ISRO’s SSLV satellite failure: What exactly went wrong? Here’s the truth

The inaugural small satellite launch vehicle (SSLV) of the Indian Space Research Organization (ISRO), carrying the earth observation satellite EOS-02 and a co-passenger student spacecraft AzaadiSAT, did not launch as planned on Sunday.

The mission failed because the SSLV-D1 placed the satellites in an elliptical orbit rather than a circular one, leaving them "unusable," as ISRO later said in a statement.

According to ISRO, "SSLV-D1 put the satellites into a 356 km x 76 km elliptical orbit rather than a 356 km circular orbit." Satellites are no longer functional. The problem has been correctly detected. The divergence was caused by the logic's failure to recognise a sensor failure and proceed with a salvage step.

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What went wrong during the satellite launch?

ISRO's first small satellite launch vehicle (SSLV) blasted out from Sriharikota at 9:18 a.m. on Sunday. The space agency's purpose was to get a bigger share of the small launch vehicle industry by placing satellites into Low Earth Orbit.

According to a source in The Wire, the issue looked to be the SSLV's terminal stage, known as the velocity trimming module (VTM). The VTM was meant to burn for 20 seconds at 653 seconds the following launch, according to the launch profile. However, it barely burned for 0.1 seconds, depriving the rocket of the necessary height boost.

After the VTM burn, the two satellites on board the rocket, the primary EOS-2 Earth-observing satellite, and the secondary AzaadiSAT student satellite, separated from the vehicle. This implies they are also likely to have deviated from their original orbital routes and entered an elliptical orbit instead.

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While providing updates on the launch on Sunday, the space agency tweeted at about 11.43 a.m. that "all the stages worked normally." Both satellites were launched. However, the orbit achieved was smaller than predicted, making it unstable.

At 2.48 pm, ISRO claimed it has identified the mission to be a failure as well as the reason for failure.

ISRO chairperson S Somanath later said in a video statement, "The vehicle took off majestically with the burning of the first stage, and the subsequent S2 and S3 performed very well." The mission performed admirably, and when it reached a height of 356 kilometers, the satellites were separated. However, we later discovered an abnormality in the satellites' orbital positioning."

The chairperson went on to explain that when a satellite is deployed in such an orbit, it cannot keep course for long and falls off. "The satellites have already descended from that orbit and are no longer usable," Somanath explained. According to the ISRO, it was "logic inability to identify a sensor"

Not the first failure

This isn't the first time ISRO has had a problem with a mission launch. The Polar Satellite Vehicle Launch (PSLV), today regarded as ISRO's reliable workhorse, failed on its first flight on September 20, 1993. The country's maiden experimental flight of SLV-3, carrying the Rohini Technology Payload, failed to deliver the satellite into its target orbit on August 10, 1979.

On September 7, 2019, ISRO suffered one of its most significant failures when the Chandrayaan 2 orbiter crashed on the lunar surface instead of softly landing and was destroyed along with the rover. Prime Minister Narendra Modi, who was present at the space agency to watch the historic flight, afterward cheered on the ISRO employees, saying what they had accomplished was no minor task.

In August 2021, the launch of GISAT-1, an earth observation satellite atop the GSLV Mk 2 rocket, failed just 350 seconds after liftoff from India's spaceport. It was caused by "a technical malfunction in the cryogenic stage," according to ISRO's preliminary study on launch day.

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