ISRO analyses SSLV-D1 failure, gears up for D2

The Indian Space Research Organisation (ISRO) on Wednesday issued an official statement explaining in detail the failure of the first development flight of the Small Satellite Launch Vehicle (SSLV) in August last year.

The space agency also spelt out corrective actions ahead of the launcher’s next development flight – SSLV-D2 – scheduled during the first quarter of 2023.

The objective of SSLV-D1/EOS-02 was to inject ISRO’s EOS-02 satellite and a student satellite, Azaadisat, into a circular orbit of 356.2 km with an inclination of 37.21°. “However, the spacecraft was injected into a highly elliptical unstable orbit due to a shortfall in velocity, leading to their decay and deorbiting immediately, in spite of normal performance of all solid propulsion stages,” ISRO said.

The mission could not be achieved due to an anomaly during the second stage (SS2) separation, which triggered a “mission salvage mode”, a procedure adopted to attempt minimum stabilised orbital conditions for the spacecraft, in case of an anomaly.

Subsequent analysis revealed that a short-duration vibration disturbance on the Equipment Bay (EB) deck during the SS2 affected the Inertial Navigation System which resulted in the declaration of the sensors as faulty. The shortage of about 56 m/s at the end of the third stage separation (SS3) burnout in the final velocity, and a loss in pointing accuracy due to sensor errors, meant that the targeted orbit could not be achieved, ISRO said.

SSLV-D1 lifted off from the Satish Dhawan Space Centre in Sriharikota on August 7, 2022. The SSLV-D2/EOS-07 Mission will launch a total payload mass of about 334 kg including the EOS-07 satellite and two co-passenger satellites.

ISRO designed the three-stage SSLV as an affordable, launch-on-demand platform for mini, micro, or nanosatellites which also proposes a low turnaround time with minimal launch infrastructure.

Corrective action

As part of the corrective measures, the system used for separating the mission’s second stage from the third has been replaced with the Marman band system which generates lesser shock. Modifications in EB and satellite decks have been implemented and NavIC data will be used to counter the possibility of a failure of inertial system sensors.

ISRO, while stating that the SSLV-D1 demonstrated a “satisfactory integrated performance” in all its systems, said SSLV-D2 would draw on the “clear identification” of the cause of the first flight’s anomalies and comply with the recommendations.