Catching a break from the weather, a United Launch Alliance Delta 2-Heavy rocket blasted off Saturday and successfully boosted two NASA science craft into space on looping trajectories to the Moon, the first step in an ambitious $496 million mission to map the cratered satellite's gravity and internal structure.

Read our full story.

And see our launch pad photos and a press site gallery.

GRAIL principal investigator Maria Zuber says NASA will hold a contest with the U.S. schoolchildren to name the two spacecraft running Oct. 14 through Nov. 11. The names will be given to the satellites before they reach the Moon.

The post-launch news conference from Kennedy Space Center is coming up at 11:45 a.m. EDT. You can watch it live in our streaming video.

"ULA is extremely proud to be a part of NASA's team for the GRAIL mission and we sincerely congratulate all of our mission partners," said Jim Sponnick, ULA vice president of mission operations, said in a post-launch statement. "Today's successful launch is the third NASA mission ULA has launched in just three months with two more to come in October and November. The timing and precision of this campaign along with a one-launch-at-a-time focus are testaments to our commitment to providing reliable and cost-effective space launch services to our customers."

"With the final launch from Complex 17, we reflect on the tremendous historical significance of this complex and the impact of the military and scientific payloads that began their missions from this site," said Michael Gass, ULA president and CEO, said in a post-launch statement. "From the Global Positioning System satellites launched for the U.S. Air Force, to NASA's Mars rovers Spirit and Opportunity, in total this complex has been the origin for 259 critical Delta missions to protect our country and explore our universe."

The power-generating solar arrays on both GRAIL spacecraft have unfolded following today's successful ascent into orbit. They have established communications with the Deep Space Network tracking station in Goldstone, California.

This is the 95th consecutive successful Delta 2 rocket launch dating back to May 1997. The Delta 2's overall history since debuting in 1989 has achieved 148 successes in 150 flights.

One more Delta 2 rocket is scheduled for this year. It will haul the NPP polar-orbiting weather satellite into space on October 25 from Vandenberg Air Force Base, California.

ULA also has five additional Delta 2 vehicles it hopes to sell for additional launches in the future.

T+plus 88 minutes, 12 seconds. GRAIL-B SEPARATION! The second of the Gravity Recovery and Interior Laboratory spacecraft has been deployed from the Delta 2-Heavy rocket's second stage to begin the journey to the Moon.

The GRAIL duo will create an unprecedented lunar gravity map that scientists can follow in their quest to determine the Moon's interior structure from crust-to-core.

T+plus 87 minutes, 45 seconds. The yaw maneuver is complete, creating a 45-degree attitude change.

T+plus 86 minutes, 35 seconds. The Delta 2 rocket is performing a maneuver to get into the proper position for releasing GRAIL-B.

T+plus 79 minutes, 54 seconds. GRAIL-A SEPARATION! The first of the Gravity Recovery and Interior Laboratory spacecraft has been released from the Delta 2-Heavy rocket.

T+plus 79 minutes, 30 seconds. Roll, pitch and yaw rates have nulled out.

T+plus 79 minutes. The rocket has repositioning itself to the proper orientation for release of GRAIL-A.

T+plus 78 minutes. Live television being downlinked from the Delta rocket via the Vandenberg Air Force Base tracking station in California to show release of GRAIL-A.

T+plus 77 minutes. Deployment of GRAIL-A is about three minutes away as the rocket flies over the eastern Pacific Ocean, nearing the coast of North America.

T+plus 74 minutes. The GRAIL spacecraft are not heading straight to their destination, instead taking a circuitous route lasting three-and-a-half months across 2.6 million miles of space before braking into lunar orbit on Dec. 31 and Jan. 1, respectively.

"If you leave Earth and go barreling to the Moon, you need a lot of fuel to slow down (and enter lunar orbit). We want to use small spacecraft with small fuel tanks. So as a consequence of that, we use something called a low-energy trajectory where we go out to a point called the Earth-Sun Lagrange Point, which is like a void in the ocean," said GRAIL principal investigator Maria Zuber.

The lengthy trip also allows the satellites to "out-gas" on the way, ensuring this phenomena isn't mistaken for gravity measurements during the science-gathering portion of the mission later.

"We need this time to do out-gassing. There's little tiny particles on the spacecraft and those need to out-gas because that's inducing a force on the spacecraft, like internal gravity," said David Lehman, GRAIL project manager from the Jet Propulsion Laboratory.

"The other reason is we have two small spacecraft on one medium-size rocket. We did that for cost savings. If we had two bigger spacecraft, we would need two rockets," Lehman added.

T+plus 70 minutes, 15 seconds. GRAIL has been accelerated to 23,907 mph.

T+plus 70 minutes, 25 seconds. SECO 2. The GRAIL twins have left Earth with that final push delivered by the Delta 2 rocket's second stage.

T+plus 70 minutes, 5 seconds. Now 23,167 mph.

T+plus 69 minutes, 40 seconds. Now 22,271 mph.

T+plus 69 minutes, 10 seconds. Delta now traveling at 21,383 mph.

T+plus 68 minutes, 35 seconds. Engine controls, chamber pressure and hydraulics all look good.

T+plus 68 minutes, 10 seconds. Velocity now 19,644 mph.

T+plus 67 minutes, 20 seconds. Good pitch and yaw controls. A very smooth flight.

T+plus 67 minutes. Delta is traveling at 17,966 mph.

T+plus 66 minutes, 35 seconds. Rock solid chamber pressure on the second stage.

T+plus 65 minutes, 55 seconds. The second stage engine has ignited for the firing to deliver its spacecraft payload on the roundabout trajectory to the Moon.

T+plus 64 minutes, 30 seconds. The official liftoff time this morning was 9:08:52.775 a.m. EDT.

T+plus 56 minutes. The next firing by the Delta rocket's second stage is coming up in 10 minutes while flying on the other side of the world from Cape Canaveral. The orbiting Tracking and Data Relay Satellite System will continue receiving the rocket's telemetry for transmission back to the launch site, providing the confirmation of the second stage burn and release of the GRAIL-A and GRAIL-B satellites, with additional coverage from the Vandenberg and White Sands ground stations.

T+plus 45 minutes. A map of the rocket's planned flight path is available here.

T+plus 35 minutes. The rocket is coasting until the second stage restarts its engine at T+plus 65 minutes, 51 seconds for a four-and-a-half-minute firing to put the vehicle into the escape trajectory from Earth. Deployment of GRAIL-A happens at T+plus 79 minutes, 53 seconds and GRAIL-B separates from the launch vehicle at T+plus 88 minutes, 8 seconds, based on the updated timeline for the mission on the 99-degree flight azimuth.

T+plus 25 minutes. As the rocket coasts in this parking orbit, it performs a "BBQ roll" maneuver to keep the thermal conditions on the vehicle equal.

T+plus 20 minutes. Live telemetry continues to be received via NASA's Tracking and Data Relay Satellite System. Today's launch is the fourth Delta 2 flight to use TDRS during the long mission instead of ordering support from mobile telemetry assets and faraway ground sites after the rocket passes out of view from the Eastern Range.

T+plus 12 minutes, 30 seconds. The preliminary parking orbit achieved by the Delta 2 rocket is right on the planned mark.

T+plus 9 minutes. Mission events have occurred at the planned times. A very good flight thus far.

T+plus 7 minutes, 45 seconds. Delta is 92.6 miles in altitude, 1,069 miles downrange from the launch pad and traveling at 16,903 mph.

T+plus 7 minutes, 20 seconds. SECO 1 has been confirmed. The second stage's Aerojet-made engine completed its initial burn for the launch. Delta and GRAIL have arrived in a preliminary orbit around Earth following launch today from Cape Canaveral. The vehicle will coast for about an hour before the second stage is re-ignited to dispatch its payload to the Moon.

T+plus 6 minutes, 30 seconds. Delta is 90 miles in altitude, 776 miles downrange from the launch pad and traveling at 16,141 mph.

T+plus 6 minutes. Second stage looking good as this initial burn continues.

T+plus 5 minutes, 30 seconds. About two minutes remain in this burn of the second stage engine to achieve the intended parking orbit.

T+plus 5 minutes, 15 seconds. The second stage engine is firing well, consuming a hydrazine propellant mixture and nitrogen tetroxide oxidizer. This burn is needed to achieve a parking orbit around Earth.

T+plus 5 minutes, 40 seconds. The vehicle is 84 miles in altitude, 588 miles downrange from the launch pad and traveling at 15,440 mph.

T+plus 4 minutes, 48 seconds. The rocket's nose cone enclosing the GRAIL twins has been jettisoned.

T+plus 4 minutes, 43 seconds. The spent first stage has been jettisoned and the Delta's second stage engine has ignited!

T+plus 4 minutes, 30 seconds. MECO. The first stage main engine cutoff is confirmed.

T+plus 4 minutes. A half-minute remaining in the first stage burn. Everything is reported normal aboard the vehicle.

T+plus 3 minutes, 30 seconds. The first stage main engine still firing well. The Pratt & Whitney Rocketdyne powerplant consumes kerosene fuel and liquid oxygen to produce about 200,000 pounds of thrust.

T+plus 2 minutes, 50 seconds. The three air-ignited solid rocket boosters have burned out and separated. The rocket is now flying solely on the power generated by the liquid-fueled first stage main engine.

T+plus 2 minutes. The vehicle is 21.8 nautical miles in altitude, 51 miles downrange from the launch pad.

T+plus 1 minute, 25 seconds. All six ground-start solid rocket boosters have burned out of propellant and separated from the Delta 2's first stage. A moment before the jettison occurred, the three remaining motors strapped to rocket ignited to continue assisting the rocket's RS-27A main engine on the push to space.

1309 GMT (9:09 a.m. EDT)

T+plus 50 seconds. The rocket has flown through the area of maximum aerodynamic pressure in the lower atmosphere.

T+plus 35 seconds. Delta has broken the sound barrier, rapidly accelerating on the power of its first stage main engine and the six ground-lit strap-on solid-fuel boosters.

T+plus 20 seconds. The Delta 2 rocket has maneuvered on the course for eastward climb to orbit.

T+plus 10 seconds. The Delta 2 rocket has cleared the tower to depart Cape Canaveral's Complex 17 for perhaps the final time. The vehicle has no future missions scheduled from the Florida spaceport.

LIFTOFF! Liftoff of the GRAIL lunar gravity mappers on their voyage from the Earth to the Moon!

T-minus 30 seconds. SRB ignitors will be armed at T-minus 11 seconds.

The launch ignition sequence will begin at T-minus 2 seconds when a launch team member triggers the engine start switch. The process begins with ignition of the two vernier thrusters and first stage main engine start. The six ground-lit solid rocket motors then light at T-0 for liftoff.

T-minus 1 minute. Sixty seconds from launch of the Delta 2-Heavy rocket. The vehicle's second stage hydraulic pump has gone to internal power after its pressures were verified acceptable.

T-minus 75 seconds. The Air Force's Eastern Range has given the all-clear to launch.

T-minus 90 seconds. First stage LOX topping to 100 percent is underway.

T-minus 2 minutes. The first stage liquid oxygen vents are now being closed so the LOX tank can be pressurized for launch. Puffs of vapor from a relief valve on the rocket will be seen in the remainder of the countdown as the tank pressure stabilizes.

T-minus 2 minutes, 30 seconds. The GRAIL payload has been declared "go" for launch.

T-minus 2 minutes, 45 seconds. Vehicle ordnance is being armed.

T-minus 3 minutes and counting down to the Delta rocket launch dedicated to sending the GRAIL spacecraft bound for lunar orbit to probe the Moon's interior structure like never before.

T-minus 3 minutes, 45 seconds and counting. The Delta 2 rocket's systems are now transferring to internal power for launch. And the launch pad water system is being enabled.

T-minus 4 minutes and counting! Clocks are ticking down the final moments for liftoff of Delta 356 with the GRAIL spacecraft. Launch is set for 9:08:52 a.m. local time from Cape Canaveral.

Now five minutes from launch! The "go" has been given for release of the hold in one minute.

The launch team has permission to resume the countdown!

Another poll of the launch team is underway to confirm systems remain ready for the Delta 2 rocket and GRAIL spacecraft.

NASA launch director Tim Dunn says all elements are ready to support liftoff at 9:08 a.m., including "most importantly" the upper level winds.

Now 10 minutes away from the final launch window for today. Shooting for the Moon at 9:08 a.m. EDT.

The final weather balloon is coming in "green" for launch at 9:08:52 a.m. EDT.

The launch weather officer had been watching anvil clouds and cloud thickness concerns moving toward the Cape from the west for the upcoming window. But he just briefed managers that the conditions won't impact a 9:08 a.m. launch time.

Additional weather balloons are being sent up to gather data on the wind speeds and directions that the Delta 2-Heavy rocket would experience during ascent. That information is then compared against the vehicle's flight profile to ensure conditions are within the rocket's capability to safely fly through.

The area of concern for upper level winds is between 15,000 and 22,000 feet. The next weather balloon information is expected at 9:01 a.m.

Two precise moments in time are available daily for liftoff to occur during GRAIL's mission launch window. The dual opportunities each day are driven by which azimuth the rocket is sent on -- either 93 or 99 degrees. The window closes in October to ensure GRAIL's mapping is completed before next June's lunar eclipse that is expected to be lethal to the satellites.

For today's launch, liftoff was planned for 8:29:45 a.m. EDT (1229:45 GMT). Since the winds aloft were not acceptable, the team will load the different flight azimuth program aboard the Delta and now shoot for liftoff at 9:08:52 a.m. EDT (1308:52 GMT).

A complete listing of the launch times can be found in our window chart.

So the countdown is being retargeted to the second of today's two available shots to send GRAIL on its way to the Moon in hopes the winds improve in the next half-hour. The launch team will be re-polled for readiness at 8:59 a.m.

The high-altitude winds were "go" earlier in the countdown before going out of limits during later checks. They had gone "green" a short time ago. But the final pre-launch weather balloon for the 8:29 a.m. liftoff time found conditions were again unfavorable.

HOLD EXTENDED. The latest balloon has found "red" upper level winds. So liftoff has been pushed back to the second launch opportunity today at 9:08:52 a.m. EDT.

NASA launch director Tim Dunn has polled his advisory team and the space agency is "go" to continue with the countdown. "The NASA team is ready for launch."

Now 10 minutes to go. Still shooting for the Moon at 8:29:45 a.m. EDT.

Downrange assets are "go" and upper level winds remain "green" for launch, just waiting for last balloon.

T-minus 4 minutes and holding. The countdown has entered the final planned built-in hold. This is a scheduled 10-minute pause leading to today's liftoff time of 8:29:45 a.m. for the Delta 2 rocket.

The first stage kerosene fuel tank is being pressurized for flight.

The upper level wind conditions are being loaded into the Delta 2 rocket's flight computer for launch.

Twenty minutes from launch. The GRAIL satellites will become the 225th and 226th primary payloads put into space by the venerable Delta 2 rocket over the past 22 years. Here's a look at some other stats about today's mission. This will be:

• The 356th Delta rocket launch since 1960
• The 232nd Delta launch with NASA involvement
• The 259th Delta launch from Complex 17
• The fifth Delta of 2011
• The 150th Delta 2 rocket mission since 1989
• The 49th Delta 2 mission overseen by NASA
• The 110th Delta 2 rocket to fly from Cape Canaveral
• The 48th Delta 2 launch from Cape's pad 17B
• The 6th Delta 2 rocket to fly in 'Heavy' configuration

The latest weather balloon data has shown "green" upper level winds. But there is one more balloon that will provide fresh data just before launch time.

T-minus 15 minutes and counting. Countdown clocks are running again following the planned 20-minute hold. The count will continue to the T-minus 4 minute mark where another hold is scheduled. Launch remains set to occur at precisely 8:29:45 a.m. local (1229:45 GMT).

A poll of the launch team confirms everyone is ready to press ahead with the countdown after this pre-planned 20-minute hold.

There high-altitude wind conditions have gone "red" based on the latest weather balloon data. But further information will be coming in later in the countdown with the hope of still launching at 8:29 a.m. EDT.

Now just 30 minutes away from blastoff.

The main engine and six of the nine strap-on solid rocket motors ignite at liftoff to begin GRAIL's ride off the planet. The Delta 2-Heavy features slightly larger solid motors, originally developed for the more-powerful Delta 3 rocket.

"We will lift off with the combined thrust of about 1.3 million pounds from six of the SRBs and the main engine on the core stage," said Vernon Thorp, United Launch Alliance's program manager for NASA missions.

Arcing eastward over the Atlantic Ocean, the six solid boosters lit on the ground extinguish 77 seconds into flight as the remaining three motors are ignited moments later. The half-dozen spent boosters are jettisoned to fall harmlessly into the sea. The air-lit motors burn out and separate two minutes, 40 seconds after liftoff.

Once the solids are discarded, the kerosene-powered main engine will continue pushing the rocket to the edge of space. The spent stage then jettisons at T+plus 4 minutes, 31 seconds to let the hydrazine-fueled second stage propel the vehicle the rest of the way into an initial orbit.

The two-piece nose cone that shrouded GRAIL the trek through the atmosphere is shed at T+plus 4 minutes, 41 seconds just moments after the second stage comes to life.

Seven minutes and 10 seconds into the ascent, the second stage completes its initial firing. The Delta settles into 90-nautical-mile parking orbit inclined 28.5 degrees, flying along a trajectory that cruises above the central Atlantic before passing Africa, the Indian Ocean and skirting over northern Australia.

The second stage reignites its engine while crossing the Pacific some 68 minutes after blastoff for a four-and-a-half-minute firing that accelerates the rocket out of Earth orbit.

Deployment of GRAIL-A occurs within view of the Vandenberg tracking station in California at T+plus 82 minutes. After the second stage reorients itself, GRAIL-B is released at T+plus 90 minutes within the Whites Sands tracking station coverage zone.

"We anticipate that our Delta 2 vehicle will perform exceptionally well, placing GRAIL on an accurate trans-lunar trajectory," said Thorp.

"We are proud to support NASA science missions, playing a critical role by delivering these one-of-a-kind spacecraft in support of the global science community. This mission represents the culmination of years of hard work by NASA, Lockheed Martin's spacecraft team and our ULA launch team."

After the GRAIL twins separate from the Delta vehicle, the second stage will perform another burn to deplete remaining propellants and place the rocket body into an orbit between Earth and Mars, Thorp said.

T-minus 15 minutes and holding. Clocks have entered the first of two planned hold periods during the final portion of the Terminal Countdown. This pause will last 20 minutes in duration.

These holds are designed to give the launch team a chance to deal with any problems and catch up on work that could be running behind schedule.

Now moving into data link checks to verify good telemetry connections.

The first stage engine steering checks are complete.

The second stage engine slews just finished. First stage tests are starting.

The launch team is beginning the "slew" or steering checks of the first and second stage engines. These are gimbal tests of the nozzles on the first stage main engine and twin vernier engines and second stage engine to ensure the rocket will be able to steer itself during launch.

Sixty minutes to launch. As this latest scientific adventure to the Moon nears liftoff, here's some thoughts by Maria Zuber, GRAIL's principal investigator:

"The Moon has played a central role in the human imagination and psyche, so much so that when humans reached out and landed on the Moon it really became a defining event for civilization.

"Since the dawn of the space age in 1959, there have been 109 missions that have targeted the Moon, 12 humans have walked on the surface of the Moon, we've brought back 842 pounds of rocks and soil that are still being analyzed today. As we speak, there are three spacecraft that are orbiting the Moon and collecting science observations."

"Given all of this activity, do we know everything that we'd like to know about Moon? In short, the answer is no.

"Trying to understand how the Moon formed and how it evolved over its history is one of the things we're trying to address with the GRAIL mission, but also how the Moon is an example of how terrestrial planets in general have formed."

The safety checks were completed satisfactorily.

Checks of the rocket's safety system will be conducted in the next few minutes of the countdown.

Loading of the Delta 2 rocket's first stage liquid oxygen tank has been accomplished. The filling process took 25 minutes and 59 seconds, ending at 7:12 a.m. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

The rocket now stands fully fueled for liftoff. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel along with the liquid oxygen over the past hour-and-a-half. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels last Friday. The nine strap-on booster rockets use solid propellants.

The first stage liquid oxygen tank just reached the 95 percent full level. The "rapid load" valve was closed, with the slower "fine load" phase continuing to fill the tank.

Liftoff is just 90 minutes away.

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Seven minutes into the flow. LOX loading is an approximate 25-minute process to fill the first stage liquid oxygen tank.

LOX loading begins! Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from the storage reservoir at Complex 17, through plumbing and into the bottom of the Delta 2 rocket. The LOX will be consumed by the first stage main engine during the first four-and-a-half minutes of flight along with the 10,000 gallons of RP-1 kerosene already loaded aboard the vehicle.

The launch team is performing the preparatory steps for filling the liquid oxygen tank.

The official "go" has been relayed to the launch team to start first stage liquid oxygen loading.

NASA launch director Tim Dunn has completed a poll to confirm the agency management team is "go" for liquid oxygen loading. No technical problems are being reported in the countdown and current upper level winds are within limits.

It's a gorgeous morning here at the Cape Canaveral Air Force Station where temperatures are in the mid 70s, skies are mostly clear and all of the weather rules are "go" for launch at this time.

The launch weather officer still puts the odds of acceptable conditions during today's launch window at 80 percent.

The official forecast just briefed to mission managers for launch time includes scattered clouds, a chance of isolated showers in the area, good visibility, southwesterly winds from 230 degrees at 10 peaking to 15 knots and a temperature in the high 70s degrees F.

Now two hours from launch of GRAIL to the Moon.

"The purpose of the mission is to precisely map the gravity of the Moon. We're going to use that data to understand the structural interior of the Moon from crust-to-core. That's the basic idea," says Dave Lehman, GRAIL project manager from the Jet Propulsion Laboratory.

"And to do that you need to use two spacecraft. They bounce radio signals off each other, and that data is used to measure the distance change very precisely between the two spacecraft. Out of that information -- going through big supercomputers -- the scientists can determine the gravitational field of the Moon very precisely."

The launch team has completed work to turn on and configure the Delta's onboard guidance computer.

The first hints of daybreak are beginning to illuminate the eastern horizon.

The next milestone in the count will be loading super-cold cryogenic liquid oxygen into the first stage starting about 30 minutes from now. The kerosene and liquid oxygen will be consumed by the stage's Pratt & Whitney Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

The first stage fuel tank of the Delta 2 rocket has been fully loaded for today's planned 8:29 a.m. EDT launch. The tank was filled with a highly refined kerosene, called RP-1, during a 19-minute, 5-second process.

Rapid-loading of the RP-1 tank has concluded with 9,800 gallons having been pumped into the rocket. Fine load is continuing.

The launch team has computed that the full load for the first stage fuel tank will be 9,989 gallons.

Once the tank is filled to the 98 percent level, or 9,800 gallons, the "rapid load" valve will be closed and the slower "fine load" phase will continue to top off the tank.

First stage propellant loading has passed the 5,000-gallon mark. This process to load the kerosene fuel takes about 20 minutes.

Some 2,000 gallons are aboard the rocket already.

Fueling begins! About 10,000 gallons of the kerosene propellant, called RP-1, are pumping into the base of the rocket from storage tanks at pad 17B as fueling of the Delta 2's first stage begins for today's launch.

Preparations for loading the Delta 2 rocket's first stage RP-1 fuel tank are beginning. After verifying valves, sensors, flow meters and equipment are ready, the highly refined kerosene fuel will start flowing into the vehicle a few minutes from now.

Pressurization of the first stage helium and nitrogen systems has been completed.

The rocket's control system and guidance computer are being turned on.

Countdown begins! The three-hour Terminal Countdown sequence has been initiated for today's launch of the Delta 2-Heavy rocket with NASA's Moon-bound GRAIL gravity mappers.

Liftoff from pad 17B is scheduled for 8:29:45 a.m. EDT (1229:45 GMT). If the launch does not occur at that precise moment, another instantaneous opportunity is available at 9:08:52 a.m. EDT (1308:52 GMT).

Between now and the launch time, the rocket's guidance system will be activated, onboard helium and nitrogen tanks brought up to pressure, the kerosene fuel and liquid oxygen supplies loaded into the first stage, checks performed on the safety system and steering tests conducted on the engines.

The launch team has reported for duty. A readiness check just occurred to verify all consoles are "go" for starting the countdown 9 minutes from now.

Workers have cleared the Complex 17 area in advance of the hazardous portion in today's launch countdown. The pad clear status will allow the start of activities such as pressurizing the helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

T-minus 150 minutes and holding. The countdown is entering the first of the planned holds that will occur over the course of the morning. This first pause is 60 minutes long.

The later holds -- at the T-minus 20 and T-minus 4 minute points -- will give the launch team some time to catch up on any work running behind and verify all is in readiness for liftoff. The holds will last 20 minutes and 10 minutes in duration, respectively.

Launch remains targeted for 8:29 a.m. EDT (1229 GMT) from Cape Canaveral, Florida.

Ready to take another run at launching the Delta 2-Heavy in the morning, the mobile service gantry has again been pulled back from the rocket at Cape Canaveral's Complex 17B.

Following Thursday's launch postponement, the tower was placed back around the Delta and worker access platforms re-established surrounding the vehicle. As part of normal scrub activities, technicians perform a thorough inspection of the rocket before the next countdown.

The tower got into position to cocoon the rocket at about 2 p.m. EDT Thursday. Now, it's once again retracted to the launch position in preparation for the second countdown to begin.

Ground teams will spend the next few of hours getting the pad configured and secured in advance of the Terminal Countdown picking up at 5:29 a.m. EDT.

The count will include fueling of the first stage with highly refined kerosene starting about 5:55 a.m. and supercold liquid oxygen propellants at 6:45 a.m. EDT.

A standard hold at the T-minus 4 minute point will give launch managers the opportunity to survey the status before countdown clocks progress into the quickly paced final minutes that see the vehicle switch to internal power, the liquid oxygen tank pressurized and systems armed for liftoff at exactly 8:29:45 a.m. EDT (1229:45 GMT).

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In the live streaming video, you can see that the tower-on-wheels continues to retract on rails on the pad's western side.

This gantry was used starting on April 7 to stack the two-stage vehicle atop the pad's launch mount, plus attach the nine strap-on solid rocket motors and the GRAIL payload. The tower also provided the primary weather protection and worker access to the rocket during its stay at the oceanside complex.

Rollback of the mobile tower has begun! The 12-story-tall Delta is about to be revealed for this final planned rocket launch from Complex 17 after 55 years of flights.

The moveable access platforms inside the gantry surrounding the rocket are being folded back now. Also, the sliding door on the upper levels where the cleanroom area is located for handling the payloads has been opened in preparation for tower rollback.

The xenon spotlights are starting to pop on as launch pad workers get ready for tonight's rollback of the gantry-like mobile service tower from around the Delta 2-Heavy rocket.

Today's management meeting has given formal approval to proceed with launch of the Delta 2-Heavy rocket and the Moon-bound GRAIL spacecraft on Saturday morning at 8:29 a.m. EDT.

In a purely precautionary move, officials opted to skip making a launch attempt today so engineers could review propulsion system data and ensure the rocket was good to fly.

After draining the supercold liquid oxygen from the first stage following yesterday's scrub, a heater system stayed on longer than planned, a NASA spokesperson explained. But today's review determined no components could have been harmed by the extra heat, clearing the rocket for launch.

The launch weather forecast for Cape Canaveral still calls for a 60 percent chance of favorable conditions. "Primary concerns for launch are thick clouds, cumulus clouds and flight through precipitation," meteorologists report.

The outlook includes scattered low- and mid-level clouds, broken high clouds, isolated showers in the area, good visibility, northwesterly winds of 10 knots and a temperature of 77 degrees F.

Meanwhile, the downrange tracking station on Antigua expects to be up and running to support tomorrow's launch despite the approaching Tropical Storm Maria. If weather severely worsens and the site isn't able to support, workarounds with space-based telemetry coverage and Florida's Jupiter Inlet facility can substitute for Antigua.

Managers are meeting at this hour to assess the situation encountered while detanking the Delta 2-Heavy rocket after yesterday's scrub and determine if the next launch attempt can proceed tomorrow.

A decision is expected within the next couple of hours, NASA says.

For now, activities are moving forward to prepare for launching the GRAIL mission at 8:29 a.m. EDT tomorrow.

The Tropical Storm Maria that is bringing bad weather to the downrange tracking station of Antigua won't be a constraint to launch. The telemetry and commanding services provided by the site can be supplied by the TDRSS satellite constellation and station in Florida, a spokesperson says.

Here's a short story recapping these two delays for the GRAIL mission that have postponed the launch until Saturday morning.

The GRAIL lunar gravity mappers will forego making another launch attempt on Friday so engineers can examine data recorded during Thursday's post-scrub defueling of the Delta 2-Heavy rocket.

Here is the NASA statement explaining the decision to slip launch until Saturday morning:

"The launch of a Delta 2 rocket carrying NASA's Gravity Recovery and Interior Laboratory (GRAIL) has been postponed one day to allow additional time to review propulsion system data from Thursday's detanking operation after the launch attempt was scrubbed due to upper level winds. The postponement will allow the launch team additional time to review the data.

"The launch now is planned for Saturday, Sept. 10 from Space Launch Complex 17B at Cape Canaveral Air Force Station, Fla. There are two instantaneous launch opportunities at 8:29:45 a.m. and 9:08:52 a.m. EDT. The forecast for Sept. 10 shows a 60 percent chance of favorable weather conditions for a Saturday morning launch."

The weather outlook for Saturday morning calls for a 60 percent chance of acceptable conditions to launch the Delta 2 rocket. The two potential worries will be violations to the cumulus cloud rules and precipitation in the rocket's flight path.

The weather trough that is draped across the Florida peninsula is expected to finally start moving away this weekend, taking most of the rain and thunderstorm activity with it, the launch weather forecasters say.

DELAY. The Friday morning launch attempt for the Moon-bound GRAIL mission has been called off tonight. Details on the reason will be forthcoming from NASA shortly.

Launch is rescheduled for Saturday at 8:29:45 a.m. EDT. A backup opportunity is available at 9:08:52 a.m. EDT.

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