Global positioning system - how does it work?
Topic: GPS / Gallileo:
GPS is also known as Global Positioning System
Since 1960 GPS is developed by US Navy and US Air Force. In 1978 first satellite in spce. In 1983 the US government decided to open the system for civil usage. 1995: Full Operational Capability, FOC. In 2000 the formally integrated deterioration is disabled and within the exactness for civil users is increased from 100 m to 20m.
On the other hand the EU is planning an alternative system.
Galileo is the first project of the European Union and the ESA( European Space Agency) and a part of TEN (Trans-European Network). The financing is organized by both organisations.
Galileo will be an alternative Positioning System against the US controlled GPS.
All system specific devices and earth stations will have been created by 2005. In 2004 Galileo wants to start the prototypes. In 2007 all satellites for Galileo will be in orbit.
Finally in 2008, it will be ready for use.
There will be 30 Galileo satellites in the altitude of 24 km. The exactness will be around 1 m.
Structure/functions of GPS:
Space segment:
- 24 satellites on 6 different orbits
- angle of inclination 55°#
- per orbit 4 satellites
- flight altitude 20200 km
control segment:
- 5 worldwide spread earth stations for controlling und observing
- Master Control Station in USA
How does GPS work?
At present 31 active satellites are available, but on earth we are capable to receive 6 to 12 of them simultaneously.
The measuring of an precise position takes place through distance measures of several satellites on known orbits. The terms of these radio signals is countable through these distance measures.
To get the precise time the satellites transmit the exact time to the receiver.
3 distance measures are sufficient to get the current position.
Method of distance measuring - one way measures
We are able to measure the position, the moving direction, the speed and the altitude.
The following information will be calculated by the GPS receiver:
distance and direction to the next waypoint, changes of courses, expected arrival, maximum speed, average speed and many more.
At least 4 satellites are needed for a three-dimensional measuring of position (longitude, latitude and altitude)
3 satellites to measure the current position with the x-axis, y-axis and z-axis and one satellite for the time.
Precision of the system
The exactness of the position ranges from 10 to 15 m.
Since the 2,May 2000, it can be used by everybody worldwide.
In excellent conditions the precision increases to 3m.
The American military can totally block civil use or can limit it in crisis zones!
Disturbances of the receiver:
Signals of satellites are straightly broadcast. However, interferences and inaccuracies are caused by valleys, mountains, buildings and tunnels. Metal, e.g.
car roofs, are disruptive elements.
Orientation of satellites:
Generally speaking, for optimal use you have to get the geometry of the satellites in correct order. On the one hand this means that the satellites must not be too close together, because the signal's intersection can't get fixed clearly. On the other hand, the distance between the satellites mustn't get too far, as the signals can be disturbed through shadows.
The measuring of the altitude is 1.7 times more worse than the horizontal line in fixing the position.
The reason for that is the earth's atmosphere, because radio signals are being refracted.
Future prospects of the GPS
Application
'Nowadays everyone has to know, how late it is. In the future nobody will get along without the determination of his exact location.' A new chip generation has to be created for this purpose. For the fulfilment of this task it is essential that the size of this chip has to be small and be available for a reasonable price (size: 49 square millimetres, price: approx. 10 $).
These are technical and economic conditions for surface covering of GPS use in mobile phones, PDAs and clocks. It is possible to integrate a satellite detection system in nearly each electronic component.
'The chances for development are tremendous. We aren't able to foresee all possible kinds of application like the development of computers 20 years ago, of the internet 10 years ago.'
New frequencies for civil users
How will GPS continue?
In February 1997 the American Department of Defence (DoD) and the Department of Transportation (DoT) announced a second GPS-frequency for civil use. Meanwhile the DoD announced to give civil users access to the L2 frequency, too.
Nowadays this frequency is limited for military use.
On March 30,1998 vice president Gore announced that a second civil frequency in the L2 band (1227,6 MHz) and an additional third civil frequency would be made available. The structure of the third frequency hasn`t been announced.
GPS-satellites broadcast 3 different frequencies:
Ø L1-frequency (1575.42 MHz) for civil use
Ø L2-frequency (1227.6 MHz), exclusively used for military purposes in former times, but nowadays it can be used by all GPS devices
Ø L3 -frequency (1381.
05 MHz) for the NDS (Nuclear detonation Detection system)
Which use can the civil user expect from the third frequency?
An essential improvement of the measured value accuracy can be achieved by the new frequency with the real time measuring procedure. Users will have the biggest advantage, because of the increased range with DGPS (differential GPS) measurement (today: 10 - 20km to 100 - 200km).
The analogue signal will be replaced by digital ones (DAB Digitally Audio Broadcasting).
When will the new frequencies be available?
In the last two years various block IIF satellites were launched to their proper position in orbit. They were planned to be launched in 1998. They are able to broadcast the new L3-frequency.
The DoD plans to complete the system till 2009. Every year the administration plans to position 3 new satellites.
However, it is to consider that the replacement of the existing satellites represents only a financial, not a technical problem. If the new system is a great use to individual users (e.g. aviation, navigation etc.
.), it is possible that these users contribute to the financing.
future development
Ø 2004: IIR-M block satellites
-M-code: military use on L1 and L2
-L2C: civil use on L2
availability of the second signal and higher accuracy
Ø 2006 beginning: IIF block satellite
-new carriers L3: only civil use
third civil signal, availability, accuracy
View on future application possibilities
Remote monitoring, detection and security of dangerous goods transport, vehicles e.g. ships, cars, agricultural machinery and airplanes.
On airplanes an electronic wall is animated around the relevant object for the prevention by terrorist attacks on buildings and persons.
If an airplane breaks through this virtual barrier, a computer registers that and switches irrevocably the autopilots on. Now the airplane is brought on the fastest way out of the danger zone, without a danger for the object.
Future prospect GALILEO
Ø own European system *
Ø should be more efficient and surely than the GPS
Ø 30 satellites, world-wide
Ø 1 meter exactly
Ø phases
-Development phase 2002-2005
-Establishment phase 2006-2007
-starting from 2008
*according to news of the day reports American armed forces will be able to switch off likewise in crisis and conflicts the European satellite navigation system GALILEO, like it already happens with the American global positioning system (GPS).
Safety political reasons and advantages of GALILEO
Ø independence
Ø smaller susceptibility to interference
Ø self-sufficiency
Ø control
Ø say
Ø security/integrity
Ø (military) efficiency
Ø accuracy
Ø higher security of the overall system (GPS + GALILEO)
Ø higher accuracy and breakdown resistance (integrity)
Ø equal say and control on the part of the European Union
Ø satellite navigation as a billion-market of the future
GALILEO as an element in the total strategy of the European Unio
| Anmerkungen: |
| impressum | datenschutz
© Copyright Artikelpedia.com
