Navigation :: Geography History Navigation Essays

Navigation Early Explorers such as Christopher Columbus and Magellan relied on landmarks for early navigation, which could result in serious miscalculations. Later explorers discovered they could use the stars as their primary choice for navigation. As technology increased the compass and sextant were used in navigation purposes. The needle of a compass always pointed north, while the sextant used adjustable mirrors to measure angles of the moon and stars. The sextant could only calculate latitude so a device called the chronometer was later invented by John Harrison to compute longitude. The sextant and chronometer were used together to compute measures of longitude and latitude. In the early 20th century many radio-based navigation systems were developed. However these radio based systems were either accurate or covered a large area of space, but not both. Scientists then decided that the only way to cover the entire world was to put high frequency radio systems in space, hence the id ea of GPS or global positioning systems was born. GPS was funded and founded by the Department of Defense. The Departmemet of Defense also controls GPS. The first GPS satellite was launched in 1978. The first ten satellites were called block I satellites. From 1989 to 1993, 23 production satellites called Block II were launched. The last satellite was launched in 1994 completing the system. From this point on with a GPS receiver costing only a few hundred dollars you could constantly learn your location on the planet. GPS is the only system available today that will tell someone their exact position on Earth at any given time in any type of weather. There are 24 satellites in all, which orbit about 11,000 nautical miles above the earth. The satellites are monitored by ground stations located around the world and can transmit signals that can be detected by anyone with a GPS receiver. Using this receiver you can determine your position on Earth with great accuracy. GPS satellites consist of 3 segments: space, control and user. The space segment consists of the 24 satellites in six orbital planes(four satellites in each plain). Each satellite repeats the same 12-hour orbit, but appears four minutes earlier each day. Each satellite orbits at 55 degrees in respect to the equatorial plane with a 12-hour period to orbit the earth.