CG-1280 Rev. N 09/13 - General Dynamics SATCOM Technologies

Overview2.9.3 SteptrackSteptrack mode provides automatic periodic positioning of the antenna for maximumreceive signal strength as measured at the ACU tracking signal input. The 7200 ACUutilizes the General Dynamics Adaptive Steptrack (AST) algorithm to perform thefunction of conventional steptrack peak signal optimization, eliminating the random"guessing" errors associated with predetermined fixed scan patterns. AST employsalternate AZ and EL peaking operations based upon a mathematical relationshipbetween the changes in receive signal level and angular antenna position. For eachaxis, an initial fixed-size step is taken; signal strength levels before and after the stepare used to determine the magnitude and direction of the corrective (peaking) steprequired. Once the peak position is determined, flags are set, indicating the directionof travel of the satellite so that the initial step for the next peaking operation will tendto move the antenna along the satellite ephemeris. This feature greatly reduces theerrors introduced by the "wrong" guess made during significant portions of the dailysatellite drift by algorithms that consistently make initial steps in a given direction.Steptrack peaking operations are performed at user-definable time intervals, or whenthe receive signal level falls below a user-settable threshold. Steptracking parameters,including tracking signal frequency, cycle time, track threshold, etc., are establishedfor each target, allowing maximum versatility for the system. (Refer to Section5.8.2.4.1)2.9.4 Star TrackingAutomatic Star tracking is provided as an aid in performing antenna gain calculationsby the radio star method. Such measurements require consistent, accuratepositioning along the path of a star with relatively high velocity. This can be done bymanual positioning, but automatic pointing yields more accurate tests, performed inless time. Based upon site location coordinates, automatic pointing for stars includingCassiopeia A, Taurus, and Orion is supported.2.9.5 Intelsat 11-element TrackIn this IESS-412 mode, the antenna is moved according to pointing data generatedusing the Intelsat Eleven Parameter Model. The ACU accepts element sets asdistributed by Intelsat, as well as local site data, and calculates the correspondingpredicted AZ and EL positions along the ephemeris. The antenna is then moved tothe predicted positions with sufficient frequency to maintain pointing within a userselectabledeadband around the theoretical values. The data for a given target ismaintained in a dedicated database for that target and is continually updated toprovide appropriate positioning anytime the target is accessed (within time of validityconstraints).2-29