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Planck spacecraft

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Planck spacecraft

Planck
NSSDC ID 2009-026B
Organization ESA, Thales Alenia Space (prime contractor)
Launch date 14 May 2009, 13:12:02 UTC
Launched from Guiana Space Centre,
French Guiana
Launch vehicle Ariane 5 ECA
Mission length
Type of orbit Lissajous
Location L2 point
(1,500,000 km / 930,000 mi)
Wavelength 350 to 10,000 µm
Instruments
Low Frequency Instrument (LFI) 30–70 GHz receivers
High Frequency Instrument (HFI) 100–857 GHz receivers
Website Planck mission site

Planck is a space observatory operated by the European Space Agency (ESA), and designed to observe anisotropies of the cosmic microwave background (CMB) at microwave and infra-red frequencies, with high sensitivity and small angular resolution. 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.

Built at 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, Planck was launched in May 2009, reaching the Earth/Sun L2 point by 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 previously measured the anisotropies at larger angular resolutions and much lower sensitivities. Planck also 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.

At the end of its mission Planck was put into a heliocentric orbit and passivated to prevent it from endangering any future missions. The final deactivation command was sent to Planck in October 2013.

Objectives

The mission has a wide variety of scientific aims, including:[1]

Planck has a higher resolution and sensitivity than WMAP, allowing it to probe the power spectrum of the CMB to much smaller scales (×3). It also observes in 9 frequency bands rather than WMAP's 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, a particularly important factor for the polarization measurements. The dominant foreground radiation depends on frequency, but could 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 nearly 830  GHz (from 30 to 857 GHz). The cosmic microwave background spectrum peaks at a frequency of 160.2 GHz.

Planck's passive and active cooling systems allow its instruments to maintain a temperature of −273.05 °C (−459.49 °F), or 0.1 degrees Celsius above absolute zero. As of July 2009, Planck is the coldest known object in space.[2]

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 is sensitive between 100 and 857 GHz, using 48 bolometric detectors, manufactured by JPL/Caltech,[3] optically coupled to the telescope through cold optics, manufactured by Cardiff University's School of Physics and Astronomy,[4] consisting of a triple horn configuration and optical filters, a similar concept to that 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), each with a bandwidth of 33%. Of these six bands, only the lower four have the capability to measure the polarisation of incoming radiation; the two higher bands do not.[1]

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.[5] 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.[5]

NASA

NASA played a role in the development of the mission and contributes to the analysis of scientific 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.[6]

Service Module


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[7] and €1,100 million for the Herschel mission.[8] 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 octagonal in shape and 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. On both spacecraft, a common design was used for the avionics, attitude control and measurement (ACMS), command and data management (CDMS), power, and tracking, telemetry and command (TT&C) subsystems. All units on the SVM are redundant.

Power Subsystem

On each spacecraft, the power subsystem consists of a solar array, employing triple-junction solar cells, a battery and the power control unit (PCU). The PCU is designed to interface with the 30 sections of each solar array, to provide a regulated 28 volt bus, to 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 rotates on its vertical axis.

Attitude and Orbit Control

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

The Planck satellite rotates at one revolution per minute, with an aim of an absolute pointing error less than 37 arc-minutes. As Planck is also a survey platform, there is the additional requirement for pointing reproducibility error less than 2.5 arc-minutes over 20 days.

The main line-of-sight sensor in both Herschel and Planck 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 manoeuvre to inject Planck into its final orbit around L2 was successfully completed on 3 July 2009, when it entered a Lissajous orbit with a 400,000 km (250,000 mi) radius around the L2 Lagrangian point.[9] 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.[10]

Decommissioning

In January 2012 the HFI exhausted its supply of liquid helium, causing the detector temperature to rise and rendering the HFI unusable. The LFI continued to be used until science operations ended on 3 October 2013. The spacecraft performed a manoeuvre on 9 October to move it away from Earth and its L2 point, placing it into a heliocentric orbit, while payload deactivation occurred on 19 October. Planck was commanded on 21 October to exhaust its remaining fuel supply; passivation activities were conducted later, including battery disconnection and the disabling of protection mechanisms.[11] The final deactivation command, which switched off the spacecraft's transmitter, was sent to Planck on 23 October 2013 at 12:10:27 UTC.[12]

Results

Planck started its First All-Sky Survey on 13 August 2009.[13] 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.[14]

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.[9]

Some planned pointing list data from 2009 have been released publicly, along with a video visualization of the surveyed sky.[13]

On 17 March 2010, the first Planck photos were published, showing dust concentration within 500 light years from the Sun.[15][16]

On 5 July 2010, the Planck mission delivered its first all-sky image.[17]

The first public scientific result of Planck is the Early-Release Compact-Source Catalogue, released during the January 2011 Planck conference in Paris.[18][19]

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.[20][21] This 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. It is currently theorised that these ripples apparently gave rise to the present vast cosmic web of galactic 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.[22][23][24] The Hubble constant was also measured to be 67.80 ±0.77 (km/s)/Mpc.[20][22][25][26][27]

Cosmological parameters from 2013 Planck results[22][23][24]
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
0.829±0.012 0.9603±0.0073 0.089+0.012
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
0.828±0.012 0.9585±0.0070 0.091+0.013
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
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


See also

References

Further reading

External links

  • ESA
    • Planck mission website
    • ESA Operations site for Planck
    • ESA Science & Technology site for Planck
    • site for Planck
    • Planck Legacy Archive
  • NASA
    • Planck mission website
    • NASA Planck Archive
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