The satellite

The Planck satellite was designed, built and tested around two major modules:

• The payload module containing an off-axis telescope with a projected diameter of 1.5m, focussing radiation from the sky onto a focal plane shared by detectors of the LFI and HFI, operating at 20K and 0.1K respectively; a telescope baffle that simultaneously provides stray-light shielding and radiative cooling; and three conical “V-groove” baffles that provide thermal and radiative insulation between the warm service module and the cold telescope and instruments.

• The service module containing all the warm electronics servicing instruments and satellite; and the solar panel providing electrical power. It also contains the cryocoolers, the main on-board computer, the telecommand receivers and telemetry transmitters, and the attitude control system with its sensors and actuators. The most relevant technical characteristics of the Planck spacecraft are detailed in the Table bellow.

Table. Planck satellite characteristics.

Diameter	4.2 m	Defined by the solar array
Height	4.2 m
Total mass at launch	1912 kg	Fuel mass = 385 kg at launch; He mass = 7.7 kg
Electrical power demand (avg)	1300 W	Instrument part: 685 W (Begining of Life), 780 W (End of Life)
Minimum operational lifetime	18 months	Planck operated for 32 months with both instruments; the LFI continues surveying the sky
Spin rate	1 rpm	$\pm 0.6$ arcmin/sec (changes due to manoeuvers); stability during inertial pointing [math]\sim 6.5\times 10^{-5}[/math] rpm/h
Max angle of spin axis to Sun	10 deg	To maintain the payload in the shade; default angle is 7.5 deg
Max angle of spin axis to Earth	15 deg	To allow communication to Earth
Angle between spin axis and telescope boresight	85 deg	Max extent of FOV∼ 8 deg
On-board data storage capacity	32 Gbit	Two redundant units (only one is operational at any time)
Data transmission rate to ground (max)	1.5 Mbps	Within 15 deg of Earth, using a 35 m ground antenna
Daily contact period	3 h	The effective real-time science data acquisition bandwidth is 130 kbps

The fully assembled Planck satellite a few days before integration into the Ariane 5 rocket. Herschel is visible by reflection on the primary reflector.

For more information, see Tauber et al. 2010, A&A 520, A1.

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