High Frequency Instrument (HFI)
See also Planck Surveyor.
ESA's Planck Surveyor satellite, which was launched on 14 May 2009, is a multiband photometer space mission that aims to make a full sky map of the CMB anisotropies. The payload consists of a 1.5-meter off-axis telescope with an optical design which minimises off-axis distortions and two focal plane instruments: LFI covering the low frequencies (30 to 70 GHz) using radio receivers covering three channels, and HFI covering the high frequencies using bolometers covering six channels between 100 and 900 GHz.
To minimize the contamination of the weak cosmic microwave background signals by strong sources of radiation in the sky (Earth, Sun and Moon), and to achieve the required thermal stability, the Planck satellite will be placed into an orbit around 1.5 million km from the Earth. The nominal mission duration 14-15 months of routine operations and will allow for two complete maps of the sky.
Following the success of the Cosmic Background Explorer (COBE),, there has been an enthusiastic resurgence of interest in the study of the anisotropies of the cosmic microwave background (CMB), fuelled by the realisation that the CMB can set very significant constraints on our current cosmological paradigm. The main objective of the Planck mission is to build on the pioneering work of COBE and fulfil this potential.
The HFI Instrument
This HFI instrument will use 48 bolometric detectors (manufactured by JPL–Caltech) optically coupled to the telescope through cold optics (manufactured by Cardiff University) consisting of a triple horn configuration and optical filters (similar concept used in Archeops ). These detection assemblies are divided into 6 frequency bands (centred at 100, 143, 217, 353, 545 and 857 GHz) with a bandwidth of 33%. Out of these 6 bands, 4 will have the capability to measure the polarisation of the incoming radiation (100, 143, 217 and 353-GHz bands).
The detectors will be cooled down to 100 mK while the filters will be located on a 1.6-K cold plate and the back-to-back horns looking directly at the telescope will be located on a 4-K cold plate.
Cooling the detectors to 0.1 K in space is a major challenge that drives the architecture of the HFI. This is achieved, starting from the passively cooled ~ 60 K stage of the payload module, by a four-stage cooling system (18 K - 4 K - 1.6 K - 0.1 K). The closed cycle 18 K cooler using Joule-Thomson (J-T) expansion of hydrogen and sorption compressors provided by NASA–JPL is common to HFI and LFI.
The 4-K stage using a cooler provided by RAL (Joule-Thomson expansion of helium compressed by mechanical compressors) protects the inner stages from the thermal radiation of the 18-K environment. It also provides electromagnetic shielding (a Faraday cage) for the high impedance part of the readout electronics. It is the envelope of the HFI focal plane unit supporting the back-to-back horns.
Lower temperatures (down to 0.1 K) are obtained by dilution of Helium-3 in Helium-4 (CRTBT ). A 1.6-K stage is generated by J–T expansion of mixed helium. This stage supports filters and intercepts heat from the 4-K stage. The 0.1-K stage supports the bolometers with their horn and filters. Its temperature is controlled thanks to a closed loop active system.
Cardiff University tasks
The role of our Group in Cardiff is to develop and test the cold optics, to integrate this optics with the bolometers provided by JPL-Caltech and to assemble and calibrate all the detection assemblies onto the cold plates before delivery to the principal institute (IAS).
Prof. Peter Ade, Prof. Matt Griffin, Mr. Brian Kiernan, Dr. Giorgio Savini, Dr. Rashmi Sudiwala, Dr. Carole Tucker, Prof Phil Mauskopf, Dr Enzo Pascale
The HFI consortium
The HFI project is led by the Institut d'Astrophysique Spatiale, Orsay, France, with Jean Loup Puget as the Principal Investigator. The institutes involved in the HFI Consortium are:
California Institute of Technology, Pasadena (USA), Cardiff University, Cardiff (UK), Centre d'Etudes Spatiales des Rayonnements, Toulouse (F), Centre de Recherche sur les tres Basses Temperatures, Grenoble (F), College de France, Paris (F), Commissariat a l'Energie Atomique, Gif-sur-Yvette (F), Danish Space Research Institute, Copenhagen (DK), Imperial College, London (UK), Institut d'Astrophysique de Paris, Paris (F), Institut d'Astrophysique Spatiale, Orsay (F), Institut des Sciences Nucléaires, Grenoble (F), Institute of Astronomy, Cambridge (UK), Jet Propulsion Laboratory, Pasadena (USA), Laboratoire de l'Accelerateur Lineaire, Orsay (F), Max-Planck-Institut fur Astrophysik, Garching (D), Mullard Radio Astronomy Observatory, Cambridge (UK), National University of Ireland, Maynooth (IR), Rutherford Appleton Laboratory, Chilton (UK), Space Science Dpt of ESA, Noordwijk (NL), Universite de Geneve, Geneva (CH), University La Sapienza, Rome (I)