PASADENA, Calif. -- NASA's Kepler mission to seek other Earth-like planets is undergoing final preparations for liftoff Friday, March 6, from Pad 17-B at Cape Canaveral Air Force Station in Florida. The spacecraft launch aboard a Delta II rocket has two windows of opportunity Friday, from 7:49 to 7:52 p.m. PST (10:49 to 10:52 p.m. EST) and 8:13 to 8:16 p.m. PST (11:13 to 11:16 p.m. EST).

Kepler is designed to find the first Earth-size planets orbiting stars in habitable zones -- regions where water could pool on the surface of the planets. Liquid water is believed to be essential for the formation of life.

"This mission attempts to answer a question that is as old as time itself -- are other planets like ours out there?" said Ed Weiler, associate administrator for NASA's Science Mission Directorate at NASA Headquarters in Washington. "It's not just a science question -- it's a basic human question."

After the clock ticks down to liftoff, the Delta II's first-stage main engine and six strap-on solid rocket boosters will ignite. Three remaining boosters will ignite 65.5 seconds later, and the first-stage main engine will continue to burn for 4.5 minutes. The second stage will then ignite, carrying Kepler into a circular orbit about 185 kilometers (115 miles) above Earth less than 10 minutes after launch. After coasting for 43 minutes, the second-stage engine will fire again, followed by second-stage shutdown and separation. The third stage will then burn for five minutes.

Sixty-two minutes after launch, Kepler will have separated entirely from its rocket and will be in its final Earth-trailing orbit around the sun, an orbit similar to that of NASA's Spitzer Space Telescope. "We are very excited to see this magnificent spacecraft come to life when it reaches space," said James Fanson, Kepler project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

After a commissioning period lasting about two months, Kepler will begin its job of staring at more than 100,000 stars for three-and-one-half years, looking for planets. Its isolated perch behind Earth will give the telescope an unobstructed view of a single, very large patch of sky near the Cygnus and Lyra constellations.

"We will monitor a wide range of stars; from small cool ones, where planets must circle closely to stay warm, to stars bigger and hotter than the sun, where planets must stay well clear to avoid being roasted," said William Borucki, science principal investigator for the mission at NASA's Ames Research Center at Moffett Field, Calif. Borucki has been working on the mission for 17 years. "Everything about the mission is optimized to find Earth-size planets with the potential for life, to help us answer the question -- are Earths bountiful or is our planet unique?"

Kepler will find planets by looking for periodic dips in starlight. Planets that happen to pass directly in front of their stars from Earth's point of view cause the stars to dim by almost imperceptible amounts. Kepler's powerful camera, the largest ever flown in space, can see the faintest of these "winks."

"Trying to detect Jupiter-size planets crossing in front of their stars is like trying to measure the effect of a mosquito flying by a car's headlight," said Fanson. "Finding Earth-sized planets is like trying to detect a very tiny flea in that same headlight."

If the mission does find Earth-size planets in the habitable zones of stars, it should find them first around stars that are smaller than our sun. This is because the habitable zone is closer for small stars; planets circling in this region would take less time to complete one lap and, theoretically, less time for Kepler to find them and for other ground-telescopes to confirm their existence. Any Earth-size planets orbiting in the habitable zones of stars like our sun -- the true Earth analogs -- would take at least three years to be confirmed.

Kepler is a NASA Discovery mission. The NASA Ames Research Center, Moffett Field, Calif., is the home organization of the science principal investigator and is responsible for the ground system development, mission operations and science data analysis. Kepler mission development is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Ball Aerospace & Technologies Corporation of Boulder, Colo., is responsible for developing the Kepler flight system and supporting mission operations.

JPL is a division of the California Institute of Technology in Pasadena.

For more information about the Kepler mission, visit: http://www.nasa.gov/kepler .