The ISRO says they have found and remedied the issue which doomed the first SSLV launch in August, as the agency prepare for the return to flight.

On February 1st, the ISRO announced that the investigation into the failed maiden flight of SSLV. They have determined that the cause of failure was an unexpectedly strong shock during second stage separation which resulted in off nominal readings from the accelerometers aboard the rocket's guidance system, thus triggered a "salvage mode" - a mode designed to mitigate loss of mission in the event of an anomaly - unfortunately the system worked in reverse.

During separation of the second stage, SSLV's 6 accelerometers measured stronger and more sustained vibrations than expected - 8ms longer (expected: 2ms; reality: 10ms). This caused the accelerometers to believe they had experienced an anomaly, however, the ISRO reports they performed nominally through the remainder of the flight.

The ISRO stresses in their statement that all stages performed nominally and this failure was a result of the salvage mode falsely triggering - thus not igniting the fourth stage “since it could be a deterrent to the success of salvage option in some cases.” the ISRO says.

As a result of the lack of fourth stage ignition, the velocity was 56 meters per second below target, which resulted in a perigee of only 75.7km, causing the payloads to re-enter Earth's atmosphere "immediately," according to an ISRO official.

Moving Forward

Moving forward, the ISRO has outlined a number of corrective measures to move forward from the anomaly, they are as follows:

• Replace the second stage separation system with the proven system used on the third stage

• Perform additional readings and for a longer duration before triggering salvage mode

• Salvage mode will use closed loop guidance

• In case of failure of inertial system sensors, the mission will be progressing using NavIC data in a closed loop guidance scheme

• In case of failure of inertial sensors and non-availability of NavIC data (for more than 10 sec), an open loop steering guidance will be executed

• Fourth stage (kick stage) usage will be considered in salvage mode

With this thorough investigation complete, the ISRO are ready to launch a second demonstration flight, NET February 10th.