First Flight of ISRO’s New SSLV Rocket Ends in Failure After Sensor Glitch

The two satellites onboard the rocket – the primary EOS-2 Earth-observing satellite and the secondary AzaadiSAT student satellite – separated from the vehicle after the VTM burn.

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New Delhi: The Indian Space Research Organisation (ISRO) launched the first developmental flight of its new Small Satellite Launch Vehicle at 9.18 am on August 7, from its spaceport in Sriharikota.

ISRO produced the SSLV to enable a quick launch cadence – once a week if required – and to launch, as its name indicates, small and micro satellites with a total payload capacity of 500 kg to the low-Earth orbit (LEO).

However, the development flight was not a success. While ISRO officials at the mission control centre reported that all of the SSLV’s stages had performed nominally, and its chairman S. Somanath said his team was preparing further updates, it became clear from independent reports that the rocket had stopped transmitting data some nine minutes into the launch and that it had missed its intended orbit.

The problem appeared to be the SSLV’s terminal stage, called the velocity trimming module (VTM). According to the launch profile, the VTM was supposed to have burnt for 20 seconds at 653 seconds after launch. However, it burnt for only 0.1 seconds, denying the rocket of the requisite altitude boost.

The two satellites onboard the rocket – the primary EOS-2 Earth-observing satellite and the secondary AzaadiSAT student satellite – separated from the vehicle after the VTM burn. This means they are likely to have missed their intended orbital trajectories as well, and entered an elliptical orbit instead. ISRO confirmed at 3 pm that the satellites are “unusable” as a result. ISRO chairman Somanath also said that the satellites had in fact already deorbited – i.e. fallen back to Earth.

Astronomer and spaceflight tracker Jonathan McDowell tweeted after the launch that because of the VTM’s failure, the part of the rocket that had to remain in orbit after launching the satellites would instead have fallen into the Pacific Ocean, after passing over Australia and New Zealand.

At around 11.43 am, ISRO posted the following update on its website: “All the stages performed normal. Both the satellites were injected. But, the orbit achieved was less than expected, which makes it unstable.”

At 2.48 pm, ISRO had said it had identified the mission to be a failure as well as the cause of failure. According to a pair of tweets posted by the organisation:

“SSLV-D1/EOS-02 Mission update: SSLV-D1 placed the satellites into 356 km x 76 km elliptical orbit instead of 356 km circular orbit. Satellites are no longer usable. Issue is reasonably identified. Failure of a logic to identify a sensor failure and go for a salvage action caused the deviation. A committee would analyse and recommend. With the implementation of the recommendations, ISRO will come back soon with SSLV-D2.”

ISRO intends to launch the SSLV in future from its upcoming spaceport in Kulasekarapattinam in Tamil Nadu. Doing so would allow the rocket to enter into a pole-to-pole, or polar, orbit in a straight geodesic over Earth. Because it was launched from Sriharikota, however, it entered into a relatively diagonal orbit. The larger PSLV rocket launches from Sriharikota and flies around Sri Lanka before entering a polar orbit because it is large enough to carry the extra fuel.

The SSLV is much smaller, with three stages plus the VTM module. It weighs a little over 120 tonnes and stands 34 metres tall. ISRO has said that India’s private industry should take advantage of the rocket’s modularity to manufacture and use it to launch satellites for their needs.

Note: This article was republished at 4:17 pm to reflect the most recent updates from ISRO.