Planet-Hunting Spacecraft To Look For Earth-Sized Worlds

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 is preparing to deliver 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.”