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

¹ Università degli Studi di Milano, Dipartimento di Fisica, via Celoria 16, 20133 Milano, Italy e-mail: marco.bersanelli@unimi.it
² INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, via Bassini 15, 20133 Milano, Italy
³ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, via P. Gobetti, 101, 40129 Bologna, Italy
⁴ Universidad de Cantabria, Departamento de Ingenieria de Comunicaciones, Av. de Los Castros s/n, 39005 Santander, Spain
⁵ Thales Alenia Space Italia S.p.A., S.S. Padana Superiore 290, 20090 Vimodrone, Milano, Italy
⁶ SISSA/ISAS, Astrophysics Sector, Via Beirut 4, 34014 Trieste, Italy
⁷ INAF - Osservatorio Astronomico di Trieste, via Tiepolo, 11, 34143 Trieste, Italy
⁸ CESR, Centre d'Étude Spatiale des Rayonnements, 9 Av. du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁹ MPA Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
¹⁰ Instituto de Fisica de Cantabria, CSIC, Universidad de Cantabria, Av. de los Castros s/n, 39005 Santander, Spain
¹¹ Jodrell Bank Centre for Astrophysics, Alan Turing Building, The University of Manchester, Manchester, M13 9PL, UK
¹² Herschel/Planck Project, Scientific Projects Dpt of ESA, Keplerlaan 1, 2200 AG, Noordwijk, The Netherlands
¹³ Istituto di Fisica del Plasma, CNR, via Cozzi 53, 20125 Milano, Italy
¹⁴ ASI, Agenzia Spaziale Italiana, viale Liegi, 26, 00198 Roma, Italy
¹⁵ Dipartimento di Fisica, Università degli Studi di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹⁶ INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
¹⁷ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹⁸ Instituto de Astrofisica de Canarias, C/ via Lactea s/n, 38200 La Laguna, Tenerife, Spain
¹⁹ Dipartimento di Fisica, Università degli Studi di Trieste, via A. Valerio 2, 34127 Trieste, Italy
²⁰ DA-Design Oy, Keskuskatu 29, 31600 Jokioinen, Finland
²¹ Ylinen Electronics Oy, Teollisuustie 9A, 02700 Kauniainen, Finland
²² Department of Physics, University of California, Santa Barbara, CA 93106, USA
²³ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
²⁴ INAF - Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
²⁵ Haverford College, 370 Lancaster Avenue, Haverford, PA 19041, USA
²⁶ National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville, VA 22903-2475, USA
²⁷ University of Helsinki, Department of Physics, PO Box 64, 00014 Helsinki, Finland
²⁸ Helsinki Institute of Physics, University of Helsinki, PO Box 64, 00014, Finland
²⁹ Metsähovi Radio Observatory, Helsinki University of Technology, Metsähovintie 114, 02540, Kylmälä, Finland
³⁰ Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
³¹ European Space Agency (ESA), Astrophysics Division, Keplerlaan 1, 2201AZ Noordwijk, The Netherlands
³² MilliLab, VTT Technical Research Centre of Finland, PO Box 1000, 02044 VTT, Finland

Received: 8 July 2009
Accepted: 15 December 2009

Abstract

In this paper we present the Low Frequency Instrument (LFI), designed and developed as part of the Planck space mission, the ESA programme 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 20 K for optimal sensitivity and the reference loads are cooled to 4 K 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.