With the Kepler spacecraft secured tightly to the top of a Delta II rocket, technicians placed the two-piece nose cone around the observatory as they continued working toward a launch no earlier than March 6 from Cape Canaveral Air Force Station on Florida's Atlantic coast.

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.

It 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.

"Kepler is a critical component in NASA's broader efforts to ultimately find and study planets where Earth-like conditions may be present," said Jon Morse, the Astrophysics Division director at NASA Headquarters in Washington.

"The planetary census Kepler takes will be very important for understanding the frequency of Earth-size planets in our galaxy and planning future missions that directly detect and characterize such worlds around nearby stars."

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.