Planck (spacecraft)

Did You Know?

• Planck was initially called COBRAS/SAMBA, standing for Cosmic Background Radiation Anisotropy Satellite/Satellite for Measurement of Background Anisotropies.
• The spacecraft was launched together with the Herschel Space Observatory aboard an Ariane 5 ECA.
• The final deactivation command was sent to Planck on 23 October 2013 at 12:10:27 UTC.

Objectives

The mission aimed to detect both total intensity and polarization of primordial CMB anisotropies at high resolution. It sought to create a catalogue of galaxy clusters via the Sunyaev–Zel'dovich effect, observe gravitational lensing of the CMB and the integrated Sachs–Wolfe effect, and study bright extragalactic radio and infrared sources. Observations of the Milky Way included the interstellar medium, synchrotron emission, and the Galactic magnetic field. Solar System studies covered planets, asteroids, comets, and zodiacal light. Planck offered higher resolution and sensitivity than WMAP, probing the CMB power spectrum to scales three times smaller, and observed in nine frequency bands to improve foreground models. Most measurements were expected to be limited by foreground subtraction rather than detector performance.

Instruments

The spacecraft carried two instruments: the Low Frequency Instrument (LFI) and the High Frequency Instrument (HFI). Together they covered a frequency range from 30 to 857 GHz, with the CMB peaking at 160.2 GHz. Passive and active cooling kept the instruments at 0.1 °C above absolute zero; from August 2009 until January 2012, Planck was the coldest known object in space. NASA's Jet Propulsion Laboratory built bolometers for the HFI, a 20-kelvin cryocooler for both instruments, and amplifier technology for the LFI. The LFI operated in three bands (30–70 GHz) using high-electron-mobility transistors. The HFI used 52 bolometric detectors manufactured by JPL/Caltech, optically coupled through cold optics from Cardiff University, divided into six frequency bands (100, 143, 217, 353, 545, and 857 GHz), each with 33% bandwidth. Only the lower four bands could measure polarization. On 13 January 2012, the helium-3 supply for the HFI's dilution refrigerator was exhausted, rendering the HFI unusable; the LFI, cooled by helium-4, was expected to continue for six to nine more months.

Service module

A common service module (SVM) was designed and built by Thales Alenia Space in Turin for both the Herschel Space Observatory and Planck. Structurally, the SVMs were octagonal, with each panel dedicated to a set of warm units. Both spacecraft shared designs for avionics, attitude control and measurement, command and data management, power, and tracking, telemetry and command subsystems; all SVM units were redundant. The power subsystem included a solar array with triple-junction solar cells, a battery, and a power control unit that provided a regulated 28-volt bus. For Planck, the circular solar array was fixed on the satellite's bottom, always facing the Sun as the satellite rotated on its vertical axis. The attitude control computer fulfilled pointing and slewing requirements; Planck rotated at one revolution per minute, with an absolute pointing error less than 37 arc-minutes and a pointing reproducibility error less than 2.5 arc-minutes over 20 days. The main line-of-sight sensor was the star tracker.

Results

Planck began its First All-Sky Survey on 13 August 2009. Preliminary results from the Planck First Light Survey, released in September 2009, indicated excellent data quality. The mission was extended by 12 months on 15 January 2010, and the Second All Sky Survey started on 14 February 2010, with last observations on 28 May 2010. The first Planck photos, published on 17 March 2010, showed dust concentration within 500 light years from the Sun. The first all-sky image was delivered on 5 July 2010. The Early-Release Compact-Source Catalogue was released in January 2011. A map of the galaxy's magnetic field was published on 5 May 2014. The Planck team and principal investigators Nazzareno Mandolesi and Jean-Loup Puget shared the 2018 Gruber Prize in Cosmology; Puget also received the 2018 Shaw Prize in Astronomy. The 2019 Cocconi Prize of the European Physical Society was awarded to the Planck collaboration jointly with the WMAP collaboration.