A new space station sensor that will lay the foundation for future long-term observations of Earth’s climate is moving ahead, despite repeated attempts by President Donald Trump’s administration to kill it. Yesterday, amid a torrent of other news, NASA quietly announced it had awarded a $57 million contract to start building the instrument, which is scheduled to launch to the International Space Station (ISS) early next decade.
Last year, the Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder was one of several earth science missions targeted by the new administration for cancellation. Although Congress ultimately rejected that request, it prompted NASA to halt work on the project in May 2017. But now, the agency said, it has awarded a contract to the Laboratory for Atmospheric and Space Physics at the University of Colorado (CU) in Boulder, to build CLARREO Pathfinder’s primary component, a specialized camera.
The revived mission joins several other earth science programs in surviving near-death threats. The Orbiting Carbon Observatory-3, which the Trump administration also proposed for cancellation, is now set to launch to the ISS in February 2019. Congress has drafted, though has not yet passed, language reinstating NASA’s Carbon Monitoring System. And the agency’s administrator, Jim Bridenstine, has pledged to follow the guidance of the earth science decadal survey, a consensus wish list of NASA missions compiled by earth scientists that has endorsed many of the missions targeted for cancellation or budget cuts.
CLARREO Pathfinder is a whole different type of earth science mission, says Bruce Wielicki, a climate scientist at NASA’s Langley Research Center in Hampton, Virginia. Rather than collecting its own observations, CLARREO Pathfinder, which will be mounted on the space station, will provide highly accurate calibration for the existing fleet of Earth-observing satellites, drastically reducing measurement uncertainties by up to a factor of 10. "We could literally be calibrating hundreds of instruments up there," Wielicki says.
Such calibration could help fill a gap in climate science. Although researchers have documented clear signs of climate change in air and ocean temperature records, they don’t have as clear a picture of how much energy, in the form of absorbed and reflected sunlight, is entering and leaving Earth at the top of the atmosphere. A fleet of instruments on several different U.S. satellites, called the Clouds and the Earth's Radiant Energy System (CERES), now collect these energy measurements. But, like most space-based assets, they can degrade because of exposure to the sun, leaving it difficult to tease out climate signals, which are minute compared with overall energy flows.
CLARREO Pathfinder will deploy a new camera that can capture nearly the entire range of reflected light in 640 different spectral channels. It will be able to move on two different axes, to mimic the observing angles of instruments it will calibrate. And it will pivot every week or so to calibrate itself against the known spectrum of the sun by staring directly at it—a feat that would burn out the optics of most other instruments. CLARREO Pathfinder will be able to provide these calibrations to instruments that use reflected sunlight monitor a wide variety of phenomena, including CubeSat imagers that track changes in land use and rainfall detectors on advanced weather satellites.
The mission's survival is welcome news, says Elizabeth Weatherhead, an atmospheric scientist at CU. "This is something the global scientific community is looking toward to as a fundamental part of our observing approach. Removing inherent uncertainty is critical for our long-term records. If we are looking for a 0.2° per decade change and our measurement uncertainty is a half a degree, we have to monitor for 25 years just to start to pull away from the measurement uncertainty."
Wielicki came to CLARREO Pathfinder after previously leading CERES, a 20-year-old mission with instruments that measure both reflected light and infrared heat. He remains most excited about how CLARREO Pathfinder, and any successors, will benefit CERES's long-term measurements of how clouds respond to climate change, one of the primary drivers of uncertainty about the speed of warming. CLARREO Pathfinder, he says, will allow them to "measure things 30 to 50 years more quickly with this accuracy."
Although the near-term future of CLARREO Pathfinder seems secure, NASA has no current plans for its full-fledged follow-up. "We're in limbo right now," Wielicki says. The newest decadal survey acknowledges—but does not give the highest priority to—the types of observations CLARREO Pathfinder would make. Still, Wielicki hopes that by demonstrating the instrument's effectiveness and reducing costs, NASA could build a satellite follow-on under a lower-cost mission line. If not, he says, another space agency, such as China’s, which is building its own CERES-like instruments, could take up the cause.