Use Case:  Prepare for Image Alignment

1. use FAS or use FSS,
2. use Nasmyth beacon or use Lab source.

Role(s)/Actor(s):
Primary: User (Operator, Maintenance, VLTI-ISS)
Secondary: Coude Beam Switching Device, Nasmyth wheel, FSS Filter Wheel, Nasmyth Beacon,  M6, FSS detector FAS detector

Priority: Major

Performance: 10 to 15 seconds

Frequency: Asynchronous, at least once a day before starting observations and up to once per hour in worst case, or any time for maintenance/test purpose

Package Assignment:  Optical Adjustments.

Preconditions:

• Coude Beam switching device is switched On and ONLINE
• Nasmyth sub-system is switched On and ONLINE
• FAS sub-system is ONLINE (if selected)
• FSS sub-system is ONLINE (if selected)
• M6 is ONLINE
• ROS shutter is open

• Send command PREPIAL to prepare for Optical Image Alignment using Nasmyth Beacon Light Source

Exception Course: Command failed
• ATCS Sets FSS Filter Wheel to the appropriate ND filter (depending on Beacon intensity level)

Exception Course: Command failed
• ATCS Sets Coude Beam switching device to the free hole (if FSS selected) or to mirror (if FAS is selected)

Exception Course: Command failed
• ATCS Sets Nasmyth Wheel to the position for Nasmyth Beacon

Exception Course: Command failed
• ATCS Centers M6

Alternate course: set M6 to "VLTI Coude pointing reference point"
Exception Course: Command failed
• ATCS Prepares FSS Strap for exposures in Closed loop on artificial beacon

Alternate Course: Prepares FAS Setup to configure FAS exposure (typ. 5s)
Exception Course: Command failed
• ATCS sets Nasmyth Beacon level

Exception Course: Command failed
• ATCS switches On Nasmyth Beacon Light Source

Exception Course: Command failed
• ATCS returns OK reply

• Send command PREPIAL to prepare for Optical Image Alignment using the retro-reflecting mirror on the Nasmyth Wheel

Exception Course: Command failed
• ATCS Sets FSS Filter Wheel to the appropriate ND filter (given by VLTI ISS)

Exception Course: Command failed
• ATCS Sets Coude Beam switching device to the free hole (if FSS selected) or to mirror (if FAS is selected)

Exception Course: Command failed
• ATCS Sets Nasmyth Wheel to the Flat Retro-Reflecting Mirror position

Exception Course: Command failed
• ATCS Centers M6

Alternate course: set M6 to "VLTI Coude pointing reference point"
Exception Course: Command failed
• ATCS Prepares FSS Strap for exposures in Closed loop on artificial beacon

Alternate Course: Prepares FAS Setup to configure FAS exposure (typ. 5s)
Exception Course: Command failed
• ATCS returns OK reply

Exception Course: Command failed

• ATCS returns ERROR reply

Postconditions:

• Devices in appropriate position for Image Alignment
• ATCS ready to receive Offset Guide Probe Command

Notes:The Telescope Optical Alignment Configuration could be a file containing all the settings of the various devices used for the alignment such as: the ND filter to be used, the light source to be used, the Nasmyth wheel position, The Coude Beam Switching Device position, etc. The actual setting of the device shall then be executed in the proper predefined sequence. It's anyway a good idea to define the parts and their respective position in a kind of configuration (if it's a file or something else, implementation issue) Actually similar to the CCD setup files associated to dedicated commands such as FLAT or STARTAG.

The Alternate course: set M6 to "VLTI Coude pointing reference point" should indeed be the default (instead of Center M6). If the reference does not exist, then center M6  should be used. This command should do the following: i) this retreives the existing reference point stored in the DB, ii) computes the M6.

What is the position of the Nasmyth wheel for the nasmyth beacon (tool1, tool2, retro, free)?
 
 
 

Last modified: Thu Jun 28 13:39:43 UTC 2001