Star Gazing Mission

Spacecraft to look for planets

One of the most boring spacecraft ever to fly is being built in Boulder, with the goal of answering one of humanity's most exciting questions:

Are we alone?

NASA's Kepler mission, a $500 million effort on the drawing board for 15 years, will stare into space, at a star field the size of an open hand at arm's length, for at least four years. It will blink only a few hours a month to turn and relay data back to Earth.

NASA's Kepler Spacecraft

NASA's Kepler spacecraft , a $500 million craft being built by Ball Aerospace & Technologies Corp. in Boulder, is scheduled for launch Nov. 1, 2008. It will stare at 100,000 stars for four years or longer in an effort to spot the subtle dimming caused by distant planets. Photo courtesy NASA

Kepler, being built by Ball Aerospace & Technologies Corp., will seek to add important members to the count of more than 200 planets discovered near distant stars - called extrasolar planets or exoplanets. Specifically, it's looking for Earth-like planets light-years away.

"Earths" are much too faint to see directly from such distance, so Kepler will focus on their stars. The spacecraft , scheduled for launch Nov. 1, 2008, will keep tabs on 100,000 of them near the constellation Cygnus.

Kepler will detect changes in brightness as subtle as one-tenth of 1 percent, the amount a sun-like star's light dims when a planet the size of Earth passes by. The clearest window blocks 10 times more light.

The mission will use Johannes Kepler's laws of motion to determine how far from the star the planet orbits, as well as how fast. Based on the computer models of solar-system formation and what's been discovered so far, Kepler scientists expect to find at least 50 or 60 terrestrial planets - and as many as hundreds - in a habitable zone such as Earth's, where temperatures let life-giving water flow.

"Kepler's going to test predictions we've made and, in some respects, it's going to open up other realms for us to think about," said University of Colorado postdoctoral researcher Sean Raymond, whose computer models suggest Earth-like planets are common.

No such planet has ever been detected. The implications of such a discovery extend from science to philosophy and, possibly, theology. Nicolaus Copernicus called into question the idea of the sun revolving around Earth; Kepler could do the same for an Earth-centric view of life itself.

"If we find a lot in the habitable zone, life is probably ubiquitous in the universe," said William Borucki, the NASA Ames Research Center scientist leading the mission.

If not, Borucki says, there will be little need for a Star Trek Enterprise: There's probably no one to visit.

A 'camcorder in space'

Borucki spoke last weekend at a workshop on extrasolar planets sponsored by CU's Laboratory for Atmospheric Space Physics, which will be handling mission operations for Kepler. He said Kepler is simple in principle - "a camcorder in space." But simple does not mean easy, he is quick to add.

The spacecraft will trail Earth in its orbit around the sun, traveling through space at 67,000 mph and about a million miles behind the planet at first. The gap will stretch a bit each year until Earth overtakes it 52 years after launch.

To ensure steady exposure to starlight, the spacecraft must have pointing accuracy to nearly a millionth of a degree. A laser with such accuracy could paint a penny from nearly 700 miles away. Once a month, Kepler must turn to blast gigabytes of data back to Earth as quickly as possible, then return to its steady gaze.

"The stability requirements on Kepler are extreme compared to any other space-based mission," said Monte Henderson, Ball Aerospace's program manager for the mission.

About 200 Ball Aerospace workers are involved in the mission, Henderson said. Kepler's 1.4-meter-wide primary mirror awaits its silver coating in March. The barrel of the 15-foot-long telescope is scheduled for delivery in March or April, he said.

Kepler is monitoring an enormous swath of sky - tens of thousands of times more expansive than the Hubble Space Telescope's field of view. It requires the biggest image sensor ever in deep space. It's a $6 million square foot of optoelectronics, Borucki said.

"You can go down to Best Buy and get your 5-megapixel digital camera," Henderson said. "We're building a 95-megapixel digital camera."

Kepler won't be sending back pretty pictures. It is a photometer, designed to measure stellar brightness. Its images will be blurry, 40 times less sharp than Hubble's.

That's intentional, Borucki said, so more potent stars don't saturate the sensor, rendering brightness a mystery and erasing hope of detecting a planet 's crossing.

Fifth time's a charm

Borucki, 68, designed heat shields for the Apollo program and instruments to observe lightning on Jupiter. In 1984, he published his first paper on the possibility of discovering planets by observing their star's dimming during transit. In 1992, Borucki first proposed the mission that would become Kepler.

Among the more than 20 scientists on that team was Carl Sagan, the Cornell University planetary scientist and author who recognized Kepler's importance in rooting out life in the cosmos.

Sagan stayed through NASA's 1992 rejection, as well as the 1994 and 1996 rejections, Borucki said.

"He said in 1996 he wanted to continue," Borucki said. "Three weeks later, he died."

Ball Aerospace stuck with Borucki as well - no small commitment given each proposal's overall cost of about $250,000, he said.

In 1998, Kepler was unsuccessful again.

But each time, Borucki said, NASA's selection committee offered suggestions the team later incorporated. In 2000, NASA selected Kepler for further study, and in late 2001 gave it the go-ahead.

Technical and scientific excellence played a role in Kepler's advance from concept to reality. But Borucki said it was more fundamental human qualities - persistence and the ability to learn from rejection - that proved decisive. That, he said, and the importance of the scientific problem.