OrbitalHub

Some of the most important questions asked in modern science are: how did the Universe begin, how did it evolve to its present state, and how will it continue to evolve in the future? To ask these questions, the remnant radiation that filled the Universe immediately after the Big Bang must be analyzed. This remnant radiation is known as the Cosmic Microwave Background (CMB).

Credits: ESA

ESA plans to answer these questions with Planck: the first European mission to study the birth of the Universe. The Planck Mission will collect CMB radiation measurements using highly sensitive sensors that are operating at very low temperatures. The measurements will be used to map the smallest variations of the CMB detected to date.

The Planck spacecraft will weigh around 1,900 kg at launch. It is 4.2 m high and has a maximum diameter of 4.2 m. There are two modules that comprise the spacecraft: a service module and the payload module.

The service module contains the systems for power generation, attitude control, data handling and communication, and the warm components of the scientific payload. The payload module contains the telescope, the optical bench, the detectors, and the cooling system (which is of critical importance, as we shall see).

The telescope is an important onboard component. The Planck telescope is a Gregorian telescope with an off-axis parabolic primary mirror 1.75 x 1.5 meters in size. A secondary mirror focuses the incoming microwave radiation on two sets of highly sensitive detectors: the Low Frequency Instrument (LFI) and the High Frequency Instrument (HFI). The Gregorian design offers two key advantages: it is compact and it does not block the optical path.

Credits: ESA/Thales

The LFI will be operating at –253 degrees Celsius. The array of twenty-two tuned radio receivers that comprise LFI will produce high-sensitivity, multi-frequency measurements of the microwave sky in the frequency range of 27 GHz to 77 GHz.

The HFI has to be cooled to –272.9 degrees Celsius in order to operate (one tenth of one degree above the absolute zero!). HFI’s fifty-two bolometric detectors will produce high-sensitivity, multi-frequency measurements of the diffuse sky radiation in the frequency range of 84 GHz to 1 THz.

A baffle surrounds the telescope and instruments. The baffle prevents light from the Sun and the Moon from altering the measurements. A complex system of refrigerators is used onboard the spacecraft in order to achieve the temperatures needed for nominal operation. The detectors have to work at temperatures close to the absolute zero, otherwise their own emissions can alter the measurements.

The two instruments will be used to measure the small variations of the CMB across the sky. By combining the measurements, a full sky map of unprecedented precision will be produced. The map will help astronomers decide which theories on the birth and the evolution of the Universe are correct. Questions like ‘what is the age of the Universe?’ or ‘what is the nature of the dark-matter?’ will be answered.

The mission was initially designed as COBRAS/SAMBA (Cosmic Background Radiation Anisotropy Satellite and Satellite for Measurement of Background Anisotropies) because it grew out of two mission proposals that had similar objectives. When the mission was approved in 1996, it was also renamed as Planck in honor of the German scientist Max Planck (1858 – 1947). Max Planck was awarded the Nobel Prize for Physics in 1918.

Credits: ESA

The mission is a collaborative effort. The Planck spacecraft was designed and built by a consortium led by Alcatel Alenia Space (Cannes, France). The telescope mirrors are manufactured by EADS Astrium (Friedrichshafen, Germany). The Low Frequency Instrument (LFI) was designed and built by a consortium led by the Instituto di Astrofisica Spaziale e Fisica Cosmica (IASF) in Bologna, Italy. The High Frequency Instrument (HFI) was designed and built by a consortium led by the Institut d’Astrophysique Spatiale (CNRS) in Orsay, France.

The Planck Mission has two predecessors: the Cosmic Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP).

Credits: ESA

The Planck spacecraft will be launched in early 2009 from Kourou, French Guiana. An Ariane 5 booster will place the spacecraft in a trajectory towards the L2 point. The L2 point stands for Second Lagrangian Point and it is located around 1.5 million kilometers away from Earth in a direction diametrically opposite the Sun. It will be a dual launch configuration, as the Herschel spacecraft will be launched together with Planck.

Between four to six months after the launch, Planck will reach its final position. It will take six more months before Planck will be declared operational.

Planck will perform scientific measurements for fifteen months, allowing two complete sky surveys. The spacecraft will be operational as along as there are resources for the cooling systems onboard.

For more details on the ESA’s Planck Mission you can visit the mission’s home page on the ESA website.