GETTING INTO SPACE
The most direct means of overcoming Earth's gravity and putting a payload, or cargo, into space is to launch it on a rocket. The velocity required is about 17,500 miles per hour (28,000 km/h). The rocket's thrust must be greater than its weight, so even a small cargo uses a lot of fuel.
One way of lessening gravity's effect and conserving fuel is to launch the rocket in an easterly direction near the Equator. Earth's rotation acts like a sling, providing extra lift. Cape Canaveral, Florida, is an ideal location, boosting a rocket's velocity by almost 900 miles per hour (1,450 km/h).
With enough speed, a rocket can place satellites or other spacecraft into one of three types of orbit: equatorial, polar, or geostationary.
Equatorial satellites usually orbit at low altitude—about 100 miles (160 km) above Earth—and, because they are launched eastward, they travel from west to east.
Polar-orbiting satellites pass over the entire Earth in high-altitude orbits at a minimum of about 1,000 miles (1,600 km). Most of these scan geological or weather phenomena, but some are dedicated to military reconnaissance. They travel north to south, or south to north. From Earth, they appear to move more slowly because of their greater altitude.
Geostationary, or geosynchronous, satellites circle Earth once a day at an altitude of 22,000 miles (36,000 km). Because their speed matches that of Earth's rotation, they remain over a fixed point. This makes them ideal for gathering weather-forecasting data and for communications such as television transmissions.