WMAP

Wilkinson Microwave Anisotropy Probe

Collage image of the Wilkinson Microwave Anisotropy Probe (WMAP) images and data. NINE-YEAR PAPERS
NINE-YEAR DATA
COSMOLOGICAL PARAMETERS TABLE
SEVEN-YEAR DATA
FIVE-YEAR DATA
THREE-YEAR DATA
FIRST-YEAR DATA
WMAP MISSION SITE

WMAP Overview

The WMAP (Wilkinson Microwave Anisotropy Probe) mission is designed to determine the geometry, content, and evolution of the universe via a 13 arcminute FWHM resolution full sky map of the temperature anisotropy of the cosmic microwave background radiation. The choice of orbit, sky-scanning strategy and instrument/spacecraft design were driven by the goals of uncorrelated pixel noise, minimal systematic errors, multifrequency observations, and accurate calibration. The skymap data products derived from the WMAP observations have 45 times the sensitivity and 33 times the angular resolution of the COBE DMR mission. The WMAP mission characteristics are summarized in the table below.

In the first release of WMAP data (February 2003), only the temperature data and analyses from the first year of operations at L2 were provided.

Much more information and data was provided in the second release (March 2006); the differences between the two are characterized by:

  • Data from the first three years of spacecraft operations at L2 are made available.
  • Polarization analysis, maps, and time-ordered data are made available.
  • The temperature analysis and maps are improved.
  • The error analysis was improved.
  • The map-making algorithm was changed.

The third data release took place in March 2008. It was characterized by:

  • Data from the first five years of spacecraft operations at L2 are made available.
  • The temperature and polarization analysis and maps are improved.
  • The error analysis was improved.
  • The calibration algorithm was improved.
  • The beam maps were improved.

The fourth release of data took place in January 2010. It is characterized by:

  • Data from the first seven years of spacecraft operations at L2 are made available.
  • The temperature and polarization analysis and maps are improved.
  • The error analysis was improved.
  • The calibration algorithm was improved.
  • The beam maps were improved.

The fifth and final release of data took place in June 2012. It is characterized by:

  • Data from the full nine years of spacecraft operations at L2 are made available.
  • The temperature and polarization analysis and maps are improved.
  • The error analysis was improved.
  • The calibration algorithm was improved.
  • The beam maps were improved.
WMAP Mission Characteristics:
  K-Banda Ka-Banda Q-Banda V-Banda W-Banda
   
Wavelength (mm)b 13 9.1 7.3 4.9 3.2
Frequency (GHz)b 23 33 41 61 94
Bandwidth (GHz)b, c 5.5 7.0 8.3 14.0 20.5
Number of Differencing Assemblies 1 1 2 2 4
Number of Radiometers 2 2 4 4 8
Number of Channels 4 4 8 8 16
Beam Size (deg)b, d 0.88 0.66 0.51 0.35 0.22
System Temperature, Tsys (K)b, e 29 39 59 92 145
Sensitivity (mK sec½ )b 0.8 0.8 1.0 1.2 1.6
           
Sky Coverage Full sky
Optical System Back-to-Back Gregorian, 1.4 x 1.6 m primaries
Radiometric System Differential polarization sensitive receivers
Detection HEMT amplifiers
Radiometer Modulation 2.5 kHz phase switch
Spin Modulation 0.464 rpm = ~ 7.57 mHz spacecraft spin
Precession Modulation 1 rev hr -1 = ~ 0.3 mHz spacecraft precession
Calibration In-flight: amplitude from dipole modulation, beam from Jupiter
Cooling System Passively cooled to ~ 90 K
Attitude Control 3-axis controlled, 3 wheels, gyros, star trackers, sun sensors
Propulsion Blow-down hydrazine with 8 thrusters
RF Communication 2 GHz transponders, 667 kbps down-link to 70 m DSN
Power 419 Watts
Mass 840 kg
Launch Delta II 7425-10 on June 30, 2001 at 3:46:46.183 EDT
Orbit 1° - 10° Lissajous orbit about second Lagrange point, L2
Trajectory 3 Earth-Moon phasing loops, lunar gravity assist to L2
Design Lifetime 27 months = 3 month trajectory + 2 yrs at L2

 
a Commercial waveguide band designations used for the five MAP frequency bands
 
 
b Typical values for a radiometer are given.
 
 
c Effective signal bandwidth.
 
  d The beam patterns are not Gaussian, and thus are not simply specified. The size given here is the square- root of the beam solid angle.  
  e Effective system temperature of the entire system.  
A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
Goddard Space Flight Center, National Aeronautics and Space Administration
HEASARC Director: Dr. Alan P. Smale
LAMBDA Director: Dr. David T. Chuss
NASA Official: Dr. David T. Chuss
Web Curator: Mr. Michael R. Greason