The Space orbiter is the orbital spacecraft of the Space Shuttle program. This space-plane carries crews and payloads, performs on-orbit operations, then re-enters the atmosphere with crews and any on-board payload to the Earth.

During an investigation of the vibration in the Space Orbiter, Raghavendra Rao, an aerospace engineer at a major aerospace and defense corporation, suspected that a structure located in the proximity of Main Engine Ignition (MEI) may vibrate as a result of resonance caused by MEI acoustic environment.

He needed to evaluate the natural frequency of a rectangular plate and make sure it is far outside the resonance zone.

Conducting an analysis of structural vibration in the space orbiter

What We Know: The structure is a rectangular plate with the following dimensions: 20″L x 12″W x 1/8″T. The material of the plate has a density of 0.0975 lb/in3, a modulus of elasticity of 10,200 ksi and a Poison’s ratio of 0.33. The plate was evaluated for two sets of boundary conditions: (1) simply supported at edges and (2) fully restrained (clamped) at the edges.

Finding the natural frequency of the structure Raghavendra starts with a search on Knovel for ‘natural frequenc*’ and retrieves page 754 of Roark’s Formulas for Stress and Strain (7th Edition). He learns that the natural frequency of the structure has to be as far as possible from the frequency of the forcing impulse: Now he has to find equations to calculate the natural frequency of the plate. Searching on ‘vibration and plate*’ The finds the title Harris’ Shock and Vibration Handbook (5th Edition) and, in the chapter Lateral Vibration of Plates, finds Table 7.9 Natural Frequencies of Rectangular Plates. and from Table 7.7 he finds additional equations: He combines his search terms to include ‘natural frequenc* and plate’ and retrieves the title AIAA Aerospace Design Engineers Guide (5th Edition), this text shows the same equations in the chapter 5.14 Plate Natural Frequency on page 5-46: Using the equations and data retrieved from Knovel, Raghavendra calculated the natural frequency and had the option to use Excel, Mathcad or a similar desktop engineering software package to complete the analysis. The last step was to check if the computed natural frequency of the structure is in or near the resonance range. See his work below:

Raghavendra was able to find the information required to accurately study the effect of MEI acoustic environment for on the orbiter structural parts located close to MEI. He concluded that the frequency computed was not in the resonance range and hence the structure did not have to be modified. The analysis performed was a key in establishing the structural integrity of the Space Orbiter.

This entry was posted on Monday, June 28th, 2010 at 11:40 pm and is filed under Summer 2010. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.