Surface control and vibration suppression of a large millimeter-wave telescope

The Large Millimeter-wave Telescope/Gran Telescopio Mili- metrico (LMT/GTM), is a 50-m diameter radio telescope designed to operate at 1-mm wavelengths. To achieve its surface accuracy require- ments, the telescope relies on an actively controlled primary surface. The active primary enables active correction of errors in the reflecting surface caused by thermal and gravitational deformations of the support- ing backstructure. In addition to these slowly varying loads, there are higher frequency disturbances caused by some observation techniques. In a conventional telescope, the observer must wait for the vibration to decay naturally before continuing an observation. However, for an active surface telescope (such as the LMT/GTM), the mass of the surface and the large number of actuators can be used to add damping to the support structure. The use of active surfaces in vibrational damping of their sup- port structures is investigated. A method is presented that enables de- coupling of the vibrational modes in such a way that the surface figure can be controlled simultaneously.