Kepler On Track After Successful Launch
Michael Mecham mecham@aviationweek.com 
A trouble-free countdown and nominal launch into clear skies sent NASA's Kepler mission to find planets outside our Solar System on its way March 6 from Cape Canaveral Air Force Station.
The 2,320-pound spacecraft, built by Ball Aerospace, was lifted into an Earth-trailing orbit by a United Launch Alliance Delta II from Cape Canaveral Air Force Station, Fla.
"With the successful launch we are now positioned to turn on the photometer and start collecting calibration data from our 95 megapixel camera," said John Troeltzsch, Ball Aerospace program manager. "That means we're one step closer to opening the dust cover and allowing the light from 4.5 million objects to pass through the telescope, which is a very rewarding place to be."
Kepler carries a single instrument: a 1.4 meter (4.6-foot) Schmidt telescope and a photometer so sensitive it can detect variations in light at 20 parts per million. Forty-two charge-coupled devices combine to produce the 95 million pixels referred to by Troeltzsch.
In a steady stare, Kepler will concentrate on 100,000 Sun-like stars amidst some 4.3 million in the Cygnus-Lyra region of the Milky Way. Its goal is to catch the faint "wink" of planets as they transit in front of their host star, causing its brightness to dim slightly.
Astronomers have discovered more than 300 planets orbiting stars outside the solar system, but none of these so-called exoplanets seen so far are the right distance from their host star to support life. Only a handful have been near Earth's size. With its superior optics, Kepler is likely to spot numerous exoplanets, but how many of them will be in a "habitable zone" -- the correct distance from their host star to have water and the potential for life -- is an open question.
The liftoff required the three-stage Delta II, flying in a 7925-10L configuration, to lift Kepler across the South Atlantic. The liquid-fueled Pratt & Whitney RS27A first stage was supplemented by nine Alliant Techsystem strap-on solid rockets. It was the 139th successful Delta II launch over the past 20 years. Kepler will require a 60 day telescope and instrument checkout before it can become operational.
The spacecraft, which stands 15.3 feet tall and is 9 feet in diameter, will slowly distance itself from Earth, reaching an operating position of 0.1 astronomical units -- about 9 million miles -- behind the planet.
At that distance Earth's gravitational tug won't upset its instruments and the planet itself won't occlude the telescope's view. It will keep drifting on its 3.5-year nominal mission, orbiting the sun every 373 days. It has sufficient fuel for six years.
Artist's concept: NASA
