A miniature military space shuttle that circled the world for 224 days on a shakedown cruise in 2010 rocketed back into orbit Tuesday to demonstrate the reusability of the X-37B spaceplane.

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"We are indeed fortunate to have a very talented 'launch team' that works so well together," said Brig. Gen. Anthony Cotton, commander, 45th Space Wing and today's Launch Decision Authority.

"The teamwork across Air Force Space Command and with our 'Team Patrick / Cape' mission partners made this launch a success and is another example of how our Air Force delivers assured space launch, range and combat capabilities for the nation."

Rocket-maker United Launch Alliance hails today's flight of the Atlas 5 rocket as a success, boosting the third Orbital Test Vehicle mission into space for the X-37B program and the Air Force's Rapid Capabilities Office.

"The ULA team is proud to have played a critical role in successfully launching these three important Orbital Test Vehicle missions for the Air Force RCO," said Jim Sponnick, ULA vice president of mission operations. "This is a unique spacecraft since it is the first to launch on an Atlas 5, return to Earth landing at Vandenberg Air Force Base in California, and then fly again on this mission."

The next Atlas 5 rocket launch is planned for Jan. 29 from Cape Canaveral, blasting off at 8:52 p.m. EST carrying NASA's Tracking and Data Relay Satellite K, or TDRS K.

And with that, the launch will go into a cloak of secrecy. Confirmation that the Orbital Test Vehicle has separated from the Centaur won't be announced live.

T+plus 17 minutes, 36 seconds. MECO. Centaur's main engine has completed its burn, the powered phase of flight has finished for today's launch.

T+plus 16 minutes, 30 seconds. Centaur remains on course and looking good.

T+plus 15 minutes, 20 seconds. Velocity now 15,300 mph.

T+plus 15 minutes. Less than three minutes are left in this burn of Centaur.

T+plus 13 minutes, 15 seconds. RL10 engine parameters still look good.

T+plus 12 minutes, 45 seconds. All systems reported stable as the Centaur fires to reach Earth orbit.

T+plus 10 minutes. Velocity has increased to 11,500 mph as Centaur tracks right on course.

T+plus 9 minutes, 30 seconds. The RL10 continues to perform well, burning liquid hydrogen and liquid oxygen propellants.

T+plus 7 minutes, 30 seconds. Centaur is traveling more than 10,000 mph as it continues to thrust to orbit.

T+plus 6 minutes, 15 seconds. The vehicle tracking right on the proper trajectory.

T+plus 6 minutes. All appears to be proceeding well in the Atlas 5 rocket's climb to orbit.

T+plus 4 minutes, 43 seconds. Centaur has ignited! The RL10 engine is up and running at full thrust for its firing to propel X-37B to orbit.

T+plus 4 minutes, 35 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.

T+plus 4 minutes, 25 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.

T+plus 3 minutes, 43 seconds. The two-halves of the Atlas 5 rocket nose cone encapsulating the X-37B spaceplane have separated. The Orbital Test Vehicle 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.

T+plus 3 minutes, 20 seconds. RD-180 is performing well as the rocket climbs away from the planet.

T+plus 2 minutes, 30 seconds. The vehicle now weighs half of what it did at liftoff. Everything still looking good.

T+plus 2 minutes. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.

T+plus 105 seconds. The engine throttle setting is easing back to 95 percent thrust.

T+plus 90 seconds. Mach 1.

T+plus 60 seconds. One minute into the ascent as the Atlas 5 climbs away from the Cape, the X-37B spaceplane riding inside the nose cone en route to orbit.

T+plus 45 seconds. Good engine performance.

T+plus 30 seconds. The vehicle is thundering away from Cape Canaveral's Complex 41 on 860,000 pounds of thrust from the RD-180 main engine.

LIFTOFF! Liftoff of Atlas 5, boosting the reusable X-37B mini military space shuttle on a repeat trip to orbit. And the vehicle has cleared the tower!

T-minus 20 seconds. "Go Atlas" and "Go Centaur" was just called by launch team during a final status check.

T-minus 40 seconds. Centaur's liquid oxygen and liquid hydrogen tanks are stable at flight pressures.

T-minus 1 minute. Now 60 seconds from the launch that will put the original X-37B spaceplane back into orbit to demonstrate its reusability.

T-minus 90 seconds. The safety system has been armed.

T-minus 1 minute, 45 seconds. Liquid oxygen and liquid hydrogen propellant topping to the Centaur upper stage is being secured.

T-minus 1 minute, 55 seconds. The launch sequencer has been commanded to start.

T-minus 2 minutes. The Atlas first stage and Centaur upper stage are now switching from ground power to internal batteries.

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.

T-minus 3 minutes. The Atlas first stage liquid oxygen replenishment is being secured so the tank can be pressurized for launch.

T-minus 3 minutes, 50 seconds. The ground pyrotechnics have been enabled.

T-minus 4 minutes and counting. Clocks have resumed for the final minutes of today's countdown to launch the Atlas 5 rocket carrying X-37B. Liftoff is set to occur at 1:03 p.m. EST.

The Orbital Test Vehicle nestled inside the nose of the Atlas 5 rocket is switching to internal power for launch.

Countdown clocks will resume in one minute.

The ULA launch director has given his permission to fly today.

Polling of the team by Atlas launch conductor has occurred. All systems are reported "go" to continue with the countdown for liftoff at 1:03 p.m. EST.

Standing by for the launch team readiness polls.

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The Atlas 5 rocket stands 196 feet tall and weighs 757,380 pounds at launch.

No problems being reported by the launch team. Countdown continues to sit in the hold period at T-minus 4 minutes, waiting for the launch window to open at 1:03 p.m. EST. The current weather over the pad is the best that it has looked all day.

United Launch Alliance's webcast has publicly announced today's opportunity features three 10-minute windows to get the X-37B off the ground. The shots open at 1:03 p.m., 2:40 p.m. and 4:18 p.m. EST.

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T-minus 4 minutes and holding. The countdown has entered the planned 20-minute hold to give the launch team a chance to review all systems and assess the weather before pressing ahead with liftoff.

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

Weather remains GO for liftoff based on the current conditions and expected to stay favorable for a 1:03 p.m. EST launch today. Forecasters are predicting conditions to worsen as the afternoon goes along.

Thirty minutes from liftoff. The countdown clocks are heading to the T-minus 4 minute mark where a planned 20-minute hold will occur. Launch of Atlas 5 remains scheduled for 1:03 p.m. EST.

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

Here's a look at some stats about today's mission. This will be:

• The 616th launch for Atlas program since 1957
• The 327th Atlas to occur from Cape Canaveral
• The 205th mission for the Centaur upper stage
• The 182nd use of Centaur by an Atlas rocket
• The 34th launch of an Atlas 5 since 2002
• The 55th Evolved Expendable Launch Vehicle flight
• The 29th Atlas 5 to occur from the Cape
• The 26th Atlas 5 under United Launch Alliance
• The 11th 500-series flight of the Atlas 5
• The 4th Atlas 5 to fly in the 501 configuration
• The 3rd Orbital Test Vehicle mission by X-37B
• The 6th Atlas launch of 2012

Now 40 minutes till launch.

Atlas 5 represents the culmination of evolution stretching back several decades to America's first intercontinental ballistic missile. At the dawn of the space age, boosters named Atlas launched men into orbit during Project Mercury and became a frequent vehicle of choice to haul civil, military and commercial spacecraft to orbit.

Topped with the high-energy Centaur upper stage, Atlas rockets have been used since the 1960s to dispatch ground-breaking missions for NASA, including the Surveyors to the Moon, Mariner flights to Mars, Venus and Mercury, and the Pioneers that were the first to visit Jupiter and beyond.

In its newest era, the Atlas 5 rocket sent the Mars Reconnaissance Orbiter to the red planet in 2005, propelled the New Horizons probe toward Pluto and the solar system's outer fringes in 2006, doubled up with the dual Lunar Reconnaissance Orbiter and LCROSS impactor to the Moon in 2009, hurled Juno to Jupiter last August and dispatched the car-sized Curiosity rover on the Mars Science Lab mission in November.

Today marks the 34th flight for Atlas 5, born of the Air Force's competition to develop next-generation Evolved Expendable Launch Vehicles. In its previous 33 missions since debuting in August 2002, the tally shows 10 flights dedicated to the Defense Department, 9 commercial missions with communications spacecraft, seven with spy satellites for the National Reconnaissance Office and seven for NASA.

Now 60 minutes from liftoff. Fueling of the Atlas rocket with cryogenic liquid oxygen and liquid hydrogen is nearly complete as the countdown continues as planned for a liftoff at 1:03 p.m. EST.

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

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

Centaur's liquid hydrogen tank is 40 percent full. The cryogenic propellant will be consumed with liquid oxygen by the stage's Pratt & Whitney Rocketdyne-made RL10 engine.

The first stage liquid oxygen has reached the 70 percent level.

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.

The Centaur engine chilldown sequence is being initiated.

Half of the Atlas liquid oxygen tank has been filled so far.

Launch of the Atlas 5 rocket is just 90 minutes away.

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First stage liquid oxygen tank is 40 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-and-a-half minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket earlier.

Upper stage liquid oxygen has reached flight level.

The Centaur liquid oxygen tank reached the 95 percent level. The topping off process is starting now.

The first stage liquid oxygen flow rate is switching from slow-fill to fast-fill mode.

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 12,700 gallons of the cryogenic propellant.

Now three-quarters full on Centaur liquid oxygen.

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

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 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 49,000 gallons of cryogenic oxidizer for the RD-180 main engine.

The Centaur liquid oxygen tank has reached the 20 percent mark.

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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 provide the thrust to put X-37B into orbit.

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.

T-minus 120 minutes and counting! The launch countdown is continuing on schedule for today's flight of the Atlas 5 rocket with the Orbital Test Vehicle No. 3 aboard.

Clocks have one more built-in hold planned at T-minus 4 minutes. That pause will last 20 minutes during which time the final "go" for launch will be given. All remains targeted for liftoff at 1:03 p.m. EST 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.

After briefing his team on procedures before entering into the final two hours of the countdown, the launch conductor at the Atlas Spaceflight Operations Center just held a pre-fueling readiness poll. All console operators reported a "ready" status.

The ULA launch director also voiced his approval for proceeding with the countdown.

Loading of cryogenic liquid oxygen and liquid hydrogen into the Atlas 5 rocket will be getting underway a short time from now.

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T-minus 2 hours and holding. The countdown has just entered the first of two planned holds over the course of the day that will lead to the 1:03 p.m. EST launch of the Atlas rocket. This initial pause lasts 30 minutes, giving 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 and will last for 20 minutes.

The Complex 41 pad and the blast danger area have been cleared of all workers for the remainder of the countdown.

The weather is gloomy at Cape Canaveral this morning, but the current observations show that all of the launch rules remain "go" right now.

The outlook for launch time now calls for scattered low clouds at 3,000 feet, a broken deck at 10,000 feet and another broken deck at 25,000 feet, showers or isolated thunderstorms in the area, visibility of 7 miles, south-southwesterly winds of 12 gusting to 16 knots and a temperature around 76 degrees F.

Forecasters believe the best chance for acceptable weather comes with an on-time launch at 1:03 p.m. EST, with strong thunderstorms developing later in the afternoon.

The outlook for the backup launch opportunity on Wednesday calls for only a 20 percent chance of acceptable liftoff conditions.

The hazard area roadblocks around the launch site's safety perimeter are being established now. And the launch team has started configuring the pad's water deluge system.

Rumbling away from the planet on nearly a million pounds of thrust, the Atlas 5 rocket will be flying in a basic, two-stage configuration without any added strap-on solid motors. The vehicle sports a voluminous nose cone that encapsulates the X-37B spaceplane during the atmospheric ascent before being shed.

In technical speak, this is the Atlas 5-501 configuration that has successfully flown three times. The first was the original X-37B launch in April 2010, then a California flight in September 2010 that deployed a classified satellite for the National Reconnaissance Office and the subsequent X-37B mission in March 2011.

With the liftoff thrust not considerably more than the rocket's weight, this Atlas will display a slow and majestic rise trailing only a flickering golden flame from its Russian-designed RD-180 main engine.

Once above the launch pad, the rocket sets sail for the eastward trek downrange over the Atlantic Ocean, constantly gaining speed as its double-nozzle engine gulps 25,000 gallons of kerosene fuel and 50,000 gallons of superchilled liquid oxygen in just four-and-a-half minutes.

The bronze first stage, its propellants depleted and job now completed, then jettisons with the help of tiny thrusters. Some 106.5 feet long and 12.5 feet around, the stage is discarded to fall back into the open sea.

The cryogenic Centaur upper stage ignites moments after shedding the lower booster, lighting the tried-and-true RL10 engine for 22,300 pounds of thrust to continue clawing toward orbit.

Covered with insulating foam, this stage stretches 41.5 feet in length and 10 feet in diameter. Centaur must perform the full burn to loft X-37B into the proper orbit around the planet.

No technical issues are being reported in the countdown and technicians are completing final preps on the Centaur upper stage liquid oxygen and liquid hydrogen systems. The launch team will soon begin a test of the S-band telemetry relay system.

Now entering the final five hours of the countdown for liftoff of the United Launch Alliance Atlas 5 rocket carrying the Orbital Test Vehicle Flight No. 3.

The day's early activities are going well, powering up the rocket, initiating system final preps on both the Atlas and Centaur stages and commencing the guidance testing. Clocks remain aimed toward a 1:03 p.m. EST launch.

The cold front is draped over Florida this morning, but at the present time none of the weather rules are being violated. Forecasters still predict a 30 percent favorable conditions for the 1:03 p.m. EST launch.

Lightning, cumulus clouds, disturbed weather and thick clouds are the potential criteria that could be impacted today.

The outlook for launch time now calls for scattered low clouds at 3,000 feet, a broken deck at 12,000 feet and another broken deck at 25,000 feet, showers or isolated thunderstorms in the area, visibility of 7 miles, south-southwesterly winds of 12 gusting to 16 knots and a temperature around 76 degrees F.

The outlook has worsened a bit for the backup launch opportunity on Wednesday, dropping odds of acceptable liftoff conditions tomorrow to only 20 percent.

The countdown is underway for today's launch of the X-37B spaceplane aboard an Atlas 5 rocket from Cape Canaveral at 1:03 p.m. EST (1803 GMT).

The launch team will soon power up the rocket to commence standard pre-flight tests. Over the next 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 C-band system used to track the rocket as it flies downrange, plus a test of the S-band telemetry relay system. The Complex 41 site will be cleared of all personnel three hours before launch.

A planned half-hour hold begins when the count reaches T-minus 120 minutes. 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 two hours before launch, followed by the first stage filling with LOX and then liquid hydrogen fuel loading for Centaur.

A final hold is scheduled at the T-minus 4 minute mark. That 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 for liftoff.

The Delta 4 rocket's cryogenic upper stage persevered through a fuel leak and the resulting low-thrust condition by autonomously engaging techniques that kept the mission on track to successfully launch a Global Positioning System satellite in October.

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On the pad! An Atlas 5 rocket has arrived atop its Cape Canaveral pad for Tuesday's reflight of the U.S. military's original X-37B spaceplane, an unmanned reusable space shuttle operated by the Air Force.

After spending 224 days orbiting Earth in 2010, that same vehicle is going back to space tomorrow for another classified mission. The Atlas will insert the winged craft into low-Earth-orbit where it will operate in secret.

Riding atop its mobile launching platform, the United Launch Alliance-built rocket left the Vertical Integration Facility for the 1,800-foot trip along rail tracks to Complex 41.

The 20-story-tall vehicle, with the Orbital Test Vehicle-Flight 3 payload enclosed within the bulbous nose cone, now begins the final pre-flight activities.

Within the next hour, the auto couplers between the pad and platform will be engaged to route umbilical connections from the ground to the rocket for tomorrow's fueling of the booster with cryogenic propellants.

Ground crews will spend a few hours conducting various test sequences and removing the undercarriages used to transport the launch platform before securing the rocket for a quiet evening.

The countdown begins Tuesday morning, leading to blastoff at 1:03 p.m. EST. The length of tomorrow's available launch opportunity hasn't been publicly announced.

So join us tomorrow on this page for live countdown and launch coverage!

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The rocket's rollout to the pad is underway! The United Launch Alliance Atlas 5 that will boost the U.S. military's experimental X-37B spaceplane into orbit is rolling to Cape Canaveral's Complex 41 pad for Tuesday's liftoff.

This slow drive from the 30-story Vertical Integration Facility to the pad uses a pair of specially-made "trackmobiles" to carry the rocket's 1.4-million pound mobile launching platform along rail tracks for the 1,800-foot trip.

The two-stage rocket and the X-37B were put together inside the assembly building in preparation for this rollout event. The Atlas 5 is designed to spend minimal time at the launch pad, which does not include a service gantry like other sites.

With liftoff targeted for 1:03 p.m. EST tomorrow, the rocket will be at the pad for less than 27 hours.

The weather forecast remains only 30 percent favorable for launch from Cape Canaveral at 1:03 p.m. EST tomorrow as a cold front moves into the local area.

Lightning, cumulus clouds, disturbed weather and thick clouds are the potential criteria that could be violated.

The outlook for launch time now calls for scattered low clouds at 3,000 feet, a broken deck at 12,000 feet and overcast skies at 25,000 feet, showers or isolated thunderstorms in the area, visibility of 7 miles, south-southwesterly winds of 12 gusting to 16 knots and a temperature around 76 degrees F.

The backup launch opportunity for Wednesday also has a 30 percent chance of acceptable liftoff conditions.

The odds of weather conditions allowing the Atlas 5 rocket to launch Tuesday have dropped to 30 percent in the latest forecast issued this morning by Air Force meteorologists. A cold front headed this way is expected to linger over Central Florida for a couple of days.

"There is some potential for thunderstorms on Tuesday and Wednesday to be strong to severe with very high moisture in-place, instability and mid- and upper-level dynamics," forecasters say.

For Monday morning's rollout of the Atlas from the assembly building to the launch pad, decent weather is expected for the move. The threat of showers increases later in the day.

"On launch day and through the count, the front is expected to be nearing North Central Florida with increasing pre-frontal cloudy conditions, showers and isolated thunderstorms in advance of the front. Winds expected from the south-southwest during the count with gusts in the mid-teens. The primary concerns for launch are lightning, cumulus clouds, disturbed weather and thick clouds," forecasters report.

The outlook for the 1:03 p.m. EST (1803 GMT) launch time now calls for scattered low clouds at 3,000 feet, scattered to broken clouds at 12,000 feet and a broken deck at 25,000 feet, showers or isolated thunderstorms in the area, visibility of 7 miles, south-southwesterly winds of 12 gusting to 16 knots and a temperature around 76 degrees F.

The backup launch opportunity for Wednesday also has a 30 percent chance of acceptable liftoff conditions.

"In the event of a 24-hour delay, the cold front remains near stationary over Central Florida with cloudy conditions, showers and the threat of isolated thunderstorms. The primary concerns for a 24-hour delay are lightning, cumulus clouds, disturbed weather and thick clouds."

A cold front pushing through Florida in the next few days is expected to bring clouds and isolated thunderstorms, putting the odds of acceptable weather at 40 percent for the Atlas 5 rocket to launch on Tuesday.

Similar conditions are forecast for the backup launch opportunity Wednesday.

"On launch day and through the count, the front is expected to be nearing North Central Florida with increasing pre-frontal clouds, showers and a threat of isolated thunderstorms in advance of the front. Winds expected from the south-southwest during the count with gusts in the mid-teens. The primary concerns for launch are lightning, cumulus clouds, disturbed weather and thick clouds," Air Force meteorologists reported today.

The outlook for the 1:03 p.m. EST (1803 GMT) launch time calls for scattered low clouds at 3,000 feet, scattered to broken clouds at 10,000 feet and a broken deck at 25,000 feet, showers or isolated thunderstorms in the area, visibility of 7 miles, south-southwesterly winds of 12 gusting to 16 knots and a temperature around 75 degrees F.

"In the event of a 24-hour delay, the cold front remains near stationary over Central Florida with cloudy conditions, showers, and the threat of isolated thunderstorms. The primary concerns for a 24-hour delay are lightning, cumulus clouds, disturbed weather and thick clouds," forecasters predict for Wednesday.

The booster rocket for the U.S. military's miniature space shuttle has been cleared for blastoff Tuesday, sending the reusable X-37B craft back into orbit for another clandestine voyage.

The Launch Readiness Review held today closed out remaining action-items and gave approval to proceed with rolling out the Atlas 5 rocket from its assembly building to Cape Canaveral's Complex 41 pad at 10 a.m. EST Monday for liftoff at 1:03 p.m. EST Tuesday.

The flight clearance was granted after two months of work to examine the low-thrust condition experienced by the RL10 upper stage engine on a Delta 4 rocket and exonerate the powerplant on the Centaur upper stage that will propel X-37B into its Earth orbit during Tuesday's launch.

"Although the GPS mission was successful and the satellite was delivered to a precise orbit, ULA and Pratt & Whitney Rocketdyne are executing an extremely robust investigation into the cause of the reduced engine performance on the recent Delta 4 mission," said Jim Sponnick, ULA vice president of mission operations.

The inquiry, which is continuing, has determined that "a fuel leak occurred in a specific area of the interior of the thrust chamber" on the Delta 4 during its initial ignition in the Oct. 4 flight, ULA said in a statement today. Inspections and analysis of the RL10 aboard the Atlas for the X-37B have revealed no areas of concern, allowing it to fly next week.

"Our 50-year heritage of launch experience and decades of launch data have enabled the robust investigation processes we perform for any flight conditions that differ from our nominal predictions, in order to continue the critical focus on mission success that our customers demand," Sponnick said.

The exhaustive process culminated with a series of engineering meetings and today's LRR, which was comprised of mission managers and the payload project leaders. In the end, officials cleared the Atlas launch operations to press onwards.

"Our flight data anomaly investigation includes substantial involvement and oversight from senior industry technical advisors, as well as our Air Force OTV customer, Air Force EELV customer, and NASA customers," said Sponnick. "We thank the OTV customer for their patience and participation throughout the flight clearance process for this important mission."

United Launch Alliance officials are working to clear the upper stage engine on the Atlas 5 rocket and put the Air Force's X-37B mini space shuttle into orbit next Tuesday.

Originally targeted for a late October blastoff from Cape Canaveral, the Pentagon's third Orbital Test Vehicle mission has been on hold while technicians assessed a low-thrust condition experienced by a similar engine used to launch a GPS navigation satellite Oct. 4.

That RL10B-2 engine, fitted to the cryogenic upper stage of a ULA Delta 4 rocket, ultimately got the military payload to the proper orbit and the ascent achieved a successful outcome. But since the Centaur upper stage of the Atlas 5 rocket is equipped with the RL10A-4-2 powerplant, officials paused preparations for the X-37B launch while the situation was sorted out.

Pratt & Whitney Rocketdyne produces both engines, which share commonality through the evolution of the venerable hydrogen-oxygen RL10.

While the investigation into the GPS launch remains ongoing, ULA officials are working through a process to establish full confidence in the engine aboard the X-37B's Atlas rocket and hope to resume their launch manifest next week.

A Launch Readiness Review will be held Friday morning at Cape Canaveral with mission managers from the rocket-maker and Pentagon officials representing the spaceplane project. The meeting is intended to reach a consensus for proceeding with rollout of the rocket to the Complex 41 pad Monday morning and launching Tuesday afternoon.

The Air Force press advisory says Tuesday's five-hour launch period opens at 1:03 p.m. EST (1803 GMT).

This launch will demonstrate the reusability of the X-37B, sending up for a second voyage the same craft that flew the original mission in 2010. It has logged 224 days in orbit.

Just like the previous two flights, the Air Force will not say how long the unmanned vehicle plans to stay in orbit or what it is carrying in the payload bay.

The second OTV flight, using a second, identical spaceplane, spent 469 days in orbit from March 2011 to this past June.