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Guide Control System (GCS)
The GCS subsystem is the control software for the LBT off-axis autoguiding and wavefront sensing hardware (AGW). The GCS will support two different types of AGW hardware units. One type of AGW is produced at the Astrophysikalisches Institut Potsdam (AIP), which will be used in conjunction with the LUCIFER instruments. The other type is built by the astronomy department of Ohio State University and will mainly be used by the MODS instruments.
Both AGW units comprise a guide camera as well as a camera with a Shack-Hartman sensor. Accordingly, GCS consists of two major modules, i.e. the off-axis autoguider and the wavefront sensing system.
The autoguiding task of the GCS consists of controlling the AGW and providing the TCS with the information on the position of the guide star. This task requires
- to position the guide probe in the field assigned for autoguiding
- to select a suitable star for autoguiding
- to collect images of the guide star
- to measure the position of the guide star (aka. centroiding) with respect to a reference
position in these images
- to provide the centroiding information (including an error estimate, FWHMs, stellar flux, and
background flux) to the TCS.
The other main task is to provide the TCS with information on the measured wavefront of the guide star. It is implied that autoguiding and wavefront sensing are performed with the same star and that wavefront sensor and guide camera use the same positioning unit in the focal area of the telescope.
This task requires
- to position the guide probe in the field assigned for autoguiding
- to select a suitable star for wavefront sensing (and autoguiding)
- to collect images of the wavefront sensing star
- to measure the position of the star in the sub-images produced by the Shack-Hartmann lense
array
- to calculate wavefront distortion information (i.e., Zernike polynomial coefficients)
- to provide this wavefront information to the TCS
As a truly integral part of the TCS, the GCS needs to meet all general architectural requirements of a TCS subsystem. It uses the internal information interchange infrastructure and adheres to the design standards established for the TCS.
But the GCS communicates not only with other TCS subsystems (like the CSQ, or the PCS). It also directs the guide probe hardware of the AGW unit, and drives the process of image exposure and acquisition for the guiding and wavefront sensing camera systems.
Like the IIF work package, the GCS comprises program code, including UML and API documentation.
The proper functioning of the software implies to control the GCS operations via suitable control panels.
Figure 4 shows the assembled AGW unit produced by the Astrophysikalisches Institut Potsdam.
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Figure 4: AGW unit at the laboratory in Potsdam (AIP)
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:: last update 2005-02-22, F. Rodler ::
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