ISRO LAUNCH VEHICLES
1. Context
Satellites, or payloads as they are often called, sit inside the rocket and are ejected once they reach their intended orbit in space. Most satellites have small propulsion systems and carry small amounts of fuel, because they encounter very little drag, or force, in outer space. Here we look at ISRO's launch vehicles.
2. Satellites and Launch Vehicles
- Satellites don’t go into space on their own. They have to be carried there by launch vehicles, or rockets, like the PSLV. The rockets have powerful propulsion systems that generate the huge amount of energy required to lift heavy objects like satellites into space, overcoming the gravitational pull of the earth.
- Both rockets and satellites are spacecraft, which is a generic term used for any object that is sent into space.
- Satellites carry one or more instruments that do the scientific work for which they are sent into space. Their operational life sometimes extends up to decades.
- But rockets, or launch vehicles, become useless after the launch. Their only job is to take the satellites to their intended orbits.
- Rockets have several detachable energy-providing parts. They burn different kinds of fuels to power the rocket.
- Once their fuel is exhausted, they detach from the rocket and fall off, often burning off in the atmosphere due to air friction, and getting destroyed.
- Only a small part of the original rocket goes to the intended destination of the satellite. Once the satellite is finally ejected, this last part of the rocket either becomes part of space debris or once again burns off after falling into the atmosphere.
3. Types of Launch Vehicles
- There are several kinds of rockets that are used. The difference is mainly in the power that they can generate, the weight they can carry, and the distance they can travel into space, all of which are related.
- It all comes down to the energy that is generated, which is a function of how efficient the engine and the fuel is. Several satellites need to be deposited only in the lower earth orbits, which start from about 180 km from the earth’s surface and extend up to 2,000 km.
- Most of the earth-observation satellites, communication satellites, and even the International Space Station, a full-fledged laboratory in space that hosts astronauts, function in this space.
- PSLV is not the only launch vehicle of ISRO. But there are other satellites that need to go much deeper in space.
- Geostationary satellites, for example, have to be deposited in orbits that are about 36,000 km from the earth’s surface.
- The planetary exploration missions also need their rockets to leave them much deeper in space. For such space missions, much more powerful rockets are used.
4. ISRO's Launch Vehicles
ISRO currently uses two launch vehicles – PSLV and GLSV (Geosynchronous Satellite Launch Vehicle), but there are lots of different variants of these. PSLV is the most reliable rocket used by ISRO till date, with 52 of its 54 flights being successful. GSLV is a much more powerful rocket, meant to carry heavier satellites much deeper into space. Till date, GSLV rockets have carried out 18 missions, of which four failed.
4.1 The first launch vehicle developed by ISRO was simply called SLV, or satellite launch vehicle.
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 with a height of 22m and capable of placing 40 kg class payloads in Low Earth Orbit (LEO).
4.2 Augmented Satellite Launch Vehicle or ASLV.
These two could carry small satellites, weighing up to 150 kg, to the lower earth orbits. ASLV operated till the early 1990s before PSLV came on the scene.
4.3 PSLVs (Polar Satellite Launch Vehicles)
- Its first launch was in 1994, and it has been ISRO’s main rocket ever since. Today’s PSLV, however, is vastly improved and several times more powerful than the ones used in the 1990s.
- Presently, it has three Variants: PSLV - CA (Core Alone), PSLV-G, and PSLV - XL.
- PSLV is the most reliable rocket used by ISRO till date, with 52 of its 54 flights being successful.
- The vehicle successfully launched two spacecraft – Chandrayaan-1 in 2008 and Mars Orbiter Spacecraft in 2013 – that later traveled to Moon and Mars respectively.
4.4 GSLVs (Geosynchronous satellite launch vehicles)
- GSLV carried the Chandrayaan-2 mission and is slated to take the Gaganyaan manned space mission as well.
- Its Mk-III version can carry satellites weighing up to 4,000 kg to the geosynchronous transfer orbit, close to 36,000 km from the earth’s
surface. - It can take 10,000-kg satellites to the lower earth orbits. Mk-III versions have made ISRO entirely self-sufficient in launching its satellites.
- Before this, it used to depend on the European Arianne launch vehicle to take its heavier satellites into space.
4.5 Small Satellite Launch Vehicle (SSLV)
- ISRO has also developed a launch vehicle specifically for small and micro-satellites. It is called Small Satellite Launch Vehicle, or SSLV, and is targeted at rising global demand for the launch of such satellites.
- SSLV is meant to offer cost-effective launch services for satellites up to 500 kg. The inaugural SSLV launch is slated for next month. It is supposed to carry an indigenous earth observation satellite EOS-03 into space.
4.6 Reusable Rockets
- The future rockets are meant to be reusable. Only a small part of the rocket would be destroyed during the mission. The bulk of it would re-enter the earth’s atmosphere and land very much like an airplane and can be used in future missions.
- Reusable rockets would cut down on costs and energy, and also reduce space debris, which is becoming a serious problem because of the large number of launches.
- Fully-reusable rockets are still to be developed, but partially-reusable launch vehicles are already in use.
4.7 RLV-TD (Reusable Launch Vehicle Technology Demonstrator)
- ISRO has also developed a reusable rocket, called RLV-TD (Reusable Launch Vehicle Technology Demonstrator) which had a successful test flight in 2016.
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The configuration of RLV-TD is similar to that of an aircraft and combines the complexity of both launch vehicles and aircraft.
For Prelims
| For Prelims: Indian space research organization (ISRO), Polar Satellite Launch Vehicles (PSLV), Geosynchronous satellite launch vehicle (GSLV), Satellite Launch Vehicle-3 (SLV-3), Low Earth Orbit (LEO), Augmented Satellite Launch Vehicle (ASLV), Small Satellite Launch Vehicle (SSLV), Reusable Rockets and Reusable Launch Vehicle Technology Demonstrator (RLV-TD). |
Source: The Indian Express
