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The Indian Space Research Organisation (ISRO) successfully launched the third developmental flight of the Small Satellite Launch Vehicle (SSLV) from the Satish Dhawan Space Centre in Sriharikota on Friday (August 16). The SSLV-D3 placed the Earth observation satellite EOS-08 precisely into orbit.
It also marks the completion of ISRO/Department of Space’s SSLV Development Project. NewSpace India Limited (NSIL), ISRO’s commercial arm, and India’s private space industry can now produce SSLVs for commercial missions.
Prime Minister Narendra Modi also congratulated ISRO in a post on X, saying “The cost-effective SSLV will play an important role in space missions and will also encourage private industry.”
We explain why SSLVs were developed and how they differ from the other major launch vehicles used thus far — the Polar Satellite Launch Vehicle (PSLV) and the Geosynchronous Satellite Launch Vehicle (GSLV).
ISRO’s Small Satellite Launch Vehicle (SSLV) is a three-stage Launch Vehicle configured with three Solid Propulsion Stages. It also has a liquid propulsion-based Velocity Trimming Module (VTM) as a terminal stage, which can help adjust the velocity as it prepares to place the satellite.
Essentially, the aim behind SSLVs is to produce low-cost launch vehicles with short turnaround times and minimal infrastructural requirements. The SSLV can launch satellites weighing up to 500kg and accommodate multiple satellites.
Before SSLVs, smaller payloads had to be sent into Space using other launch vehicles carrying multiple, bigger satellites. They depended upon the launch schedules of those satellites.
As The Indian Express has earlier reported, with the entry of more and more businesses, government agencies, universities and laboratories in the realm of launching satellites in recent years, “the constraints of a piggyback ride have started to hurt.” These organisations usually need to launch smaller payloads.
Former ISRO chairman K Sivan had stated in 2019 at the ISRO headquarters during an annual press conference that “The SSLV is the smallest vehicle at 110-ton mass at ISRO. It will take only 72 hours to integrate, unlike the 70 days taken now for a launch vehicle. Only six people will be required to do the job, instead of 60 people. The entire job will be done in a very short time and the cost will be only around Rs 30 crore. It will be an on-demand vehicle.”
The Polar Satellite Launch Vehicle (PSLV) is the third generation of Indian satellite launch vehicles. first used in 1994. More than 50 successful PSLV launches have taken place to date. It has also been called “the workhorse of ISRO” for consistently delivering various satellites into low earth orbits (less than 2,000 km in altitude) with a high success rate. The PSLV-XL can carry around 1,860 kg of payload.
On the other hand, Geosynchronous Satellite Launch Vehicles (GSLVs) have been instrumental in launching communication satellites in the geosynchronous transfer orbit. According to the European Space Agency (ESA), telecommunications satellites are usually placed in geostationary Earth orbit (GEO). It is a circular orbit 35,786 kilometres above Earth’s equator.
GSLVs have a higher capacity because sending satellites deeper into space requires greater power. Therefore, cryogenic engines consisting of liquid hydrogen and liquid oxygen are used in GSLVs as they provide greater thrust than the engines used in the older launch vehicles. The GSLV Mk-II can carry satellites weighing up to 2,200 kg, while the Mk-III can carry up to 4,000 kg.
