Science and Technology Notes 03

Satellite Navigation

Satellite navigation systems are constellations of artificial satellites that provide autonomous geo-spatial positioning. A user with a small electronic receiver can determine their location (latitude, longitude, and altitude), velocity, and time with high precision. This is achieved through a process called trilateration. The receiver calculates its distance from multiple satellites by measuring the time it takes for a radio signal to travel from the satellite to the receiver. To determine a precise three-dimensional position, a receiver must be in the line of sight of at least four satellites; signals from three satellites are used to pinpoint the location, while the fourth is used to correct for timing errors in the receiver’s clock.

Major global and regional navigation satellite systems include:

• GPS (Global Positioning System) - USA: Originally named NAVSTAR GPS, it was developed by the United States Department of Defense and became fully operational in 1995. While initially for military use, it was later made available for civilian use worldwide. It operates with a constellation of over 30 satellites in Medium Earth Orbit (MEO) at an altitude of approximately 20,200 km.
• GLONASS (Global Navigation Satellite System) - Russia: A Soviet-era development, GLONASS was declared fully operational in 2011. It also uses a constellation of 24 operational satellites in MEO.
• Galileo - European Union: A global system created by the EU through the European Space Agency (ESA), it began offering initial services in 2016. It is designed for civilian and commercial use and aims to provide higher precision than GPS or GLONASS.
• Beidou (BDS) - China: China’s system evolved from a regional system (Beidou-1) to a global one (Beidou-3), which was completed in 2020. It offers global coverage with a large constellation of satellites in MEO, Geostationary Orbit (GEO), and Inclined Geosynchronous Orbit (IGSO).

NAVIC (Navigation with Indian Constellation)

• Introduction: NAVIC is an autonomous regional satellite navigation system developed by the Indian Space Research Organisation (ISRO). Its official name is the Indian Regional Navigation Satellite System (IRNSS). It was conceptualized following the 1999 Kargil War when the US denied India access to GPS data for the region, highlighting the strategic need for an indigenous system.
• Constellation and Orbits: The NAVIC constellation comprises seven operational satellites (originally IRNSS-1A to 1G). The system was later augmented with additional satellites.
  • Three satellites are placed in Geostationary Orbit (GEO) at an altitude of approximately 36,000 km. These satellites appear stationary from the Earth and are located at 32.5° E, 83° E, and 131.5° E longitudes.
  • Four satellites are placed in Geosynchronous Orbit (GSO) with an inclination of 29° to the equatorial plane. These satellites appear to trace a figure ‘8’ in the sky and are placed in two pairs in two different orbital planes.
  • This unique orbital arrangement ensures that at any given time, all seven satellites are visible to a ground receiver within the primary service area, ensuring high precision and availability.
• Services: NAVIC provides two types of services:
  • Standard Positioning Service (SPS): This is provided to all users and is primarily for civilian purposes. It operates on the L5 and S frequency bands and offers an accuracy of better than 20 meters.
  • Restricted Service (RS): This is an encrypted service provided only to authorized users, such as the military and security agencies. It is more accurate than SPS.
• Comparison: NAVIC vs. GPS

Feature	NAVIC	GPS
Coverage	Regional: India and a region extending up to 1,500 km beyond its borders.	Global: Provides worldwide coverage.
No. of Satellites	A smaller constellation of 7-8 satellites.	A larger constellation of over 30 satellites.
Orbital Altitude	Geostationary (36,000 km) and Geosynchronous (36,000 km).	Medium Earth Orbit (MEO) at approx. 20,200 km.
Positional Accuracy	SPS accuracy is better than 20 meters over the primary service area.	SPS accuracy is generally around 4.9 meters globally.
Frequency Bands	Uses L5 (1176.45 MHz) and S-band (2492.028 MHz) frequencies. This dual-frequency approach helps correct for ionospheric delay errors.	Primarily uses L1 and L2 frequencies, with modern satellites also using L5 for improved civilian service.
Cost	Significantly lower development and operational cost due to regional focus and fewer satellites.	Higher development and maintenance costs due to its global scale and larger constellation.

• Applications:
  • Terrestrial, Aerial, and Marine Navigation: Guiding vehicles, ships, and aircraft within its coverage area.
  • Disaster Management: Providing precise location information for relief and rescue operations, and disseminating warnings for natural disasters like tsunamis.
  • Vehicle Tracking and Fleet Management: Mandatory for commercial vehicles in India since 2019 for tracking purposes.
  • Integration with Mobile Phones: Several mobile chipsets from manufacturers like Qualcomm and MediaTek now support NAVIC, enabling its use in consumer smartphones.
  • Precise Timing: Distributing precise time signals, crucial for power grids, financial transactions, and communication networks.
  • Geodetic Data Capture and Mapping: Assisting in creating detailed maps and for scientific research.

GAGAN (GPS-Aided GEO Augmented Navigation)

• Introduction: GAGAN is a Satellite-Based Augmentation System (SBAS) jointly developed by the Airports Authority of India (AAI) and ISRO. It is not an independent navigation system but an enhancement system for GPS.
• Function: Its primary purpose is to improve the accuracy, integrity, and availability of GPS signals over the Indian Flight Information Region. It corrects for ionospheric disturbances, timing errors, and satellite orbit errors in the GPS signals.
• Working Principle:
  1. A network of Indian Reference Stations (INRES) across the country receives GPS signals.
  2. These stations calculate the errors in the GPS signals.
  3. The Master Control Centre (INMCC) collects this data, processes it, and generates correction messages.
  4. These correction messages are then uplinked to geostationary satellites (GSAT-8, GSAT-10, GSAT-15) which broadcast them back to receivers on aircraft.
• Application: It is primarily used for civil aviation, enabling aircraft to rely on satellite navigation for all phases of flight, including precision approaches like ‘APV 1’ (Approach with Vertical Guidance) which were previously not possible in India without expensive ground-based instrument landing systems. India is the fourth country in the world to have an operational SBAS, after the US (WAAS), Europe (EGNOS), and Japan (MSAS).

Launch vehicles of ISRO

A launch vehicle or rocket is a vehicle designed to carry a payload (such as a satellite, spacecraft, or crew module) from the Earth’s surface into space.

• Major Components:
  • Payload Fairing: A nose cone that protects the payload from aerodynamic stress and heating during atmospheric flight. It is jettisoned once the vehicle reaches a certain altitude.
  • Stages: A launch vehicle is typically composed of multiple stages, each with its own engine and propellant. Staging allows the rocket to shed dead weight (empty propellant tanks and engines) as it ascends, making it more efficient.
  • Engines: These generate thrust to propel the vehicle.
    • Non-Air Breathing Engines: These engines carry both fuel and an oxidizer on board. They can operate in the vacuum of space. Examples include solid rocket motors, liquid-propellant rocket engines, and cryogenic engines used in ISRO’s PSLV and GSLV rockets.
    • Air-Breathing Engines: These engines use atmospheric oxygen as the oxidizer, which significantly reduces the weight of the vehicle. However, they can only operate within the atmosphere. Examples include turbojets, ramjets (for supersonic speeds), and scramjets (for hypersonic speeds). ISRO successfully tested a scramjet engine in 2016.
  • VIKAS Engine: A family of liquid-fueled rocket engines developed by a team led by Nambi Narayanan at the Liquid Propulsion Systems Centre in the 1970s. It is a workhorse engine for ISRO, used in the second stage of the PSLV, as boosters and the second stage of the GSLV Mk-II, and the core liquid stage of the LVM3. It uses storable liquid propellants: Unsymmetrical Dimethylhydrazine (UDMH) as fuel and Nitrogen Tetroxide (N₂O₄) as an oxidizer.

Rocket Fuel (Propellant)

• Solid Propellants:
  • Composition: A mixture of a solid fuel and a solid oxidizer, bound together in a rubbery matrix. A common example used by ISRO is HTPB (Hydroxy-terminated Polybutadiene) which acts as both fuel and binder, with Ammonium Perchlorate as the oxidizer.
  • Advantages: They are simpler in design, relatively safer to handle and store for long periods, and provide very high thrust, making them ideal for the first stage of a rocket to overcome Earth’s gravity.
  • Disadvantages: Once ignited, they cannot be throttled (controlled) or shut down. The combustion process continues until all propellant is exhausted.
• Liquid Propellants:
  • Composition: A liquid fuel and a liquid oxidizer are stored in separate tanks and pumped into a combustion chamber where they mix and ignite.
    • Storable Liquids: Can be stored at ambient temperatures for long periods. Examples include UDMH and Mono-Methyl Hydrazine (MMH) as fuel, and Nitrogen Tetroxide (N₂O₄) or a mix of nitrogen oxides (MON) as oxidizer.
    • Cryogenic Liquids: Must be stored at extremely low temperatures. Example: Liquid Hydrogen (LH2) at -253°C as fuel and Liquid Oxygen (LOX) at -183°C as oxidizer.
  • Advantages: The flow of propellants to the engine can be controlled, allowing the thrust to be throttled up or down, and the engine can be shut down and even restarted in space. This provides greater control over the trajectory.
  • Disadvantages: They require complex plumbing, pumps, and valves, making the engines heavier and more expensive. Cryogenic propellants pose significant challenges in storage and handling due to their extremely low temperatures.

Evolution of ISRO’s Launch Vehicles

• (a) Past:
  • SLV (Satellite Launch Vehicle): India’s first experimental launch vehicle. It was a four-stage, all-solid propellant vehicle. Its first successful launch was on July 18, 1980, placing the Rohini RS-1 satellite into orbit, making India the sixth nation with orbital launch capability. This project was directed by Dr. A.P.J. Abdul Kalam.
  • ASLV (Augmented Satellite Launch Vehicle): A five-stage, all-solid propellant vehicle designed to place 150 kg satellites into Low Earth Orbit (LEO). It served as a testbed for new technologies but had a mixed success record.
• (b) Present:
  • PSLV (Polar Satellite Launch Vehicle): Known as the “workhorse of ISRO,” it is a highly reliable and versatile four-stage vehicle. The stages alternate between solid and liquid propellants (Solid - Liquid - Solid - Liquid). It has launched numerous key Indian missions including Chandrayaan-1 (2008) and the Mars Orbiter Mission (Mangalyaan, 2013). It has a capacity of 1,750 kg to a 600 km Sun-Synchronous Polar Orbit (SSPO) and 1,425 kg to a Geosynchronous Transfer Orbit (GTO).
  • GSLV Mk II (Geosynchronous Satellite Launch Vehicle Mk II): A three-stage vehicle designed to launch communication satellites into GTO. Its key feature is the indigenously developed cryogenic upper stage (CUS). Stages: Solid - Liquid (Vikas Engine) - Cryogenic. It has a capacity of about 2,500 kg to GTO and 5,000 kg to LEO.
  • LVM3 (Launch Vehicle Mark 3) / GSLV Mk III: ISRO’s most powerful launcher, often called “Bahubali”. It is a three-stage heavy-lift vehicle. Its stages are: two S200 solid strap-on boosters, the L110 core liquid stage (powered by two Vikas engines), and the C25 cryogenic upper stage. It is capable of launching 4,000 kg to GTO and about 8,000 kg to LEO. It was used for the Chandrayaan-2 (2019) mission and the upcoming Gaganyaan human spaceflight mission. It has also undertaken commercial launches, notably deploying 36 OneWeb satellites in a single mission.
  • SSLV (Small Satellite Launch Vehicle): A three-stage, all-solid vehicle with a liquid-fueled Velocity Trimming Module (VTM) for precise satellite injection. It is designed for the commercial small satellite market, offering low-cost, on-demand launch services with a quick turnaround time. It can place up to 500 kg in LEO. After an initial failure in its first developmental flight (SSLV-D1, August 2022), the second flight (SSLV-D2, February 2023) was successful.
• (c) Future:
  • NGLV (Next Generation Launch Vehicle): A futuristic, reusable rocket concept being developed by ISRO. It aims to be a three-stage, heavy-lift vehicle capable of launching 10,000 kg to GTO. It is envisioned to be cost-effective, using semi-cryogenic propulsion. A key feature will be reusability, aiming to recover and reuse the first stage, drastically reducing launch costs.
  • Scramjet Engine: A supersonic-combustion ramjet. While ramjets are limited to speeds around Mach 5-6, scramjets can operate at hypersonic speeds (above Mach 6). ISRO successfully conducted a flight test of its scramjet engine in August 2016. This technology is critical for developing future reusable launch vehicles and hypersonic cruise missiles, as it reduces the need to carry heavy oxidizers.

Cryogenic Stage

The term “cryo” refers to very low temperatures. A cryogenic rocket stage uses propellants that are liquefied and stored at extremely low temperatures.

• Propellants: The most common combination is Liquid Hydrogen (LH2) as fuel and Liquid Oxygen (LOX) as an oxidizer.
• Significance: Cryogenic engines are highly efficient and provide more thrust for every kilogram of propellant consumed compared to solid or storable liquid propellants. This high specific impulse makes them ideal for the upper stages of a launch vehicle, which are responsible for pushing heavy payloads into high-energy orbits like GTO or interplanetary trajectories.
• Challenges: The engineering of cryogenic stages is complex. It involves handling propellants at temperatures below -183°C, which poses significant thermal and structural challenges. Materials can become brittle, and preventing the propellants from boiling off requires advanced insulation and venting systems. India’s mastery of this technology with the GSLV Mk II was a major milestone, achieved after facing technology-denial regimes like the Missile Technology Control Regime (MTCR).

Prelims Pointers

• To determine a precise location, a navigation receiver needs to be in line of sight of at least four satellites.
• Global Navigation Satellite Systems:
  • GPS: USA
  • GLONASS: Russia
  • Galileo: European Union
  • Beidou: China
• NAVIC (Navigation with Indian Constellation):
  • Also known as Indian Regional Navigation Satellite System (IRNSS).
  • Developed by ISRO.
  • Constellation consists of 7 satellites.
  • Orbits: 3 in Geostationary Orbit (GEO) and 4 in Geosynchronous Orbit (GSO).
  • Coverage: India and a region extending up to 1,500 km beyond its borders.
  • Services: Standard Positioning Service (SPS) for civilians and Restricted Service (RS) for military.
• GAGAN (GPS-Aided GEO Augmented Navigation):
  • A Satellite-Based Augmentation System (SBAS).
  • Jointly developed by the Airport Authority of India (AAI) and ISRO.
  • Primary use is for civil aviation to improve GPS accuracy.
• ISRO Launch Vehicles:
  • PSLV: Four stages (Solid, Liquid, Solid, Liquid). Known as the “workhorse of ISRO”.
  • GSLV Mk II: Three stages (Solid, Liquid, Cryogenic). Features an indigenous cryogenic upper stage.
  • LVM3 (GSLV Mk III): Three stages (2 Solid boosters, 1 Liquid core, 1 Cryogenic upper stage). ISRO’s most powerful rocket.
  • SSLV: Three solid stages plus a liquid-based Velocity Trimming Module (VTM). For small satellites.
• Rocket Propellants:
  • Solid Fuel Example: HTPB (Hydroxy-Terminated Polybutadiene).
  • Liquid Fuel Example: UDMH (Unsymmetrical Dimethylhydrazine) + N₂O₄ (Nitrogen Tetroxide).
  • Cryogenic Fuel Example: Liquid Hydrogen (LH2) + Liquid Oxygen (LOX).
• Key ISRO Engines:
  • VIKAS Engine: A liquid-fueled engine used in PSLV and GSLV stages.
• Cryogenic Stage: Uses propellants (like LH2 and LOX) stored at very low temperatures. Provides high specific impulse (high efficiency).
• Air-breathing Engines: Use atmospheric oxygen as an oxidizer. Examples: Ramjet, Scramjet.

Mains Insights

1. Strategic Imperative of Indigenous Navigation Systems (GS-III):

   • Cause-Effect: The denial of GPS data during the Kargil War (1999) was a direct cause for India to expedite the development of its own regional navigation system, NAVIC. The effect is enhanced strategic autonomy.
   • Significance: Having NAVIC reduces India’s dependence on foreign systems (like GPS), which can be degraded or denied by their operators during geopolitical conflicts. It ensures guaranteed and secure positioning services for the Indian military, paramilitary forces, and critical infrastructure.
   • Geopolitical Angle: An operational navigation system is a marker of a major space power. Offering NAVIC services to SAARC nations and other neighbours enhances India’s diplomatic influence and soft power in the region, countering China’s influence via its Beidou system.
   • Economic Angle: NAVIC promotes ‘Atmanirbhar Bharat’ by creating an ecosystem for domestic hardware and software development. It has applications in logistics, transportation, agriculture, and disaster management, contributing to economic growth.

2. Evolution of ISRO’s Launch Capability: A Reflection of India’s Ambitions (GS-III):

   • From SLV to LVM3: This journey represents a systematic and incremental growth in technological capability. SLV and ASLV were about mastering basic launch technology. PSLV established India as a reliable and cost-effective launch service provider. GSLV demonstrated mastery over complex cryogenic technology. LVM3 gives India the capability for heavy satellite launches, interplanetary missions, and human spaceflight (Gaganyaan).
   • Historiographical Viewpoint: The development of ISRO’s launch vehicles can be seen as a success story of a state-led development model in a high-technology sector, driven by visionary leaders like Vikram Sarabhai and Satish Dhawan, who emphasized self-reliance and societal applications.
   • Debate: While ISRO’s success is commendable, a debate exists on whether its state-led monopoly has hindered the growth of a private space ecosystem. The recent creation of IN-SPACe and NSIL is an attempt to address this by encouraging private participation.

3. The Cryogenic Conundrum: Technology Denial and Self-Reliance (GS-III):

   • Historical Context: In the early 1990s, India had an agreement with Russia for the transfer of cryogenic engine technology. However, under pressure from the US and the MTCR (Missile Technology Control Regime), this deal was cancelled.
   • Challenge to Opportunity: This technology denial regime, intended to curb India’s missile program, became a catalyst for ISRO to develop its own cryogenic technology from scratch.
   • Significance of Achievement: Mastering cryogenic technology is a litmus test for an advanced space program. India’s success with the GSLV Mk-II’s indigenous upper stage placed it in an elite club of nations with this capability. It is crucial for launching heavier communication satellites to GTO, saving significant foreign exchange.

4. India’s Foray into the Commercial Space Market (GS-III):

   • SSLV & NGLV: The development of the Small Satellite Launch Vehicle (SSLV) is a direct response to the booming global market for small satellite launches. Its “launch-on-demand” feature aims to capture a significant share of this market. The future Next Generation Launch Vehicle (NGLV), with its focus on reusability, is designed to compete with global players like SpaceX and Blue Origin by drastically cutting launch costs.
   • Cause-Effect Relationship: The high cost of traditional launches created a demand for cheaper alternatives. This led to the rise of small satellites and the need for dedicated small launchers like SSLV. Similarly, the high cost of expendable rockets is the primary driver for developing reusable technology (NGLV).
   • Institutional Reforms: The establishment of NewSpace India Limited (NSIL) as the commercial arm of ISRO is a key policy step to move from a supply-driven model to a demand-driven one, helping ISRO focus on R&D while NSIL handles commercial aspects.