GPS Satellite Frameworks and Constellation - Coursework Example

GPS satellite Frameworks and Constellation No: GPS satellite Frameworks and Constellation The GPS constellation comprises of 24 satellites which in 6 orbital planes. The constellation has four satellites per plane. The constellation can further accommodate only 2 satellites to fill the slots. There are certain satellites, which change their position and do not occupy a fix position in the constellation. Orbital radius is about 16000 miles from centre of the earth. At present, there are 4 GPS satellite constellation which includes, Block 1, Block 2, Block 2a and Block 2r satellite constellations. There is different control segments used in relation to GPS. Those segments will be explained in the essay. It was ensured by launching 24 satellites that at least 4 satellites will be visible at a time in every part of the world to get the requisite data. Lock series was launched in 80s to replenish the orbit and replace the faulty satellites of the constellation (Kinder, 2012). US, Germany, France and Russia have their own system to meet the requirements of their states. Comprehensive policies have been made and implemented by all countries to make the system error free (Rizos, 1999). Now there are 27 satellites of Block series present in the orbit. There task is mainly to replace satellites on failure that is why these satellites are treated as spares. “Moth-balled” satellites are present to meet the requirement of replenishment in the constellation. Block 1 satellites are different from other Block series satellites. These all have been launched to different inclination in their orbits (Rizos, 1999). The block 1 satellites were launched in 80s as testing satellites to test the different systems. This mission did not succeed because out of 11 launched satellites, none gave the desired results. The Block II satellites were launched one by one and nine spacecrafts were launched. The Block IIA satellites were a more up graded than Block 11. The second batch of these satellites comprised of 19 spacecraft of the operational series. The Block IIR satellites were a replacement series launched after Block 11A (Rizos, 1999). User segment comprises of the all GPS users in different countries. GPS receivers have been provided with antenna using different frequencies received from satellites. The clock used in the system is known as crystal oscillator. GPS display screen has multiple options for users. They can navigate to different locations using the user screen. The number of channel for receiver has been increased from few receiver to about 100 (Leick, 1995). The wide area augmentation system is a part of the GPS constellation to perform different tasks. It comprises of 2 geostationary satellites located at 107 degree longitude and 133 degree latitude. In 2010 the tracking system of one wide area satellite failed, efforts are still in hand to put the system right. This satellite has been assigned the job of meeting the requirement of user receiver during performance of vertical operations. (United Nations, 2010) Ground system Is very important equipment of GPS system. The ground system comprises of four subsystems. These subsystems consist of a master control system, an alternate system, antennas and widely spread monitor system. Schriever air force base Colorado US is provided with master control system. It serves as central control node for GPS constellations. Operations and tasks are performed round the clock from this station. This system caters for the aspects like constellation command and control. In addition to this, the control system performs the following tasks (Leick, 1995). Routine monitoring of satellites, troubleshooting of satellites if any error occurs, ensuring quality of signals in the space, updating and upload of message data with high accuracy to maintain high performance at all times, it performs detection and fixation of signal problems in space, high quality signal monitoring system with double coverage meeting the success rate of almost 99 percent. Besides all these functions, it provides back up capacity as well (Leick, 1995). Different wide area reference systems have been positioned in different states of US. Mainly these are located in Canada, Mexico, Alaska and Hawaii. These stations have the responsibility of processing the GPS signals. The up gradation and signal monitoring of satellites is planned by the US aviation authority. Their prime task is to process the new GPS L5 signals (Leick, 1995). There are different category approach procedures used in US based GPS constellations. US developed local area augmentation system as a primary ground base system to get precision approach capability for certain aviation tasks. It fulfills the three dimensional navigational requirements. System ahs little space between to perform super density operations. It provided three-dimensional data to parallel runways having very les distance in-between. The first certified system of this nature is in operation at Memphis international airport in US. Category three-capability system is likely to be functioning by 2012 (United Nations, 2010). US coast guard manages and operates differential GPS. The complete system comprises of 50 maritime, 29 land sites and 9 waterway sites. This is a global system providing dual coverage to some extent. System is very precise and used for different delicate tasks like survey, agricultural and natural resources management (United Nations, 2010). The US operates many reference stations in the states with the cooperation of National Geodetic survey. The system comprises of 1300 sites that also includes academic institutes, as well. The system is so precise that system at each site provides additional feature of code range measurement for centimeter-level data acquisition throughout the country (United Nations, 2010). Civilian navigation system is also very advanced in US. Satellites containing a code-ranging signal for peaceful use transmit the L1 frequency. Precision and accurate code ranging coupled with navigation data message is allowed to users with valid cryptographic keys. Now the advanced research on GPS is focused on the field of adding new navigation signals to GPS constellation. Now the new advanced signal system is incorporated in new GPS satellites while replacing the old version satellites (United Nations, 2010). Signals regarding space navigation message keeps offset data for drawing relation between GPS time with coordinated universal time as per set procedures of US naval observatory. The World Geodetic System uses the geodetic reference system for unenhanced GPS (WGS-84). Better accuracy of approximately 6 cm is achieved by combination of WGS-84 and international terrestrial reference frame (Leick, 1995). After the initial performance capacity of GPS, with the passage of time actual GPS performance achieved the standards specified in the Standard Positioning Service Performance. GPS service users can now expect improvement over minimum performance specifications. If we give an example of 2008, well designed GPS receivers achieved horizontal and vertical accuracy of 3 and 5 meters respectively. This makes 95 percent of the time accuracy (United Nations, 2010). Standard position service and precise position service are the two types of services provided by GPS. Standard position service normally uses C/A code on L1 frequency and precise service uses both L1 and L2 frequencies (United Nations, 2010). Due to accuracy and secrecy, the precise service is used by limited circle of users including military, intelligence agencies and certain allies of US have access to this facility. Contrary to that, the standard positioning service users have a wide circle and it is available worldwide users without directly charging them the expenditure. GPS standard service performance standards contain all the feature that GPS open service provides to a user. The US defence department is a major user of GPS services worldwide. The department intends using codeless and semi-codeless GPS services till 2020. By that time, the department will be able to use the facility of modern L2C and L5 signals on 24 latest GPS satellites (United Nations, 2010). According to survey regulations of 2005, bearings and horizontal distances be determined with the help of boundary lines using a GPS. GPS has many benefits for cadastral surveyor (Van Sickle, 2008). Major advantage is that GPS can be used with flexibility during night and day. The system is not restricted to any specific area and can be used any where in the world. Two receivers used for differential procedure for more accuracy do not need line of sight inter visibility. Survey becomes very easy as more accuracy over the distance can be achieved. This makes GPS a very reliable source for accurate survey (Van Sickle, 2008). Differential GPS system uses ground station for optimum accuracy to attain high level precise and accurate data. Errors can be reduced to centimeters while using the system over thousand kilometers (Van Sickle, 2008). It should be kept in mind that traversing is not the most important thing for knowing GPS observation procedure. Therefore, the notion of traverse closure is not right for GPS surveys. If each line is being obtained from an independent observation station, then GPS loop closures are effectively applicable. Procedures used in survey must be re evaluated and redesigned to meet the present day requirements including statistics and least squares (Van Sickle, 2008). Despite all the advancements in GPS and related ground systems, it is important to minimize disruptions and delays caused and also to enhance safety of the system. All sort of transmissions are strictly recorded and monitored/ regulated by federal provisions. In US, two regulatory bodies have been assigned the responsibility of overseeing the radio frequency field. For achieving the aim of enhanced security, federal communication commission has been tasked to follow all non-federal use of signals. Similarly, national telecommunication department looks after the field usage of the government. This department also hosts an advisor committee that included professionals to act as service providers for government usage. This measure has been taken for safety and secrecy of life bands (Kennedy, 2010). There is a dire need that US government must approach other states to and go beyond domestic boundaries for security of system. In 2007, keeping in view the threats to GPS system US department of homeland security developed a comprehensive plan to look after the security aspects. The plan includes, National positioning, navigation and detection plan and then certain measures to overcome the related problems (Kennedy, 2010). In January 2008, the plan was presented for implementation including techniques to identify problems and measures to solve the problems. Further steps have been taken to respond in less time and accurate navigation procedures. This document provides complete details and framework in performing the related duties to achieve desired results efficiently (Kennedy, 2010). GPS constellation is a very efficient system to meet the requirement of all type of survey, military and civil needs. Civil and military GPS can use relative facility to attain desired results. Different segments help in creating a complete system in all respects to cater for, user and control requirements. USA and other countries have made very workable committees to look after the issues of security and error elimination. There is a need to further enhance the capability to make it completely an error free system. Bibliography Kennedy M (2010) The global positioning system. 3rd Ed. Boca Raton: CRC Press. Kinder S (2012) GPS Satellite Constellation. Available at: http://www.streetdirectory.com/travel_guide/115652/gps_vehicle_tracking/gps_satellite_constellation.html (accessed 11 June 2012) Leick A (1995) GPS Satellite Surveying. New York: John Wiley and Sons. Rizos C (1999) The GPS Satellite Constellation. Available at: http://www.gmat.unsw.edu.au/snap/gps/gps_survey/chap2/222sats.htm (accessed 11 June 2012) United Nations (2010) Current and planned global and regional navigation satellite systems and satellite-based augmentation systems. International Committee on Global Navigation Satellite Systems Providers’ Forum. Van Sickle J (2008) GPS for Land Surveyor. 3rd Ed. London: CRC Press. Read More