by Gurbir Singh
SLV-3 was broadly based on the American Scout rocket. Its name derived from the acronym, Solid Controlled Orbital Utility Test rocket, with which countries outside the US were very familiar. The US had invited experiments from other nations that they launched aboard a Scout. The public offer was announced in The Hague at the March 1959 meeting of the COSPAR.[525] Thus technical details of the Scout were more readily available than others launch vehicles. While SLV-3 was not an exact copy of the Scout, a Scout-like design was a natural choice given its success rate of 96% and the experience that Indian scientists had gained during their brief time in the US.
Around 50 industries and institutions from outside ISRO were required to develop and build the major subsystems of SLV-3. The new set of technologies included designing, building and deploying modern instruments and subsystems typically found in all launch vehicles. They include
Inter-stages (small sections between stages)
Heat shield (usually considered for re-entry, but the speed during ascent is sufficiently high to require one too.) Also known as the Payload Fairing.
Self-destruct mechanism (a safety precaution should the launch vehicle veer off course)
Stage-separation mechanism using flexible linear explosive cords
Gyroscopic stabilised platform for IGS
Kevlar epoxy motor casings[526]
Silica and carbon composite nozzles
Multi-source tracking for range safety
Each stage of the SLV-3 had an independent system for directional control. The first stage used the SITVC for the first 17 seconds after launch and then an electro-hydraulically operated fin control after that. The second and third stages used a red fuming nitric acid (RFNA) and hydrazine-powered RCS, and the fourth stage was spin-stabilised. SLV-3 used two distinct methods for stage separation.[527] The separation between the first two stages was carried out by initiating the flexible linear charge located between the stages, and a ball-lock separation system was employed for the third and fourth stages.
The initial SLV-3 plan incorporated a sub-orbital launch using only two of the four stages (S2 and S4) prior to the first orbital flight. However, following a successful RH-560 launch, SLV-3 Project Director Kalam was convinced by his colleague Abdul Majeed’s suggestion that it would be beneficial for the project to scrap the S2+S4 sub-orbital flight and go instead straight for the orbital flight.[528] Following a single board meeting, the sub-orbital flight was dropped, and the SLV-3 programme was fast-tracked to proceed with the first orbital experimental flight.
The first launch attempt of the SLV-3 in August 1979 failed, and the launch vehicle was lost 317 seconds after launch. Once the Failure Analysis Committee (FAC) completed its investigation, Kalam described the painful failure “it was found that even while the rocket was on the launch pad, a full 8 minutes before the take-off, all the RFNA had leaked out. At T minus 8 minutes, a warm-up test was done on the second-stage RCS, as scheduled. A solenoid valve that was designed to close after the warm-up test did not close.
The resulting leak led to the complete depletion of the RFNA.[529] After launch, the first stage worked as planned, but without a working RCS on the second stage, the launch vehicle lost directional control. The flight was terminated, and the whole vehicle was lost prior to the ignition of the third and fourth stages. In July 1980, the second SLV-3 successfully placed India’s first satellite, the Rohini Satellite (RS-1), in Earth orbit. Almost two hours after launch, RS-1’s orbit brought it over the horizon in India, and a tracking station in Trivandrum (now Thiruvananthapuram) detected its signals. With this success, India became the sixth nation with the capability to design, build and launch its own satellites. Each of the four SLV-3 flights saw gradual improvement. Eighteen major improvements were implemented in the fourth flight, the most significant of which was the improved fibre-reinforced material used in the manufacture of the casing of the fourth stage, which reduced its weight from 26 kg to 16 kg. This single modification allowed an increase in the fuel it carried from 270 kg to 320 kg, which increased the orbit to 919 km from 438 km. During its short lifetime, SLV-3 made four flights, the first two were classed as experimental and the other two as developmental. The first flight failed, the third was mostly successful and the other two were recorded as entirely successful.
Sarabhai had established the principle that buying ready-built satellites and launch services from foreign countries was not sufficient; India needed to build the capability within India. Speaking at the press conference soon after the third SLV-3 launch, Dhawan stated “the cost of the total programme, in which 10,000 bright Indians have worked, we could hardly have bought two satellites” and insisted that “if you don't build your nation yourself, nobody else is going to come and build it for you.”[530] The success of the fourth SLV-3 launch attracted widespread international attention and was a morale boost for the nation, as well as the engineers involved.
Prime Minister Indira Gandhi was present at the launch and commented “For me, it was a special thrill. Although I am well above 60, I have not lost the sense of wonder and marvel at what man can achieve.”[531] Satish Dhawan continued to carry the torch of nation-building, crystallising what Sarabhai's imagination had woven into the space programme. A year later, Dhawan and Kalam received two of India’s highest awards, Padma Vibhushan and Padma Bhushan, respectively.[532]
Date
Payload
Result
Notes
10 Aug 1979
Rohini Technology Payload (RTP) 35 kg
Experimental flight. Failure.
A faulty valve caused a fuel leak in the second-stage RCS eight minutes prior to launch, resulting in loss of control and the flight was terminated. The vehicle crashed into the Bay of Bengal 317 seconds after launch. The payload was designed to monitor and provide telemetry on the performance of the launch vehicle.
18 Jul 1980
Rohini RS-1 35 kg
Experimental flight. Success.
RS-1 delivered to the orbit of 305 × 919 km with an inclination of 44.7° and remained in orbit for 20 months.
31 May 1981
Rohini RS-D1 38 kg
Development flight. Partial Success.
One of the SLV-3 stages underperformed, and although RS-D1 arrived in orbit, it was much lower than the intended altitude and did not last long. The planned orbit was 296 × 834 km, but the actual orbit achieved was 186 × 418 km with an inclination of 46°. The orbit decayed after 9 days.
17 April 1983
Rohini RS-D2 41.5 kg
Development flight. Success.
RS-D2 was placed into an orbit of 371 × 861 km with an inclination of 46°. It was in operation for 17 months and remained in orbit until April 1990. Its primary payload, a smart sensor camera, took over 2,500 pictures.
Table 10‑4 SLV-3 Launch History
The fourth SLV-3 was so successful that the two subsequent SLV-3 launches planned were abandoned so that work on the next launch vehicle, the ASLV, could begin earlier. Through the development of SLV-3, ISRO proved its capability in successfully developing a launcher and placing an operational satellite in orbit. ISRO’s next launcher, the ASLV, needed an enhanced launch capacity to put larger satellites into higher orbits.
Augmented Satellite Launch Vehicle (ASLV)
The Government of India approved the ASLV in 1981 (a year after the first successful launch of the SLV-3) to validate new technologies needed for future launch vehicles, such as strap-on boosters, canted nozzles, a bulbous heat shield to carry a large payload, vertical integration of the launch vehicle and inertial guidance system for navigation. The need for vertical integration also motivated the development of the FLP with a mobile service tower at Sriharikota. The FLP is still in active service.[533]
One of the key design changes in ASLV compared to SLV-3 was the use of strap-on boosters. To test strap-on (SO) technology before the first ASLV test, ISRO launched a two-stage hybrid launch vehicle, SO-300-200, constructed from a RH-300 cor
e stage with two RH-200 strap-ons. This launch on 16 October 1985 allowed ISRO engineers to build and test canted nozzles, explosive bolts for strap-on separation and asymmetric ignition, strap-on (RH-200) ignition at launch and ignition of the core stage (RH-300) during flight.[534]
ASLV was conceptually a simple modification of SLV-3. It was SLV-3 with two strap-ons. The first stage of SLV-3 was augmented with another SLV-3 first stage on each side as strap-on boosters.[535] Although ASLV used solid fuel for propulsion in all stages, it used a small quantity of liquid fuel for directional control.[536] While SLV-3 had four stages, ASLV had five. However, to maintain consistency with the existing naming convention, the two strap-on boosters were referred to as stage zero or simply the booster stage. The rest of ASLV was pretty much SLV-3. At launch, ASLV weighed 40 tonnes, stood 24 m high and had a total flight duration of 640 seconds to reach the orbit. Compared to the SLV-3, the ASLV payload capability increased to 150 kg to LEO of 400 km.
At launch, only the two strap-on boosters of ASLV ignited. The core stage ignited at T+49 seconds, just after the boosters were exhausted. The booster separation occurred at T+55, while the first stage was active. At T+1 minute and 35 seconds, the first-stage propellant was exhausted and the stage discarded. The second stage ignited and burned for 36 seconds. During this phase, with ASLV is in space at an altitude of 120 km, the heat shield was discarded.
There was a pause after the third stage as ASLV coasted for 294 seconds. Then, the final stage ignited. This fourth stage burned for 32 seconds and generated the spin required for payload stability. After a total flight of 10 minutes and 40 seconds, the spinning satellite separated from the launcher and entered orbit.[537] The propellant used in all stages of ASLV was solid but of two distinct types, polybutadiene acrylonitrile (PBAN) and High Energy Fuel (HEF-20) developed by ISRO.[538] HEF-20 is a more efficient propellant than PBAN. PBAN was used in the first two stages so that its weight was discarded early in the flight, and HEF-20 was used in the final two stages, just as in SLV-3.
SLV-3
Stage 1
Stage 2
Stage 3
Stage 4
Burn Time (second)
49
40
45
3
Propellant (tonne)
8.6
3
1
0.26
Length × Width (m)
10 × 1
6.4 × 0.8
2.5 × 0.8
1.5 × 0.7
Lift-off Weight (tonne)
10.8
4.9
1.5
0.4
ASLV
Stage 0
Stage 1
Stage 2
Stage 3
Stage 4
Burn Time (second)
46
46
36
43
32
Propellant (tonne)
10 × 2
10
3.8
1.2
0.4
Length × Diameter (m)
10 × 1
10 × 1
6.4 × 0.8
2.5 × 0.8
1.4 × 0.65
Lift-off Weight (tonne)
2 X 8.6
8.8
3.1
1.1
0.3
Table 10‑5 A Comparison of SLV-3 and ASLV[539]
In total, four ASLV launches attempted to place a satellite of the Stretched Rohini Satellite Series (SROSS) carrying a science payload into LEO. All ASLV flights were designated development flights and therefore were identified with the prefix D. The SROSS series (SROSS A, B, C and C2) satellites were small solar-powered, spin-stabilised satellites with a mass of around 106 kg with two science instruments to collect data on the plasma within the Earth’s ionosphere and cosmic gamma-ray radiation. The primary objective of SROSS-A was to test and evaluate the performance of the ASLV launcher itself, so it did not have a science payload. Instead, it had an optical reflector so its position could be located using ground-based lasers to assist with trajectory determination.
ASLV-D1, the first ASLV, was launched at 12:09 IST on 24 March 1987. However, 46 seconds after launch, the mission was lost. The two strap-ons (stage 0) were exhausted, but the core stage did not ignite as scheduled. The FAC identified the fault with the electrical signal for the ignition of the first stage. The electrical ignition signal for the first stage did not reach it. Why that happened remained unclear. Perhaps, the vibration at launch or the strong high-speed winds at 10-km altitude dislodged connections resulting in an open circuit, or perhaps, there was an inadvertent short circuit in both the primary and backup ignition circuits, or maybe, there was a random malfunction of the safety circuit that arms the ignition system. In its report, the FAC recommended an additional redundant ignition system to prevent a repetition.
Just over a year later, the ASLV-D2 flight also failed at about the same time in the flight (around T+50 seconds). After a successful booster phase, the first stage ignited, but then the launch vehicle lost attitudinal control and broke up. Following two failures in succession, two committees, one within ISRO headed by S.C. Gupta and another with a broader national remit headed by Roddam Narasimha were established to investigate the cause and make recommendations. The FAC concluded that the second failure was not a repeat of the first. This time, the second stage had ignited, but after a brief, fatal delay. The investigation revealed that the strap-ons had burned out 1.5 seconds earlier than expected.[540] The transition from the first stage to the second occurred at 10 km, where the wind gusts were strong. While each of the stages had a SITVC control mechanism, during those 1.5 (some sources indicate 0.5) seconds, neither was actively controlling the launch vehicle. Like a car without a driver, the launch vehicle deviated and no longer pointed in the direction of travel. At high-speed the formidable aerodynamic forces resulted in catastrophic failure.[541]
Additional redundancy for booster separation and a Real-Time Decision System (RTDS) to prevent a ‘no control zone’ were recommended. The RTDS would continually monitor the thrust of the strap-ons and ignite the first stage once the thrust of the strap-on drops to a pre-specified threshold. Fins for vertical stabilisation used in SLV-3 but removed initially for ASLV were restored. The inclusion of the RTDS and other recommendations resulted in a reduction of payload capacity from 150 kg to 106 kg.
Figure 10‑4 ISRO’s First Hybrid Launch Vehicle with Strap-On, SO-300-200, to Test Strap-On Technology. 16 October 1985. Credit ISRO
ASLV D-3 was launched in May 1992 and placed SROSS-C in orbit but lower than the intended one. A problem in the final stage prevented SROSS-C from attaining the expected orbit of 938 km by 437 km. It only managed a lower orbit of 391 km by 267 km. Although tenuous, the atmosphere caused sufficient drag for SROSS-C to re-enter two months after the launch. The fourth and final launch, ASLV-D4, in May 1994 placed SROSS-C2 in the intended orbit. It carried enhanced science payloads and exceeded in all its mission objectives. SROSS-C2 had a planned mission lifetime of only six months but operated for four years. During its operational life, SROSS-C2 discovered 12 gamma-ray sources and was included in NASA’s Third Interplanetary Network.[542] The ASLV programme provided engineers with the opportunity to understand and experience deploying and operating a Closed Loop Guidance System (CLGS), which constantly monitored the launch vehicle’s position, velocity, direction and attitude.
Launch Date
Payload
Result
Notes
24 March 1987 ASLV-D1
SROSS-A. 150 kg. Carried two retro-reflectors for tracking.
Development flight. Failure.
The first stage failed to ignite. The launch vehicle achieved a maximum altitude of only 10 km.
13 July 1988 ASLV-D2
SROSS-B. 150 kg. Carried a West German optical scanner and ISRO's gamma-ray burst experiment.
Development flight. Failure.
The boo
ster phase ended about one second prematurely. The launch vehicle lost directional control and broke up.
20 May 1992 ASLV-D3
SROSS-C. 106 kg. Carried a gamma-ray burst experiment and a retarded potential analyser experiment.
Development flight. Partial Failure.
Partial failure of the fourth stage resulted in a lower than planned orbit of 391 km × 267 km with an inclination of 46°. The satellite operated from 25 May 1992 until re-entry on 15 July 1992.
4 May 1994 ASLV D4
SROSS-C2. 115 kg. Carried enhanced versions of a gamma-ray burst experiment and a retarded potential analyser experiment (a plasma detector).
Development flight. Success.
SROSS-C2 was placed in an orbit of 600 km × 430 km with an inclination of 45° as planned and remained in orbit until 12 July 2001. It discovered 12 gamma-ray burst sources.
Table 10‑6 ASLV Launch History
It maintained the desired trajectory by commanding course changes using the SITVC and RCS systems. The CLGS used accelerometers and gyroscopes on the launch vehicle to provide real-time information for navigational manoeuvres during ascent. SLV-3 had used an Open Loop Guidance System (OLGS), in which the launch vehicle was pre-programmed with a set of manoeuvres prior to launch. The technology for OLGS as used in launch vehicles is almost identical to that used by early missiles. Initially, India had acquired assistance with OLGS from France; the US had refused.[543] Unlike CLGS, OLGS operated in the absence of real-time feedback. Once launched, the course changes were conducted as programmed without catering for trajectory variations that may result from inconsistent thrust or dynamic atmospheric turbulence. The CLGS could deliver the satellite to orbit with high precision. The SLV-3 D2 flight using OLGS had delivered the RS-D2 satellite within 62 km of the designated apogee (furthest point of the orbit from Earth), whereas the fourth flight of ASLV, using CLGS, delivered the SROSS-C2 satellite to within 18 km of the planned apogee.[544]