In technical speak, this is the Atlas 5-501 configuration that has successfully flown five times. The first was the original X-37B launch in April 2010.
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 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 RL10 engine 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.
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 in August 2011 and dispatched the car-sized Curiosity rover on the Mars Science Lab mission in November 2013.
Today marks the 54th flight for Atlas 5, born of the Air Force's competition to develop next-generation Evolved Expendable Launch Vehicles. In its previous 53 missions since debuting in August 2002, the Atlas 5 has flown 19 flights dedicated to the Defense Department, 12 for NASA, 11 with spy satellites for the National Reconnaissance Office. and 11 commercial missions with communications and Earth-observing spacecraft.
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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 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.
Clocks have one more built-in hold planned at T-minus 4 minutes. During that pause the final "go" for launch will be given. All remains targeted for liftoff at 11:05 a.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.
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.
The outlook predicts scattered clouds at 3,000 and 30,000 feet, isolated showers, good visibility, southwesterly winds of 10 gusting to 13 knots, a temperature in the low 80s degrees F.
The Atlas-Centaur rocket has been powered up at Complex 41 and guidance system testing is getting started for today's launch, as the countdown progresses as planned.
Clocks are picking up the seven-hour sequence of work that will prepare the booster, payload and ground systems for blastoff some time after 10:45 a.m. EDT (1445 GMT).
The exact launch time is yet to be announced.
Soon 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 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, 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 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 unclassified launch period extends to 2:45 p.m. EDT (1845 GMT).
Liftoff of the Orbital Test Vehicle mission No. 4 is slated for some time after 10:45 a.m. EDT. The exact time remains classified until launch morning.
The 20-story-tall booster was wheeled out aboard a mobile platform, emerging from the assembly building where the rocket’s two stages and the payload were integrated over the past few weeks.
The slow drive from the 30-story Vertical Integration Facility to the launch pad, which began shortly after 9 a.m., used 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 launch will deliver the X-37B into a low-Earth orbit. Deployment of the spacecraft occurs less than 20 minutes after liftoff.
On Monday, officials from United Launch Alliance and the Air Force gathered for the Launch Readiness Review. All systems were verified ready to proceed with today's rollout and the start of launch pad operations.
The rocket is flying the 501 vehicle configuration for the sixth time in 54 flights. The version features two stages and a five-meter-diameter nose cone. It is powered off the launch pad by an RD AMROSS RD-180 main engine. The Centaur upper stage is equipped with an Aerojet Rocketdyne RL10.
Countdown clocks begin ticking seven hours before launch, leading to activation of the rocket, final testing and system preps.
The day’s launch period begins at 10:45 a.m.and closes at 2:45 p.m. EDT. The usable launch window, which remains classified, falls within that broad, four-hour period.
There is a 60 percent chance of acceptable weather, with conditions expected to be more favorable earlier in the period than later.
It will be the fourth flight of the military’s X-37B program, also known as Orbital Test Vehicle mission No. 4. The project is run inside the Pentagon at the Rapid Capabilities Office.
Liftoff is scheduled for some time during a four-hour, unclassified period that extends from 10:45 a.m. to 2:45 p.m. EDT (1445-1845 GMT) from Complex 41 at Cape Canaveral Air Force Station in Florida. The actual target time will be announced on launch day.
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