Atlas 5 dubbed 'dial-a-rocket' for its flexibility
BY JUSTIN RAY
Adapted from story originally posted: August 14, 2002
The Atlas 5 rocket represents the pinnacle of evolution for Lockheed Martin's family of expendable launchers.
Born of the U.S. Air Force's competition to develop next-generation rockets, the Atlas 5 is expected to be around through 2020, providing dependable and more affordable access to space over current boosters as part of the Evolved Expendable Launch Vehicle program, or EELV.
Atlas 5 is built to be more robust and reliable over earlier Atlas and Titan 4 vehicles, and streamlined production has resulted in fewer opportunities for human error.
The new launcher builds upon the success of its predecessors, using the same Russian-made RD-180 main engine, stretched Centaur upper stage and its RL-10 engine that have already been proven to work during Atlas 3 flights.
The key piece that sets Atlas 5 apart, however, is the new rigid body Common Core Booster that serves as the rocket's first stage. The CCB replaces the "balloon" pressure-stabilized stage used by previous Atlas vehicles. The booster stage is 106.6 feet long and 12.5 feet diameter.
As the CCB's name suggests, the stage is common and will be used in all the various configurations of the Atlas 5 family. The stretched Centaur also will be common across the Atlas 5 fleet.
The 400 series uses a four-meter diameter payload shroud; the 500 series features a five-meter fairing. The 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 Centaur can use one or two engines, depending on what type of orbit the satellite is headed. The various options have prompted Lockheed Martin to give Atlas 5 the nickname "dial-a-rocket" because of its flexibility.
Customers can have another solid added to their rocket if the satellite cargo becomes heavier than expected during construction -- a cheaper alternative than moving to a more powerful launcher such as switching from an Atlas 2AS to an Atlas 3A.
The first Atlas 5 launch carried the Eutelsat Hot Bird 6 satellite, an Alcatel-built craft weighing 8,591 pounds at liftoff. Based on that size, the least powerful version of the Atlas 5 -- the 401 configuration -- was capable of delivering the direct-to-home TV broadcasting satellite into the targeted geosynchronous transfer orbit for that mission of 170 by 24,757 nautical miles at 17.57 degrees inclination.
Up to three solids can be added to a 400 series, with each Aerojet-made solid gradually increasing the amount of cargo the rocket can carry to transfer orbit:
Lockheed Martin limits to three the number of solids on the 400 series due to structure loads on the rocket during flight. In addition, payloads that need more lift than three solids inevitably would be large enough to require the wider five-meter fairing of the 500 series.
"If you put a fourth solid on there, we'd be screaming...already at three solids we are throttled back significantly (on the RD-180 engine)."
"You get to point where we got so much more thrust...thrust to weight on that rocket is 2 to 1, it leaps off the pad and it just causes more loads on the rocket."
The second Atlas 5 mission launched the Greek Hellas Sat communications satellite aboard another 401-version.
The Atlas 500
The 500 series can use up to five solids, any more would exceed the load capability of the rocket. Here are the versions' capabilities to geosynchronous transfer orbit:
"Essentially we carry an extra solid to compensate for the five-meter fairing," Karas said. "A 431 is about the same as a 541 because the larger five-meter fairing really detracts from your performance and it takes about a solid to compensate."
"If we were to fly dual engines on a Centaur to GTO, we would actually lose performance because we are dragging an extra engine. We don't need the thrust, so we lose a few hundred pounds of performance," said Karas.
"Typically when you want to throw a lot of mass into low Earth orbit and you still have gravity losses, you need the thrust so you need the second engine."
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.
Centaur upper stage
The Centaur will fire twice during launch, initially boosting itself and attached satellite into a parking orbit around Earth after separation from the first stage. A second burn propels the payload into the planned transfer orbit.
The stage is 38.5 feet long and 10 feet diameter. It also carries the rocket's guidance brain -- the Inertial Navigation Unit.
"When it comes to expendables, Atlas 5 is about it," Karas said. "As always, we have a set of improvements that we would like to phase into Atlas 5. We always try to keep our product fresh. You have to refresh your product or else it dies. There are a bunch of upgrades that we've talked about. You're never perfect. There are some upgrades that help improve reliability and improve operations.
Former shuttle astronaut Mike Coats is leading the company's studies of such a reusable launcher, which John Karas hopes will use some of Atlas' technologies.
"The big thing Lockheed Martin is working is really second-gen that is not really under the Atlas purview but is under Mike Coats and the reusable launch system guys. I personally think just as we have evolved and used the rule of wing-walking for Atlas 1, 2, 2A, 2AS, 3A, 3B, Atlas 5 400, 500, Heavy, that there is an evolution plan that can bridge the gap between expendables and reusables, probably more than the nation has been focused in on lately.
"The next generation is probably going to be reusable and I'd like to think that we can do something evolved from Atlas 5 towards the reusability end of it. But right now Atlas 5 is pretty good because it's a single failure tolerant machine, essentially, except for the booster engine and the upper stage engine. There are a few single point failures that we plan to design out. Reliability-wise that is as good as you are going to get with an expendable."
MISSION STATUS CENTER