The Near Earth Space Surveillance Initiative (NESSI) Precision Astrometric and Photometric Survey

The Near Earth Space Surveillance Initiative (NESSI), an AFRL-funded collaboration between the University of Texas at Austin and the University of New Mexico, includes a unique 1.8-m imaging astrometric and photometric telescope and a large, segmented-mirror, dedicated spectroscopic telescope. We describe design aspects of the imaging telescope, including the optical system, structure, focal plane mosaic and the detector readout system that allows precise astrometric and photometric measurements.

The scientific design drivers for the imaging telescope include: 1. Discovery and measurement of motion and distance for late M, L and T stars, which drives robust detection of faint objects with unique (red) colors, and astrometric precision for precise position and parallax determination, 2. Synoptic photometric monitoring of active galactic nuclei (AGN) which drives time-domain characterization of faint, variable objects, and 3. Discovery and near real-time spectroscopic follow-up of distant supernovae and AGN outbursts, which drives immediate target-of-opportunity detection and response.

These drivers are addressed in the design of a wide field-of-view stationary telescope that employs the time-delay and integrate (TDI) readout mode for CCD detectors to produce a deep, multicolor image of the sky every clear night. Because the telescope is stationary, it observes approximately the same region of the sky on successive nights, and a complete small circle on the sky after a year. This strip geometry produces the time domain photometric and repeated astrometric measurements required to address the science drivers.

The telescope, its focal plane mosaic and the data system all incorporate unique and innovative elements that support future sky surveys.