Transit (satellite)
Introduction
Transit is a series of artificial satellites designed for navigation purposes. The Transit system, also known as NAVSAT or NNSS (for Navy Navigation Satellite System), was developed by the U.S. Navy in the late 1950s and early 1960s. It was the first satellite navigation system to be used operationally, providing a method for ships and submarines to accurately determine their geographical position.
Development and History
The development of the Transit system was initiated in response to the military's need for a reliable and accurate method of navigation. The concept of using satellites for navigation was first proposed by researchers at the Johns Hopkins University's Applied Physics Laboratory (APL) in 1958. The first successful launch of a Transit satellite, Transit 1B, took place on April 13, 1960.
The Transit system was declared operational by the U.S. Navy in 1964. Over the next several decades, the system was continually updated and improved, with new satellites launched to replace older ones. The final Transit satellite was launched in 1988, and the system was officially decommissioned in 1996, replaced by the more advanced Global Positioning System (GPS).
Design and Operation
Transit satellites were small, weighing approximately 130 kilograms and measuring about 0.9 meters in diameter. They were powered by solar panels and had a lifespan of approximately 1 to 3 years.
The satellites operated in polar orbits at an altitude of approximately 1,100 kilometers. This allowed them to cover the entire Earth's surface, with each satellite making a complete orbit approximately every 100 minutes.
The primary payload of a Transit satellite was a highly stable atomic clock. This clock was used to generate a time-coded signal, which was transmitted to receivers on the ground. By comparing the time of arrival of signals from multiple satellites, a receiver could calculate its precise location.
Impact and Legacy
The Transit system had a significant impact on navigation, particularly for naval vessels. Prior to the introduction of satellite navigation, ships and submarines relied on a combination of celestial navigation, dead reckoning, and radio navigation. These methods were often inaccurate and could be affected by weather conditions and other factors.
The introduction of the Transit system provided a reliable and accurate method of navigation that was not affected by weather or other environmental conditions. This greatly improved the ability of naval vessels to navigate accurately, particularly in the open ocean or under the polar ice cap.
While the Transit system has been replaced by the more advanced GPS system, it played a crucial role in the development of satellite navigation. Many of the concepts and technologies developed for Transit, such as the use of atomic clocks in satellites, are still used in modern satellite navigation systems.