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FOMS Menu 165 (GPS Status Program)

Note: The following descriptions represent the typical access and privileges afforded to users designated as Dispatch Managers/Supervisors. Users with dispatcher privileges will have limited access to a subset of the screens presented.


This program allows the Almanac data for each of the satellites in the GPS constellation to be stored. This data includes all of the orbital parameters which enable the GPS Fault Detection and Exclusion routine to predict the position of any of the satellites at any time. This program also permits users to virtually disable a satellite in the event that one should be NOTAMed to be out of service for any reason. The Almanac Data is automatically downloaded from the Internet on a weekly basis and written to this data file.

The available modes are:







Edit Mode

The only fields which are editable on this screen are the Status, Remarks and Start/Stop fields.

SATELLITE ID: Enter the ID umber of the satellite whose information you wish to edit. The valid range is 1 to 32. The record will be retrieved and displayed.

STATUS: Enter either <A> for available or <U> for Unavailable. Any satellite marked Unavailable will be considered to be out of service and excluded from consideration in the FDE verification process.

START/STOP: If you set a satellite status to unavailable, enter the date and time to define the beginning and ending of the unavailable period.

REMARKS: Enter any remarks that you feel are appropriate.

Video Mode

This mode allows you to view the data for one GPS satellite at a time, and to scroll through the entire file. The file is sorted numerically by Satellite Number. Use the up and down arrows to view the data for the next satellite in file.

Health: This field displays the health of the satellite signal. Satellite health of 0 indicates that the satellite is functional. Any other value indicates that the satellite is offline.

Week: This field displays the week.

Eccentricity: This field displays the eccentricity of the satellite orbit. This is the amount of the orbit deviation from circular (orbit).

Time of Applicability (s): This field displays the time of applicability. This is the number of seconds the satellite was in the orbit when the almanac was published.

Orbital Inclination (rad): This field displays the orbital inclination. This is the angle to which the satellite orbit meets the equator (GPS is at approximately 55 degrees) expressed in radians.

Rate of Right Ascen (r/s): This field displays the rate of change in the measurement of the angle of right ascension, expressed in radians per second.

SQRT(a) (M^1/2): This field displays the square root of the semi-major axis. This is defined as the measurement from the center of the orbit to either the point of apogee or the point of perigee.

Right Ascen at TOA (rad): This field displays the right ascension at Time of Almanac (TOA), i.e., when the almanac was published, expressed in radians.

Argument of Perigree (rad): This field displays the argument of perigree. This is an angular measurement along the orbital path measured from the ascending node to the point of perigee, measured in the direction of the satellite's motion. This is expressed in radians.

Mean Anom (rad): This field displays the mean anomaly in radians. This is the angle (arc) traveled past the longitude of ascending node. When the satellite has passed perigee and heading towards apogee, the mean anomaly is positive. After the point of apogee, the mean anomaly value will be negative to the point of perigee.

Af0 (s): This field displays the satellite clock bias in seconds.

Af1 (s/s): This field displays the satellite clock drift in seconds per second.

Screen Mode

This mode will permit you to view a report of the oribital parameters for a selected range of satellites.

Report Type: Enter <D> for detailed report, or <S> for summary report.

Hardcopy Mode

Hardcopy mode functions in the same manner as Screen mode, with the exception that the report is sent to the printer and that hence you do not have the ability to terminate the report in mid-stream.

Quit Mode

Entering <Q> from the Command Line will return the Next PROGRAM-NUMBER prompt so that you have the option of going directly to your next program if you know the menu number, or of returning to the previous menu if you simply press <Enter>.

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