Wilkinson Microwave Anisotropy Probe

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Wilkinson Microwave Anisotropy Probe

Structure of WMAP
NSSDC ID 2001-027A
Mission goal Heliocentric L1 orbit
Client National Aeronautics and Space AdministrationNASA NASA
Launcher Delta-II 7425-10
Takeoff mass 840 kg
Course of the mission
Start date June 30, 2001, 19:46 UTC
launch pad Cape Canaveral , LC-17B
End date 20th September 2010
June 30, 2001 begin
October 1, 2001 Orbit around L2
8/20/2010 Last data transfer
September 20, 2010 Cemetery orbit for sun

Wilkinson Microwave Anisotropy Probe ( WMAP , formerly MAP , also Explorer 80 ) is a US space probe launched in 2001 that was in operation until 2010.

Name and Mission

“MAP” is an abbreviation for “ Microwave Anisotropy Probe ” and is used to research irregularities in the cosmic background radiation . A map should be made of this radiation, which is why the abbreviation “MAP” also fits. In December 2002 the probe was renamed "WMAP", the "W" standing for the physicist David Todd Wilkinson (1935–2002), one of the discoverers and researchers of cosmic background radiation.

WMAP is the successor to the Cosmic Background Explorer (COBE) satellite , which researched this radiation from an earth orbit between 1989 and 1992 . WMAP should create a map that was improved by a factor of 20. The instruments can measure temperature differences in the range of 20 millionths of a degree. A new observation site was also selected for WMAP: the Lagrange point L 2, facing away from the sun . That is why WMAP is classified here as a space probe and not a satellite . The 840 kg WMAP probe is also classified as " Explorer 80 ".

From August 2009 to October 2013, the European Planck space probe measured the radiation with three times the resolution - with better suppression of the interference radiation. However, the WMAP mission continued through 2010.

WMAP is a cooperation between Princeton University (responsible: Lyman Page ) and NASA Goddard Space Flight Center . The project leader is Charles L. Bennett . Gary Hinshaw is in charge of data analysis .

Description of the probe

WMAP rotates around its own axis more slowly than in this animation

WMAP is a probe that rotates around its own axis in about 129 seconds. Its main body is roughly tower-shaped and carries an instrument called a "pseudo-correlation radiometer", with two Gregory antennas of 1.4 m × 1.6 m primary mirror size attached back to back . The secondary mirrors are 0.9 m × 1.0 m in size. It measures on the frequencies 22, 30, 40, 60 and 90 GHz. The signal components that are identical for both antennas are not registered. The remaining signal is measured. The tower stands in the center of an almost circular, fold-out sunshade, the spokes of which are six solar cell wings , the solar cells of which are attached to the underside. The underside of the sunshade is constantly facing the sun , so that it shields the probe from the sun. The actual probe body is therefore constantly in the shade and therefore has a very low equilibrium temperature between the heat generation on board and the heat radiation into space. The operating temperature of the pseudo-correlation radiometer is therefore less than 95 K (−178.15 ° C) to suppress noise .

Course of the mission

WMAP's flight to L 2

WMAP was launched on 30 June 2001 on a Delta II 7425-10 carrier rocket into a highly elliptical orbit, where she performed three Erdumläufe before the fourth round, a swing-by maneuvers carried out at the moon and the direction L 2 was thrown . The probe entered the Lissajous orbit around L 2 on October 1, 2001. On August 20, 2010, WMAP sent scientific data for the last time and on September 20, the control jets were fired, causing WMAP to leave its Lissajous orbit around L 2 and have now reached a park orbit around the sun. However, NASA continued to finance the data analysis for two years.


Matter or energy share of the universe at the current point in time (above) and at the time of decoupling (below), 380,000 years after the Big Bang
Temperature fluctuations in cosmic background radiation, measured by WMAP. Red corresponds to higher temperatures, blue to lower temperatures.

The main task of WMAP is to measure the temperature distribution of cosmic background radiation (the Planck radiation temperature is measured ). The measurements cover the entire sky. The measured temperature fluctuations reflect the distribution of matter in the universe at the point in time when radiation and matter were decoupled a few hundred thousand years after the Big Bang that occurred around 13.7 billion years ago . Overall, the radiation is extremely homogeneous, the fluctuations relative to the mean value, which is currently around 2.7 Kelvin, are around 5 · 10 −5 . The WMAP results are of paramount importance for cosmology :

  • For the composition of the universe, WMAP results in values ​​of 4.6% conventional matter , 23% dark matter and 72% dark energy (In the early phase of the universe the composition was different.)
  • The data suggests a universe with flat (Euclidean) spatial geometry.
  • The expansion of the universe continues forever because of the significant contribution of dark energy.
  • The age of the universe is estimated to be 13.7 billion years.
  • The first stars existed in the universe 13.5 billion years ago.

Successor Mission

A follow -up mission , the Planck Space Telescope , was launched in May 2009 with an Ariane rocket.


See also

References and footnotes

  1. WMAP Optics. NASA, April 16, 2010, accessed March 2, 2012 .
  2. Bernd Leitenberger: Special astronomical satellites. Retrieved March 2, 2012 .
  3. WMAP Mission Specifications. NASA, April 16, 2010, accessed March 2, 2012 .
  4. NASA's WMAP Project Completes Satellite Operations. NASA, October 6, 2010, accessed October 8, 2010 .
  5. Stephen Clark: WMAP finishes nine-year probe of infant universe. Spaceflight Now, October 6, 2010, accessed October 8, 2010 .

Web links

Commons : Wilkinson Microwave Anisotropy Probe  - Collection of images, videos and audio files