GREENBELT, Md. — The Global Precipitation Measurement (GPM) satellite NASA is developing with the Japan Aerospace Exploration Agency has been fitted with its two main instruments, putting the fully integrated spacecraft on track to enter environmental testing at the Goddard Space Flight Center here by September, the project’s manager said.

“We have all the instruments already integrated fully and working very well on the satellite,” Art Azarbarzin, GPM project manager, said here May 15. Environmental testing — a lengthy series of electromagnetic interference, vibration and thermal vacuum tests meant to verify the spacecraft is ready to withstand the rigors of launch and on-orbit operations —is due to begin in August or September, he said.

The 3,850-kilogram GPM satellite, the largest ever built at Goddard, hosts the GPM Microwave Imager, built by Ball Aerospace & Technologies Corp., of Boulder, Colo., and the Japanese-built Dual-frequency Precipitation Radar.

“These two instruments together allow us to measure the lightest rainfall rates that you might see all the way up to hurricane-strength downpours,” Gail Skofronick-Jackson, GPM’s deputy project scientist. The satellite, which will traverse all but the polar latitudes, will also be one of the first spacecraft designed to detect snowfall, a necessary capability for its mission to expand understanding of the Earth’s water cycle. GPM is a successor to the Tropical Rainfall Measuring Mission, another joint effort between the U.S. and Japanese space agencies that also monitors precipitation, albeit only in tropical latitudes. That mission launched in 1997 and is still operating.

Azarbarzin said the GPM satellite is slated to be flown aboard a U.S. Air Force C-5 cargo plane to the Tanegashima Space Center in Japan in October. The mission is slated to launch in February 2014 aboard Japan’s H-2A rocket, which will send the satellite to an altitude of 400 kilometers to monitor snow and rainfall across the globe. It is designed for a three-year mission but will carry sufficient propellant to remain in service for five, he said.

After it achieves orbit, GPM will undergo a two-month checkout period. Once the project team can verify that data derived from the satellite’s instruments can be made available on Earth within three hours of observation, it will turn the keys over to the GPM operational team. That team also is based at Goddard. After checkout, it will take GPM six months to build up an accurate database of global precipitation rates. Once that exists, it, and future GPM data, will be provided to the public for free, Azarbarzin said.

GPM is expected to cost NASA about $933 million by the time it completes its nominal mission. Azarbarzin, in a May 15 interview, said the project was well within that budget. When it was approved in 2009, NASA expected to spend about $975 million for the project. Development and projected operations costs dropped after the White House, in its 2012 budget request, cut funding for a second microwave imager that Ball was under contract to build for the mission. There are about 110 civil servants and about 180 contractors working on GPM, said Candace Carlisle, NASA’s GPM deputy project manager.

GPM had been slated to launch in July 2013, but NASA in October approved a revised plan that pushed launch out to 2014. Late delivery of the spacecraft’s two main instruments were to blame, the agency said in budget documents released in February. The Japanese instrument, which arrived at Goddard in April, was supposed to have gotten there last July. Delivery was held up by the earthquake and tsunami that struck Japan in March 2011. Azarbarzin counts his team lucky to have gotten the instrument when it did.

“For them to deliver nine months after a major earthquake like that is a miracle,” Azarbarzin said. “We thought these guys were going to be a year and a half late. But for them to recover and deliver in nine months? That was phenomenal.”

GPM will be at the center of an ad hoc constellation of international climate monitoring satellites. The spacecraft will eventually siphon data from as many as nine other satellites at a time, said Arthur Hou, GPM project scientist.

Some of these satellites have yet to be launched, and some are already on-orbit. The full constellation will contain nine spacecraft built by “international partners from the United States, Japan, France, India and the European community,” Hou said. “Each member can have a unique scientific or operational objective, but they all contribute data to GPM to produce a unified global precipitation data product.”

Of these satellites, four are already on-orbit and a fifth, Metop-B, is expected to launch in late July aboard a Russian Soyuz rocket from the Baikonur Cosmodrome in Kazakhstan. Metop-B, built by Astrium Satellites of France for Europe’s Eumetsat meteorological satellite organization, was to have launched May 23, but Russia postponed the launch to address concerns about Soyuz dropping its spent lower stage on Kazakh soil.

Meanwhile, the Japan Aerospace Exploration Agency launched May 17 what will be the fourth satellite in the GPM constellation, the Global Change Observation Mission 1st-Water satellite.

The other three operational satellites that will eventually contribute to the GPM mission are: NASA’s Suomi NPP weather- and climate-monitoring satellite, launched in October; Megha-Tropiques, a Franco-Indian satellite launched in October to observe tropical monsoons; and National Oceanic and Atmospheric Administration-19, a polar-orbiting weather satellite formerly known as NOAA N-Prime, which launched in 2009.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.