Pointing error as the platform is rotated.

  jun12
Links:
Computing the pointing error
comparing the computed error with the measured error.
     
 The platform can be rotated by pulling on the tie downs or redistributing weight on the platform.

Computing the pointing error:


The picture below shows the different parts of the platform rotation:

rotating the platform about the main cables.Computing the pointing error

    The distance the horn moves increases as the zenith angle increases. The sky angle is the purple distance divided by 435 feet. The platform angle is the distance divided by the blue line. The sky rotation will be about 6 times smaller than the platform rotation because of the ratio of the distances.

    The picture below shows the ratio of SkyRotationAngle/PlatFormRotationAngle as a function of zenith angle:

SkyAngle/PlatformAngle vs za

The ratio changes because the distance from the center of rotation of the platform to the horn changes with za.
The idl routine platrotosky will compute the positions of the horn as the platform rotates as well as the rotation angle on the sky.

The plots show the computed pointing error for different platform rotation angles (.ps) (.pdf):

Az, Za variation of the platform tilt:

processing: x101/120618/pntErrVsRot.pro

Comparing the computed and measured tilt errors.

      A test was done using the source  B2209+080 to check the tilt computations.

Processing the data:

The plots show the pointing errors as we tilted the platform (.ps) (.pdf):

Summary:

processing: x101/120606/x102sbn.pro

 home_~phil