Yes, IS-GPS-200 does not currently explicitly prohibit two different satellites from broadcasting a) the same TOA, and yet b) different almanac parameters.

The reasons for this can include:

a) Differences in almanac generation & upload processing between IIA and IIR satellites.

• Block IIA satellites strictly bent pipe a bit for bit broadcast of what is uploaded to the satellite. But in Block IIR satellites, the uploaded almanac contains more precision in four almanac terms than is broadcast in the navigation message. Specifically, the four terms are Af0, Af1, Omega_dot, and Sqrt(A). The Block IIR Nav payload rounds these terms down to the Nav message precision for broadcast. Therefore, one may observe a one IS-GPS-200 LSB difference in the broadcast almanac for any of those four terms when comparing IIR to IIA broadcast almanac for the same Toa. The other almanac terms are bent pipe in a Block IIR should match the Block IIA.

b) The Master Control Station (MCS) executing almanac generation at different times using the same TOA.

• Normally, the MCS only updates the almanac parameters once per day at approximately 2200 Zulu. Sometimes it is necessary to re-generate the almanac parameters at a later time. Standard procedure is to use the same TOA as the almanac generated at 2200Z. Because the MCS’s orbital estimations are constantly updated, there is the possibility that a difference will exist in the final parameters. Due to the coarseness of the almanac, however, users should not see a significant difference in satellite locations.
• Users need to remember that even though the MCS updates the almanac parameters at 2200Z each day, these parameters are not immediately uploaded to all satellites. The new almanac parameters will not appear in the broadcast from a satellite until the MCS makes contact with that satellite and updates its navigation message.

The GWCC resides within the 2d Space Operations Squadron and is the DoD’s focal point for operational issues and questions concerning military use of GPS.  The GWCC is responsible for:

1. Receiving reports and coordinating responses to radio frequency interference in the use of GPS in military operations;
2. Providing prompt responses to DoD user problems or questions concerning GPS;
3. Providing official USSTRATCOM monitoring of GPS performance provided to DoD users on a global basis;
4. Providing tactical support for planning and assessing military missions involving the use of GPS.

As the DoD’s focal point for GPS operational matters, the GWCC serves as the interface to the civil community, through the US Coast Guard’s Navigation Center and Federal Aviation Administration’s National Operations Control Center. 

The Right Ascension in the YUMA almanac is NOT the Right Ascension of the Ascending Node.  Rather, it is the Geographic Longitude of the Ascending Node of the Orbit Plane at the Weekly Epoch.

The answer to this question will vary greatly depending on the type of receiver you are using, its mask angle, and the number of channels it has access to, but there are certain effects which will remain constant regardless of your receiver. The first, and most basic, is that a receiver must first generate an SVs PRN code before it can lock up on the SVs navigation signal. When first attempting to acquire lock, the receiver must use the almanac to predict what SVs will be in view and thus which PRN codes to generate. If the almanac currently loaded into your receiver is new, there will be little to no difference between the SVs predicted position and its actual position. As the almanac in your receiver ages, however, the difference between the predicted position and the actual position will begin to increase. The position difference can cause a delay in initial acquisition only if the SVs predicted position is above the horizon and the actual position is below the horizon. The following angular errors as a function of age of almanac were derived by GPSOC analysts during an analysis for a specific customer.

Age of Almanac	Angular Error
7 Days	± 0.23 Degrees
14 Days	± 0.48 Degrees
21 Days	± 0.95 Degrees
28 Days	± 1.45 Degrees

The following link explains this issue:   Point Vs. Region

Spherical Error Probable (SEP) and Circular Error Probable (CEP) are statistical values representing the median in a range of data.  The median is the value in the middle when the data items are arranged in ascending order (rank ordered from smallest to largest).  For example, lets assume that you have 101 random numbers.  To find the median, you'd arrange the numbers in a list from smallest to largest.  The median value would then be the number in the center of your list (the 51st number).  If you had 100 random numbers (an even number of values), you'd rank order the numbers and then take the average of the middle two numbers (the 50th and 51st).  As you can see, this is very different from taking a range of data's average.

In more practical terms, SEP and CEP refer to the radius in which 50% of your munitions are likely to land.  By point of example:  An F/A-18 drops 101 JDAMS on a known benchmark.  The horizontal miss distances for all 101 weapons are entered into a spreadsheet and sorted in ascending order.  The miss distance in row 51 of your spreadsheet is found to be 8 meters.  This is your CEP value.  What does this tell you?  Half of your munitions hit within 8 meters of your known target location.  The other half hit somewhere outside of 8 meters.  How far outside cannot be determined by looking at CEP.  This example holds for SEP as well, with the exception that SEP factors in vertical as well as horizontal error (a sphere in space rather than a circle on the ground).

The 2nd Space Operations Squadron at Schriever AFB, CO controls the production and distribution of NANUs.

Though there are time tags for different elements of the navigation message (time of almanac, etc), there is not an immediately obvious time tag for the navigation upload itself. A paper presented by Steven Hutsell at the 2000 ION-GPS in Salt Lake City (www.ion.org) details how to extract a navigation upload time tag from the Navigation Message Correction Table (NMCT). The title of the paper is "How Old Is Your Navigation Message?". Details on the NMCT can be found in ICD-GPS-200.

Yes, the Ionosphere can and does affect GPS signals.  This is the main reason why military GPS receivers are dual frequency.  The two frequencies allow a receiver to compensate for ionospheric error.  Single frequency users must use a correction algorithm to compensate for ionospheric error, and that is only about 50% effective.

The International Earth Rotation and Reference Systems Service is responsible for determining when a Leap Second needs to be added or removed. Their web site is: http://www.iers.org

The GPS Wing controls distribution of all GPS ICDs. Interested parties can petition the GPSW for access via the website at this link...

http://www.losangeles.af.mil/library/factsheets/factsheet.asp?id=9364

The reason is because this site uses SSL encryption and the issuing authority (DoD) of the PKI certificate is not configured as a trusted certificate authority on your computer. You may click the Continue to this website link and still access the site. To prevent the warning screen from displaying in the furure you will need to install the DoD Root CA 2 certificate from DISA. For instructions on downloading and installing the certificate click on the following link...

http://dodpki.c3pki.chamb.disa.mil/rootca.html

NGA Precise Ephemeris (Antenna Phase Center based or SV Center of Mass based are available), and daily NGA EOPP bulletins are posted to the following website.

http://earth-info.nga.mil/GandG/sathtml/index.html

No promises or pledges can be made with respect to the time the health setting is changed prior to a Delta-V.  It often changes from one maneuver to another, and there really is no nominal case.  The IS-GPS-200 does not state any requirements associated with time span between health downgrades and Delta-Vs.

A. Yes.  Reference CJCSI 6130.01C, 31 March 03, Enclosure A, page A-2, paragraph 2.e.(1)