Pradeep's Space Newsletter #46
SSLV's return to flight, ISRO, and Twitter updates
ISRO successfully completed the second developmental flight of the Small Satellite Launch Vehicle (SSLV) on February 10, 2023 at 09:18 hours IST from the first launch pad at Satish Dhawan Space Center, Sriharikota.
It completed its fifteen minute long mission to insert EOS-07, Janus-1, and AzaadiSat-2 into a 450 km orbit. You can watch the lift-off and on-board camera views here.
The first developmental flight of the SSLV flew on 7th August 2022 at 09.18 Hrs IST ended in failure. The objective was to place the EOS-2 satellite and co-passengers into a 356 km circular orbit with an inclination of 37.21°.
Instead, the satellites were placed in a 360.56 km x 75.66 km with an inclination of 36.56°. This meant that the satellites were placed in an elliptical orbit with the farthest point from Earth (apogee) of 360.56 km and a closest point from Earth (perigee) of 75.66 km.
This meant that the satellite was well below the internationally recognised Karman line (100 km). This is also below the 80 km target beyond which satellites are known to survive in highly elliptical orbits, according to research by astronomers Jonathan McDowell and Thomas Gangale.
In case of such failures, ISRO constitutes a Failure Analysis Committee which submits a report on the causes and suggests rectification to avoid failures in the future. ISRO had published these reports publicly in the past. We saw a trend where some of these reports were withheld in the late 2010s and I’m happy to see the practice reinstituted.
The SSLV is a three stage rocket with each stage carrying solid fuel. It has a fourth stage that has a Velocity Trimming Module that ISRO does not call a stage. The Module is a liquid fuel engine that provides final velocity and attitude to the satellite. The rocket’s computers are located on top of the Velocity Trimming Module.
At the point at which the second stage separated from the rest of the rocket, the vibration was large for such a long time that the on-board computer put the rocket in salvage mode. In Salvage Mode, the computer tried to put the satellites in an orbit from which the satellites could use it’s on-board fuel to move to a stable orbit. If you wish to read the more technical explanation, you can find it here.
The launch vehicle did not achieve this but you can see that it almost reached there in terms of altitude but did not have the velocity to stay in that orbit.
The point to note here is that they applied the fixes and flew the next development flight in six months.
Image: SSLV-D2 ready on the launch pad. Image Credit: ISRO
Image: SSLV-D2 lift-off. Image Credit: ISRO
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Twitter Updates
Excellent info as always. Thanks, Pradeep!