Planck (spacecraft)

Planck

File:Planck satellite.jpg
COSPAR ID	2009-026B
SATCAT no.	34938
Website	Planck Science Team Home
Start of mission
Launch date	2009-05-14 13:12:02 UTC

Planck is a space observatory designed to observe the anisotropies of the cosmic microwave background (CMB) over the entire sky, using high sensitivity and angular resolution. Planck was built in the Cannes Mandelieu Space Center by Thales Alenia Space and created as the third Medium-Sized Mission (M3) of the European Space Agency's Horizon 2000 Scientific Programme. The project—initially called COBRAS/SAMBA after its approval—is named in honour of the German scientist Max Planck (1858–1947), who won the Nobel Prize for Physics in 1918.

The mission will complement and improve upon observations made by the NASA Wilkinson Microwave Anisotropy Probe, which has measured the anisotropies at larger angular scales and lower sensitivity than Planck. Planck will provide a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early universe and the origin of cosmic structure.

Objectives

The mission has a wide variety of scientific aims, including:

• High resolution detections of both the total intensity and polarization of the primordial CMB anisotropies
• Creation of a catalogue of galaxy clusters through the Sunyaev-Zel'dovich effect
• Observations of the gravitational lensing of the CMB, as well as the integrated Sachs–Wolfe effect
• Observations of bright extragalactic radio (active galactic nuclei) and infrared (dusty galaxy) sources
• Observations of the Milky Way, including the local interstellar medium, distributed synchrotron emission and measurements of the galactic magnetic field.
• Studies of the local Solar System, including planets, asteroids, comets and the zodiacal light.

Planck represents an advance over WMAP in several respects.

• It has higher resolution, allowing it to probe the power spectrum of the CMB to much smaller scales (x3).
• It has higher sensitivity (x10).
• It observes in nine passbands rather than five with the goal of improving the astrophysical foreground models.

It is expected that most Planck measurements will be limited by how well foregrounds can be subtracted, rather than by the detector performance or length of the mission. This is particularly important for the polarization measurements. The dominant foreground depends on frequency, but examples include synchrotron radiation from the Milky Way at low frequencies, and dust at high frequencies.

Instruments

The spacecraft carries two instruments; the Low Frequency Instrument (LFI) and the High Frequency Instrument (HFI). Both instruments can detect both the total intensity and polarization of photons, and together cover a frequency range of 30 to 857 GHz. The cosmic microwave background spectrum peaks at a frequency of 160.2 GHz

Low Frequency Instrument

Frequency (GHz)	Bandwidth ($\Delta \nu /\nu$)	Resolution (arcmin)	Sensitivity (total intensity) $\Delta T/T$, 14 month observation (10−6)	Sensitivity (polarization) $\Delta T/T$, 14 month observation (10−6)
30	0.2	33	2.0	2.8
44	0.2	24	2.7	3.9
70	0.2	14	4.7	6.7

The LFI has three frequency bands, covering the range of 30–70 GHz. The detectors use High Electron Mobility Transistors.

High Frequency Instrument

Frequency (GHz)	Bandwidth ($\Delta \nu /\nu$)	Resolution (arcmin)	Sensitivity (total intensity) $\Delta T/T$, 14 month observation (10−6)	Sensitivity (polarization) $\Delta T/T$, 14 month observation (10−6)
100	0.33	10	2.5	4.0
143	0.33	7.1	2.2	4.2
217	0.33	5.5	4.8	9.8
353	0.33	5.0	14.7	29.8
545	0.33	5.0	147	N/A
857	0.33	5.0	6700	N/A

The HFI has six frequency bands, between 100 and 857 GHz. They use bolometers to detect photons. The four lower frequency bands have sensitivity to linear polarization; the two higher bands do not.

NASA

NASA played a role in the development of the mission and will contribute to the analysis of science data. Its Jet Propulsion Laboratory built components of the science instruments, including bolometers for the high-frequency instrument, a 20 Kelvin cryocooler for both the low- and high-frequency instruments, and amplifier technology for the low-frequency instrument.

Service Module – a common development for Herschel and Planck

A common service module (SVM) was designed and built by Thales Alenia Space in its Turin plant, for the Herschel and Planck missions combined into one single program .

Structurally the Herschel and Planck SVM's are very similar. Both SVM's are of octagonal shape and for both, each panel is dedicated to accommodate a designated set of warm units, while taking into account the dissipation requirements of the different warm units, of the instruments as well as the spacecraft.

Furthermore, on both spacecraft a common design for the avionics, the attitude control and measurement system (ACMS) and the command and data management system (CDMS), and power subsystem and the tracking, telemetry and command subsystem (TT&C) has been achieved.

All spacecraft units on the SVM are redundant.

Power Subsystem

On each spacecraft, the power subsystem consists of the solar array, employing triple-junction solar cells, a battery and the power control unit (PCU). It is designed to interface with the 30 sections of each solar array, provide a regulated 28 V bus, distribute this power via protected outputs and to handle the battery charging and discharging.

For Planck, the circular solar array is fixed on the bottom part of the satellite, facing always the sun, as the satellite is spinning around its vertical axis.

Attitude and Orbit Control

This function is performed by the attitude control computer (ACC) which is the platform for the ACMS. It is designed to fulfil the pointing and slewing requirements of the Herschel and Planck payload.

The Planck satellite is spun at one revolution per minute, the absolute pointing error needs to be less than 37 arc min. For Planck being a survey platform, there is also a requirement to be met on pointing reproducibility error to be less than 2.5 arc min over 20 days.

The main sensor of the line of sight in both spacecraft is the star tracker.

Launch and orbit

The satellite was successfully launched, along with the Herschel Space Observatory, at 13:12:02 on 14 May 2009 aboard an Ariane 5 ECA heavy launch vehicle. The launch placed the craft into a very elliptical orbit (perigee: 270 km, apogee: more than 1,120,000 km), bringing it near the L₂ Lagrangian point of the Earth-Sun system, 1.5 million kilometers from the Earth.

The maneuver to inject Planck into its final orbit around L₂ was successfully completed on July 3, 2009, when it entered a Lissajous orbit of 400,000 km radius around the L₂ Lagrangian point. The temperature of the High Frequency Instrument reached just a tenth of a degree above absolute zero (0.1 K) on July 3, 2009, placing both the Low Frequency and High Frequency Instruments within their cryogenic operational parameters, making Planck fully operational.

Results

A part of the Herschel Planck team, from left to right : Jean-Jacques Juillet, Head of scientific programmes Thales Alenia Space ; Marc Sauvage, CEA, responsible Herschel PACS Experience ; François Bouchet, IAP, responsible Planck exploitation ; Jean-Michel Reix, Head of Herschel & Planck Programmes, Thales Alenia Space, for the presentations of the first results of Herschel & Planck missions, Cannes, October 2009

On September 2009, ESA announced the preliminary results from the Planck First Light Survey (performed to demonstrate the stability of the instruments and the ability to calibrate them over long periods). The results indicated that the data quality is excellent.

The final results (with all processed data) are expected to be delivered to the worldwide community towards the end of 2012.

See also

• List of cosmic microwave background experiments
• List of space telescopes
• Observational cosmology
• Herschel Space Observatory

References

• Dambeck, Thorsten (2009). "Planck Readies to Dissect the Big Bang". Sky and Telescope: 24-28. {{cite journal}}: Unknown parameter |month= ignored (help)

External links

• Planck Science Team website
• Planck Spacecraft Operations website
• Planck Science & Technology website
• Planck mission overview at NASA.gov
• Jettison of encapsulated Planck as seen from Herschel
• Looking inside Plank on YouTube