BOULDER,
Colo. - NASA's Kepler space telescope, a
sharp-eyed spacecraft designed to hunt for Earth-like planets, is ready to ship
out for an early March launch.
Ball
Aerospace & Technologies Corp. - the Boulder, Colo.-based NASA contractor
responsible for developing the Kepler flight system and supporting mission
operations - recently completed the spacecraft's final pre-ship checkout and delivered the spacecraft to Cape
Canaveral Air Force Station, Fla., for a March 5 liftoff on a Delta
2 booster.
"In order
to find Earth-sized planets, you need to stare at the same place in space and
look for dips in the light curve," said John Troeltzsch, Ball Aerospace program manager for civil space systems. Kepler initially will look at 140,000 stars, with project
scientists paring the field of study down to 100,000 stars, Troeltzsch said. Building the NASA Discovery-class
Kepler has meant harnessing a trio of key capabilities: pointing accuracy, a very large field of view and
low-noise electronics to maximize the ability to read data from the sensitive
detection system.
"It's a
very sophisticated machine," Troeltzsch told Space News in a Dec. 16 interview. The technology to
undertake Kepler was not available until just a few years
ago, he said, "so we really are at the right place at the right time."
Part of
that opportune timing has been the increasing number of
extrasolar planets detected to date, most of which have been at least the size of Jupiter.
Over its three and a half year mission, Kepler will attempt to detect planets 30 to 600 times
smaller than Jupiter. Given that Earth-sized worlds do exist around stars like the sun, Kepler is expected to be the
first to find them, and the first to measure their frequency. Locating
rocky worlds like Earth, including those that lie in a star's habitable
zone, could mean identifying planets where liquid water, and perhaps life,
could exist.
Using a
0.95-meter diameter telescope and an array of 42 charge-coupled devices - the
light-sensitive microchips at the heart of the most common digital cameras - Kepler will measure the change in brightness
that occurs when a planet transits across the face of its parent star.
From that light fluctuation in starlight - and time between transits -
scientists can determine the size of the planet, the size of the planet's orbit, and
even approximate the planet's temperature.
"What we're
interested in are light curves over time," Troeltzsch said. "There are no
pretty pictures" like Hubble Space Telescope images or Spitzer Space Telescope
infrared observations, he said, but Kepler is perfectly optimized for its
search duties.
"I grew up
watching 'Star Trek,' so I'm confident that there are a lot
of planets out there," Troeltzsch said. "If we get no result, that's going to
be just as profound."
Exo-planet research on the rise
Following
launch, Kepler will be nudged into an Earth-trailing
heliocentric orbit with a period of 372.5 days. Once on duty and collecting
data, the spacecraft rolls every 30 days to align a fixed high-gain antenna to
download that month's gathered readings to NASA's Deep Space Network. Kepler
also carries out a 90-degree roll every 90 days to keep its solar panels always
pointed at the sun, Troeltzsch noted.
Kepler data
is to be relayed to the Data Management Center at the Space Telescope Science
Institute in Baltimore, with science data analysis carried
out by the NASA Ames Research Center at Moffett Field, Calif.
The search
for exo-planets in the last decade has escalated from something hardly conceivable to an active and enthusiastic scientific
endeavor, said Bill Borucki, the science
principal investigator for the Kepler Mission at NASA Ames.
Kepler has
taken a long road to reach the launch pad.
Using the
transit technique for spotting Earth-sized planets by a spacecraft was first
suggested by Borucki in 1984.
"I pursued
this for 14 years ... I did get an award for being persistent," Borucki said,
recalling the critics who told him what he was proposing would never work. But time, technology and perseverance eventually won out, he said, with Kepler gaining flight approval
as a NASA Discovery mission in late 2001.
However, the price tag for the
Discovery-class mission has risen several times since its 2001
selection, with the total cost of the mission rising more than 20 percent,
topping $550 million before the team asked for an additional $50 million in the spring of 2007.
NASA's associate administrator for science at the time, Alan Stern, directed the Kepler
team to find a way to deliver the mission without a new cash infusion or face cancellation.
"We were determined to get the
program back on track. And that's exactly what we did. It was a very
difficult period. There was a lot of pressure," Troeltzsch said. The re-plan Stern set in motion was a
"catalyzing event," he said, causing a flurry of management changes at Ball, Ames and elsewhere.
"We held to the Stern agreement of
no cost increase ... no more money, and that's what we did," Troeltzsch said.
"Stability is a large part of it ... of suppliers and funding. But you have to
live in the world you live in."
Kepler-ready students
The Laboratory for Atmospheric and
Space Physics (LASP) at the University of Colorado here is
under contract to Ball Aerospace to operate Kepler. The mission operations center will be
staffed by a mix of students and professionals from the university and technicians from nearby
Ball Aerospace.
"Our job is
to do on-orbit commanding," said Bill Possel, director of mission operations and
data systems at LASP. LASP is currently flying four Earth-orbiting satellites,
he said: the Aeronomy of Ice in the Mesosphere; the Solar Radiation and Climate
Experiment; the Ice, Cloud, and land Elevation Satellite (ICESat); and the
Quick Scatterometer.
In terms of
the challenge presented by operating Kepler, Possel said it is "maybe a notch
above" the level of complexity of ICESat.
Possel said
a compliment of eight to 10 students are presently considered
Kepler-ready, in addition to a mix of professionals from the
university and Ball. Using LASP for Kepler mission operations not only
saves NASA money, he said, it also provides an invaluable,
career-enhancing opportunity for students.
"We're the
first line of defense for the spacecraft, instrument health and safety," Possel
added. "It's a win-win ... for the science team because it's less expensive and
the aerospace industry wins because you get a trained engineer that has
hands-on experience for the work force."
This all
adds up to getting more science at lower cost, a LASP credo, Possel said.
"For the
students, Kepler is so cool," Possel said. "To look for habitable-sized planets
... and doing it as a student. The science is complex, but not complex enough
that you can't explain it to your parents."
Spotter-scope capability
The ongoing search for exo-planets is an
exciting field, said James Fanson, Kepler project manager at NASA's Jet Propulsion
Laboratory in Pasadena, Calif.
"Kepler
fits very timely into this growing field by giving us an opportunity for the
first time to determine how frequently Earth-size planets form and orbit in a
habitable zone around other stars," Fanson said. "We're focused on trying to
find Earth analogs. So we've designed Kepler specifically to detect planets
that are the size of the Earth and even slightly smaller."
Kepler will serve as a spotter
scope, Fanson said, finding candidate planets that can then be targeted by
Earth-based observations to rule out false-positive detections.
Of course,
Kepler could come up dry in its hunt for Earth-sized planets circling distant stars. Conversely,
there exists the prospect of discovering scads of Earth-sized planets, thereby
adding more gusto to the belief that Earth is part of a rich tapestry of
habitable worlds.
"Personally,
the way I think about it is that we just have no data. We just don't know the
answer," Fanson said. "We're simply privileged to live at a time when we have
the technology and the science to actually answer that question finally for
humankind."
Borucki of NASA Ames said Kepler is a step forward, offering a
spotter-scope capability that will support future decision-making about building more powerful
spacecraft to home in on candidate worlds capable of
sustaining life.
"We need to know if this is a wild
goose chase or not," Borucki added. "We're at a bifurcation point and Kepler is
just a step, one step in many steps as we explore the galaxy."
Leonard
David has been reporting on the space industry for more than four decades. He
is past editor-in-chief of the National Space Society's Ad Astra and Space
World magazines and has written for SPACE.com since 1999.
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