what is “rh” on an indian sounding rocket

RH on an Indian sounding rocket stands for "Rohini," which is the name of the rocket family developed by the Indian Space Research Organisation (ISRO) ). The rockets in the Rohini series are designated with the letters RH, followed by a number corresponding to the diameter (in millimeters) of the rocket. For example, the RH-75 was the first sounding rocket developed by India, with a diameter of 75 millimeters (3.0 in) ). The RH-200, RH-300, and RH-560 are other rockets in the Rohini series, with the number in the name indicating the diameter of the rocket in millimeters.