Linear Coupled Loads Analysis

Accurate determination of a structural component’s dynamic response in a coupled system subject to external forces requires what is commonly known as a coupled loads analysis (CLA). For launch vehicle/payloads, CLAs are utilized in design assessments and in the final structural certification for flight. These analyses entail the prediction of payload response due to transient and quasi-static forces including main engine thrust and side-loads, ground winds, solid rocket motor thrust build-up, ignition over-pressure pulses, vehicle pad separation, aerodynamic loads, gusts, buffet, staging, and transients due to engine startups and shutdowns.

ASD engineers have extensive experience with linear CLAs, beginning with the early development of the Space Shuttle Orbiter cargo integration function and inclusive of multiple expendable launch vehicles. All ASD CLAs are executed utilizing NASA/industry accepted system level component modal synthesis techniques and time history integration methods. All component time history recoveries are performed via the accurate “modal acceleration” method. ASD has the capability of incorporating multiple forms of damping, from system modal level definition of damping, component level definition of damping, through hybrid and/or combinations for the damping definition.

ASD CLA experience and expertise have been incorporated into our commercially available ASD/CLAS software tool. ASD/CLAS has set the industry standard for efficient, accurate, and fast turnaround linear and nonlinear CLAs and is licensed by major contractors. For example, Lockheed Martin which has utilized ASD/CLAS on linear, nonlinear, and variational (parametric) design and mission critical loads cycles, including the Space Shuttle Program.

ASD has conducted well over 2000 linear CLAs for our clients which include large scale variational (parametric/sensitivity) coupled loads analyses each involving 100s of individual CLAs in order to characterize payload environments as a function of payload's mass, C.G., and frequencies. (see Minotaur under Case histories)

Case Histories

• Minotaur CLAs (ORS, NASA, DesignNet, Instar, Orbital): ASD was tasked to develop payload envelopes for certain classes of DoD payloads, the goal being that such payloads could benefit from a greatly simplified flight certification process. Payload variations included mass, C.G., and frequencies for both isolated and hard mounted payloads. Flight events included pre-ignition, liftoff, transonic, supersonic and second stage ignition. ASD conducted over 600 CLAs, made possible only by the enabling technologies in its ASD/CLAS software, in a short period of time. The payload envelopes are germane to a particular launch vehicle.
• Constellation CLAs (NESC, NASA/Langley, ATK): ASD was tasked to conduct linear and nonlinear CLAs in support of the MLAS alternate astronaut escape system for the Orion spacecraft. Utilizing ASD/CLAS, ASD was able to quickly conduct and turnaround the required linear and nonlinear CLAs and provide the NESC with all requested data. The CLAs involved flight vehicle separation from the launch stool at multiple cant angles utilizing the Henkel-Mar pad separation method. Flight events included ignition, pad-separation, liftoff, max air loads, and boost ring separation.
• Space Shuttle Mission ULF1.1 IV&V CLA (Lockheed Martin): Independent verification & validation (IV&V) coupled loads cycle and recover of MPLM loads for ULF1.1 Cycle 3.
• Space Shuttle Mission 12A.1 CLA (EADS, Spacehab): Multiple design CLA cycles
• Space Shuttle Mission 13A.1 CLA (EADS, Spacehab): Multiple design CLA cycles
• Space Shuttle Mission ULF1.1 CLA (EADS, Spacehab): Multiple design CLA cycles
• Space Shuttle Mission ULF1.1 IV&V CLA (Spacehab, EADS)
• Space Shuttle Mission 12A.1 IV&V CLA (Spacehab, EADS)
• Space Shuttle Mission LF-1 IV&V CLA (Lockheed Martin)
• Space Shuttle CLAs to validate proposed ASD isolated cross-bay carrier design concept (Blackhawk, NASA)