Satellite Launch: Decoded


Author: Parveen Kaswan ( Author is an Aerospace Engineer and holds a Masters degree in Engineering Designs from Indian Institute of Science, Bangalore )

All satellites today get into orbit by riding on a rocket. Many used to hitch a ride in the cargo bay of the space shuttle. Several countries and businesses have rocket launch capabilities, and satellites as large as several tons make it safely into orbit regularly. ISRO’s Launch facility is located at Satish Dhavan Space Centre SHAR and Thumba Equatorial Rocket Launching Station (TERLS) from where Launch Vehicles and Sounding Rockets are launched.

For most satellite launches, the scheduled launch rocket is aimed straight up at first. This gets the rocket through the thickest part of the atmosphere most quickly and best minimizes fuel consumption.

After a rocket launches straight up, the rocket control mechanism uses the inertial guidance system to calculate necessary adjustments to the rocket’s nozzles to tilt the rocket to the course described in the flight plan. In most cases, the flight plan calls for the rocket to head east because Earth rotates to the east, giving the launch vehicle a free boost. The strength of this boost depends on the rotational velocity of Earth at the launch location. The boost is greatest at the equator, where the distance around Earth is greatest and so rotation is fastest. (Talking for Geostationary orbits)


How big is the boost from an equatorial launch? To make a rough estimate, we can determine Earth’s circumference by multiplying its diameter by pi (3.1416). The diameter of Earth is approximately 7,926 miles (12,753 kilometers). Multiplying by pi yields a circumference of something like 24,900 miles (40,065 kilometers). To travel around that circumference in 24 hours, a point on Earth’s surface has to move at 1,038 mph (1,669 kph).

Considering that rockets can go thousands of miles per hour, you may wonder why this difference would even matter. The answer is that rockets, together with their fuel and their payloads, are very heavy. It takes a huge amount of energy to accelerate such a mass and therefore a significant amount of fuel. Launching from the equator makes a real difference.

That’s why French Guinea is an important Space Launch Centre, because of its close proximity to equator. Then other profit of selecting ‘ French Guinea’ as launching centre is that it lies on the eastern coast of South America, it means in eastern side of launch centre there is a huge water body. If any incident happens with the launch, it can be called off in the mid air and the launch vehicle will land into sea or get destroyed above the Atlantic Ocean(You remember the flight plan calls for the rocket to head east because Earth rotates to the east), not creating any problem for the people.

Now French Guinea is near the Equator, and that is good for setting the Launch Centre there . Why India launches its Satellites form this space centre?

Basically two major reasons: One is that we don’t have capability to launch satellite which are heavier than 2000 kg, that is why we are so keen in developing our own cryogenic engine that will provide boost to our GSLV programme. This cryogenic engine will provide capability of launching heavier satellites. Now the example is when India’s first exclusive defence satellite GSAT-7 was launched by European space consortium Arianespace’s Ariane 5 rocket from Kourou spaceport in French Guiana which had mass of 2625 kg . In this way we are using this facility on pay per launch basis. The launch cost for ISRO for GSAT-7 was around Rs 470 crore, including insurance and the satellite cost was Rs.185-crore.

The second reason is economic one, in this case we also send our lighter satellites by this service. For example we have to park a single small satellite in Earth’s orbit, then just using their launch facility will be an economically viable option. Same as sharing an auto is profitable than hiring a single alone.

(In response to a question asked by Follower)


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