SOHEIL
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SLV-3 & ASLV
With the establishment of the Indian Space Research Organization (ISRO) in the year 1969 began also India with the development of a space-rocket, to launch earth-satellites. For it certain experiences could be used of the manufacture of solid propellant motors for sounding rockets, to build the first four-stage rocket SLV-3.
The first sounding rocket RH-75 (the number gives the interior diameter of the nozzle in mm) had been launched in November 1967 from the Thumba launch site. It followed the sounding rockets RH-100, RH-125, RH-300 and RH-560 .
The first launcher SLV-3 weighed 17 tons and was 22 m high with a 1 m diameter. Its payload mass in circular 500 km orbit was around 40 kg.
The four stages are solid propellant type. The first stage is of 1,000 mm diameter and carries 8.6 tonnes of PBAN (Polybutadine Acrylo Nitrate) propellant developed indigenously. The motor case fabricated from 15 CDV6 steel sheets and forgings is in three longitudinal segments. Propellant is cast separately in each segment and then joined together. The segmented motor technology has been specifically developed for the first stage motor. This motor develops an average thrust of 46 tonnes and burns for 50 seconds with a specific impulse value of 254 seconds (vacuum). The second stage motor is of 800 mm diameter and carries 3 tonnes of PBAN propellant in a single monolithic grain. This motor is also made of 15 CDV6 steel sheets and forgings. The motor has an average thrust of 20 tonnes and burns for 44 seconds and gives a specific impulse of 268 seconds (vacuum). The third and fourth stage motors use fibre reinforced plastic motor cases and high energy propellant (HEF 20). Third stage with a diameter of 800 mm houses one tonne of propellant and gives an average thrust of 6.3 tonnes. Fourth stage has a diameter of 650 mm, carries 262 kg propellant and provides a thrust of 2.4 tonnes. The specific impulse of fourth stage is 284 seconds (vacuum).
The ASLV was derived from SLV-3 by the addition of two boosters which dimensions and performances were similar to those of the first stage. Those boosters provided the takeoff of the vehicle. This caused the first stage to be modified to operate in the air. ASLV capacity reached 150 kg payload in LEO.
Rockets were launched from the Sriharikota base on the Indian East coast. This site is operational since the success of a RH-125 sounding rocket in October 1971.
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