page_title: Planck (spacecraft)
section_title: High Frequency Instrument
hierarchical_section_title: Planck (spacecraft) / Instruments / High Frequency Instrument
caption_attribution_description: English: Planck HFI qualification model.
context_page_description: Planck was a space observatory operated by the European Space Agency from 2009 to 2013, which mapped the anisotropies of the cosmic microwave background at microwave and infra-red frequencies, with high sensitivity and small angular resolution. The mission substantially improved upon observations made by the NASA Wilkinson Microwave Anisotropy Probe. Planck provided a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early Universe and the origin of cosmic structure. Since the end of its mission, Planck has defined the most precise measurements of several key cosmological parameters, including the average density of ordinary matter and dark matter in the Universe and the age of the universe.
  The project was started around 1996 and was initially called COBRAS/SAMBA: the Cosmic Background Radiation Anisotropy Satellite/Satellite for Measurement of Background Anisotropies. It was later renamed in honour of the German physicist Max Planck, who derived the formula for black-body radiation.
context_section_description: The HFI was sensitive between 100 and 857 GHz, using 48 bolometric detectors, manufactured by JPL/Caltech, optically coupled to the telescope through cold optics, manufactured by Cardiff University's School of Physics and Astronomy, consisting of a triple horn configuration and optical filters, a similar concept to that used in the Archeops balloon-borne experiment. These detection assemblies are divided into 6 frequency bands (centred at 100, 143, 217, 353, 545 and 857 GHz), each with a bandwidth of 33%.  Of these six bands, only the lower four have the capability to measure the polarisation of incoming radiation; the two higher bands do not.
  On 13 January 2012, it was reported that the on-board supply of helium-3 used in Planck's dilution refrigerator had been exhausted, and that the HFI would become unusable within a few days. By this date, Planck had completed five full scans of the CMB, exceeding its target of two.  The LFI (cooled by helium-4) was expected to remain operational for another six to nine months.
caption: The High Frequency Instrument qualification model.
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