Dynamic validation of the Planck/LFI thermal model

TL;DR

This paper presents the dynamic validation of the Planck/LFI thermal model through ground tests, confirming its accuracy and revealing better-than-expected thermal damping, which enhances the instrument's scientific performance.

Contribution

It introduces an experimental validation of the LFI thermal model, demonstrating improved damping and analyzing the causes of thermal contact effects.

Findings

Measured thermal damping exceeds predictions

Thermal properties show better damping, reducing systematic effects

Non-ideal thermal contacts explain increased damping

Abstract

The Low Frequency Instrument (LFI) is an array of cryogenically cooled radiometers on board the Planck satellite, designed to measure the temperature and polarization anisotropies of the cosmic microwave backgrond (CMB) at 30, 44 and 70 GHz. The thermal requirements of the LFI, and in particular the stringent limits to acceptable thermal fluctuations in the 20 K focal plane, are a critical element to achieve the instrument scientific performance. Thermal tests were carried out as part of the on-ground calibration campaign at various stages of instrument integration. In this paper we describe the results and analysis of the tests on the LFI flight model (FM) performed at Thales Laboratories in Milan (Italy) during 2006, with the purpose of experimentally sampling the thermal transfer functions and consequently validating the numerical thermal model describing the dynamic response of the LFI focal plane. This model has been used extensively to assess the ability of LFI to achieve its scientific goals: its validation is therefore extremely important in the context of the Planck mission. Our analysis shows that the measured thermal properties of the instrument show a thermal damping level better than predicted, therefore further reducing the expected systematic effect induced in the LFI maps. We then propose an explanation of the increased damping in terms of non-ideal thermal contacts.