Image: ISRO, via Wikimedia Commons (GODL-India) — a PSLV lifts off from Sriharikota. The 12 November PS3 test was a ground firing of the third-stage motor, not a launch; this is a PSLV-C59 launch photo from December 2024.
TL;DR: ISRO PSLV third stage test explained: on 12 November 2026, ISRO successfully fired a modified PS3 solid motor on the ground at Sriharikota — the first major step toward returning the PSLV to flight after the C61 and C62 missions both failed in the third stage. ISRO has strengthened the nozzle, the seals and its quality checks, but it has not yet declared the rocket ready to fly, and further tests will follow a detailed review of the test data.
Key Highlights
- ISRO conducted a ground static test of the modified PSLV third stage (PS3) solid motor at the Satish Dhawan Space Centre, Sriharikota, on 12 November 2026 — and it passed.
- The redesign follows two consecutive PSLV failures, C61 in May 2025 and C62 in January 2026, both traced to anomalies in the third stage.
- ISRO changed the nozzle configuration, strengthened the mechanical interfaces, added redundancy to the sealing systems, and tightened raw-material acceptance, assembly procedures and non-destructive testing.
- Further tests are planned after a detailed analysis of the test data; ISRO has announced no return-to-flight date.
- The PSLV has flown 64 times with four failures in total — a success rate of about 94% — and remains ISRO's workhorse for Earth-observation and small-satellite launches.
What happened at Sriharikota on 12 November?
ISRO said on Thursday that the ground static test of the PSLV's third stage (PS3) was successfully conducted at the Static Test Facility at the Satish Dhawan Space Centre in Sriharikota. In a static test, the motor is bolted to a test stand and fired while it stays on the ground, so engineers can measure thrust, chamber pressure, vibration and temperature without risking a rocket or a payload.
The test matters because it is the first public proof that ISRO's fix for the third stage actually works. The agency said the PS3 configuration had been comprehensively reviewed after the anomalies in the PSLV-C61/EOS-09 mission in May 2025 and the PSLV-C62/EOS-N1 mission in January 2026, and that "the new version of the PS3 Solid motor stage is realised and tested successfully". The statement is careful, though: it promises further tests based on a detailed analysis and review of the test data. A successful ground firing is a milestone, not a flight clearance.
ISRO PSLV third stage test: what changed in the modified PS3 motor
ISRO's statement lists a set of changes across the motor's design, materials and manufacturing process. Here is what was changed and why each item matters.
| What changed | What ISRO said |
|---|---|
| Nozzle configuration | Improved to enhance the design margins of the stage |
| Mechanical interfaces | Strengthened, with the adequacy of the design margins verified |
| Sealing systems | Redundancy added, so a single seal problem is less likely to cause a leak |
| Raw material acceptance | Acceptance criteria reviewed and tightened |
| Assembly procedures | Procedures updated, with non-destructive tests added during integration and transportation |
| Quality checks | Design margins, assembly procedures and quality checks comprehensively reviewed |
One thing ISRO has not done is name a single root cause for the two failures, or publish the Failure Analysis Committee's report on them. That is worth stating plainly: the public record shows what went wrong in each flight — a pressure drop in C61, a roll-rate disturbance in C62 — but the detailed findings behind the redesign have not been released. The test result is the evidence ISRO is offering instead, and the next test will be whether the data holds up under the review the agency itself has promised.
Why the third stage failed twice: PSLV-C61 and PSLV-C62
The two failures are the reason this test exists. Both rockets flew normally through their first two stages and then ran into trouble in the third.
| Mission | Date | Payload | What happened |
|---|---|---|---|
| PSLV-C61 | 18 May 2025 | EOS-09, a 1,696 kg Earth-observation satellite | Chamber pressure in the PS3 motor case fell about 203 seconds into the flight; the mission could not be accomplished. PSLV's 63rd flight. |
| PSLV-C62 | 12 January 2026 | 16 satellites — EOS-N1 (DRDO's Anvesha hyperspectral satellite) plus 15 co-passengers | A roll-rate disturbance near the end of the third stage threw the vehicle off its flight path; all 16 satellites were lost. PSLV's 64th flight. |
ISRO chairman V. Narayanan said after C61 that there had been a fall in the chamber pressure of the motor case during the third stage, and after C62 that performance had been normal until the end of the third stage, "but later a roll-rate disturbance and flight-path deviation were observed". PSLV did not fly again for about eight months after C61 while ISRO reviewed the stage and tightened quality control — and then C62 failed in the same stage, which is why the November test is being watched so closely. Two failures in a row in the same stage turned a reliability question into a credibility question, and a ground test is the cheapest way to start answering it.
Illustrative image: a PSLV in flight, with strap-on boosters separating. Image: ISRO, via Wikimedia Commons (GODL-India) — PSLV-C59/PROBA-3 launch, December 2024.
Why is the PSLV third stage so hard to get right?
The PSLV is a four-stage rocket with alternating solid and liquid propulsion: a solid first stage (PS1), a liquid second stage (PS2), a solid third stage (PS3) and a liquid fourth stage (PS4). The third stage is the sprinter of the four. It ignites about 262 seconds after liftoff and burns for a planned 122 seconds, pushing the rocket's speed from about 4 km per second to about 6 km per second so it can reach the roughly 26,000 to 28,000 km per hour needed to stay in orbit.
Three things make that stage unforgiving. First, it uses a solid motor — the S7 motor, burning HTPB fuel — and once a solid motor is lit it cannot be throttled, adjusted or shut down; it burns until the fuel is gone. Second, the stage fires high in space, in very different conditions from the near-Earth environment where the first stage ignites. Third, the PS3 motor has no roll control of its own — it provides forward thrust only, and roll stability depends on the small thrusters of the fourth stage. If gas leaks from the nozzle or the motor casing, the escaping gas can spin the vehicle, and the fourth stage's thrusters may not be strong enough to stop it. That is the mechanism analysts have pointed to for both failures: a pressure loss in C61, and a roll-rate disturbance consistent with a gas leak in C62.
None of this makes the PSLV a bad rocket. Before C61 it had a long record of reliability, and its only other failures were the maiden flight in 1993 and a payload-fairing failure in 2017. But it does explain why a single stage, tested on the ground, is the right place to start: the fix has to prove itself in the motor before it can be trusted in flight.
What this means for India — and should you care?
✅ If you follow ISRO, Indian space startups or satellite launches: yes — the PSLV is the vehicle that carries India's Earth-observation satellites and most of its commercial small-satellite rideshares, and its grounding has left a gap that no other Indian rocket fills at the same price. ❌ If you were expecting a launch date: no — ISRO has announced no return-to-flight mission, and the next step is data analysis and more tests, not a countdown. ⏳ Verdict: a genuine, measured step forward. A successful static test does not erase two failures, but it is the first hard evidence that the redesigned motor works — and the honest test of it will be the next flight, not this firing. We have not tested anything ourselves; everything here comes from ISRO's statement and independent reporting.
For India, the stakes are practical as well as symbolic. The C62 failure destroyed payloads from Indian startups and academic institutions alongside DRDO's Anvesha satellite, and every month the PSLV stays grounded is a month of delayed Earth-observation data, delayed commercial launches and delayed revenue for the space startups that depend on affordable rides to orbit. The same discipline is visible elsewhere in ISRO's programme: the agency also ground-tested an upgraded third stage for its smaller SSLV rocket on 30 December 2025, firing it for 108 seconds with around 233 sensors monitoring it. For wider context on how ISRO qualifies its hardware, see our explainers on ISRO's GSLV-F19 cryogenic engine test and ISRO's plan for four launch pads by 2029.
What happens next?
ISRO's own sequence is clear: detailed analysis of the 12 November test data, a review of the findings, and then further tests. The agency has not said how many tests, when they will happen, or which mission will carry the redesigned stage first. That is the next announcement to watch for — a second successful test, or a named return-to-flight mission, would be the signal that the PSLV is genuinely back.
Until then, the honest summary is that the rocket's most troublesome stage has passed its first exam and still has more to sit. The PSLV earned its "workhorse" reputation over three decades and 64 flights; it will have to earn it again, one verified test at a time. For the latest on ISRO's other launch vehicles, see our explainer on ISRO's NVS-03 navigation satellite launch.
FAQs
What is the third stage of the PSLV?
The third stage, PS3, is the PSLV's solid-fuel S7 motor. It ignites about 262 seconds after liftoff and burns for a planned 122 seconds, accelerating the rocket from about 4 km per second to about 6 km per second so it can reach orbital speed. It is the stage that gives the rocket its final push toward orbit before the liquid-fuelled fourth stage takes over for precise satellite placement.
Why did PSLV-C61 and PSLV-C62 fail?
Both missions failed during the third stage. In May 2025, PSLV-C61 lost chamber pressure in the PS3 motor case about 203 seconds into the flight, so the engine could not produce enough thrust and the EOS-09 satellite never reached orbit. In January 2026, PSLV-C62 suffered a roll-rate disturbance near the end of the third stage, the vehicle deviated from its flight path, and all 16 satellites on board were lost. ISRO has not publicly released the Failure Analysis Committee's report or named a single root cause.
What did ISRO change in the modified PS3 motor?
ISRO improved the nozzle configuration to increase the design margins, strengthened the mechanical interfaces, added redundancy to the sealing systems, and tightened raw-material acceptance criteria, assembly procedures and quality checks — including non-destructive tests during integration and transportation. The modified motor was then fired successfully in a ground static test at Sriharikota on 12 November 2026.
When will PSLV fly again?
ISRO has not announced a return-to-flight date. The agency says further tests are planned after a detailed analysis and review of the 12 November test data, and it has not said how many tests there will be or which mission will use the redesigned stage first. A named mission and date will be the real sign that the PSLV is back in service.
Takeaway
ISRO's modified PSLV third stage has passed its first ground test after two failures in the same stage — a real step toward bringing India's workhorse rocket back, but not yet a return to flight. The test data, and the tests that follow it, will decide when the PSLV flies again.
Watch for ISRO's next statement on the test data — and if you want to see how ISRO qualifies a very different engine, read our explainer on ISRO's GSLV-F19 cryogenic engine test.
Sources
ISRO successfully conducts ground test of PSLV third stage at Sriharikota — The Tribune (ISRO statement, 12 November 2026)
After back-to-back failures, ISRO successfully tests modified PSLV 3rd stage — The Times of India (12 November 2026)
ISRO Successfully Conducts Ground Static Test of PSLV's Third Stage at Sriharikota — Republic World (12 November 2026)
ISRO successfully conducts ground static test of PSLV's third stage at Sriharikota — Devdiscourse (12 November 2026)
Behind ISRO rocket's second straight failure is a third-stage problem — The Indian Express (12 January 2026)
What do two PSLV mission failures in a row mean for ISRO? — The Hindu (January 2026)
PSLV suffers stage-3 failure in ISRO's first 2026 launch: What went wrong? — Business Standard (12 January 2026)
Why the third stage in ISRO rockets is tricky — Hindustan Times (January 2026)
ISRO Tests Upgraded SSLV Third Stage Successfully — GKToday (SSLV SS3 ground test, 30 December 2025)
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