"India successfully launched its latest fourth generation satellite 'INSAT-4B' from the Spaceport of Kourou in French Guyana. ISRO Chairman G Madhavan Nair termed the launch an important one to the country and complimented Arianespace for a precise launch. Moving on to Sports, the ninth edition of the World Cup........."

Bharat sat glued to the television set that was showing pictures of the inauguration ceremony of the world cup, for the 100th time, but his mind seemed to be occupied somewhere else.

"Hey Dad. Can I ask you a question?"

"Yes but make it simple. I am already late for work and I am in a hurry". Morning time was always tense for Raj. He never planned and always did things at the last minute. But that's how most of the science research scholar's were.

"Did you hear about the INSAT-4B launch? I have a question on that".

"Yeah." INSAT-4B. A 200 Crore satellite targeted towards the geosynchronous orbit which would give a big boost to the Directto-Home TV transmission.

"Why did we have to launch it from French Guyana? Don't we have our own launch pads in India? We have one in Sriharikota, right?"

Raj stood stunned for a minute. There was no one word answer for this question. This needed some explanation and he was already late. However he felt proud that his 9th grade son was not just taking in news but was also questioning them.

"If we already have our own launch pads why do we need to launch this from French Guyana?" Bharat repeated the question.

Raj took a chair and sat next to Bharat. He decided to explain how things worked and that meant he would be late for work. But it was better than leaving Bharat with unanswered questions.

"OK. Listen carefully. I am going to explain this only once. I will give you pointers and you take it from there."

Bharat took a pen and a paper and keenly listened.

"If I throw a ball upwards the ball travels for a few distance but finally falls down. Why?"

"Gravitational pull, dad"

"Ok. If I don't want the ball to fall down. What should I do?"

"The force in which the ball is thrown should be more than the escape velocity, dad".

"Very Good. In the same way, a rocket has to be launched with a minimal speed that is greater than the escape velocity. Do you agree?"

"Yes"

"To achieve the minimal speed enormous amount of fuel has to be burnt, right. And energy is not cheap."

"Now here is the important thing to note. Remember that the earth spins around itself which means that it carries us around 25,000 miles a day. Now If I have to cover 25,000 miles in a day, I should be traveling at nearly 464 metres/second."

"So u say that the earth's circumference is 25,000 miles?" interrupted Bharat

"Approximately, yes. The earth's circumference is measured across the equator. So if I am standing at the equator I am traveling 464 metres/second."

"Now, if I start moving away from the equator towards the poles, the speed I travel around the earth decreases with the cosine of the latitude. The simple formula for earth's rotational velocity is 464 m/s * Cos (θ) where θ is the latitude."

"Are you still with me Bharat?"

"Yes..I think so."

"Good. Now If I am hurtled on to space from the equator my escape velocity is less compared to when I am hurtled from near the poles. Do you accept it?"

"Because you already travel at a greater speed near the equator compared to the poles?"

"Exactly. And remember I should travel east, along with the earth's rotation."

"There are two things to note here.

• Rockets are always launched towards the east.
• It's advantages to have rocket launches from near the equator.

Now coming back to your original question. French Guyana is only 5 degrees from the equator compared to Sriharikota which is around 14 degrees from the equator.

Image Courtesy : http://worldatlas.com/webimage/countrys/samerica/g...

Kourou Spaceport in French Guyana.

Image Courtesy : http://www.eumetsat.int/Home/Main/What_We_Do/Satel...

"French Guyana has couple of advantages compared to Sriharikota. You need less energy for the launch and 90% of the country is covered with forest and it is near the seas, which means in the event of a mishap, the rocket falls in the water."

"Now. I am now going to leave you with this, Bharat. I want you to take it from here and learn more about satellite launches. Is that OK?".

"OK. Thanks dad. This is fascinating stuff. I am going to dig up all the information I can."

"I have to rush now. I am already late. I am not sure how I am going to beat the traffic".

"Don't worry dad. You are already traveling at 464 m/s. You will be there in a jiffy. See ya."