SAN FRANCISCO — In spite of widespread agreement among international organizations on the need for more accurate climate change forecasts, two satellite missions designed to provide precise measurements of key climate variables have struggled for years to obtain funding.
In an attempt to revive the stalled missions, researchers leading the United Kingdom’s Traceable Radiometry Underpinning Terrestrial and Helio Studies (TRUTHS) mission and the U.S. Climate Absolute Radiance and Refractivity Observatory (CLARREO) are exploring international partnerships and devising strategies to make the missions more affordable.
The team behind the TRUTHS mission, which includes the U.K.’s National Research Laboratory, Imperial College London, Rutherford Appleton Laboratory and Surrey Satellite Technology Ltd. (SSTL), is drafting plans to for a scaled-down version of the mission with funding from the U.K. Space Agency’s Center for Earth Observation Instrumentation.
“If we can get something launched quickly and prove unequivocally it does what we say it does, it helps to turn TRUTHS from a science mission into a potential operational mission,” said Nigel Fox, head of Earth observation and climate at the National Physical Laboratory.
The goal of TRUTHS is to measure key climate variables, including the sun’s energy, clouds and solar energy reflected by Earth, 10 times more accurately than existing space-based observations. TRUTHS seeks to achieve that high level of accuracy by launching a single spacecraft that includes Earth observation sensors as well as a miniature standards laboratory designed to calibrate instruments to measure accuracy according to the International System of Units.
Half TRUTHS
TRUTHS team members are discussing concepts for a scaled-down version of TRUTHS, known as TRUTHS-Lite. “It is too early to say exactly what the new mission will entail since we are still at an early stage of concept development,” said Mike Cutter, head of SSTL’s optical payload group. However, the team is evaluating ways to simplify mission elements to make them more affordable and reliable, Cutter said.
Their goal is to create a TRUTHS-Lite mission that would obtain many of the same benefits of the full-scale mission at a fraction of the cost. For example, on-board sensors could be designed to gather spectral data in the range from visible light to short-wave infrared, instead of also measuring ultraviolet radiation, Fox said. TRUTHS-Lite also could be designed for a mission life of three years instead of five or six years as planned for the original mission, Fox said.
Similarly, NASA scientists are looking for ways to reduce the cost of CLARREO, a mission listed as a top priority in the National Research Council’s 2007 Earth science decadal survey. CLARREO passed a NASA mission concept review in November 2010 and appeared to be on track for 2017 launch but was halted in 2011 due to funding constraints.
Like TRUTHS, CLARREO includes on-board calibration equipment and instruments to measure reflected solar energy. In addition, CLARREO features GPS radio occultation receivers to monitor atmospheric pressure, temperature and water vapor as well as infrared spectrometers designed to gather data “across the entire spectrum from the ultraviolet to the far infrared,” said Bruce Wielicki, CLARREO science team leader.
To lower CLARREO’s price tag, mission planners are studying whether CLARREO instruments could operate onboard the international space station instead of on dedicated satellites as originally proposed. Placing the instruments on the space station would achieve more than 70 percent of the mission’s science objectives for approximately 40 percent of the cost, Wielicki said. However, NASA’s current budget does not include funding to carry out the plan, he added.
Until money is available, the CLARREO team will continue to refine the scientific objectives of the mission and test mission components to ensure they will perform as intended after launch. “We remain confident in the feasibility, the critical scientific contributions and the readiness of CLARREO to carry out those contributions once the nation is ready to build it,” Wielicki said.
In addition to seeking funding from the U.K. Space Agency, TRUTHS mission planners are eager to establish bilateral or multilateral partnerships. “We are open to working with anyone because it is imperative that this mission happens,” Fox said. CLARREO and TRUTHS mission teams already share all science and engineering studies, Wielicki said.
With their wide range of complementary observations, the CLARREO and TRUTHS missions could improve the calibration of 30 to 40 other sensors operating in low Earth and geosynchronous orbit to monitor weather, survey land resources and conduct research, Wielicki said. That improved accuracy is needed to determine the real effect of global climate change, Fox said.
