Thursday, February 3, 2011

FTV 2/3/11

When someone is on land, they can know exactly where they are by the countless roads, building, and landmarks. On the sea, it is an entirely different story. There are no skyscrapers or roadways to help you figure out where you are. The ocean isn't broken up into cities and streets either. The ocean is divided up into large parts such as; the Caribbean Sea, the Atlantic Ocean, and the Pacific Ocean. There are subparts such as the Gulf of Mexico or the Strait of Gibraltar, but saying you are located in one of those places is like saying you are somewhere in Nevada. This is why Merchant Mariners adopted the use of GPS.

GPS stands for Global Positioning System and was originated by the United States Government for military purposes. GPS is made up of three parts: space, control, and user segments. The space segment includes 21 operational satellites and 3 emergency satellites. The satellites orbit the Earth once every 12 hours on 6 different orbital planes. This allows at least 4 satellites to be seen from any location on Earth at any time. However, it is possible for a satellite to develop error which is why there is a control segment. The control segment is composed of a Master Control Station, several monitoring stations and ground antennas. Since these stations do not move in retrospect to the Earth, they can be used to correct any error a satellite may develop.

They send signals to the satellites to make sure they are relaying the proper location to the users. The users make up the user segment. Every navigational GPS device whether it is a phone, car, or a simple GPS is part of the user segment. It takes all three of these segments to find a location. The user can be anywhere in the world. At least three satellites are needed to create spheres of position of that user. The three spheres of position all come together at exactly one point. That one point is the location of the user. The control segment makes sure that the satellites are actually displaying the proper information in order to avoid false locations from being sent out. Our ship has a couple of GPS devices on board; this allows us to check the accuracy of each device against the others.

Currently the T.S. Kennedy is bound for Bridgetown, Barbados our ETA is 0800 Friday morning. It won't be long until the cadets are under the hot sun on the tropical beaches that Barbados has to offer.


  • What is the GPS location of Massachusetts Maritime Academy?
  • What was the name of the first satellite ever launched? (Hint: The Russians launched it.)
  • What other function could the GPS provide? (Hint: Every satellite has an atomic clock onboard)

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