RC3000 Antenna Controller Appendix TLE Two Line Element Tracking
TLE-4
TILT ESTIMATE
As discussed in section 2.3.2 of this appendix, the elevation angle derived from the inclinometer
(referenced to local horizontal) and the elevation resolver angle (referenced to the platform) may be
compared to determine tilt of the platform.
The first step of this process will move the antenna to the DEPLOY position. Comparing the inclinometer
and resolver angles will essentially determine the pitch of the platform.
A second movement will rotate the antenna in azimuth in order to characterize the roll of the platform.
How the azimuth moves is based on the nominal azimuth target initially calculated. In order to save time,
azimuth will move in the direction (clockwise or counterclockwise) of the nominal azimuth target. If the
nominal azimuth target is greater than 45 degrees, then the movement will be to the azimuth target. If the
target is less than 45 degrees, azimuth will move to the 45 degree position in order to obtain enough
rotation to adequately characterize roll.
EPHEMERIS POINTING SOLUTION
After the tilt calculation, the LOCATE function will recalculate a target azimuth and elevation for the
satellite at the current date and time. While this calculation is being done, the azimuth and elevation
targets inside parenthesis will flash “TLE” as the current target is being calculated. The following shows
how the screen will appear as a TLE orbit prediction is being calculated.
AZIM: 0.0 ( TLE ) LOCATE
ELEV: -61.7 ( TLE ) SAT:GALAXY 7
POL: 0.0 ( -45.0)
MOVING TO (TARGETS) <STOP>HALT MOTION
The orbital prediction calculation may take several seconds. After the calculation is performed, the
calculated azimuth and elevation targets for the current time of day will be displayed within the
parenthesis. Immediately following the calculation the automatic movement to the predicted targets will
begin.
3.2.2.3.4 Spiral Search Autopeak
Having ephemeris data available allows the RC3000 to predict where an inclined orbit satellite should be
at the current time of day. Having this knowledge allows the controller to perform a more efficient search
for the inclined orbit satellite.
When ephemeris data is available, the RC3000 will perform a “flat spiral” search instead of the expanding
spiral search used for an inclined orbit satellite that does not have ephemeris data associated with it.
Rather than moving to the nominal target and beginning the expanding spiral, the RC3000 will move to
the target elevation (for the current time of day) and search the full range in azimuth before adjusting
elevation. As described in the baseline manual, the azimuth search will account for errors in the azimuth
pointing target mainly due to error from the compass’ heading reading. This movement will be referred to
as a “flat spiral” search pattern.
The flat spiral search pattern always starts at the CCW edge of the pattern’s limits. As with the expanding
spiral search, the flat spiral search will terminate when a signal strength indication above the search
threshold is found. The flat spiral search may be manually stopped at any time by pressing the MODE or
STOP keys.
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