Rohini (rocket family)

Rohini is a series of sounding rockets developed by the Indian Space Research Organisation (ISRO) for meteorological and atmospheric study. These sounding rockets are capable of carrying payloads of 2 to 200 kg between altitudes of 100 to 500 km. The ISRO currently uses RH-200, RH-300,Mk-II, RH-560 Mk-II and RH-560 Mk-III rockets, which are launched from the Thumba Equatorial Rocket Launching Station (TERLS) in Thumba and the Satish Dhawan Space Centre in Sriharikota. Various programs such as Equatorial ElectroJet (EEJ), Leonid Meteor Shower (LMS), Indian Middle Atmosphere Programme (IMAP), Monsoon Experiment (MONEX), Middle Atmosphere Dynamics (MIDAS), and Sooryagrahan-2010 have been conducted using the Rohini sounding rocket series. It has been the forerunners for ISRO's heavier and more complex launch vehicles, with continued usage even today for atmospheric and meteorological experiment and research. Currently, three versions are offered as operational sounding rockets, which cover a payload range of 8-100 Kg and an apogee range of 80-475 km. Several scientific missions with national and international participation have been conducted using the Rohini sounding rockets.

Brief History
On November 21, 1963, the American Nike-Apache was the first sounding rocket to launch from Thumba. Following that, two-stage rockets from France (Centaure) and Russia (M-100) were launched. In 1967, the Rohini RH-75, an ISRO variant, was launched. The Rohini Sounding Rocket (RSR) Programme was established in 1975 to encompass all sounding rocket operations.

Nomenclature
The rockets in the series are designated with the letters RH (for "Rohini"), followed by a number corresponding to the diameter (in millimetres) of the rocket.

RH-75
The RH-75, the first sounding rocket developed by India, It weighed 32 kg, had a diameter of 75 mm and flew 15 times between November 1967 and September 1968.

RH-100
The RH-100 was a single-stage solid-fuel rocket that was capable of carrying its payload up to an altitude of 55 km or more. When paired with a 650mm long by 40mm wide copper shaft dart used for meteorological research, it was referred to as a Menaka-I rocket.

RH-125
This rocket was launched on October 9, 1971, from Sriharikota. It was a single-stage rocket using a solid propellant, carrying a 7 kg payload to 19 km in altitude. It flew twice between January 1970 and October 1971. It was used in testing and perfecting various techniques like staging, destruct system, separation devices and clustering. It was also used as a booster to the weather forecasting rockets. As such it was named as Menaka II which worked along with Menaka I.

RH-200
The RH-200 is a two-stage rocket that can reach up to a maximum altitude of 80 km. Solid motors power the first and second stages of the RH-200. A polyvinyl chloride (PVC)-based propellant had previously been employed with the RH-200 rocket. In September 2020, a new propellant based on hydroxyl-terminated polybutadiene (HTPB) was successfully used to flow it from the TERLS.

RH-300
The RH-300 is a single stage sounding rocket, derived from French Belier rocket engine technology. It has a launch altitude of 100 km (62 mi). A variant, the RH-300 Mk-II, has a maximum launch altitude of 116 km. It has ability to lift a payload up to 80 kilograms (20 kg of scientific payload) having volume measuring 380*500 mm in diameter. It is capable of reaching very high acceleration (20 G to M6). Numerous payloads can be tested in a single flight.

RH-560
This two stage vehicle is derived from French Stromboli engine technology. Another variant, the RH-560 Mk-II, can reach a maximum launch altitude of 548 km. The RH-560 Mk-III variant's maiden flight (the flight was successful) was 12 March 2021. It achieved an apogee of 511.73 kms against the pre-flight prediction of 476 kms. The payloads were Electron and Neutral Wind Probe (ENWi), Langmuir Probe (LP) and Tri Methyl Aluminium (TMA).

Applications
The RH-200 is used for meteorological studies, the RH-300 Mk-II for Middle atmospheric studies and the RH-560 Mk-II for Upper atmospheric studies and ionospheric studies. The RH-200 was used as the rocket for the first payload launch in India made by students of VIT University in Vellore.