A windowless, robotic space shuttle with stubby wings, two tail fins, its belly covered with black thermal tiles, clam-shell doors that swing open to reveal a small payload bay and a solar array that unfurls for powering ultralong-duration missions rode back into orbit Wednesday on the fourth mission of the Air Force's reusable X-37B spaceplane project.

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

"ULA is honored to launch this unique spacecraft for the U.S Air Force. Congratulations to the Air Force and all of our mission partners on today’s successful launch! The seamless integration between the Air Force, Boeing, and the entire mission team culminated in today’s successful launch of the AFSPC-5 mission," said Jim Sponnick, ULA vice president of mission operations.

The next Atlas 5 rocket launch is planned for July 15 from Cape Canaveral carrying the Global Positioning System 2F-10 navigation satellite.

And with that, the launch will go under a veil of secrecy. Confirmation that the Orbital Test Vehicle has arrived in space or separated from the Centaur won't be announced live.

T+plus 4 minutes, 44 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, 33 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, 50 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 the Atlas 5 rocket with the X-37B mini shuttle for its fourth trip to space. And the tower is clear!

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 X-37B spaceplane back into orbit.

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 11:05 a.m. EDT.

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 and Air Force mission director have given their 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 11:05 a.m. EDT.

Standing by for the launch team readiness polls.

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The Atlas 5 rocket stands 20 stories tall and weighs 757,000 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 11:05 a.m. EDT.

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

• The 636th launch for Atlas program since 1957
• The 342nd Atlas launch from Cape Canaveral
• The 225th mission of a Centaur upper stage
• The 202nd use of Centaur by an Atlas rocket
• The 44th Atlas 5 launch from Cape Canaveral
• The 458th production RL10 engine to be launched
• The 60th flight of the RD-180 main engine
• The 54th launch of an Atlas 5 since 2002
• The 20th Air Force mission for an Atlas 5
• The 83rd Evolved Expendable Launch Vehicle flight
• The 96th United Launch Alliance flight overall
• The 64th United Launch Alliance flight from Cape Canaveral
• The 46th Atlas 5 under United Launch Alliance
• The 19th 500-series flight of the Atlas 5
• The 6th Atlas 5 to fly in the 501 configuration
• The 3rd Atlas 5 launch of 2015

Weather remains GO for liftoff based on the current conditions and expected to stay favorable for an 11:05 a.m. EDT launch today. Forecasters are predicting conditions to worsen as the afternoon goes along.

Thirty minutes from liftoff.

T-minus 4 minutes and holding. The countdown has entered the planned 30-minute hold to give the launch team a chance to review all systems and assess the weather before pressing ahead with liftoff.