Isro.Us | Space Exploration

Launch Vehicles are used to transport and put satellites or spacecrafts into space. In India, the launch vehicles development programme began in the early 1970s. The first experimental Satellite Launch Vehicle (SLV-3) was developed in 1980. An Augmented version of this, ASLV, was launched successfully in 1992. India has made tremendous strides in launch vehicle technology to achieve self-reliance in satellite launch vehicle programme with the operationalisation of Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV).

PSLV represents ISRO's first attempt to design and develop an operational vehicle that can be used to orbit application satellites. While SLV-3 secured for India a place in the community of space-faring nations, the ASLV provided the rites of passage into launch vehicle technology for ISRO. And with PSLV, a new world-class vehicle has arrived. PSLV has repeatedly proved its reliability and versatility by launching 30 satellites / spacecrafts (14 Indian and 16 for international customers) into a variety of orbits so far.

ISRO also makes the Rohini series of sounding rockets used by the Indian and international scientific community to launch payloads to various altitudes for atmospheric research and other scientific investigations. These rockets are also used to qualify some of the critical systems used for advanced launch vehicles.

Indigenous Cryogenic Engine

Cryogenic Stage is a rocket stage that is much more efficient and provides more thrust for every kilogram of propellant it burns compared to solid and earth-storable liquid propellant stages. Specific impulse (a measure of the efficiency) achievable with cryo fluids (liquid Hydrogen and liquid Oxygen) is of the order of 450 sec compared to 300 sec for earth storable and solid fuels, giving a substantial payload advantage for an upper stage, with every one second increase in the specific impulse, the payload gain is of the order of 15 kg.

However, cryogenic stage is technically a very complex system compared to solid or earth-storable liquid propellant stages due to the use of propellants at extremely low temperatures and the associated thermal and structural problems. Oxygen liquefies at -183 deg C and Hydrogen at -253 deg C. The propellants, at these low temperatures, are to be pumped using turbo pumps running at around 40,000 rpm. It also entails complex ground support systems like propellant storage and filling systems, cryo engine and stage test facilitates transportation and handling of cryo fluids and related safety aspects.

The indigenous Cryogenic Upper Stage (CUS) is powered by a regenerative cooled cryogenic engine, which works on staged combustion cycle. The main engine and two smaller (cryogenic) steering engines together develop a nominal thrust of 73.55 KN in vacuum. The main engine of CUS achieves a specific impulse of 452 seconds. During the flight, CUS fires for a nominal duration of 720 seconds. The other stage systems of CUS include insulated propellant tanks, booster pumps, inter stage structures, fill and drain systems, pressurization systems, gas bottles, command block, igniters, pyro valves and cold gas orientation and stabilization system.

Liquid Oxygen (LOX) and Liquid Hydrogen (LH2) from the respective tanks are fed by individual booster pumps to the main turbo pump, which rotates at 39,000 rpm to ensure a high flow rate of 16.6 kg/sec of propellants into the combustion chamber. The main turbine is driven by the hot gas produced in a pre burner. Thrust control and mixture ration control are achieved by two independent regulators. LOX and Gaseous Hydrogen (GH2) are ignited by pyrogen type igniters in the pre burner as well as in the main steering engines during initial stages.

Apart from the complexities in the fabrication of stage tanks, structures, engine ad its subsystems and control components, CUS employs special materials like Aluminum, Titanium, Nickel and their alloys, bi-metallic materials and polyimide’s. Stringent quality control and elaborate safety measures have to be ensured during assembly and integration.

ISRO's Cryogenic Upper Stage Project (CUSP) envisaged the design and development of the indigenous Cryogenic Upper Stage to replace the stage procured from Russia and used in GSLV flights. CUSP was intended to develop a cryogenic stage with regenerative cooled engine, producing a thrust of 69.5 kilo Newton (KN) in vacuum. As part of this effort, cryogenic engines were realized and tested earlier for a cumulative duration of 7760 sec. In the stage level hot test apart from cryogenic engine, all other stage elements worked in unison as per flight standards.

The journey of ICE development

Semi Cryogenic Engine

ISRO will develop a semi cryogenic engine using liquid oxygen (LOX) and kerosene under a Rs. 1,798 crore six year project cleared by the Union Cabinet on December 19, 2008. The project envisages foreign collaboration with a foreign exchange component of Rs. 588 crores.

The liquid stages of PSLV and GSLV engines use toxic propellants that are harmful to the environment. The trend worldwide is to change over to eco-friendly propellants. Liquid engines working with cryogenic propellants (liquid oxygen and liquid hydrogen) and semi cryogenic engines using liquid oxygen and kerosene are considered relatively environment friendly, non-toxic and non corrosive. In addition, the propellants for semi-cryogenic engine are safer to handle and store. It will also reduce the cost of launch operations.

This advanced propulsion technology is now available only with Russia and USA. The world’s most powerful liquid engine, the Russian RD 170, is powered by a LOX - kerosene combination. LOX - Kerosene engines have powered several American launchers as well, including Saturn V, which carried American astronauts to the moon. For India it is the beginning to rise in to the moons and the stars.

The semi cryogenic engine will facilitate applications for future space missions such as the Reusable Launch Vehicle, Unified Launch Vehicle and vehicle for interplanetary missions.