Introducing the “coolest” spacecraft in the Universe UK involvement in ESA’s Planck mission

Professor Keith Mason, Chief Executive Officer of the Particle Physics and Astronomy Research Council (PPARC), who fund the UK involvement in the mission, said, “Planck presents a tremendous opportunity to further our knowledge and understanding of the parameters that control the functioning of our Universe. The integration of the instruments into the spacecraft is a significant milestone that marks a major step towards launch next year.”

Planck will travel back to the dawn of time to investigate with the highest precision ever the cosmic microwave background (CMB) – the remnants of the radiation that filled the Universe immediately after the Big Bang some 14 billion years ago. Planck will be sensitive to temperature variations of a few millionths of a degree and will map the full sky in nine wavelengths. The tiny differences in the CMB are like the marks in a fossil, revealing details about the organism they come from – in this case, the physical processes at the beginning of the Universe.

The mission will address a number of fundamental questions, such as the initial conditions for the evolution of our Universe’s structure, the nature and amount of dark matter and the nature of dark energy and the expansion of the Universe itself.

Planck involves an international collaboration of scientists and industrialists from around the World. UK scientists from the University of Cambridge, Cardiff University, Imperial College London, University of Manchester, Jodrell Bank and Rutherford Appleton Laboratory have key roles – with involvement in the planning of the mission as well as building hardware for the sensitive instruments onboard, the data analysis and the science operations after launch.

Professor George Efstathiou, a member of the Planck science team and co-investigator on the High Frequency instrument (HFI) on Planck, from the University of Cambridge said, “The accuracy of the instruments on board Planck will allow us to measure the temperature variations across the cosmic microwave background with much better sensitivity than ever before providing astronomers with an unprecedented view of our Universe when it was extremely young – just 300,000 years old.”

Planck carries a 1.5 metre diameter telescope that feeds the microwave radiation to two instruments which will image the sky at different frequencies:- the Low Frequency Instrument (LFI) consisting of an array of ultra sensitive radiometers and the High Frequency Instrument (HFI), an array of highly sensitive microwave detectors known as bolometers.

The conditions that Planck will be studying present real challenges when it comes to the technological requirements of the instruments onboard. In order to achieve its science objectives, Planck’s detectors have to operate at very low and stable temperatures. The spacecraft is equipped with a sophisticated cryogenic cooling system which cools the instruments to levels close to absolute zero (-273.15 degrees C), ranging from -253 degrees Celsius to only a tenth of a degree above absolute zero.

Dr Tom Bradshaw from CCLRC’s Rutherford Appleton Laboratory works on the cooling system developed for the High Frequency Instrument. He comments, “Planck presents real technological challenges with regard to the temperatures that the instruments need to operate at. The spacecraft has a layered cooling system, akin to a Russian doll, which keeps the instruments cooled so that their own heat does not interfere with the science measurements.”

After integration which is due to be completed by the end of February, Planck will move to Liege in Belgium to undergo a series of tests to measure the performance of the instruments at extreme temperatures. Planck is scheduled to be launched on 31st July 2008 on an Ariane 5 rocket from Kourou in French Guiana. It will be launched in a dual configuration with Herschel, ESA’s mission to study the formation of galaxies, stars and planetary systems in the infrared. Once operational both missions will study different aspects of the “cold” cosmos providing complimentary information on previously unknown regions of the Universe.

Planck will build on the heritage of previous NASA CMB missions – Cosmic Background Explorer (COBE) and Wilkinson Map Anisotropy Probe (WMAP) – the latter of which is still operating. Professor George Smoot, lead scientist for COBE, who was awarded the 2006 Nobel Prize for Physics for his work on cosmic microwave background, is a co-investigator on Planck.