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Why Sriharikota is India’s Rocket Launchpad

Why Sriharikota is India’s Rocket Launchpad

Have you ever wondered why an athlete getting ready to throw a discus pivots on their foot and circles round and round before making the throw? What they are doing is gaining velocity before they release the discus. And the greater the velocity, the further the throw. Easy peasy.

Now, zoom out of the athletics field and hover over the earth, in space. If the athlete was aiming to launch the discus along the path of the equator, wouldn’t it be easier if he or she were aligned with the equator, or at least close to it?

That’s what happens every time India launches a rocket or a satellite from the Satish Dhawan Space Centre, or the Sriharikota High Altitude Range, India’s primary spaceport or rocket launching station. It’s been a 51-year odyssey that began in 1969, when the space centre was set up on the coast of Andhra Pradesh by the Indian Space Research Organisation (ISRO).

So why was Sriharikota chosen over other locations as India’s main satellite launch station? And what do satellites have to do with a discus throw? Here’s how it all ties in.

  1. Equatorial Equation: Most satellites orbit the earth around the equator, and Southern India is closer to the equator than other regions of the country. So launching from here saves expensive rocket fuel. 

Did you know that satellites that orbit the earth at the equator are called ‘geostationary’ satellites and that they play a crucial role in weather and communications? Moving along the equator, these satellites take the same time to revolve around the earth as the earth takes to rotate on its own axis. Therefore, they always present the same face to the earth, and appear to be, well, stationary or ‘geostationary’.

| https://gisgeography.com/
  1. Velocity, Velocity, Velocity: Remember the discus thrower and how he or she gains velocity by turning round and round? Well, as the earth rotates from west to east, like the discus thrower’s circular movement, it generates velocity. This is greatest at the equator and near-zero at the poles. So launching a satellite in an eastward direction, as close to the equator as possible, gives the launch vehicle, or the space equivalent of the discus, extra thrust. This, in turn, saves precious rocket fuel. 

Since Sriharikota is close to the equator, it checks two critical boxes.

Pulicat Lake | Manvendra Bhangui via Wikimedia Commons
  1. East Coast Sriharikota is a large barrier island, that is, it is a long, broad sandy island parallel to the shore with Pulicat Lake separating the two. To its right is the expanse of the Bay of Bengal.

Spaceports must be as far from human habitation as possible and are usually on coastal strips, islands or in deserts. Sometimes, rockets shed components after lift-off; at other times, they disintegrate in space and rain debris down on earth; also, each stage of a multistage rocket necessarily falls to earth after launch.

Imagine what would happen if space debris were to crash into cities and towns below. An eastward launch from the east coast of India means the rocket’s trajectory would pass over the Bay of Bengal and all post-launch debris, if any, would drop into the sea.

Doglegged flight path of a PSLV launch to polar inclinations avoiding Sri Lankan landmass. | Wikimedia Commons

So we’ve figured out why the east coast is critical but why not pick a spaceport further south? Wouldn’t it be even closer to the equator and therefore more ideal? 

Absolutely. The only problem is, eastward launches from a coastal location deep in the south would mean the rockets’ flight path would pass over Sri Lanka and, clearly, we don’t want rocket components and debris raining down on Sri Lanka!

Moving up the coast, from Nagapattinam to Chennai, there isn’t an extruding island that would be suitable for a spaceport. The nearest one is Sriharikota, 70 km north of Chennai.

Inside of the Vehicle Assembly Building at Sriharikota

A New Launching Station

Sriharikota has been at the forefront of India’s space programme and the launchpad for all its high-profile missions, including the Chandrayaan and Mars Orbiter Missions. It was established as a satellite launching station in 1969. But it had humble beginnings. 

It sent its first rocket into space on 9th October 1971. This was an RH-125, small sounding rocket, which studied weather and other aspects of the atmosphere. Sounding rockets are launched to a maximum distance of 100 km from the earth as opposed to 36,000 km for satellites, and they usually carry a payload of scientific instruments.

Sriharikota graduated to launching satellites (vis-a-vis sounding rockets) when it sent the country’s first satellite into space on 10th August 1979. It was an experimental satellite, Rohini 1A. Although the launch was not entirely successful, it was a massive milestone in India’s space programme.

But it might surprise you to know that Sriharikota is not India’s first spaceport. That honour goes to the Thumba Equatorial Rocket Launching Station, in Thiruvananthapuram, Kerala. On 21st November 1963, a sounding rocket was launched from Thumba, marking the beginning of the country’s space programme. 

Now India’s space programme is getting extra thrust, with plans moving forward for a second major rocket launching station. It will be located in Kulasekarapattinam, in coastal Tamil Nadu, close to the southern tip of India. But wouldn’t that mean rocket debris would rain down on Sri Lanka?

Not really. Kulasekarapattinam is being developed for ISRO’s Small Satellite Launch Vehicle (SSLV) programme, which is leveraging the emerging global small satellite service market. The SSLV programme will launch small, commercial satellites that orbit pole-to-pole. 

Polar satellites that currently lift off from Sriharikota take off south-eastward and are then sharply steered southwards, towards the South Pole. The extra fuel this requires would compromise the commercial viability of the SSLV programme. The Kulasekarapattinam spaceport is being developed to avoid this manoeuvre and save money.

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