Why did Isro's maiden SSLV mission fail? We have an answer (2024)

New Delhi,UPDATED: Feb 2, 2023 11:28 IST

The Indian Space Research Organisation (ISRO) has finally revealed what happened during its maiden launch of the newly developed Small Satellite Launch Vehicle (SSLV), which failed to deliver satellites into space. The launch vehicle, unveiled to cater to the massive small satellite launch market, injected the satellite into an unstable orbit minutes after it was launched on August 7, 2022, from Sriharikota.

“SSLV-D1 placed the satellites in a 356 km by 76 km elliptical orbit instead of a 356 km circular orbit. Satellites are no longer usable. The issue is reasonably identified. Failure of logic to identify a sensor failure and go for salvage action,” Isro had said in a statement.

The Indian space agency has now released the details of the investigation behind the loss of the maiden mission, as it preps to conduct the second demonstration mission of its shiny new launch vehicle.

WHAT HAPPENED WITH SSLVD1 MISSION?

Isro said that the mission failed after the upper stage of the SSLV launch vehicle injected the satellites into a highly elliptical unstable orbit due to a shortfall in velocity, leading to their decay and deorbiting immediately, in spite of the normal performance of all solid propulsion stages.

The investigation revealed that there was a vibration disturbance for a short duration on the Equipment Bay (EB) deck during the second stage separation. SSLV is a three-solid-stage launch vehicle unlike the PSLV, which is a four-stage rocket. The vibration affected the Inertial Navigation System (INS), resulting in declaring the sensors faulty by the logic in the Fault Detection & Isolation (FDI) software.

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Isro said that the SSLV uses a newly developed inertial navigation system that consists of six gyros that measure the rotation rates. The failure detection logic identified a degraded accelerometer and isolated it for improved mission performance. During the second stage separation, all six accelerometers experienced measurement saturation due to high vibration levels for a short duration.

"The shock response measured at the bay during the second stage separation exceeded the expectations and ground test levels both in low and high frequency as well as in time duration. The shock from such events lasts for about 2 milliseconds, whereas here a shock of 2-3 millisecond duration and subsequent oscillations lasting for more than 10 milliseconds was observed," Isro said.

This malfunction initiated a salvage mode with the purpose of saving the mission, but it could not inject the satellites into a safe orbit. The third stage ignition was commanded by the sequence program, but there was a shortage of 56 meters per second speed at the end of the third stage in the final velocity, which led to poor orbit insertion and mission failure.

WHAT IS SSLV?

Designed as an able partner of PSLV, the SSLV will share the burden of launching smaller satellites as Isro focuses PSLV on bigger missions. SSLV has been designed to launch a 500-kilogram payload into a 500-kilometer planar orbit. Designed as an able partner of PSLV, the SSLV will share the burden of launching smaller satellites as Isro focuses PSLV on bigger missions. SSLV has been designed to launch a 500-kilogram payload into a 500-kilometer planar orbit.

Isro has marketed the launch vehicle as the one with the quickest turn-around time and it can be prepared for launch in just 72 hours, as against over 60 days needed for PSLV.

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WHAT'S NEXT FOR SSLV?

Isro is readying the vehicle for a second demonstration mission after executing changes to the mission following the failure of the maiden demonstration launch.

"The next development flight SSLV-D2 is planned to be executed complying with the recommendations, its satisfactory implementation, review, and approval by the authorised committees. The second developmental flight of SSLV is scheduled in the first quarter of 2023 and will launch a total payload mass of about 334 kg including the Earth Observation Satellite-07 and two co-passenger satellites," Isro said.

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