Orthogonal Transfer CCD in Pan-STARRS Camera

The dangerous asteroids search project Pan-STARRS uses 1.4 Giga-pixel camera. It's sensor is 64 x 64 array of CCD devices, each containing approximately 600 x 600 pixels. The individual CCD cells are grouped in 8 x 8 arrays on a single silicon chip called an orthogonal transfer array (OTA), which measures about 5 cm square. There are a total of 64 OTAs in the focal plane of each telescope.

An Orthogonal Transfer Charge Coupled Device (OTCCD) is a device that allows for image motion compensation in the focal plane itself. During an exposure, selected bright stars have their positions rapidly monitored in order to calculate the immediate effects of atmospheric phase fluctuations. In a traditional "tip-tilt" adaptive optics system, these position errors are fed back to a small mirror whose angle is rapidly adjusted to compensate for the atmospheric disturbance. An OTCCD achieves the same goal by electronically shifting the image within the CCD itself rather than by moving a mirror.

The read noise in the orthogonal transfer CCDs will be about 5 electrons and the sky background will be about 7 electrons per pixel with the broadband filter. Thus, sky noise will dominate read noise in exposures of 15 seconds or more.

The immediate goal of Pan-STARRS is to discover and characterize Earth-approaching objects, both asteroids & comets, that might pose a danger to our planet. Pan-STARRS stands for Panoramic Survey Telescope & Rapid Response System. It is being developed at the University of Hawaii's Institute for Astronomy.