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NASA and United Launch Alliance resolved a minor technical issue today, clearing the way for the planned launch early Saturday of a Delta II Heavy rocket and twin NASA spacecraft that will map the gravitational field of the moon.
The mirror-image lunar explorers are now set to blast off from Launch Complex 17B at Cape Canaveral Air Force Station at 8:29 a.m. A second opportunity would come at 9:08 am. if need be.
The weather forecast calls for a 60 percent chance conditions will be acceptable for launch. However, meteorologists are concerned about the possibility that thick, electrically charged clouds or rains showers could sweep into the area, prohibiting a launch.
In the event of a weather delay, NASA and United Launch Alliance would aim to make another attempt on Sunday. The launch times that day would be 8:26 a.m. or 9:05 a.m. There is a 70 percent probability of acceptable conditions on Sunday.
Check out THE OFFICIAL FORECAST from the Air Force 45h Space Wing Weather Squadron.
An initial launch attempt Thursday was scrubbed as a result of higher-than-allowable upper-altitude winds that could haved knocked the rocket off course in flight. The launch was rescheduled for today, but managers late Thursday decided to postpone the attempt to give engineers more time to evaluate a potential problem with heaters in the rocket's first stage.
The heaters are designed to keep components in the first-stage engine section at proper temperatures while they are exposed to supercold liquid oxygen, which is Minus 298 degrees Fahrenheit. The cryogenic propellant and a highly refined kerosene are used to power the stage's Rocketdyne RS-27A engine.
After the postponement, the first-stage propulsion system was drained of all propellant as part of routine 24-hour turnaround procedures. However, the heaters did not turn off when they were supposed to, and engineers wanted to make sure none of the components in the engine section were exposed to temperatures that would compromise their ability to perform as designed.
Engineers and managers ultimately determined that none of the components could have been damaged as a result of the glitches with the heaters.
The 12-story rocket is the 110th and final scheduled flight of a Delta II rocket at Cape Canaveral. The NASA moon mission is also the last scheduled flight from Launch Complex 17.
Precise measurements of the lunar gravitational field will enable scientists to determine the exact make up the moon from crust to core. That information, in turn, will shed new light on the origin and evolution of the moon as well as rocky planets -- Mercury, Venus, Earth and Mars -- in the inner solar system.