Iridium satellite

SAN FRANCISCO — The Johns Hopkins University Applied Physics Laboratory (APL) is seeking NASA funding for a plan to send 66 sensors into orbit on the Iridium Next constellation of mobile communications satellites to shed light on the imbalance between incoming solar energy and the Earth’s thermal energy reflected back into space.

APL proposed the project, known as Earth’s Radiation Imbalance System (ERIS), as a candidate in the space agency’s Earth Venture program of science-driven missions that can be launched within five years and completed for $150 million or less.

“If you want to measure outgoing radiation with the accuracy necessary to understand global climate change, you have to make measurements everywhere, all the time,” said Lars Dyrud, APL’s ERIS principal investigator.

Iridium Next, a constellation of 66 satellites operating in low-Earth orbit to provide global communications coverage, offers a unique opportunity to determine the total amount of radiation the Earth is reflecting into space as well as to create maps showing how reflected energy varies at different times and in different areas, Dyrud said. The project could make significant contributions to scientific understanding of the role clouds play in trapping or reflecting the Earth’s radiation, he added.

Other NASA space-based sensors provide information on incoming solar and outgoing reflected energy. For example, four Clouds and Earth’s Radiant Energy System (CERES) instruments have been flying for more than a decade aboard NASA’s Terra and Aqua Earth-observing system satellites to investigate that phenomenon. CERES provides information on the average amount of radiation each month, however, while ERIS would use highly calibrated infrared sensors to make hourly measurements, Dyrud said.

That accuracy is important because imbalances as small as 1 percent between the amount of the sun’s energy reaching Earth and the amount of energy radiated into space can lead to significant changes in the global climate, Dyrud said. While space-based instruments have succeeded in measuring incoming solar radiation with accuracy of greater than 0.03 percent, outgoing radiation measurements have achieved an accuracy of only 1 percent, which is not enough to highlight the imbalance, he added.

The science leader for the ERIS team is Warren Wiscombe, former chief scientist for the U.S. Department of Energy’s Atmospheric Radiation Measurement program and a senior scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. The team also includes deputy principal investigator Steven Lorentz, former leader of the National Institute of Standards and Technology’s low-background infrared facility and founder of L-1 Standards and Technology of Cambridge, Mass. The ERIS science team includes researchers from NASA, the National Center for Atmospheric Research, Brookhaven National Laboratory and U.S. and Canadian universities.

If APL wins a NASA contract, engineers at the Charles Stark Draper Laboratory, also in Cambridge, would be responsible for building the ERIS instruments, including their mechanical, electrical and data handling components. Draper Laboratory officials also would support APL in its systems engineering work, said Shawn Murphy, Draper Laboratory program manager for Earth and space science.

Last year, Draper Laboratory held a conference on the challenges of developing an international network capable of providing long-term climate monitoring. Participants at that conference discussed the possibility of flying Earth observation sensors as hosted payloads on various satellite constellations, including McLean, Va.-based Iridium Communication’s Iridium Next and the U.S. government’s GPS navigation satellites. “Commercial, government or nongovernment satellites could provide scientists with an opportunity to put payloads in space for a fraction of the cost of developing [independent] missions,” said Seamus Tuohy, Draper Laboratory space systems director.

Claude Rousseau, a senior analyst at the consulting firm Northern Sky Research, agreed. Hosted payload arrangements offer government agencies, which provide most of the international funding for Earth observation payloads, with the advantages of reducing the cost of flying sensors and decreasing the time it takes to deploy them, he said in an Oct. 6 email. “For the scientific community, hosted payloads can help launch instruments to monitor the Earth and space environment as well as support emergency and disaster preparedness,” Rousseau added.

If the ERIS project is selected to receive funding under the Earth Ventures 2 program, Draper would begin building 66 instruments plus spares in batches of 10 or 20, said Stefan Slagowski, Draper Laboratories systems engineer. The first set of instruments would be delivered in 2014 to Iridium Next builder Thales Alenia Space, Slagowski added. Iridium Communications plans to launch satellites into the Iridium Next constellation from 2015 to 2017.

NASA plans to announce the missions selected to fly as part of the Earth Venture 2 program in April 2012. The space agency’s budget includes $150 million for the program. Based on the cost of the missions selected, space agency officials will determine whether they can pay for more than one mission, said NASA spokesman Steve Cole.

APL’s ERIS project would cost approximately $150 million, Dyrud said.

APL officials also have briefed the National Oceanic and Atmospheric Administration (NOAA) on the ERIS plan. “I’m hopeful that if our proposal does not get picked up by NASA, then NOAA will pick it up,” Dyrud said.

Debra Werner is a correspondent for SpaceNews based in San Francisco. Debra earned a bachelor’s degree in communications from the University of California, Berkeley, and a master’s degree in Journalism from Northwestern University. She...