Collaboration Case:  Field Stabilization Monitoring Loop

Description:  The Field Stabilization Loop is triggered by a timer and is responsible for updating the Interaction Matrix on the FSS Strap for field rotation compensation.

Priority: Major

Performance: TBD

Frequency: Up to 10 Hz

Package Assignment:  Field Stabilization.

Preconditions: 

• ATCS is ONLINE Tracking and Guiding
• FSS sub-system is ONLINE
• FS is active
• TRS timer is running

Basic Course: 

• TRS timer trigger. This FS monitoring loop is synchronized with the STRAP disgnostic loop and NOT with the STRAP closed control loop, that has much higher frequency.
• ATCS Checks Autoguiding Conditions (for field stabilization). Typically this check is not performed at every loop, but with a lower frequency.
  Exception Course: Guiding conditions not met
• ATCS Retrieve and Check Error Vector from FSS Strap
  Exception Course: No error vector

Exception Course:  No error vector

• ATCS logs an error
• ATCS checks for too many consecutive invalid error vectors
  (to allow for temporary failures, like in the case of a cloud passing by).
  Exception Course: Too many errors

Exception Course:  Too many errors

• ATCS Stops Field Stabilization

Exception Course: Guiding conditions not met

• ATCS logs an error
• ATCS Stops Field Stabilization

Exception Course: Command failed

• ATCS logs an error
• ATCS Stops Field Stabilization

Postconditions: 

• FS is active

Issues to be Determined or Resolved:

The synchronization procedure with the STRAP diagnostic loop must be analyzed in detail. It is important:

• To warrant that a coherent set of diagnostic data can be read (no write while reading)
• To measure timing jittering and maximum delay for the delivery of diagnostic data.

The diagnostic data loop will be used for real time synchronization and must be very well characterized.

There are two possible ways for synchronization:

• A user function (name defined via database) is called at every cycle and receives the diagnostic data in the parameters buffer. This is done on the TCCD software and works quite well.
• A database flag is written when new data is available. To avoid that data is overwritten, a semaphore flag should be added or a minimum time delay before overwriting should be defined.

Note: For next iteration, add the UC that catches the FSS Translation Table alarm indicating the vicinity of the limit (end of possible tracking).