Feb 08, 2023
Summary of Failure Analysis of SSLV-D1 Mission & Recommendations for SSLV-D2
Small Satellite Launch Vehicle (SSLV) of ISRO is designed to be affordable and amenable to industry
production and will function as a launch-on-demand platform for Mini, Micro or Nano satellites. It is
a three-stage vehicle with all solid propulsion stages and liquid propulsion-based Velocity Trimming
Module (VTM) as the terminal stage. The launcher also targets many novel features including low
turn-around time, flexibility in accommodating multiple satellites, launch-on-demand, minimal launch
infrastructure requirements, etc.
The first developmental flight of Small Satellite Launch Vehicle (SSLV) lifted off from Satish Dhawan
Space Centre (SDSC) on 7
August 2022 at 09.18 Hrs IST. The objective of the mission
(SSLV-D1/EOS-02) was to inject EOS-02 satellite of ISRO into a circular orbit of 356.2 km with an
inclination of 37.21Â°. Azaadisat, a student satellite was also accommodated in the mission, authorized
However, the spacecraft were 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. The orbit achieved was 360.56 km x 75.66 km with an inclination of
36.56.Initial investigations with the flight data indicated that the lift-off of SSLV D1 was normal
along with normal performance of all solid propulsion stages.
However, the mission could not be achieved due to an anomaly during the second stage (SS2) separation,
which triggered a mission salvage mode (which is a procedure adopted to attempt minimum stabilized
orbital conditions for the Spacecraft in case of an anomaly in the vehicle system).
Subsequent detailed analysis of the flight events and observations ranging from countdown,
lift-off, propulsion performance, stage separations and satellite injection revealed that
there was a vibration disturbance for a short duration on the Equipment Bay (EB) deck
during the second stage (SS2) separation, that affected the Inertial Navigation System
(INS), resulting in declaring the sensors faulty by the logic in Fault Detection &
Isolation (FDI) software
SSLV Inertial Navigation System
Shock and Vibrations during stage separation
Satellite injection into an unintended orbit
Change of Separation System
MINS FDI logic
Dynamic characterization and design modification of structures
Usage of NaVIC data
VTM will be in loop for salvage mode
Getting ready for SSLV-D2
The SSLV-D1 was the first developmental mission of this new launch vehicle.
The objective of development missions is to prove the launch vehicle design and architecture and
to bring out any residual unknowns not identified in the qualifications tests and analysis during
its development journey. SSLV-D1 mission demonstrated the satisfactory integrated performance of
SSLV in all its systems including its flight through the aerodynamic regime, which is an
accomplishment by itself.
Considering the clear identification of the cause of the flight anomaly and
suggested corrective actions, the next development flight (SSLV-D2) is planned to be executed
complying to the recommendations, its satisfactory implementation, review and approval by the
The second developmental flight of SSLV (SSLV-D2/EOS-07 Mission) is scheduled in
the first quarter of 2023 and will launch a total payload mass of about 334 kg including EOS-07
satellite and two co-passenger satellites.
for more details