The payload fairing, also called a shroud, is a protective cover that shields the spacecraft as the rocket zooms thorugh the lower atmosphere. Heat builds up on the surface of the rocket during the acceleration into space because of the friction with the air. The fairing is split in two pieces that open and fall away when the rocket reaches layers of very thin air, which do not threaten the spacecraft. This is the first mission with the ability to find planets like Earth — rocky planets that orbit sun-like stars in a warm zone where liquid water could be maintained on the surface. Liquid water is believed to be essential for the formation of life. The Kepler spacecraft will watch a patch of space for 3.5 years or more for signs of Earth-sized planets moving around stars similar to the sun. The patch that Kepler will watch contains about 100,000 stars like the sun. Using special detectors similar to those used in digital cameras, Kepler will look for slight dimming in the stars as planets pass between the star and Kepler. The Kepler's place in space will allow it to watch the same stars constantly throughout its mission, something observatories like Hubble cannot do.
(Source: NASA Kepler site. Photo: Workers attach the two-part payload fairing over the Kepler spacecraft in preparation for launch. The cover, designed to jettison shortly after launch, protects the spacecraft from the friction and turbulence as it speeds through the atmosphere during launch. Image credit: NASA/Jack Pfaller)