NavIC Reality Check: Clocks, Constellation, and What Actually Matters

[Amber G.]

NavIC: Degraded, Not Dead — A Technical Look at India’s Navigation System

Starting a new thread - Hopefully with Bradmin's Blessing.

There’s been a lot of noise lately around “NavIC is dead.” That framing is neither technically accurate nor particularly useful.

Let’s step back and look at what’s actually going on with NavIC from an engineering/physics/India_centric perspective.

NavIC is a regional GNSS, designed around a 7-satellite architecture (GEO + IGSO). That choice trades global coverage for lower cost, continuous regional visibility, and strong signals. The flip side is low redundancy—losing even a couple of satellites has a visible impact.

What has actually happened is fairly well understood:

Several first-generation satellites (e.g., IRNSS-1F) have suffered rubidium atomic clock failures
Without a working clock, a satellite cannot support precision navigation, even if otherwise healthy
Some satellites therefore move to limited roles (e.g., messaging, timing support)
Replacement cadence has lagged due to launch setbacks and transition to second-generation satellites

That leads to a degraded constellation, not a dead system.

A few points often missed in public discussion:

1. This is a timing problem, not a “satellite died” problem
GNSS is fundamentally about precise time transfer. Lose the clock → lose navigation.

2. Small constellations look fragile by design
Compare this with Global Positioning System or Galileo, which have ~30 satellites. They can lose several without visible impact. NavIC cannot.

3. “No NavIC = no navigation” is incorrect
Real systems—civilian and military—use multi-GNSS + inertial navigation. NavIC’s role is sovereign assurance, not exclusivity.

4. The fix is already in motion
Second-generation satellites (e.g., NVS-01) introduce:

Indigenous atomic clocks
Improved reliability
L1 compatibility for wider adoption

This is a classic first-generation → second-generation transition, not a conceptual failure.

Why this matters for defence

Even in a degraded state:

NavIC still provides regional timing backbone
Military systems rely on INS + GNSS fusion, not a single constellation
GEO satellites offer continuous visibility over India, which is valuable for timing and coordination
(India's defense is SOLID)

The real question is not “Is NavIC dead?” but:
==> How quickly can the constellation be restored, and how robust is the next generation?

If people are interested, we can dig into specifics:

Atomic clock failure modes
GEO vs MEO geometry trade-offs
Why S-band was chosen (and later corrected with L1)
Practical military usage under degraded constellation

Let’s keep this thread focused on engineering reality rather than headlines.

Notes: Questions/Criticism/Pushbacks are welcome. I will share my perspectives, Newspaper Articles/comments , and xpost some of the posts from other dhaga.

Amber G.

[Amber G.]

Sharing a piece which I wrote some time ago (my SM)
See links for various newspaper articles (Economic Times, GPS World, Deccan Herald) and other resources in the end

Big picture

-India’s NavIC is facing a temporary capability drop mainly due to atomic clock failures on multiple satellites, most recently IRNSS-1F.

1. Why atomic clocks are critical
Navigation = precise timing measurement
Satellites send time-stamped signals
Position is computed from signal travel time

Even tiny errors matter: nanosecond-level errors → meters of position error


If the atomic clock fails, the satellite cannot provide accurate navigation, even if everything else works.

2. What exactly failed
Each NavIC satellite carries 3 rubidium atomic clocks
Many early satellites used imported clocks
Several of these have failed prematurely
-IRNSS-1F lost its last working clock → no longer usable for navigation
-IRNSS-1A lost all 3 clocks (2016)
Multiple satellites have had similar issues over time
Result: satellites become “partially alive” — usable for messaging, not navigation.

3. Why this is hurting NavIC now

Navigation systems require: ≥4 satellites visible simultaneously for positioning

But: Several NavIC satellites are now degraded, Some replacements failed or underperformed
==> The constellation has dropped below optimal strength
Positioning reliability is reduced
Users must rely more on GPS or other GNSS

4. Root cause: clock reliability + dependence on imports
Early NavIC satellites used foreign-made atomic clocks
These showed reliability issues in orbit
Similar issues were also seen in Galileo (not unique to India)

Satellites themselves are otherwise healthy
It’s specifically the clock subsystem that is the weak link

5. Compounding problems
The situation worsened due to programmatic setbacks:
Replacement satellite launch failure (IRNSS-1H)
Delays in user ecosystem development
Issues with newer satellites (e.g., orbit problems in replacements)

So the constellation was not refreshed fast enough as old satellites aged.

6. Current status
NavIC is not fully dead, but degraded
Some satellites still provide signals
Others only provide limited services (messaging, alerts)
System reliability for positioning is reduced

7. The fix underway
Launch next-generation NVS satellites
Use indigenous atomic clocks
Improve reliability and add L1 compatibility

This is essentially a replacement cycle + technology upgrade

Bottom line
The crisis is real but technical, not mysterious
The core issue is atomic clock reliability, not satellite failure as a whole
NavIC is in a transition phase between generations
Recovery depends on successful deployment of new satellites

Links:
[1]Isro's NavIC down to 3 satellites: What it means for India's GPS ..."
[2]Indian Regional Navigation Satellite System"
[3]: Explainer: What is an atomic clock and why is it crucial for navigation ..."
[4] NavIC Satellite Clock Failure Explained: What It Means for India's GPS"

[Amber G.]

NavIC: India’s “jinxed” navigational program, or a cornerstone of India’s misplaced space priorities? - Ajay Lele, The Space Review

India’s NavIC (Navigation with Indian Constellation) is a regional satellite navigation system developed to provide accurate positioning, navigation, and timing (PNT) services across India and up to 1,500 kilometers beyond its borders, with plans for a further extension out to 3,000 kilometers. Originally known as the Indian Regional Navigation Satellite System (IRNSS), it has been designed, developed, and operated by the Indian Space Research Organisation (ISRO).
<snip>

]

My Take:

The article gets several things right—especially the atomic clock failures and delayed replenishment—but it overreaches in calling the system “dysfunctional.” NavIC is degraded, not dead; satellites like IRNSS-1F losing clocks affects navigation, not the entire spacecraft. In a 7-satellite regional architecture, even a couple of failures look dramatic—unlike Global Positioning System or BeiDou with large redundancy. This is a first-generation reliability + replacement cadence issue, not evidence of a flawed concept or misplaced priorities.

Selective technical critique (Points where article does not get it right/ or overstates.

1. “Only 3 satellites → system dysfunctional” (overstated)
You need ≥4 for a full position fix, yes—but:

degraded satellites still provide timing / messaging
3 satellites are sufficient for precise timing + constrained solutions
military systems combine INS + timing updates

In practice (including recent ops), impact is near-zero for mission-critical use, not system collapse.

2. “Insufficient redundancy” (misframed)
NavIC was designed with minimal satellites:

GEO + IGSO → continuous regional visibility
trade-off → low redundancy, high regional performance

This is an intentional architecture, not a design flaw.

3. “Failures show deeper systemic issues” (partly true, partly stretched)
Correct: clock reliability, replacement delays

(similar issues occurred in Galileo)

This is a known subsystem reliability problem, not unique systemic weakness.

4. “User segment failure / satellites idle” (overstated)
NavIC rollout was:
strategic-first, civilian adoption later

Ecosystem lag is normal for new GNSS systems.

5. “Misplaced priorities (Moon/Mars vs NavIC)” (weak argument)
This assumes a zero-sum model:

in reality, programs run in parallel with different resources

This is policy rhetoric, not technical analysis.

6. “Strategic vulnerability vs BeiDou” (not really)
Modern military PNT:
INS is the gold standard
GNSS provides timing correction / anti-spoofing reference

Even with partial NavIC:

-known ground reference points + timing → high accuracy maintained
-drone swarms and networks rely heavily on synchronized timing, not just position

3 satellites are enough for robust timing even under GNSS denial/spoofing

The effect is incremental degradation (at worst), Most likely NEAR ZERO disruption- not operational failure.

In Short:

The article correctly identifies real engineering and program gaps, but overstates their impact.
NavIC is degraded but still strategically useful, especially as a secure regional timing backbone, which is often the more critical function in modern military systems.

BTW - NavIC is (and increasingly will be in the near future) used as a precise national time distribution system for telecom, power, finance, and networks.

In many real-world systems, timing is actually the more critical function than positioning—which is why even a “degraded” NavIC constellation still has significant strategic value.


(I can expand on it more - if some are interested)

[Amber G.]

xpost(s) for clarity:

Is there an estimate on how many satellites in LEO orbit would be required to have at least 5 satellites overhead the Indian landmass at any given time?

It would be interesting to see how the economics stacks up this way as opposed to geosats.

Is there an estimate on how many satellites in LEO orbit would be required to have at least 5 satellites overhead the Indian landmass at any given time?

It would be interesting to see how the economics stacks up this way as opposed to geosats.

FWIW My take (Assuming the question is serious:- please read on)

Good question—but it’s not a simple apples-to-apples swap.
You can absolutely build a LEO-based regional system—but it trades:

Fewer, expensive, long-lived GEO sats
for
many, cheaper, short-lived LEO sats + higher operational complexity

That’s why most GNSS (and NavIC) chose the high-orbit route—not because LEO is impossible, but because the total system economics and stability tend to favor fewer satellites at higher altitude.

Basics:
For continuous coverage over India with ≥5 satellites visible at all times, a rough order-of-magnitude is :
~ 50 LEO satellites (depending on altitude, inclination, and elevation mask)

Why so many? LEO sats (~500–1000 km) move fast → each is visible only 5–10 minutes per pass
You need multiple orbital planes + phasing to maintain continuous overlap
And you need margin for GDOP, not just visibility.. (If you want, I can sketch a quick back-of-the-envelope constellation (planes, inclination, revisit time) to show where this about 50 number comes from )

GEO is ~40× higher orbit and much stricter insertion precision.

Economics vs GEO (like NavIC)

LEO approach:

Lower per-satellite cost, Easier launches (smaller rockets), Many more satellites (~50 vs ~7), Continuous replenishment every ~5 years -- MUCH larger ground/control complexity

GEO/IGSO (NavIC):

Very few satellites (~7), Continuous coverage over India, Long lifetimes (~10–12 years), Higher per-satellite cost, Demanding launch precision

Why wouldnt it be a serious question?

Access to space is getting easier and cost per kg is falling year on year. However, this is for lower orbits where there are lots of players. At LEO we can benefit from a smaller size satellite hopefully as power requirements are lesser for transmitted power due to closer distance, which means a smaller solar panel, antenna etc. This would translate to smaller payload. I have no idea what weight would be but perhaps PSLV could launch 2 at a time?

Although the 50 number was more than I expected, I sort of thought it to be closer to 30 for no reason. The economics wont work out in that case I would guess. If we have 3 geosats working, perhaps some sort of coverage could be worked out with lesser number of LEO satellites

>>> Detail response (ignore if not interested)

It’s a perfectly valid question—but once you run the geometry and operational constraints, the picture changes quite a bit.

My own estimate is that you’re not looking at 30–50 LEO satellites for a serious system, but closer to ~100 (order-of-magnitude) if you want continuous ≥4–5 satellite visibility with reasonable GDOP and some wartime robustness. That’s not a precise number—depends on altitude, inclination, elevation mask, etc.—but it’s the right scale.

A useful sanity check is existing systems:

Global Positioning System → ~24–31 satellites at ~20,200 km
GLONASS → ~24 satellites at ~19,100 km
Galileo → ~30 satellites at ~23,200 km
BeiDou → ~30+ (mixed MEO/GEO/IGSO)

These are at ~20,000+ km altitude, yet still need ~30 satellites globally. Drop to LEO (~500–1000 km), and:

footprint shrinks drastically
satellites move fast (minutes of visibility)
geometry degrades unless you increase numbers
AND AIR-DRAG changes orbits and needed clock and orbit position will be VERY complex and error-prone.

So for a regional system over India, maintaining continuous coverage with good geometry pushes you toward dozens → realistically ~100-class constellations.

On economics:

Yes, LEO satellites are:

smaller
lower power
cheaper per unit

But the system-level costs shift to:

many more satellites
frequent replenishment (~5-year lifetimes)
multi-plane constellation management
higher ground/control complexity

So LEO makes each satellite cheaper, but the system larger and more complex.

The wartime aspect is actually the decisive factor:

LEO sats are easier to target (lower energy ASAT)
shorter lifetimes anyway
high attrition risk
GEO sats (like NavIC at ~36,000 km):
much harder to reach
persistent coverage
fewer assets to manage

And importantly:

Managing and defending ~100 moving LEO satellites is far more complex than managing ~7 high-value GEO/IGSO assets.

Lose even a fraction of a LEO constellation and local GDOP can degrade quickly.

A hybrid approach (GEO/IGSO + some LEO augmentation) is interesting and can improve availability, but LEO does not substitute for a NavIC-type architecture—it’s a different design point entirely.

Bottom line (my take):
If you push LEO seriously for navigation-grade coverage and resilience, you’re looking at something like ~100 satellites, with MUCH higher operational burden and vulnerability. That’s exactly why most GNSS systems settled on fewer satellites at higher orbits—it’s the better balance of geometry, stability, and robustness.

— Amber G.

[Amber G.]

NaviC system is NOT Dead.
NavIC as a time distribution system
Beyond positioning, NavIC is intended to act as a regional precise time dissemination network.

In practice, this means:

Broadcasting Indian Standard Time (IST)-traceable signals from space
Allowing ground systems to synchronize to sub-microsecond (and often much better) accuracy
Providing an independent timing source, not reliant on foreign GNSS


Some practical examples:

1. Telecom networks (4G/5G)
Base stations require tight synchronization (ns–µs level)
Timing errors → dropped calls, reduced capacity

NavIC can provide trusted timing input for telecom infrastructure.

2. Power grids
Grid stability depends on phase synchronization across regions
Phasor Measurement Units (PMUs) need precise timestamps

NavIC helps maintain grid coherence and fault detection.

3. Financial systems
High-frequency trading and transaction logging require accurate timestamps
Regulatory compliance often mandates traceable time

4. Broadcasting / internet infrastructure
Network synchronization (e.g., NTP/PTP hierarchies)
TV/radio broadcast timing

Strategic angle

Using NavIC for timing gives:

Sovereignty (no dependence on Global Positioning System)
Resistance to denial/spoofing scenarios
A trusted national time backbone

Subtle but important point (which most people miss)

Even if navigation degrades:

Timing service can still remain highly usable
You don’t need full 4-satellite geometry for high-quality timing
GEO satellites (a NavIC strength) are excellent continuous timing beacons


Yes — NavIC is (and increasingly will be) used as a precise national time distribution system for telecom, power, finance, and networks.

In many real-world systems, timing is actually the more critical function than positioning—which is why even a “degraded” NavIC constellation still has significant strategic value.
- Amber G.

[Mukesh.Kumar]

AmberG-ji, thank you for starting this thread. Your posts are really appreciated for making difficult concepts simpler to comprehend without any fluff.

Interesting poits you bring out below from a system perspective:

On economics:

Yes, LEO satellites are:

smaller
lower power
cheaper per unit

But the system-level costs shift to:

many more satellites
frequent replenishment (~5-year lifetimes)
multi-plane constellation management
higher ground/control complexity

So LEO makes each satellite cheaper, but the system larger and more complex.

The wartime aspect is actually the decisive factor:

LEO sats are easier to target (lower energy ASAT)
shorter lifetimes anyway
high attrition risk
GEO sats (like NavIC at ~36,000 km):
much harder to reach
persistent coverage
fewer assets to manage

And importantly:

Managing and defending ~100 moving LEO satellites is far more complex than managing ~7 high-value GEO/IGSO assets.

Lose even a fraction of a LEO constellation and local GDOP can degrade quickly.

A hybrid approach (GEO/IGSO + some LEO augmentation) is interesting and can improve availability, but LEO does not substitute for a NavIC-type architecture—it’s a different design point entirely.

Bottom line (my take):
If you push LEO seriously for navigation-grade coverage and resilience, you’re looking at something like ~100 satellites, with MUCH higher operational burden and vulnerability. That’s exactly why most GNSS systems settled on fewer satellites at higher orbits—it’s the better balance of geometry, stability, and robustness.

[pravula]

In engineering terms, it’s no longer “fit for purpose”. U may word smith it degraded, but engineers know it’s a failed system

[Amber G.]

@Mukesh.Kumar Thanks for kind words.

****

Meanwhile, here is one more piece from Chindu (not that we need them to validate what we know): https://www.thehindu.com/news/national/ ... 783744.ece

This article follows a familiar pattern: factually anchored, but technically overstretched in interpretation. A few clear overstatements / inaccuracies

1. “Security capability reduced” (overstated)

Implies operational impact on defence is significant.

Reality:

Military PNT = INS + multi-GNSS + local references
NavIC is one layer, not the sole dependency
Impact is incremental degradation at most, not a capability loss -- practically NIL in actual practice (IMO)

2. “System unable to function” (technically inaccurate)

Suggests NavIC is effectively non-operational.

Reality:

Satellites like IRNSS-1F lost clocks → navigation degraded, not total failure
System still provides:
timing
messaging
partial geometry
- This is reduced performance, not “non-functioning”

3. “Dependence on foreign systems” (misleading framing)

Implies this is a new or critical vulnerability.

Reality:

All modern receivers are multi-GNSS by design
Even major powers use multiple constellations opportunistically

- NavIC’s role is sovereign assurance, not exclusivity

4. Ignoring small-constellation physics

Article treats satellite loss as exceptional failure.

Reality:

NavIC has ~7 satellites
Losing 1–2 → visible degradation
Compare with Global Positioning System (~30 satellites)

-This is expected behavior, not abnormal fragility

5. Lack of distinction: “satellite failure” vs “clock failure”

The nuance is lost.

Reality:

Most spacecraft are still functional
Failure is subsystem-specific (atomic clocks)

- Important because it’s a fixable engineering issue, not total satellite loss

6. Underplaying ongoing fixes

Minimal mention of:

NVS-01
indigenous clocks
L1 signal expansion

- Creates a static failure narrative, ignoring transition



Most of these reports are technically correct on failures, but conflate degradation with collapse and ignore how GNSS systems are actually used in practice.

[Amber G.]

In engineering terms, it’s no longer “fit for purpose”. U may word smith it degraded, but engineers know it’s a failed system

“In engineering terms”?
Which engineering system are we talking about—standalone civilian SPS, or actual operational PNT stacks?

Because unless we’re invoking Jihn’s Third Law of Engineering (right after thermodynamics and astrology ), “fit for purpose” depends on use case. For real systems, it’s INS + multi-GNSS + timing discipline, not a single constellation. By that standard, a degraded NavIC is still very much fit for purpose as a timing/augmentation layer.

If the claim is “not sufficient as a standalone 4-satellite navigation solution, *at this moment* ” that’s fair. Calling the whole system “failed” is just… creative definitions. /sigh/

(Hint: For all/most real-world use—civilian or military—India’s military and other users are'nt , wouldn’t have been relying solely on 4 satellites,,)

[pravula]

In engineering terms, it’s no longer “fit for purpose”. U may word smith it degraded, but engineers know it’s a failed system

“In engineering terms”?
Which engineering system are we talking about—standalone civilian SPS, or actual operational PNT stacks?

Because unless we’re invoking Jihn’s Third Law of Engineering (right after thermodynamics and astrology ), “fit for purpose” depends on use case. For real systems, it’s INS + multi-GNSS + timing discipline, not a single constellation. By that standard, a degraded NavIC is still very much fit for purpose as a timing/augmentation layer.

If the claim is “not sufficient as a standalone 4-satellite navigation solution,” that’s fair. Calling the whole system “failed” is just… creative definitions. /sigh/

(Hint: For all/most real-world use—civilian or military—India’s military and other users are'nt , wouldn’t have been relying solely on 4 satellites,,)

You can roll on the floor all you want. I am using the definition similar to https://csrc.nist.gov/glossary/term/fit_for_purpose

“that is capable of meeting its objectives or service levels”. Which per your post, this does not.

[Amber G.]

Instead of embarrassing yourself with 'roll on the floor' theatrics, let’s stick to the engineering reality you claim to champion.

You are misapplying the NIST definition. In complex systems, 'Fit for Purpose' is defined by the specific mission objective:

* Strategic Timing: NavIC is currently providing IST-traceable synchronization for telecom and power grids. In this capacity, it is 100% functional and meeting its service levels.
* PNT Stacks: For military and high-end civilian users, NavIC is an augmentation layer in a multi-GNSS/INS stack. It provides sovereign assurance even in a degraded state.

*** An example I will give:

A bridge with a load-bearing restriction is 'degraded' but still 'fit for purpose' for cars. It only 'fails' if it collapses. NavIC has multiple healthy, broadcasting satellites and is in the middle of a documented replacement cycle (NVS-01).

Calling a functioning, broadcasting constellation 'failed' because it doesn't meet your specific, narrow definition of civilian 3D-fix consistency isn't engineering—it's just creative semantics.. stunt like, as I said RG tactics which, honestly getting tiring.

As I often tell my students:
अनभ्यासे विषं शास्त्रम् (Anabhyase visham shastram) > “Knowledge without practical application is poison.” >

Stick to the physics/engineering ; it’s less embarrassing than the semantics!

[Amber G.]

xpost:

NVS-03 and 04 is planned to be launched in 2026. The failure of NVS-02 to the reach the intended orbit was studied, identified and fixed. So with these two launches, in 2026, the system will start gaining numbers.

https://indianexpress.com/article/techn ... 6-10147979

The first of the three, NVS-03, is scheduled to be launched by year-end. The other two, NVS-04 and NVS-05, will be launched after that “with a gap of six months,” as per data.

[pravula]

Instead of embarrassing yourself with 'roll on the floor' theatrics, let’s stick to the engineering reality you claim to champion.

You are misapplying the NIST definition. In complex systems, 'Fit for Purpose' is defined by the specific mission objective:

* Strategic Timing: NavIC is currently providing IST-traceable synchronization for telecom and power grids. In this capacity, it is 100% functional and meeting its service levels.
* PNT Stacks: For military and high-end civilian users, NavIC is an augmentation layer in a multi-GNSS/INS stack. It provides sovereign assurance even in a degraded state.

*** An example I will give:

A bridge with a load-bearing restriction is 'degraded' but still 'fit for purpose' for cars. It only 'fails' if it collapses. NavIC has multiple healthy, broadcasting satellites and is in the middle of a documented replacement cycle (NVS-01).

Calling a functioning, broadcasting constellation 'failed' because it doesn't meet your specific, narrow definition of civilian 3D-fix consistency isn't engineering—it's just creative semantics.. stunt like, as I said RG tactics which, honestly getting tiring.

As I often tell my students:
अनभ्यासे विषं शास्त्रम् (Anabhyase visham shastram) > “Knowledge without practical application is poison.” >

Stick to the physics/engineering ; it’s less embarrassing than the semantics!

Madam, you are the one who posted "rolling on the floor" emoji, so maybe take your own advice and stop the theatrics. As I said, you have conveniently expanded your defn of the system, by talking about system-of-systems.

Let me give you an example, so even you may understand. If my car's gearbox fails and is stuck on 2nd gear, I can still start it, go to grocery store, office and heck, can even pick up my kids. So in by your defn, its fine, nothing to see here. Show me one mechanic who will say its cool...Maybe some ivory tower academic will, but we all know thats just trying to blow smoke up someone's ....

[Amber G.]

I’ll ignore the 'ivory tower' jabs and stick to the technical facts.

First, I am not expanding the definition. I have clearly and consistently defined NavIC by its actual, documented mission parameters—which explicitly include sovereign timing and augmentation. You are the one arbitrarily shrinking the definition of the system just to force a 'failure' narrative.

Second, your car analogy is somewhat flawed. A stuck gearbox compromises a car's primary physical function: movement. A much more accurate analogy for NavIC’s current state is a car where the built-in navigation screen or the dashboard clock has stopped working.

Is it suboptimal? Yes. Would you complain to the dealer if it were under warranty? Absolutely. But standing in the driveway claiming the vehicle provides zero useful transportation and is completely 'dead' isn't the assessment of a mechanic—it’s just dramatic hyperbole.

The system is degraded, not dead. In engineering, that distinction matters.

Since this discussion is devolving into semantic gymnastics rather than engineering, I'll leave it at that. Take care.

अलम् अतिविस्तरेण (Enough with the excessive elaboration / Enough said.)

[Amber G.]

@Tanaji ( yours was a perfectly valid/serious question) and @Mukes - thanks - quoting and adding to my own:

<snip>

Managing and defending ~100 moving LEO satellites is far more complex than managing ~7 high-value GEO/IGSO assets.

Lose even a fraction of a LEO constellation and local GDOP can degrade quickly.

A hybrid approach (GEO/IGSO + some LEO augmentation) is interesting and can improve availability, but LEO does not substitute for a NavIC-type architecture—it’s a different design point entirely.

Bottom line (my take):
If you push LEO seriously for navigation-grade coverage and resilience, you’re looking at something like ~100 satellites, with MUCH higher operational burden and vulnerability. That’s exactly why most GNSS systems settled on fewer satellites at higher orbits—it’s the better balance of geometry, stability, and robustness.

— Amber G.

Moving ~100's LEO is far more complex: but as said the idea of more sats - little farther make sense!
With NavIC- architecture - We are looking at along with about 12 ( - planned - expanded from current 7 ) GEO AND about 24~ 30 of planned MEO sats (approximately 20,000 km) in the next level of our (India's) Global system)

[Amber G.]

https://indianexpress.com/article/techn ... 6-10147979

The first of the three, NVS-03, is scheduled to be launched by year-end. The other two, NVS-04 and NVS-05, will be launched after that “with a gap of six months,” as per data.

The NavIC (Navigation with Indian Constellation) system is currently in a major transition phase, moving from its first-generation IRNSS satellites to a more robust second-generation (NVS series) and eventually a global network.

As of March 2026, from what I know, here is the breakdown of the planned expansion:

1. Near Future: The NVS Series (11-12 Satellites)
In the immediate roadmap, ISRO is working to expand the constellation from its original 7-satellite design to 11 or 12 satellites.

• • Purpose: To improve redundancy and coverage.
  • The "NVS" Generation: These new satellites (NVS-01 to NVS-05) are designed to replace aging IRNSS units. They feature:

• o L1 Band: A new frequency that makes NavIC compatible with common smartphones and wearable devices.
  o Indigenous Atomic Clocks: Rubidium clocks developed in India to avoid the reliability issues seen in previous Swiss-made clocks.
  o Extended Range: The goal is to push the coverage from 1,500 km to 3,000 km beyond India’s borders.

2. Long-Term Vision: NavIC 2.0 (24–30 Satellites)
To move beyond a regional system and become a "Global Indian Navigation System" (GINS), ISRO has proposed a much larger constellation.

Current/Near Term (11–12 Satellites Regional (India + 3,000 km)
Future (NavIC 2.0) 24–30 Satellites MEO Global

While the current satellites sit "stationary" over the Indian Ocean (GEO/GSO), global systems like GPS use Medium Earth Orbit (MEO). ISRO's plan for NavIC 2.0 involves adding 12 to 24 satellites in MEO . This would allow India to provide navigation services anywhere on Earth, putting it in the same league as the US (GPS), Russia (GLONASS), Europe (Galileo), and China (BeiDou).

Summary
• Current status: 11 launched, but only 3–4 functional for active positioning.
• Next 2–3 years: Complete the 12-satellite regional "base layer" using the NVS series.
• Post-2028: Begin launching the MEO constellation for global coverage.

- Amber G.

[Lisa]

In case nobody as asked, would you care to speculate on how/why would so many Rubidium clocks fail. It just seems so odd.

[drnayar]

In case nobody as asked, would you care to speculate on how/why would so many Rubidium clocks fail. It just seems so odd.

if i remember right those clocks were imported

First Generation (IRNSS): The initial seven satellites (IRNSS-1A to 1G) launched between 2013 and 2018 were equipped with rubidium clocks imported from the Swiss manufacturer SpectraTime.
Second Generation (NVS): To achieve technological self-reliance, the Indian Space Research Organisation (ISRO) developed the Indian Rubidium Atomic Frequency Standard (iRAFS).The NVS-01 satellite, launched in May 2023, was the first to carry this home-grown rubidium clock.

To improve reliability, ISRO plans to equip future satellites with five atomic clocks instead of the original three.

SpectraTime (now Orolia/Safran) rubidium atomic frequency standards (RAFS) have experienced notable failures in space applications, specifically in Galileo and NavIC satellites. While early Galileo FOC satellites saw multiple failures, likely due to short circuits, NavIC experienced widespread failures in 1st gen satellites, leading to mission disruption.

Galileo Failures: As of early 2017, three Spirent reported and later up to 4+ RAFS clocks failed on the Full Operational Capability (FOC) satellites.
NavIC Failures: Multiple SpectraTime Rb clocks failed across India's IRNSS satellites since 2016. Reports suggested that by 2018, many of the 21 imported rubidium clocks on the first 7 NavIC satellites showed significant errors, contributing to a critically low constellation in 2026.

Despite space failures, the underlying industrial SpectraTime rubidium technology is often marketed with designed operating lives exceeding 15–20 years in less demanding applications.

[Amber G.]

Adding to above ..

In case nobody as asked, would you care to speculate on how/why would so many Rubidium clocks fail. It just seems so odd.

Lisaji - Good question, ( But in ISRO.scientists circle - everyone is asking it seriously and trying to solve this)..

From my count (one can check Google):
As of March 2026, the total number of failed imported rubidium clocks has reached 20, leaving the constellation in a sate it is.

Each of the first-generation IRNSS satellites (1A through 1I) was equipped with three rubidium clocks for redundancy. Because the failure was systemic to the specific batch of clocks provided by the European supplier, they didn't just fail individually; they often failed in "batches" on the same satellite.

The Breakdown of Clock Failures According to the latest disclosures from ISRO (recent mission updates from March 2026), here is the status of the clocks across the fleet:

IRNSS-1A 3 Defunct. All clocks failed by 2017.
IRNSS-1C 3 Defunct. All clocks failed.
IRNSS-1D 3 Defunct. All clocks failed.
IRNSS-1E 3 Defunct. All clocks failed.
IRNSS-1G 3 Defunct. All clocks failed.
IRNSS-1F 3 Recently Defunct. The final clock failed on March 13, 2026.
IRNSS-1B 2 Limping. Operating on its last clock; past its 10-year life.
IRNSS-1I Unspecified Operational. Launched in 2018 as a replacement.
Total Failures ~20+ (Includes total and partial failures.)
________________________________________

I may give my take on what's next (see next post)

The Recent 2026 Crisis: The Fall of IRNSS-1F

The most recent and significant failure occurred just days ago. IRNSS-1F, with its last remaining functional clock, finally saw that clock fail on March 13, 2026.

(This is a major blow because a navigation system requires a minimum of four functional satellites to provide a 3D position (latitude, longitude, and altitude/time correction). With the loss of 1F, the number of PNT-capable (Position, Navigation, and Timing) satellites has dropped to three: (This is causing all the hulla gulla publicly)

1. IRNSS-1B (Very old, launched 2014) - Past its expiration date
2. IRNSS-1I (Launched 2018)
3. NVS-01 (Launched 2023, uses indigenous clocks)


You mentioned it seemed odd that so many would fail. It is indeed rare for space-qualified hardware to have such a high failure rate. The reason ISRO (and Europe's Galileo, which used the same clocks) was hit so hard is that the failure was latent.

The clocks passed all ground tests, but the testing itself likely caused "stress" (suspected short circuits) that only turned into a terminal failure after the satellite spent years in the thermal cycles of space. Because the design was identical across the batch, it was essentially a "time bomb" for every satellite that carried them.

ISRO is now in a "replenishment" phase. They have successfully shifted to indigenous rubidium clocks (developed by the Space Applications Centre in Ahmedabad), which are currently powering the NVS-01 satellite. However, the launch of the next replacement, NVS-02, suffered an orbital failure in 2025, which has delayed the recovery of the full constellation.

[Lisa]

Thank you. As ever an education. May please ask "failure was latent." means what to an uneducated one.

Also, not that I have proof, the nature of failures always looks like sabotage to me. In case you did not follow,

https://en.wikipedia.org/wiki/Operation_Rubicon

[Amber G.]

Lisa - Thank you! These kind of questions are great.

Allow me to give a detail reply - My take but things can be easily checked by reportable sources.

It is a fascinating—and by all accounts frustrating—technical mystery that nearly grounded India's "Desi GPS." You aren't alone in noticing the pattern; the high failure rate of these clocks became a major point of study for both ISRO and the European Space Agency (ESA), and curious scientists like us.

The short answer is that the failures weren't necessarily a result of "bad luck" or poor satellite design by ISRO, or sabotage, but rather a systemic manufacturing flaw in a specific batch of imported hardware.

The Source of the Problem:

The atomic clocks in the first generation of NavIC (IRNSS) satellites were Rubidium Atomic Frequency Standards (RAFS) imported from a Swiss company called SpectraTime (now part of Safran).

The "oddness" you noted is explained by the fact that Europe’s Galileo constellation used the exact same clocks and suffered the exact same "sudden death" syndrome. At one point, *many* clocks in the Galileo fleet had failed, mirroring the crisis in the NavIC constellation where multiple satellites (like IRNSS-1A) lost all three of their redundant clocks.

Why did they fail? (My Take )

While space agencies are often tight-lipped about exact post-mortem details for proprietary reasons but we know that:

The "Short Circuit" Theory: The most likely technical cause identified by ESA was a latent short circuit in the clock's electronic circuitry. Specifically, it was suspected that a particular ground testing procedure performed before launch was too strenuous, creating microscopic stress or damage that only manifested as a total failure after several months in the harsh environment of space.

Tin Whiskers: In the world of high-reliability electronics, "tin whiskers" are a recurring nightmare. These are microscopic, needle-like filaments of tin that spontaneously grow from lead-free solder. In a vacuum, these whiskers can bridge gaps between circuits, causing a short. If the SpectraTime batch had a specific plating issue, it could explain why so many clocks failed in a similar window.

The "Power Cycle" Bug: It was discovered that some clocks failed specifically after being turned off and then back on. In space, parts "outgas" or undergo thermal expansion/contraction. If a clock is powered down, the internal temperature shift can cause a marginal connection to finally snap or a "whisker" to make contact.

How NavIC is Fixing It

ISRO didn't just wait for the Swiss manufacturer to fix the issue. They took a "never again" approach:

1. ISRO developed its own Indigenous Rubidium Atomic Clock. The first of these was successfully launched on the NVS-01 satellite in 2023 and has been performing well.
2. Newer satellites are being designed to carry more clocks or different types to ensure that a single batch-related flaw can't wipe out an entire satellite's utility.
3. Following the Galileo investigation, mission controllers changed how they "handshake" with the clocks in orbit, avoiding unnecessary power cycles to keep the delicate internal physics stable.

It really highlights the "single point of failure" risk in global supply chains—even for something as advanced as an atomic clock.

If people like to know more about how these indigenous clocks differ from the imported ones I can put something here from what I know,

[Lisa]

"If people like to know more about how these indigenous clocks differ from the imported ones I can put something here from what I know"

Please if you could.

Also, anything to say on Cesium clocks and their Indian development?

[Amber G.]

^<deleted by author>

[Amber G.]

"If people like to know more about how these indigenous clocks differ from the imported ones I can put something here from what I know"

Please if you could.

Also, anything to say on Cesium clocks and their Indian development?

From what I know :

The "oddness" of the Rubidium (Rb) clock failures in NavIC (and Europe’s Galileo) has fundamentally changed how space agencies approach timing. And IMO, ISRO is no longer just "looking" at advances—it is in a race to deploy them.

Here is the breakdown of the technical advances currently being planned or researched for NavIC (and other Global Navigation Satellite Systems (GNSS) for perspective.) .

1. NavIC’s Immediate "Fix" - The indigenous Rubidium Atomic Frequency Standard (iRAFS).

• The "Anti-Fragile" Design: Unlike the hyper-miniaturized Swiss clocks that failed, the Indian iRAFS is significantly more robust. It is roughly twice the mass (~7.6 kg) and consumes more power (~40 W). This "over-engineering" provides better thermal inertia, making the clock less sensitive to the extreme temperature fluctuations of space that likely triggered the original short circuits.

• Triple-Clock Redundancy: New NVS-series satellites (like NVS-01) now carry a hybrid suite of up to five clocks (a mix of indigenous and modified imported ones) to ensure that a single batch-related manufacturing flaw cannot take down a whole satellite again

.

2. ISRO’s Next Step: Passive Hydrogen Masers (PHM)

While Rubidium is the workhorse, ISRO’s Space Applications Centre (SAC) is actively developing Passive Hydrogen Masers.

• Rubidium clocks drift by about 1 second every 10 million years; PHMs are 10 times more stable. By adding PHMs to future NavIC satellites, India can achieve "Galileo-level" precision, which is critical for high-end military applications and autonomous drone navigation.

• PHMs are traditionally much larger and heavier than Rubidium clocks. ISRO is working on "space-qualifying" a compact version that fits the standard satellite bus.

3. Global GNSS Advances (2026 and Beyond)
Other major systems are also moving toward technologies.

Digital Atomic Clocks GPS III (SV10) / Moves signal processing from analog to digital, reducing "noise" and improving jam-resistance.
Mercury Ion Clocks Galileo (G2) / Far more stable than Rubidium and less sensitive to magnetic fields or temperature.
Iodine Optical Clocks Galileo (G2) /Uses laser-trapped atoms; potentially 100x more accurate than current standards.
Nuclear Clocks GLONASS (Russia) / Targets a stability of $10^{-20}$. These use nuclear transitions rather than electron transitions, making them virtually immune to external interference.

4. Why the shift to "Optical" and "Digital"?
The reason so many clocks are failing or being replaced isn't just about reliability; it's about Strategic Autonomy.
- Higher clock stability allows for much "narrower" signal bands, which are significantly harder for adversaries to jam or spoof.
-Intersatellite Links (ISL): GPS III and Galileo G2 are now using Optical Crosslinks (lasers) to talk to each other. If a ground station is destroyed or jammed, the satellites can "sync" their clocks with each other in space, maintaining a perfect time grid without any input from Earth for weeks.

Current Status Check

With the loss of IRNSS-1F, the NavIC constellation is currently at a critical 3-satellite minimum. ISRO has three replacement satellites (NVS-03, 04, and 05) scheduled for launch later this year. These will be the true test for the new indigenous clock architecture.

[Lisa]

Thank you. You have already answered the next 2 questions, Passive Hydrogen Masers and Intersatellite Links. On a tangent from Intersatellite Links, I am assuming Earth Links are also made as planetary stability can be taken advantage of both for correction and maybe redundancy, as in mirroring?

[Amber G.]

Sharing Swarajyamag's detailed article:
NavIC's Clock Crisis, And The Indian Clocks That Could Fix It

[SriniY]

Slightly off topic but there is a strong interest in LEO based PNT systems with constellations of hundreds of satellites.

One example is the proposed Pulsar constellation from Xona.
https://www.businesswire.com/news/home/ ... Navigation

Another example is the European Ublox
https://insidegnss.com/u-blox-explores- ... te-launch/

[Amber G.]

Slightly off topic but there is a strong interest in LEO based PNT systems with constellations of hundreds of satellites.

One example is the proposed Pulsar constellation from Xona.
https://www.businesswire.com/news/home/ ... Navigation

Another example is the European Ublox
https://insidegnss.com/u-blox-explores- ... te-launch/

Thanks. This is absolutely — not off-topic. In the context of the current "NavIC Reality Check" thread, LEO-PNT is the logical technical evolution for several reasons:

Allow me to expand the links you gave:

- Xona Space Systems: They are developing the Pulsar constellation. The referenced news notes a major funding milestone ($170M Series C) aimed at deploying a high-performance satellite navigation service that promises better security and precision than legacy systems.

u-blox: The European chipmaker is exploring LEO PNT integration following the ESA "Celeste" launch. Their focus is on how user-end hardware can leverage these new signals for faster, more resilient positioning.

----
(Many points we have discussed before - but stating again):

- Solving the "Clock" Problem: Traditional GNSS relies on ultra-stable (and expensive) atomic clocks because the satellites are 20,000 to 36,000 km away. LEO satellites are much closer (500-2,000 km), which allows for stronger signals and potentially different timing architectures that could mitigate the "sudden death" clock issues discussed earlier in the thread

Signal Strength & Anti-Jamming- Because LEO satellites are closer to Earth, their signals can be significantly stronger (~1,000 times or more) than MEO/GEO signals. This makes them much harder to jam or spoof—a critical requirement for the sovereign "strategic assurance" India seeks with NavIC.Rapid Refresh Cycles: As noted in the forum posts, NavIC has struggled with a slow replenishment cadence.

LEO constellations use smaller, cheaper satellites with shorter lifespans (5 years), allowing for much faster technology insertion. If a batch of clocks fails, a LEO system can be updated with new hardware much more quickly than a GEO-based one.Integrating a LEO augmentation layer into NavIC (a hybrid approach) would likely solve many of the geometry and reliability issues I was describing .

----
From what I know, in future roadmaps of ISRO's NavIC 2.0 the role of LEO/MEO is evolving from a research concept into a strategic augmentations layer. I may post (or someone else may like to do that) what I know later.

[Amber G.]

^^^
The current and future roadmaps for ISRO’s NavIC (Navigation with Indian Constellation), the role of Low Earth Orbit (LEO) is evolving from a research concept into a strategic augmentation layer.

Based on current technical discussions and ISRO's developmental trajectory (from what I know) here is how LEO fits into the roadmap:

1. The Current Roadmap (Transition to NVS Series)

The immediate priority is the NVS (Navigation Vehicle System) series, which is focused on stabilizing the existing 7-satellite regional constellation. In this phase, LEO is not a primary orbital slot for the core constellation.

• The MEO Shift: Instead of jumping to LEO for the main constellation, ISRO's "NavIC 2.0" vision primarily targets Medium Earth Orbit (MEO). To transition from a regional to a global system (Global Indian Navigation System - GINS), ISRO plans to launch 24 to 30 satellites in MEO (at ~20,000 km), similar to GPS or Galileo.

• LEO as a "Space Service" User: Currently, NavIC satellites in GEO/IGSO provide positioning for LEO satellites themselves (like the IRS series or Gaganyaan).

2. Future Roadmap: LEO-PNT Augmentation
While the core of NavIC 2.0 is MEO-based, ISRO is actively exploring LEO-PNT (Positioning, Navigation, and Timing) as a "resilience layer." Its roles include:

• Signal Strengthening: Because LEO satellites are closer to Earth (500–2,000 km), their signals are much stronger than MEO signals. This is critical for anti-jamming and providing deep-indoor or "urban canyon" coverage—a major goal for the 2028–2030 timeframe.

• Rapid Geometry Change: LEO satellites move much faster relative to the Earth's surface than GEO or MEO satellites. This helps receivers achieve a Faster Time to First Fix (TTFF) and improves the accuracy of Precise Point Positioning (PPP).

• Intersatellite Links (ISL): Future NavIC 2.0 satellites are expected to use laser-based ISLs to communicate with LEO constellations. This would allow the navigation system to remain synchronized and operational even if ground control stations are compromised (sovereign assurance).

3. Comparison of Orbital Roles in NavIC 2.0

Code: Select all

Feature	GEO/IGSO (Current)			MEO (Future Core)	LEO (Planned Augmentation)
Primary Role	Regional/Timing Backbone		Global Coverage	Signal Resilience & Urban Accuracy
Altitude		about 36,000 km			about 20,000 km	~500 - 1,000 km
Status		Operational/Replenishing		Planned (Post-2028)	R&D / Demonstration Phase
Advantage	High Persistence over India	Full Global Utility	High Signal Power / Anti-Jam

Summary: In the NavIC 2.0 roadmap, LEO is an "Augmentation Layer" rather than a replacement. ISRO's strategy is a Multi-Orbit Architecture:
1. GEO/IGSO for regional timing and persistent strategic coverage.
2. MEO for global civilian and military navigation.
3. LEO for high-accuracy, jam-resistant signals to support autonomous systems and 5G/6G timing.

[drnayar]

https://arxiv.org/html/2502.06083v1

Geolocation with Large LEO Constellations: Insights from Fisher Information

[drnayar]

Emerging LEO Integration for the Army

To address the vulnerabilities of traditional geostationary systems, the Indian Army is transitioning toward LEO-based architectures:

Military Communication: The Indian Army Central Command has partnered with BSNL to deploy high-speed internet in remote and high-altitude regions using a LEO satellite constellation.

Resilient PNT (Positioning, Navigation, and Timing): Indian startups like VyomIC are developing private LEO constellations (125–150 satellites) designed to be jamming-resistant and provide sub-meter accuracy.

Space-Based Surveillance (SBS-III): A massive project is underway to launch 52 dedicated military satellites by 2029. These will operate in a multi-orbit configuration, including LEO, to provide real-time AI-backed surveillance of border regions.

[Amber G.]

sharing:
US Space Force's Broken OCX GPS Faces Cancellation After 16 Years And $8 Billion Of Investment

[Amber G.]

Sharing: What if GPS dies? Why USS Abraham Lincoln's crew still uses 18th-century system to steer a warship