HAMPTON, Va. — NASA’s Langley Research Center here has been tapped to manage one of the U.S. space agency’s biggest climate research missions in recent years at a projected cost of $600 million to $800 million, according to NASA officials.

Dubbed the Climate Absolute Radiance and Refractivity Observation (CLARREO) mission, the observatory satellite effort is a joint NASA-National Oceanic and Atmospheric Administration mission given top priority by the National Research Council’s 2007 Earth science decadal survey. One of 17 missions recommended by the National Research Council (NRC), CLARREO is among four top-tier projects identified in the 10-year plan for space-based Earth observation.

The NRC envisions CLARREO as part of a national climate research program used for long-term study of changes in the Earth’s temperature. CLARREO’s role is to help develop a database that will enable scientists to more accurately predict climate change on an annual basis as well as decades into the future.

Although the decadal survey estimated  CLARREO as a $265 million undertaking comprising three small satellites, Langley engineers here have determined CLARREO’s science objectives can be better accomplished with just two satellites, albeit at a cost much higher than the decadal survey estimated.

“If you take a nominal-sized mission, these days those are between $500 [million] and $800 million,” said Stephen Sandford, NASA’s CLARREO mission formulation manager and director of Langley’s Systems Engineering Directorate. “And if you build two copies of those and fly those, you can see it’s not going to be $200 million. And we’re working very hard to keep it under $1 billion.”

CLARREO has been in the formulation phase at Langley for the past year, where Sandford is overseeing nearly 50 scientists and engineers working to define the NASA mission concept. CLARREO’s two spacecraft will fly three instruments each — one to measure emitted infrared radiation with high-spectral resolution, one to measure reflected radiation  and a GPS occultation antenna — to produce irrefutable climate records that will be used to support national and international policy.

“CLARREO is really targeted at observing a system of decade time scales, so that already brings in an incredible focus on accuracy beyond a normal mission,” said Bruce Wielicki, CLARREO’s science team lead. “Our accuracy will be anywhere from factors of two to 10 beyond what we normally put in space.”

CLARREO will also provide benchmark measurements for calibrating operational sensors, making it a cornerstone of NASA’s next-generation Earth observing system, Wielicki said. Using measurements tied to the National Institute of Standards and Technology (NIST), the data from the CLARREO observatory satellites will be used to calibrate other solar and infrared space-borne sensors, improving the accuracy of a wide range of sensors flying aboard U.S. Earth observing spacecraft.

“We’ve worked closely with NIST in all aspects of the calibration, using them to demonstrate the traceability of the measurements,” said CLARREO chief engineer Mike Gazarik. “That’s the thing that gives you confidence that your error margins are low enough to make policy decisions.”

Calibrating data to NIST standards will also mean that gaps in the instruments’ measurement records will be more tolerable.

“One of the great advantages of building these instruments so accurately and being able to trace measurements back to NIST standards is that you can tolerate a gap in your measurement record,” Sandford said. “If we’re successful in doing what we’re setting out to do, we don’t actually have to have the instruments flying in an absolutely continuous fashion with no break.”

Sandford emphasized that NASA’s CLARREO mission objectives are still being defined, and that the agency’s budget likely would be a constraining factor as the project moves ahead.

“We’re working very hard to constrain the scope of the mission, and that is critically important if you want to constrain the cost,” Sandford said. “One of our big jobs has been to control mission creep, and to do what’s called for in the decadal survey, but to be very clear and focused about what it is CLARREO is and what it is CLARREO is not.”

However, Sandford noted that U.S. President Barack Obama has indicated support for climate change research. This year his administration called for an additional $1.3 billion between 2009 and 2013 to accelerate work on the NRC’s top four missions, including CLARREO.

“If the administration is as committed to climate issues as they say, this will be a top-priority mission,” Sandford said. “This is a fundamental element of any attack on understanding climate change better.”

In the meantime, a formal decision on whether to embark on the CLARREO mission is expected by June 2010, followed by the release of an acquisition strategy not later than January 2011.

Currently, the Langley team is targeting a 2016 launch for CLARREO’s two observatory spacecraft, which are likely to be co-manifested aboard a single Delta 4 or Atlas 5 rocket with a dual-payload adapter system designed to put the satellites into different polar orbits.

Sandford said CLARREO will begin a multidecade climate-change record, taking global and zonal measurements with high-absolute accuracy “in continuous fashion” for at least a decade, though the mission duration is unclear.

“Right now the baseline is a three-year design with a five-year mission consumable lifetime,” Sandford said. “That’s a trade that’s under way right now to make sure we do the most cost-effective thing for the long term.”

CLARREO’s spacecraft platforms are likely to be procured from industry. Instrument development could be done by NASA in-house.

“The data, and the instruments that produce that data, that’s a more complicated question,” Sandford said. “All options are open, including having them built in industry or having them built in government labs. The key issue is this data is going to be used to set national and international policy, so the validation of that data, including the understanding of the instruments that produced it to a level required for policymaking, is a major factor in our acquisition strategy thinking.”

Langley’s last large mission, the U.S.-French Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), encountered some schedule delays and cost growth. Launched aboard a Delta 2 rocket with another cloud-monitoring satellite, CloudSat, in April  2006, CALIPSO’s launch took place some three years after its targeted date, due to a variety of issues ranging from a labor strike to failed communications links between France and the United States. The satellite is currently on orbit, studying the impact of clouds and aerosols on the Earth’s radiation budget and climate in formation with five other satellites flying in the so-called  A-Train constellation.