satellite
What is a satellite?
A satellite is an object that goes around, or orbits, a larger object, such as a planet. While there are natural satellites, like the moon, hundreds of man-made satellites also orbit the Earth.

What are the components of a human-made satellite? * communication capabilities with Earth * a power source * a control system to accomplish its mission
Communications antennae, radio receivers and transmitters enable the satellite to communicate with one or more ground stations, called command centers. Messages sent to the satellite from a ground station are "uplinked"; messages transmitted from the satellite to Earth are "downlinked."
Many satellites are powered by rechargeable batteries, taking advantage of the ultimate battery charger, the sun. Silvery solar panels are prominent features on many satellites. Other satellites have fuel cells that convert chemical energy to electrical energy, while a few rely on nuclear energy. Small thrusters provide attitude, altitude, and propulsion control to modify and stabilize the satellite's position in space.
Specialized systems accomplish the tasks assigned to the satellite. These often include sensors capable of imaging a range of wavelengths. Telecommunications satellites require no optics, while environmental satellites do. Environmental satellites transmit images as numbers to a computer on Earth, which translates this digital data into images.
Some of the data can be enhanced to look like photographs. Bright colors (false colors) are often added to enhance the contrast, make details stand out, or allow us to see what was recorded in the wavelengths beyond our visual range. The false colors do not necessarily correspond to the colours we expect to see. For example, a field of wheat might look pink; clear water may appear black.

How are satellites launched?
The trick to launching a satellite is getting it high enough to do its job without losing the capsule to outer space. It's a delicate balance of push and pull, accomplished by the inertia of the moving object and the Earth's gravity. If you launch a satellite at 17,000 mph, the forward momentum will balance gravity, and it will circle the Earth. On the other hand, if the satellite is launched faster than 23,500 mph, it will leave the gravitational pull of the Earth.

Why does a satellite stay in orbit?
Due to the balance of two effects:
(1) velocity, or the speed at which it would travel in a straight line,
(2) the gravitational pull between the Earth and the satellite.
To illustrate this principle, attach a small weight or a ball to a string, and swing it around in a circle. If the string were to break, the ball would fly off in a straight line. But because it is tethered (like gravity tethers a satellite), it orbits your hand.
Imagine that you could climb an imaginary mountain whose summit pokes above the Earth's atmosphere (it would be about ten times higher than Mt. Everest). If you threw a baseball from the mountain top, it would fall to the ground in a curving path. Two motions act upon it: travelling in a straight line and falling toward Earth. The faster you throw the ball, the farther it will go before it hits the ground. If you could throw the ball at a speed of 17,000 mph, the ball wouldn't reach the ground. It would circle the Earth in a curved path; it would be in orbit. (It would be traveling at 5 miles per second and take about 10 minutes to cross the United States.) This is the speed needed to put satellites into orbit, which is why the Space Shuttle