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Kepler's Search for Small Worlds Hampered by Noisy Electronics
MOUNTAIN VIEW, Calif. — In spite of electronic components that are creating extraneous noise on board the Kepler space telescope, NASA officials are confident the mission will be able by 2011 to either detect Earth-size planets or reveal that those planets are uncommon, said James Fanson, Kepler project manager at the Jet Propulsion Laboratory in Pasadena, Calif.
During an Oct. 29 meeting here, William Borucki, Kepler principal investigator at the NASA Ames Research Center, told members of the NASA Advisory Council that noise produced by three of the 42 amplifiers used to boost signals from the telescope’s charge-coupled devices was creating image artifacts, or features present in the Kepler data sets that reflect noise rather than an accurate picture of the stars.
“Those image artifacts are slowing our data analysis,” Borucki told the panel. “Mitigation work to flag and correct those problems will be complete in 2011.”
That does not mean, however, that Kepler will be unable to discover Earth-size planets before 2011, Fanson told Space News Nov. 5. Data obtained last summer when the Kepler team was using the telescope to observe a previously identified gas giant indicated that the instrument is sensitive enough to detect far smaller objects, including planets the size of Earth. What is more, those measurements were taken on the channel with the noisiest amplifier, Fanson said.
“Kepler measurements are at least 100 times more sensitive than measurements obtained from telescopes on Earth,” he said. The quality of the light curve is so extraordinary, in fact, that one mission official wept with joy when he saw the data, Fanson added.
Nevertheless, Kepler officials say it will take longer than previously anticipated to create computer programs capable of filtering out the systemic noise. “It does add difficulty and delays the ability to find small planets in short-period orbits,” Borucki said. “Future missions should look very carefully at the flaws in our electronic design. Some of the amplifiers we use oscillate. Different amplifiers would not do that.”
In recognition of the problem, Kepler prime contractor Ball Aerospace and Technologies Corp. is contributing “a small portion of our fee to help cover the
cost of the added software complexity,” John Troeltzsch, program manager for the Boulder, Colo.-based company, wrote in an e-mail to Space News. NASA and Ball Aerospace officials declined to comment on the amount of money Ball is contributing.
“Ball offered to return some money to the government to pay for software development to correct systemic noise sources because they are very committed to the success of the mission,” Fanson said.
Kepler, which was launched in March by a Delta 2 rocket, uses a 0.95-meter aperture photometer with a 1.4-meter primary mirror to study a swath of the Milky Way searching for planets roughly the size of Earth orbiting nearby stars in the habitable zone, the region where liquid water could remain on a planet’s surface. Engineers designed the telescope to detect extremely slight decreases in the brightness of stars because any dips in luminosity could indicate a planet is passing in front of the star.
Because Kepler was designed to detect faint changes in a star’s brightness, mission planners set stringent requirements on the telescope’s electronic noise levels. Based on measurements taken in space, Kepler is achieving its goal of limiting random noise fluctuations to a very low level, Troeltzsch said.
Systemic noise, however, which is created by the imperfect nature of any measuring device, is greater than expected. “We won’t get that fixed for a couple of years,” Borucki said. With additional funding, the Kepler data could be cleaned up more quickly, he added, but tight budgets make that prospect unlikely.
That computer processing work is going on at Ames, the NASA center responsible for overseeing Kepler data analysis, mission operations and ground system development. The Jet Propulsion Laboratory manages the project.
Kepler is an ambitious mission that has faced challenges along the way, including delays in manufacturing the precision optics, problems with its avionics system, management upheavals and budget cuts that pushed back the launch and trimmed the program’s promised mission duration. Kepler flight operations are scheduled to end in November 2013, although the NASA program plan includes a possible extension of the mission until May 2015.
NASA spent roughly $530 million on Kepler’s formulation and development, about 25 percent more than intended, according to a March report by the U.S. Government Accountability Office. A further $63 million was budgeted for mission operations.
In spite of the most recent noise issues, NASA officials say they are confident the Kepler mission will be successful. In January, mission officials plan to announce the discovery of large Jupiter-like planets at the American Astronomical Society meeting in Washington, Borucki said.
“All the data we are collecting from Kepler right now is good data,” Fanson said. “We need to process that data on the ground. Each time we develop systemic noise correction tools, we reprocess that data.”
It is also important to remember that the Kepler mission is not a race to identify new planets but rather an effort to monitor more than 150,000 stars in a swath of the Milky Way galaxy and measure the fraction of stars with Earth-like planets, Fanson said.
Even when scientists identify changes in the brightness of a star that may indicate a planet passing by, it will take months or years to confirm the existence of a new sphere. Scientists wait to observe at least three dips in light before they seek confirmation of their finding with ground-based telescopes, NASA officials said. Gaining access to those telescopes, which are in constant demand, presents mission officials with another challenge, Borucki said. NASA headquarters officials are helping to remedy that situation by giving the Kepler team priority access to the ground-based telescopes, he added.