Planck pre-launch status: Design and description of the Low Frequency Instrument

TL;DR

The paper details the design, development, and specifications of the Low Frequency Instrument (LFI) for the Planck mission, aimed at precise CMB measurements across three frequency bands.

Contribution

It presents the comprehensive design and technical solutions of the LFI, including cryogenic systems and calibration, for the first time in pre-launch documentation.

Findings

Design achieves high sensitivity and stability

Ground calibration results validate performance

Instrument meets stringent systematic effect rejection

Abstract

In this paper we present the Low Frequency Instrument (LFI), designed and developed as part of the Planck space mission, the ESA program dedicated to precision imaging of the cosmic microwave background (CMB). Planck-LFI will observe the full sky in intensity and polarisation in three frequency bands centred at 30, 44 and 70 GHz, while higher frequencies (100-850 GHz) will be covered by the HFI instrument. The LFI is an array of microwave radiometers based on state-of-the-art Indium Phosphide cryogenic HEMT amplifiers implemented in a differential system using blackbody loads as reference signals. The front-end is cooled to 20K for optimal sensitivity and the reference loads are cooled to 4K to minimise low frequency noise. We provide an overview of the LFI, discuss the leading scientific requirements and describe the design solutions adopted for the various hardware subsystems. The main drivers of the radiometric, optical and thermal design are discussed, including the stringent requirements on sensitivity, stability, and rejection of systematic effects. Further details on the key instrument units and the results of ground calibration are provided in a set of companion papers.