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On September 4, 2026, the Indian Space Research Organisation (ISRO) successfully launched the GSLV-F17/EOS-05 mission. This success comes in the wake of two consecutive failures of the Polar Satellite Launch Vehicle (PSLV). On May 18, 2025, PSLV-C61 failed following an anomaly during the third stage while carrying the EOS-09 satellite. This was followed by the failure of PSLV-C62 on 12 January 2026, shortly before third-stage separation. Following the January 2026 failure, ISRO remained without a launch for nearly seven months.

There could understandably have been some apprehension within the ISRO community about this launch as well, given the historically challenging and unforgiving nature of the Geosynchronous Satellite Launch Vehicle (GSLV) and particularly its cryogenic upper stage. The PSLV, long regarded as ISRO’s workhorse launcher, had experienced two consecutive failures in the recent past. On the other hand, the performance of the GSLV has historically been mixed. The GSLV Mk I, which used a Russian cryogenic upper stage and is now retired, undertook six missions, including two outright failures and two partial failures. The GSLV Mk II, equipped with an indigenous cryogenic stage and still in service, had completed 12 missions, with 10 successes before this mission. Promisingly, the GSLV Mk II’s success rate has been significantly better than that of the earlier Mk I configuration.

Illustration: Pariplab Chakraborty.

Interestingly, ISRO appears to have revised the nomenclature of its GSLV missions, with the earlier GSLV Mk I now being referred to as GSLV Mk II, while the vehicle previously designated GSLV Mk II is now simply referred to as GSLV. Following the failure of the GSLV-F10 mission in 2021, the subsequent four missions of the GSLV have been successful, indicating a period of improved reliability. The previous GSLV mission, GSLV-F16, had........

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