ISRO Launches New SSLV Rocket, Suffers Fourth Stage Failure

The ISRO (Indian Space Research Organization) launches it new small satellite launches, the SSLV or Small Satellite Launch vehicle on Sunday, August 7 at 03:48 UTC from Sriharikota, India. The first 3 stages flew nominally but an issue with the fourth stage resulted in the satellites being deployed in an unstable orbit.

The SSLV program came from the 2015 National Institute of Advanced Studies proposal to create a “small satellite launch vehicle” to launch small national security payloads on demand with a low cost and higher launch cadence that the ISRO’s existing rockets fleet.

In 2016, the director of ISRO’s Liquid Propulsion Systems Centre spoke at India’s National Space Science Symposium stating the need for a cost-effective launch vehicle capable of launching 500 kilograms to low Earth orbit.

The SSLV program started officially in late 2017 in response to calls for a small satellite launcher. One year later, the Vikram Sarabhai Space Centre (VSSC) finished the design of the vehicle, which is 34 meters tall, two meters in diameter, and weighs 120 tons.

The SSLV consists of three solid-fueled stages and a fourth stage known as the VTM (Velocity Trimming Module). 

The VTM, which uses storable liquid monomethylhydrazine (MMH) and mixed oxides of nitrogen (MON3), provides roll control for the second and third stages as well as the ability to inject multiple payloads into different orbits.

The SSLV was designed to launch up to 500kg to a 500km low Earth orbit at a 45-degree inclination or 300kg to a 500km sun-synchronous polar orbit. The SSLV can carry various combinations of CubeSats, micro sats and mini sats ranging up to 64 2U CubeSats or 24 6U CubeSats into orbit, or combinations of different sizes.

The SSLV is designed to have a high launch cadence by using far less infrastructure than earlier Indian space launch vehicles. The SSLV is designed to take 72 hours to set up, with a team of just six people to oversee all launch preparations. In comparison, the PSLV requires a larger team and up to 70 days of launch prep.

The SSLV was scheduled to fly in late 2019, with commercial launches starting in early 2020. However, the pandemic shut down the Indian space program for an extended period. In March 2021 the test of the first stage (SS1) failed failure delaying the program. 

SSLV-D1’s mission was to carry the EOS-02 Earth observation microsatellite as its primary payload to an altitude of 356.2 kilometers in an orbit inclined 37.21 degrees to the equator. This inclination was to allow EOS-02 to observe all of India. 

The SSLV successfully lifted off from the First Launch Pad at the Satish Dhawan Space Centre. The SS1 stage separated at 127.5 seconds into the flight. The payload fairings separated at the 161.9-second mark, and SS2 separated at 336.9 seconds. SS3 ignition occurred at 342.2 seconds after a short coast period, and separated at 633.3 seconds.

After another coast period, the VTM ignited its thrusters at 642 seconds, however only for a 0.1 second burn was seen on the mission control screens during the ISRO webcast. 

At 742 seconds into the flight, EOS-02 was to separate, and the mission was to end at 792 seconds with the AzaadiSAT separation.

All these events were not seen live, with data issues cited. Hours later the ISRO Chairman confirmed the mission failed came later in the day.