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Another excellent article from the stables tof Tarmak. A well researched comprehensive article on the HSTDV which provide new insights into the ginormous challenges posed and the Titanic efforts needed by all the stakeholders involved.

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Some important points from the above piece.

1. The HSTDV project was conceived in early 2000s.

2. Feasibility studies were carried out from 2004. Dr Pannerselvam, a pioneer in aerodynamics was the first project director of HSTDV.

3. The lead agency in the conceptualisation design, and developement of HSTDV is DRDL.

4. As inferred and said earlier , due to the massive aerodynamic heating, the HSTDV needed to be encapsulated within a protective fairing. It's a split fairing system of 7 metres+ length and 1 metre dia. So the actual HSTDV is around 7 metres in length. Dimensions of HSTDV had been revealed earlier by DRDO in various Defexpos and Aero India.

5. An Agni 1 booster was used. Every Dick Harry and Marty know this. What isn't known is that the designers faced several controllability issues with the existing booster. So they had to redesign and tweak with the control surfaces of the Agni 1 booster. So our booster isn't a vanila booster taken from an existing Agni-1.

6. The designers faced thermal buckling issues with the airframe and some sub systems of the HSTDV which were then ironed out.

7. Extensive studies were done on hypersonic aerodynamics, aero thermodynamics and intake, combustor aerodynamics. Material guys played an important role . Rather it would be an understatement. Intake lip, combustor and nozzle materials were a challenge.

8. The Agni 1 booster faced a high dynamic pressure fluctuations of around 5 bar which is very high for a launch vehicle . So adequate mods were made. In a ballistic missile launch, the booster usually goes up in a parabolic trajectory . Soon it reaches the low density upper atmospheres where kinetic friction is less and also the pressures faced. Here, the booster has to cruise for sometime in the high density portions till the adequate release conditions were realised.

9. The pyro mechanisms needed for the split door fairings were a challenge since all the peyo motors had to function in a text book manner within milliseconds so as to split open and eject the fairings . According to the DRDO guys , no one else had ever tried out such a fairing ejection at this temperature and speed regime before. It was a challenge and Terminal ballistics research l rose to the challenge.

10. The HSTDV was designed to cruise at 29-34 km at 5.8-6.5 Mach no. Great specs for the very first iteration of our HSTDV . I am certain with further testing and refinements and mods , we will improve upon these nos by atleast 25-30 percent.

In earlier posters of HSTDV in various expos DRDO had given the length of the cruise vehicle at 5.6 metres. But 7 metre long fairings were used. The extra length is probably of the conical portion of the fairings at the nose. Some length will be taken up by the payload adapters. HSTDV may have been lengthened a bit.

All in all, the Tarmak article throws light on the huge quantum of research that is going on in multiple fields in the country and the level of technological maturity that our scientists engineers and technicians have managed to achieve.