ISRO’s PSLV-C51 launch : Learning Basics

Indian Space Research Organisation(ISRO) launched the Polar Satellite Launch Vehicle (PSLV)-C51, with a load of a primary satellite called Amazonia-1 and it belongs to Brazil from the Satish Dhawan Space Centre (SDSC).

                  The 637-kg Amazonia-1 is the optical earth observation satellite of the National Institute for Space Research (INPE), the research unit of Brazil’s ministry of science.

                    The additional 18 co-passenger satellites include three UNITYsats from the consortium of three Indian academic institutes, one Satish Dhawan Sat from Space Kidz India and 14 from NSIL. 

                PSLV-C51/Amazonia-1 is the first dedicated commercial mission of New Space India Limited (NSIL), a Government of India company under the Department of Space. The mission conducted by NSIL comes under a commercial arrangement with Spaceflight Inc. USA

             PSLV-C51 is using the ‘DL’ variant of PSLV equipped with two solid strap-on boosters, according to ISRO.



The Polar Satellite Launch Vehicle, PSLV is capable of launching 1600 kg satellites in 620 km sun-synchronous polar orbit and 1050 kg satellite in geo-synchronous transfer orbit.

        In the standard configuration, it measures 44.4 m tall, with a lift off weight of 295 tonnes. PSLV has four stages using solid and liquid propulsion systems alternately. The first stage is one of the largest solid propellant boosters in the world and carries 139 tonnes of propellant. A cluster of six strap-on is attached to the first stage motor.

ISRO: It was established with it’s headquarter at Bangalore in 1969. It functions under overall control of department of space. K Sivan; the current Chairman of Space Commission, Secretary, Department of Space, Government of India and Chairman of ISRO.


Different orbits serve different purposes. An orbit is a curved path of a celestial object around another celestial object due to the force of gravity. Orbits are everywhere in our universe. The Moon orbits the Earth, and the Earth orbits the Sun, and the Sun orbits around the center of the galaxy.

The  near polar orbits have an inclination near 90 degrees. This allows the satellite to see virtually every part of the Earth as the Earth rotates underneath it.

Sun-Synchronous orbit; the satellite travels from the north to the south poles as the Earth turns below it.   the satellite passes over the same part of the Earth at roughly the same local time each day. These orbits allows a satellite to pass over a section of the Earth at the same time of day.

These satellites orbit at an altitude between 700 to 800 km. These orbits are used for satellites that need a constant amount of sunlight. Satellites that take pictures of the Earth would work best with bright sunlight, while satellites that measure longwave radiation would work best in complete darkness. When a satellite has a sun-synchronous orbit, it means that it has a constant sun illumination through inclination and altitude. For sun-synchronous orbits, it passes over any given point on Earth’s surface at the same local solar time.

A geosynchronous orbit is an orbit around the Earth, where the object orbits once per day. A common kind of geosynchronous orbit is called a geostationary orbit, where the object orbits above the same part of the Earth at all times. Geostationary satellites are launched into orbit in the same direction the Earth is spinning. When the satellite is in orbit at a specific altitude, it will exactly match the rotation of the Earth. The Earth actually takes 23 hours, 56 minutes, and 4.09 seconds to make one full revolution. So this would put the satellite at approximately 35,790 km above the Earth.

This is an extremely useful type of orbit and is used for anything where a satellite needs to send or receive signals from the same part of the Earth all the time. It’s used for cell phone satellites, television satellites, weather satellites, as well as some military satellites.


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