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The GPS satellite constellation
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50 SW completes GPS constellation expansion

Posted 6/16/2011   Updated 6/22/2011 Email story   Print story


50th Space Wing Public Affairs

6/16/2011 - SCHRIEVER AIR FORCE BASE, Colo.  -- The 50th Space Wing successfully completed a two phase Global Positioning System constellation expansion known as "Expandable 24" June 15. This expansion increased global GPS coverage and is now providing civil, military and commercial GPS users with a more robust signal and a higher probability of signal acquisition in terrain challenged environments.

The GPS constellation consists of 24 operational slots positioned within six equally-spaced orbital planes surrounding the earth. This plane/slot scheme and enhanced satellite placement ensure GPS users receive the most accurate navigation data at any time, at any place around the world.

"This marks another successful milestone in our continued commitment to modernize our weapon system," said Lt. Col. Jennifer Grant, 2nd Space Operations Squadron commander. "We take great pride in providing GPS performance that exceeds our requirements for the system, which we have been doing since 1995."

Expandable 24 is a U.S. Strategic Command commander directed initiative, executed by 2 SOPS, to reposition six satellites in the current GPS constellation. Given the strength and number of satellites in the current constellation, Air Force Space Command was in a unique position to enact this revolutionary strategy to benefit global users. AFSPC acted on this opportunity to increase the robustness of satellite availability and overall signal in space performance by expanding three of the baseline 24 constellation slots.

Phase one of Expandable-24 began in January 2010 when 2 SOPS performed maneuvers to reposition three GPS satellites, one of which took 351 days to maneuver. The last of the satellites completed repositioning January 18. Phase two began in August 2010 when 2 SOPS maneuvered the final three satellites to their new locations and completed June 15 when the last satellite arrived at its new location.

"From the planning phases in the fall of 2009 to its completion today, 2 SOPS operators, engineers, analysts and support personnel have done an incredible job in making the Expandable 24 GPS initiative a reality," said Maj. Benjamin Barbour, assistant director of operations. "It's an exciting time to be a part of GPS. This is a huge milestone and everyone in the squadron is excited about the accomplishment and proud to have played a part in continuing GPS's position as the 'gold standard' for global navigation space systems."

The GPS constellation has now attained the most optimal geometry in its 42 year history, maximizing GPS coverage for all users worldwide.

1/17/2014 4:52:14 AM ET
The current constellation has improved.However in 2013 PRN 8-9 and 6-27 are flying together. PRN 3-27-9 are flying in a chain. This is good if the old PRN 3 or 9 fails as PRN27 is already in place and the same is true for PRN8-9.However if one does not use a minimum elevation of 5 degrees but uses 7 degrees as PPP does or 10 as PPP-RTK does or 15 for RTK users there are satellite holes in the current configuration. Also not all customers do have clear view to the sky up to 5 degrees so will have moments of degraded performance.
Hans Visser, Netherlands
12/10/2013 6:19:18 AM ET
So how many operational GPS satellites do we have in our constellation I am getting 27 here 31 on and 32 on other sites. I am a little mixed up. Could someone help clear this up for me If there is only 27 operational is there a diagram available to see how the new slots are set up in the existing planes There still is only six planes correct
Matthew Trautman, Pittsburgh
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