Japan launched a $1.2 billion joint satellite mission with NASA on Thursday to measure global rain and snowfall, filling coverage gaps and anchoring an international orbital network to supply scientists and forecasters a radar-like snapshot of global precipitation every three hours.

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NASA says the power-generating solar panels have deployed.

The spacecraft's two solar panels have started deploying.

Art Azarbarzin, GPM project manager at NASA, described what the spacecraft will go through in the moments after separating from the H-2A rocket.

About ten minutes after separation, the spacecraft is programmed to unfurl its two solar panels, which extend about the width of the the wingspan of a business jet.

"Then the spacecraft will point itself toward the sun and stabilize," Azarbarzin said.

"About an hour and a half after that, the high gain antenna comes out and then we maintain our communications through TDRSS (NASA's tracking satellite network) to the ground. Prior to that we do have omni antennas which have for the purpose of communications and contingency activities prior to getting the high gain antenna," Azarbarzin said.

Activation of the GPM Microwave Imager is scheduled about a day after launch, followed by the switch-on of the Dual-frequency Precipitation Radar about a week later.

The spacecraft is planned for a 60-day commissioning phase before becoming operational.

The spacecraft is on battery power until the twin solar panels are extended. The panel deployment is expected to begin in about 10 minutes.

GPM separation! JAXA has confirmed the spacecraft has been deployed into the planned orbit.

T+plus 15 minutes, 23 seconds. The second stage's LE-5B engine has cut off and the H-2A rocket should now be in orbit. Deployment of the GPM spacecraft is moments away.

NASA says the GPM spacecraft has begun transmitting telemetry to the mission operations center at Goddard Space Flight Center in Maryland.

T+plus 10 minutes. No problems have been reported thus far in the launch phase of the mission. Second stage cutoff is scheduled for T+plus 14 minutes, 58 seconds.

T+plus 7 minutes, 20 seconds. First stage main engine cutoff, staging and second stage ignition have all occurred on time, according to JAXA. Velocity is now about 4,700 meters per second.

The second stage LE-5B engine will fire for more than eight minutes during this first burn of the mission to place the vehicle into low Earth orbit.

T+plus 4 minutes, 25 seconds. JAXA reports the four-meter-diameter payload fairing has been released from the rocket. The H-2A is now being powered by its LE-7A main engine at an altitude of 152 kilometers and a velocity of 2,350 meters per second.

T+plus 2 minutes. Burnout and separation of the twin solid rocket boosters that provided the bulk of thrust at liftoff. Altitude is now about 55 kilometers.

T+plus 60 seconds. The 17-story rocket has surpassed Mach 1 and is now experiencing the most extreme aerodynamic forces of its flight.

Liftoff of a Japanese H-2A rocket with GPM, a mission to fill critical knowledge gaps in Earth's water cycle.

T-minus 60 seconds and counting. Thousands of gallons of water are now being poured over the launch platform to cushion the structure from intense acoustic vibrations at launch. In the countdown's final minute, the rocket will be armed and the guidance system will start.

The ignition sequence of the first stage engine begins 5.2 seconds before liftoff. Solid rocket booster ignitions occurs at T-zero.

T-minus 90 seconds. The first and second stage propellant systems have been readied for launch.

T-minus 3 minutes. The H-2A rocket has switched to internal power.

T-minus 4 minutes, 30 seconds. The automatic countdown sequence has started and the H-2A rocket's propellant tanks will soon be pressurized for flight.

T-minus 5 minutes, 30 seconds. The weather is acceptable for launch today, according to JAXA. The current conditions are a temperature of 57 degrees Fahrenheit and northeast winds of about 10 mph.

T-minus 7 minutes. The range safety system is reported ready for launch.

T-minus 10 minutes. The GPM spacecraft is now operating on internal battery power as the satellite and launcher are configured for liftoff at 1837 GMT (1:37 p.m. EST).

T-minus 12 minutes. In the final minutes of the countdown, an automated sequencer will control the final crucial steps before launch.

The automatic sequence will begin at T-minus 4 minutes, 30 seconds and computers will pressurize the H-2A's propellant tanks for flight at about T-minus 4 minutes, 20 seconds.

At about T-minus 3 minutes, the launcher will transition to internal battery power and remove external power.

Water will be released onto the launch pad deck beginning at T-minus 73 seconds to help suppress sound and acoustics during the ignition and liftoff. The vehicle's pyrotechnic and ordnance systems will be armed at T-minus 30 seconds and the rocket's guidance system initializes at T-minus 18 seconds. Batteries controlling solid rocket booster ignition are activated at T-minus 15 seconds.

Sparklers underneath the rocket's main engine ignite at T-minus 11.7 seconds to burn off residual hydrogen that could be an explosive hazard at main engine start.

T-minus 20 minutes. Engineers are uploading the latest upper level wind data into the H-2A's flight computer. The rocket will use the information to compute a specific steering profile based on the real launch day weather conditions.

At liftoff, the H-2A will be propelled upward from the launch pad on the power of a single hydrogen-burning LE-7A main engine and two solid rocket motors. The total liftoff thrust of the rocket is approximately 1.6 million force pounds.

The rocket will pitch southeast from Tanegashima, racing through the speed of sound in less than a minute and reaching an altitude of more than 30 miles in the first two minutes of flight.

After consuming their pre-packed solid propellant, the two strap-on boosters will jettison in two pairs just before two-minute point. The 13.1-foot diameter payload shroud will separate at T+plus 4 minutes, 5 seconds after the H-2A rocket ascends above the discernable traces of Earth's atmosphere.

First stage main engine cutoff, stage separation and ignition of the second stage's LE-5B engine will occur nearly seven minutes into the mission. The second stage will burn for more than eight minutes before shutting down at T+plus 14 minutes, 58 seconds.

Deployment of the GPM satellite is expected at T+plus 15 minutes, 49 seconds. GPM will begin extending its solar panels about 10 minutes after spacecraft separation.

Seven other small satellites will be released through the T+40 minute point.

Some statistics on today's launch:

• 23rd H-2A launch since 2001
• 34th H-2 family launch since 1994
• 12th launch of the H-2A (202) configuration
• 1st launch from Tanegashima in 2014
• 9th space launch attempt worldwide in 2014

Now 60 minutes from the planned launch of the H-2A rocket.

Officials just gave the "go" to enter the terminal count, which began at 15 GMT. The final hour of the countdown will prepare the rocket, the payloads, and ground systems for flight.

The H-2A rocket for today's launch is flying in the "202" configuration with two large 15-meter-long (49-foot) solid rocket boosters and without any of the smaller strap-on boosters sometimes used to augment the launcher's thrust.

It also features a standard four-meter (13.1-foot) diameter nose shroud, which encloses the GPM spacecraft for the first few minutes of flight through the lower atmosphere.

The lead contractor for the H-2A rocket is Mitsubishi Heavy Industries.

A second steering check of the rocket's engines has been accomplished, according to Mitsubishi Heavy Industries.

Another "go/no go" decision point is coming up soon, before the countdown enters the terminal phase at T-minus 60 minutes.

The GPM spacecraft is heading for an orbit 407 kilometers, or 253 miles, in altitude with an inclination of 65 degrees.

There are 90 minutes left in today's countdown before liftoff of the H-2A rocket with Global Precipitation Measurement Core Observatory, a joint mission by NASA and the Japan Aerospace Exploration Agency.

GPM weighs about 8,488 pounds at the time of launch. It was built in the United States at NASA's Goddard Space Flight Center in Maryland.

The spacecraft is fitted with two instruments -- a Dual-frequency Precipitation Radar and the GPM Microwave Imager.

Gail Skofronick-Jackson, NASA's deputy GPM project scientist, compares the mission to a health check-up for the planet.

With the dual-frequency radar, "we are able to have what we call a CT scan, it's a three-dimensional view of the precipitation and it's just like seeing three-dimensional within the cloud," Skofronick-Jackson says. "The GMI, on the other hand, I like to describe as an X-ray through the cloud. It's a projection of all the liquid and all the ice in the cloud.

"Just like a doctor uses CT scans and X-rays to diagnose what's happening in the human body, GPM Core Observatory is going to use the measurements of the radar and the radiometer to diagnose the precipitation strucutures within the cloud."

GPM is a follow-on mission to expand observations by the joint NASA-JAXA Tropical Rainfall Measuring Mission launched in 1997.

See the launch timeline for details on the H-2A rocket's ascent into orbit with the GPM Core Observatory.

We have also posted a cutaway diagram of the H-2A launch vehicle.

Radio checks have been completed between the rocket and ground stations.

Mitsubishi Heavy Industries, the H-2A rocket's contractor and commercial operator, reports the liquid hydrogen and liquid oxygen tanks aboard the launcher are now full of super-cold cryogenic propellant.

The next few hours of the countdown will be spent activating and checking out a variety of rocket systems, including radio frequency links with tracking stations. Another steering check of the rocket's main engine is also planned.

After testing is completed, officials will give the go-ahead for the terminal countdown scheduled to start at 1737 GMT. Liftoff remains set for 1837 GMT (1:37 p.m. EST), or 3:37 a.m. local time at the Tanegashima Space Center in southern Japan.

Slew checks of the H-2A rocket's first stage engine have been completed, verifying the powerplant will be able to steer the launcher during ascent.

Safety officials have established road blocks 400 meters from Launch Pad No. 1 of the Yoshinobu launch complex. The Yoshinobu launch complex was built for the H-2 rocket program that began operations in 1994 and has since been modified for use by the more powerful and reliable H-2A rocket family.

The pads are positioned on a rocky outcrop on the southeastern flank of Tanegashima Island, which lies about 80 miles south of Kagoshima, Japan.

The complex features two pads for the H-2A and H-2B rockets. Launch Pad No. 2 has been used for four flights of the H-2B rocket with the H-2 Transfer Vehicle, an unmanned cargo ship for the International Space Station. In all, 33 rockets have departed Earth from the Yoshinobu complex since 1994. The most recent flight was an H-2B rocket launch in August 2013.

Launch officials report they are go for cryogenic fueling of the H-2A rocket. The launcher's two stages consume liquid hydrogen and liquid oxygen propellants. Two strap-on boosters attached to the first stage are already packed with solid fuel.

The LE-7A and LE-5B engines on each stage burn the super-cold propellants during the flight. Because the propellant is stored under cryogenic conditions, it must be gradually replenished throughout the countdown to ensure proper levels of fuel are inside the rocket at liftoff.

JAXA and Mitsubishi Heavy Industries, the H-2A rocket's prime contractor, report all systems are functioning well.

The weather forecast continues to look favorable for launch at 1837 GMT (1:37 p.m. EST).

The H-2A rocket for Thursday's launch just arrived at the pad after a half-hour rollout from the Vehicle Assembly Building.

Once the launch platform is firmly attached to the pad, workers will begin connecting fuel lines and data and electrical cables between the complex and the rocket.

Fueling of the H-2A rocket should begin about eight hours before liftoff, which remains scheduled for 1837 GMT (1:37 p.m. EST).

The launch will mark the 23rd flight of Japan's H-2A rocket since it debuted in 2001. All but one of the missions have been successful.

The launch readiness review has cleared the H-2A rocket and a flagship Earth science observatory for liftoff Thursday from Tanegashima Island in southern Japan.

Jointly designed and funded by NASA and the Japanese government, the Global Precipitation Measurement Core Observatory will peer into rain and snow storms to study the dynamics of precipitation over a swath of the globe home to the bulk of the world's population.

The launch window has been adjusted and now opens at 1837 GMT (1:37 p.m. EST) Thursday and extends for one hour. The window begins at 3:37 a.m. Japan Standard Time on Friday.

Officials adjusted the launch time after a collision avoidance analysis between the GPM satellite and the International Space Station.

Rollout of the 17-story rocket from the vehicle assembly building to Launch Pad No. 1 at Tanegashima will begin around 0400 GMT (11 p.m. EST). The trip should take about a half-hour.

Soon after the H-2A rocket arrives at the launch pad, control teams will oversee the filling of the launcher's first and second stages with liquid hydrogen and liquid oxygen propellants.

The weather forecast calls for favorable conditions with scattered clouds and winds around 13 mph, well below the H-2A rocket's constraint of 47 mph. Good weather is also predicted for rollout.

Japan is preparing to launch a U.S.-built satellite Thursday to track rainfall and snowfall over the bulk of the world's population, anchoring an international initiative to better understand Earth's water cycle and its relationship to storms, droughts and climate change.

The Global Precipitation Measurement Core Observatory is set for liftoff in a two-hour launch window opening at 1807 GMT (1:07 p.m. EST) aboard a Japanese H-2A rocket from the Tanegashima Space Center in southern Japan.

The launch window begins at 3:07 a.m. Japan Standard Time on Friday.

"The water cycle, so familiar to all school-age young scientists, is one of the most interesting, dynamic, and important elements in our studies of the Earth’s weather and climate," said John Grunsfeld, associate administrator for NASA's science mission directorate. "GPM will provide scientists and forecasters critical information to help us understand and cope with future extreme weather events and fresh water resources."

Built at NASA's Goddard Space Flight Center in Maryland, the satellite was shipped by air and sea in November to Tanegashima, an island spaceport situated south of Kyushu, the southernmost of Japan's main islands.

Since its arrival in Japan late last year, the satellite was fueled and tested by a team of U.S. and Japanese technicians before it was handed over to rocket engineers earlier this month for attachment to the H-2A launcher.

Workers completed fueling the spacecraft with hydrazine propellant in early February, then transferred into an encapsulation hall to be enclosed inside the H-2A rocket's four-meter (13.1-foot) diameter payload fairing, which shields the spacecraft during final launch preparations and the first few minutes of flight through the lower atmosphere.

The H-2A rocket's two stages arrived at Tanegashima Space Center on Jan. 21 from a factory at Mitsubishi Heavy Industries Ltd. in Nagoya.

Crews assembled the hydrogen-fueled rocket and its twin solid rocket boosters inside a vertical integration building less than a half-mile from the launch pad.

Mitsubishi engineers transferred the GPM Core Observatory inside the payload fairing to the H-2A vehicle assembly building Feb. 18. The spacecraft was lifted by crane and hoisted atop the rocket's second stage to top off the 174-foot-tall launch vehicle.

Rollout of the H-2A rocket to the launch pad is scheduled about 12 hours before liftoff.

The GPM Core mission follows the joint U.S.-Japanese Tropical Rainfall Measuring Mission launched in 1997, but the new satellite will cover more of the planet from a high-inclination orbit 250 miles above Earth.

The spacecraft's microwave imager and dual-frequency radar will peer inside clouds to measure the type and intensity of precipitation, studying everything from winter storms to hurricanes.

Scientists are interested in tracking cyclones as they move from the tropics to higher latitudes to see how the storms evolve as they move through different climate zones.