On May 18, 2025, the PSLV-C61 mission was a rare launch failure for the Indian Space Research Organization (ISRO). The rocket has a reputation as a ‘workhorse’ as ISRO had many successes with it and each of those launches was completely fit for purpose. However, today ISRO is facing two consecutive PSLV mission failures after the apparent non-completion of the PSLV-C62 mission.
On January 12, about 50 minutes after the PSLV-C62 mission lifted off at 10.17 am from Sriharikota, ISRO Chairman V. Narayanan confirmed that there had been an anomaly in the rocket’s third stage. He said ISRO will further analyze the performance of the platform and come back with more details.
PS3 solid motor
The PSLV rocket has four stages. The C61 mission saw the rocket in its XL configuration, with six boosters on its first stage. Its primary payload was the EOS-09 (aka RISAT-1B) satellite, a heavy radar-imaging satellite designed to observe the Earth’s surface in all weather conditions, and was to be used for disaster response and strategic surveillance. The rocket was to place it in a sun-synchronous polar orbit at an altitude of about 529 km.
Lift-off was normal. The first and second stages performed nominally according to plan and the rocket was on the correct trajectory in these stages. This anomaly occurred while the third stage, PS3 – a motor using solid fuel – was operating.At approximately 203 seconds into flight, telemetry data indicated a sharp and unexpected drop in motor chamber pressure within the third stage motor.The deceleration resulted in the engine not being able to generate the required thrust, causing the rocket to not reach its intended orbit. ISRO then aborted the mission and the rocket, along with the EOS-09 satellite, fell back.
Following the incident, a Failure Analysis Committee (FAC) worked and (presumably) determined the problem to be the PS3 solid motor system. The specific fault appears to be a structural or physical failure within the third stage nozzle or casing system, which led to a loss of pressure. Questionable system? A possible problem with the flex nozzle control system or insulation lining, which failed to contain the pressurized gases, effectively inhibiting engine power.
ISRO also responded by halting all PSLV launches for approximately eight months while it implemented strict quality control measures and strengthened the third stage design.
Failure Analysis Committee Report
Note the use of words like “likely”, “presumably”, “appears”, “suspected”, etc. in the previous paragraph – they are not accidental. This is because ISRO comes under the Department of Space, which comes under the Prime Minister’s Office (PMO). The FAC submitted its report to the PMO, but the PMO has not approved the report to be released publicly.
The most plausible reason for secrecy is not the rocket but the payload. EOS-09 (RISAT-1B) was a military-grade synthetic aperture radar asset. ISRO has released detailed failure reports for other rockets, such as when the cryogenic engine of the GSLV-F10 mission failed relatively early. A full failure report would need to disclose the satellite’s exact flight profile and deployment sequence. And what is technically a spy satellite, revealing how it broke up or what debris survived reentry, could reveal classified material technologies or specific orbital intent that the military wants to keep from the public record.
But this is not the complete picture. ISRO is aggressively pursuing PSLV as a commercial product through NewSpace India Limited (NSIL). The PS3 has a solid fuel motor and technologically mature components; It should not fail. So failure here indicates a lapse in quality assurance or supply chain management rather than a design flaw In fact,
If the root cause was simple negligence, such as a manufacturing defect – as was hinted at in media reports of the FAC’s findings – or a missed inspection, then publicly admitting this could have been devastating to PSLV’s commercial insurance premiums and reputation. It is plausible, though to what extent is not clear, that the report is being withheld to prevent claims of gross negligence by commercial partners or even to avoid ‘scare’ the market just ahead of the PSLV-C62 launch.
Second, technically speaking, saying that the mission failed due to “chamber pressure drop” is a cliché: it is describing the symptom, not the cause. This is like saying that a person suffering from a serious illness died of heart failure or brain death. Ultimately a person in India may die from these causes alone, yet it is not useful for someone studying the disease and trying to understand how it caused harm.
A sudden pressure drop in a solid motor usually causes the casing to crack (explode) or the nozzle to burst. If the nozzle burst, such an incident would raise significant questions about the integrity of materials used throughout the fleet. By keeping the report classified, ISRO avoided publicly answering whether it was a bad batch of materials that would delay the fleet for a long time, or whether the lone “workhorse” rocket was lacking in fundamental design.
Overall, there are reasons to believe that the FAC report is not stuck with the PMO alone. It is commendable that this is being prevented because the truth involves either sensitive military data or embarrassing lapses in quality control that would harm India’s nascent efforts to privatize space and spaceflight efforts.
Effects of Unexpected Role
This is the context against which the failure of the PSLV-C62 mission operates. ISRO Chairman V. Narayanan said after the PSLV-C62 launch that PS3 “suffered a roll rate disturbance, which led to deviation in its flight path”.
Roll refers to the rotation of the rocket around its longitudinal axis, which is the imaginary line running from the nose cone to the tail.
For a rocket to reach orbit, it must maintain a very precise orientation. While some rotation, called spin stabilization, is sometimes done intentionally, an unintended roll, or yaw, can be fatal for two reasons. First, the rocket’s ‘brain’, the inertial navigation system, uses gyroscopes to know which way is ‘up’. If the rocket achieves a high roll rate, that is, if it begins to rotate violently, the sensors may become saturated or become dizzy, causing the system to no longer track where it is pointing. Ultimately it cannot guide the rocket towards the correct orbit.
Second, while the PS3 motor generally provides thrust, it does not have its own roll control thruster. Instead it uses small thrusters from the stage sitting on top of it, i.e. the PS4 stage, to keep it stable. The malfunctions reported during the PSLV-C62 mission suggest that something happened to the PS3 motor, for example gas leakage from the side of the nozzle generated a large twisting force. This torque could have been stronger than the smaller PS4 thrusters, causing the corkscrew rocket to spin out of control.
Of course, this is a preliminary analysis. Think of it as an educated guess. Only a complete failure analysis by ISRO’s technical teams can reveal what exactly went wrong. Considering that the PSLV-C62 mission involves the EOS-N1 satellite, which is also technically a ‘spy satellite’, the possibility of the PMO releasing the FAC report seems unlikely, he said.
big picture
That being said, given the obvious manner in which the PSLV-C62 mission failed, it is hard to believe that two consecutive failures are unrelated. PSLV-C61 suffered a “pressure drop”, which suggests that the nozzle throat may have worn out too rapidly or the casing may have ruptured, allowing gas to escape sideways. Assuming that PSLV-C61 had the same problem and assuming that PSLV-C62 had the same violation in a slightly different way – say, a jet of gas leaked out the side of the nozzle joint – this would have created a large pinwheel effect, causing the rocket to spin out of control.
However, regardless of the exact reasons for the failure, the fact that it happened at all is an indictment of the decision to keep the PSLV-C61 FAC report internal. Because by doing so, ISRO also avoided external scrutiny of its ‘return to flight’ criteria, which will now come under greater scrutiny, including consideration of whether ISRO has implemented a superficial improvement.
In other words, whatever is still up in the air, the bigger picture at the moment is certainly that ISRO launched the PSLV-C62 mission eight months after a major failure while hiding the test results.
