Planck-HFI

Planck-HFI
Name	High Frequency Instrument
Mission	Planck
Operator	European Space Agency
Launch	2009-05-14
Mass	66 kg
Type	Imaging bolometer array
Wavelength	350 μm – 3 mm
Status	Decommissioned

Planck-HFI is the High Frequency Instrument flown on the Planck mission, developed to map the cosmic microwave background with high sensitivity at submillimetre and millimetre wavelengths. Designed and built by a consortium led by the Institut d’Astrophysique Spatiale and the Centre National d'Études Spatiales, HFI complemented the Low Frequency Instrument to provide full spectral coverage for cosmological and astrophysical studies. The instrument operated from the Lagrange point L2 after the 2009 launch, contributing to major data releases and cosmological parameter estimation used by teams across European Space Agency, NASA, and international research centers.

Overview

HFI was a cryogenically cooled imaging array of cryogenic bolometers mounted in the Planck focal plane, intended to measure anisotropies in the Cosmic Microwave Background and foreground emission from the Milky Way, Galaxy clusters, and extragalactic sources. Its frequency bands spanned channels centered near 100, 143, 217, 353, 545, and 857 GHz, selected to separate thermal dust emission, the Sunyaev–Zel'dovich effect, and primordial CMB signatures. The instrument formed part of a broader effort linking observations from facilities such as the Wilkinson Microwave Anisotropy Probe, the Atacama Cosmology Telescope, and the South Pole Telescope to refine constraints on models like Lambda-CDM model and parameters including the Hubble constant and baryon acoustic oscillation scales.

Instrument Design and Detectors

HFI employed spider-web bolometers with neutron transmutation doped thermistors developed in collaboration with laboratories including the National Physical Laboratory (United Kingdom), the Max Planck Institute for Astrophysics, and the Institute for Space Astrophysics and Planetology. The focal plane used feedhorn-coupled detectors and quasi-optical filters derived from design work at the Laboratoire de Physique Subatomique et de Cosmologie and the University of Cardiff. Polarization-sensitive bolometers measured linear polarization in selected bands, enabling synergy with polarimeters on missions such as WMAP and ground experiments like BICEP2 and POLARBEAR. The optical chain was integrated with the Planck telescope mirrors manufactured by industry partners and characterized against standards from the European Southern Observatory and calibration facilities tied to the National Institute of Standards and Technology.

Cryogenics and Cooling System

HFI’s sensitivity relied on a complex cryogenic chain culminating in a 0.1 K dilution cooler developed by partners including the Centre Spatial de Liège and Airbus Defence and Space. The system combined passive radiative cooling toward the Lagrange point L2 with active mechanical coolers—the sorption cooler and helium-4 Joule–Thomson stages—derived from engineering heritage at European Space Agency testbeds and the Jet Propulsion Laboratory. The instrument’s cryostat and focal plane assembly drew on cryogenic techniques used for instruments on Herschel Space Observatory and laboratory systems in the CERN cryogenics community. Operational lifetime was constrained by the finite expendable helium and the stability requirements of the dilution refrigerator.

Calibration and Data Processing

Absolute and relative calibration used celestial calibrators such as the Cosmic Microwave Background dipole, planets like Jupiter and Mars, and diffuse emission regions studied by the IRAS and COBE missions. The data processing pipeline was developed within the Planck Collaboration and implemented at data centers across the European Space Agency, the CNRS, the Max Planck Society, and partner universities. Time-ordered data were cleaned for cosmic-ray glitches, thermal fluctuations, and electronic artifacts using algorithms inspired by methods from the Herschel Space Observatory and the Spitzer Space Telescope teams, then projected into maps and spectral-domain products used by cosmology groups at institutions including Princeton University, University of Cambridge, and University of Oxford.

Scientific Objectives and Results

Primary objectives included precision measurement of the CMB anisotropy power spectrum, constraints on inflationary models such as those predicting primordial tensor perturbations, and characterization of foregrounds including interstellar medium dust and extragalactic infrared sources. HFI data underpinned key results reported by the Planck Collaboration: refined cosmological parameters for the Lambda-CDM model, improved maps of the polarized sky used to study galactic magnetic fields and lensing-induced B-modes, and catalogs of galaxy clusters detected through the Sunyaev–Zel'dovich effect. HFI observations were combined with measurements from facilities like BICEP/Keck, DES, and SDSS to test models of neutrino mass and dark energy.

Performance and Systematic Errors

HFI achieved detector noise levels and angular resolution that surpassed predecessors such as COBE and rivaled contemporaries like WMAP in sensitivity per beam. Systematic error sources included cosmic-ray induced glitches, thermal instabilities linked to the dilution cooler, beam asymmetries from mirror imperfections, and bandpass uncertainties affecting component separation. These systematics were characterized via end-to-end simulations, cross-checks with external datasets from Herschel Space Observatory and IRAS, and null tests employed by the Planck Collaboration to quantify residuals in cosmological likelihood analyses used by teams at Institut d’Astrophysique de Paris and the University of California, Berkeley.

Mission History and Operations

HFI was launched on 14 May 2009 aboard an Ariane 5 rocket from Guiana Space Centre together with the Planck payload and operated at Lagrange point L2 under ESA direction. The instrument produced multiple public data releases culminating in legacy temperature and polarization maps used in subsequent cosmology papers and legacy archives maintained by the European Space Agency. Operations included in-orbit commissioning, cryogenic performance verification, and an early end to HFI cryogenic life when the dilution cooler exhausted expendables; subsequent analyses and reprocessing efforts were led by international consortia across the Planck Collaboration.

Category:Spacecraft instruments Category:Cosmic microwave background experiments