Wilkinson Microwave Anisotropy Probe - Launch, Trajectory, and Orbit

Launch, Trajectory, and Orbit

The WMAP spacecraft arrived at the Kennedy Space Center on April 20, 2001. After being tested for two months, it was launched via Delta II 7425 rocket on June 30, 2001. It began operating on its internal power five minutes before its launching, and so continued operating until the solar panel array deployed. The WMAP was activated and monitored while it cooled. On July 2, it began working, first with in-flight testing (from launching until August 17), then began constant, formal work. Afterwards, it effected three Earth-Moon phase loops, measuring its sidelobes, then flew by the Moon on July 30, enroute to the Sun-Earth L₂ Lagrangian point, arriving there on October 1, 2001, becoming, thereby, the first CMB observation mission permanently posted there.

The spacecraft's location at Lagrange 2, (1.5 million kilometers from Earth) minimizes the amount of contaminating solar, terrestrial, and lunar emissions registered, and thermally stabilizes it. To view the entire sky, without looking to the sun, the WMAP traces a path around L₂ in a Lissajous orbit ca. 1.0 degree to 10 degrees, with a 6-month period. The telescope rotates once every 2 minutes, 9 seconds" (0.464 rpm) and precesses at the rate of 1 revolution per hour. WMAP measures the entire sky every six months, and completed its first, full-sky observation in April 2002.