FUNCTIONAL SPECIFICATION

Actors are the system itself and any other external entity (people or other systems), that interacts with the system to achieve a desired goal.

At the level of requirement specification, Use Cases see the system as a black box and no indication of the internal architecture is provided.

At analysis and design level, Collaboration Cases are used to "open" the black box and show the interactions between the components internal to the system. In this phase Use and Collaboration Cases are assigned to software packages and extended adding specific design level details. When Use Cases and Collaboration Cases are read from the Requirements point of view, the Design level details are filtered out and removed.

Use Cases can also be directly used to verify compliance of the development system to the requirements. The acceptance test of the system consists in verifying one by one all the use cases specified at requirements level and whenever possible an automatic regression test will be developed for each Use Case.

Use Cases are grouped according to their functionality.

In general, the ATCS includes six categories of software:

• Coordinating Software
• Subsystem Software
• Special Interface Software
• Command Interface Software
• User Interface Software
• Engineering and Maintenance

The tasks of the Auxiliary Telescope Coordinating Software are:

• to manage high level tasks of combined, coordinating nature, which involve often simultaneous actions executed on several subsystems
• to send the low level commands to the subsystems in the proper sequence

The Coordinating Software consists of the following groups of:

• Mode Switching
  The Mode Switching functions are used to command the AT Control System as a whole and to provide information regarding its global operational state.
• Presetting
  The Presetting functions shall take care of requests to move the telescope to a new target position.
• Pointing Modelling
  The Pointing Modelling software creates and updates, automatically or interactively, pointing models used to improve the telescope pointing accuracy, by compensating geometrical misalignments and structural flexures.
• Optical Adjustments
  Comprises all activities related to adjustments of optical devices (Mirrors, Wheels, Filters, ...)
• Tracking
  The Tracking software shall implement the function that drives the telescope to follow the apparent motion of an astronomical object.
• Field Acquisition
  The Field Acquisition functions provide a high level control of the Field Acquisition Sensor, which supplies an image of the stellar field from the Coudé Focus.
• Autoguiding
  The Autoguiding software shall intervene to correct telescope position errors of low frequency
• Field Stabilization
  The purpose of the Field Stabilization is to make position corrections faster than those achievable by Autoguiding. Modifying the tip/tilt angle of M6 performs such corrections.
• Chopping
  Describes the functions needed for tip-tilt of the M6 to achieve chopping.

• Altitude drive
  Position control of the telescope altitude axis, including motor, amplifier, tachometer, encoder, brakes and limit switches.
• Azimuth drive
  Position control of the telescope azimuth axis, including motor, amplifier, tachometer, encoder, brakes and limit switches.
• M2
  Control of the focusing, centering and tilt mechanism, switching of the pupil beacon light source.
• M6 (to be replaced by Deformable Mirror)
  Control of the High Frequency M6 tilt motions, required for field stabilization and chopping. For Adaptive Optics, the M6 will be replaced by a deformable mirror controlled by appropriate electronics.
• M10 (to be replaced by Dual Feed Mirror)
  Control of the Dual Feed mirrors (when implemented) for output pupil position adjustment as well as reference object selection and tracking. Control of the two low frequency M10 tilt motions, required for output pupil position adjustment.
• Coudé Beam Switching Device
  Control of the selection of the different elements that can be inserted in the beam before the Coudé sensor. It consists of 5 elements, namely a Mirror reflecting the beam to FAS only, a Beam Splitter sending the beam to both FAS and FSS, a Free Hole to FSS only, the FSS pupil viwer and a Light Stop that prevents the beam to reach neither FAS nor FSS.
• Nasmyth wheel
  Control of the position of the wheel, including motor, tachometer, encoder and limit switches. Switching on/off the image beacon light source. This 4-element device consists of Flat Retro-Reflecting mirror, a Free Hole and 2 positions for dedicated Alignment Tools (light beacons).
• Field Acquisition Sensor (FAS)
  Control of the Field Acquisition Sensor components (CCD head, pre-amplifier, temperature sensor, liquid cooling) The Field Acquisition Sensor is used also as the detector for Auto Guiding.
• Field Stabilization Sensor (FSS)
  Control of the Field Stabilization Sensor components (detector, real time electronics, communication link to M6).
• FSS Filter Wheel
  Control of the position of the filter wheel that allows the insertions of 6 neutral density filters before the FSS.
• FSS Translation Stage
  Control of the XY translation stage used as support for the FSS, including motor, tachometer, encoder and reference switches.
• Air Conditioning
• Thermal Control inside the telescope dome
• Telescope Temperature Sensors
  Monitor and record the values provided by the temperature sensors installed on the telescope structure.
• Relay Optics Structure (ROS) Shutter
  Open/Close control.
• Enclosure
• Anemometer
  Monitor the wind speed measured by the anemometer placed at the AT enclosure.
• Open/close control,
• Emergency and redundant closing
• Transporter
  Monitor the status of the transporter and in particular of the anchoring system.
• Service modules
  Monitor the status of:
• Auxiliary power
• Hydraulic and pneumatic systems incl. On/Off control
• Liquid Cooling Module incl. Flow meter monitoring

At each instant in time the ATCS can assume one of a predefined set of states:

• OFF
  The system is not operational. The control system is entirely or partly switched off, or the control software is not loaded or not initialized, or the control hardware is not configured, or some controlled devices are in unknown state. To go to the STAND-BY state, a cold-start procedure is required (power-on, loading, initialization).
• STAND-BY
  The system is not operating, but nevertheless the control software is loaded, initialized and running. All equipment are switched off, except those functional units which are required for thermal stability. Required mechanical safety systems are activated to prevent any degradation. This state is used when the AT is not performing an observation, a relocation, or a maintenance procedure, and provides a safe configuration against environmental aggression. This is the typical state during day-time.
• ONLINE
  The system is completely ready and available for the observation run or already observing. Two main substates are identified:
• Idle
  The system is ready to operate or is operating and is waiting for a command.
• Presetting
  The telescope is performing a "Preset Sequence" moving to point a selected object in the sky or to a selected absolute position. Part of the "Preset Sequence" is the setup of all the sub-systems selected for observation in the given setup.

• Idle
  The system is ready to operate and is waiting for a command.
• Presetting
  The telescope is moving to point a selected object in the sky or to a selected absolute position, or the telescope position is being corrected by a user offset command.
• Tracking
  The telescope is following the apparent motion of the pointed object in the sky. A further level of specification, kept in a separate sub-state, identifies the type of tracking based on the guiding mode:
• none (blind tracking) The telescope is continuously pointing the object under observation using its theoretical trajectory, taking into account the sidereal motion, the complete standard coordinate conversion, atmospheric refraction as well as telescope-dependent errors included in the pointing model. It involves the motion of the telescope's axes only.
• autoguiding It is similar to blind tracking, except that a low frequency error signal is provided by the Field Acquisition Sensor from the measurement of the actual object image. The error signal is used to correct the position of the telescope's axes.
• field stabilization It is similar to autoguiding, but in this case a high frequency error signal is provided by the Field Stabilization Sensor from the actual star position, to correct atmospheric turbulence effects and remaining telescope tracking errors. The error signal drives the tip/tilt control of the fast steering mirror M6 for compensation. The telescope's axes follow a control law that performs the offload the M6 tip/tilt position.
• RELOCATION
  The system is performing all the necessary steps to move the AT from one observing station to another. An operator performs the relocation under "manual" control using control panels. The AT Control Software plays no role in this operation, if not monitoring passively the status of sub-systems. For example an accelerometer could be added to monitor the acceleration of the transporter during relocation.
• MAINTENANCE
  The system is under maintenance procedures, such as tuning, calibration and performance monitoring.

State information about other components of the AT Control System is available. In particular, specific state information is maintained for the Chopping software.