New version of Atlas 5 rocket to launch Thursday
BY JUSTIN RAY
Posted: July 15, 2003
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.
"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
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 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.
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.
Solid motors give Atlas 5 a boost
"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.
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
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.
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