Updated Aug. 10 with new launch window.

The Japanese space agency said Wednesday the launch of an H-2A rocket with the countrys third navigation satellite was preemptively delayed at least 24 hours to Saturday to avoid thunderstorms with lightning in the forecast later this week.

The 174-foot-tall (53-meter) rocket, currently standing inside the vertical assembly building at the Tanegashima Space Center, is now scheduled to launch some time during an unusually-long window Saturday that opens at 0440 GMT (12:40 a.m. EDT; 1:40 p.m. Japan Standard Time) and extends nearly nine hours.

The launch was originally scheduled for Friday.

Rollout of the H-2A rocket to the launch pad at Tanegashima is scheduled around a half-day before liftoff. Technicians will connect the two-stage rocket to the pads electrical, telemetry and cryogenic propellant infrastructure before the final countdown.

The payload aboard the H-2A rocket is Michibiki 3, the third member of a four-satellite network Japan is deploying to supplement GPS navigation coverage over its territory. The launch of the 4.4-ton (4-metric ton) Michibiki 3 satellite comes after the delivery of two similar navigation stations to orbit by H-2A rockets in September 2010 and in June.

Another Michibiki satellite is scheduled for launch on an H-2A rocket as soon as late this year.

The four-satellite fleet, entirely compatible with the GPS network, is being positioned in orbits loitering over Japan at altitudes more than 20,000 miles (33,000 kilometers) above Earth. The first two Michibiki spacecraft went into inclined geosynchronous-type orbits that oscillate between the northern and southern hemispheres, while Michibiki 3 will launch into a geostationary orbit that hovers over the equator.

GPS satellites, operated by the U.S. Air Force, circle Earth in lower orbits, meaning different spacecraft are visible in the sky at different times, acting as navigation beacons to triangulate the location of ground users.

Japans Quasi-Zenith Satellite System will add more beacons to the sky over the Asia-Pacific, resulting in more precise position estimates and improved service in urban areas and remote regions, where high-rise buildings and mountains can obstruct signals from GPS satellites low on the horizon.

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Poor weather forecast delays launch of Japanese navigation ... - Spaceflight Now