ABSTRACT
Some spacecrafts are crewed, such as the space shuttle, but most are un-crewed, such as National Aeronautics and Space Administration's Hubble Space Telescope. Application satellites survey the Earth's resources whether on the ground, beneath the ground, or inside water bodies. The number of operational satellites, as detected at the end of 2015, has marked a 39% increase over 5 years, compared to 986 operational satellites reported in 2011. This chapter briefly mentions the types of commercial satellites and leaves the detailed description of these satellites, in a different order. Satellites stay in orbit due to the balance of two effects: velocity, or the speed at which it would travel in a straight line, and the gravitational pull between the Earth and the satellite. Satellites that orbit the Earth also follow Kepler's laws that apply to the motion of the planets around the Sun. Remote-sensing satellites orbit hundreds or even thousands of miles above the Earth.
