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GPS Satellite Outages

GPS satellite outages are determined by the US Air Force using a Notice Advisory to Navstar Users (NANU). NANUs are categorized by their type and can represent forecasted, current or summary outages. See the full list of outage types on the CelesTrak website.

NOTE: The Satellite Outage File supplied by 2SOPS and made available to the public on the NAVCEN website has inconsistencies. I have worked with Analytical Graphics Inc. to produce a consistent Satellite Outage File. I use this consistent file to display the outages on this page. Please contact me to learn more about how this file was modified.


Current Time


Current Outages

GPS satellite outages identified as current by the US Air Force. Current outage types are usually reserved for unscheduled outages.

There are no current outages at this time.

Predicted Outages

GPS satellite outages identified as predicted by the US Air Force.

PRNSVNNANUTypeOutage startOutage stopDuration
24652021019FCSTMXApr 12, 2021 15:45:00Apr 26, 2021 15:45:0014d:00h:00m:000s
7482021021FCSTDVApr 22, 2021 11:30:00Apr 22, 2021 23:30:0000d:12h:00m:000s

Recent Outages

GPS satellite outages identified as historical by the US Air Force, occurring within the last month.

PRNSVNNANUTypeOutage startOutage stopDuration
9682021018FCSTSUMMApr 01, 2021 11:43:00Apr 01, 2021 17:45:0000d:06h:02m:000s
28442021020FCSTSUMMApr 08, 2021 17:01:00Apr 08, 2021 23:00:0000d:05h:59m:000s

Last checked for outage data: 2021-04-21 19:28:22Z


Other links

GPS outages in a calendar format from AGI can be found here:

GPS Satellite Outage Calendar

Historical GPS Outages can be found here:

Historical GPS Satellite Outages


Satellite Outage File Inconsistencies

ICD-GPS-240C defines the Satellite Outage File fields in Section 30: Appendix 3. In that section, specific NANU types are associated with specific Satellite Outage File states; Historical, Predicted and Current. In the currently published satellite outage files, there is a NANU type that is not covered: FCSTUUFN. This NANU type is defined in the ICD, but not covered by the SOF definition in Appendix 3, so there is no ICD controlled way to add this outage type to the SOF.


Navigation blog entries

Gps Basics
The basics of how GPS works with some technical content.

How Long Can You Use an Almanac?
GPS position data is contained in almanac files. Learn how long you can use these for analysis.


Selection of my published papers

Understanding GPS Navigation in Contested Environments
Review of GPS errors, their source and how we can mitigate them. Review of terrain datums and their operational usage and an overview of alternative navigation techniques.

Operational Considerations for Improved Accuracy with an IOC Galileo Constellation
This paper looks at how the Galileo operators can improve the performance of an initial Galileo constellation by managing their ephemeris and clock errors. Keeping those errors small can help keep initial positioning errors small, even when large DOPs are present.

Long term prediction of GPS accuracy - Understanding the Fundamentals
Topics on prediction methods for GPS and how long GPS errors can be predicted. Starting from an understanding of the elements of prediction, including almanac use and ephemeris and clock errors, I look at the statistics of GPS position error predictions under various scenarios.

Statistical Analysis of Military and Civilian Navigation Error Data Services
This paper examines the difference between ephemeris and clock errors generated using civilian data versus those generated using military data. The different data sources result from civilian GPS receiver and military GPS receiver.