MASS ACCELERATION CURVES Revision A By Tom Irvine Email: tom@vibrationdata.com May 20, 2014 ________________________________________________________________________ STS/IUS/Galileo Mass Acceleration Curves, NASA-HDBK-7005 Figure 1. Introduction The mass acceleration curve (MAC) method was developed by JPL to perform preliminary structural sizing. It is a semi-empirical method to determine the upper bound for the low-frequency dynamic loads at the payload and for its subsystems and components. But it is not a simulation of the actual response. The MAC curves may be given as function of either physical mass or modal mass, per Reference 3. Modal Mass Case The MAC method is inexpensive to apply. It requires only payload modes. It can be verified or refined by coupled-loads analysis (CLA). Individual acceleration values are calculated for each mode, per the effective modal mass. The resulting load is then taken as the square-root-of-the-sum-of-the-squares. The rigid-body acceleration load from the launch vehicle thrust should be added for the analysis in the loads should also be included, vehicle’s longitudinal axis. Other relevant such as pressure, thermal, misalignment, etc.
MASS ACCELERATION CURVES Revision A By Tom Irvine Email: tom@vibrationdata.com May 20, 2014 ________________________________________________________________________ STS/IUS/Galileo Mass Acceleration Curves, NASA-HDBK-7005 Figure 1. Introduction The mass acceleration curve (MAC) method was developed by JPL to perform preliminary structural sizing. It is a semi-empirical method to determine the upper bound for the low-frequency dynamic loads at the payload and for its subsystems and components. But it is not a simulation of the actual response. The MAC curves may be given as function of either physical mass or modal mass, per Reference 3. Modal Mass Case The MAC method is inexpensive to apply. It requires only payload modes. It can be verified or refined by coupled-loads analysis (CLA). Individual acceleration values are calculated for each mode, per the effective modal mass. The resulting load is then taken as the square-root-of-the-sum-of-the-squares. The rigid-body acceleration load from the launch vehicle thrust should be added for the analysis in the vehicle’s longitudinal axis. Other relevant loads should also be included, such as pressure, thermal, misalignment, etc.