NASA TV
Launch controllers skipped an attempt at 8:29 a.m. EDT when weather balloon data indicated upper-level winds exceeded safe levels.
NASA TV
Liftoff came in the second 1-sec. launch window at 9:08 a.m. EDT. The solid-fuel boosters separated as planned, as did subsequent staging and upper-stage ignition, setting up spacecraft separation an hour and a half after launch.
NASA TV
Saturday's launch came after an earlier attempt Thursday was scrubbed because high winds over the launch site at Cape Canaveral AFS, Fla., threatened to push the rocket off course on its way to space. Engineers took an extra day to check out the propulsion system when a heater stayed on too long after the propellant tanks were drained following the scrub.
Grail consists of two identical satellites that will orbit the Moon in the same orbit 50 kilometers above the surface. As they move over the surface, changes in the density of the terrain below them will change the distance between them, allowing scientists to map variations in the Moon's gravity with unprecedented precision.
The twin Grail orbiters - which were based on the experimental U.S. Air Force satellite XSS-11 launched in 2005 to save on development costs and stay within its $425 million cost cap under NASA's Discovery program - will take three-and-a-half months to get to the Moon.
The two spacecraft will use a low-thrust trajectory that passes through the Earth-Moon L1 Lagrangian point to work them into lunar orbit. Controllers at Lockheed Martin's facility in Denver and at the Jet Propulsion Laboratory in Pasadena, Calif., will use that time to gain experience operating the orbiters.
It will also allow the materials that went into building the spacecraft to outgas before they reach orbit. The measurements they will make are so precise -- less than the diameter of a red blood cell, according to NASA planetary science chief Jim Green -- that outgasing could throw them off.
Mission planners also took into account thermal heating of the spacecraft and even shifts in the tectonic plates beneath Deep Space Network antennas in setting up the mission.
At the level of precision Grail planners hope to achieve, the mission should be able to resolve gravity down to the rims of craters on the surface. Maria Gruber, the MIT planetary scientist who organized Grail as the mission's principal investigator, says that degree of accuracy will allow her and her colleagues to determine the internal structure of the Moon and, from that information, better understand how it was formed.
That, in turn, will give new clues to the early solar system, because the Moon's cratered surface retains evidence of the "heavy bombardment" period almost 4 billion years ago when the primordial rubble was coalescing into the planets and moons that we know today.
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