Pier vibration isolation for lightweight interferometry telescopes

The Navy Prototype Optical Interferometer (NPOI) in Flagstaff, Arizona, makes use of separate smaller telescopes spaced along a Y-array and used simultaneously to simulate an equivalent single large telescope. Each telescope is mounted on a massive reinforced concrete pier tied to bedrock. The mass of the pier dampens most, but not all, of the unwanted vibration in the required spectrum. The quality and resolution of a stellar image depends on minimizing movement of the mirrors due to vibration. The main source of pier vibration is due to the soil-pier interaction. Surrounding environmental and man-made vibration propagates through the soil as body and surface waves, and forces the pier to move. In this paper, a concept based on a sleeve/air gap system to isolate the soil from the pier is used to minimize the vibration input to the telescope. An example of the concept is presented with respect to the future implementation of a 1.4-m diameter composite telescope at the Navy Prototype Optical Interferometer.