The LSPE-Strip Pointing Reconstruction and Star Tracker

TL;DR

This paper details the development and validation of a pointing reconstruction model and a star tracker prototype for the LSPE-Strip CMB telescope, achieving high accuracy in pointing calibration and error analysis.

Contribution

It introduces a formal Pointing Reconstruction Model and demonstrates a star tracker prototype with sub-arcminute accuracy for the LSPE-Strip telescope.

Findings

Star Tracker RMS accuracy of ~3 arcseconds

Systematic errors below 10 arcseconds

Intercalibration accuracy between 0.25 and 1 arcminute

Abstract

This paper aims to describe the Pointing Reconstruction Model (PRM) and the prototype Star Tracker, which will be mounted on LSPE-Strip, a microwave Q- and W-band CMB telescope planned for installation at the "Observatorio del Teide" in Tenerife. The PRM integrates information on the instantaneous attitude provided by the telescope control system to determine the actual pointing direction and focal plane orientation of the telescope. It accounts for various non-idealities in the telescope setup, represented by eight configuration angles, which will be calibrated using the Star Tracker. Following the derivation of the PRM formalism and its implementation, we investigate the pointing errors caused by incorrect calibration of these configuration angles to validate the required 1 arcminute maximum systematic pointing error for the LSPE-Strip survey. This paper also describes the main structure and operations of the Star Tracker and presents the results of a campaign of actual sky observations conducted with a prototype. The results demonstrate a Star Tracker RMS accuracy of approximately 3 arcseconds, while systematic errors remain below 10 arcseconds. Based on these results, we analyzed the problem of reconstructing the PRM configuration angles. Two methods for intercalibrating the Star Tracker's pointing direction with respect to the focal plane's pointing direction were examined: (1) observations of planets and (2) observations of a drone carrying both an optical beacon and a radio beacon. In the first case, an intercalibration accuracy between 1/3 arcminute and 1 arcminute is achievable. In the second case, the expected intercalibration accuracy ranges from 0.25 arcminute to 1 arcminute.