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The Mission

Rocket: Atlas 5 (AV-010)
Payload: New Horizons
Date: January 19, 2006
Time: 1:08-3:07 p.m. EST (1808-2007 GMT)
Site: Complex 41, Cape Canaveral, Florida
Broadcast: AMC 6, Transponder 17, 72° West

Video coverage

Overview of the mission

Mission Status Center

Daily launch windows

Launch ground track

New Horizons trajectory

The science goals

Craft/instrument details

Student Dust Counter

Illustrations of the probe

Atlas 5 rocket info

Cape's Complex 41

New Horizons stories

Atlas archive

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Mounted atop Atlas 5
After reaching Lockheed Martin's Vertical Integration Facility following the early morning drive across the Cape, a crane lifts the New Horizons spacecraft into the 30-story building for mounting atop the awaiting Atlas 5 vehicle.

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Leaving the hangar
The New Horizons spacecraft, mounted atop a special transporter, departs Kennedy Space Center's Payload Hazardous Servicing Facility after spending three months in the building undergoing testing, final closeouts, filling of its hydrazine fuel, mating with the third stage kick motor and spin-balance checks. The probe was driven to the Atlas 5 rocket's assembly building at Complex 41 for mating with the launcher.

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Mission logo
With New Horizons enclosed within the Lockheed Martin Atlas 5 rocket's nose cone, a large decal reading: "New Horizons: Pluto-Kuiper Belt Mission" is applied to the payload fairing.

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Nose cone encapsulation
The New Horizons is packed away for its launch to Pluto as workers slide the two-piece Atlas 5 rocket nose cone around the spacecraft at the Kennedy Space Center Payload Hazardous Servicing Facility. The Swiss-made shroud protects the spacecraft during ascent through Earth's atmosphere.

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Science of New Horizons
The first robotic space mission to visit the distant planet Pluto and frozen objects in the Kuiper Belt is explained by the project's managers and scientists in this NASA news conference from the agency's Washington headquarters on Dec. 19.

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Follow the countdown and launch of the Lockheed Martin Atlas 5 rocket with NASA's New Horizons spacecraft bound for Pluto and beyond. Reload this page for the latest on the mission.

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2245 GMT (5:45 p.m. EST)

This was the seventh flight of Lockheed Martin's next-generation Atlas 5 rocket, all of which have been successful. It also extends the string of successful missions by the Atlas family to 78 dating back to 1993.

"Today's launch once again demonstrates the capabilities and flexibility of the Atlas 5," said Mark Albrecht, president of the International Launch Services firm that markets the Atlas. "This mission had a need for speed, so we provided our biggest and most powerful vehicle. This was our seventh Atlas 5 flight, and the second Atlas 5 mission for NASA. We're proud that Atlas vehicles of all configurations have launched a total of 135 NASA missions."

The next Atlas 5 is scheduled for mid-April to launch the commercial Astra 1KR direct-to-home television broadcasting satellite.

2225 GMT (5:25 p.m. EST)

Our first batch of pictures from today's launch is available here.

2134 GMT (4:34 p.m. EST)

"Today, NASA began an unprecedented journey of exploration to the ninth planet in the solar system," says Dr. Colleen Hartman, Deputy Associate Administrator for NASA's Science Mission Directorate, Washington, D.C. "Right now, what we know about Pluto could be written on the back of a postage stamp. After this mission, we'll be able to fill textbooks with new information."

"The United States of America has just made history by launching the first spacecraft to explore Pluto and the Kuiper Belt beyond," says Dr. Alan Stern, New Horizons principal investigator, from Southwest Research Institute in Boulder, Colo. "No other nation has this capability. This is the kind of exploration that forefathers, like Lewis and Clark 200 years ago this year, made a trademark of our nation."

"This is the gateway to a long, exciting journey," says Glen Fountain, New Horizons project manager from Johns Hopkins University Applied Physics Laboratory. "The team has worked hard for the past four years to get the spacecraft ready for the voyage to Pluto and beyond, to places we've never seen up close. This is a once-in-a-lifetime opportunity, in the tradition of the Mariner, Pioneer, and Voyager missions to set out for first looks in our solar system."

2118 GMT (4:18 p.m. EST)

New Horizons principal investigator Alan Stern confirms that ashes of Pluto discoverer Clyde Tombaugh are aboard the spacecraft. The American astronomer found Pluto in 1930.

2109 GMT (4:09 p.m. EST)

NASA's Deep Space Network tracking station in Canberra, Australia acquired the first signals from the newly-launched New Horizons spacecraft at 2:50 p.m. EST, about five minutes after the third stage separation. Telemetry from the probe indicates all systems are operating normally, project manager Glen Fountain says.

The RTG nuclear power source aboard the craft is generating 180 watts right now. That will build up to 240 watts during the next few hours. Over 200 watts of power will be expected when New Horizons reaches Pluto.

2104 GMT (4:04 p.m. EST)

"The United States has a spacecraft on its way to Pluto, the Kuiper Belt and then the stars. This is really a historic day," New Horizons principal investigator Alan Stern says.

2100 GMT (4:00 p.m. EST)

The post-flight news conference is now underway.

2010 GMT (3:10 p.m. EST)

A supercharged Atlas 5 rocket carrying NASA's Pluto-bound New Horizons probe roared to life and vaulted away from Earth today on a three-billion-mile, nine-year voyage to the frigid edge of the solar system. Read our full story.

1950 GMT (2:50 p.m. EST)

NASA Launch Manager Omar Baez says today's launch of New Horizons spacecraft has been a success. The probe appears to be right on the mark.

A post-launch press conference is coming up in about an hour to provide more information on the spacecraft's health and status.

Stay tuned for continuing coverage including lots of video clips and photo galleries.

1946 GMT (2:46 p.m. EST)

New Horizons will fly past Jupiter next February, receiving a sling-shot boost from the giant planet's gravity to speed the trip to the outskirts of the solar system. The spacecraft will make its close encounter with Pluto on July 14, 2015.

1944 GMT (2:44 p.m. EST)

T+plus 44 minutes, 55 seconds. SPACECRAFT SEPARATION! The New Horizons spacecraft has been released from the third stage! The probe has departed Earth for its voyage to Pluto and the Kuiper Belt.

1944 GMT (2:44 p.m. EST)

T+plus 44 minutes. No problems have been reported during today's launch.

1942 GMT (2:42 p.m. EST)

T+plus 42 minutes, 20 seconds. Deployment of the spacecraft from the third stage is less than three minutes away.

1941 GMT (2:41 p.m. EST)

T+plus 41 minutes, 41 seconds. Third stage burnout. The motor has finished its firing over the Indian Ocean.

1941 GMT (2:41 p.m. EST)

T+plus 41 minutes. The third stage was provided by Boeing. The Lockheed Martin Atlas 5 rocket has now completed its job in the launch.

1940 GMT (2:40 p.m. EST)

T+plus 40 minutes, 30 seconds. The solid-fueled ATK-made Star 48 motor is up and firing with good pressures reported.

1940 GMT (2:40 p.m. EST)

T+plus 40 minutes, 15 seconds. Ignition of the third stage!

1939 GMT (2:39 p.m. EST)

T+plus 39 minutes, 45 seconds. Third stage separation! The upper stage has spun up and separated from the spent Centaur.

1939 GMT (2:39 p.m. EST)

T+plus 39 minutes, 26 seconds. MECO 2! The Centaur's Pratt & Whitney RL10 engine has shut down as expected.

1938 GMT (2:38 p.m. EST)

T+plus 38 minutes, 30 seconds. A minute to engine cutoff.

1937 GMT (2:37 p.m. EST)

T+plus 37 minutes, 40 seconds. Engine performance and chamber pressures look good as this lengthy burn continues.

1935 GMT (2:35 p.m. EST)

T+plus 35 minutes, 30 seconds. Just under four minutes left in this firing of the RL10 engine. After the Centaur completes this burn, the solid-fuel third stage will spin up and separate with the New Horizons spacecraft. The third stage then ignites to accelerate the probe to Pluto.

1934 GMT (2:34 p.m. EST)

T+plus 34 minutes, 10 seconds. All Centaur systems still reported normal.

1933 GMT (2:33 p.m. EST)

T+plus 33 minutes. The RL10 engine is burning its mixture of liquid oxygen and liquid hydrogen.

1931 GMT (2:31 p.m. EST)

T+plus 31 minutes. Centaur continues to perform well.

1930 GMT (2:30 p.m. EST)

T+plus 30 minutes, 12 seconds. Engine performance looks good.

1929 GMT (2:29 p.m. EST)

T+plus 29 minutes, 59 seconds. Centaur is firing again! The single RL10 engine has reignited as planned for a nine-and-a-half minute burn to accelerate New Horizons out of Earth orbit for the journey across the solar system. This firing will put the orbit out to the asteroid belt.

1928 GMT (2:28 p.m. EST)

T+plus 28 minutes, 45 seconds. Tank pressures on the Centaur are reported normal as the coast mode continues.

1927 GMT (2:27 p.m. EST)

T+plus 27 minutes, 30 seconds. The stage is performing a maneuver to improve antenna pointing for relay coverage.

1924 GMT (2:24 p.m. EST)

T+plus 24 minutes, 40 seconds. Centaur continues to roll at one degree per second. Rates are normal.

1920 GMT (2:20 p.m. EST)

T+plus 20 minutes. About 10 minutes remain until the RL10 engine is reignited.

1917 GMT (2:17 p.m. EST)

T+plus 17 minutes. The rocket has reached the proper parking orbit altitude around Earth.

1914 GMT (2:14 p.m. EST)

T+plus 14 minutes. Centaur is in a gentle roll to keep the thermal heating even across the stage.

1911 GMT (2:11 p.m. EST)

T+plus 11 minutes. The Centaur stage is reorienting itself following the first burn.

1910 GMT (2:10 p.m. EST)

T+plus 10 minutes, 12 seconds. MECO 1. Centaur's main engine has cut off following its first burn this morning. The rocket will coast in this preliminary orbit for about 20 minutes before the RL10 is reignited to propel New Horizons out of Earth orbit.

1909 GMT (2:09 p.m. EST)

T+plus 9 minutes, 30 seconds. The vehicle is 1,628 miles downrange, speeding along at 16,852 mph.

1909 GMT (2:09 p.m. EST)

T+plus 9 minutes. The Atlas 5 is tracking right now the planned flight track.

1908 GMT (2:08 p.m. EST)

T+plus 8 minutes, 30 seconds. Less than two minutes remain in this first burn of Centaur. The rocket is 110 miles above Earth and traveling over 16,000 mph.

1907 GMT (2:07 p.m. EST)

T+plus 7 minutes, 30 seconds. No problems reported with the RL10 engine or Centaur operations.

1907 GMT (2:07 p.m. EST)

T+plus 7 minutes. Centaur has performed a planned roll maneuver to aid communications.

1905 GMT (2:05 p.m. EST)

T+plus 5 minutes, 30 seconds. Centaur is up and firing. The rocket is 93 miles in altitude, 591 miles downrange and traveling over 14,000 mph.

1904 GMT (2:04 p.m. EST)

T+plus 4 minutes, 42 seconds. Centaur's RL10 main engine has ignited!

1904 GMT (2:04 p.m. EST)

T+plus 4 minutes, 38 seconds. Main engine cutoff confirmed. And the first stage has been jettisoned!

1904 GMT (2:04 p.m. EST)

T+plus 4 minutes. Less than a half-minute remaining in the first stage burn. The rocket is 67 miles in altitude, 78 miles downrange and traveling at 9,800 mph.

1903 GMT (2:03 p.m. EST)

T+plus 3 minutes, 50 seconds. The two-halves of the Atlas 5 rocket nose cone encapsulating the New Horizons spacecraft have separated. The Pluto-bound probe is now exposed to space. Also jettisoned was the Forward Load Reactor, a two-piece deck that rings the Centaur stage to support the bulbous fairing during launch.

Eight seconds after the shroud jettison, the RD-180 engine will throttle up to 100 percent again until reaching 5 G's. Throttle eases back to hold the five times gravity until 11 seconds before engine cutoff. It then throttles down to 4.6 G's to sense propellant depletion for engine shutdown.

1903 GMT (2:03 p.m. EST)

T+plus 3 minutes. No problems have been reported during this seventh launch of Lockheed Martin's Atlas 5 rocket. The rocket is 50 miles up, 59 miles downrange and traveling at 6,800 mph.

1902 GMT (2:02 p.m. EST)

T+plus 2 minutes. The Atlas 5 continues powering to space solely on the RD-180 first stage main engine now. The powerplant will keep its throttle setting at 100 percent until reaching 2.5 G's acceleration. Then the engine ramps down the throttle to maintain two-and-a-half times gravity through jettison of the rocket's nose cone, expected about 85 seconds from now.

1901 GMT (2:01 p.m. EST)

T+plus 1 minute, 55 seconds. All five solid rocket boosters have been jettisoned from the Atlas 5, having completed their job of adding a powerful kick at liftoff. The Aerojet-made boosters are the world's longest single-segment solids.

1901 GMT (2:01 p.m. EST)

T+plus 100 seconds. The five solid rocket boosters have burned out. They will remain attached to the vehicle for a little while longer, with two separating at T+plus 1 minute, 47 seconds and the other three spent casings jettisoning one-and-a-half seconds later.

1901 GMT (2:01 p.m. EST)

T+plus 75 seconds. Main engine is throttling down to 75 percent is preparation for burnout of the solid rocket boosters. After the five solid-propellant motors have consumed all of their fuel and that burnout detection is made, the Atlas 5 will throttle the RD-180 engine back to 100 percent thrust.

1901 GMT (2:01 p.m. EST)

T+plus 60 seconds. One minute into the flight of Atlas 5 and New Horizons. The rocket is roaring skyward on a mission to give humanity its first up-close look at the planet Pluto.

1900 GMT (2:00 p.m. EST)

T+plus 45 seconds. The RD-180 first stage engine is throttling up to 86 percent. The Max Q region has been passed and the greater thrust will increase the rocket's control authority and performance.

1900 GMT (2:00 p.m. EST)

T+plus 20 seconds. The main engine is easing back to two-thirds throttle to help the vehicle's passage through the area of maximum aerodynamic pressure.

1900 GMT (2:00 p.m. EST)

LIFTOFF! Liftoff of the Atlas 5 rocket launching New Horizons to Pluto and beyond -- the first mission of exploration to the outer frontier of our solar system!

1859 GMT (1:59 p.m. EST)

T-minus 20 seconds. "Go Atlas," "Go Centaur" called by launch team, verifying all systems are ready.

1859 GMT (1:59 p.m. EST)

T-minus 1 minute. New Horizons is poised to begin its flight of exploration and discovery.

1858 GMT (1:58 p.m. EST)

T-minus 80 seconds. The third stage is armed.

1858 GMT (1:58 p.m. EST)

T-minus 90 seconds. Launch control system is enabled. The Flight Termination System has been armed.

1858 GMT (1:58 p.m. EST)

T-minus 1 minute, 50 seconds. The automatic computer sequencer is in control of all the critical events through liftoff.

1858 GMT (1:58 p.m. EST)

T-minus 2 minutes. The Atlas first stage and Centaur upper stage are now switching to internal power. Liquid oxygen and liquid hydrogen topping for Centaur will be stopped in about 10 seconds.

1857 GMT (1:57 p.m. EST)

T-minus 2 minutes, 45 seconds. New Horizons has been declared "go" for launch.

1857 GMT (1:57 p.m. EST)

T-minus 3 minutes. The Atlas first stage liquid oxygen replenishment is being secured so the tank can be pressurized for flight. Also, the RP-1 tank is being pressurized to flight level.

1856 GMT (1:56 p.m. EST)

T-minus 3 minutes, 45 seconds. Ground pyrotechnics have been enabled.

1856 GMT (1:56 p.m. EST)

T-minus 4 minutes and counting. The final phase of today's countdown has begun for the launch of Lockheed Martin Atlas 5 and the New Horizons spacecraft bound for Pluto!

1855 GMT (1:55 p.m. EST)

Countdown clocks will resume in one minute. We are now five minutes from launch.

1853 GMT (1:53 p.m. EST)

The Atlas launch director Jerry Jamison has voiced his "go" for liftoff at 2:00 p.m.

1853 GMT (1:53 p.m. EST)

The Lockheed Martin Atlas launch team has been polled again to ensure all systems are still in readiness after this extended hold. No problems were reported.

1852 GMT (1:52 p.m. EST)

The NASA management team has reported it is "go" for launch.

1849 GMT (1:49 p.m. EST)

The Range says it is "go" for launch at 2:00 p.m.!

1846 GMT (1:46 p.m. EST)

NEW LAUNCH TIME. Liftoff is officially reset for 2:00 p.m., weather permitting.

1842 GMT (1:42 p.m. EST)

A firm launch time target has not been established yet. But officials are looking at 1:55 p.m. as the earliest.

1840 GMT (1:40 p.m. EST)

Engineers are loading an updated flight profile into the rocket's guidance computer based on the latest upper level winds. This is necessary because the preview profile expired at 1:45 p.m.

1833 GMT (1:33 p.m. EST)

Another launch time has not been selected yet. Countdown clocks remain holding at T-minus 4 minutes.

1831 GMT (1:31 p.m. EST)

The clouds are still the problem. The Range had reported its approval for launch at 1:40 p.m., then a few minutes later said the cloud ceiling rule would prevent liftoff at the latest in a series of new launch times set today.

1831 GMT (1:31 p.m. EST)

Range is 'no go' now!

1829 GMT (1:29 p.m. EST)

Range is 'go' for launch! The cloud conditions are now acceptable, safety officials have determined.

1827 GMT (1:27 p.m. EST)

The new timeline calls for the launch team readiness poll at 1:33 p.m., resumption of the countdown at 1:36 p.m. and liftoff at 1:40 p.m. EST (1840 GMT), if the clouds will allow.

1825 GMT (1:25 p.m. EST)

The cloud rule at issue here in the ceiling limit. Range Safety requires that it can track the rocket unobstructed through the first 6,000 feet of flight.

1823 GMT (1:23 p.m. EST)

NEW LAUNCH TIME. The Atlas team is targeting 1:40 p.m. EST.

1821 GMT (1:21 p.m. EST)

Range is 'no go' for launch at 1:30 p.m. because of clouds obscuring the optics for tracking the rocket at liftoff.

1820 GMT (1:20 p.m. EST)

Liftoff time is now 10 minutes away. Everyone is awaiting word whether the Range Safety is "go" for launch.

1812 GMT (1:12 p.m. EST)

This extra five minutes allows the Range to complete another sweep of the restricted area around the launch site.

1811 GMT (1:11 p.m. EST)

NEW LAUNCH TIME! Liftoff has been re-targeted again. Launch is now set for 1:30 p.m. EST.

1810 GMT (1:10 p.m. EST)

The Range says it cannot support a 1:25 p.m. launch.

1810 GMT (1:10 p.m. EST)

The low clouds have been drifting ashore from the Atlantic all morning. There are small breaks in the cloud cover that gives hope of launching through a hole.

1805 GMT (1:05 p.m. EST)

NEW LAUNCH TIME! The launch will be pushed back further to 1:25 p.m. EST to wait for the cloud cover to clear.

1803 GMT (1:03 p.m. EST)

Liftoff has been reset for 1:13 p.m. EST, the Range says.

1803 GMT (1:03 p.m. EST)

NO GO. Range Safety says the cloud ceiling remains below the 6,000 foot limit. The countdown will not resume for liftoff at 1:08 p.m. EST.

1802 GMT (1:02 p.m. EST)

Veteran launch conductor Ed Christiansen, seated in the Atlas Spaceflight Operations Center four miles from the pad, has polled the various console operators to ensure all systems are ready to proceed with the countdown. The 'go' status was passed to launch director Jerry Jamison located above and behind the launch team in the management room.

The launch will be stopped at T-minus 60 seconds if clouds remain "no go."

1801 GMT (1:01 p.m. EST)

The cloud ceiling rule is in violation at the moment.

1800 GMT (1:00 p.m. EST)

Eight minutes from liftoff time.

1758 GMT (12:58 p.m. EST)

NASA launch manager Omar Baez has polled the agency oversight team. There are no problems being reported with the Atlas 5, New Horizons spacecraft or ground systems. "NASA is ready to release the hold at T-minus 4 minutes," Baez said.

1757 GMT (12:57 p.m. EST)

A break in the clouds seems to be moving overhead. There is hope of launching on-time today, if the weather will cooperate.

1755 GMT (12:55 p.m. EST)

The New Horizons team reports the spacecraft is ready to proceed with launch.

1754 GMT (12:54 p.m. EST)

T-minus 4 minutes and holding. The countdown has entered the planned 10-minute hold hold. The low-cloud cover above the Cape could delay liftoff, however.

1753 GMT (12:53 p.m. EST)

T-minus 5 minutes. Standing by to go into the built-in hold.

1752 GMT (12:52 p.m. EST)

All three cryogenic fuel tanks aboard the rocket are now reported at flight level.

1752 GMT (12:52 p.m. EST)

The fuel-fill sequence for the first stage main engine is reported complete.

1750 GMT (12:50 p.m. EST)

The cloud deck over the pad is creating a ceiling at 3,500 feet, the launch weather officer says. He expects there to be the opportunity for the clouds to scatter out during the window. There is a launch rule calling for the ceiling to be no lower than 6,000 feet.

1748 GMT (12:48 p.m. EST)

Twenty minutes to go.

1747 GMT (12:47 p.m. EST)

The latest guidance and steering data have been loaded into the rocket's flight computer based on today's upper level wind conditions.

1738 GMT (12:38 p.m. EST)

Now 30 minutes from launch. Flight control final preps are complete.

1734 GMT (12:34 p.m. EST)

The Centaur liquid oxygen and liquid hydrogen tanks have been reported at flight level.

1733 GMT (12:33 p.m. EST)

The rocket's "pogo" suppressor has been charged for launch. This energy absorption device aboard the rocket is used to damp out oscillations during flight.

1728 GMT (12:28 p.m. EST)

T-minus 30 minutes and counting. The countdown clocks are heading to the T-minus 4 minute mark where a planned 10-minute hold will occur. Launch remains set for 1:08 p.m. EST. Weather conditions are looking good right now.

1720 GMT (12:20 p.m. EST)

Fast-filling of the first stage liquid oxygen tank has been completed. Topping mode is now underway.

1715 GMT (12:15 p.m. EST)

The liquid hydrogen tank in the Centaur upper stage has just reached 97 percent full. Topping is now beginning.

1710 GMT (12:10 p.m. EST)

The first stage liquid oxygen tank is 80 percent full, Centaur liquid hydrogen tank is reached the 70 percent mark and the Centaur oxygen tank is already fully loaded.

1708 GMT (12:08 p.m. EST)

Launch is now just 60 minutes away.

1705 GMT (12:05 p.m. EST)

The first stage liquid oxygen tank is now 70 percent full.

1703 GMT (12:03 p.m. EST)

The flight control final preparations are starting.

1702 GMT (12:02 p.m. EST)

The Centaur liquid hydrogen tank has reached the 20 percent level. The cryogenic propellant will be consumed with liquid oxygen by the stage's Pratt & Whitney-made RL10 engine.

1701 GMT (12:01 p.m. EST)

The Centaur engine chilldown is being initiated.

1656 GMT (11:56 a.m. EST)

First stage liquid oxygen tank is now half full. Chilled to Minus-298 degrees F, the liquid oxygen will be used with RP-1 kerosene by the RD-180 main engine on the first stage during the initial four-and-a-half minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket on Monday.

1655 GMT (11:55 a.m. EST)

Chilldown of the liquid hydrogen system is now complete, allowing the super-cold fuel to begin filling the Centaur upper stage.

1647 GMT (11:47 a.m. EST)

The first stage liquid oxygen tank is 30 percent full.

1644 GMT (11:44 a.m. EST)

The Centaur liquid oyxgen tank has reached flight level.

1641 GMT (11:41 a.m. EST)

Ten percent of the first stage liquid oxygen tank has been filled so far. The stage's bronze skin is icing over as the super-cold liquid oxygen flows into the vehicle.

1638 GMT (11:38 a.m. EST)

Now 90 minutes to launch. The Centaur liquid oxygen tank has now reached the 95 percent level. The topping off process is starting.

1637 GMT (11:37 a.m. EST)

The Atlas first stage liquid oxygen loading is transitioning from the slow-fill to the fast-fill mode.

1632 GMT (11:32 a.m. EST)

The chilldown conditioning of liquid hydrogen propellant lines at Complex 41 is now starting to prepare the plumbing for transferring the Minus-423 degree F fuel into the rocket. The Centaur holds about 13,000 gallons of the cryogenic propellant.

1631 GMT (11:31 a.m. EST)

The Centaur liquid oxygen tank is now 70 percent full.

1628 GMT (11:28 a.m. EST)

The chilldown conditioning of the systems for the first stage liquid oxygen tank have been completed. And a "go" has been given to begin pumping super-cold liquid oxygen into the Atlas 5's first stage. The Atlas liquid oxygen tank is the largest tank to be filled today. It holds about 50,000 gallons of cryogenic oxidizer for the RD-180 main engine.

1624 GMT (11:24 a.m. EST)

Forty percent of the Centaur liquid oxygen tank has been filled so far.

1617 GMT (11:17 a.m. EST)

The Centaur liquid oxygen tank is now 10 percent full.

1611 GMT (11:11 a.m. EST)

Following the thermal conditioning of the transfer pipes, filling of the Centaur upper stage with 4,300 gallons of liquid oxygen has begun at Cape Canaveral's Complex 41.

The liquid oxygen -- chilled to Minus-298 degrees F -- will be consumed during the launch by the Centaur's single RL10 engine along with liquid hydrogen to be pumped into the stage a little later in the countdown. The high-energy Centaur will perform two firings today to propel the New Horizons spacecraft out of Earth orbit.

1606 GMT (11:06 a.m. EST)

The Centaur liquid oxygen pad storage area has been prepped. The next step is conditioning the transfer lines, which is now beginning to prepare the plumbing for flowing the cryogenic oxidizer.

1603 GMT (11:03 a.m. EST)

Today's launch window extends from 1:08 to 3:07 p.m. EST. However, there will be two points in time in which liftoff cannot occur because the rocket's trajectory would take it too close another object already in space. Those Collision Avoidance blackout periods, or COLAs, are 1:20 and 2:55 p.m. EST.

1558 GMT (10:58 a.m. EST)

Chilldown thermal conditioning of the mobile launch platform upon which the rocket stands is beginning. This is meant to ease the shock on equipment when supercold cryogenic propellants start flowing into the rocket a short time from now.

1558 GMT (10:58 a.m. EST)

T-minus 120 minutes and counting! Countdown clocks are running again for launch of the Atlas 5 rocket and New Horizons headed for Pluto. Clocks have one more built-in hold planned at T-minus 4 minutes. That pause will last 10 minutes, giving the launch team one last chance to catch up on work running late or deal with any problems.

Read our earlier Mission Status Center coverage.

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