In the 1960s, ISRO started to build sound rockets for upper atmosphere research. These sound rockets were simple by nature and go 20–50 kilometres into the atmosphere. Large numbers of sounding rockets have been developed and launched from Thumba Equatorial Rocket Launching Station (TERLS).
ISRO has developed a series of sounding rockets called Rohini series, important among them being RH-200, RH-300 and RH-560, number in the name indicating the diameter of the rocket in mm. These rockets weigh up to few hundreds of kilograms.
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The weight of SLV was 17 tons. Next ISRO builds a bigger rocket ASLV in the 1980s. ASLV failed all its test flight. But ISRO got valuable experience and data. Based on that experience in the 1990s, ISRO has developed 200 tons plus PSLV. And in the 2000s, ISRO builds a much bigger GSLV.
So we can see ISRO gradually developed its knowledge, technology and skills from smaller less complex rocket (the 1970s) to bigger very complex rockets (2000s). ISRO does not try to build PSLV and GSLV directly. If it had tried to build PSLV directly without developing smaller and less complex rockets then it would fail.
Kaveri is an 8000 kg to 10,000 kg thrust engine. Technology for such a high thrust engine is too much complex.
DRDO has directly tried to build such complex technology without developing a less complex jet engine. GTRE was established in the late 1950s. If they followed the same path as the ISRO, then they would not fail in the Kaveri project. If GTRE starts developing small jet engines for trainer aircraft in the 1960s then they would be much more mature to take the Kaveri project.
DRDO always tried to develop a cutting edge without basic knowledge and experience in that technology and failed. HAL has understood this gap of knowledge. So in the 1960s, HAL has started a jet engine project for jet trainer aircraft. in 1965, HAL has started a 2.5 KN thrust capable turbojet engine, which was named HJE-2500.
It was supposed to be integrated with HJT-16 training aircraft. All ground test was successfully completed. Now IAF’s permission was seeking to integrate it into HJT-16. But IAF was not tested to use a new engine for HJT-16. Because IAF was found that HF-24 will be retired soon.
As HF-24 was only in use as tactical light attack aircraft. So its engine will be less in use. After retirement, more than 250 engines of HF-24 will be in IAF’s inventory without use. So IAF wants to use those engines for its HJT-16.
So HJE-2500 was rejected. HAL also did not continue this project. Neither HAL took any other jet engine project for the next 40 years.
