FRIDAY, SEPTEMBER 9, 2016
RECAP STORY: Like reaching back in time to examine the conditions that existed in the ancient solar system, NASA has launched a robotic probe to visit Asteroid Bennu and return an unspoiled sample of the primitive body that may hold the seeds of life.

Read our launch story.

0055 GMT (8:55 p.m. EDT Thurs.)
A video replay of today's launch is posted here.
0028 GMT (8:28 p.m. EDT Thurs.)
“ULA and our heritage vehicles have successfully launched NASA missions to every planet in our solar system,” said Maginnis. “ULA’s commitment to mission launch is unparalleled, and we’re proud of our team for continuing our unprecedented track record of 100 percent mission success.”
0025 GMT (8:25 p.m. EDT Thurs.)
"We are honored to be chosen by NASA to launch this historic mission,” said Laura Maginnis, ULA vice president of Custom Services. “Thank you to our NASA customer and mission partners for the outstanding teamwork and attention to detail as we successfully started OSIRIS-Rex on its seven-year journey to Bennu.”
0020 GMT (8:20 p.m. EDT Thurs.)
The post-launch news conference from Kennedy Space Center is coming up at 9 p.m. EDT.
0015 GMT (8:15 p.m. EDT Thurs.)
This was the 136th successful Atlas program launch in a row spanning more than two decades and the 65th for an Atlas 5.
0014 GMT (8:14 p.m. EDT Thurs.)
Flight controllers report that telemetry from OSIRIS-REx confirms deployment of the two power-generating solar arrays, a key post-launch milestone.
0010 GMT (8:10 p.m. EDT Thurs.)
The next Atlas 5 rocket launch is only a week away from Vandenberg Air Force Base in California. That commercial mission next Friday will deliver the WorldView 4 Earth-imagery satellite into polar orbit. Launch time is 11:30 a.m. local (2:30 p.m. EDT; 1830 GMT).

The next Atlas 5 from Cape Canaveral is planned for Oct. 3 to deploy the Air Force's third Space Based Infrared System Geosynchronous satellite, or SBIRS GEO Flight 3, into space for missile launch detection and warning. Liftoff will occur during a 40-minute launch window opening at 3:47 a.m. EDT (0747 GMT).

0008 GMT (8:08 p.m. EDT Thurs.)
MISSION SUCCESS is declared in this evening's OSIRIS-REx launch performed by the Atlas 5 rocket from Cape Canaveral.

"This was an excellent launch," says Tim Dunn, the NASA launch director. "Not a single anomaly was worked during the countdown."

0004 GMT (8:04 p.m. EDT Thurs.)
T+plus 59 minutes, 11 seconds. SPACECRAFT SEPARATION! The Centaur upper stage has deployed NASA's OSIRIS-REx spacecraft, embarking on a journey to Asteroid Bennu and back.
2354 GMT (7:54 p.m. EDT)
T+plus 49 minutes. Now 10 minutes until spacecraft deploy to complete the launch.
THURSDAY, SEPTEMBER 8, 2016
2352 GMT (7:52 p.m. EDT)
T+plus 46 minutes, 30 seconds. The second burn by Centaur was nominal and the results match expected parameters. OSIRIS-REx is en route to Bennu.
2350 GMT (7:50 p.m. EDT)
T+plus 45 minutes. This will be a 15-minute coast to put the rocket in view of the Canberra tracking station in Australia at the time of separation.
2349 GMT (7:49 p.m. EDT)
T+plus 44 minutes, 12 seconds. MECO 2. Centaur has completed its second burn of the day, propelling the OSIRIS-REx spacecraft on its interplanetary trajectory.
2347 GMT (7:47 p.m. EDT)
T+plus 42 minutes, 30 seconds. Five minutes into the burn. Centaur is performing well.
2346 GMT (7:46 p.m. EDT)
T+plus 41 minutes. All parameters from the Centaur are reported normal as the burn continues.
2345 GMT (7:45 p.m. EDT)
T+plus 40 minutes. The RL10 engine is consuming the liquid oxygen and liquid oxygen loaded into the vehicle just two hours ago.
2347 GMT (7:47 p.m. EDT)
T+plus 39 minutes, 40 seconds. Speed now 19,854 mph.
2344 GMT (7:44 p.m. EDT)
T+plus 39 minutes. RL10 engine parameters look good.
2342 GMT (7:42 p.m. EDT)
T+plus 37 minutes, 27 seconds. Ignition! The Centaur's single RL10-A-4-2 engine has re-ignited to boost OSIRIS-REx on Earth-escape trajectory.
2341 GMT (7:41 p.m. EDT)
T+plus 36 minutes. Centaur pressurization sequence complete. Liquid hydrogen and liquid oxygen system prestarts are about to begin.
2340 GMT (7:40 p.m. EDT)
T+plus 35 minutes. Less than two minutes from ignition. Centaur is reorienting to the proper position for the next engine firing.
2334 GMT (7:34 p.m. EDT)
T+plus 29 minutes. Tank pressures, battery voltages are good as the Centaur travels over 17,000 mph.
2325 GMT (7:25 p.m. EDT)
T+plus 20 minutes. Everything looking normal with Centaur during this coast.
2323 GMT (7:23 p.m. EDT)
To recap, the United Launch Alliance Atlas 5 rocket departed Cape Canaveral atop 1.2 million pounds of thrust at 7:05 p.m. EDT (2305 GMT) today to send NASA's OSIRIS-REx spacecraft on a seven-year, 4.4-billion-mile mission to rendezvous with Asteroid Bennu and bring a sample of the primordial object back to Earth.

It is the 65th Atlas 5 launch.

Another burn by the Centaur upper stage is upcoming to put the spacecraft on an escape trajectory to the asteroid.

2321 GMT (7:21 p.m. EDT)
T+plus 16 minutes. Good performance from the vehicle has resulted in a nominal orbit being achieved.
2317 GMT (7:17 p.m. EDT)
T+plus 12 minutes, 41 seconds. MECO 1. Centaur's main engine has shut down following its first burn today, achieving a preliminary Earth parking orbit with OSIRIS-REx. The rocket will coast in this orbit for about 20 minutes before the RL10 engine re-ignites to send the spacecraft on its way to Bennu.
2317 GMT (7:17 p.m. EDT)
T+plus 12 minutes, 20 seconds. Now at orbital velocity.
2316 GMT (7:16 p.m. EDT)
T+plus 11 minutes, 30 seconds. About one minute is left in this burn of Centaur.
2315 GMT (7:15 p.m. EDT)
T+plus 10 minutes. All systems reported stable as the Centaur fires to reach an initial Earth orbit.
2314 GMT (7:14 p.m. EDT)
T+plus 9 minutes. Centaur performance is reported right on target.
2312 GMT (7:12 p.m. EDT)
T+plus 7 minutes. The rocket is tracking right down the planned flight path.
2311 GMT (7:11 p.m. EDT)
T+plus 6 minutes. Proper first stage performance has been reported from the launch team.
2310 GMT (7:10 p.m. EDT)
T+plus 5 minutes. Centaur engine readings look good as this burn gets underway.
2309 GMT (7:09 p.m. EDT)
T+plus 4 minutes, 45 seconds. The rocket now weighs just 6 percent of its liftoff mass.
2309 GMT (7:09 p.m. EDT)
T+plus 4 minutes, 33 seconds. The two halves of the 14-foot-diameter Atlas 5 rocket nose cone encapsulating the spacecraft have separated.
2309 GMT (7:09 p.m. EDT)
T+plus 4 minutes, 24 seconds. Centaur has ignited! The RL10 engine is up and running at full thrust to put the OSIRIS-REx payload into orbit.
2309 GMT (7:09 p.m. EDT)
T+plus 4 minutes, 14 seconds. The Atlas 5's Common Core Booster first stage has been jettisoned, and the Centaur upper stage's liquid hydrogen and liquid oxygen systems are being readied for engine start.
2309 GMT (7:09 p.m. EDT)
T+plus 4 minutes, 6 seconds. BECO. Booster Engine Cutoff is confirmed as the RD-180 powerplant on the first stage completes its burn. Standing by to fire the retro thrusters and separate the spent stage.
2308 GMT (7:08 p.m. EDT)
T+plus 3 minutes, 30 seconds. The vehicle weighs just a quarter of what it did at liftoff.
2308 GMT (7:08 p.m. EDT)
T+plus 3 minutes, 15 seconds. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.
2308 GMT (7:08 p.m. EDT)
T+plus 3 minutes. Everything still looking good on the first stage as the rocket powers downrange on the thrust being produced by the main engine.
2307 GMT (7:07 p.m. EDT)
T+plus 2 minutes, 50 seconds. Reaction control system has been activated.
2307 GMT (7:07 p.m. EDT)
T+plus 2 minutes, 35 seconds. Atlas continues tracking on course.
2307 GMT (7:07 p.m. EDT)
T+plus 2 minutes, 30 seconds. The RD-180 main engine continues to perform as expected.
2307 GMT (7:07 p.m. EDT)
T+plus 2 minutes, 21 seconds. The Aerojet Rocketdyne-made solid rocket motor has successfully separated from the Atlas 5, having completed its job of adding a powerful kick at liftoff.
2307 GMT (7:07 p.m. EDT)
T+plus 2 minutes. The vehicle weighs just half of what it did at liftoff.
2306 GMT (7:06 p.m. EDT)
T+plus 93 seconds. Solid rocket booster burnout has occurred. But the spent motor will remain attached to the first stage until the Atlas 5 reaches a point where the airborne dynamic pressure reduces to an allowable level for a safe jettison.
2306 GMT (7:06 p.m. EDT)
T+plus 70 seconds. The period of maximum dynamic pressure experienced by the rocket has been passed.
2306 GMT (7:06 p.m. EDT)
T+plus 60 seconds. We are one minute into the ascent of OSIRIS-REx on a 4.4-billion-mile trek.
2305 GMT (7:05 p.m. EDT)
T+plus 57 seconds. Mach 1.
2305 GMT (7:05 p.m. EDT)
T+plus 30 seconds. The vehicle is heading on a flight azimuth of 89 degrees.
2305 GMT (7:05 p.m. EDT)
T+plus 15 seconds. Pitch, yaw and roll maneuvers are underway as the Atlas 5 thunders away from Cape Canaveral with its RD-180 engine and solid rocket booster burning.
2305 GMT (7:05 p.m. EDT)
LIFTOFF! Liftoff of the Atlas 5 rocket launching OSIRIS-REx to Bennu and back in the search for the origins of life!
2304 GMT (7:04 p.m. EDT)
T-minus 20 seconds. "Go Atlas", "Go Centaur" and "Go OSIRIS-REx" was just called by launch team during a final status check.
2304 GMT (7:04 p.m. EDT)
T-minus 40 seconds. Centaur's liquid oxygen and liquid hydrogen tanks are stable at flight pressures.
2304 GMT (7:04 p.m. EDT)
T-minus 55 seconds. Range is green.
2304 GMT (7:04 p.m. EDT)
T-minus 1 minute. Now 60 seconds away from launching the 7-year, round trip voyage to Bennu and back.
2303 GMT (7:03 p.m. EDT)
T-minus 90 seconds. The rocket's safety system has been armed.
2303 GMT (7:03 p.m. EDT)
T-minus 1 minute, 45 seconds. Liquid oxygen and liquid hydrogen propellant topping to the Centaur upper stage is being secured.
2303 GMT (7:03 p.m. EDT)
T-minus 1 minute, 55 seconds. The launch sequencer has been commanded to start.
2303 GMT (7:03 p.m. EDT)
T-minus 2 minutes. The Atlas first stage and Centaur upper stage are now switching from ground power to internal batteries.
2302 GMT (7:02 p.m. EDT)
T-minus 2 minutes, 30 seconds. The first stage RP-1 kerosene fuel tank and the liquid oxygen have stepped up to proper flight pressure levels.
2302 GMT (7:02 p.m. EDT)
T-minus 3 minutes. The Atlas first stage liquid oxygen replenishment is being secured so the tank can be pressurized for launch.
2301 GMT (7:01 p.m. EDT)
T-minus 3 minutes, 50 seconds. The ground pyrotechnics are enabled.
2301 GMT (7:01 p.m. EDT)
T-minus 4 minutes and counting. Clocks have resumed for the final minutes of today's countdown to launch the Atlas 5 rocket from Cape Canaveral, Florida.
2300 GMT (7:00 p.m. EDT)
Standing by to pick up the count.
2259 GMT (6:59 p.m. EDT)
The ULA launch director has given the final approval to resume the countdown.
2258 GMT (6:58 p.m. EDT)
Polling of the team by Atlas launch conductor just occurred. All systems are reported GO for flight.
2256 GMT (6:56 p.m. EDT)
OSIRIS-REx is switching to internal battery power for launch.
2255 GMT (6:55 p.m. EDT)
Standing by for the final readiness check to be conducted. The launch team will be polled for a "go" or "no go" to proceed with the count.
2253 GMT (6:53 p.m. EDT)
NASA Launch Director Tim Dunn has performed the agency's clear-to-launch poll and the advisory team is working no issues.
2252 GMT (6:52 p.m. EDT)
The Atlas 5 rocket stands 189 feet tall and weighs 840,000 pounds at launch. It will lift off on 1.2 million pounds of thrust.
2250 GMT (6:50 p.m. EDT)
Here's a look at some stats about today's mission. This will be:
2247 GMT (6:47 p.m. EDT)
The vehicle's three cryogenic tanks are at flight level.
2246 GMT (6:46 p.m. EDT)
T-minus 4 minutes and holding. The countdown has entered the planned 15-minute hold to give the launch team a chance to review all systems before pressing ahead with liftoff.
2244 GMT (6:44 p.m. EDT)
T-minus 6 minutes. Standing by to go into the final built-in hold.
2236 GMT (6:36 p.m. EDT)
Weather is observed GO for liftoff based on the current conditions and forecast to stay favorable for an 7:05 p.m. EDT (2305 GMT) launch today.
2235 GMT (6:35 p.m. EDT)
Just 30 minutes until liftoff time. Standing by for the final status check on the weather.
2234 GMT (6:34 p.m. EDT)
The fuel-fill sequence for the first stage main engine is starting.
2225 GMT (6:25 p.m. EDT)
Today's launch uses a rocket like no other, a vehicle with a single solid-fuel booster mounted to its side, to launch NASA's OSIRIS-REx probe to Asteroid Bennu.

The United Launch Alliance Atlas 5 rocket in the unique 411 configuration has successfully flown three times before, successfully launching the commercial European TV satellite, called ASTRA 1KR, from Cape Canaveral in 2006 and two National Reconnaissance Office spy satellite deployment missions -- NROL-28 and NROL-34 -- from Vandenberg Air Force Base in 2008 and 2011. All were performed nominally.

The strange-looking rocket is all part of the "dial-a-rocket" approach that designers took when creating the Atlas 5 family of vehicles to tailor each launch to the payload. The unconventional 411 variant is not too strong and not too weak, providing just the right amount of power for OSIRIS-REx.

The configuration is unique because rockets typically fly with either no strap-on boosters or multiple motors. While the appearance is stark, many Atlas 5 launches have flown successfully with uneven numbers of boosters attached to the first stage, like the 551 version with three on one side and two on the other.

The SRB's stationary nozzle is oriented to mitigate the offset thrust, leaving the Atlas 5’s dual-nozzle main engine to provide the control authority to steer the rocket smoothly through the sky.

"It is unique and different,” said NASA Launch Director Tim Dunn. “The first part of the question is why only one solid? The easy answer there is performance. We needed just a little more performance than the basic 401 could provide. The addition of one solid rocket booster satisfies that…and getting the mass of OSIRIS-REx on its way to the asteroid.

“Then, how do you fly with that one solid hanging off the side? In simplest terms, you let the flight control systems of the Atlas 5 sort it all out. It is a fixed nozzle on the solid strap-on but you have the two vectorable nozzles from the RD-180 engine. They can easily adjust slightly to offset that single thrust moment that is coming from one particular side of the Atlas 5.

“The actuators that steer the nozzles in the pitch and yaw directions, and can also roll the vehicle, they counteract the asymmetrical thrust from the single solid to enable the rocket to fly straight as we like it to.”

2220 GMT (6:20 p.m. EDT)
Now 45 minutes from liftoff. Today marks the 65th flight for Atlas 5, born of the Air Force's competition to develop next-generation Evolved Expendable Launch Vehicles. In its previous 64 missions since debuting in August 2002, the Atlas 5 has flown 25 flights dedicated to the Defense Department, 14 commercial missions, 13 for the National Reconnaissance Office and 12 for NASA.
2210 GMT (6:10 p.m. EDT)
The 840,000-pound Atlas 5 rocket now stands fully fueled with its cryogenic liquid oxygen and liquid hydrogen as the countdown continues on schedule for a liftoff at 7:05 p.m. EDT (2305 GMT).
2209 GMT (6:09 p.m. EDT)
Fast-filling of the first stage liquid oxygen tank has been completed. Topping mode is now underway.
2207 GMT (6:07 p.m. EDT)
The liquid hydrogen tank in the Centaur upper stage just reached the 96 percent level. Topping is beginning.
2205 GMT (6:05 p.m. EDT)
Now 60 minutes from liftoff.

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2200 GMT (6:00 p.m. EDT)
First stage liquid oxygen tank is 80 percent full thus far. 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 minutes of flight today. The 25,000 gallons of RP-1 were previously loaded into the rocket.
2156 GMT (5:56 p.m. EDT)
Centaur's liquid hydrogen tank is 20 percent full. The cryogenic propellant will be consumed with liquid oxygen by the stage's Aerojet Rocketdyne-made RL10 engine.
2149 GMT (5:49 p.m. EDT)
Chilldown of the liquid hydrogen system has been accomplished. The launch team has received the "go" to begin filling the Centaur upper stage with the supercold fuel.
2146 GMT (5:46 p.m. EDT)
The first stage liquid oxygen tank has reached the 50 percent mark.
2141 GMT (5:41 p.m. EDT)
The Centaur engine chilldown sequence is being initiated.
2136 GMT (5:36 p.m. EDT)
Centaur liquid oxygen tank has reached flight level.
2133 GMT (5:33 p.m. EDT)
The countdown remains on schedule and the launch team is working no issues.
2130 GMT (5:30 p.m. EDT)
The Centaur liquid oxygen tank reached the 96 percent level. The topping off process is starting now.
2127 GMT (5:27 p.m. EDT)
The first stage liquid oxygen loading is transitioning from slow-fill to fast-fill mode.
2126 GMT (5:26 p.m. EDT)
Now at the 80 percent level on the Centaur upper stage's liquid oxygen tank.
2126 GMT (5:26 p.m. EDT)
The chilldown conditioning of liquid hydrogen propellant lines at Complex 41 is starting to prepare the plumbing for transferring the Minus-423 degree F fuel into the rocket. The Centaur holds about 12,300 gallons of the cryogenic propellant.
2120 GMT (5:20 p.m. EDT)
Now half-full on the Centaur upper stage's liquid oxygen tank.
2119 GMT (5:19 p.m. EDT)
The conditioning of the systems for the first stage liquid oxygen tank have been completed. And a "go" has been given to begin pumping supercold liquid oxygen into the Atlas 5's first stage.

The Common Core Booster stage's liquid oxygen tank is the largest tank to be filled today. It holds 48,800 gallons of cryogenic oxidizer for the RD-180 main engine.

2115 GMT (5:15 p.m. EDT)
Now at the 30 percent level on the Centaur upper stage's liquid oxygen tank.
2110 GMT (5:10 p.m. EDT)
Passing the 10 percent level on the Centaur upper stage's liquid oxygen tank.
2104 GMT (5:04 p.m. EDT)
Filling of the Centaur upper stage with about 4,150 gallons of liquid oxygen has begun at Cape Canaveral's Complex 41 following the thermal conditioning of the transfer pipes.

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 Centaur will perform the firings required to propel the OSIRIS-REx spacecraft on its intended flight path today.

2057 GMT (4:57 p.m. EDT)
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.
2050 GMT (4:50 p.m. EDT)
T-minus 2 hours and counting! The launch countdown has resumed for today's flight of the Atlas 5 rocket to send OSIRIS-REx on its 4.4-billion-mile mission.

Clocks have one more built-in hold planned at T-minus 4 minutes. During that 15-minute pause, the final "go" for launch will be given. All remains targeted for liftoff at 7:05 p.m. EDT (2305 GMT) from Cape Canaveral's Complex 41.

In the next couple of minutes, chilldown thermal conditioning of the mobile launch platform upon which the rocket stands will begin. This is meant to ease the shock on equipment when supercold cryogenic propellants start flowing into the rocket.

2047 GMT (4:47 p.m. EDT)
All console operators have reported READY status during the pre-fueling readiness poll. The ULA launch director also voiced his approval for moving forward with the countdown as scheduled today.

The loading of nearly 66,000 gallons of cryogenic liquid oxygen and liquid hydrogen into the Atlas 5 rocket will be getting underway a short time from now.

2045 GMT (4:45 p.m. EDT)
The ULA launch conductor at the Atlas Spaceflight Operations Center is briefing his team on procedures before entering into the final two hours of the countdown.
2042 GMT (4:42 p.m. EDT)
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2040 GMT (4:40 p.m. EDT)
"Man stations for cryogenic tanking."
2035 GMT (4:35 p.m. EDT)
T-minus 2 hours and holding. The countdown has just entered the first of two planned, 15-minute holds over the course of the day that will lead to the 7:05 p.m. EDT (2305 GMT) launch of the Atlas rocket. The holds give the team some margin in the countdown timeline to deal with technical issues or any work that is running behind. The final hold is scheduled to occur at T-minus 4 minutes.
2032 GMT (4:32 p.m. EDT)
The final hands-on work has wrapped up at the launch pad and technicians have departed the complex. Safety officials just confirmed that the surrounding danger area has been cleared of all workers for the remainder of the countdown.
2017 GMT (4:17 p.m. EDT)
In the pre-fueling briefing, the launch weather officer from the Air Force reports conditions are stable and favorable this afternoon at Cape Canaveral.

The odds of acceptable weather have improved to 90 percent.

2010 GMT (4:10 p.m. EDT)
The Atlas 5 rocket and OSIRIS-REx spacecraft are reporting GO status at this hour. The vehicle is powered up and gone through a few hours of testing so far.
1917 GMT (3:17 p.m. EDT)
The early portion of the countdown is proceeding smoothly. "Everything is tickey boo. Nothing is amiss," a NASA spokesman says.

In about 90 minutes, the launch team will be polled for readiness to begin fueling the Atlas 5 rocket. Tanking starts around 5 p.m.

1905 GMT (3:05 p.m. EDT)
Now just four hours away from the launch of OSIRIS-REx on its daring sample return mission to Asteroid Bennu.

"Sample return is really at the forefront of planetary exploration," said Dante Lauretta, the principal investigator. "Not only are we going to get this material into our laboratories for precise chemical analyses that can't be duplicated by spacecraft instruments, but this is going to be a treasure trove of information and material for scientists yet to come."

This robotic mission will bring back pristine samples from Bennu, potentially with organic molecules.

"One of the leading theories for delivery of organic molecules to the surface of the Earth is delivery from asteroids and comets," Lauretta said. "Meteorites, once they're on the surface of the Earth, are very quickly contaminated, organically. Microbes love these materials. The things we're looking for are the things these bacteria are made out of, the amino acids that make up their proteins.

"We're really interested in what (was in the) original inventory of materials, the seeds of life these carbon-rich asteroids and comets may have brought to the surface."

1615 GMT (12:15 p.m. EDT)
The countdown just began for this evening's launch of the Atlas 5 rocket to dispatch NASA's OSIRIS-REx spacecraft on a 7-year adventure to Asteroid Bennu to capture primordial material from the mountain-sized rock and bring it back to Earth.

Clocks are picking up the seven-hour sequence of work that will prepare the booster, payload and ground systems for blastoff at 7:05 p.m. EDT (2305 GMT).

The launch team will begin powering up the rocket to commence standard pre-flight tests. Over the subsequent few hours, final preps for the Centaur's liquid oxygen and liquid hydrogen systems will be performed, along with a test of the rocket's guidance system and the first stage propulsion and hydraulic preps, internal battery checks and testing of the GPS metric tracking system used to follow the rocket as it flies downrange, plus a test of the S-band telemetry relay system.

A planned 15-minute hold begins when the count reaches T-minus 2 hours. Near the end of the hold, the team will be polled to verify all is in readiness to start fueling the rocket for launch.

Supercold liquid oxygen begins flowing into the Centaur upper stage, followed by the first stage filling. Liquid hydrogen fuel loading for Centaur will be completed a short time later.

A final hold is scheduled at the T-minus 4 minute mark. That 15-minute pause will give everyone a chance to finish any late work and assess the status of the rocket, payload, Range and weather before proceeding into the last moments of the countdown.

The launch window tonight lasts two hours to 9:00 p.m. EDT (0100 GMT).

1430 GMT (10:30 a.m. EDT)
In this morning's weather update, the outlook still looks the same -- and favorable -- for flight of the Atlas 5 rocket this evening. Odds of good weather for the launch window stand at 80 percent.

"There is no change to today's launch forecast," the Air Force meteorology team reports.

"Low-level moisture is increasing over the Space Coast, but the mid- and upper-levels remain dry and weather is favorable for launch. The Bermuda High ridge continues to build in to the north, and with the Space Coast between the high pressure ridge to the north and a trough stretching from the Bahamas though Cuba, the pressure gradient will cause breezy conditions along the coast.

"Additionally, the sea breeze will develop late morning and migrate inland in the early afternoon causing isolated showers along the boundary, but there is a low thunderstorm threat as the sea breeze pushes inland.

"Isolated coastal showers are possible this evening and during the launch window, and winds will be from the east-northeast with gusts in the mid- to upper- teens during the count and mid-teens during the window."

The outlook predicts just scattered low- and high-level clouds, good visibility, easterly winds of 10 to 15 knots and a temperature of 83 degrees F.

THURSDAY, SEPTEMBER 8, 2016
0001 GMT (8:01 p.m. EDT Wed.)
The seven-hour countdown begins at mid-day Thursday for the sequence of final preparations, testing and fueling of the United Launch Alliance Atlas 5 rocket that will propel NASA's OSIRIS-REx asteroid probe on its round trip odyssey to Bennu and back.

Liftoff is targeted for 7:05 p.m. EDT (2305 GMT) at the opening of a two-hour launch window.

"I'm absolutely not nervous because we have a phenomenal team, and they know what they are doing and they have my full trust and faith that they are going to get this job done," said Dante Lauretta, the OSIRIS-REx mission leader.

"I am anxious because I've been working on this program for 12 years now and I really want to fly this spacecraft that Lockheed Martin has built for us.

"But those are two very different states of mind, I want to make sure you understand how much faith I have in this crew."

The rocket was positioned atop Complex 41's launch pad on Wednesday morning, following rollout from the vehicle assembly building.

See ULA photos of the rocket rollout. A separate gallery of NASA photos is available too.

Weather forecasters predict an 80 percent chance of acceptable conditions for the launch opportunity.

"The seabreeze will develop late morning and migrate inland early afternoon with isolated showers along the boundary. There is a low thunderstorm threat as the seabreeze pushes to the mainland. Afternoon and evening showers and thunderstorms continue to favor the interior with a coastal shower threat during the evening and overnight hours," forecasters say.

The launch time outlook calls for scattered low- and high-level clouds, good visibility, easterly winds of 10 to 15 knots and a temperature of 83 degrees F.

Watch this page for live coverage throughout the countdown and flight of the Atlas-Centaur rocket.

Be sure to sign up for our Twitter feed to get occasional countdown updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

Public viewing options are described by LaunchPhotography.com. Get directions here.

The Atlas 5, designated AV-067, will be making its 65th flight since 2002 and flying for the fourth time in the particular 411 configuration with a single solid rocket booster. Stacking began Aug. 8.

The OSIRIS-REx spacecraft, since arriving at Kennedy Space Center from Lockheed Martin's Denver factory on May 20, has undergone a series of final checks, spin-balance testing for weight and center of gravity determinations, removal of the solar arrays for cleaning and re-installation, the loading of 2,700 pounds of maneuvering fuel and buttoning up of the thermal blankets. It was encapsulated on Aug. 24 and mated atop the Atlas 5 on Aug. 29.

OSIRIS-REx is derived from other Lockheed Martin-built spacecraft: Mars Reconnaissance Orbiter, Juno and MAVEN, coupled with the Sample Return Capsule that "is almost an exact copy of what was returned to Earth on Stardust," said Rich Kuhns, OSIRIS-REx program manager with Lockheed Martin Space Systems in Denver.

WEDNESDAY, SEPTEMBER 7, 2016
ROLLOUT: Poised to embark on a 7-year adventure to Asteroid Bennu and back, NASA’s OSIRIS-REx sample return spacecraft was moved to the launch pad today aboard its Atlas 5 rocket for liftoff Thursday evening.

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TUESDAY, SEPTEMBER 6, 2016
LRR: Mission leaders Tuesday gave approval for rollout of the United Launch Alliance Atlas 5 rocket to its pad on Wednesday morning, leading to liftoff Thursday evening of a NASA probe to rendezvous with an asteroid and bring a sample back to Earth.

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MONDAY, SEPTEMBER 5, 2016
PREVIEW: What began as a concept scribbled on a cocktail napkin in a Tucson bar 12 years ago -- sending a spacecraft to an asteroid and retrieving a pristine sample to bring back to Earth for study -- becomes reality Thursday with the launch of NASA's OSIRIS-REx mission.

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SUNDAY, SEPTEMBER 4, 2016
WEATHER: Prognosticators are predicting favorable weather conditions to launch an Atlas 5 rocket Thursday and send NASA's OSIRIS-REx spacecraft on its interplanetary journey to interrogate an asteroid and collect a surface sample for return to Earth.

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