Comments on: How do GPS satellites stay in perfect position with out drifting out of position in time? http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/ Wed, 16 May 2012 21:23:33 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Charles Malke http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-3314 Charles Malke Mon, 12 Apr 2010 03:03:49 +0000 http://gpsmaestro.com/?p=162#comment-3314 They stay in orbit around the earth. Just like the moon. They stay in orbit around the earth. Just like the moon.

]]> By: bikenbeer2000 http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-237 bikenbeer2000 Tue, 27 Jan 2009 17:14:40 +0000 http://gpsmaestro.com/?p=162#comment-237 The GPS satellites orbit the earth twice a day. It isn't necessary for them to stay in perfect position. The crucial point is that each satellite should "know" where it is. Tracking stations around the world allow the orbits of the satellites to be calculated, that information is sent to the satellites and the satellites, in turn, broadcast that data to the GPS receiver on the ground. When a GPS receiver picks up broadcasts from 4 or more satellites, it can determine its position relative to those satellites and hence derive its geographical location. The GPS satellites orbit the earth twice a day. It isn’t necessary for them to stay in perfect position. The crucial point is that each satellite should “know” where it is. Tracking stations around the world allow the orbits of the satellites to be calculated, that information is sent to the satellites and the satellites, in turn, broadcast that data to the GPS receiver on the ground. When a GPS receiver picks up broadcasts from 4 or more satellites, it can determine its position relative to those satellites and hence derive its geographical location.

]]> By: ANDRE L http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-236 ANDRE L Sun, 25 Jan 2009 00:36:00 +0000 http://gpsmaestro.com/?p=162#comment-236 The Block II GPS satellites have been deployed: * In 6 nearly circular orbital planes. * With 4 satellites equally spaced within the plane (the 3 in-orbit spares are spread across different orbital planes). * In orbital planes at an inclination of 55 degrees. * At altitudes of approximately 20200km above the earth. As the GPS satellites are in nearly circular orbits, at an altitude of approximately 20200km above the earth, this has a number of immediate effects which make the prediction of satellite location comparatively easy: * Their orbital period is approximately 11hrs 58mins, so that each satellite makes two revolutions in one sidereal day (the period taken for the earth to complete one rotation about its axis with respect to the stars). * At the end of a sidereal day (approximately 23hrs 56mins in length) the satellites are again over the same position on earth. * Reckoned in terms of a solar day (24hrs in length), the satellites are in the same position in the sky about four (4) minutes earlier each day. * The orbit groundtrack approximately repeats each day, except that there is a small drift of the orbital plane to the west (-0.03 per day). [end quotes] The orbits are well known and tracked, and it is the combination of signals form several satellites that allows the user the accuracy of data. The Block II GPS satellites have been deployed:
* In 6 nearly circular orbital planes.
* With 4 satellites equally spaced within the plane (the 3 in-orbit spares are spread across different orbital planes).
* In orbital planes at an inclination of 55 degrees.
* At altitudes of approximately 20200km above the earth.
As the GPS satellites are in nearly circular orbits, at an altitude of approximately 20200km above the earth, this has a number of immediate effects which make the prediction of satellite location comparatively easy:
* Their orbital period is approximately 11hrs 58mins, so that each satellite makes two revolutions in one sidereal day (the period taken for the earth to complete one rotation about its axis with respect to the stars).
* At the end of a sidereal day (approximately 23hrs 56mins in length) the satellites are again over the same position on earth.
* Reckoned in terms of a solar day (24hrs in length), the satellites are in the same position in the sky about four (4) minutes earlier each day.
* The orbit groundtrack approximately repeats each day, except that there is a small drift of the orbital plane to the west (-0.03 per day). [end quotes]
The orbits are well known and tracked, and it is the combination of signals form several satellites that allows the user the accuracy of data.

]]> By: Morningfoxnorth http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-235 Morningfoxnorth Sat, 24 Jan 2009 07:33:27 +0000 http://gpsmaestro.com/?p=162#comment-235 It doesn't matter if the satellites drift or not -- what matters is that the GPS units know what the drift is. The satellites broadcast their exact position all the time. Actually, they broadcast the numbers for an equation that can be used to calculate the position. Then your car GPS unit calculates the equation to find out how far away the satellite is. When this is done for 3 or 4 satellites, the car unit can figure out where the car is and how fast it's going. The GPS ground station figures out the orbit equations for the satellites, several times a day. Then they send the equations up to the satellites by radio, and the satellites broadcast the equations to the whole world. It doesn’t matter if the satellites drift or not — what matters is that the GPS units know what the drift is. The satellites broadcast their exact position all the time. Actually, they broadcast the numbers for an equation that can be used to calculate the position. Then your car GPS unit calculates the equation to find out how far away the satellite is. When this is done for 3 or 4 satellites, the car unit can figure out where the car is and how fast it’s going.

The GPS ground station figures out the orbit equations for the satellites, several times a day. Then they send the equations up to the satellites by radio, and the satellites broadcast the equations to the whole world.

]]> By: Tina L http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-234 Tina L Thu, 22 Jan 2009 16:01:59 +0000 http://gpsmaestro.com/?p=162#comment-234 the ground stations monitor the locations of the satellites and adjust them as needed. teh satellites transmit data that describe their orbits. gps receivers use this information. the ground stations monitor the locations of the satellites and adjust them as needed.

teh satellites transmit data that describe their orbits. gps receivers use this information.

]]> By: cactii10 http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-233 cactii10 Wed, 21 Jan 2009 01:52:13 +0000 http://gpsmaestro.com/?p=162#comment-233 There are a few sites on the earth that have been set up to monitor and track the satellites. Their positional information is calculated and then sent to them to update the onboard computers. A complete explanation can be found at You can also find more information about GPS devices at There are a few sites on the earth that have been set up to monitor and track the satellites. Their positional information is calculated and then sent to them to update the onboard computers.

A complete explanation can be found at

You can also find more information about GPS devices at

]]> By: Loren S http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-232 Loren S Mon, 19 Jan 2009 12:55:45 +0000 http://gpsmaestro.com/?p=162#comment-232 since the earth is a little less than 25000 miles in circumference the satellite is positioned at about 1100 miles from earth surface, the necessary speed computed to maintain it at the exact speed of the earths rotation at that height and the satellite speed set to maintain position at that point. try this link for further information. since the earth is a little less than 25000 miles in circumference the satellite is positioned at about 1100 miles from earth surface, the necessary speed computed to maintain it at the exact speed of the earths rotation at that height and the satellite speed set to maintain position at that point. try this link for further information.

]]> By: cyswxman http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-231 cyswxman Fri, 16 Jan 2009 22:00:34 +0000 http://gpsmaestro.com/?p=162#comment-231 I believe they do have small thruster jets on them that allow controllers to make small orbital adjustments when needed. I believe they do have small thruster jets on them that allow controllers to make small orbital adjustments when needed.

]]> By: planman1994 http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-230 planman1994 Fri, 16 Jan 2009 04:32:32 +0000 http://gpsmaestro.com/?p=162#comment-230 they can calculate their position, and when they move out of the position they should be in, the use engines to put themselves back into the correct position they can calculate their position, and when they move out of the position they should be in, the use engines to put themselves back into the correct position

]]> By: epic_ru http://gpsmaestro.com/how-do-gps-satellites-stay-in-perfect-position-with-out-drifting-out-of-position-in-time/comment-page-1/#comment-229 epic_ru Thu, 15 Jan 2009 21:13:39 +0000 http://gpsmaestro.com/?p=162#comment-229 They don't drift away because they can calculate their position very accurately using atomic clock! They don’t drift away because they can calculate their position very accurately using atomic clock!

]]>