Steven Griffin (Boeing)
Keywords: jitter, daylight imaging, 3.6
Abstract:
Unsteady wind loading is the largest dynamic loading on most large ground telescopes. The maximum operational windspeed not only sets requirements on the wind load rejection performance of the mount control system but also is a significant driver for tracker error rejection. In addition, turbulence due to the wind contributes to wavefront distortion. With the recent interest in daylight imaging, introduction of a baffle that reduces background light during the day may further accentuate wind loading on the 3.6 m telescope. The initial daylight configuration of the telescope has been to operate without a baffle and to use operational constraints to avoid angles close to the sun. This configuration offers reasonable daylight performance but is susceptible to stray light that limits achievable signal-to-noise ratio. Also under test is a unique baffled configuration where the telescope is shrouded to increase target signal-to-noise ratio. Traditional baffles increase jitter and wind loading due to increased exposed area to the wind and increase wavefront distortion due to thermal gradients introduced by the baffle. The 3.6 m telescope baffle has been designed out of an opaque fabric to limit the negative impacts on jitter and wavefront distortion while increasing signal-to-noise ratio for daylight imaging. The intent of the design is to limit high frequency transmission of wind loading by the relatively compliant fabric and to allow some circulation using the fabrics porosity to limit thermal gradients. The fabric design also facilitates the extension to a deployable design, since it is relatively easy to deploy and stow compared to a traditional approach. This paper will present analytical results predicting jitter and mount control performance with and without the baffle as well as signal-to-noise ratio predictions with and without the baffle. The jitter results will use measured wind loading in conjunction with a system line-of-sight model for performance prediction. The analytical results will also be compared to measured jitter performance with and without the baffle on the 3.6 m telescope.
Date of Conference: September 10-13, 2013
Track: Poster