NX and Teamcenter® software
Siemens PLM Software
Plano, TX

One of ATK Aerospace Group’s current projects involves the Space Launch System (SLS). The SLS is the largest rocket ever built for entirely new human exploration missions beyond Earth’s orbit, and will take astronauts farther into space, eventually including missions to Mars. Its first flight is scheduled for 2017.

ATK’s work involves the SLS solid rocket boosters, the twin external structures on either side of the core stage that provide extra thrust for the first two minutes of flight. Early SLS missions will use modified space shuttle solid rocket boosters, also designed by ATK.

ATK uses product lifecycle management (PLM) technology from Siemens PLM Software utilizing NX software for design, and Teamcenter software to manage product information and processes. The size of the advanced booster rocket’s nozzle will increase to provide better performance from the motors. There are a lot of structures that a larger nozzle could possibly hit on its way off the launch pad. The aft end of the booster has a skirt, and attached to that skirt are launch mounts that hold the rocket in place while it is on the launch pad. ATK is designing retractable mounts that will retract at launch so the nozzle won’t hit them.

Using NX, ATK modeled the aft end of the booster, including the skirt and the retractable launch mount assembly. That digital geometry was then used for two different types of analysis: motion analysis and finite element analysis (FEA).

ATK used NX Motion to simulate the movement of the launch mounts during liftoff. For the speed of the rocket, a curve was input into Excel, and the motion simulation speed was linked to that spreadsheet, showing thrust versus time. The simulation even includes a launch mount’s 4" bolt, which drops away at launch due to a frangible nut. Using motion simulation, ATK soon got to the point where the launch mounts retracted correctly.

Next, the team undertook FEA. Starting with design geometry, ATK used NX CAE to prepare the finite element model of the booster rocket’s aft assembly. Changes made to the assembly model are maintained in the finite element model, so all connections made in the assembly stay in the assembly through the FEA. ATK was able to model bolts quickly as beam elements and spider elements. All of the parts free-floating in space could be tied together by selecting all surfaces or edges of the bolt hole, and then automatically creating beam elements.

Although ATK did some FEA to determine whether the launch mounts were strong enough to handle their loads, more of the FEA was directed at the aft skirt, the interface between the rocket and the launch pad that must withstand the weight of the rocket as well as hurricane-force wind loads.

In addition to saving time, the more important benefit to ATK of having integrated design and analysis was that it gave the company confidence that its model was accurate. ATK spent less time checking analysis models. In addition, this process is less error-prone in general since there are no translations between software packages.

Integrating analysis into the design process includes the use of Teamcenter for managing CAE workflows, as well as the use of the Teamcenter data vault to store CAE models, results, reports, and links to the product structures. This ensures that engineers don’t analyze the wrong parts or configurations, and that analysts stay in sync with design changes, reducing CAE rework. Teamcenter is also used to keep analysis projects on time by tracking project status, cycle time, and first-pass yields.

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