<title>Active segmented primary reflector and pointing accuracy of the Large Millimeter Telescope (LMT)</title>

Abstract

The LMT is a 50-meter-diameter fully-steerable radio telescope to be used for astronomy at millimeter wavelengths. The specifications call for a surface accuracy of 70 micrometer RMS and a pointing accuracy of 0.7 arc sec RMS. This paper addresses two critical issues of the design development. To achieve the required accuracy it was proposed that the primary reflector of the LMT utilize an actively controlled segmented surface with a real time closed loop control system. In the approach developed for the preliminary design systematic deformations of the segments result in the magnification and propagation of surface errors; this problem is examined and possible solutions presented. Limits on the applicability of homology to the design of millimeter wave radio telescopes are discussed in the context of the need for an active surface. A proposed approach for computing in real time the pointing errors due to thermal deformations is evaluated. The results show the limits of applicability of this approach.