The Indian Space Research Organization (ISRO) has recently made the headlines after successfully launching an Earth Observation Satellite (EOS-04), along with two smaller satellites, into space. This achievement marks the 54th flight of ISRO’s Polar Satellite Launch Vehicle (PSLV) rocket. In light of this recent development, it seems apt to delve deeper into our understanding of launch vehicles and satellites, their functions, types, and the different variants used by ISRO.
Understanding Launch Vehicles and Satellites
Launch vehicles, more commonly known as rockets, have powerful propulsion systems. These systems generate the enormous amount of energy needed to lift heavy objects like satellites into space, thus overcoming the earth’s gravitational pull.
On the other hand, satellites are equipped with one or more instruments used to carry out scientific tasks for which they are launched into space. These satellites can function for extended periods that sometimes span several decades. However, unlike satellites, launch vehicles become redundant after fulfilling their purpose of transporting satellites to their intended orbits.
A rocket is composed of several detachable, energy-providing segments that burn various kinds of fuels. Once the fuel in a particular segment is exhausted, it detaches from the main body of the rocket and usually burns off in the earth’s atmosphere due to air friction, thus getting destroyed. The journey concludes with only a small part of the original rocket making it till the satellite’s intended destination. This remaining part either becomes part of space debris or burns off upon re-entering the earth’s atmosphere.
Different Types of Launch Vehicles
Depending on the mission, different varieties of launch vehicles are used to transport satellites into either lower or higher earth orbits.
For Lower Earth Orbits: This starts from approximately 180 km from the earth’s surface and extends up to 2,000 km. Here, most of the earth-observation satellites, communication satellites, and even the International Space Station (a full-fledged laboratory in space that hosts astronauts), function. Rockets used for this purpose are usually smaller and less powerful due to the lower energy requirement.
For Higher Orbits: Some missions demand the launch of satellites much deeper into space. Geostationary satellites, which need to be positioned in orbits approximately 36,000 km from the earth’s surface, and planetary exploration missions require more potent rockets.
The Arsenal of ISRO Launch Vehicles
ISRO has a rich history of developing robust launch vehicles.
Satellite Launch Vehicle (SLV): The first rocket developed by ISRO, SLV, was followed by the Augmented Satellite Launch Vehicle or ASLV. Both were designed to carry small satellites, weighing up to 150 kg, to lower earth orbits.
Polar Satellite Launch Vehicle (PSLV): Having had its first launch in 1994, PSLV has been ISRO’s primary rocket. Today’s PSLV is significantly more advanced and several times more robust than the original versions. Notably, it is the first Indian launch vehicle equipped with liquid stages.
Geosynchronous Satellite Launch Vehicle (GSLV): A much more potent rocket designed to transport heavier satellites deep into space.
Small Satellite Launch Vehicle (SSLV): Targeting the rising global demand for launching small and micro-satellites, SSLV was developed to offer cost-effective launch services for satellites up to 500 kg.
Looking Towards the Future: Reusable Rockets
To minimize costs, energy consumption, and reduce space debris, future rockets are deemed to be reusable. In this case, only a minor portion of the rocket will be destroyed during a mission. The majority of the rocket would re-enter the earth’s atmosphere and land similar to an airplane, ready to be utilized in future missions.
While fully-reusable rockets are yet to be developed, partially-reusable launch vehicles are already in use. ISRO has developed a reusable rocket, the RLV-TD (Reusable Launch Vehicle Technology Demonstrator), which had a successful test flight in 2016.
