Live: Atlas V moving toward Thursday launch

Today's scrub of shuttle Endeavour's launch came early enough for NASA to press forward with a Thursday afternoon launch of two satellites to the moon.

Today at 10 a.m., United Launch Launch Alliance plans to roll a 19-story Atlas V rocket carrying the two spacecraft to the pad at Cape Canaveral Air Force Station's Launch Complex 41.

The first opportunity for liftoff Thursday is 5:12 p.m. Two more one-second opportunities follow at 5:22 p.m. and 5:32 p.m.

Air Force forecasters on Monday gave a 60-percent chance of good enough weather for the launch, with concerns throughout the week about development of afternoon thundershowers.

NASA had said Endeavour's scrub would have to occur before midnight Tuesday for the Air Force's Eastern Range to have enough time to turn around its vehicle tracking and range safety systems.

The scrub officially came at 1:55 a.m. today, but the Air Force says it will be ready for a Thursday launch, according to ULA.

Managers for a moon-mapping orbiter and a secondary payload that will crash into a lunar crater had given up a launch slot this afternoon to allow Endeavour a second chance to get to the International Space Station.

The secondary mission, called the Lunar Crater Observation and Sensing Satellite, was reluctant to lose the slot and eager to fly as soon as possible this week.

That's because the sooner the launch, the more people in the United States will be able to observe the planned October impacts on the moon of the Atlas V's Centaur upper stage and the LCROSS spacecraft.

The four-day launch window from today through Saturday today also allows the impactors to approach the moon at a very steep angle, more than 80 degrees, which maximises the amount of debris that will be kicked up.

And the four-month journey would require less propellant now than during the next launch window, which would start June 30.

With a Thursday launch, people in the Central time zone and further west may be able to witness the Centaur's impact flash and debris plume through 10- to 12-inch telescopes, if the sky is clear.

Ground-based observatories will also help collect science data.

The impacts are an effort to determine if water ice exists on the moon.

Lunar Reconnaissance Orbiter, the primary mission, will create highly detailed maps of the moon to scout out landing sites and resources available to future explorers.

The two missions combined cost $590 million.

IMAGE NOTE: The Lunar Reconnaissance Orbiter and Lunar Crater Observation and Sensing Spacecraft have been loaded atop an Atlas V rocket for launch to the moon. Credit: NASA/Dimitri Gerondidakis.