The radiation is then directed to the focal planes of the two instruments (LFI Low Frequency Instrument and the HFI High Frequency Instrument). LFI is designed to convert the lower energy microwaves into electrical voltages, rather like a transistor radio. HFI works by converting the higher energy microwaves to heat, which is then measured by a tiny electrical thermometer.


 
This artist's impression shows the focal plane unit of the Planck telescope.

Planck's instruments will operate at a few degrees above absolute zero. To achieve this, a series of cooling stages are required. Without any additional cooling, the spacecraft itself can passively cool to around 50 K (about -223ºC).

For the Low Frequency Instrument (LFI) the focal plane is cooled to around 20 K (about -253ºC). The signals received in the instrument horns are amplified and passed through waveguides to a back-end unit (which is at around 300 K, or about 27ºC) where the signals are processed.

The High Frequency Instrument (HFI) unit is more compact and sits entirely within the LFI housing at about 18 K (about -255ºC). The bolometers (devices for measuring incident electromagnetic radiation) are then stage cooled to just 0.1 K (-273.14ºC) with the detected signals again processed in a warmer back-end readout and data processing unit.

Isolating the various components and cooling only small volumes to the coldest temperatures the optimum efficiencies and mission achieve lifetime.


 
This artist's impression shows Planck in its cruise phase, to its operational orbit around the second Earth-Sun Lagrange point (L2), 1.5 million km away from Earth.


 
Artist's impression of the Planck spacecraft


 
This artist's impression shows the focal plane of the two instruments on board ESA's Planck spacecraft. The instruments detect the collected radiation differently.

The Low Frequency Instrument (LFI) is designed to convert the lower energy microwaves into electrical voltages, rather like a transistor radio. The High Frequency Instrument (HFI) works by converting the higher energy microwaves to heat, which is then measured by a tiny electrical thermometer. The instruments share a common telescope.

Mission
 

 
Planck's routine observations are planned to last 15 months, allowing two complete surveys of the sky.

What's special?
 

 
The Cosmic Microwave Background is visible in all directions with (almost) the same intensity. This was confirmed by the COBE satellite, which measured (almost) the same temperature of 2.7 Kelvin everywhere on the sky.

However, the very existence of other galaxies points to the fact that there should be very small changes in the measured 'temperature' of the CMB. These changes, or fluctuations, would have provided the seeds for the formation of the galaxies that we see today.

Planck will be able to measure these tiny fluctuations, up to 5 millionths of a degree.

Spacecraft
 

 
Planck satellite on display at Thales Alenia Space in Cannes, France, on 1 February 2007. Thales Alenia Space is the Prime Contractor for building the satellite.



Last update: 19 August 2009