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{{DISPLAYTITLE:The spacecraft}}
 
{{DISPLAYTITLE:The spacecraft}}
 
==Overview==
 
==Overview==
The Planck satellite was designed, built and tested around two major modules.
+
The Planck spacecraft 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 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.
+
*'''The service module''' containing all the warm electronics servicing instruments and spacecraft, 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.
  
  
 
{| border="1" cellpadding="2"
 
{| border="1" cellpadding="2"
 
|- valign="top"
 
|- valign="top"
|+ '''Planck satellite characteristics'''
+
|+ '''Planck spacecraft characteristics'''
 
|width="30%"|'''Diameter'''
 
|width="30%"|'''Diameter'''
 
|width="20%"|4.2 m
 
|width="20%"|4.2 m
Line 33: Line 33:
 
|'''Spin rate'''
 
|'''Spin rate'''
 
|1 rpm
 
|1 rpm
|+/-0.6 arcmin/sec (changes due to manoeuvers); stability during inertial pointing <math>\sim 6.5\times 10^{-5}</math> rpm/h
+
|&plusmn;0.6 arcmin/sec (changes due to manoeuvers); stability during inertial pointing &asymp;6.5&times;10^-5 rpm/h
 
|- style="vertical-align:top;"
 
|- style="vertical-align:top;"
 
|'''Max angle of spin axis to Sun'''
 
|'''Max angle of spin axis to Sun'''
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|'''Angle between spin axis and telescope boresight'''
 
|'''Angle between spin axis and telescope boresight'''
 
|85 deg
 
|85 deg
|Max extent of FOV∼ 8 deg
+
|Max extent of FOV &asymp;8 deg
 
|- style="vertical-align:top;"
 
|- style="vertical-align:top;"
 
|'''On-board data storage capacity'''
 
|'''On-board data storage capacity'''
Line 60: Line 60:
 
|}
 
|}
  
[[File:381-Herschel_reflection_in_Primary_Reflector_H.jpg | 500px  | center | thumb | '''The fully assembled Planck satellite a few days before integration into the Ariane 5 rocket. Herschel is visible by reflection on the primary reflector.''']]
+
[[File:381-Herschel_reflection_in_Primary_Reflector_H.jpg | 500px  | center | thumb | '''Fully assembled Planck satellite a few days before integration into the Ariane 5 rocket. Herschel is visible by reflection in the primary reflector.''']]
  
 
For more information, see {{PlanckPapers|planck2011-1-1}}.
 
For more information, see {{PlanckPapers|planck2011-1-1}}.
Line 66: Line 66:
 
==The service module==
 
==The service module==
 
The service module provides the various equipment and instruments housed in it with suitable mechanical and thermal environments during launch and orbit. It is formed by an octagonal box, built around a conical tube, which supports the following subsystems intervening in flight operations:
 
The service module provides the various equipment and instruments housed in it with suitable mechanical and thermal environments during launch and orbit. It is formed by an octagonal box, built around a conical tube, which supports the following subsystems intervening in flight operations:
*Command and data management.
+
*Command and data management;
*Attitude control and measurement.
+
*Attitude control and measurement;
*Power control.
+
*Power control;
*Reaction control.
+
*Reaction control;
*Telemetry, tracking and command.
+
*Telemetry, tracking and command;
 
*Thermal control.
 
*Thermal control.
  
The service module contains all the warm satellite and payload electronic units, with the only exception of the box containing JFETs for impedance-matching to the HFI bolometers, which is mounted on the primary reflector support panel, to allow the operation of the JFETs at an optimal temperature of ∼130 K. The service module holds:
+
The service module contains all the warm satellite and payload electronic units, with the only exception of the box containing JFETs for impedance-matching to the HFI bolometers, which is mounted on the primary reflector support panel, to allow the operation of the JFETs at an optimal temperature of around 130 K. The service module holds:
*Main computer
+
*Main computer;
*Attitude control computer
+
*Attitude control computer;
*Data processing units
+
*Data processing units;
*Star trackers
+
*Star trackers;
*LFI electronics
+
*LFI electronics;
*Dilution control unit
+
*Dilution control unit;
*HFI readout electronics
+
*HFI readout electronics;
*4K compressors
+
*4K compressors;
*Helium tanks: 36000 litres of <math>^{4}</math>He, and 12000 litres of <math>^{3}</math>He gas are stored in four high-pressure tanks.
+
*Helium tanks, 36000 litres of <sup>4</sup>He, and 12000 litres of <sup>3</sup>He gas stored in four high-pressure tanks;
*Sorption cooler radiator
+
*Sorption cooler radiator;
*Sorption cooler electronics
+
*Sorption cooler electronics;
*Sorption compressors (2 redundant units)
+
*Sorption compressors (two redundant units);
*Hydrazine tanks
+
*Hydrazine tanks;
*Medium-gain antenna
+
*Medium-gain antenna;
 
*Telemetry subsystem.
 
*Telemetry subsystem.
  
[[File:SVM.png | 500px  | center | thumb | '''The Planck service module. Figure courtesy of Thales Alenia Space (France).''']]
+
[[File:SVM.png | 500px  | center | thumb | '''Planck service module. Figure courtesy of Thales Alenia Space (France).''']]
  
 
For more information, see {{PlanckPapers|tauber2010a}}.
 
For more information, see {{PlanckPapers|tauber2010a}}.
  
 
==Thermal design==
 
==Thermal design==
The performance of the Planck instruments in space is enabled by their low operating temperatures, 20 K for LFI and 0.1 K for HFI, achieved through a combination of passive radiative cooling and three active  coolers. The scientific requirement for very broad frequency coverage led to two detector technologies with widely different temperature and cooling needs. Active coolers could satisfy these needs; a helium cryostat, as used by previous cryogenic space missions (IRAS, COBE, ISO, Spitzer, AKARI), could not. Radiative cooling is provided by three V-groove radiators and a large telescope baffle. The active coolers are a [[LFI_design,_qualification,_and_performance#The Sorption Cooler|hydrogen sorption cooler]] (<20 K), a <math>^{4}</math>He [[HFI cryogenics#The 4K J-T cooler|Joule-Thomson cooler]], also known as 4K cooler, (4.7 K), and a <math>^{3}</math>He-<math>^{4}</math>He [[HFI cryogenics#The dilution cooler|dilution cooler]] (1.4 K and 0.1 K). The flight system was at ambient temperature at launch and cooled in space to operating conditions. The HFI bolometer plate reached 93 mK on 3 July 2009, 50 days after launch. The solar panel always faces the Sun, shadowing the rest of Planck, and operates at a mean temperature of 384 K. At the other end of the spacecraft, the telescope baffle operates at 42.3 K and the telescope primary mirror operates at 35.9 K. The temperatures of key parts of the instruments are stabilized by both active and passive methods. Temperature fluctuations are driven by changes in the distance from the Sun, sorption cooler cycling and fluctuations in gas-liquid flow, and fluctuations in cosmic ray flux on the dilution and bolometer plates. These fluctuations do not compromise the science data.
+
The performance of the Planck instruments in space is enabled by their low operating temperatures, 20 K for LFI and 0.1 K for HFI, achieved through a combination of passive radiative cooling and three active  coolers. The scientific requirement for very broad frequency coverage led to two detector technologies with widely different temperature and cooling needs. Active coolers could satisfy these needs; a helium cryostat, as used by previous cryogenic space missions (IRAS, COBE, ISO, Spitzer, Akari), could not. Radiative cooling for Planck was provided by three V-groove radiators and a large telescope baffle. The active coolers were a [[LFI_design,_qualification,_and_performance#The Sorption Cooler|hydrogen sorption cooler]] (<20 K), a <math>^{4}</math>He [[HFI cryogenics#The 4K J-T cooler|Joule-Thomson cooler]], also known as the 4K cooler (actually 4.7 K), and a <math>^{3}</math>He-<math>^{4}</math>He [[HFI cryogenics#The dilution cooler|dilution cooler]] (1.4 K and 0.1 K). The flight system was at ambient temperature at launch and cooled in space to operating conditions. The HFI bolometer plate reached 93 mK on 3 July 2009, 50 days after launch. The solar panel always faced the Sun, shadowing the rest of Planck, and operated at a mean temperature of 384 K. At the other end of the spacecraft, the telescope baffle operated at 42.3 K and the telescope primary mirror operated at 35.9 K. The temperatures of key parts of the instruments were stabilized by both active and passive methods. Temperature fluctuations were driven by changes in the distance from the Sun, sorption cooler cycling and fluctuations in gas-liquid flow, and fluctuations in cosmic ray flux on the dilution and bolometer plates. These fluctuations did not compromise the science data.
  
The contrast between the high power dissipation in the warm service module (<math>\sim</math> 1000 W at 300 K) and that at the coldest spot in the satellite (<math>\sim</math>100 nW at 0.1 K) are testimony to the extraordinary efficiency of the complex thermal system which has to achieve such disparate ends simultaneously while preserving a very high level of stability at the cold end. More details on the thermal design of the Planck satellite can be found in {{PlanckPapers|planck2011-1-3}}.
+
The contrast between the high power dissipation in the warm service module (<math>\sim</math> 1000 W at 300 K) and that at the coldest spot in the satellite (<math>\sim</math>100 nW at 0.1 K) are testimony to the extraordinary efficiency of the complex thermal system which had to achieve such disparate goals simultaneously, while preserving a very high level of stability at the cold end. More details on the thermal design of the Planck satellite can be found in {{PlanckPapers|planck2011-1-3}}.
  
 
==The Standard Radiation Environment Monitor==
 
==The Standard Radiation Environment Monitor==
Line 103: Line 103:
 
a particle detector developed for satellite applications. It
 
a particle detector developed for satellite applications. It
 
measures high-energy electrons and protons of the space environment
 
measures high-energy electrons and protons of the space environment
with a <math>\pm</math>20<math>^\circ</math> angular resolution, spectral information
+
with <math>\pm</math>20<math>^\circ</math> angular resolution, as well as spectral information,
and provides the host spacecraft with radiation information.
+
and provides the host spacecraft with radiation data.
 
SREM was developed and manufactured by Contraves Space in
 
SREM was developed and manufactured by Contraves Space in
 
cooperation with the Paul Scherrer Institute under a development
 
cooperation with the Paul Scherrer Institute under a development
 
contract of the European Space Agency.
 
contract of the European Space Agency.
SREM is the second generation of instruments in a programme,
+
SREM is the second generation of instruments in a programme
which was established by ESA’s European Research
+
that was established by ESA’s European Research
 
and Technology Centre (ESTEC) to:
 
and Technology Centre (ESTEC) to:
#Provide minimum intrusive radiation detectors for space applications;
+
#provide minimum intrusive radiation detectors for space applications;
#Provide radiation hazard alarm function to instruments on board spacecraft;
+
#provide radiation hazard alarm function to instruments on board spacecraft;
#Assist in investigation activities related to possible radiation related anomalies observed on spacecraft;
+
#assist in investigation activities related to possible radiation-related anomalies observed on spacecraft;
#Assist in in-flight Technology Demonstration Activities.
+
#assist in in-flight Technology Demonstration Activities.
The design goals are low weight, small dimensions, low
+
The design goals are low weight, small dimensions, and low
 
power consumption, combined with the ability to provide particle
 
power consumption, combined with the ability to provide particle
 
species and spectral information.  
 
species and spectral information.  
  
In the case of Planck, the use of the SREM was entirely within the scope of bullets 1 and 3 above as due to the nature of operations no real time alarms where possible
+
In the case of Planck, the use of the SREM was entirely within the scope of bullets 1 and 3 above, since, due to the nature of operations, no real time alarms were possible
  
 
The SREM consists of three detectors (D1, D2, and D3) in
 
The SREM consists of three detectors (D1, D2, and D3) in
two detector heads configurations. One system is a single silicon
+
two detector head configurations. One system is a single silicon
 
diode detector (D3). The main entrance window is covered
 
diode detector (D3). The main entrance window is covered
 
with 0.7 mm aluminum, which defines the lower energy
 
with 0.7 mm aluminum, which defines the lower energy
threshold for electrons to <math>\sim</math> 0.5 MeV and for protons to
+
threshold for electrons to about 0.5 MeV and for protons to
<math>\sim</math> 10MeV. The other system uses two silicon diodes (detectors
+
about 10MeV. The other system uses two silicon diodes (detectors
 
D1/D2) arranged in a telescope configuration. The main entrance
 
D1/D2) arranged in a telescope configuration. The main entrance
of this detector is covered with 2 mm aluminum giving a
+
of this detector is covered with 2 mm of aluminium giving a
proton and electron threshold of 20 and 1.5 MeV, respectively.A
+
proton and electron threshold of 20 and 1.5 MeV, respectively. A
1.7-mm-thick aluminum and 0.7–mm-thick tantalum layer separate
+
1.7-mm-thick aluminium and 0.7–mm-thick tantalum layer separate
 
the two diodes of the telescope configuration.  
 
the two diodes of the telescope configuration.  
  
Line 137: Line 137:
 
the shielding between the two diodes in the telescope prevents
 
the shielding between the two diodes in the telescope prevents
 
the passage of electrons. However, protons with energies greater
 
the passage of electrons. However, protons with energies greater
than <math>\sim</math> 30 MeV go through. Thus, using the two diodes in coincidence
+
than about 30 MeV go through. Thus, using the two diodes in coincidence
gives pure proton count rates allowing subtraction of the
+
gives pure proton count rates, allowing subtraction of the
 
proton contribution from the electron channels. A total of 15 discriminator
 
proton contribution from the electron channels. A total of 15 discriminator
 
levels (see table below) are available to bin the energy of the detected
 
levels (see table below) are available to bin the energy of the detected
Line 149: Line 149:
 
!scope="col"| Logic
 
!scope="col"| Logic
 
!scope="col"| Particle
 
!scope="col"| Particle
!scope="col"| Energy (<math>M\!e\!v</math>)
+
!scope="col"| Energy [MeV]
 
|-
 
|-
 
|width="50" | TC1
 
|width="50" | TC1
Line 242: Line 242:
 
|}
 
|}
  
The detector electronics is capable
+
The detector electronics are capable
 
of processing a detection rate of 100 kHz with dead-time
 
of processing a detection rate of 100 kHz with dead-time
 
correction below 20%.
 
correction below 20%.
The SREM is contained in a single box of 20<math>\times</math>12<math>\times</math>10
+
The SREM is contained in a single box of size 20cm &times; 12cm &times; 10cm
 
and weighs 2.6 kg. The box contains the detector
 
and weighs 2.6 kg. The box contains the detector
systems with the analog and digital front-end electronics, a
+
systems with the analogue and digital front-end electronics, a
 
power supply, and a TTC-B-01 telemetry and Telecommand
 
power supply, and a TTC-B-01 telemetry and Telecommand
 
interface protocol. By virtue of a modular buildup, the interface
 
interface protocol. By virtue of a modular buildup, the interface
Line 255: Line 255:
 
rates, in terms of particle fluxes, are the energy dependent
 
rates, in terms of particle fluxes, are the energy dependent
  
The SREM data are provided in the [[PLA quick start guide | Planck Legacy Archive]] in the form of individual FITS files per calendar day. The SREM data is described [[SREM | here]].
+
The SREM data are provided in the [[PLA quick start guide | Planck Legacy Archive]] in the form of individual FITS files per calendar day. The SREM data are described [[SREM | here]].
  
==The Fiber Optic Gyro unit==
+
==The Fibre-optic gyro unit==
The Fiber-Optic Gyro unit (FOG) is an extra payload on-board Planck which is not used as part of the attitude control system. The FOG functioning is based on the physical phenomenon called ''Sagnac effect''::
+
The fibre-optic gyro unit (FOG) is an extra payload on-board Planck, which is not used as part of the attitude control system. The FOG functioning is based on the physical phenomenon called the ''Sagnac effect''::
  
 
"''a solid-state optical interferometer enclosing a surface located on a rotating support will detect a phase difference of the optical signal, which is proportional to the angular rate and to the surface enclosed by the optical path''".
 
"''a solid-state optical interferometer enclosing a surface located on a rotating support will detect a phase difference of the optical signal, which is proportional to the angular rate and to the surface enclosed by the optical path''".
  
The FOG features the following architecture:
+
The FOG features the following architecture.
  
*An optical path enclosing a maximal surface: this is realized through the 1 km long fibre optic, winded many time round, in order to make a reasonable sized interferometer (< 120 mm in diameter).
+
*An optical path enclosing a maximal surface: this is realized through the 1 km long fibre optic, wound many times round, in order to make a reasonable sized interferometer (< 120 mm in diameter).
 
*A source, to deliver the light to the interferometer.
 
*A source, to deliver the light to the interferometer.
*A multifunction Integrated Optical Circuit, which closes the interferometer, to share the light between the two extremities of the fiber optic coil, to filter undesirable polarization.
+
*A multifunction Integrated Optical Circuit, which closes the interferometer, to share the light between the two extremities of the fibre-optic coil, to filter undesirable polarization.
 
*A coupler to extract the optical signal coming back from the ring interferometer, which is the signal carrying the Sagnac inertial information, and to direct it towards an optical detector.
 
*A coupler to extract the optical signal coming back from the ring interferometer, which is the signal carrying the Sagnac inertial information, and to direct it towards an optical detector.
 
*A detection module to convert this light signal into an electrical signal.
 
*A detection module to convert this light signal into an electrical signal.
*A closed-loop signal processing to increase the dynamic range and remove the effect of fluctuations of the optical power and of the gain of the detection chain, allowing an easy auto-calibration of the system and excellent scale factor stability and linearity.
+
*A closed-loop signal processing system to increase the dynamic range and remove the effect of fluctuations of the optical power and of the gain of the detection chain, allowing an easy auto-calibration of the system and excellent scale factor stability and linearity.
 
*A biasing modulation allowing the measurement of very low rotation rates as well as the sign of those rotations.
 
*A biasing modulation allowing the measurement of very low rotation rates as well as the sign of those rotations.
  
Redundancy is offered by providing four skewed gyro channels, allowing the Attitude Control and Measurement Subsystem to use any triplet among the four axes to determine the spacecraft three axes rates. Nominally the four channels are activated, in case of failure or thermal criticalities a subset of channels could be used.
+
Redundancy is offered by providing four skewed gyro channels, allowing the Attitude Control and Measurement Subsystem to use any triplet among the four axes to determine the spacecraft three axis rates. Nominally the four channels are activated, but in case of failure or critical thermal situations a subset of channels could be used.
 +
 
 +
There is no dangerous FOG flight command. The FOG is designed to operate five years ON in orbit, withstanding 1000 ON/OFF cycles, and its performance is guaranteed under rotations of <math>\pm10</math> deg/second, and over the temperature range of 253 K to 333 K. Power dissipation levels are in the range of 5.5 to 6.7 W/channel.
  
There is no dangerous FOG flight command. The FOG is designed to operate five years ON in orbit, withstanding 1000 ON/OFF cycles, and its performance is guaranteed under rotations of <math>\pm10</math> deg/second, and at the temperature range of 253 K up to 333 K. Power dissipations are in the range of 5.5 up to 6.7 W/channel.
 
 
==The telescope==
 
==The telescope==
The telescope is an off-axis aplanatic design with two elliptical reflectors and a 1.5 m projected diameter and an overall emissivity <math>\lesssim 1\%</math>. The optical system was optimized for a set of representative detectors (eight HFI and eight LFI). The performance of the aplanatic configuration is not quite as good on the optical axis as the so-called Dragone-Mizuguchi Gregorian configuration, which eliminates astigmatism on the optical axis, but is significantly better over the large focal surface required by the many HFI and LFI feeds.
+
The telescope is an off-axis aplanatic design with two elliptical reflectors, a 1.5-m projected diameter, and an overall emissivity below about 1\%. The optical system was optimized for a set of representative detectors (eight HFI and eight LFI). The performance of the aplanatic configuration is not quite as good on the optical axis as the so-called Dragone-Mizuguchi Gregorian configuration (which eliminates astigmatism on the optical axis), but is significantly better over the large focal surface required by the many HFI and LFI feeds.
  
 
The Planck telescope consists of:
 
The Planck telescope consists of:
  
1. '''The primary and secondary reflectors''' (PR and SR), designed and manufactured by Astrium (Friedrichshafen, Germany);
+
1. '''the primary and secondary reflectors''' (PR and SR), designed and manufactured by Astrium (Friedrichshafen, Germany);
  
2. '''The support structure''', designed and manufactured by Oerlikon Space (Zurich, Switzerland).
+
2. '''the support structure''', designed and manufactured by Oerlikon Space (Zurich, Switzerland).
  
 
[[File:FocalPlane.png | 500px  | center | thumb | '''The footprint of the focal plane as seen by an observer at infinity.''']]
 
[[File:FocalPlane.png | 500px  | center | thumb | '''The footprint of the focal plane as seen by an observer at infinity.''']]
Line 289: Line 290:
  
 
==The instruments==
 
==The instruments==
A complete technical description of the teo Planck instruments can be found here: [[HFI design, qualification, and performance|HFI]], [[LFI_overview|LFI]].
+
A complete technical description of the two Planck instruments can be found here: [[HFI design, qualification, and performance|HFI]], [[LFI_overview|LFI]].
  
 
==References==
 
==References==

Latest revision as of 09:37, 3 February 2015

Overview[edit]

The Planck spacecraft 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 spacecraft, 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.


Planck spacecraft 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 continued surveying the sky for an additional 20 months
Spin rate 1 rpm ±0.6 arcmin/sec (changes due to manoeuvers); stability during inertial pointing ≈6.5×10^-5 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 with 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 Between 2 and 4 hours (as required by operational needs) Effective real-time science data acquisition bandwidth 130 kbps
Fully assembled Planck satellite a few days before integration into the Ariane 5 rocket. Herschel is visible by reflection in the primary reflector.

For more information, see Planck-Early-I[1].

The service module[edit]

The service module provides the various equipment and instruments housed in it with suitable mechanical and thermal environments during launch and orbit. It is formed by an octagonal box, built around a conical tube, which supports the following subsystems intervening in flight operations:

  • Command and data management;
  • Attitude control and measurement;
  • Power control;
  • Reaction control;
  • Telemetry, tracking and command;
  • Thermal control.

The service module contains all the warm satellite and payload electronic units, with the only exception of the box containing JFETs for impedance-matching to the HFI bolometers, which is mounted on the primary reflector support panel, to allow the operation of the JFETs at an optimal temperature of around 130 K. The service module holds:

  • Main computer;
  • Attitude control computer;
  • Data processing units;
  • Star trackers;
  • LFI electronics;
  • Dilution control unit;
  • HFI readout electronics;
  • 4K compressors;
  • Helium tanks, 36000 litres of 4He, and 12000 litres of 3He gas stored in four high-pressure tanks;
  • Sorption cooler radiator;
  • Sorption cooler electronics;
  • Sorption compressors (two redundant units);
  • Hydrazine tanks;
  • Medium-gain antenna;
  • Telemetry subsystem.
Planck service module. Figure courtesy of Thales Alenia Space (France).

For more information, see Planck-PreLaunch-XI[2].

Thermal design[edit]

The performance of the Planck instruments in space is enabled by their low operating temperatures, 20 K for LFI and 0.1 K for HFI, achieved through a combination of passive radiative cooling and three active coolers. The scientific requirement for very broad frequency coverage led to two detector technologies with widely different temperature and cooling needs. Active coolers could satisfy these needs; a helium cryostat, as used by previous cryogenic space missions (IRAS, COBE, ISO, Spitzer, Akari), could not. Radiative cooling for Planck was provided by three V-groove radiators and a large telescope baffle. The active coolers were a hydrogen sorption cooler (<20 K), a [math]^{4}[/math]He Joule-Thomson cooler, also known as the 4K cooler (actually 4.7 K), and a [math]^{3}[/math]He-[math]^{4}[/math]He dilution cooler (1.4 K and 0.1 K). The flight system was at ambient temperature at launch and cooled in space to operating conditions. The HFI bolometer plate reached 93 mK on 3 July 2009, 50 days after launch. The solar panel always faced the Sun, shadowing the rest of Planck, and operated at a mean temperature of 384 K. At the other end of the spacecraft, the telescope baffle operated at 42.3 K and the telescope primary mirror operated at 35.9 K. The temperatures of key parts of the instruments were stabilized by both active and passive methods. Temperature fluctuations were driven by changes in the distance from the Sun, sorption cooler cycling and fluctuations in gas-liquid flow, and fluctuations in cosmic ray flux on the dilution and bolometer plates. These fluctuations did not compromise the science data.

The contrast between the high power dissipation in the warm service module ([math]\sim[/math] 1000 W at 300 K) and that at the coldest spot in the satellite ([math]\sim[/math]100 nW at 0.1 K) are testimony to the extraordinary efficiency of the complex thermal system which had to achieve such disparate goals simultaneously, while preserving a very high level of stability at the cold end. More details on the thermal design of the Planck satellite can be found in Planck-Early-II[3].

The Standard Radiation Environment Monitor[edit]

The standard radiation environment monitor (SREM)[4] is a particle detector developed for satellite applications. It measures high-energy electrons and protons of the space environment with [math]\pm[/math]20[math]^\circ[/math] angular resolution, as well as spectral information, and provides the host spacecraft with radiation data. SREM was developed and manufactured by Contraves Space in cooperation with the Paul Scherrer Institute under a development contract of the European Space Agency. SREM is the second generation of instruments in a programme that was established by ESA’s European Research and Technology Centre (ESTEC) to:

  1. provide minimum intrusive radiation detectors for space applications;
  2. provide radiation hazard alarm function to instruments on board spacecraft;
  3. assist in investigation activities related to possible radiation-related anomalies observed on spacecraft;
  4. assist in in-flight Technology Demonstration Activities.

The design goals are low weight, small dimensions, and low power consumption, combined with the ability to provide particle species and spectral information.

In the case of Planck, the use of the SREM was entirely within the scope of bullets 1 and 3 above, since, due to the nature of operations, no real time alarms were possible

The SREM consists of three detectors (D1, D2, and D3) in two detector head configurations. One system is a single silicon diode detector (D3). The main entrance window is covered with 0.7 mm aluminum, which defines the lower energy threshold for electrons to about 0.5 MeV and for protons to about 10MeV. The other system uses two silicon diodes (detectors D1/D2) arranged in a telescope configuration. The main entrance of this detector is covered with 2 mm of aluminium giving a proton and electron threshold of 20 and 1.5 MeV, respectively. A 1.7-mm-thick aluminium and 0.7–mm-thick tantalum layer separate the two diodes of the telescope configuration.

The telescope detector allows measurement of the high-energy proton fluxes with enhanced energy resolution. In addition, the shielding between the two diodes in the telescope prevents the passage of electrons. However, protons with energies greater than about 30 MeV go through. Thus, using the two diodes in coincidence gives pure proton count rates, allowing subtraction of the proton contribution from the electron channels. A total of 15 discriminator levels (see table below) are available to bin the energy of the detected

events.

SREM counters
Name Logic Particle Energy [MeV]
TC1 D1 protons >20
S12 D1 protons 20 - 550
S13 D1 protons 20 - 120
S14 D1 protons 20 - 27
S15 D1 protons 20 - 34
TC2 D2 protons >39
S25 D2 ions 150 - 185
C1 D1[math]*[/math]D2 coinc. protons 40 - 50
C2 D1[math]*[/math]D2 coinc. protons 50 - 70
C3 D1[math]*[/math]D2 coinc. protons 70 - 120
C4 D1[math]*[/math]D2 coinc. protons >130
TC3 D3 electrons >0.5
S32 D3 electrons 0.55 - 2.3
S33 D3 protons 11 - 90
S34 D3 protons 11 - 30
PL1 D1 Dead Time NA
PL2 D2 Dead Time NA
PL3 D3 Dead Time NA

The detector electronics are capable of processing a detection rate of 100 kHz with dead-time correction below 20%. The SREM is contained in a single box of size 20cm × 12cm × 10cm and weighs 2.6 kg. The box contains the detector systems with the analogue and digital front-end electronics, a power supply, and a TTC-B-01 telemetry and Telecommand interface protocol. By virtue of a modular buildup, the interface can be adapted to any spacecraft system. The power consumption is approximately 2.5 W. An essential input for the interpretation of the detection rates, in terms of particle fluxes, are the energy dependent

The SREM data are provided in the Planck Legacy Archive in the form of individual FITS files per calendar day. The SREM data are described here.

The Fibre-optic gyro unit[edit]

The fibre-optic gyro unit (FOG) is an extra payload on-board Planck, which is not used as part of the attitude control system. The FOG functioning is based on the physical phenomenon called the Sagnac effect::

"a solid-state optical interferometer enclosing a surface located on a rotating support will detect a phase difference of the optical signal, which is proportional to the angular rate and to the surface enclosed by the optical path".

The FOG features the following architecture.

  • An optical path enclosing a maximal surface: this is realized through the 1 km long fibre optic, wound many times round, in order to make a reasonable sized interferometer (< 120 mm in diameter).
  • A source, to deliver the light to the interferometer.
  • A multifunction Integrated Optical Circuit, which closes the interferometer, to share the light between the two extremities of the fibre-optic coil, to filter undesirable polarization.
  • A coupler to extract the optical signal coming back from the ring interferometer, which is the signal carrying the Sagnac inertial information, and to direct it towards an optical detector.
  • A detection module to convert this light signal into an electrical signal.
  • A closed-loop signal processing system to increase the dynamic range and remove the effect of fluctuations of the optical power and of the gain of the detection chain, allowing an easy auto-calibration of the system and excellent scale factor stability and linearity.
  • A biasing modulation allowing the measurement of very low rotation rates as well as the sign of those rotations.

Redundancy is offered by providing four skewed gyro channels, allowing the Attitude Control and Measurement Subsystem to use any triplet among the four axes to determine the spacecraft three axis rates. Nominally the four channels are activated, but in case of failure or critical thermal situations a subset of channels could be used.

There is no dangerous FOG flight command. The FOG is designed to operate five years ON in orbit, withstanding 1000 ON/OFF cycles, and its performance is guaranteed under rotations of [math]\pm10[/math] deg/second, and over the temperature range of 253 K to 333 K. Power dissipation levels are in the range of 5.5 to 6.7 W/channel.

The telescope[edit]

The telescope is an off-axis aplanatic design with two elliptical reflectors, a 1.5-m projected diameter, and an overall emissivity below about 1\%. The optical system was optimized for a set of representative detectors (eight HFI and eight LFI). The performance of the aplanatic configuration is not quite as good on the optical axis as the so-called Dragone-Mizuguchi Gregorian configuration (which eliminates astigmatism on the optical axis), but is significantly better over the large focal surface required by the many HFI and LFI feeds.

The Planck telescope consists of:

1. the primary and secondary reflectors (PR and SR), designed and manufactured by Astrium (Friedrichshafen, Germany);

2. the support structure, designed and manufactured by Oerlikon Space (Zurich, Switzerland).

The footprint of the focal plane as seen by an observer at infinity.

For more information, see Planck-PreLaunch-XII[5].

The instruments[edit]

A complete technical description of the two Planck instruments can be found here: HFI, LFI.

References[edit]

  1. Planck early results. I. The Planck mission, Planck Collaboration I, A&A, 536, A1, (2011).
  2. Planck pre-launch status: The Planck mission, J. A. Tauber, N. Mandolesi, J.-L. Puget, T. Banos, M. Bersanelli, F. R. Bouchet, R. C. Butler, J. Charra, G. Crone, J. Dodsworth, et al., A&A, 520, A1+, (2010).
  3. Planck early results. II. The thermal performance of Planck, Planck Collaboration II, A&A, 536, A2, (2011).
  4. The ESA Standard Radiation Environment Monitor program first results from PROBA-I and INTEGRAL, A. Mohammadzadeh, H. Evans, P. Nieminen, E. Daly, P. Vuilleumier, P. Buhler, C. Eggel, W. Hajdas, N. Schlumpf, A. Zehnder, J. Schneider, R. Fear, Nuclear Science, IEEE Transactions on, 50, 2272-2277, (Dec.).
  5. Planck pre-launch status: The optical system, J. A. Tauber, H. U. Nørgaard-Nielsen, P. A. R. Ade, J. Amiri Parian, T. Banos, M. Bersanelli, C. Burigana, A. Chamballu, D. de Chambure, P. R. Christensen, O. Corre, A. Cozzani, B. Crill, G. Crone, O. D'Arcangelo, R. Daddato, D. Doyle, D. Dubruel, G. Forma, R. Hills, K. Huffenberger, A. H. Jaffe, N. Jessen, P. Kletzkine, J. M. Lamarre, J. P. Leahy, Y. Longval, P. de Maagt, B. Maffei, N. Mandolesi, J. Martí-Canales, A. Martín-Polegre, P. Martin, L. Mendes, J. A. Murphy, P. Nielsen, F. Noviello, M. Paquay, T. Peacocke, N. Ponthieu, K. Pontoppidan, I. Ristorcelli, J.-B. Riti, L. Rolo, C. Rosset, M. Sandri, G. Savini, R. Sudiwala, M. Tristram, L. Valenziano, M. van der Vorst, K. van't Klooster, F. Villa, V. Yurchenko, A&A, 520, A2+, (2010).

(Planck) Low Frequency Instrument

(Planck) High Frequency Instrument

revolutions per minute

Field-Of-View

Space Radiation Environment Monitor

European Space Agency

European Space TEchnology and Research Centre

Flexible Image Transfer Specification

Fiber Optic Gyroscope