Highly accurate photogrammetric measurements of the Planck reflectors

Abstract

The Planck mission of th e Europea n Space Agency (ESA) i s designed t o image the ani sotropies of t he Cosmic Background Radiation Field over the whole sky. To ac hieve this aim, sophisticated reflectors are used as part of the Planck telescope receiving system. The system consists of secondary and primary r eflectors wh ich are sections of t wo di fferent ellipsoids o f revolution wi th mean diameters of 1 and 1.6 meters. Deformations of the reflectors which influence the optical parameters and the gain of receiving signals are investigated in vacuum and at v ery lo w tem peratures. For th is i nvestigation, am ong the various high accuracy measurement techniques, photogrammetry was selected. With respect to the photogrammetric measurements, s pecial considerations had to be taken into account in design steps, measurement arrangement and data processing to achieve very high accuracies. The determinability of additional parameters of t he cam era under the gi ven network configuration, datum definition, reliab ility and precision issues as well as workspace limits and propagating errors from different sources are c onsidered. We have designed an optimal photogrammetric network by heuristic simulation for the flight model of the pr imary and th e secondary reflectors with relative p recisions better than 1:1000’000 and 1:400’000 t o achieve t he requested acc uracies. A least squares best fit ellipsoid method was developed to determine the optical parameters of the reflectors. In this paper we will report ab out t he procedures, the network design and the results of real measurements.