Various versions of the Atlas rocket launched earlier constellations of U.S. Navy communications satellites, and now the family's biggest booster will begin deploying a new generation of spacecraft this week.

Scheduled for rollout to the Cape Canaveral launch pad Wednesday morning in preparation for blastoff Thursday evening, the first Mobile User Objective System satellite, dubbed MUOS 1, will be hauled into orbit for a 15-year mission to provide communications to U.S. and allied military forces on the move.

An Atlas 5-551 launches Juno. Credit: NASA

Liftoff is scheduled for 5:46 p.m. EST (2246 GMT) aboard a United Launch Alliance Atlas 5 from the Florida spaceport's Complex 41.

Towering 206 feet tall and generating two-and-a-half-million pounds of thrust at launch, the rocket will place the 15,000-pound satellite into its preliminary geosynchronous transfer orbit three hours into flight.

You can follow Thursday's launch in our Mission Status Center with live journal updates and streaming video.

Atlas-Centaur 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.

For the U.S. Navy, Atlas has been the launcher of choice for 11 spacecraft in the Ultra High Frequency Follow-On communications satellite series from 1993 through 2003. A combination of Atlas 1, Atlas 2, Atlas 2A and Atlas 3B vehicles were used on the those missions from Complex 36 as the family evolved into larger, more capable rockets.

And before that, the previous satellite generation called the Navy's Fleet Satellite Communications System, FLTSATCOM, flew aboard Atlas-Centaur vehicles from the Cape to log a half-dozen successes between 1978 and 1989.

Now, the sophisticated MUOS satellite network of five spacecraft that harnesses commercial 3G cellular telephone technology to serve mobile warfighters will ride Atlas 5s to orbit starting Thursday night.

Meet the Atlas 5

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.

An Atlas 5-551 vehicle. Credit: NASA

The rocket launching MUOS 1 was born of the Air Force's competition to develop next-generation Evolved Expendable Launch Vehicles. It has flown 28 times since debuting in 2002, carrying out nine commercial flights with communications spacecraft, eight dedicated to the Defense Department, five missions with spy satellites for the National Reconnaissance Office and six for NASA.

Atlas 5 was built to be more robust and reliable over earlier Atlas and Titan heavy-lift vehicles, and streamlined production has resulted in fewer opportunities for human error.

The new launcher builds upon the success of its predecessors, using the Russian-made RD-180 main engine, a stretched Centaur upper stage and its RL10 engine that were proven during the Atlas 3 program.

The key piece that sets Atlas 5 apart, however, was the rigid body Common Core Booster serving as the rocket's first stage. The CCB replaced the "balloon" pressure-stabilized stage used by previous Atlas vehicles.

As the CCB's name suggests, the stage is common and is used in all the various configurations of the Atlas 5 family. The booster stage is 106.6 feet long and 12.5 feet diameter.

There are three distinct versions of Atlas 5 rockets -- the 400 series, 500 series and Heavy -- each tailored to launching a certain class of satellite.

The 400 series uses a four-meter diameter payload shroud and has flown 19 times. The 500 series, distinguished by a five-meter fairing, has launched 9 times. The proposed Heavy is a future Atlas 5 version that would take three Common Core Boosters to form a powerful triple-body rocket.

To match an Atlas 5 with the size of its payload, up to five solid rocket motors can be strapped to the rocket to give extra boost at liftoff and the two different types of nose cones are available to enclose the satellite atop the launcher. The various options give Atlas 5 the nickname "dial-a-rocket" because of its flexibility.

An artist's concept of the Atlas 5 rocket with MUOS 1. Credit: United Launch Alliance

MUOS will fly on the 551 configuration, the most powerful version of the Atlas 5 currently available. This translates to a rocket with the bulbous five-meter fairing, five solid rocket boosters and one RL-10 engine on the Centaur upper stage.

The energetic version has been used twice before, launching NASA's New Horizons probe to Pluto in 2006 and the Jupiter-bound Juno orbiter last August.

Russian lift

Powering the Atlas 5 during the first four minutes of flight is the RD-180 liquid-fueled engine. The liquid oxygen/kerosene powerplant is a two-thrust chamber, two-nozzle engine made by NPO Energomash of Khimky, Russia. It was developed from the RD-170 engine used by Russia's Energia-Buran space shuttle, the Energia-M and Ukrainian Zenit rockets.

An Atlas 5 first stage. Credit: NASA

Featuring hypergolic ignition, the engine produces 860,000 pounds of thrust and is throttled up and down to ease the stresses the rocket experiences throughout the launch. And its dual nozzles provides superior steering control during the climb out.

The American propulsion firm Pratt & Whitney financed the development of the RD-180 for the Atlas program. Pratt and NPO Energomash are equal partners of RD AMROSS, the joint venture formed to market, sell and distribute the RD-180 engines.

Solid motors give Atlas 5 a boost

Giving the rocket an added kick off the launch pad are five solid-propellant boosters made by Aerojet. Considered the world's longest monolithic -- or single-segment -- solid boosters, the motors provide the extra thrust needed to increase the Atlas 5's payload-carrying capacity.

An Atlas 5 solid rocket booster. Credit: NASA

Each booster stands 67 feet tall, has a diameter of just over five feet and weighs 102,000 pounds at launch. The slender white rockets have a lightweight graphite epoxy casing with an erosion-resistant insulation. The solid fuel is high-performance class 1.3 HTPB propellant.

Atop the booster is an aerodynamically-shaped graphite epoxy nose fairing. Each motor has forward and aft attachment structures to the Atlas 5's first stage. The motor nozzle is carbon-phenolic.

The motor burns for 90 seconds, producing a maximum thrust of approximately 400,000 pounds and an average of 280,000 pounds.

The Russian RD-180 first stage main engine can accomplish the entire job of steering the Atlas 5 during launch, thus the solid boosters feature simple, fixed nozzles.

Big fairing makes 500-series

RUAG Space of Zurich, Switzerland produces the five-meter diameter nose cone that covers the satellite cargo during the first minutes of launch as the rocket accelerates through the atmosphere. The Atlas 5 shrouds are the largest lightweight composite payload fairings ever built.

An Atlas 5 fairing. Credit: NASA

For Atlas 5's 500-series, the fairings are about 17 feet in diameter. A "medium" version, which will be used for MUOS, is 77 feet long and weighs 8,800 pounds.

A layer of cork is applied to the outer surface of the fairing to shield against the heating of ascent. An electrically conductive white paint is then applied over the cork to avoid electrical charges. The inside has an acoustic protection system to lessen the intense sound during launch for the payload.

To give the fairing structural support against lateral loads during the ascent, the "Centaur Forward Load Reactor" deck was designed. This aluminum ring extends from the Centaur to the fairing's inner wall. It separates in two halves moments after the fairing is jettisoned during launch.

Centaur upper stage

The workhorse Centaur upper stage has flown in various configurations for decades and will be making its 200th mission with MUOS 1. For this launch, the stage will use one Pratt & Whitney-built RL10A-4-2 liquid oxygen/liquid hydrogen engine that develops a thrust of about 22,300 pounds.

A Centaur upper stage. Credit: NASA

The Centaur will fire three times during ascent, initially boosting itself and attached satellite into a parking orbit around Earth after separation from the first stage. A second burn then propels the payload into a highly elliptical geosynchronous transfer orbit, followed by a long coast phase before a final push is delivered to raise the orbit's low point and reduce inclination relative to the equator.

The stage is 41.5 feet in length and 10 feet it diameter. It also houses the navigation unit that serves as the rocket's guidance brain.

The launch of MUOS 1 will mark the milestone 200th mission for the Centaur dating back to 1962. See our feature story about the stage's history and upcoming landmark launch.