The conceptual image depicts how the Atlas 5 rocket will appear on the launch pad with its larger fairing and strap-on solid boosters. Credit: Lockheed Martin

The largest and most capable Atlas rocket in history will take flight Thursday evening from Cape Canaveral as Lockheed Martin's launcher fleet evolves to carry larger and heavier cargos into space.

Looking remarkably different on the outside, this third launch of the Atlas 5 will introduce a massive new nose cone and two powerful strap-on solid-fuel boosters. But the rocket's core stages and engines are unchanged, giving Lockheed Martin confidence that the launch will be successful.

"We have really implemented a very low-risk evolutionary approach where we have taken very measured steps in introducing new series of capabilities with the vehicle," said Jim Sponnick, Lockheed Martin's Atlas program vice president.

Since the commercial Atlas era began in 1990, seven new rocket configurations have debuted, all successfully. Atlas 1, 2, 3 and 5 rockets have flown 74 missions during that time, and a string of 65 consecutive successes has amassed since 1993.

"This evolutionary process has served the program very well," said Sponnick.

The first two Atlas 5 missions performed over the past 11 months used the rocket's most basic configuration with two stages, no solid boosters and a four-meter diameter nose cone to enclose the satellite cargo during ascent through the atmosphere. Lockheed Martin calls this the Atlas 5 400-series, distinguishing it by the payload shroud's size.

The Atlas 5's 400-series rocket (top) and the 500-series (bottom) are compared in these illustrations. Credit: Lockheed Martin

Thursday will mark the debut of the Atlas 5's 500-series version.

"It is clearly a very significant step for the program. It does introduce the remaining vehicle elements that truly round out of the 400 and 500 family," said Sponnick. "With this flight, they will all be fully operational."

The Swiss-made, five-meter diameter nose cone will make its inaugural flight on Atlas 5. The voluminous shroud, which encloses not only the payload but also the rocket's Centaur upper stage, allows much larger satellites to be carried aloft by the Lockheed Martin launcher.

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

The solids can be used on either the 400- or 500-series, but will be launching for the first time Thursday.

To keep pace with the ever-growing weight and size of satellites, launch vehicles must be enhanced to lift the payloads.

"With the flight qualifications with this mission, we expect a great many customers to be coming to us to satisfy their needs," said Mike Jensen, vice president and chief technical officer for International Launch Services, the marketer of Atlas.

Big fairing makes 500-series
Contraves Space of Zurich, Switzerland was tapped in 1999 to develop and build the payload fairings for Lockheed Martin's Atlas 5 rockets. The shrouds protect the satellite cargo during the first minutes of launch as the rocket accelerates through the atmosphere.

The company has produced more than 160 nose cones since the 1970s for Europe's Ariane rockets and the U.S. commercial Titan boosters.

The Atlas 5's fairing components are explained in this chart. Credit: Lockheed Martin

For Atlas 5's 500-series, the fairings are about 17 feet in diameter. A "short" version, which will be used Thursday, is 68 feet long and weighs 7,770 pounds. A "medium" version that stands 77 feet tall and weighs 8,900 pounds also is available.

"The volume within the payload fairing is greater than the volume within an average single family home," Sponnick noted.

The Atlas 5 nose cones are the largest lightweight composite payload fairings ever built.

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.

The fairing for this week's launch of Rainbow 1. Credit: ILS

Given the diameter of the nose cone and its effects on the rocket, designers decided to make the fairing long enough to encapsulate the Centaur upper stage. That is a departure from other versions of Atlas rockets flying today.

With the satellite payload and Centaur now enclosed in the same environment during launch, steps have been taken to ensure the upper stage doesn't harm the multi-million dollar spacecraft.

The Centaur is always covered with orange foam to insulate its super-cold fuel tanks. But to guard fine particles from contaminating the satellite, the Centaur has been coated with a white decal material.

"That is simply to keep from having any shedding of particulates during the flight," explained Sponnick. "The Centaur, as well as the spacecraft, are encapsulated in the same interior volume of the payload fairing. So that is strictly a matter of keeping any contaminates from ever being shed from the foam."

To give the fairing structural support during the ascent, the "Centaur Forward Load Reactor" deck has been designed by Contraves. 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.

"Due to (the fairing's) length and the need to accommodate the lateral loads that can be induced on the vehicle in flight, we have incorporated a Centaur Forward Load Reactor," Sponnick explained.

The separation test of the Atlas 5 fairing is performed. Credit: Contraves Space

Sensors on the fairing gather measurements of conditions during launch. When the fairing separates from the rocket nearly four minutes into flight, a 36-foot data cable is spooled out. This line allows one-second of telemetry to be relayed to Atlas 5, and subsequently back to Earth, so engineers can determine the fairing's behavior during jettison, said Frank Bader of Contraves marketing.

Solid motors give Atlas 5 a boost
The Atlas 5 uses the longest monolithic -- or single-segment -- solid-propellant rocket motor in the world.

"This is a single-piece composite case with a single cast of propellant," said Mike Martin, the president of Sacramento, California-based Aerojet.

"If you can do a single-wrapped case, a single, continuous cast, have no segments, at a decent-rate production, you should be more efficient from a manufacturing point of view and more reliable from a motor point of view," Martin said.

A previous Atlas 5 solid rocket booster hot-fire test. Photo: Aerojet

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.

Depending on a payload's weight, mission planners add strap-on solid boosters to the Atlas 5 to incrementally increase the amount of cargo the rocket can carry. For Thursday's launch, two solids are being used.

For the Atlas 5's 400-series, up to three solids can be used. The 500-series is capable of flying with five.

"We are able to accommodate a wide variety of different mission demands by configuring the vehicle with a unique number of solids," said Sponnick.

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.

TV satellite rides third Atlas 5 rocket
Riding atop this mission -- designated AV-003 -- is the Rainbow 1 direct-to-home TV relay spacecraft. Built by Lockheed Martin's satellite-manufacturing arm, the A2100AX-model craft is headed for geostationary orbit 22,300 miles above the equator.

An illustration of Rainbow 1 in space. Credit: Lockheed Martin

Weighing 9,542 pounds at launch, Rainbow 1 features 36 active Ku-band transponders, 22 programmable spot beams and an expected service life of 18 years.

The satellite will be used to create a new direct broadcasting system across the United States, delivering entertainment programming to subscribers' homes outfitted with 18-inch rooftop dishes.

Using an "ascending node" launch profile, the Atlas 5 will need an hour and 40 minutes to ferry Rainbow 1 from the launch pad to its targeted geosynchronous transfer orbit.