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| WMAP (spacecraft) | |
|---|---|
| Name | WMAP |
| Names list | Wilkinson Microwave Anisotropy Probe |
| Mission type | Astrophysics, Cosmology |
| Operator | NASA / Princeton University |
| Cospar id | 2001-030A |
| Satcat | 26933 |
| Mission duration | 9 years (operational) |
| Manufacturer | Princeton University, NASA Goddard Space Flight Center |
| Launch date | 2001-06-30 |
| Launch rocket | Delta II |
| Launch site | Cape Canaveral Air Force Station |
| Orbit reference | Sun–Earth L2 |
| Instruments | 5 frequency bands (K, Ka, Q, V, W) |
WMAP (spacecraft) was a NASA astrophysics satellite mission led by Princeton University in collaboration with Goddard Space Flight Center and other institutions to map the temperature anisotropies of the cosmic microwave background across the full sky. Building on earlier measurements from COBE and contemporaneous with experiments like BOOMERanG and MAXIMA, WMAP produced high-fidelity all-sky maps that constrained fundamental parameters of the Big Bang cosmological model and influenced subsequent missions such as Planck (spacecraft). The mission operated from a halo orbit about Sun–Earth L2, delivering publicly archived data used by researchers at Harvard University, MIT, Caltech, and numerous observatories worldwide.
WMAP, formally the Wilkinson Microwave Anisotropy Probe, was named in honor of cosmologist David Wilkinson. The satellite measured fluctuations in the cosmic microwave background across five frequency bands (K, Ka, Q, V, W) to separate primordial signal from foreground emission such as from Milky Way synchrotron, free–free, and dust radiation. WMAP’s precision angular power spectra of temperature and polarization anisotropies enabled tight constraints on parameters including the Hubble constant, baryon density, dark matter density, spectral index, and optical depth to reionization, influencing theoretical work from proponents at Institute for Advanced Study to teams at University of Cambridge and Max Planck Institute for Astrophysics.
The primary objective was to produce full-sky, high signal-to-noise maps of the cosmic microwave background to test predictions of the Lambda-CDM model and measurements of inflationary perturbations. Specific aims included measuring the angular power spectrum over multipoles from the Sachs–Wolfe plateau through the first several acoustic peaks, quantifying temperature–polarization cross-correlation, and providing robust estimates of cosmological parameters used by theorists at institutions such as Princeton, Columbia University, and University of Chicago. WMAP sought to reduce systematic errors that limited earlier missions like COBE while complementing ground-based interferometers at Atacama and balloon experiments supported by NASA. The mission also targeted mapping Galactic foregrounds to support research at European Space Agency and other space agencies.
WMAP was a differential microwave radiometer satellite built under leadership at Princeton University with hardware and systems engineering contributions from Lockheed Martin and NASA Goddard Space Flight Center. The instrument suite consisted of ten differential radiometers in five frequency bands (K band ~23 GHz, Ka ~33 GHz, Q ~41 GHz, V ~61 GHz, W ~94 GHz). Detectors were pseudo-correlation radiometers using high-electron-mobility transistor amplifiers developed with partners at RCA-legacy groups and tested at facilities linked to Jet Propulsion Laboratory. The optical system used back-to-back Gregorian reflectors and a passive thermal design to achieve stability, with attitude control supplied by reaction wheels and star trackers comparable to those used on missions like Hubble Space Telescope. Data handling systems downlinked to Deep Space Network stations and were processed by teams at Princeton University and participating centers.
Launched on a Delta II from Cape Canaveral Air Force Station on 2001-06-30, WMAP transferred to a halo orbit around Sun–Earth L2 where thermal and stray-light conditions were favorable for microwave observations. The operations team included engineers and scientists from NASA and academic partners who scheduled continuous sky scans with a scanning strategy that minimized 1/f noise and systematic offsets. Routine calibrations used observations of Jupiter and the CMB dipole associated with the Solar System motion relative to the CMB rest frame. The mission produced successive data releases (first-year, three-year, five-year, seven-year, nine-year) with incremental improvements in systematics and analysis by groups at University of California, Berkeley and University of Wisconsin–Madison.
Raw telemetry were converted to calibrated time-ordered data, with foreground separation algorithms developed by teams at Princeton, NASA Goddard, and collaborating universities to isolate CMB anisotropy from Galactic emission and extragalactic point sources such as Seyfert galaxies and radio galaxies. Power spectrum estimation used maximum-likelihood and pseudo-Cl methods applied by researchers at Rutgers University and Lawrence Berkeley National Laboratory. Cosmological parameter estimation employed Markov Chain Monte Carlo techniques implemented by groups at LAMBDA consortium and analyzed in conjunction with external datasets from Type Ia supernova surveys, Baryon Acoustic Oscillations studies by teams at Sloan Digital Sky Survey, and local H0 measurements from the Hubble Space Telescope Key Project.
WMAP established that the universe is spatially flat to high precision, measured the baryon-to-photon ratio consistent with Big Bang nucleosynthesis predictions, and determined the composition of the universe: roughly 4–5% baryonic matter, ~23% cold dark matter, and ~72% dark energy consistent with a cosmological constant. The mission detected the acoustic peak structure predicted by adiabatic perturbation models of inflationary cosmology and provided evidence for a nearly scale-invariant primordial power spectrum characterized by a spectral index less than but close to unity. WMAP measured the epoch of reionization, indicating substantial star formation by redshift z ~10, informing studies at Keck Observatory and Spitzer Space Telescope. Polarization detections of the temperature–E-mode cross-correlation constrained models of early-universe physics considered by theorists at CERN and Perimeter Institute.
WMAP transformed precision cosmology by moving cosmological parameter estimation into a precision era that guided theory and observation across institutions like Stanford University, University of Oxford, and Princeton University. Its publicly released datasets fostered widespread analysis, sparking follow-up missions such as Planck (spacecraft) and ground facilities including Atacama Cosmology Telescope and South Pole Telescope. WMAP’s results influenced Nobel-level recognition of contributions to observational cosmology and shaped research programs at agencies such as NASA and European Space Agency, while training generations of researchers at universities worldwide. Category:NASA satellites