Revision summary
GPS SPS is the open civil positioning service; PPS is the encrypted military service with better integrity. India does not control GPS and can face denial, jamming, or a time outage in a crisis. IRNSS uses seven GEO and geosynchronous satellites to cover India and a 1,500 km belt. It offers an Indian open service and a Restricted Service for authorised users. Gains are strategic autonomy, defence use, disaster and transport applications, and indigenous timing for critical infrastructure.
Model answer
Copper italics in this answer — like this — are the key facts. Each one is unpacked in the Facts & figures rail.
Introduction
Global Positioning System (GPS) is a United States satellite service that gives position, velocity, and time. It offers a civil Standard Positioning Service (SPS) and a military Precise Positioning Service (PPS). Indian Regional Navigation Satellite System (IRNSS), later called Navigation with Indian Constellation (NavIC), uses seven satellites over India. The aim is sovereign timing and location so India is not a guest on another country’s system in peace or in war.
Body
Standard Positioning System
- SPS is the open civil service of GPS: a coarse acquisition code on the civil frequency that any receiver can use without a military key.
- Typical civilian accuracy is a few metres in the open sky after Selective Availability was switched off in 2000; it is still weaker than the encrypted military service and can be jammed or degraded by the owner of the constellation.
- SPS is enough for cars, phones, fishing boats, and many survey jobs, but it is not under Indian control, and India cannot guarantee the signal in a crisis.
- Civil users also depend on GPS time for telecom, power grids, and banks; a foreign outage or denial would hit those clocks, not only maps.
Precision Positioning System
- PPS is the restricted military service: encrypted ranging codes, anti-spoof features, and higher integrity for weapons, aircraft, and authorised forces.
- Only users with cryptographic keys (mainly the United States and allies) get the full PPS; others cannot lawfully copy it.
- PPS is more jam-resistant and more accurate than SPS, which is why a regional power that fights with GPS-guided systems wants its own restricted service, not a borrowed one.
- IRNSS copies this two-layer idea: an open Standard Positioning Service for civilians and a Restricted Service for authorised Indian users, rather than renting US PPS.
Why seven satellites are enough for India
- GPS needs a global 24-plus constellation because it must cover the whole Earth; IRNSS only needs India and about 1,500 km around it.
- Three satellites in geostationary orbit and four in geosynchronous inclined orbits stay in view over the region, so seven birds can give continuous geometry that a global system would need many more satellites to match in this slice of sky.
- Dual-frequency civil signals (including L5 and S-band) help Indian receivers cut ionospheric error, which is large near the equator.
Advantages India perceives
- Strategic autonomy: the signal cannot be switched off or selectively denied by a foreign government, a lesson often linked to Kargil-era GPS dependence.
- Defence and internal security: Restricted Service can support navigation, timing, and later weapon-guidance without a US key.
- Civilian public goods: disaster warning, vehicle and rail tracking, surveying, fishing-zone alerts, and precise farming on an Indian clock.
- Critical infrastructure timing: telecom, power synchrophasors, and financial stamps can rest on an Indian primary time source, with GPS as backup.
- Industrial and diplomatic gain: Indian industry builds receivers and the ground segment (control at Hassan and a second centre), and neighbours can be offered a regional service without joining a US or Chinese global system.
- Cost and complexity stay lower than a full global constellation, which is the point of a regional seven-satellite design.
Way forward
- Finish and replenish the seven-satellite fleet, keep spare launches, and harden ground stations against cyber and physical attack.
- Mandate NavIC in public vehicles, phones sold in India, and disaster sirens so the civil SPS is actually used, not only demonstrated.
- Pair NavIC with GAGAN and later multi-GNSS chipsets so users are not blind if one system fails.
Flow diagram
flowchart TD GPS[GPS constellation] --> SPS[SPS civil open] GPS --> PPS[PPS military encrypted] IRN[IRNSS seven satellites] --> ISPS[Indian open SPS] IRN --> RS[Restricted Service] ISPS --> AUT[Sovereign PNT over India] RS[RS] --> AUT[AUT]
Conclusion
SPS is the open civil GPS fix; PPS is the encrypted military fix. IRNSS copies that split on seven regional satellites that stay over India. The advantage is not beating GPS worldwide. It is an Indian signal, Indian time, and an Indian restricted service when a foreign owner could deny or degrade GPS.
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Next question on this syllabus topic (2015 · Q12). View answer →
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Why not just keep using GPS phones?
Phones can use GPS in peacetime. A sovereign constellation is for denial, jamming, and national timing when the foreign owner’s interest is not India’s.
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Can seven satellites match GPS accuracy worldwide?
No. They are meant to serve a region well. Global coverage still needs GPS, GLONASS, Galileo, or BeiDou as complements.
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