Difference between revisions of "The Planck mission WiP"

From Planck Legacy Archive Wiki
Jump to: navigation, search
(→‎Introduction)
m
 
(50 intermediate revisions by 3 users not shown)
Line 1: Line 1:
−
{{DISPLAYTITLE:The Planck mission}}
+
{{DISPLAYTITLE:Introduction}}
  
−
== Introduction ==
 
  
−
Planck is a satellite of the European Space Agency designed to answer key cosmological questions.
+
== The Planck mission ==
−
Its main goal is to determine the geometry and content of the Universe, and to distinguish between specific theories describing the birth and evolution of the Universe. To achieve this ambitious objective, it observed the [http://pdg.lbl.gov/2013/reviews/rpp2013-rev-cosmic-microwave-background.pdf  cosmic microwave background radiation]  (CMB), emitted about 14 billion years ago, around 380,000 years after the Big Bang. The CMB permeates the Universe and is observed to have a blackbody spectrum with a temperature of about 2.7 K. Small deviations from isotropy encode a wealth of information on the properties of the Universe in its infancy. The objective of Planck is to measure these properties with an unprecedented accuracy and level of detail.
 
  
−
[[file:Planck_Logos.jpg|thumb|300px|The Planck collaboration institutes and agencies.]]
+
[http://www.esa.int/Planck Planck] is a mission of the European
 +
Space Agency - ESA. The Planck satellite carried instruments provided by two scientific Consortia funded by ESA member
 +
states (in particular the lead countries: France and Italy) with contributions from [https://www.nasa.gov/ NASA] (USA), and
 +
telescope reflectors provided in a collaboration between ESA and a scientific Consortium led and
 +
funded by Denmark.
  
−
As with all ESA scientific missions, Planck was developed in a partnership with the
+
Planck was conceived in 1992, in the wake of the release of the results from the
−
European scientific community. [[Planck Collaboration|Two consortia of scientific institutes]] (supported by several funding agencies),
+
Cosmic Background Explorer ([https://science.nasa.gov/missions/cobe COBE]) satellite, notably its measurement of the shape of the spectrum of the  
−
each led by a Principal Investigator, developed and delivered to ESA an instrument designed specifically for
+
[http://pdg.lbl.gov/2017/reviews/rpp2016-rev-cosmic-microwave-background.pdf cosmic microwave background]
−
Planck. Each of these instruments targets a specific number of wavelength bands within the
+
(CMB), and its
−
range where the CMB is observable. Together, the two instruments are capable of collecting
+
detection of the spatial anisotropies of the temperature of the CMB. The
−
data of sufficient quality to measure the CMB signal and distinguish it from other confusing
+
latter result in particular led to an explosion in the number of ground-based and suborbital
−
sources. A large telescope collected the light from the sky and delivered it to the instruments
+
experiments dedicated to mapping of the anisotropies, and to proposals for space experiments both in
−
for measurement and analysis. The reflectors of the Planck telescope were developed and
+
Europe and the USA.
−
delivered to ESA by a Danish consortium of institutes.  NASA also contributed significantly to Planck.
 
−
ESA retains overall management of the project, including the responsibility to develop and procure the spacecraft, integrate
 
−
the instruments into the spacecraft, and launch and operate it. Planck was launched on May 14th 2009 on an Ariane 5 rocket,
 
−
together with the Herschel Space Observatory. After launch, they were both
 
−
placed into orbits around the second Lagrange point of the Sun-Earth system, located about 1.5 million km from the Earth. From that far
 
−
vantage point, Planck swept the sky regularly in large swaths, and covered it fully
 
−
about five times for the HFI and eight times for the LFI.
 
−
Each of the two instrument consortia operated their respective instrument and processed
 
−
all the data into usable scientific products. At specific intervals the consortia delivered the data products to ESA, which archives them
 
−
and distributes them to the community.
 
  
−
The last command to the Planck satellite was sent on the 23 October 2013, marking the end of operations.
+
The main objective of Planck was to measure the spatial anisotropies of the temperature of the CMB, with an accuracy set by fundamental astrophysical limits. Its level of performance enabled Planck to extract essentially all the information in the CMB temperature anisotropies. Planck also measured to high accuracy the polarization of the CMB anisotropies, which encodes not only a wealth of cosmological information, but also provides a unique probe of the thermal history of the Universe during the time when the first stars and galaxies formed. In addition, the Planck sky surveys produced a wealth of information on the properties of extragalactic sources and on the dust and gas in our own Galaxy. The scientific objectives of Planck as conceived in 2005 (4 years before launch) were described in detail in the {{PlanckPapers|Bluebook}}.
−
[[file:PlanckMissionTimelineV2.png|thumb|480px|Timeline of the Planck operations and archiving.]]
 
  
−
== Early operations and transfer to orbit ==
+
The development of Planck began with two proposals presented to the
−
Planck was launched from the Centre Spatial Guyanais in
+
European Space Agency (ESA) in May of 1993, for the [https://dms.cosmos.esa.int/cs/livelink/Open/3557509 Cosmic Background Radiation Anisotropy Satellite] (COBRAS)
−
Kourou (French Guyana) on 14 May 2009 at its nominal lift-off
+
and the [https://dms.cosmos.esa.int/cs/livelink/Open/3557510 Satellite for Measurement of Background Anisotropies] (SAMBA). Each of these proposed a payload formed by an offset
−
time of 13:12 UT, on an Ariane 5 ECA rocket of Arianespace.
+
Gregorian telescope focussing light from the sky onto an array of
−
ESA’s Herschel observatory was launched on the same rocket.
+
detectors (based on high-electron-mobility transistor [HEMT] low
−
At 13:37:55 UT, Herschel was released from the rocket at an altitude
+
noise amplifiers for COBRAS and very low temperature bolometers for
−
of 1200 km; Planck followed suit at 13:40:25UT. The separation
+
SAMBA) fed by corrugated horns. The two proposals were used by an
−
attitudes of both satellites were within 0.1° of prediction.
+
ESA-led team to design a payload where a single COBRAS-like
−
The Ariane rocket placed Planck with excellent accuracy (semimajor
+
telescope fed two instruments, a COBRAS-like Low Frequency
−
axis within 1.6% of prediction), on a trajectory towards
+
Instrument (LFI), and a SAMBA-like High Frequency Instrument (HFI),
−
the second Lagrangian point of the Earth-Sun system (L2). The orbit describes a Lissajous trajectory
+
sharing a common focal plane. A period of study of this concept
−
around L2 with a roughly six month period that avoids crossing
+
culminated in the selection by ESA in 1996 of the COBRAS/SAMBA
−
the Earth penumbra for at least four years.
+
satellite (described in the so-called {{PlanckPapers|Redbook}})
 +
into its programme of scientific satellites. At the time of
 +
selection the launch of COBRAS/SAMBA was expected to be in 2003.
 +
Shortly after the mission was approved, it was renamed in honour of
 +
the German scientist [https://www.cosmos.esa.int/web/planck/max-planck Max Planck] (1858-1947), winner of the Nobel
 +
Prize for Physics in 1918.
  
−
[[file:HerschelPlanckLaunch.jpg|thumb|200px|Herschel and Planck spacecraft in the launch vehicle configuration.]]
+
Shortly after its selection, the  development of Planck was joined
 +
with that of ESA's [https://www.cosmos.esa.int/web/herschel Herschel Space Telescope], based on a number of
 +
potential commonalities, the most important of which was that both
 +
missions targeted orbits around the second Lagrangian point of the
 +
Sun-Earth system and could therefore share a single heavy launcher.
 +
In practice the joint development meant that a single ESA
 +
engineering team led the development of both satellites by a
 +
single industrial prime contractor, leading to the use of many
 +
identical hardware and software subsystems in both satellites, and a
 +
synergistic sharing of engineering skills and manpower. The
 +
industrial prime contractor, Thales Alenia Space France, was
 +
competitively selected in early 2001. Thales Alenia Space France was
 +
supported by two major subcontractors: Thales Alenia Space Italy for
 +
the Service Module of both Planck and Herschel; and EADS Astrium
 +
GmbH for the Herschel Payload Module.  There were also contributions from many other industrial
 +
subcontractors from all ESA member states (the industrial team is described [http://sci.esa.int/planck/34787-industrial-team/  here] ).
  
−
[[file:PLANCK_HERSCHEL_LAUNCH.jpg|thumb|200px|Herschel and Planck launch by an Ariane 5 ECA rocket in May 2009.]]
+
In early 1999, ESA selected two Consortia of scientific institutes to provide the two Planck
 +
instruments that were part of the payload described in the {{PlanckPapers|Redbook}}: the Low Frequency Instrument
 +
was developed by a consortium led by N. Mandolesi of the [http://www.iasfbo.inaf.it/en/ Istituto di Astrofisica Spaziale e Fisica
 +
Cosmica] (CNR) in Bologna (Italy); and the High Frequency Instrument by a consortium led by J.-L.
 +
Puget of the [https://www.ias.u-psud.fr/ Institut d'Astrophysique Spatiale] (CNRS) in Orsay (France).  
  
−
After release from the rocket, three large manoeuvres were
+
In early 2000, ESA and the [http://www.space.dtu.dk/english Danish National Space Institute] (DNSI) signed a Letter of Agreement for
−
carried out to place Planck in its intended final orbit.
+
the provision of the two reflectors that are used in the Planck telescope. DNSI led a Consortium of
−
Once in its final orbit, very small manoeuvres were required at approximately
+
Danish institutes, which together with ESA subcontracted the development of the Planck reflectors to
−
monthly intervals (1 m/s per year) to keep Planck
+
EADS Astrium GmbH (Friedrichshafen, D), now part of the Airbus group, who have manufactured the reflectors using state-of-the-art
−
from drifting away from its intended path around L2. The attitude
+
carbon-fibre technology.
−
manoeuvres required to follow the scanning strategy need
 
−
about 2.6 m/s per year. Overall, the excellent performance
 
−
of launch and orbit manoeuvres led to a large amount of fuel remaining on board at end of mission operations.
 
  
−
Planck started cooling down radiatively shortly after launch.
+
In total, more than 40 European
−
Heaters were activated to hold the focal plane at 250 K, which
+
institutes, and some from the USA and Canada joined forces to constitute the [https://www.cosmos.esa.int/web/planck/planck-collaboration Planck Collaboration], and carry out the development, testing, and in-flight operations of these
−
was reached around 5 h after launch. The valve opening the exhaust
+
instruments, as well as the ensuing data analysis
−
piping of the dilution cooler was activated at 03:30 UT,
+
and initial scientific exploitation.  
−
and the 4He-JT cooler compressors were turned on at low stroke
 
−
at 05:20 UT. After these essential operations were completed,
 
−
on the second day after launch, the focal plane temperature was allowed to descend to 170 K for out-gassing and decontamination
 
−
of the telescope and focal plane.
 
  
−
== Commissioning and initial science operations ==
+
[[file:Planck_Logos.jpg|thumb|center|500px|The Planck Collaboration's institutes and agencies.]]
  
−
=== Commissioning ===
 
  
−
The first period of operations focussed on commissioning activities,
+
The development history of the Planck satellite is summarised [https://www.cosmos.esa.int/web/planck/mission-history here].
−
i.e., functional check-out procedures of all sub-systems and
+
It culminated with the successful launch of Planck and Herschel on 14
−
instruments of the Planck spacecraft, in preparation for running
+
May 2009.
−
science operations related to calibration and performance verification
+
After a period dedicated to Commissioning and Performance Verification, Planck started its planned survey observations on 12 August 2009.  
−
of the payload. Planning for commissioning operations
+
It carried on observing for a period of about 30 months, around twice the span originally required, and completed five full-sky surveys with both instruments. The Low Frequency Instrument (LFI), which was able to work at higher temperatures than HFI,  continued to survey the sky for a large part of 2013, providing even more data to improve the final Planck results.  
−
was driven by the telescope decontamination period of 2 weeks
+
The last command to the Planck satellite was sent on the 23 October 2013, marking the end of operations.
−
and the subsequent cryogenic cool-down of the payload and instruments.
 
−
The overall duration of the cool-down was approximately
 
−
2 months, including the decontamination period.
 
−
The commissioning activities were executed very smoothly and
 
−
all sub-systems were found to be in good health.
 
−
The commissioning activities were formally completed at the
 
−
time when the HFI bolometer stage reached its target temperature
 
−
of 100 mK, on 3 July 2009 at 01:00 UT. At this time all the
 
−
critical resource budgets (power, fuel, lifetime, etc.) were found
 
−
to contain very significant margins with respect to the original
 
−
specification.
 
  
−
[[file:Cooldown.jpg|thumb|400px|Schematics of the cool-down sequence, from Planck Coll. 2011, A&A 536, A1.]]
+
<!-- [[file:PlanckMissionTimelineV2.png|thumb|480px|Timeline of the Planck operations and archiving.]] -->
  
−
=== Calibration and performance verification ===
+
== The Planck data products and papers ==
  
−
Calibration and performance verification (CPV) activities
+
The Data Products of Planck have been released in four different stages of increasing scope and quality.
−
started during the cool-down period and continued until the end
 
−
of August 2009.
 
−
On completion of all the
 
−
planned activities, it was concluded that the two instruments were fully tuned and ready for routine
 
−
operations. No further parameter tuning was expected
 
−
to be needed, except for the sorption cooler, which required
 
−
a weekly change in operational parameters.
 
−
The scientific performance parameters of both instruments
 
−
were in most respects as had been measured on the ground before
 
−
launch. The only significant exception was that, due to
 
−
the high level of Galactic cosmic rays, the bolometers of HFI
 
−
were detecting a higher number of glitches than expected,
 
−
causing a modest (about 10%) increase of systematic effects on
 
−
their noise levels. The satellite did not introduce any major systematic effects
 
−
into the science data. In particular, the telemetry transponder
 
−
did not result in radio-frequency interference, which implies
 
−
that the data acquired during visibility periods is usable for
 
−
science.
 
  
−
=== First-Light Survey ===
+
* The first set of scientific data, the Early Release Compact Source Catalogue (ERCSC; {{PlanckPapers|planck2011-1-10}}), was published in January 2011. At the same time, a set of 26 papers related to astrophysical foregrounds was published in a special issue of Astronomy and Astrophysics (Vol. 536, 2011), among which there is an overview paper ({{PlanckPapers|planck2011-1-1}}).
 +
* The second set of data products (sometimes referred to as Planck Release 1 or “PR1,” because it was the first release of cosmologically useful data) was based on data acquired during the so-called nominal mission, i.e. from start of routine operations to 28 November 2010. These products were based on temperature analysis of the whole sky, and were released in March of 2013. The data and associated scientific results are described in a set of 32 papers in another special issue of A&A (Vol. 571, 2014), among which there is another overview ({{PlanckPapers|planck2013-p01}}).
 +
* The third set of data products (and second set of cosmological data, hence “PR2”) and scientific results released by Planck, was based on the data acquired during the complete Planck mission from 12 August 2009 to 23 October 2013, and hereafter referred to as the “2015 products.” They are based on both temperature and polarization analysis of the entire sky, and were released between February and July 2015. The data and associated scientific results are described in a set of 28 papers published in a third special issue of A&A (Vol. 594, 2016). Again there is an overview paper paper ({{PlanckPapers|planck2014-a01}}).
 +
* The fourth set of scientific data (and third set of cosmological data, hence "PR3") was based on the full mission, focussing on inclusion of the polarization data.  The data and associated scientific results are described in a series of 11 papers, including a final "Legacy" which also includes an overview of this release ({{PlanckPapers|planck2016-l01}}.
  
−
The First Light Survey (FLS) was the last major activity planned
+
In addition to the above listed four groups of data-release-related papers, the Planck Collaboration has published more than 50 “Intermediate” papers containing further astrophysical investigations. These papers are usually based on data products that are either already public or about to become public at the time of publication.  
−
before the start of routine surveying of the sky. It was conceived
 
−
as a two-week period during which Planck would be fully tuned
 
−
up and operated as if it was in its routine phase. This stable
 
−
period could have resulted in the identification of further tuning
 
−
activities required to optimise the performance of Planck in
 
−
the long-duration surveys to come. The FLS was conducted between
 
−
13 and 27 August, and in fact led to the conclusion that
 
−
the Planck payload was operating stably and optimally, and required
 
−
no further tuning of its instruments. Therefore the period
 
−
of the FLS was accepted as a valid part of the first Planck survey.
 
  
−
== Routine operations phase ==
+
All of the Planck Collaboration papers are listed in and can be downloaded from [https://www.cosmos.esa.int/web/planck/publications]. At the current time, we encourage people interested in an overview on Planck to start with the latest overview paper ({{PlanckPapers|planck2016-l01}}), and follow references to more specific areas of interest.
−
The routine operations phase of Planck is characterized by continuous
 
−
and stable scanning of the sky and data acquisition by
 
−
LFI and HFI. It started with the FLS on 13 August 2009.
 
  
−
The Planck satellite generated (and stored on-board) data
+
== The Planck Legacy Archive ==
−
continuously at the following typical rates: 21 kilobit/s (kbps)
 
−
of house-keeping (HK) data from all on-board sources, 44 kbps
 
−
of LFI science data and 72 kbps of HFI science data. The data
 
−
were brought to ground in a daily pass of approximately 3 h duration.
 
−
Besides the data downloads, the passes also acquired realtime
 
−
HK and a 20 min period of real-time science (used to monitor
 
−
instrument performance during the pass). Planck utilized the
 
−
two ESA deep-space ground stations in New Norcia (Australia)
 
−
and Cebreros (Spain). Scheduling of the daily
 
−
telecommunication period was quite stable, with small perturbations
 
−
due to the need to coordinate the use of the antenna with
 
−
other ESA satellites (in particular Herschel).
 
−
At the ground station the telemetry was received by redundant
 
−
chains of front-end/back-end equipment. The data flowed to the
 
−
mission operations control centre (MOC) located at ESOC in
 
−
Darmstadt (Germany), where they were processed by redundant mission
 
−
control software (MCS) installations and made available to
 
−
the science ground segment. To reduce bandwidth requirements
 
−
between the station and ESOC only one set of science telemetry
 
−
was usually transferred. Software was run post-pass to check the
 
−
completeness of the data. This software check was also used to
 
−
build a catalogue of data completeness, which was used by the science
 
−
ground segment to control its own data transfer process.
 
−
Where gaps were detected, attempts to fill them were made as an
 
−
offline activity (normally next working day), the first step being
 
−
to attempt to reflow the relevant data from station. Early in
 
−
the mission these gaps were more frequent, with some hundreds
 
−
of packets affected per week (impact on data return of order
 
−
50 ppm), due principally to a combination of software problems
 
−
with the data ingestion and distribution in the MCS, and imperfect
 
−
behaviour of the software gap check. Software updates implemented
 
−
during the mission improved the situation, such
 
−
that gaps became much rarer, with a total impact on data return well
 
−
below 1 ppm.
 
−
Redump of data from the spacecraft was attempted when there
 
−
had been losses in the space link. This was only necessary
 
−
on very few occasions. In each case the spacecraft redump
 
−
successfully recovered all the data.
 
  
−
All the data downloaded from the satellite, and processed
+
The [http://pla.esac.esa.int/ Planck Legacy Archive] (PLA) contains all public products originating from the Planck mission, and provides an online interface to select and retrieve them. The majority of the scientific data products from Planck have been produced by the LFI and HFI Data Processing Centres on behalf of the [[Planck Collaboration|Planck Collaboration]].  
−
products such as filtered attitude information, were made available
 
−
each day for retrieval from the MOC by the LFI and HFI
 
−
data processing centres (DPCs).
 
  
−
The scanning strategy was the following: the spin axis follows a cycloidal path on the sky by step-wise displacements of 2 arcmin
+
The data products distributed by PLA are classified into the following categories.
−
approximately every 50 min. The dwell time (i.e., the duration of
+
* "Timelines" contain time series of data acquired. The types of data provided are:
−
stable data acquisition at each pointing) varied sinusoidally
+
** "semi-raw timelines" containing data samples per detector, which have been very minimally processed after retrieval from the satellite;
−
by a factor of approximately 2.
+
** "calibrated timelines" containing data samples per detector after cleaning and calibration.
−
Planck’s scanning strategy resulted
+
* "Rings" are timelines that have been binned into individual periods of fixed spin axis pointing. Each ring traces a quasi-large circle on the sky.
−
in significantly inhomogeneous depth of integration time
+
* "Maps" are generally all-sky maps in HEALPix format. There are two major types of Planck maps:
−
across the sky; the areas near the ecliptic poles were observed
+
** "frequency maps" are maps as observed at one of the nine frequency channels of Planck, containing at least temperature, and in the later versions also polarization, and existing in many varieties of maps, depending on which detectors and/or time coverage is included in their production;
−
with greater depth than all others.
+
** "component maps" are maps of diffuse emission of specific physical components, including the CMB, Galactic, and extragalactic foregrounds, which are constructed from Planck observations using different methods.
 +
* The "Likelihood code" is the software used by the Planck Collaboration to extract the values of cosmological parameters from the Planck data. The code is bundled with the data set (from Planck and other experiments) that it needs to run.
 +
* "Catalogues" contain lists of compact or point-like sources extracted from the Planck maps. The basic Planck catalogues have been extracted without regard to the type of source, but some specialized lists of specific source types are also available.
 +
* "Cosmological data" contain results of some of the cosmological analyses that formed the main objective of Planck, i.e. CMB angular power spectra, cosmological model parameters, etc.
  
−
The scanning strategy for the second year of Routine
+
In addition to the above, the PLA also includes a wide variety of additional products:
−
Operations was exactly the same as for the
+
* external scientific data that were used in the generation of Planck products;
−
first year, except that all pointings were shifted by 1 arcmin along
+
* data characterizing the Planck payload;
−
the cross-scanning direction, in order to provide finer sky sampling
+
* operational data.
−
for the highest frequency detectors when combining two
 
−
years of observations.
 
  
−
The remaining two years of operations, including Surveys 6 to 8 of the LFI-only phase, made use of a change in the cycloid phase of 90 degrees in order to spread out scanning directions over the sky.
+
All of the Planck products are labelled according to their release: ERCSC-A 2012; PR1 2013; PR2 2015; and PR3 2018. In addition, the product most recommended for use is labelled as the "Legacy" product. The PLA interface allows the user to search the Archive using a wide variety of parameters. It also provides the possibility to extract parts of the products, e.g. a section of the sky, and in some cases to modify them. The PLA also makes it easy to transfer products to generic data analysis tools for further analysis, e.g. Aladin for maps, and Topcat for catalogues.
  
−
Orbit maintenance manoeuvres were carried out at approximately
+
Finally, the PLA also contains some selected data products that are based on Planck data, but have not been produced by the Planck Collaboration. These data are labelled as "Community" products.  
−
monthly intervals. Although the manoeuvres only
 
−
required a few minutes, preparations, post-manoeuvre mass properties
 
−
calibration, and re-entry into scientific slewing mode
 
−
increased the overhead to several hours. The manoeuvres were
 
−
carried out without disturbing the path of the spin axis from its nominal scanning law. The dwell times of pointings before and
 
−
after the execution of the manoeuvre were reduced to allow all
 
−
pre-planned pointings to be carried out.
 
  
−
While the Planck detectors were scanning the sky, they also naturally
+
All the PLA products can be accessed via its [http://pla.esac.esa.int/pla/#home graphical interface]. Some of the products can also be extracted via a [http://pla.esac.esa.int/pla/#aio machine interface].
−
observed celestial calibrators. The main objects used for this
 
−
purpose were the Crab Nebula, and the bright planets Mars, Jupiter, and Saturn.
 
  
−
==Major operational milestones==
+
== This Explanatory Supplement ==
−
Planck was launched from the Centre Spatial Guyanais in
 
−
Kourou (French Guyana) on 14 May 2009 at its nominal lift-off
 
−
time of 13:12 UT, on an Ariane 5 ECA rocket of Arianespace.
 
  
−
On 13 August 2009, Planck started its first all-sky survey after successfully concluding its commissioning phase.
+
This Explanatory Supplement (ES) has been built by the Planck Collaboration and the Planck Science Office. It contains:
 +
* general technical information on the Planck satellite, its payload, and its operations;
 +
* specific information for each of the products being distributed by the PLA.
  
−
On 14 January 2012, Planck’s HFI completed its survey of the early Universe after running out of coolant as expected. Able to work at higher temperatures, the LFI continued surveying the sky until 3 October 2013.
+
The ES can be accessed online independently or can be called directly from the PLA interface (in this case it will direct the user to the appropriate sections). In general, it will display descriptions appropriate to the "Legacy" products. However,  descriptions specific for each of the four Planck releases can be found at the end of each of the ES sections; the background colour of the ES page identifies the release it refers to.  
  
−
On 4 October 2013 Planck ended its routine operations, after executing its last observation of the Crab Nebula, and started its decommissioning activities.
+
We emphasize that the ES  contains a bare minimum of necessary information on the data products. We strongly recommend that users read the scientific papers by the Planck Collaboration that are closest to their own application. Those papers contain the most relevant and useful information on the quality and limitations of the Planck products, which has often not been fully captured in the ES.
  
−
On 19 October 2013, the sorption cooler and the two instruments (LFI and HFI) were switched off.
+
==For more information==
  
−
The final command to the Planck satellite was sent on 23 October 2013, marking the end of operations.
+
A complete list of Planck publications can be found [http://www.sciops.esa.int/index.php?project=PLANCK&page=Planck_Published_Papers here].
−
 
 
−
==Contingencies==
 
−
 
 
−
The main unplanned events included the following.
 
−
 
 
−
* Very minor deviations from the scanning law included occasional (on the average about once every two months) under-performance of the 1-N thrusters used for regular manoeuvres, which implied that the corresponding pointings were not at the intended locations. These deviations had typical amplitudes of 30 arcsec, and had no significant impact on the coverage map.
 
−
 
 
−
* The thruster heaters were unintentionally turned off between 31 August and 16 September 2009 (the so-called “catbed” event).
 
−
 
 
−
* An operator error in the upload of the on-board command timeline led to an interruption of the normal sequence of manoeuvres and therefore to Planck pointing to the same location on the sky for a period of 29 h between 20 and 21 November 2009 (“the day Planck stood still”). Observations of the nominal scanning pattern resumed on 22 November, and on 23 November a recovery operation was applied to survey the previously missed area. During the recovery period the duration of pointing was decreased to allow the nominal law to be caught up with. As a side effect, the RF transmitter was left on for longer than 24 h, which had a significant thermal impact on the warm part of the satellite.
 
−
 
 
−
* As planned, the RF transmitter was initially turned on and off every day in synchrony with the daily visibility window, in order to reduce potential interference by the transmitter on the scientific data. The induced daily temperature variation had a measurable effect throughout the satellite. An important effect was on the temperature of the 4He-JT cooler compressors, which caused variations of the levels of the interference lines that they induce on the bolometer data (Planck HFI Core Team 2011a). Therefore the RF transmitter was left permanently on starting from 25 January 2010 (257 days after launch), which made a noticeable improvement on the daily temperature variations.
 
−
 
 
−
* During the coverage period, the operational star tracker switched autonomously to the redundant unit on two occasions (11 January 2010 and 26 February 2010); the nominal star tracker was restored a short period later (3.37 and 12.75 h, respectively) by manual power-cycling. Although the science data taken during this period have normal quality, they have not been used, because the redundant star tracker’s performance is not fully characterized.
 
−
 
 
−
For more information, see {{BibCite|planck2011-1-1}}. For a complete list of operational events, including contigencies, see the [[Planck operational state history | POSH]] (Planck operational state history).
 
−
 
 
−
==For more information==
 
  
−
A complete overview of the Planck mission and its science programme can be found in the [http://www.sciops.esa.int/SA/PLANCK/docs/Bluebook-ESA-SCI%282005%291_V2.pdf Blue Book].
+
Suggestions or questions should be sent to the [https://support.cosmos.esa.int/pla/ Helpdesk].
  
−
More details on the Planck mission performance can be found in {{BibCite|planck2011-1-1}}, .
+
==Acknowledgments==
 +
The development of Planck has been supported by: ESA; CNES and
 +
CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA);
 +
STFC and UKSA (UK); CSIC, MICINN, JA, and RES (Spain); Tekes, AoF, and CSC
 +
(Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO
 +
(Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and PRACE
 +
(EU). A description of the Planck Collaboration and a list of its members,
 +
including the technical or scientific activities in which they have been
 +
involved, can be found at  [http://www.cosmos.esa.int/web/planck/planck-collaboration this site].
  
−
A complete list of Planck publications can be found [http://www.sciops.esa.int/index.php?project=PLANCK&page=Planck_Published_Papers here].
 
  
 
==References==
 
==References==
Line 250: Line 157:
 
   
 
   
  
−
 
−
[[Category:Introduction|001]]
 
 
[[Category:PSOBook]]
 
[[Category:PSOBook]]

Latest revision as of 12:43, 17 July 2018


The Planck mission[edit]

Planck is a mission of the European Space Agency - ESA. The Planck satellite carried instruments provided by two scientific Consortia funded by ESA member states (in particular the lead countries: France and Italy) with contributions from NASA (USA), and telescope reflectors provided in a collaboration between ESA and a scientific Consortium led and funded by Denmark.

Planck was conceived in 1992, in the wake of the release of the results from the Cosmic Background Explorer (COBE) satellite, notably its measurement of the shape of the spectrum of the cosmic microwave background (CMB), and its detection of the spatial anisotropies of the temperature of the CMB. The latter result in particular led to an explosion in the number of ground-based and suborbital experiments dedicated to mapping of the anisotropies, and to proposals for space experiments both in Europe and the USA.

The main objective of Planck was to measure the spatial anisotropies of the temperature of the CMB, with an accuracy set by fundamental astrophysical limits. Its level of performance enabled Planck to extract essentially all the information in the CMB temperature anisotropies. Planck also measured to high accuracy the polarization of the CMB anisotropies, which encodes not only a wealth of cosmological information, but also provides a unique probe of the thermal history of the Universe during the time when the first stars and galaxies formed. In addition, the Planck sky surveys produced a wealth of information on the properties of extragalactic sources and on the dust and gas in our own Galaxy. The scientific objectives of Planck as conceived in 2005 (4 years before launch) were described in detail in the Bluebook[1].

The development of Planck began with two proposals presented to the European Space Agency (ESA) in May of 1993, for the Cosmic Background Radiation Anisotropy Satellite (COBRAS) and the Satellite for Measurement of Background Anisotropies (SAMBA). Each of these proposed a payload formed by an offset Gregorian telescope focussing light from the sky onto an array of detectors (based on high-electron-mobility transistor [HEMT] low noise amplifiers for COBRAS and very low temperature bolometers for SAMBA) fed by corrugated horns. The two proposals were used by an ESA-led team to design a payload where a single COBRAS-like telescope fed two instruments, a COBRAS-like Low Frequency Instrument (LFI), and a SAMBA-like High Frequency Instrument (HFI), sharing a common focal plane. A period of study of this concept culminated in the selection by ESA in 1996 of the COBRAS/SAMBA satellite (described in the so-called Redbook[2]) into its programme of scientific satellites. At the time of selection the launch of COBRAS/SAMBA was expected to be in 2003. Shortly after the mission was approved, it was renamed in honour of the German scientist Max Planck (1858-1947), winner of the Nobel Prize for Physics in 1918.

Shortly after its selection, the development of Planck was joined with that of ESA's Herschel Space Telescope, based on a number of potential commonalities, the most important of which was that both missions targeted orbits around the second Lagrangian point of the Sun-Earth system and could therefore share a single heavy launcher. In practice the joint development meant that a single ESA engineering team led the development of both satellites by a single industrial prime contractor, leading to the use of many identical hardware and software subsystems in both satellites, and a synergistic sharing of engineering skills and manpower. The industrial prime contractor, Thales Alenia Space France, was competitively selected in early 2001. Thales Alenia Space France was supported by two major subcontractors: Thales Alenia Space Italy for the Service Module of both Planck and Herschel; and EADS Astrium GmbH for the Herschel Payload Module. There were also contributions from many other industrial subcontractors from all ESA member states (the industrial team is described here ).

In early 1999, ESA selected two Consortia of scientific institutes to provide the two Planck instruments that were part of the payload described in the Redbook[2]: the Low Frequency Instrument was developed by a consortium led by N. Mandolesi of the [http://www.iasfbo.inaf.it/en/ Istituto di Astrofisica Spaziale e Fisica Cosmica] (CNR) in Bologna (Italy); and the High Frequency Instrument by a consortium led by J.-L. Puget of the Institut d'Astrophysique Spatiale (CNRS) in Orsay (France).

In early 2000, ESA and the Danish National Space Institute (DNSI) signed a Letter of Agreement for the provision of the two reflectors that are used in the Planck telescope. DNSI led a Consortium of Danish institutes, which together with ESA subcontracted the development of the Planck reflectors to EADS Astrium GmbH (Friedrichshafen, D), now part of the Airbus group, who have manufactured the reflectors using state-of-the-art carbon-fibre technology.

In total, more than 40 European institutes, and some from the USA and Canada joined forces to constitute the Planck Collaboration, and carry out the development, testing, and in-flight operations of these instruments, as well as the ensuing data analysis and initial scientific exploitation.

The Planck Collaboration's institutes and agencies.


The development history of the Planck satellite is summarised here. It culminated with the successful launch of Planck and Herschel on 14 May 2009. After a period dedicated to Commissioning and Performance Verification, Planck started its planned survey observations on 12 August 2009. It carried on observing for a period of about 30 months, around twice the span originally required, and completed five full-sky surveys with both instruments. The Low Frequency Instrument (LFI), which was able to work at higher temperatures than HFI, continued to survey the sky for a large part of 2013, providing even more data to improve the final Planck results. The last command to the Planck satellite was sent on the 23 October 2013, marking the end of operations.


The Planck data products and papers[edit]

The Data Products of Planck have been released in four different stages of increasing scope and quality.

  • The first set of scientific data, the Early Release Compact Source Catalogue (ERCSC; Planck-Early-VII[3]), was published in January 2011. At the same time, a set of 26 papers related to astrophysical foregrounds was published in a special issue of Astronomy and Astrophysics (Vol. 536, 2011), among which there is an overview paper (Planck-Early-I[4]).
  • The second set of data products (sometimes referred to as Planck Release 1 or “PR1,” because it was the first release of cosmologically useful data) was based on data acquired during the so-called nominal mission, i.e. from start of routine operations to 28 November 2010. These products were based on temperature analysis of the whole sky, and were released in March of 2013. The data and associated scientific results are described in a set of 32 papers in another special issue of A&A (Vol. 571, 2014), among which there is another overview (Planck-2013-I[5]).
  • The third set of data products (and second set of cosmological data, hence “PR2”) and scientific results released by Planck, was based on the data acquired during the complete Planck mission from 12 August 2009 to 23 October 2013, and hereafter referred to as the “2015 products.” They are based on both temperature and polarization analysis of the entire sky, and were released between February and July 2015. The data and associated scientific results are described in a set of 28 papers published in a third special issue of A&A (Vol. 594, 2016). Again there is an overview paper paper (Planck-2015-A01[6]).
  • The fourth set of scientific data (and third set of cosmological data, hence "PR3") was based on the full mission, focussing on inclusion of the polarization data. The data and associated scientific results are described in a series of 11 papers, including a final "Legacy" which also includes an overview of this release (Planck-2020-A1[7].

In addition to the above listed four groups of data-release-related papers, the Planck Collaboration has published more than 50 “Intermediate” papers containing further astrophysical investigations. These papers are usually based on data products that are either already public or about to become public at the time of publication.

All of the Planck Collaboration papers are listed in and can be downloaded from [1]. At the current time, we encourage people interested in an overview on Planck to start with the latest overview paper (Planck-2020-A1[7]), and follow references to more specific areas of interest.

The Planck Legacy Archive[edit]

The Planck Legacy Archive (PLA) contains all public products originating from the Planck mission, and provides an online interface to select and retrieve them. The majority of the scientific data products from Planck have been produced by the LFI and HFI Data Processing Centres on behalf of the Planck Collaboration.

The data products distributed by PLA are classified into the following categories.

  • "Timelines" contain time series of data acquired. The types of data provided are:
    • "semi-raw timelines" containing data samples per detector, which have been very minimally processed after retrieval from the satellite;
    • "calibrated timelines" containing data samples per detector after cleaning and calibration.
  • "Rings" are timelines that have been binned into individual periods of fixed spin axis pointing. Each ring traces a quasi-large circle on the sky.
  • "Maps" are generally all-sky maps in HEALPix format. There are two major types of Planck maps:
    • "frequency maps" are maps as observed at one of the nine frequency channels of Planck, containing at least temperature, and in the later versions also polarization, and existing in many varieties of maps, depending on which detectors and/or time coverage is included in their production;
    • "component maps" are maps of diffuse emission of specific physical components, including the CMB, Galactic, and extragalactic foregrounds, which are constructed from Planck observations using different methods.
  • The "Likelihood code" is the software used by the Planck Collaboration to extract the values of cosmological parameters from the Planck data. The code is bundled with the data set (from Planck and other experiments) that it needs to run.
  • "Catalogues" contain lists of compact or point-like sources extracted from the Planck maps. The basic Planck catalogues have been extracted without regard to the type of source, but some specialized lists of specific source types are also available.
  • "Cosmological data" contain results of some of the cosmological analyses that formed the main objective of Planck, i.e. CMB angular power spectra, cosmological model parameters, etc.

In addition to the above, the PLA also includes a wide variety of additional products:

  • external scientific data that were used in the generation of Planck products;
  • data characterizing the Planck payload;
  • operational data.

All of the Planck products are labelled according to their release: ERCSC-A 2012; PR1 2013; PR2 2015; and PR3 2018. In addition, the product most recommended for use is labelled as the "Legacy" product. The PLA interface allows the user to search the Archive using a wide variety of parameters. It also provides the possibility to extract parts of the products, e.g. a section of the sky, and in some cases to modify them. The PLA also makes it easy to transfer products to generic data analysis tools for further analysis, e.g. Aladin for maps, and Topcat for catalogues.

Finally, the PLA also contains some selected data products that are based on Planck data, but have not been produced by the Planck Collaboration. These data are labelled as "Community" products.

All the PLA products can be accessed via its graphical interface. Some of the products can also be extracted via a machine interface.

This Explanatory Supplement[edit]

This Explanatory Supplement (ES) has been built by the Planck Collaboration and the Planck Science Office. It contains:

  • general technical information on the Planck satellite, its payload, and its operations;
  • specific information for each of the products being distributed by the PLA.

The ES can be accessed online independently or can be called directly from the PLA interface (in this case it will direct the user to the appropriate sections). In general, it will display descriptions appropriate to the "Legacy" products. However, descriptions specific for each of the four Planck releases can be found at the end of each of the ES sections; the background colour of the ES page identifies the release it refers to.

We emphasize that the ES contains a bare minimum of necessary information on the data products. We strongly recommend that users read the scientific papers by the Planck Collaboration that are closest to their own application. Those papers contain the most relevant and useful information on the quality and limitations of the Planck products, which has often not been fully captured in the ES.

For more information[edit]

A complete list of Planck publications can be found here.

Suggestions or questions should be sent to the Helpdesk.

Acknowledgments[edit]

The development of Planck has been supported by: ESA; CNES and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MICINN, JA, and RES (Spain); Tekes, AoF, and CSC (Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and PRACE (EU). A description of the Planck Collaboration and a list of its members, including the technical or scientific activities in which they have been involved, can be found at this site.


References[edit]

  1. ↑ The Planck Bluebook, The Scientific Programme of Planck, Planck Collaboration, 2005, ESA Publication ESA-SCI(2005)01
  2. ↑ 2.02.1 The Planck Redbook, Report on the Phase A Study of COBRAS/SAMBA, 1996, ESA Publication D-SCI(96)3
  3. ↑ Planck early results. VII. The Early Release Compact Source Catalogue, Planck Collaboration VII, A&A, 536, A7, (2011).
  4. ↑ Planck early results. I. The Planck mission, Planck Collaboration I, A&A, 536, A1, (2011).
  5. ↑ Planck 2013 results. I. Overview of Products and Results, Planck Collaboration, 2014, A&A, 571, A1.
  6. ↑ Planck 2015 results. I. Overview of products and results, Planck Collaboration, 2016, A&A, 594, A1.
  7. ↑ 7.07.1 Planck 2018 results. I. Overview, and the cosmological legacy of Planck, Planck Collaboration, 2020, A&A, 641, A1.

European Space Agency

Cosmic Microwave background

High Electron Mobility Transistor

(Planck) Low Frequency Instrument

(Planck) High Frequency Instrument

Early Release Compact Source Catalog

Planck Legacy Archive

(Hierarchical Equal Area isoLatitude Pixelation of a sphere, <ref name="Template:Gorski2005">HEALPix: A Framework for High-Resolution Discretization and Fast Analysis of Data Distributed on the Sphere, K. M. Górski, E. Hivon, A. J. Banday, B. D. Wandelt, F. K. Hansen, M. Reinecke, M. Bartelmann, ApJ, 622, 759-771, (2005).

Explanatory Supplement

Solar System Object

Retrieved from ‘https://wiki.cosmos.esa.int/planck-legacy-archive/index.php?title=The_Planck_mission_WiP&oldid=14387’