Just down the road from where the shuttle Atlantis is being prepped for flight, the U.S. Air Force launched its own unmanned reusable spaceplane to orbit aboard an Atlas 5 rocket Thursday evening on a round-trip shakedown mission.

The military space shuttle does not carry a crew, but it relies on a laundry list of new technologies that Air Force officials hope will revolutionize how the Pentagon executes its space programs.

"Fundamentally, this is an updated version of the space shuttle," said Gary Payton, the U.S. Air Force's top civilian leader for military space programs. "The Air Force has a suite of military missions in space. This new vehicle could potentially help us do those missions better."

Built by Boeing Phantom Works, the 29-foot-long, 11,000-pound X-37B spacecraft sports a modest cargo bay, a powerful maneuvering engine, a deployable solar array, and stubby wings to guide the ship back to Earth after its mission.

Liftoff occurred on time at 7:52 p.m. EDT (2352 GMT).

Read our full story.

Also check out another gallery of the Atlas 5 rocket's spectacular sunset blastoff.

Our gallery of launch photos taken at the Kennedy Space Center Press Site is posted here.

"ULA is proud to have played a critical role in the success of this important test mission of the Orbital Test Vehicle," said Mark Wilkins, ULA vice president of Atlas programs. "This was a tremendous launch campaign highlighted by close teamwork between the U.S. Air Force, the ULA launch team and our many mission partners that made today's successful launch possible."

Today's launch has been a success.

Centaur's main engine has performed its burn today to achieve orbit.

T+plus 16 minutes, 25 seconds. Everything looking normal with one minute to go in this burn.

T+plus 14 minutes. Centaur systems remain in good shape.

T+plus 13 minutes, 25 seconds. About four minutes are left in this burn of Centaur.

T+plus 12 minutes, 15 seconds. The RL10 continues to perform well, burning liquid hydrogen and liquid oxygen propellants.

T+plus 10 minutes, 20 seconds. Good engine performance continues.

T+plus 9 minutes, 50 seconds. Bus and battery voltages, tank pressures and other system measurements look good.

T+plus 9 minutes. The rocket is tracking right down the planned track.

T+plus 7 minutes, 40 seconds. All systems reported stable as the Centaur fires to reach an initial Earth orbit.

T+plus 6 minutes. The rocket is 192 miles in altitude, some 390 miles downrange and traveling over 9,840 mph already.

T+plus 5 minutes, 20 seconds. Centaur engine readings look good as this burn gets underway.

T+plus 4 minutes, 45 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, 37 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, 28 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, 15 seconds. RD-180 is performing well as the rocket climbs away from the planet.

T+plus 3 minutes. The rocket is 37 miles in altitude, some 36 miles downrange and traveling over 4,082 mph already.

T+plus 2 minutes. The rocket is 11 miles in altitude, some 8 miles downrange and traveling over 2,136 mph already.

T+plus 1 minutes, 45 seconds. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.

T+plus 90 seconds. Mach 1.

T+plus 60 seconds. One minute into the ascent as the Atlas 5 climbs away from the Cape at sunset.

T+plus 40 seconds. A slow and steady rise for the Atlas booster, delivering a thunderous roar across Cape Canaveral.

T+plus 15 seconds. The vehicle has cleared the towers at Complex 41 on 860,000 pounds of thrust from the RD-180 main engine.

LIFTOFF! Liftoff of the Atlas 5 rocket launching U.S. military's X-37B spaceplane, the experimental prototype for an unmanned reusable space shuttle.

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 X-37B into orbit for its technology demonstrations.

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

T-minus 1 minute, 50 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 tonight's countdown to launch the Atlas 5 rocket carrying X-37B. Liftoff is set to occur at 7:52 p.m. EDT.

Countdown clocks will resume in one minute.

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

The ULA launch director has given his "go" for today's liftoff.

Polling of the team by Atlas launch conductor just occurred. All systems are reported "go" to continue with the countdown for liftoff at 7:52 p.m. EDT.

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

• The 603rd launch for Atlas program since 1957
• The 317th Atlas to occur from Cape Canaveral
• The 21st launch of an Atlas 5 since 2002
• The 19th Atlas 5 to occur from the Cape
• The 13th Atlas 5 under United Launch Alliance
• The 1st Atlas 5 to fly in the 501 configuration
• The 8th Department of Defense launch of Atlas 5
• The 2nd Atlas launch of 2010

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 before pressing ahead with liftoff.

The first stage liquid oxygen tank and Centaur's liquid oxygen and liquid hydrogen tanks are reported at flight level.

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

The fuel-fill sequence for the first stage main engine has been completed.

Out at the launch pad, winds are easterly at 10 knots and the temperature is 72 degrees F.

Thirty minutes from liftoff. The countdown clocks are heading to the T-minus 4 minute mark where a planned 10-minute hold will occur. Launch of Atlas 5 remains scheduled for 7:52 p.m. EDT.

The earlier issue reported by ground electrical isn't a constraint to launch.

Live video of the Atlas launch is streaming on this page. Hit reload for the video to activate.

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

Now 60 minutes from liftoff. Fueling of the Atlas rocket with cryogenic liquid oxygen and liquid hydrogen is proceeding as planned for a liftoff at 7:52 p.m. EDT.

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

The first stage liquid oxygen tank is 80 percent full now.

Centaur's liquid hydrogen tank is 50 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.

The team has cleared the one issue on the liquid oxygen pump inlet backup temperature measurement sensor.

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

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.

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.

The Centaur engine chilldown sequence is being initiated.

The team's also looking at a first stage pump inlet temperature sensor.

Upper stage liquid oxygen has reached flight level.

The ground electrical console is reporting an issue that the anomaly team is discussing.

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

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

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 12,680 gallons of the cryogenic propellant.

Now three-quarters full on Centaur liquid oxygen.

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 48,860 gallons of cryogenic oxidizer for the RD-180 main engine.

The Centaur liquid oxygen tank has reached the 40 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 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 7:52 p.m. EDT 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.

T-minus 2 hours and holding. The countdown has just entered the first of two planned holds over the course of the afternoon that will lead to the 7:52 p.m. EDT 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.

Check out today's gallery of photos showing the Atlas 5 rocket poised on the launch pad here.

The guidance system testing and flight control operational test have been reported complete.

An open-loop test of the C-band system used to track the rocket as it flies downrange has been conducted.

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.

The early countdown activities are going well, officials report, as the Atlas 5 rocket is readied for flight tonight. No technical issues are being worked and the weather is spectacular.

The countdown clocks have started ticking for today's launch of the X-37B spaceplane aboard an Atlas 5 rocket from Cape Canaveral, Florida.

The launch team is beginning to power up the rocket and 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 at 7:30 a.m.

A planned half-hour hold begins at 5:02 p.m. when the count reaches T-minus 120 minutes. Near the end of the hold, the team will be polled at 5:29 p.m. to verify all is in readiness to start fueling the rocket for launch.

Supercold liquid oxygen begins flowing into the Centaur upper stage around 5:49 p.m., followed by the first stage filling around 6:02 p.m. 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 starting at 7:28 p.m. That 20-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 for liftoff at 7:52 p.m. EDT.

A 9-minute window extends to 8:01 p.m. EDT, if an ontime launch isn't possible due to the weather or some other reason.

A gallery of photos covering the Atlas 5 rocket's rollout to the launch pad is posted here.

Its cost and mission are classified, but a first-of-a-kind reusable miniature military space shuttle is on the launch pad ready to soar into orbit on an Atlas 5 rocket Thursday evening.

Under the cover of the Atlas 5's payload shroud, the X-37B is scheduled for launch at 7:52 p.m. EDT (2352 GMT) from Complex 41 at Cape Canaveral, Fla. The launch window extends for 9 minutes.

The 196-foot-tall booster rolled to the launch pad Wednesday morning.

"Fundamentally, this is an updated version of the space shuttle," said Gary Payton, the U.S. Air Force's top civilian leader for military space programs. "The Air Force has a suite of military missions in space. This new vehicle could potentially help us do those missions better."

Read our full story.

An Atlas 5 rocket was rolled to its Cape Canaveral pad this morning for Thursday's launch of the U.S. military's experimental X-37B spaceplane, the prototype for an unmanned reusable space shuttle.

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 payload enclosed within the bulbous nose cone, reached the pad at 11 a.m. EDT to begin 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 at mid-day Thursday, leading to blastoff at 7:52 p.m. EDT. The day's available launch opportunity closes at 8:01 p.m. EDT.

We will provide extensive live countdown and launch coverage here on this page!

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The rocket is passing through the pad entrance gate.

Meteorologists continue to predict an 80 percent chance of acceptable weather during Thursday's launch window. Violation of the cumulus cloud criteria is the only concern.

"A cold (cool) front in the northern peninsula will slowly push south through the day. The heavier showers and isolated thunderstorms pushed through during the overnight hours. Isolated showers remain a threat through the afternoon with a drying trend by this evening. There is a small threat of isolated thunderstorms through the afternoon with the threat ending by early evening. High pressure builds in on launch day with fair weather conditions expected through the count," the weather team reported this morning.

"For MLP roll and pre-launch activities today, isolated showers are possible with the cold front over the central peninsula. There remains a small threat of an isolated thunderstorm as the boundary transits the area. Winds are expected to be from the south to southwest gusting in the low to mid teens.

"On launch day, high pressure builds in with fair weather conditions. Winds are expected from the east by the launch window gusting in the mid teens. The primary concerns for launch day are cumulus clouds."

The launch window specifics include some scattered low and high clouds, easterly winds from 090 degrees at 12 to 16 knots and a temperature of 71 degrees F.

Rollout begins! The United Launch Alliance Atlas 5 rocket that will boost the U.S. military's experimental X-37B spaceplane into orbit just began a slow half-hour drive from the 30-story Vertical Integration Facility to Cape Canaveral's Complex 41 pad for Thursday evening's liftoff.

A pair of specially-made "trackmobiles" are carrying the Atlas 5 rocket's 1.4-million pound mobile launching platform along rail tracks for this third-of-a-mile trip.

Technicians spent the past two months assembling and testing the rocket inside the Vertical Integration Facility. The Atlas 5 is designed to spend minimal time at the actual launch pad, which does not include a service gantry like other sites. With liftoff targeted for 7:52 p.m. EDT tomorrow, the rocket will be at the pad only less than 34 hours.

At Cape Canaveral's Complex 41, the giant sliding doors on the Vertical Integration Facility are open and the Atlas 5 rocket appears ready to emerge for today's rollout to the launch pad. The towering booster plans to blast off Thursday night.

Air Force officials say everything remains on schedule for Thursday evening's launch of the X-37B Orbital Test Vehicle.

The weather continues to look favorable for Thursday's launch window, which opens at 7:52 p.m. EDT (2352 GMT).

"The weather does look good for launch Thursday evening," said Clay Flinn, the launch weather officer. "We have high pressure building in with clear skies. Winds are below liftoff constraints. We should have winds from the east at 12 knots gusting to 16 [knots] and scattered sky conditions."

The forecast is still calling for an 80 percent chance of acceptable weather for liftoff Thursday.

The weather forecast for Thursday's launch window shows improvement, and meteorologists are calling for just a 20 percent chance of weather conditions prohibiting liftoff.

Forecasters are expecting scattered cumulus and cirrus clouds at 3,000 and 25,000 feet, isolated showers, winds out the east at 12 to 16 knots, a temperature of about 70 degrees Fahrenheit, and a visibility of 7 miles.

The primary weather concerns for launch are cumulus clouds. The outlook for Friday also calls for a 20 percent chance of weather violating launch constraints.

"A weak cold front over the Northern peninsula with a low pressure system over the Southern peninsula and Western Atlantic results in an influx of tropical moisture and isolated showers through the day. On Tuesday, low pressure continues to track East in the Atlantic with a gradual drying trend and reduced coverage of isolated showers. Tuesday evening and into MLP roll day on Wednesday, an upper level disturbance transits the peninsula and associated surface trough develops in North Florida with an increase in moisture during the overnight hours. The surface trough transits the Central peninsula through early Wednesday afternoon with a gradual drying trend expected through the afternoon and evening," Air Force weather officials wrote in Monday's forecast.

"For MLP roll, isolated showers are possible with the cold front over the Central peninsula. Although not expected, there is a small threat of an isolated thunderstorm as the boundary transits the area. Winds are expected to be from the South to Southwest gusting in the low to mid teens (230 feet). On launch day, high pressure builds in with fair weather conditions. Winds are expected from the East gusting in the mid teens (230 feet). The primary concerns for launch day are Cumulus Clouds. In the event of a 24 hour delay, similar conditions persist. The primary concerns for a 24 hour delay are Cumulus Clouds."

The delayed landing of the shuttle Discovery will push the Atlas 5 launch of an Air Force spaceplane to Thursday. The slip gives the Air Force Eastern Range enough time to reconfigure from the landing to support the Atlas launch.

The launch window Thursday opens at 7:52 p.m. and closes at 8:01 p.m. EDT. The times previously announced by the Air Force were launch periods.

Air Force weather forecasters are projecting possible concerns with clouds holding up Wednesday night's scheduled launch of the Atlas 5 rocket carrying the military's new X-37B spaceplane.

The odds say there's a 40 percent chance of cumulus clouds violating the weather rules during the evening's launch window of 6:44 to 9:07 p.m. EDT.

"High pressure retreats into the Atlantic as the next cold front slowly transits the Florida peninsula Sunday. A developing low pressure system in the Caribbean results in an in-flux of tropical moisture coupled with the front. Pre-frontal isolated showers with the front to the North and low pressure to the South encroach into the Southern peninsula Saturday evening. Low pressure persists over the Southern peninsula/Western Atlantic through Monday with showers over Central Florida Sunday and Monday," meteorologists said today.

For the rocket's rollout to the pad on Tuesday, "a slight drying trend reduces the coverage of isolated showers during the roll and pre-launch countdown; however, the threat of isolated showers persists. Winds are expected to be from the Northeast gusting in the low to mid teens," meteorologists say.

"On launch day, an upper level disturbance and associated surface trough develops in North Florida with increasing moisture over the peninsula. There is a small threat of an isolated thunderstorm. Winds are expected from the East- southeast gusting in the mid to upper teens (230 feet). The primary concerns for launch day are Cumulus Clouds associated with isolated showers.

"In the event of a 24-hour delay, high pressure builds in with a gradual drying trend and slightly reduced shower threat. The primary concerns for a 24-hour delay are Cumulus Clouds."

The new target launch for X-37B is April 21 during a window of 6:44 to 9:07 p.m. EDT.

Launch of the Atlas 5 rocket has been pushed back a day to April 20 during a window of 6:46 to 9:10 p.m. EDT.

More than a decade after its conception in the halls of NASA, and having snaked its way through multiple Pentagon bureaucracies, an unmanned military spaceplane is finally on the verge of launching on an unprecendented test flight.

A stubby-winged spaceship called the Orbital Test Vehicle will fly into orbit on an Atlas 5 rocket, taking a round-trip shakedown voyage for the U.S. Air Force.

"What it offers that we have seldom had is the ability to bring back payloads and experiments to examine how well the experiments performed on-orbit," said Gary Payton, the undersecretary of the Air Force for space programs. "That's one new thing for us."

Read our full story.

At Cape Canaveral's Complex 41 today, the Atlas rocket was fueled up for its countdown dress rehearsal.

After initially targeting a mock liftoff time of 1 p.m. EDT, clocks went inside T-minutes 30 seconds before the first simulation ended. The team recycled the countdown and performed another sequence at 2 p.m. EDT to run the clocks all the way down.

The rocket's supercold fuels will be offloaded this afternoon and the vehicle allowed to warm up before it is transported back to the assembly building on Saturday.

The United Launch Alliance Atlas 5 rocket that will propel the U.S. military's Orbital Test Vehicle into space was rolled to the Complex 41 pad at Cape Canaveral this morning.

The giant booster consisting of its bronze-colored first stage and Centaur upper stage was recently assembled together atop the mobile launching platform at the Vertical Integration Facility.

This morning's rollout, which happened between 10 and 11 a.m. EDT, is part of the Wet Dress Rehearsal activities that each Atlas undergoes prior to launch. The rocket will be fully fueled Friday for a realistic practice countdown.

The event is designed to iron out any problems with the hardware and exercise the launch team.

Once the simulated launch day is completed, the rocket will be rolled back to the assembly building for final pre-flight work. Attachment of the X-37B payload will occur in the coming days.

Liftoff remains targeted for the evening hours of April 19.

A secretive military spacecraft resembling a small space shuttle orbiter flew to Florida in the belly of a cargo plane this week to undergo final processing for launch on April 19.

Read our full story.

The U.S. Air Force has released new images of its experimental new X-37B space plane as the secretive mission's launch date next April draws near.

Read our full story.