AR114471 - DSS27 Slews Through Neutral Point Causes Runaway Antenna

This page documents the occurrences of AR114471 in the SPSOPS environment;

A script that detects the anomaly (scanFor114471.sh) runs periodically and checks all completed work orders in the SPSOPS environment. Each time the script runs, a log is produced in the Log File Archive. Each time the script detects a new occurrence of the anomaly, a warning is mailed to the distribution list. A copy of the warning message is also saved in the Warnings Archive. Every time the script runs, it builds the table at the bottom of this page, which contains a summary of all work orders where the anomaly occurs.

Warnings Archive - One file for each work order containing the anomaly

Log File Archive - One log file for each invocation of the script

Last Updated: 2007 232 // 16:51:00

Summary: Last 1 days: WOs Checked: 63, Anomaly Occurrences: 0

Although this anomaly actually occurs in the (AMC) Antenna Monitor and Control Software, the SPS can cause this problem to be avoided by setting the cable wrap bits in the PX6 prediction to zero, or Not Applicable, while the antenna is in the vicinity of zero degrees of azimuth (Due North).

The workaround for this problem should be to set the cable wrap bits to zero only in the near vicinity of zero degrees, and events can be added to the APS file to indicated exactly when the antenna moves into and out of this zone. The workaround would be to modify the recommend cable wrap transitions to include setting the bits to zero at the appropriate time. Unfortunately, there is a bug in the current MPG code which effectively prevents the user from doing this.

As an interim workaround, the cable wrap processing may be disabled defining DSS27 as a non-AzEl station in a special MPG Station Parameters File. Setting ITYPE(27) in this file to a value other than one will cause Px6Gen and DorGen to set all cable wrap bits to zero.

Note: This interim workaround may cause tracking outages, because the recommended cable wrap transitions in the APS file, which are correct, will be ignored. The SPA must verify that the APS does not call for cable wrap reversals with the antenna at the wrap limit in the pre-cal period. If it does, then a fallback to planetary predicts is required.