The Small Satellite Launch Vehicle (SSLV) is a small-lift launch vehicle developed by ISRO with payload capacity to deliver 500 kg (1,100 lb) to low Earth orbit (500 km (310 mi)) or 300 kg (660 lb) to Sun-synchronous orbit (500 km (310 mi))[7] for launching small satellites, with the capability to support multiple orbital drop-offs.[11][12][13] SSLV is made keeping low cost, low turnaround time in mind with launch-on-demand flexibility under minimal infrastructure requirements.[14]
The maiden flight SSLV-D1 was conducted on 7 August 2022,[8][15] from the First Launch Pad, but failed to orbit.[16] A second flight on 10 February 2023 successfully delivered payloads to orbit.[17]
EOS 02 spacecraft and VTM upper stage integrated in a cleanroom facility.
The SSLV was developed with the aim of launching small satellites commercially at drastically reduced price and higher launch rate compared to Polar Satellite Launch Vehicle (PSLV). The development cost of SSLV is ₹169.07 crore (US$21 million)[16][2] and the manufacturing cost is expected to be ₹30 crore (US$3.8 million) to ₹35 crore (US$4.4 million).[3][23][4]
The projected high launch rate relies on largely autonomous launch operation and on overall simple logistics. To compare, a PSLV launch involves 600 officials while SSLV launch operations would be managed by a small team of about six people. The launch readiness period of the SSLV is expected to be less than a week instead of months.[25][26] The launch vehicle can be assembled both vertically like the existing PSLV and Geosynchronous Satellite Launch Vehicle (GSLV) and horizontally like the retired Satellite Launch Vehicle (SLV) and Augmented Satellite Launch Vehicle (ASLV).[27]
The first three stages of the vehicle use HTPB based solid propellant, with a fourth terminal stage being a Velocity-Trimming Module (VTM) with eight 50 N thrusters for reaction control and eight 50 N axial thrusters for changing velocity.[10] With these VTM can add delta-v of up to 172 m/s.[28]
The first stage (SS1) and third stage (SS3) of SSLV are newly developed while second stage (SS2) is derived from third stage (HPS3) of PSLV.[29][30][31]
The early developmental flights and those to inclined orbits will launch from Sriharikota,[19] at first using existing launch pads and later from dedicated facility called SSLV Launch Complex (SLC) in Kulasekharapatnam.[34][18] Tenders related to manufacturing, installation, assembly, inspection, testing and Self Propelled launching Unit (SPU) were released in October 2019.[35][36][37]
In 2016, a National Institute of Advanced Studies report by Rajaram Nagappa proposed development path of a 'Small Satellite launch Vehicle-1' to launch strategic payloads.[40] In National Space Science Symposium 2016,[41] then Director of Liquid Propulsion Systems Centre, S. Somanath also acknowledged a need for identifying a cost effective launch vehicle configuration with 500 kg payload capacity to LEO[42] and by November 2017, development of such launch vehicle was underway.[43]
In December 2020, all booster segments for SSLV first stage (SS1) static test (ST01) were received and assembly was done in Second Vehicle Assembly Building (SVAB).[45]
The first static fire test (ST01) of the SS1 first-stage booster conducted on 18 March 2021 was unsuccessful.[46][47] About 60 seconds into the test, oscillations were observed and after 95 seconds, the nozzle of SS1 stage disintegrated. The nominal duration of test was 110 seconds.[48] To qualify for flight, SSLV's solid first stage SS1 has to perform two consecutive nominal static fire tests.[48]
The SSLV Payload Fairing (SPLF) functional qualification test was completed in August 2021.[49]
The second static fire test of SSLV first stage SS1 was conducted on 14 March 2022 at SDSC-SHAR and met the required test objectives.[50][51]
Operational history
SSLV-D1
The first developmental flight of the SSLV occurred on 7 August 2022. The flight mission was named SSLV-D1. The SSLV-D1 flight failed to achieve its mission objectives.
The rocket had a three stage configuration with a fourth Velocity Trimming Module (VTM). In its D1 configuration, the rocket was 34m tall with a diameter of 2m and a lift-off mass of 120t.[52]
The rocket carried EOS 02, an Earth observation satellite that weighed 135 kg and AzaadiSAT, a CubeSat payload that weighed 8 kg, developed by Indian students to promote inclusivity in STEM education. The SSLV-D1 was supposed to place the two satellite payloads in a circular orbit of altitude 356.2 km with 37.2° inclination.
The official explanation by the ISRO for the mission failure was software malfunction.[53][54][55] According to the ISRO, the mission software detected an accelerometer anomaly during the second stage separation. This caused the rocket navigation to switch from a closed loop guidance to an open loop guidance.[56] Even though, this switch in guidance mode was part of the redundancy built into the rocket's navigation, it could not salvage the mission.
During the open loop guidance mode, the final VTM stage only managed to fire for 0.1s instead of the intended 20s.[57] This led to the two satellites as well as the VTM stage of the rocket being injected into an unstable elliptical transatmospheric orbit of 360.56×75.66 km with an inclination of 36.56°.[55]
The SSLV-D1’s final VTM stage had 16 hydrazine (MMH+MON3) fueled thrusters. Eight of those were to provide altitude control and the remaining eight for controlling the orbital velocity.[58] The VTM stage also provided pitch, yaw and roll control during the orbital insertion maneuvers.[59] The three main stages of the SSLV-D1 functioned normally. But, that was not enough to impart adequate impulse for the two satellite payloads to achieve stable orbits. For the injection of the two satellite payloads into their intended stable orbits, the VTM stage had to fire for at least 20 seconds, to impart enough additional orbital velocity and altitude corrections. Instead the VTM kicked-in at 653.5s and shut itself down at 653.6s, post lift-off.[60] Following the partial firing of the VTM stage, the EOS 02 was released at 738.5s and AazadiSAT at 788.4s, post-liftoff. These failures transpired, resulting in the satellites entering an unstable orbit and subsequently destroyed upon reentry.
The first developmental flight of SSLV. The mission target was a circular orbit of altitude 356.2 km with 37.2° inclination. The mission carried two satellite payloads. The 135 kg EOS 02, an Earth observation satellite and the 8 kg AzaadiSATCubeSat.[9][62][63]
Due to sensor failure coupled with shortcomings of onboard software, the stage as well as the two satellite payloads were injected into an unstable transatmospheric Earth orbit measuring 356×76 km and subsequently destroyed upon reentry.[54] According to S. Somanath, an anomaly lasting 2 seconds in one of the accelerometers during second stage separation initiated salvage mode by onboard computer. Guidance, navigation, and control software switched from 'closed loop guidance' where it received real-time feedback from all sensors to an 'open loop guidance' where accelerometer data gets isolated and a predetermined path is followed.[64] This resulted in velocity shortfall from the required 7.3 km/s to 7.2 km/s. Being in salvage mode, Velocity-Trimming Module didn't rectify this shortfall which led to mission failure.[28][57]
^ ab"Satellite Launch Vehicle"(PDF). 16 December 2021. The development of SSLV is in the final stages and the first developmental flight of SSLV is targeted during the first quarter of 2022. The Government has sanctioned a total cost of Rs.169.07 Crores for the development project including the development & qualification of the vehicle systems and the flight demonstration through three development flights (SSLV-D1, SSLV-D2 & SSLV-D3)((cite web)): CS1 maint: url-status (link)
^ abRamachandran, R. (26 August 2022). "First SSLV flight fails to put satellites in correct orbit". frontline.thehindu.com. Retrieved 31 August 2022. According to a former ISRO scientist, the VTM can correct for a velocity shortfall of up to 172 metres/s. The rocket used for SSLV-D1 was a 34 m tall, 2 m diameter vehicle having a lift-off mass of 120 t.
^SHAR Director Rajarajan Press Meet. 15 August 2022. Event occurs at 2 minutes 40 seconds. Two solid stages are new, fully developed. That is SS1 with 85-90 tonnes and SS3 with 4.5 tonnes whereas SS2 is almost identical to the HPS3 of PSLV.
^"TENDER NOTICE NO. SDSC SHAR/Sr.HPS/PT/RO/03/2019-2020"(PDF). isro.gov.in. Retrieved 30 October 2019. REQUEST FOR PROPOSAL (RFP) FOR PROCUREMENT, MANUFACTURE, SUPPLY, TESTING and COMMISIONING [sic] OF SELF PROPELLED UNITS FOR SLC
^Nagappa, Rajaram (December 2015). "The Promise of Small Satellites for National Security"(PDF). Archived(PDF) from the original on 14 January 2017. Retrieved 21 March 2022. By appropriate choice from among the solid propellant stages available with ISRO and DRDO, a launch vehicle could be configured and designated Small Satellite Launch Vehicle (SSLV-1). The performance of SSLV-1 was estimated using the in house developed trajectory-modelling programme QuoVadis. The performance runs show that SSLV-1 is capable of putting a 350 kg satellite in a polar orbit of 511 km x 497 km orbit and a 400 kg satellite in an orbit of 425 x 401 km (higher payloads are possible in equatorial orbit). This payload capability allows the launch of microsatellites with optical imaging and radar imaging payloads as well as individual intelligence satellites. Satellite life for the 400 kg mass satellite may be short in the 400 km orbit.
^"Department of Space, Annual Report 2021-22"(PDF). 27 April 2022. Archived from the original(PDF) on 27 April 2022. The first static test of SS1 solid motor was conducted and the performance of SS1 ignition system, propellant system and Flex Nozzle Control (FNC) system was evaluated. Various design modifications have been incorporated to resolve the anomalies observed in the first static test (…)
^"Department of Space, Annual Report 2020-2021"(PDF). ISRO. p. 23. Archived(PDF) from the original on 4 March 2021. Retrieved 6 March 2021. EOS-02: EOS-02 is configured around MicroSat-TD bus platform to demonstrate launch on demand capability with SSLV. It is expected to meet the ever-increasing user demands for cartographic applications, urban and rural management, coastal land use and regulation, utilities mapping, development and various other GIS application. The mission life of the satellite is 9 months.
^"Application for Earth Exploration Satellite Service by BlackSky Global, LLC"(PDF). FCC. 25 July 2019. p. 6. Archived from the original(PDF) on 28 July 2019. Retrieved 28 July 2019. Global-5 through Global-8 are currently scheduled to be launched in November 2019 on a Small Satellite Launch Vehicle (SSLV) by the Indian Space Research Organization from its Satish Dhawan Space Center This article incorporates text from this source, which is in the public domain.
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