(CNN) -- The U.S. space agency NASA will launch its first ever mission Friday to find Earth-like planets in our region of the Milky Way.
NASA's confident Kepler will find Earth-sized planets in our region of the Milky Way -- if they are there.
Scientists will be holding their breath as the Kepler spacecraft -- mounted with the biggest telescope ever to be launched into space -- lifts off from the Cape Canaveral Air Force Station in Florida.
"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?," said the man leading the mission, Bill Borucki, science principal investigator for the mission at NASA's Ames Research Center.
Scientists will be hoping for more success than last week when NASA's $273 million dollar Orbiting Carbon Observatory failed to reach orbit and plunged into the ocean within minutes of its launch. Read about the failed launch
The Kepler spacecraft has just two three-minute windows of opportunity to blast off on Friday, from 10.49pm to 10.52pm EST, or slightly later at 11.13 to 11.16pm EST.
If the launch goes to plan, Kepler will spend the next three and a half years monitoring more than 100,000 stars in a single patch of star-rich sky in "our region of the Milky Way galaxy," near the Cygnus and Lyra constellations.
Its activities will be restricted to the "habitable zone," where scientists think there's the best chance of finding life.
"The habitable zone is where we think water will be," explains Borucki. "That zone is not too close to the star because it's too hot and the water boils, and not too far away where the water is condensed and ice-covered with glaciers."
"It's the goldilocks realm, not too hot, not too cold, just right for life," he added.
The telescope won't take photos like NASA's Hubble or Spitzer infrared telescopes. It's fitted with a specially-designed telescope called a photometer or light meter designed to detect small variations in the brightness of stars.
"What we aim to do is to measure the brightness of stars very accurately for a very long period of time without blinking," says Patricia Boyd, a NASA scientist on the Kepler program.
"When the planet passes in front of the star, the light output from the star is going to dim just a little bit, that star is going to blink for about 12 hours," she said.
The size of the "blink" will determine the planet's orbital size. That information will be used to calculate the planet's mass and temperature.
"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 Kepler project manager James Fanson.
"Finding Earth-sized planets is like trying to detect a very tiny flea in that same headlight," he added.
NASA is confident Kepler will detect Earth-like planets -- if they are there. And, the space agency says if Earth-size planets are common, Kepler should find hundreds of them.
However, the space agency has no plans to mount any manned missions to planets showing life; the closest star is four light years away and would take thousands of years to reach, even in the fastest of today's rockets.
The more likely response would be to further investigate the planet's atmosphere to determine whether it's capable of sustaining life. NASA's planning two missions that may be able to do just that: the Space Interferometry Mission (SIM) and the James Webb Space Telescope (JWST).
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