Planck (spacecraft)

General information 2009-026B European Space Agency, Thales Alenia Space (prime contractor) 14 May 2009, 13:12:02 UTC Guiana Space Centre, French Guiana Ariane 5 ECA elapsed: 4 years and 26 days Lissajous L2 point (1,500,000 km / 930,000 mi) 350 to 10,000 µm 30–70 GHz receivers 100–857 GHz receivers Planck mission site

Planck is a space observatory of the European Space Agency (ESA) designed to observe the anisotropies of the cosmic microwave background (CMB) over the entire sky, at microwave and infra-red frequencies with high sensitivity and small 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, is named in honour of the German physicist Max Planck (1858–1947), who won the Nobel Prize in Physics in 1918.

Planck was launched in May 2009, reaching the Earth/Sun L2 point in July, and by February 2010 had successfully started a second all-sky survey. On 21 March 2013, the mission's all-sky map of the cosmic microwave background was released.

The mission complements and improves upon observations made by the NASA Wilkinson Microwave Anisotropy Probe (WMAP), which has measured the anisotropies at larger angular scales and lower sensitivity than Planck. Planck provides 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:[1]

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 (×3).
• It has higher sensitivity (×10).
• It observes in 9 frequency bands rather than 5, 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).[1] 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
(Δν/ν)
Resolution
(arcmin)
Sensitivity (total intensity)
ΔT/T, 14 month observation
(10−6)
Sensitivity (polarization)
ΔT/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, covering the microwave to infra-red regions of the electromagnetic spectrum. The detectors use high-electron-mobility transistors.[1]

High Frequency Instrument

Frequency
(GHz)
Bandwidth
(Δν/ν)
Resolution
(arcmin)
Sensitivity (total intensity)
ΔT/T, 14 month observation
(10−6)
Sensitivity (polarization)
ΔT/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.[1] The HFI instrument uses 48 bolometric detectors (manufactured by JPL/Caltech)[2] optically coupled to the telescope through cold optics (manufactured by Cardiff University's School of Physics and Astronomy)[3] consisting of a triple horn configuration and optical filters (similar concept used in the Archeops balloon-borne experiment). These detection assemblies are divided into 6 frequency bands (centred at 100, 143, 217, 353, 545 and 857 GHz) with a bandwidth of 33%. Out of these 6 bands, 4 will have the capability to measure the polarisation of the incoming radiation (100, 143, 217 and 353 GHz bands).

On 13 January 2012, it was reported that the on-board supply of helium-3 used in Planck's dilution refrigerator had been exhausted, and that the HFI would become unusable within a few days.[4] By this date, Planck had completed five full scans of the CMB, exceeding its target of two. The LFI (cooled by helium-4) was expected to remain operational for another six to nine months.[4]

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.[5]

Service Module

Some of the Herschel-Planck team, from left to right: Jean-Jacques Juillet, director of scientific programmes, Thales Alenia Space; Marc Sauvage, project scientist for Herschel PACS experiment, CEA; François Bouchet, Planck operations manager, IAP; and Jean-Michel Reix, Herschel & Planck operations manager, Thales Alenia Space. During presentations of the first results for the missions, Cannes, October 2009

A common service module (SVM) was designed and built by Thales Alenia Space in its Turin plant, for both the Herschel Space Observatory and Planck missions, combined into one single program.[1]

The overall cost is estimated to be €700 million for the Planck[6] and €1,100 million for the Herschel mission.[7] Both figures include their mission's spacecraft and payload, (shared) launch and mission expenses, and science operations.

Structurally the Herschel and Planck SVMs are very similar. Both SVMs 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 volt 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 of the satellite, always facing the sun as the satellite spins 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 arcminutes 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 UTC 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 [170 mi], apogee: more than 1,120,000 km [700,000 mi]), bringing it near the L2 Lagrangian point of the Earth-Sun system, 1,500,000 kilometres (930,000 mi) from the Earth.

The maneuver to inject Planck into its final orbit around L2 was successfully completed on 3 July 2009, when it entered a Lissajous orbit of 400,000 km (250,000 mi) radius around the L2 Lagrangian point.[8] The temperature of the High Frequency Instrument reached just a tenth of a degree above absolute zero (0.1 K) on 3 July 2009, placing both the Low Frequency and High Frequency Instruments within their cryogenic operational parameters, making Planck fully operational.[9]

Results

Comparison of CMB results from COBE, WMAP and Planck

Planck started its First All-Sky Survey on 13 August 2009.[10] In September 2009, the European Space Agency announced the preliminary results from the Planck First Light Survey, which was 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.[11]

On 15 January 2010 the mission was extended by 12 months, with observation continuing until at least the end of 2011. After the successful conclusion of the First Survey, the spacecraft started its Second All Sky Survey on 14 February 2010, with more than 95% of the sky observed already and 100% sky coverage being expected by mid-June 2010.[8]

Some planned pointing list data from 2009 have been released publicly, along with a video visualization of the surveyed sky.[10]

On 17 March 2010 the first Planck photos were published, showing dust concentration within 500 light years from the Sun.[12][13]

On 5 July 2010, the Planck mission delivered its first all-sky image.[14]

The first public scientific result of Planck is the Early-Release Compact-Source Catalogue, released during the January 2011 Planck conference in Paris.[15][16]

2013 data release

On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map of the cosmic microwave background.[17][18] The map suggests the universe is slightly older than thought. According to the map, subtle fluctuations in temperature were imprinted on the deep sky when the cosmos was about 370,000 years old. The imprint reflects ripples that arose as early, in the existence of the universe, as the first nonillionth (10-30) of a second. Apparently, these ripples gave rise to the present vast cosmic web of galaxy clusters and dark matter. According to the team, the universe is 13.798 ± 0.037 billion years old, and contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy.[19][20][21] Also, the Hubble constant was measured to be 67.80 ± 0.77 (km/s)/Mpc.[19][22][17][23][24]

Cosmological parameters from 2013 Planck results[19][20][21]
Parameter Age of the universe (Gy) Hubble's constant
( kmMpc·s )
Physical baryon density Physical cold dark matter density Dark energy density Density fluctuations at 8h−1 Mpc Scalar spectral index Reionization optical depth
Symbol $t_0$ $H_0$ $\Omega_b h^2$ $\Omega_c h^2$ $\Omega_\Lambda$ $\sigma_8$ $n_s$ $\tau$
Planck
Best fit
13.819 67.11 0.022068 0.12029 0.6825 0.8344 0.9624 0.0925
Planck
68% limits
13.813±0.058 67.4±1.4 0.02207±0.00033 0.1196±0.0031 0.686±0.020 0.834±0.027 0.9616±0.0094 0.097±0.038
Planck+lensing
Best fit
13.784 68.14 0.022242 0.11805 0.6964 0.8285 0.9675 0.0949
Planck+lensing
68% limits
13.796±0.058 67.9±1.5 0.02217±0.00033 0.1186±0.0031 0.693±0.019 0.823±0.018 0.9635±0.0094 0.089±0.032
Planck+WP
Best fit
13.8242 67.04 0.022032 0.12038 0.6817 0.8347 0.9619 0.0925
Planck+WP
68% limits
13.817±0.048 67.3±1.2 0.02205±0.00028 0.1199±0.0027 0.685+0.018
−0.016
0.829±0.012 0.9603±0.0073 0.089+0.012
−0.014
Planck+WP
+HighL
Best fit
13.8170 67.15 0.022069 0.12025 0.6830 0.8322 0.9582 0.0927
Planck+WP
+HighL
68% limits
13.813±0.047 67.3±1.2 0.02207±0.00027 0.1198±0.0026 0.685+0.017
−0.016
0.828±0.012 0.9585±0.0070 0.091+0.013
−0.014
Planck+lensing
+WP+highL
Best fit
13.7914 67.94 0.022199 0.11847 0.6939 0.8271 0.9624 0.0943
Planck+lensing
+WP+highL
68% limits
13.794±0.044 67.9±1.0 0.02218±0.00026 0.1186±0.0022 0.693±0.013 0.8233±0.0097 0.9614±0.0063 0.090+0.013
−0.014
Planck+WP
+highL+BAO
Best fit
13.7965 67.77 0.022161 0.11889 0.6914 0.8288 0.9611 0.0952
Planck+WP
+highL+BAO
68% limits
13.798±0.037 67.80±0.77 0.02214±0.00024 0.1187±0.0017 0.692±0.010 0.826±0.012 0.9608±0.0054 0.092±0.013

References

1. Planck: The Scientific Programme. ver. 2. European Space Agency. 2005. ESA-SCI(2005)1. Retrieved 6 March 2009.
2. ^ "The Planck High Frequency Instrument (HFI)". Caltech.edu. Jet Propulsion Laboratory. Retrieved 22 March 2013.
3. ^ "High Frequency Instrument (HFI)". Cardiff.ac.uk. Cardiff University. Retrieved 22 March 2013.
4. ^ a b Amos, Jonathan (13 January 2012). "Super-cool Planck mission begins to warm". BBC News. Retrieved 13 January 2012.
5. ^ "Planck: Exploring the Birth of Our Universe". NASA.gov. Retrieved 26 September 2009.
6. ^ "Planck: Fact Sheet". ESA.int. European Space Agency. 20 January 2012. Archived from the original on 16 October 2012.
7. ^ "Herschel: Fact Sheet". ESA.int. European Space Agency. 28 April 2010. Archived from the original on 13 October 2012.
8. ^ a b "Planck: Mission Status Summary". ESA.int. European Space Agency. 19 March 2013. Retrieved 22 March 2013.
9. ^ "Planck instruments reach their coldest temperature". ESA.int. European Space Agency. 3 July 2009. Retrieved 5 July 2009.
10. ^ a b "Simultaneous observations with Planck". ESA.int. European Space Agency. 31 August 2009. Retrieved 17 August 2012.
11. ^ "Planck first light yields promising results". ESA.int. European Space Agency. 17 September 2009.
12. ^ "Planck sees tapestry of cold dust". ESA.int (European Space Agency). 17 March 2010.
13. ^ "New Planck images trace cold dust and reveal large-scale structure in the Milky Way". ESA.int. European Space Agency. 17 March 2010. Retrieved 17 August 2012.
14. ^ "Planck unveils the Universe – now and then". ESA.int. European Space Agency. 5 July 2010. Retrieved 22 March 2013.
15. ^ "2011 Planck Conference". Planck2011.fr. Retrieved 22 March 2013.
16. ^ "Planck Legacy Archive". ESA.int. European Space Agency.
17. ^ a b Clavin, Whitney; Harrington, J. D. (21 March 2013). "Planck Mission Brings Universe Into Sharp Focus". NASA.gov. Retrieved 21 March 2013.
18. ^ "Mapping the Early Universe". The New York Times. 21 March 2013. Retrieved 23 March 2013.
19. ^ a b c Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; et al. (Planck Collaboration) (22 March 2013). "Planck 2013 results. I. Overview of products and scientific results - Table 9.". Astronomy and Astrophysics (submitted). arXiv:1303.5062.
20. ^ a b Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; et al. (Planck Collaboration) (31 March 2013). "Planck 2013 Results Papers". Astronomy and Astrophysics (submitted). arXiv:1303.5062.
21. ^ a b Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; et al. (Planck Collaboration) (22 March 2013). "Planck 2013 results. XVI. Cosmological parameters". Astronomy and Astrophysics (manuscript no. draft˙p1011). arXiv:1303.5076.
22. ^ "Planck reveals an almost perfect Universe". ESA.int. European Space Agency. 21 March 2013. Retrieved 21 March 2013.
23. ^ Overbye, Dennis (21 March 2013). "Universe as an Infant: Fatter Than Expected and Kind of Lumpy". The New York Times. Retrieved 21 March 2013.
24. ^ Boyle, Alan (21 March 2013). "Planck probe's cosmic 'baby picture' revises universe's vital statistics". Cosmic Log via NBC News. Retrieved 21 March 2013.