WASHINGTON A NASA climate-monitoring satellite is set to launch in late February on a three-year mission to improve scientific understanding of how the Earth’s energy balance affects global warming.

NASA’s Glory satellite, which is equipped with a suite of instruments to measure solar output and particles in the Earth’s atmosphere, arrived at Vandenberg Air Force Base, Calif., on Jan. 11, in preparation for a planned Feb. 23 launch.

The Glory satellite is designed in part to continue NASA’s 32-year record of monitoring the total solar irradiance that reaches the Earth, an important variable in the study of global climate change. In addition, it will be NASA’s first satellite capable of identifying and quantifying the man-made and natural aerosols in the atmosphere that may be one of the least well understood variables affecting Earth’s climate.

The 525-kilogram Glory satellite was built and integrated by Dulles, Va.-based Orbital Sciences Corp. using a satellite platform that was originally intended for the Vegetation Canopy Lidar mission NASA canceled in 2001. Orbital Sciences will launch the satellite aboard its Taurus XL rocket, which is making its return to flight two years after it failed in an attempt to launch NASA’s Orbiting Carbon Observatory satellite. Glory will be placed into a 705-kilometer near-polar orbit, joining five other NASA spacecraft flying in close proximity that are collectively known as the A-train.

The $424.1 million Glory mission is some 16 months behind its original launch schedule. Most of the delay was attributed to development troubles with the Aerosol Polarimetry Sensor built by Raytheon Space and Airborne Systems of El Segundo, Calif. The satellite was most recently planned for launch in November until a problem arose with the assembly that turns its solar arrays. NASA turned to Honeybee Robotics of New York, which in two months designed, built, installed and tested a new twisting mechanism for the assembly.

Glory is the successor to NASA’s Solar Radiation and Climate Experiment satellite, which has been on orbit for eight years and is well beyond its design life. Glory’s Total Irradiance Monitor instrument was built by the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder. Solar measurements recorded by this instrument will be three times more precise than measurements taken by the existing instrument, said Greg Kopp, a University of Colorado instrument scientist.

The sun had been the primary agent of climate change on Earth for millions of years, but since the Industrial Revolution spun into full swing during 19th century, man-made effects are thought to have become a far greater factor than the sun.

“Prior to about 150 years ago a lot of the Earth’s climate variability was driven by the sun,” Kopp said in an interview. “Since then, anthropogenic effects … like greenhouse gases have really taken over what’s driving climate change. The sun is still an influence, but more at the 15 percent level. So when we’re trying to discriminate how much of climate change is due to human-caused effects versus natural effects, we need to be monitoring the sun to attribute the appropriate amount due to variability in the sun.”

The sun goes through 11-year cycles of brightening and dimming that have been recorded by observers for centuries. NASA has launched six satellites since 1978 that collectively have provided continuous measurements of solar irradiance from space. The instruments have been very good at detecting the net change in total solar output over a single cycle. But because of the imprecision of the instruments on previous satellites, and the fact that these types of satellites have a relatively short lifespan, it is difficult to compare data from one solar cycle to the next.

“What we aren’t certain about yet is how well the sun comes back to some base level, or if it does come back,” Kopp said.

One way NASA mitigates the differences in calibration from one satellite to the next is by having them on orbit at the same time. But after Glory, the space-based solar irradiance measurements face an uncertain future. There would have been a solar irradiance sensor on the joint military-civilian National Polar-orbiting Operational Environmental Satellite System, but the White House dismantled that program last year. The first spacecraft being built for the replacement civilian weather satellite system, known as the Joint Polar Satellite System, will not have a solar instrument. The best hope for maintaining solar irradiance data continuity is to build and launch a dedicated solar irradiance satellite by about 2014, but there are no firm plans to do so, Kopp said.

Whereas the Total Irradiance Monitor will be a continuation of decades of space-based solar observations, the Aerosol Polarimetry Sensor represents an entirely new category of satellite observation for NASA. Aerosols — tiny solids or liquids that are suspended in the Earth’s atmosphere — are believed to have a significant effect on the Earth’s climate. But whether the cumulative effect warms or cools the planet is unknown. There is little debate that greenhouse gases contribute to the warming of the planet. But aerosols, depending on their chemical composition and reflectivity, can either cool the Earth by reflecting sunlight or warm the Earth by absorbing and re-emitting solar energy. To develop accurate climate change models, scientists need better information about the total content and composition of aerosols in the atmosphere, said Brian Cairns, an aerosol instrument scientist at NASA’s Goddard Institute for Space Studies in New York.

“The climate is being forced by greenhouse gases and by aerosols,” Cairns said in an interview. “And we don’t really know how much the aerosols are offsetting the greenhouse gasses.”

The 69-kilogram Aerosol Polarimetry Sensor will measure aerosols from more than 250 angles using nine spectral bands to determine their composition. The sensor will sweep around the Earth covering 5.9-kilometer-wide swaths on a track that repeats every 16 days. The result will be “jail bar” coverage that does not scan every cubic kilometer of the Earth’s atmosphere but can be extrapolated to determine the total amount and composition of aerosols in the atmosphere. Scientists will be able to track changes from month to month, and this new data record will greatly improve future climate change models, Cairns said.