Use Case:  Start Autoguiding

Description:  The Autoguiding Loop is started with the current configuration parameters, after having checked that all start conditions are satisfied. If the system is already in closed loop when a START is received, it continues with no error indication.

Role(s)/Actor(s): 
Primary: Operator,Maintenance
Secondary: FAS sub-system, tracking axes, TRS

Priority: Major

Performance: A couple of seconds

Frequency: After each preset when guiding is enabled with autoguiding, or at any time manually during operation while tracking or for test purpose.

Package Assignment:  Auto Guiding.

Preconditions: 

• AG is Idle
• FAS sub-system is ONLINE
• Coude Beam Switching device allows light path to FAS

  Interface:  IfBeamSwitchingDevice.Encoder.ReadoutPosition

• Guide star available
• Guiding Reference point is set
• FAS setup is available (Window size, etc...)

Basic Course: 

• Send command STARTAG to start Autoguiding
  Exception Course: Command failed

  Variations: Use STARTAG command to immediately start Autoguiding Use BOX2GS measure the error vectors and counter-move the Guiding Window the same amount.

• ATCS Checks Autoguiding Conditions at start for autoguiding
  Exception Course: Command failed
• ATCS Prepares FAS Setup with selected setup configuration in window mode, display, centroid calculation
  
• ATCS Starts FAS Acquisition in Closed Loop sending command STARTAG
  Exception Course: Command failed
  Postcondition: FAS active : window + display
  
• ATCS launches a TRS timer with the given period for the Auto Guiding Loop
  Exception Course: Command failed
• ATCS returns OK reply

Exception Course: Command failed

• Start FAS Acquisition with full frame setup
  Postcondition: FAS active : full frame + display
  
• ATCS returns ERROR reply
  Postcondition: AG is Idle

Postconditions: 

• AG is active
• TRS timer is running
• AG error vectors are sent to the axes with the selected frequency
• FAS displays guiding window

Issues to be Determined or Resolved: 

Notes:

• Autoguiding and Field Stabilization are mutually exclusive, since only one detector is used for both. The Auto Guider sends the corrections to the Axis while alternatively FS sends corrections to M6 that in turn recenters itself on 1 second period by sending the corresponding corrections to the Axis.
  It is the same scheme as for the UTs, having M6 playing the same role as M2 for the UTs (see M6 Control Loop).
  
• See AG/FS Analysis for UTs The algorithm for differential refraction handling (different wavelength of target and guide star) could be taken from the UT adapter/rotator implementation.

Last modified: Fri Oct 26 13:41:03 UTC 2001