Why is there a count down till zero before launching a satellite or a rocket?

Question

you would have noticed that before launching a satellite there is count down till zero. Can you help me find its answer


thank you

Answer 1

There is a need to ensure that a large number of things happen in the correct order to have a successful launch of a rocket that is going to make it into orbit. The method chosen to ensure that these many things that need to be done occur in the right order is to specify the time that each task is to be performed. Since the launches could happen at any time of the day or night and since many of the people involved in the launching of the first satellites had been in the second world war they chose the launch time as time equals zero. Time before the launch was represented by seconds minutes and hours before the launch and time after the launch was similarly represented. To distinguish the two, time before was represented as negative numbers and time after as positive.

Answer 2

countdown

A countdown is the backward counting to indicate the seconds, days, etc. remaining before an event occurs or a deadline expires. Typical events for which a countdown is used include the launch of a rocket or spacecraft, the explosion of a bomb, the start of a race, or the New Year.

In the context of a rocket launch, the "T minus Time" is the time before launch, e.g. "The countdown was held at T minus 5 minutes for 3 minutes and 40 seconds". The last ten seconds are usually counted down aloud "10, 9, 8, 7, 6, 5, 4, 3, 2, 1, Lift off!"

The first known use with respect to launching a rocket occurred in Fritz Lang's 1929 film Frau im Mond. In the film, after each number the words "seconds to go" was repeated.

When counting down to the launch of an explosive, e.g. when testing a new model of gun, it is customary to omit "5" from the countdown sequence because "five" sounds too similar to "Fire!".

Answer 3

The computers that track the satellite, and in the satellite, use a clock that counts the seconds since launch. So the time before launch is T-10, T-9, ... T-1, T-0. And the time from launch is T+1, T+2, ... and so on.

Answer 4

I guess they could do a countdown to 1, but that wouldn't make any sense would it? Zero's the end, finale.

Answer 5

http://www.nasa.gov/returntoflight/launch/countdown101.html

Answer 6

To get ready and be set to go and lunch.