Indian Space Research Organisation (ISRO) had put in place a project in 2018 to develop a Small Satellite Launch Vehicle (SSLV) to cater to the requirement for launching 500 kg satellites to Low Earth Orbits (LEO). On Feb 10, 2023, ISRO successfully launched three small satellites powered by its SSLV-D2 launch vehicle from Satish Dhawan Space Centre at Sriharikota. Unfortunately, earlier on Aug 07, 2022, the first developmental flight of the SSLV (SSLV-D1) had failed. However, within six months, ISRO was able to identify and rectify the fault and ensure the first success for their new launch vehicle.
ISRO is a globally recognised space agency for its quality of work and successfully managing difficult space missions for a fraction of cost in comparison with other global space players. One limitation of ISRO has been that, it has not invested much towards developing different categories of launch vehicles. They have been mostly satisfied with tweaking the existing vehicles based on the mission requirements. Hence, one can see different configurations (no change in basic design) of their launch vehicles like Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV). The first flight of GSLV (Mk-2) had happened on Apr 18, 2001 and now after a gap of more than two decades, ISRO has tested a new launch vehicle. At the backdrop of this, it could be of interest to trace back the history of ISRO’s launch vehicle programme.
The launch of the first sounding rocket from a small village called Thumba (in the state of Kerala) on Nov 21, 1963, could be said to have marked the beginning of the Indian Space Programme. India begun with launching of indigenously built (initial assistance was from the US and France) sounding rockets around 1965. This programme was consolidated under the Rohini Sounding Rocket (RSR) Programme after a decade. It gave India’s scientific community experience towards grasping solid propellant technology. On April 19, 1975, India launched its first satellite called Aryabhata. However, at that time India was not ready with its own launch vehicle and hence the satellite was put in space by the Soviet Union’s Kosmos-3M rocket from Kapustin Yar.
The first launch vehicle developed by ISRO was SLV-3, a four-stage vehicle using all solid propellants and had a capability of placing 40 kg payload into the LEO. It had the technologically challenging and very important subsystem called the heat-shield, required to protect satellite from the aerodynamic heating. Also, for this rocket other important mechanisms like analogue autopilot, on-board event programmer, inertial altitude measurement system and telemetry, tracking and tele-command avionics were developed. The first SLV-3 launch attempt on Aug 10, 1979 had failed. However, the subsequent analysis indicated that various sub-systems of SLV-3 had functioned correctly and there were only some minor glitches responsible for the vehicle to fail. Subsequently, on July 18, 1980 a successful launch of SLV-3 took place and Rohini satellite was placed in a correct orbit. With this India became the sixth member of an exclusive club of space-faring nations.
SLV-3 was a first step by ISRO towards developing rocket launcher technology, one of the most difficult aspects of rocket technology to master. There was a realisation that having a capability of putting 40 kg payload in LEO has not much of future and there is a need to improve on the success of SLV-3. Hence, the Augmented Satellite Launch Vehicle (ASLV) Programme was designed to increase the payload capacity to 150 kg, almost thrice that of SLV-3, for LEO. Four developmental flights were undertaken under the ASLV programme. The first two developmental flights which took place, respectively on March 24, 1987 and July 13, 1988, failed. The third developmental flight, ASLV-D3 held on May 20, 1992 and the fourth on May 4, 1994, turned successful. This programme was not extended further since it was designed for a limited mandate mainly for validating various critical technologies.
The turning point came in the history of India’s space programme with the arrival of PSLV, the third generation launch vehicle and the first Indian launch vehicle to be equipped with liquid stages. First mission on Sep 20, 1993 was not a success. The first success was tested during October 1994 and since then PSLV has established itself as a reliable and versatile workhorse launch vehicle of India. As of July 1, 2022 the PSLV has made 55 launches, with 52 successes, two outright failures and one partial failure. This is a four-stage rocket, with two solid and two liquid stages and has a success rate of around 95 per cent. Over the years ISRO has developed five different models of this vehicle and this vehicle, which has been mainly designed for the purposes of putting satellites weighing two tonnnes in LEO, has even been used for Moon (Chandrayaan-1) and Mars missions.
GSLV is the fourth launch vehicle developed by ISRO and is a vehicle which took maximum period for its development. The need for putting a satellite in the geostationary orbit for the purposes of communication was identified much before this vehicle became a reality. There was much emphasis put by Bhabha-Sarabhai duo during 1960s about the need for the capability to put communications satellites into the geostationary orbit. But only by April 18, 2001, ISRO was able to launch the geosynchronous satellite from the Indian soil. This vehicle can put a payload 2,250 kgto geosynchronous transfer orbit or geostationary transfer orbit (GTO) and 6,000 kg to LEO. This is a three-stage vehicle with solid, liquid and the cryogenic stages. There is a long history of India’s cryogenic programme; transfer of this technology from Russia to India did not happen during 1991, owing to the pressure from the United States (US) and ISRO took many years to develop this technology indigenously.
ISRO’s GSLV Mk-3 programme is about putting 4,000 kg in GTO and 8,000 kg in LEO. The first successful orbital launch of GSLV Mk-3 took place on Jun 05, 2017. This vehicle has been developed primarily for putting communication and weather satellites into geostationary orbit. This vehicle was also used for India’s second mission to Moon called Chandrayaan-2. When this vehicle gets used for launching satellites in LEO, it is called as the Launch Vehicle Mk-3 (LVM-3). ISRO undertook a successful commercial launch of this vehicle by launching 36 One Web satellites into LEO on Oct 22, 2022.
This entire development process of ISRO’s launch vehicle programme demonstrates that ISRO has good capabilities for launching satellites into LEO. The LMV-3 launch carried the payload of 5,796 kg to LEO, while the maximum weight carried during the GSLV Mk-3 mission was 3,850 kg (Chandrayaan-2). Modern day communications satellites normally carry a payload of six to eight tonnnes. Hence, there is a requirement for ISRO to leapfrog in the area of launching heavy satellites into geostationary orbits. This would also help them to establish capability to carry more than 10,000 kgs to LEO. ISRO is required to develop semi-cryogenic to carry more weight into the space. It needs to be noted that there is a good commercial market available for launching heavy satellites. However, it would take some more years for ISRO to fully operationalise its heavy satellite (say eight/ten-tonne category) launch programme. Possibly, hence ISRO has decided to grab the ‘low hanging fruit’ first. All this offers a perspective for ISRO’s SSLV programme.
ISRO is expecting great future for its SSLV programme from commercial point of view. At present, there is a major global market for small satellite launches. Till recently, ISRO was using the additional weight carrying capability (when available and feasible) of PLSV rockets for commercial purposes. Over the years PSLV has allowed ISRO to launch various mini/micro/nano satellites. Now with SSLV (also with LMV-3) in place, ISRO can plan for exclusive commercial launches. Already, this vehicle has started attracting global customers. SSLV is designed for carrying a payload of 500kg (or 300 kg to Sun synchronous orbit) in 500km planar orbit. The key features of SSLV are low cost, low turn-around time, flexibility towards housing multiple satellites and requirement of minimal launch infrastructure.
At this stage, ISRO requires to push for the full operationalisation of SSLV. The first two developmental flights (one was a success) carried less than 200 kg payload. The SSLV-D1 mission had carried two satellites namely EOS 02 and AzaadiSAT. This mission had a total weight of (135 kg+ 8 kg) around 143 kg. The SSLV-D2 has successfully placed three satellites in the space namely: EOS-07, Janus-1 and AzaadiSAT-2. The total weight carried was (156.3 kg+10.2 kg+ 8.7 kg) 175.2 kg. It is likely that two more missions with this vehicle would happen during 2023. What is important for ISRO is to quickly demonstrate to the global customers that the SSLV is fully capable of carrying a payload of 500 kg and putting it safely at an altitude of 500km. ISRO is also required to ensure that the proposed second spaceport at Kulasekharapatnam in south Tamil Nadu becomes operational quickly. In future all SSLV mission are expected to happen from this launch pad.
SSLV has a major commercial angle associated with it and ISRO is expected to transfer the vehicle development technology to the private sector for conducting these launches in the future. SSLV is also a good news for the Indian armed forces, since it has got significant strategic utility too. This vehicle could be used to launch military satellites too and is expected to realise the military requirement of ‘launch on demand’. Let us hope that SSLV also emerges as a reliable workhorse (or a pony!) for India’s private space industry and the armed forces.
– The writer is a Consultant with MP-IDSA, New Delhi. The views expressed are of the writer and do not necessarily reflect the views of Raksha Anirveda
