The Spacecraft

The Planck spacecraft is 4.2 metres high and has a maximum diameter of 4.2 metres, with a launch mass of around 1.9 tonnes. The spacecraft comprises a service module, which houses systems for power generation and conditioning, attitude control, data handling and communications, together with the warm parts of the scientific instruments, and a payload module. The payload module consists of the telescope, the optical bench, with the parts of the instruments that need to be cooled - the sensitive detector units - and the cooling systems.

The Telescope and Instruments

The Planck telescope is an off-axis tilted Gregorian design with a primary mirror measuring 1.9 × 1.5 m and with a projected aperture of 1.5 m diameter. The 1.1 × 1.0 m secondary mirror focuses the collected light onto the two scientific instruments:

• LFI (Low Frequency Instrument), an array of radio receivers using high electron mobility transistor mixers
• HFI (High Frequency Instrument), an array of microwave detectors using spider bolometers equipped with neutron transmutation doped germanium thermistors

Planck Capabilities

Planck will provide a map of the Cosmic Microwave Background (CMB) field at all angular resolutions greater than 10 arcminutes and with a temperature resolution of the order of one part in 10⁶. The simultaneous mapping of the sky at a wide range of frequencies will enable the separation of the Galactic and extragalactic foreground radiation from the primordial cosmological background signal.

The Questions Planck Will Answer

The questions that Planck will seek answers to include:

• What are the (more precise) values of fundamental cosmological parameters such as the Hubble constant?
• Can it be shown conclusively that the early Universe passed through an inflationary phase?
• What is the nature of the dark matter that dominates the present Universe?

Joint Launch

Planck has been carried into space by an Ariane 5 ECA launcher on 14 May 2009 and within two months after the launch will reach its orbit around L2. For reasons of cost effectiveness, ESA decided to launch Planck together with Herschel, an infrared space telescope. The two spacecraft separated soon after launch and now operate independently.

L2 Orbit

Planck's operational orbit is located 1.5 million kilometres away from the Earth in a direction diametrically opposite the Sun, at the second Lagrange point of the Sun-Earth system (L2). The spacecraft will be operated in a Lissajous orbit around the L2 point with an average amplitude of about 400 000 km.

Mission Lifetime

Planck has a nominal operational lifetime of fifteen months from the end of the Calibration and Performance Verification Phase.

Planck's Predecessors

The Cosmic Background Explorer (COBE) was launched on 18 November 1989. COBE determined that the CMB exhibits anisotropies at a level of one part in 10⁵ and showed that the CMB spectrum matched that of a black body with a temperature of 2.725 K ± 2 mK.

The Wilkinson Microwave Anisotropy Probe (WMAP) was launched on 30 June 2001 and has made measurements of the CMB enabling the creation of a map of the anisotropies with much higher spatial and temperature resolution and improved accuracy compared to the COBE results.