Launch Vehicle technology and Indian Launch Vehicles

Introduction

The primary instruments for space applications are satellites but they must be placed in carefully determined orbits in order to be useful. A variety of rocket systems have been developed for this purpose. Launch vehicles that send satellites and other spacecraft into space must be far more powerful than other types of rockets, because they carry more cargo farther and faster than other rockets.  

A launch vehicle is a rocket-powered vehicle used to transport a spacecraft beyond Earth’s atmosphere, either into orbit around Earth or to some other destination in outer space. The launch vehicles have been used to send crewed spacecraft, unscrewed space probes and satellites into space since the 1950s.

Different stages of rockets

To place an object into orbit around Earth, the launch vehicle must reach a velocity of about 30,000 km/h. To escape Earth’s gravitational pull entirely and head into deep space, these rockets must attain the escape velocity of about 40,000 km/h. The most efficient way for launch vehicles to reach these speeds is to use staged rockets, or rockets divided into different stages, one atop another. This is why launch vehicles often use several stages during a mission.

In rockets that use stages, the stages are stacked on top of each other. The stage on the bottom of the stack is the first one to fire. In some rockets that use stages the first stage has additional rockets attached to the outside, acting as a booster to further increase the thrust. After the fuel in each stage has been consumed, the empty stage drops away from the spacecraft. Rockets can theoretically use any number of stages, but the complications caused by coordinating the firing times of the stages make it impractical to have too many.

The first and most powerful stage lifts the launch vehicle into the upper atmosphere. The first stage then separates from the rest of the rocket and falls towards earth. Some first stages, such as the space shuttle’s booster rockets, can be recovered. Others burn up in the atmosphere once their fuel is expelled and they drop off the launch vehicle.

The second stage carries less weight than the first stage, because the first stage, because the first stage has dropped off of the rocket. When the second stage takes over, the vehicle reaches a much higher speed; the second stage, however, also uses up its fuel and drops off. The third stage fires and places the spacecraft into orbit. On deep space missions, the third stage allows the spacecraft to reach escape velocity and head away from Earth. For some missions, even the three stages may not be adequate.

Actually the technology to build space-launch vehicles is closely akin to that for long-range ballistic missiles. So, the USSR and the USA were the only two countries that had the ability to launch satellites from 1957 to 1965. In subsequent years France, Japan, the European Space Agency, China and India developed this capability.

India’s Satellite Launchers

SLV-3: The Satellite Launch Vehicle-3 (SLV-3) was India’s first experimental satellite launch vehicle, which was an all solid, four stage vehicle weighing 17 tonnes. It had a height of 22m and it was capable of placing 40 kg class payloads in Low Earth Orbit (LEO).

SLV-3 was successfully launched on July 18, 1980 from Sriharikota Range (SHAR), when Rohini satellite, RS-1, was placed in orbit, thereby making India the sixth member of an exclusive club of space-faring nations. SLV-3 employed an open loop guidance to steer the vehicle in flight along a pre-determined trajectory. The first experimental flight of SLV-3, in August 1979, was only partially successful. Apart from the July 1980 launch, there were two more launches held in May 1981 and April 1983, orbiting Rohini satellites carrying remote sensing sensors.

The successful culmination of the SLV-3 project showed the way to advanced launch vehicle projects such as the Augmented Satellite Launch Vehicle (ASLV), Polar Satellite Launch Vehicle (PSLV) and the Geosynchronous satellite Launch Vehicle (GSLV).

Augmented Satellite Launch Vehicle (ASLV):  It had a lift off weight of 40 tonnes. The 24 metre tall ASLV was configured as a five stage, all-solid propellant vehicle, with a mission of orbiting 150 kg class satellites into 400 km circular orbits.

The Augmented Satellite Launch Vehicle (ASLV) Programme was designed to augment the payload capacity to 150 kg, thrice that of SLV-3, for Low Earth Orbits (LEO). While building upon the experience gained from the SLV-3 missions, ASLV proved to be a low cost intermediate vehicle to demonstrate and validate critical technologies. Such technologies like strap-on technology, inertial navigation, bulbous heat shield, vertical integration and closed loop guidance etc. later proved useful in further missions. Under the ASLV programme four developmental flights were conducted.  

Polar Satellite Launch Vehicle (PSLV)

Polar Satellite Launch Vehicle (PSLV) is the third generation launch vehicle of India. It is the first Indian launch vehicle to be equipped with liquid stages. After its first successful launch in October 1994, PSLV emerged as the reliable and versatile workhorse launch vehicle of India with 39 consecutively successful missions by June 2017. During 1994-2017 period, the vehicle has launched 48 Indian satellites and 209 satellites for customers from abroad. Besides, the vehicle successfully launched two spacecraft – Chandrayaan-1 in 2008 and Mars Orbiter Spacecraft in 2013 – that later travelled to Moon and Mars respectively.

PSLV earned its title “the workhorse of ISRO” through consistently delivering various satellites to Low Earth Orbits, particularly the IRS series of satellites. It can take up to 1,750 kg of payload to sun-synchronous polar orbits of 600 km altitude. Due to its unmatched reliability, PSLV has also been used to launch various satellites into Geosynchronous and Geostationary orbits, like satellites from the IRNSS constellation. The PS4 is the uppermost stage of PSLV, comprising of two Earth storable liquid engines. 

Geosynchronous Satellite Launch Vehicle (GSLV)

The main reason behind the advent of the GSLV is the capability to lift greater loads into space. While the PSLV can only lift slightly over a ton of payload to GTO (Geostationary Transfer Orbit), the GSLV is capable of lifting more than double with a rated capacity of 2 to 2.5 tons.

One of the main reasons why the GSLV has such an increased load is its utilization of a cryogenic rocket engine for its last stage. The cryogenic rocket engine provides more thrust than conventional liquid rocket engines but the fuel and oxidizer needs to be super cooled in order to keep them in a liquid state.

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.

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 and France.

ISRO started launching indigenously made sounding rockets from 1965 and experience gained was of immense value in the mastering of solid propellant technology. 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. Several scientific missions with national and international participation have been conducted using the Rohini sounding rockets.

GSLV Mk III

GSLV Mk III is a three-stage heavy lift launch vehicle developed by ISRO. The vehicle has two solid strap-ons, a core liquid booster and a cryogenic upper stage. GSLV Mk III is designed to carry 4 ton class of satellites into Geosynchronous Transfer Orbit (GTO) or about 10 tons to Low Earth Orbit (LEO), which is about twice the capability of GSLV Mk II.

The first developmental flight of GSLV Mk III, the GSLV-Mk III-D1 successfully placed GSAT-19 satellite to a Geosynchronous Transfer Orbit (GTO) on June 05, 2017 from SDSC SHAR, Sriharikota.

GSLV Mk III will be capable of placing the 4 tonne class satellites of the GSAT series into Geosynchronous Transfer Orbits. The powerful cryogenic stage of GSLV Mk III enables it to place heavy payloads into Low Earth Orbits of 600 km altitude. The Cryogenic Upper Stage (C25) is powered by CE-20, India’s largest cryogenic engine, designed and developed by the Liquid Propulsion Systems Centre. GSLV Mk III uses two S200 solid rocket boosters to provide the huge amount of thrust required for lift off. The S200 was developed at Vikram Sarabhai Space Centre.

Reusable Launch Vehicle – Technology Demonstrator (RLV-TD)

Reusable Launch Vehicle – Technology Demonstrator (RLV-TD) is one of the most technologically challenging endeavours of ISRO towards developing essential technologies for a fully reusable launch vehicle to enable low cost access to space. The configuration of RLV-TD is similar to that of an aircraft and combines the complexity of both launch vehicles and aircraft.

The winged RLV-TD has been configured to act as a flying test bed to evaluate various technologies, namely, hypersonic flight, autonomous landing and powered cruise flight. In future, this vehicle will be scaled up to become the first stage of India’s reusable two stage orbital launch vehicle.

RLV-TD consists of a fuselage (body), a nose cap, double delta wings and twin vertical tails. It also features symmetrically placed active control surfaces called Elevons and Rudder. This technology demonstrator was boosted to Mach no: 5 by a conventional solid booster (HS9) designed for low burn rate.  The selection of materials like special alloys, composites and insulation materials for developing an RLV-TD and the crafting of its parts is very complex and demands highly skilled manpower. Many high technology machinery and test equipment were utilised for building this vehicle.

Objectives of RLV-TD:

  • Hypersonic aero thermodynamic characterisation of wing body;
  • Evaluation of autonomous Navigation, Guidance and Control (NGC) schemes;
  • Integrated flight management;
  • Thermal Protection System Evaluation;

Achievements:

RLV-TD was successfully flight tested on May 23, 2016 from SDSC SHAR Sriharikota validating the critical technologies such as autonomous navigation, guidance & control, reusable thermal protection system and re-entry mission management.

Scramjet Engine - TD

The satellites are launched into orbit by multi-staged satellite launch vehicles that can be used only once i.e. they are expendable. These launch vehicles carry oxidiser along with the fuel for combustion to produce thrust. Launch vehicles designed for one time use are expensive and their efficiency is low because they can carry only 2-4% of their lift-off mass to orbit. Thus, there is a worldwide effort to reduce the launch cost.

Nearly 70% of the propellant (fuel-oxidiser combination) carried by today’s launch vehicles consists of oxidiser. Therefore, the next generation launch vehicles must use a propulsion system which can utilise the atmospheric oxygen during their flight through the atmosphere which will considerably reduce the total propellant required to place a satellite in orbit.

Also, if those vehicles are made re-usable, the cost of launching satellites will further come down significantly. Thus, the future re-usable launch vehicle concept along with air-breathing propulsion is an exciting candidate offering routine access to space at far lower cost.

Considering the strategic nature of air-breathing technology which has the potential to bring a significant shift in the launch vehicle design, worldwide efforts are on to develop the technology for air breathing engines. Ramjet, Scramjet and Dual Mode Ramjet (DMRJ) are the three concepts of air-breathing engines which are being developed by various space agencies.

A ramjet is a form of air-breathing jet engine that uses the vehicle’s forward motion to compress incoming air for combustion without a rotating compressor. Fuel is injected in the combustion chamber where it mixes with the hot compressed air and ignites. A ramjet-powered vehicle requires an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust.

Ramjets work most efficiently at supersonic speeds around Mach 3 (three times the speed of sound) and can operate up to speeds of Mach 6. However, the ramjet efficiency starts to drop when the vehicle reaches hypersonic speeds.

A scramjet engine is an improvement over the ramjet engine as it efficiently operates at hypersonic speeds and allows supersonic combustion. Thus it is known as Supersonic Combustion Ramjet, or Scramjet.

A dual mode ramjet (DMRJ) is a type of jet engine where a ramjet transforms into scramjet over Mach 4-8 range, which means it can efficiently operate both in subsonic and supersonic combustor modes. An important development in ISRO’s Air Breathing Propulsion Project (ABPP) occurred on August 28, 2016, which was the successful flight testing of its Scramjet.

The first experimental mission of ISRO’s Scramjet Engine towards the realisation of an Air Breathing Propulsion System was successfully conducted from Satish Dhawan Space Centre SHAR, Sriharikota on August 28, 2016. With this flight, critical technologies such as ignition of air breathing engines at supersonic speed, holding the flame at supersonic speed, air intake mechanism and fuel injection systems have been successfully demonstrated. The Scramjet engine designed by ISRO uses Hydrogen as fuel and the Oxygen from the atmospheric air as the oxidiser. The August 28 test was the maiden short duration experimental test of ISRO’s Scramjet engine with a hypersonic flight at Mach 6.

ISRO’s Advanced Technology Vehicle (ATV), which is an advanced sounding rocket, was the solid rocket booster used for this test of Scramjet engines at supersonic conditions. Some of the technological challenges handled by ISRO during the development of Scramjet engine include the design and development of Hypersonic engine air intake, the supersonic combustor, development of materials withstanding very high temperatures, computational tools to simulate hypersonic flow, ensuring performance and operability of the engine across a wide range of flight speeds, proper thermal management and ground testing of the engines. India is the fourth country to demonstrate the flight testing of a Scramjet Engine.

Conclusion

The space technology is constantly evolving for the better. Many promising options for cost reduction and higher speed to cut journey time are being pursued in different countries including India. Today’s expendable launchers have effectively reached a technology plateau. Novel solutions are required to reduce the cost of access to space. Reusability is a key area of focus. The development of newer materials like composites, smart materials, structures and propulsion systems such as nuclear, laser, microwave, anti-matter, plasma, electric, and the magnetic rail launching system are in the anvil. The Air-breathing propulsion system is also pursued by different advanced countries as well as by developing countries like India. This will give higher aviation speed and will reduce cost of space exploration.

The journey beyond Moon calls for a better propulsion system, materials, structures and the relevant navigation control system. The interplanetary missions will present another set of complex challenges.

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