Transport, Communications and Trade, p.56-57

2. Working Principle of Navigation: Trilateration (intermediate)

To understand how Global Navigation Satellite Systems (GNSS) like GPS help us find exact locations (FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Geography as a Discipline, p.9), we must look at the geometry behind it. This process is called Trilateration. Unlike triangulation, which uses angles, trilateration uses distances. Imagine a satellite as a point in space emitting a signal. Your receiver (like a smartphone) calculates how long that signal took to travel. Since the signal travels at the speed of light, the receiver can determine its distance from the satellite (Distance = Speed × Time).

Think of it this way: if you know you are exactly 20,000 km away from Satellite A, you could be anywhere on the surface of a giant imaginary sphere with a radius of 20,000 km. If you then get a distance from Satellite B, you are now on the circle where those two spheres intersect. Adding a third satellite narrows your position down to just two points. One of those points is usually impossible (e.g., deep in space), leaving the other as your precise location on Earth's coordinate system (Physical Geography by PMF IAS, Latitudes and Longitudes, p.240).

While three satellites can theoretically provide a 2D position (latitude and longitude), we typically require four satellites to calculate a reliable 3D position (latitude, longitude, and altitude). The fourth satellite is essential because it corrects the time offset between the satellite’s highly accurate atomic clock and your receiver’s much cheaper quartz clock. This high level of precision allows for advanced applications like navigating drones and heavy farming vehicles remotely (Indian Economy, Vivek Singh (7th ed. 2023-24), Agriculture - Part II, p.359) or managing missions for India's IRNSS (NavIC) constellation (Geography of India, Majid Husain, Transport, Communications and Trade, p.58).

Sources: FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Geography as a Discipline, p.9; Physical Geography by PMF IAS, Latitudes and Longitudes, p.240; Indian Economy, Vivek Singh (7th ed. 2023-24), Agriculture - Part II, p.359; Geography of India, Majid Husain, Transport, Communications and Trade, p.58

3. Indian Regional Navigation Satellite System (NavIC) (intermediate)

The Indian Regional Navigation Satellite System (NavIC), also known by its operational name IRNSS, is India's answer to the need for sovereign, high-precision positioning data. While systems like the US-based GPS provide global coverage, NavIC is an autonomous regional system designed specifically to provide accurate real-time positioning and timing services over India and an area extending approximately 1500 km around its mainland Indian Economy, Service Sector, p.434. This strategic move ensures that India is not dependent on foreign navigation systems, which could be restricted or denied during geopolitical tensions.

The architecture of NavIC is fascinating from a technical standpoint. Unlike GPS, which uses a massive constellation of 24+ satellites in Medium Earth Orbit (MEO), NavIC originally launched with a 7-satellite constellation. These satellites are positioned much higher:

• 3 satellites are in Geostationary Orbit (GEO): These appear stationary over a fixed point on the equator.
• 4 satellites are in Geosynchronous Orbit (GSO): These follow a 'figure-8' path in the sky, maintaining a constant longitudinal position over the Indian region.

This specific configuration allows the satellites to remain permanently visible over the Indian subcontinent, ensuring consistent signal strength and accuracy in the region. Between 2013 and 2018, ISRO successfully deployed several IRNSS satellites (from IRNSS-1A to IRNSS-1I) using the PSLV launch vehicle to complete this network Geography of India, Transport, Communications and Trade, p.58.

NavIC provides two primary services: the Standard Positioning Service (SPS), which is open to all civilian users, and the Restricted Service (RS), which is an encrypted signal reserved for authorized users like the Indian military. One technical advantage NavIC holds over GPS in our region is its use of dual-frequency bands (L5 and S-band). While many GPS receivers rely on a single frequency, NavIC's dual-band capability allows it to better correct for atmospheric (ionospheric) errors, potentially providing higher accuracy for Indian users in dense urban environments or mountainous terrain.

Sources: Indian Economy, Service Sector, p.434; Geography of India, Transport, Communications and Trade, p.58

4. Remote Sensing vs. Communication Satellites (basic)

To understand the vast landscape of space technology, we must distinguish between the two "workhorses" of the Indian space program: Remote Sensing and Communication satellites. Think of Remote Sensing satellites as the "Eyes in the Sky" and Communication satellites as the "Global Switchboard." While both orbit the Earth, they differ fundamentally in their purpose, orbit, and the sensors they carry.

Remote Sensing Satellites are designed to observe the Earth's surface and atmosphere. They collect data by sensing reflected or emitted radiation across various spectral bands. In India, this is managed through the Indian Remote Sensing (IRS) satellite system, which became operational with the launch of IRS-1A in 1988 NCERT Class XII India People and Economy, Transport and Communication, p.84. These satellites are typically placed in Low Earth Orbit (LEO) or Sun-synchronous Polar Orbits to get high-resolution images. Their data is vital for agriculture, monitoring forest cover, and natural resource management, with the National Remote Sensing Centre (NRSC) in Hyderabad handling the data processing NCERT Class XII India People and Economy, Transport and Communication, p.84.

Communication Satellites, on the other hand, act as relay stations. They receive signals from Earth and beam them back to other locations, enabling telecommunications, television broadcasting, and weather forecasting. The Indian National Satellite (INSAT) system is the backbone of this sector. Unlike remote sensing satellites, these are usually placed in Geostationary Orbits (GEO)—about 36,000 km above the equator—so they appear fixed over one spot on Earth. India's journey here began with the INSAT-1 series in the early 1980s Majid Husain, Geography of India, Transport, Communications and Trade, p.56.

Feature	Remote Sensing (IRS)	Communication (INSAT/GSAT)
Primary Role	Earth Observation & Mapping	Data Relay & Broadcasting
Typical Orbit	Polar/Sun-Synchronous (LEO)	Geostationary (GEO)
Key Use-Case	Natural Resource Management	Tele-education, TV, Mobile signals
Common Launcher	PSLV	GSLV (for heavier payloads to GEO)

Sources: NCERT Class XII India People and Economy, Transport and Communication, p.84; Majid Husain, Geography of India, Transport, Communications and Trade, p.56-57

5. Major Global Navigation Satellite Systems (GNSS) (exam-level)

To understand Global Navigation Satellite Systems (GNSS), we must first distinguish between the generic technology and the specific brands. GNSS is the overall umbrella term for any satellite constellation that provides geospatial positioning with global coverage. While most people use the term "GPS" colloquially, GPS (Global Positioning System) is actually the specific system owned and operated by the United States. A GNSS receiver calculates its position—specifically latitude, longitude, and altitude—by measuring the time it takes for signals to travel from multiple satellites to the device.

To achieve a precise 3D position (including altitude), a receiver generally requires signals from at least four satellites. While three satellites can provide a 2D fix (latitude and longitude), the fourth is essential to synchronize the receiver's clock with the atomic clocks on the satellites, thereby calculating height. Today, modern devices use Multi-GNSS receivers, which draw signals from various international constellations simultaneously to improve accuracy and reliability, especially in dense urban environments.

System Name	Country / Region	Status
GPS	United States	Global
GLONASS	Russia	Global
Galileo	European Union	Global
BeiDou (BDS)	China	Global
NavIC (IRNSS)	India	Regional
QZSS	Japan	Regional

India has made significant strides in this field. As noted in Geography of India, Majid Husain, Transport, Communications and Trade, p.58, India successfully deployed its own IRNSS (Indian Regional Navigation Satellite System), popularly known as NavIC, using the PSLV launch vehicle (specifically the PSLV-C22 and C33 missions). Unlike the global systems, NavIC is designed to provide accurate positioning specifically over India and the surrounding region. Additionally, India utilizes GAGAN (GPS-Aided GEO Augmented Navigation), a system developed by ISRO and the Airports Authority of India to enhance the accuracy of GPS signals for civil aviation Indian Economy, Nitin Singhania, Service Sector, p.434.

Sources: Geography of India, Majid Husain, Transport, Communications and Trade, p.58; Indian Economy, Nitin Singhania, Service Sector, p.434

6. Diverse Applications of Satellite Navigation (exam-level)

While we often think of satellite navigation simply as a tool for finding our way to a new restaurant, its professional applications are transformative. At its core, GNSS provides three critical pieces of data: precise 3D positioning (latitude, longitude, and altitude), velocity, and highly accurate timing. These pillars allow us to move from generalized management to "micro-management" across various sectors, most notably in agriculture and disaster response.

In the realm of Precision Farming, GNSS is the engine of efficiency. Unlike traditional farming where inputs are spread uniformly across a field, precision farming uses satellite data to identify and manage variability. For instance, heavy farming vehicles can be navigated remotely or autonomously to perform specific tasks, while drones equipped with GPS and sensors conduct imaging, mapping, and surveying Indian Economy, Vivek Singh (7th ed. 2023-24), Agriculture - Part II, p.359. This data allows farmers to apply water, fertilizers, and pesticides only where needed, optimizing profitability and land protection Indian Economy, Vivek Singh (7th ed. 2023-24), Agriculture - Part II, p.358.

During Disaster Management, GNSS becomes a literal lifeline. When natural calamities like tsunamis or cloudbursts strike, the landscape is often unrecognizable, rendering traditional maps useless. Satellite navigation enables the quick rescue of stranded people buried under debris and the coordination of medical help to survivors Geography of India, Majid Husain (9th ed.), Contemporary Issues, p.36. It provides the spatial data required for evacuation logistics and ensures that relief and rehabilitation measures reach the exact coordinates of the affected populations without discrimination Environment and Ecology, Majid Hussain (3rd ed.), Natural Hazards and Disaster Management, p.38.

Sector	Key GNSS Application	Primary Benefit
Agriculture	Variable Rate Technology (VRT) & Drone Surveying	Optimized resource use and increased crop yields.
Disaster Management	Real-time tracking & Search and Rescue (SAR)	Faster response times during the "Golden Hour" to save lives.
Infrastructure	Geodetic Surveying & Timing	Precise boundary delineation and synchronization of power grids.

Sources: Indian Economy, Vivek Singh (7th ed. 2023-24), Agriculture - Part II, p.358-359; Geography of India, Majid Husain (9th ed.), Contemporary Issues, p.36; Environment and Ecology, Majid Hussain (3rd ed.), Natural Hazards and Disaster Management, p.38

7. Solving the Original PYQ (exam-level)

This question beautifully brings together the building blocks of Satellite Navigation Systems you just studied. To solve this, you must synthesize the functional purpose of the technology—determining latitude and longitude—with its physical architecture, which is a constellation of satellites orbiting the Earth. As you learned in the concept modules, the term 'GPS' is often used both as a specific US system and colloquially to refer to the broader field of GNSS (Global Navigation Satellite Systems). This explains why the Russian system GLONASS is considered 'associated' here; they are the two pioneering pillars of global positioning that work toward the same goal of navigation.

When walking through the reasoning, first identify the primary function: if a system provides navigation, it must calculate coordinates (statements 1 and 4). Next, consider the infrastructure: as detailed in FAA GNSS Overview, these calculations require a constellation (statement 2) to ensure a signal is always available from multiple satellites simultaneously. The inclusion of GLONASS (statement 3) is a classic UPSC 'contextual' step—it tests whether you recognize GPS as part of a global family of technologies. Since all four statements correctly describe the identity, mechanism, comparative context, and utility of the system, the correct answer is (D) 1, 2, 3 and 4.

UPSC often sets traps by providing 'only' options like (A) or (B) to tempt students into being overly pedantic. For example, a student might think that because GPS is an American system, it has nothing to do with the Russian system. However, in the Science and Technology section, association implies the broader technological ecosystem. Modern receivers are almost always 'multi-GNSS,' meaning they use GPS and GLONASS together to improve accuracy, a point emphasized in NOAA Multi-GNSS Research. Therefore, excluding any of these points would leave you with an incomplete picture of how global positioning works in the real world.