The Indian Space Programme
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It is expected to become operational around the end of 2017.[502] Since its establishment, Sriharikota has conducted just over 50 launches of substantial payloads to Earth, Lunar and Martian orbits. When eventually built, the TLP at Sriharikota will be subject to the same restrictions of launch trajectory as the exiting launch pads. ISRO contemplated the idea of establishing another launch site south from Sriharikota from where PSLV could be launched due south, directly into polar orbit, the proposal was initially dropped but the lobbying continues.[503] One proposal for a TLP would have placed it near the southern tip of India (Kulasekarapattinam in Tamil Nadu), which could have increased the launch capacity of a PSLV by about 300 kg.
This increase in capacity would come from the more southerly (closer to the equator) location and a reduction in the post-launch manoeuvre required to avoid countries in the ground track of its trajectory.[504] In addition, the site is conveniently located close to IPRC. Scientists, engineers and politicians have been championing the Tamil Nadu site for the TLP but appear to have lost out for the present.[505] As India's space operations continue to evolve, perhaps the Kulasekarpattinam site will be commissioned in the future.
Chapter Ten
ISRO's Rockets
S pace is only a 100 km away, less than the distance to Chennai from Sriharikota. Officially designated as the Karman line[506], an altitude of 62 miles (100 km) is internationally recognised as the boundary between Earth and space. A spacecraft at an altitude of 100 km or above is in space. As with the Earth’s equator, there is no visible indicator marking the Karman line. At an altitude of 100 km, the Earth’s atmosphere is so negligible that wings cannot generate lift, and the absence of oxygen prevents combustion engines from working, so flight by aircraft is technically impossible. Getting to space is about velocity not altitude. Rockets, or launch vehicles, are the only means by which a spacecraft can be delivered to space with the required velocity to stay there. Unless a spacecraft has a velocity of at least 5 miles/s (8 km/s), it will fail to maintain orbit and fall back to Earth. It is the job of the launch vehicle, the rocket, to give the spacecraft this initial velocity essential for it to reach and stay in space.
The heavier the payload or higher the orbit, the larger the rocket has to be to carry the additional fuel. India’s primary launch vehicle is just over 300 tonnes, while European Space Agency’s (ESA) Ariane 5 is about 780 tonnes. The American Saturn 5 rocket that took three men a quarter of a million miles to the Moon weighed 3,000 tonnes. Saturn 5 was and remains the largest and most powerful rocket ever flown (USSR’s N1 rocket was equally powerful but not successfully flown).
The first goal that ISRO (then INCOSPAR) set itself following the successful launch of the Nike-Apache rockets in 1962 was to develop its own rockets. In the years that followed, young Indian rocket engineers gradually developed the technology and techniques to produce rocket fuel and build rockets. They also built the infrastructure necessary to launch, track and communicate with a spacecraft beyond the Karman line. While the USSR and US engaged in the space race and developed the technology for human spaceflight and the Moon landing, most other nations engaged in the more prosaic use of rockets (initially sounding rockets) for the scientific investigation of the Earth’s upper atmosphere. During the early 1960s, many nations were preoccupied with their commitments to the IGY (1957-58). Experiments using sounding rockets spread around the world to places, including India, Argentina, Canada, Japan, Pakistan, Denmark, Norway, France, Germany, Spain, Sweden, the UK, US and the USSR.[507]
Figure 10‑1 ISRO Family of Launch Vehicles. (Left to Right) SLV-3, ASLV, PSLV, GSLV Mk2, GSLV-Mk3. Credit Wikimedia Commons
Sounding rockets were used to investigate (to “sound” out) the upper regions of the atmosphere made accessible with the advent of rockets. They could study the regions of the Earth’s atmosphere above where balloons could go and below where satellites orbit. India’s first sounding rocket was the RH-75 weighing just 7 kg. It was first tested in November 1967. RH was the abbreviation for the name Rohini and 75 its diameter in millimetres. RH-75 used a cordite, a mixture of nitro-glycerine and nitrocellulose, manufactured in cylinders with a hollow core in a factory in Tamil Nadu and transported by road to Thumba. Fuelling the RH-75 required sliding the cordite cores into an aluminium casing and inserting a black-powder based igniter at the base.[508]
Between 1967 and 1995, eight versions of the Rohini were developed, each successively more powerful, with a capacity to deliver a heavier payload to a higher altitude.[509] Over 1,200 RH-200 were launched from Thumba and Sriharikota for science programmes, such as Monsoon Experiment, Equatorial Wave Studies and Dynamic Middle Atmosphere.[510] In November 1997, an Indian-built sounding rocket was launched from outside India for the first time. A RH-300 Mk11 was launched from Svalbard Rocket Launching Range in Norway. At a latitude of 78ºN, Svalbard is one of the northern-most launch sites on Earth. [511]
Propellant Type
Typical Isp
Characteristics
Solid
250
Cheap, relatively easy to manufacture, store and transport. Rocket-motor technology is not complex. Its main disadvantage is that once ignition starts, it cannot be stopped or regulated. Typically, HTPB, a common solid fuel used in the first stage of the PSLV, has an Isp of 247.
Liquid
335
An engine using liquid propellant can be started and stopped and restarted multiple times. This ability to regulate flow and thus control thrust is a necessary requirement to place spacecraft in a precise orbit and later help maintain that orbit.
Semi-Cryogenic
370
Semi-cryogenic rocket propellant is one of the oldest, and still very common, a combination of fuel and oxidiser. The fuel is typically kerosene, and liquid oxygen at -183°C is the oxidiser.
Cryogenic
455
The most efficient rocket engines in common use today. A cryogenic engine uses LH2 at -253°C and LOX at -183 °C, which is a formidable engineering challenge.
Table 10‑1 Relative Differences between Propellant Types
These sounding rockets did not represent profound technological achievements. They provided the initial experience necessary on the road to a national space programme. During the late 1960s, Indian scientists and engineers went to study and train in France, and French engineers came to Thumba to help set up plants for the local manufacture of the Centaure rocket stages and its propellant. Sarabhai envisaged this as a necessary phase for a transition from permanent reliance on foreign nations and insisted that “space technology was acquired under licence from abroad only as a means to buy time.”[512] Between 1965 and 1988, 81 Centaurs were launched from Thumba; all but 10 had been manufactured in India under licence.
Engines that use solid, liquid, semi-cryogenic and cryogenic propellants have a respectively higher Isp. For example, to generate 1 tonne of thrust, 3.8 kg of solid, 3.5 kg of liquid or just over 2 kg of cryogenic propellant is required per second.[513] Each propellant type has unique characteristics, ease of manufacture, storage, transport, cost and hazards associated with its handling. Electric propulsion is the most efficient with an Isp of over 1000 but has low thrust. Whilst it can manoeuvre spacecraft in orbit slowly over time with much greater efficiency then chemical propellant, it lacks the required thrust for use at launch.
Starting in the 1960s with rocket motors that used solid propellants, India has now developed rocket engines that use liquid, semi-cryogenic and cryogenic technologies, too. [514] Engineers measure the efficiency of a rocket motor or engine using the concept of Specific Impulse (Isp). One Isp is the thrust generated by 1 kg of propellant in 1 second of combustion measured in units of seconds.[515] The higher the Isp of a rocket engine, the more efficient it is. The more efficient the engine, the less the propellant required to place a given payload in orbit.
Launch
Vehicle
SLV
ASLV
PSLV
GSLV
Period of Development
1972–1983
1982–1994
1982–2017
1991–2017
Mass at Launch (tonne)
17
40
320
640
Length × Width (m)
22 × 1
24 × 1
44 × 2.8
51 × 4
Max Payload (kg)
40
150
1,400
2,500
Number of Stages
4
5
4
3
Propellant Type
Solid
Solid
Solid and Liquid
Solid, Liquid and Cryogenic
Guidance
Open Loop Inertial
Closed Loop Inertial
Closed Loop Inertial
Closed Loop Inertial
Orbit Type and Altitude (km)
LEO
400
LEO
400
LEO and SSPO
800
GTO
36,000
Total launches (mid 2017)
4
4
40
17
Table 10‑2 Key Characteristics of ISRO's Launch Vehicles up to mid- 2017[516]
In January 2014, ISRO overcame the final challenge and successfully flight-tested its own cryogenic engine with the launch of GSLV-Mk2 that carried GSAT-14. From the tiny RH-75, ISRO has gone on in every successive decade to develop a launch vehicle with enhanced capabilities, SLV-3 in the 1970s, ASLV in the 1980s, PSLV in the 1990s and GSLV since the 2000s. It has not been a smooth, clean serial development. There have been overlaps, with many teams working on multiple technologies simultaneously and that approach continues today.
ISRO has two operational launch systems, PSLV and GSLV, and is actively developing new systems for the future. Larger rockets are required to take heavier payloads to higher orbits. There are broadly three types of Earth orbits used by ISRO's satellites, LEO at 200–2,000 km parallel with the Earth’s equator, a pole to pole Sun-synchronous polar orbit (SSPO) at 600–800 km and GEO at 36,000 km also parallel to the equator.
GSLV has placed a few payloads into orbit, but with almost 40 successful launches, the PSLV is ISRO’s current launcher of choice. The LVM3, first launched in December 2014 to a sub-orbital flight, matured into the GSLV-Mk3 and in June 2017 successfully placed the GSAT-19 in orbit. The Unified Launch Vehicle (ULV) and Heavy Lift Launch Vehicle (HLV) are ISRO's next evolutionary step in launch vehicle design. Still, in the early design stage, the ULV and HLV will use semi-cryogenic and cryogenic technologies. The initial configuration is designed to deliver six tonnes and more to GTO and eventually replace the PSLV and GSLV in the coming decades.
Inertial Guidance System
Rocket engines provide the power to place a spacecraft in orbit. One of the many onboard subsystems is the Inertial Guidance System (IGS), which is the directional control system ensuring that the satellite is delivered to the designated orbit with high precision. IGS technology is highly classified since it can be used by rockets or missiles. Developing IGS technology was one of the many “formidable problems” that ISRO had to overcome.[517] IGS uses the basic principle that if the starting place and time are known, and all changes in speed, direction and duration are measured during the journey, then position and distance to the desired destination can be calculated at any stage in the journey.
In the past, IGS relied only on mechanical components engineered with high precision, analogue signals and mechanical actuators. Today, they are likely to be digital (commonly found in smartphones), but the principle remains the same. Three accelerometers detect motion in each of the three directions, east-west, north-south and up-down. A set of three specially positioned gyroscopes can detect rotation in each of the three planes. Like a compass floating in a bath of water on a moving ship, these sensors are fixed to a platform within the launch vehicle to maintain the original orientation irrespective of the direction of the launch vehicle. As the launch vehicle moves from take-off to its destination in orbit, electronic signals generated by the sensors are sent to the onboard computer. The computer detects where the launch vehicle is, knows where it should be, dynamically calculates the required directional change and activates the directional control mechanism to achieve it.
Figure 10‑2 Inertial Guidance System. Credit GEC Marconi
There are four primary control techniques used as steering mechanisms for launch vehicles, secondary injection thrust vector control (SITVC), Flex Nozzle Control System, Engine Gimbal and reaction control system (RCS). SITVC is used on a solid stage at the nozzle where the high-temperature exhaust is escaping. Small quantities of strontium perchlorate are injected at particular points around the nozzle to create a differential thrust to modify direction.[518] An alternative to SITVC is to implement a flex nozzle where the nozzle is not fixed and can move to change the direction of flight.[519] Engine gimbaling is similar to flex nozzle but is a more sophisticated technique, where the whole nozzle can be moved, like a ship's rudder, to modify the direction of flight.
The RCS is a mini rocket engine (also known as a vernier engine) with either a rotatable nozzle or multiple fixed nozzles pointing in different directions. The direction of the launch vehicle is controlled by firing this small engine in a specific direction. Since directional control is required from the moment of launch to the moment of orbit insertion, each rocket stage has its own individual control mechanism that manipulates the direction of the flight in three axes. The single IGS system to which each of the stages is electronically connected is located in the equipment bay of the final stage, along with the computer that receives input and issues instructions to control the direction of flight to each successive stage.
Figure 10‑3 Attitude Control. Left: SITVC used by PSLV-XL booster for roll control. Centre: PSLV Second Stage engine gimbaling. Right: GSLV-CUS with Two Vernier Engines (circled). Credit Adapted from ISRO
To arrive at the prescribed orbit, the launch vehicle must be physically steered during the entire flight by the computer-controlled IGS. As ISRO evolved its launch systems, it also developed its competence in the IGS and the four control systems it operated, SITVC, flex nozzle, engine gimbaling and RCS. The SLV-3 and ASLV used solid propellants and relied on SITVC and small RCS for directional control. The second and fourth stages of the PSLV use liquid propellant employing engine gimbaling. The GSLV’s cryogenic upper stage (CUS) uses two vernier RCS.
Satellite Launch Vehicle (SLV-3)
As the first men to walk on the Moon returned to Earth, Vikram Sarabhai was setting down his vision for India’s space technology in the new decade. In his landmark paper published in 1970, he articulated in detail his plans for India to develop the indigenous capability to build and launch satellites during the decade 1970–1980. This capability was essential if India was to benefit from applications of space in the fields of communication, meteorology and remote sensing.
At the outset, ISRO had relied on the USSR, US or ESA to launch Indian satellites. By the late 1960s, ISRO had already attained a significant level of competence and confidence in producing and using solid fuel. The development of liquid propellant within ISRO was then at an early stage.[520] The SLV-3 was India’s first launch vehicle with a capability to deliver a significant payload to orbit. ISRO had already developed the capacity to design and build satellites. With SLV-3, India was able to place them in orbit and for the first time attain self-sufficiency. For the next step ISRO would also need to develop unique materials and methods of construction requiring advanced aerospace engineering.[521]
By the time Sarabhai published this paper, a feasibility study and much of the preliminary work for SLV-3 had already been completed, so he was able to share some of the specifications. Through the new launcher’s name, ISRO
reaffirmed its aspiration. It wanted to build its own capability for launching satellites.[522] Following Sarabhai’s sudden and unexpected death on 30 December 1971 and the consequent reorganisation, Satish Dhawan eventually took over the role of Chairman of ISRO. He appointed Abdul Kalam as Project Director for the SLV-3 programme, which formally kicked off on 3 November 1973.
SLV-3
Stage 1
Stage 2
Stage 3
Stage 4
Burn time (second)
49
40
45
33
Thrust (tonne)
56
30
10
2.9
Length × width (m)
10 × 1
6.4 × 0.8
2.4 × 0.8
1.4 × 0.7[523]
Weight of propellant (tonne)
10.8
4.9
1.5
0.4
Table 10‑3 Key Design Features of SLV-3
The step from a sounding rocket to a launch vehicle capable of placing a significant payload in Earth orbit was one of ISRO’s earliest challenges. The US had used the same approach with the Viking/Vanguard and France with Diamant/L3S; for India, it would be SLV-3. SLV-3 comprised 44 major subsystems, 7,000 electrical components and 25 km of internal wiring.[524] As Sarabhai had outlined, the final specification of SLV-3 was a four-stage, solid fuel, 22-m high rocket with a diameter of 1 m. Weighing 17 tonnes, it was designed to launch a 40-kg spacecraft into LEO.