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Sounding Rockets

Sounding rockets are one or two stage solid propellant rockets used for probing the upper atmospheric regions and for space research. 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. With the establishment of the Thumba Equatorial Rocket Launching Station (TERLS) in 1963 at Thumba, a location close to the magnetic equator, there was a quantum jump in the scope for aeronomy and atmospheric sciences in India.

Vikram A. Sarabhai, who scripted a vision for India in space research in the early sixties, had no doubt that a good understanding of science and its sound application in the form of technology is absolutely essential for development of a nation. It is this clear thinking that helped him counter those who raised eyebrows about India embarking on a space program while its people were finding it hard to have two square meals a day. He also believed that India should not make the mistake of initiating scientific research in new and fashionable fields for the sake of prestige. The selection of a field of activity, he felt, should depend upon the contribution it can make to the defined national goals. In line with these goals, he identified three specific applications for space research in India: remote sensing, communications and meteorology. Even today, these three areas remain the raison d’etre of the Indian space program.

Thanks to Sarabhai’s persistent efforts, the Indian space program, had a humble birth in a sleepy fishing hamlet, outside Trivandrum town (now Thiruvananthapuram) in Kerala, when Indian National Committee for Space Research (INCOSPAR), set up in 1959, chose this location for setting up a sounding rocket launching facility four years later. A team of six young scientists and engineers, all in their twenties, were sent to the U.S. for training, before they were asked to proceed to Thumba to launch a Nike-Apache rocket procurred from NASA. Their trials and tribulations and sweet success at the end had been well recorded in the annals of history of Indian science.

The launch of the first sounding rocket from Thumba near Thiruvananthapuram, Kerala on 21 November 1963, marked the beginning of the Indian Space Programme . Sounding rockets made it possible to probe the atmosphere in situ using rocket-borne instrumentation. The first rockets were two-stage rockets imported from Russia (M-100) and France (Centaure). While the M-100 could carry a payload of 70 kg to an altitude of 85 km, the Centaure was capable of reaching 150 km with a payload of approximately 30 kg. ISRO started launching indigenously made sounding rockets from 1965 and experience gained was of immense value in the mastering of solid propellant technology.

Four years later, first indigenously designed and built sounding rocket, weighting just 10 kg and having a diameter of 75 millimetre (Rohini-75), was launched from the Thumba Equatorial Rocket Launching Station (TERLS). It attained an altitude of 4.2 kilometers. Rohini-75 (RH-75) might have been a plaything, if compared to the GSLV which was 40,000 times heavier, but it helped Indian space scientists establish a strong foundation in rocketry. Subsequent years saw India building and launching taller and heavier sounding rockets to higher altitudes using home-made propellants. In a matter of five years, the launch weight of Indian rockets increased from 60 kg to over two tonnes. There was a substantial increase in number of subsystems and components that went into rockets as well.

Scientists soon realized the importance of developing and producing suitable propellants for the rocket program. Propellants which supply energy to the rocket are generally divided into two classes - solid or liquid. While sounding rockets generally use solid propellants, heavier satellite launchers use a combination of solid and liquid propellants. While solid propellants are relatively easy to produce, they have an inherent disadvantage; they cannot be switched off, once ignited. On the other hand, liquid propellant technology is complex, but the energy efficiency of liquid propellants is high.

As the know-how to develop propellants was closely-guarded, as being part of missile technology abroad, India embarked on a program to develop indigenous propellant technology right from the start. While the first few sounding rockets launched from Thumba such as RH-75, RH-100 and RH-125 (numbers indicate the diameter of the rockets) used cordite (a mixture of nitroglycerine and nitrocellulose) procurred from a factory in the neighbouring State of Tamil Nadu, the need for developing a new propellant in-house was felt. The efforts to develop new propellants were independently led by two eminent scientists - Vasant Gowariker, who later became the Director of Vikram Sarabahi Space Centre (VSC), Thiruvananthapuram, and Secretary of Department of Science and technology (DST) and A E Muthunayagam, later Secretary of the Department of Ocean Development (DoD).

Gowariker, a chemical engineer of repute, was working with the UK Atomic Energy Authority, before he was wooed away by Sarabhai to make propellants for Indian rockets. Gowariker, years later, was quoted as jocularly saying his first laboratory in Thumba was housed in a cowshed, adjacent to the St. Mary Magdalene’s church!

Whatever be the conditions in which these two teams were working, both were successful in independently developing new solid propellants based on raw materials available in the country. During these initial years of space research in the country, Sarabhai and his band of young scientists were using lightweight sounding rockets for various atmospheric phenomena. Untimely death of Vikram A. Sarabhai on December 30, 1971, at the age of 52, was a major blow to the Indian space program. A visionary par excellence, Sarabhai’s contribution to diverse fields such as science, business and administration was unparallel in the Indian history.

In 1975, all sounding rocket activities were consolidated under the Rohini Sounding Rocket (RSR) Programme. RH-75, with a diameter of 75mm was the first truly Indian sounding rocket, which was followed by RH-100 and RH-125 rockets. The sounding rocket programme was the bedrock on which the edifice of launch vehicle technology in ISRO could be built. It is possible to conduct coordinated campaigns by simultaneously launching sounding rockets from different locations. It is also possible to launch several sounding rockets in a single day. 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.