ISRO eyeing 200th successful launch of Rohini RH-200

Context

In a few weeks’ time, the Indian Space Research Organisation (ISRO) hopes to achieve a remarkable feat — the 200th successful launch of the Rohini RH-200 sounding rocket in a row.

About Sounding Rocket

• Sounding rockets are one or two stage solid propellant rockets used for probing the upper atmospheric regions and for space research. 
• Sounding in the rocket context is equivalent to "taking a measurement".
• The rockets are used to launch instruments from 48 to 145 km above the surface of the Earth, the altitude generally between weather balloons and satellites.
• The maximum altitude for balloons is about 40 km and the minimum for satellites is approximately 121 km.
• They also serve as easily affordable platforms to test or prove prototypes of new components or subsystems intended for use in launch vehicles and satellites.

About Rohini RH-200

• RH-200 is a two-stage rocket capable of climbing to a height of 70 km bearing scientific payloads.
• The first and second stages of RH-200 are powered by solid motors. 
• The ‘200’ in the name denotes the diameter of the rocket in mm.
• Other operational Rohini variants are RH-300 Mk-II and RH-560 Mk-III.
• For years, the RH-200 rocket had used a polyvinyl chloride (PVC)-based propellant.
• The first RH-200 to use a new propellant based on hydroxyl-terminated Polybutadiene (HTPB) was successfully flown from the TERLS in September 2020.
• The first and second stages of the RH200 rocket are powered by solid motors.
• Since the inception of the RH200 rocket, both solid stages have been processed using polyvinyl chloride (PVC) based propellant.
• As compared to PVC based propellants, HTPB based propellant is more energetic, has higher mechanical & interface properties and has less defects due to lower processing temperature.

History of sounding rockets in India

• Sounding rockets have an important place in the ISRO story.
• The first sounding rocket to be launched from Thumba was the American Nike-Apache — on November 21, 1963.
• After that, two-stage rockets imported from Russia (M-100) and France (Centaure) were flown. The ISRO launched its own version — Rohini RH-75 — in 1967.
• The ISRO has launched more than 1,600 RH-200 rockets so far.
• Currently, the RH200, RH300 MkII and RH560 Mk-III rockets are operational which were developed during the early phase of our journey in rocketry.