NASA’s CATS Ready To Comb the Clouds

by

SAN FRANCISCO — The eruption of Iceland’s Eyjafjallajökull volcano brought air traffic to a halt across much of northern Europe for eight days in April 2010. Airlines lost an estimated $2 billion in revenue due, in part, to the inability of carriers to determine the exact location of the ash clouds that posed a serious threat to aircraft engines.

A NASA instrument scheduled for installation on the outside of the international space station later this year could help remedy that problem. NASA’s Cloud-Aerosol Transport System (CATS), based on technology developed for the space agency’s Cloud Physics Lidar used on an unmanned Global Hawk to study storms, will provide detailed observations of the location and composition of clouds and tiny airborne particles, including volcanic ash, said Matthew McGill, CATS principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

CATS also is designed to publicize the international space station’s utility as a platform for future Earth science instruments. NASA began building CATS and ISS-RapidScat, a wind measurement mission scheduled to travel to the space station later this year, soon after completing construction of the U.S. portion of the orbiting outpost in 2011.

“They are harbingers of the instruments that are going to be coming forward over subsequent years until we have all 25 [space station] external sites completely full,” Julie Robinson, NASA’s international space station chief scientist, said during a Sept. 8 press briefing.

The CATS project was conceived by researchers at Goddard  as a way to improve forecasts of atmospheric clouds and aerosols, demonstrate advanced technology applicable to future spaceflight missions and carry on the observations provided by NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission launched in 2006.

“CALIPSO is in the ninth year of its [planned] two-year mission,” McGill said. “We don’t have a new lidar sensor ready to go in the United States. So CATS can provide a stopgap measurement.”

CATS is scheduled to travel to the space station on the fifth NASA cargo resupply mission of Space Exploration Technologies’ Falcon 9 rocket and Dragon spacecraft, slated for early December. Once there, space station officials plan to use the orbiting outpost’s Canadarm2 robot to remove CATS from Dragon’s trunk and hand it off to the robotic arm attached to the space station’s Japanese Experiment Module, where the payload will be installed, Melanie Miller, lead robotics officer at NASA Johnson Space Center in Houston, said during the Sept. 8 briefing. “This will be the first time we have to do a robotic handoff on station,” McGill added.

Although it is unclear exactly how long it will take to move CATS into position, NASA officials are confident the new sensor will begin generating data by early 2015 if it launches in early December. When it begins to operate, the sensor is expected to produce a nearly continuous stream of information because unlike CALIPSO and other free-flying satellites that transmit observations only when they pass over ground stations, CATS will rely on the space station’s data link.

Program officials expect data to be transmitted from the space station to the ground within 30 minutes of observations. Program officials will then process the information immediately and use it to improve the accuracy of aerosol forecast models that show, for example, the location of volcanic ash plumes and smoke from forest fires.

One of the major weaknesses of current aerosol models is their lack of data on the vertical distribution of airborne particles, which CATS is designed to provide. “If we can get data to the ground, get it processed and get it into the models, we can have an impact on the models,” McGill said.

To gather data, CATS will rely on new technology that also could be used on NASA’s Aerosol-Cloud-Ecosystem, an Earth science mission scheduled to launch in 2021. The CATS lidar gathers data by sending out rapid laser pulses in three wavelengths, 1,064 and 532 nanometers, which CALIPSO also uses, as well as 355 nanometers. The addition of the 355-nanometer wavelength coupled with receivers designed to count individual photons reflected by atmospheric particles will allow CATS to determine the size and location of particles more precisely than its predecessor, McGill said.

The precision of CATS data is likely to help researchers improve climate models. “There are a lot of properties of clouds we don’t understand well,” John Yorks, CATS co-investigator, said.  “One big uncertainty in climate predictions is how aerosols and clouds interact with one another.”

Although those questions helped define CATS’s goals, they were not used to establish ambitious requirements. Instead, the mission was designed based on available funding and the offer of a space station external platform.

“The International Space Station Program Office gave us $13 million and told us to have an instrument ready in 24 months,” McGill said.

Those constraints helped to focus the effort. In addition, the CATS team was able to save time and money by not worrying about the cost of launching the 500-kilogram instrument, because NASA’s space station program provided the transportation.

“We weren’t driven to save every gram of weight or use exotic materials,” McGill said. “We were allowed to use commercial off-the-shelf parts. That’s how we could build it for reasonable price.”