Package Assignment:  Auto Guiding.

Use Case:  Center Guide Star

Description:  Move the telescope in order to center the identified guide star on the guiding reference point. Actual guide star position can be selected automatically using the Autoguiding error vector evaluation fuctions or manually by using the FAS display.

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

Priority: Desirable

Performance: Typically a few seconds. Max 30 seconds

Frequency: At preset time

Preconditions: 

• ATCS is ONLINE Tracking
• AG / FS are Idle
• FAS is ONLINE
• FSS Strap is ONLINE (if automatic centering with FSS requested)
• FSS Translation Table is tracking (if automatic centering with FSS requested)
• Coude Beam Switching device allows light path to FAS and/or FSS

  Interface:  IfBeamSwitchingDevice.Encoder.ReadoutPosition

• a Guide Reference Point is defined

Basic Course:  Automatic centering with FAS

• Send command DETGS/DETCGS to center guide star automatically from FAS
  Exception course: Command failed
• ATCS Prepare the FAS Setup for 1 single exposure in window mode with error vector calculation
  Exception Course: Command failed
  
• ATCS Start Field Acquisition to take the needed exposure
  Exception Course: Command failed
  
• ATCS Retrieve and Check Error Vector from the FAS
  Exception Course: No error vector
  
• ATCS sends Autoguider Offset to the tracking axes
  Exception Course: Command failed
• ATCS returns OK reply

Alternate Course: Automatic centering with FSS Strap

• Send command to center guide star automatically from FSS
  Exception course: Command failed
• ATCS Prepares FSS Setup for 1 single sequence of measurements (Open loop, no M6 corrections)
  Exception Course: Command failed
  
• ATCS Start FSS Acquisition to take the needed exposure
  Exception Course: Command failed
  
• ATCS Retrieve and Check Error Vector from the FSS Strap
  Exception Course: No error vector
  
• ATCS sends Autoguider Offset to the tracking axes
  Exception Course: Command failed
• ATCS returns OK reply

Alternate Course: Manual centering

• Send command to center guide star manually with guide star actual coordinates
  Exception course: Command failed
• ATCS calculates error vector from the given coordinates and the guide reference point
  
• ATCS sends Autoguider Offset to the tracking axes
  Exception Course: Command failed
• ATCS returns OK reply

Exception Course: No error vector

• ATCS returns ERROR reply

Exception Course: Command failed

• ATCS Stops Autoguiding
  Alternate Course: ATCS Stops Field Stabilization
• ATCS returns ERROR reply

Postconditions: 

• Guide star is centered on the Guide Reference Point

Issues to be Determined or Resolved: 

Notes:

Last modified: Fri Feb 22 12:19:56 UTC 2002