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An Examination of Launch Vehicle Loads Reanalysis TechniquesThe typical approach to calculating dynamic launch loads in aerospace applications is coupled loads analysis (CLA). A component mode model of the launch vehicle is coupled with a component mode model of a payload, system modes are calculated, forcing functions are applied, and the dynamic responses are computed. This approach requires the explicit knowledge of the component models for the launch vehicle and payload, as well as the forcing functions. In many situations, the launch vehicle and forcing functions do not change from one analysis to the next only the payload is different. For this type of application, a method called reanalysis was developed to compute the response of a modified payload on the same launch vehicle. If the launch forcing functions are also the same, the approach eliminates the need for the launch vehicle model and the forcing functions and dramatically reduces the computation time. This work investigates the application and accuracy of three previously developed reanalysis methods using a typical launch vehicle and two different payloads. All three methods are based on knowledge of system modes from the original CLA, and Hurty/Craig-Bampton (HCB) models of the original and new payloads. The first method was developed at JPL (Jet Propulsion Lab) and is often referred to as substitution. It is a frequency-domain method, which requires transformation of time signals to and from the frequency domain. The other two methods are time-domain methods that more closely mimic the CLA process. The three methods were applied to two simple examples and a more complex one. The results indicate that the time-domain methods are considerably more robust with respect to modal truncation and other numerical errors than the frequency-domain JPL method.
Document ID
20180007518
Acquisition Source
Langley Research Center
Document Type
Contractor Report (CR)
Authors
Kammer, Daniel C. (ATA Engineering, Inc. San Diego, CA, United States)
Blelloch, Paul A. (ATA Engineering, Inc. San Diego, CA, United States)
Date Acquired
November 6, 2018
Publication Date
September 1, 2018
Subject Category
Ground Support Systems And Facilities (Space)
Report/Patent Number
NF1676L-31346
NASA/CR-2018-220091
Funding Number(s)
WBS: WBS 869021.03.07.01.05
CONTRACT_GRANT: NNL12AA09C
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Reanalysis
Substitution Analysis
Spacecraft Loads
Coupled Loads Analysis

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