1 YamSat Bus Structures Analysis Tsai Ming-Hsien 蔡明憲 2005/03/24 YamSat

2 OBJECTIVE The objective of this lecture is not to provide a comprehensive listing of design criteria. It is intent to discuss the assumptions used in deriving the criteria and how to balance the stiffness and strength requirements for weight saving purpose. YamSat Structural Design Criteria

3 YamSat Description of Structural Design Criteria Stiffness Design Criteria: *Required by Launch Vehicle Contractor *Required for Clearance *Required for Alignment *Required for Good Design Practice Strength Design Criteria: *Margin of Safety *Fracture Control *Stress Corrosion

4 YamSat Stiffness Design Criteria S/C Minimum Frequency Requirements:(Launch vehicle) To avoid dynamic coupling between the low frequency vehicle and spacecraft structure modes, the stiffness of the spacecraft structure should be designed to produce fundamental frequencies above 35 Hz in the thrust axis and 15 Hz in the lateral axes for spacecraft hard mounted at the spacecraft separation plane(I.e without attach fitting and separation clamp) For payloads unable to meet these criteria, It is necessary to coordinate the structural design closely with the program office so that appropriate analysis can be performed if necessary to better define loading conditions.

5 YamSat Stiffness Design Criteria Required for Clearance No contact between the S/C internal components and no contact between the S/C and launch vehicle faring. Required for Alignment Sufficient stiffness to preserve the alignment of the antenna subsystem and the attitude control sensors within their budgeted values after exposure to the launch and thermal environment of the mission life. Required for good design practice To avoid dynamic coupling between secondary structures,subsystem, and components with the S/C modes. To preclude dynamic interactions with the launch vehicle and spacecraft attitude control system.

6 YamSat Strength Design Criteria Maintain positive margins of safety(M.S.) for all loading conditions: Allowable Stress or Loads M.S.= - 1 Max.Stress or Loads x Factor of Safety Allowable stresses or loads cab be obtained from handbooks, calculations, or test data. The environmental effects should be accounted for in defining the allowable. Maximum stress or loads are determined based on the pre- launch, launch, on-orbit, and test environments. Factor of safety

7 YamSat Key Requirements SMS Key requirements - The Spacecraft shall be compatible with the small class of launchers such as Delta2 and Dnepr, as a minimum. -Spacecraft shall have sufficient strength to maintain positive margin of safety -Stiffness Satisfy minimum frequency defined by the candidate LV -Safety Factor * Yield allowable stress  1.25 * Ultimate allowable stress  1.25 * Fitting factor  1.15 against ultimate allowable loads

8 Requirements Constraints Design Process Design Loads Structure Elements Load Path Structure Sizing Major Factors YamSat

9 Design Process MissionRequirements SystemRequirements Configuration PreliminarySizing Finite Element Model PreliminaryDesignSMSRequirements Payload Selection Payload Selection Orbit Orbit Candidate LV Candidate LV Design Loads Design Loads Min. Frequency Min. Frequency Design Margin Design Margin Sizing Sizing Surface Area Surface Area FOV FOV DetailedDesign YamSat

10 YamSat Major YamSat Requirements YamSat System Requirement Document General YamSat Requirement Document Launcher Environmental Synthesis Bus Structure Engineering Specification YamSat Requirements

11 YamSat  Lateral: > 25 Hz  Longitudinal: > 40 Hz Candidate launchers: Major YamSat Requirements - Satellite Stiffness -

12 YamSat  Longitudinal (qual load):14.2 g (from Minotaur )  Lateral (qual load):8.7g (from Minotaur) Note: The numerator contains static components of g-load while the denominator -the dynamic ones Axial,lateral, and static components of g-loads act simultaneously while dyamic ones act within the rang of f=2….20 Hz. (Dnepr from the Russian ) Major YamSat Requirements - Quasi-Static and dynamic Loads -

13 YamSat AxialLateral Major YamSat Requirements - Sinusoidal Vibration Loads - Lateral Axial

14 YamSat Spectral density Requirements

15 YamSat Shock Spectral Requirements

16 YamSat Acoustic loads Requirements

17 YamSat Major YamSat Requirements - Quasi-Static and dynamic Loads - P-POD Maximum force during launch: 15g’s Dynamic loads : Lateral: > 25 Hz Longitudinal: > 40 Hz

18 YamSat Safety Factor * For yielding stress =1.25 * For ultimate stress =1.25 Load Cases and Safety Factor Load cases P-POD requirements

19 YamSat FEM Elements Description Yamsat FEM elements No. of GRID : 1017 No. of CBAR : 240 No. of CQUAD4 : 1040 No. of Bolts : 24 (new), 36 (old) Material:7075-T6 Total Weight :0.991Kg C.G: X= mm Y= 2.14 mm Z= mm

20 YamSat Unit enforced displacement and rotation check D I S P L A C E M E N T V E C T O R POINT ID. TYPE T1 T2 T3 R1 R2 R G E G E E E E E E G E E E E E E G E E E E E E G E E E E E E-11 ………………………………… Unit gravity loading checking D I S P L A C E M E N T V E C T O R POINT ID. TYPE T1 T2 T3 R1 R2 R G G E E E E E E G E E E E E E G E E E E E E G E E E E E E-06 ………………………………… FEM Elements check

21 YamSat Yamsat Stress Distribution

22 YamSat Lateral mode : 221 Hz >> 25Hz Longitudinal mode : 1156Hz >> 40Hz Conclusion :The results for stress and dynamic analyses are acceptable. Stress & Dynamic Analysis Results

23 YamSat M2 bolts are used for Yamsat with ultimate stress allowable =700Mpa yield stress allowable = 560Mpa nominal tightening torque = 0.21 Nm Conclusion :All M.S. for bolts analysis are acceptable. P.S. : The bolt analytical results are provided by Chi-Wei, Chou Margins of safety for Bolts analysis

24 YamSat YAMSAT _Test sequences and test conditions 1. Sine Sweep Test (1) Test freq range: 1600 Hz Sweep rate: 2 oct/min Test level: 0.2g 2. Sine Burst Test Test freq : 20 Hz Test cycle: 40 cycles Test level: 10.25g 3. Random Vibration Test(Table) 4. Sine Sweep Test (2) Test freq range: 1600 Hz Sweep rate: 2 oct/min Test level: 0.2g

25 YamSat 1.Sine Sweep Test (1) along X axis 2.Sine Burst Test along X axis 3.Random Vibration Test along X axis 4.Sine Sweep Test (2) along X axis YAMSAT Vibration Test Along X axis

26 YamSat YAMSAT Vibration Test Along Y axis 1.Sine Sweep Test (1) along Y axis 2.Sine Burst Test along Y axis 3.Random Vibration Test along Y axis 4.Sine Sweep Test (2) along Y axis

27 YamSat 1.Sine Sweep Test (1) along Z axis 2.Sine Burst Test along Z axis 3.Random Vibration Test along Z axis 4.Sine Sweep Test (2) along Z axis YAMSAT Vibration Test Along Z axis

28 YamSat From the modal analysis results, the longitudinal mode(x) is about 1156 Hz and lateral mode(Y, Z)is about 221 Hz. YAMSAT Vibration Test Results

29 YamSat * From the above test results, we found not much frequency difference between the pre-test Sweep sine and post-test both in first mode and the second mode. * A visual inspection has been made at the end of tests. No structure deformation,screw drop out, or solar cell crack were found. Two antennas are still stowed inside the satellite. * Some electrical functional tests have been done. No electrical function fault appeared after vibration test. * Finally, we consider that Yamsat is very successful in dynamic environmental tests. YAMSAT Conclusion

30 YamSat SFM 結構體測試驗證 音振艙測試 振動測試 爆振測試 太陽電能版展開測試 衛星質量特性量測 TV 熱真空艙測試 EMI/EMC 測試 衛星 Alignment 量測 Rocsat-2 Environmental Testing

31 YamSat a) Behavior as Cantilever Beam b) Ceiling panel’s vibration c) Load Estimation d) Countermeasure for vibration(Antennae) Tokyo_cubesat Strength Analysis

32 YamSat Harmonic Frequency is around [kHz] The Harmonic Frequency largely depends on the thickness of the panel. The thicker the panel is designed, the higher the Harmonic Frequency becomes. Tokyo_cubesat Ceiling Panel’s vibration [1]

33 YamSat To avoid ceiling panel’s vibration we have to design it as possible as thick. For this design, Total Mass is large problem Eventually,we have to choose around mm Tokyo_cubesat Ceiling Panel’s vibration [2]

34 YamSat The 3rd CubeSat experiences maximum load while 2nd stage flight The maximum stress is 0.011kgf/mm 2 (enough for Aluminum use) P-POD Maximum Stress 7.7g(max) Tokyo_cubesat Load Estimation

35 YamSat To complete any mission, fastening and deploying antennae is very important. It is difficult to simulate the behavior of the antenna, so we conduct some experiments to confirm the feasibility of this design. Fixing antennae with several points. Tokyo_cubesat Countermeasure for vibration(Antennae)

36 1. Describe major factors to be considered for structure design, I.e weight,etc. 2. Describe the process for structure subsystem design. 3.Define environmental loads for Picosat design. 4.Describe how these loads are applied to the structure design. 5.Define requirements for the structure design. 6.Define configuration for your Picosat structure design, 7.Describe basic structure element in each part of your structure design, i.e. Panels, etc. Home work for SMS Subsystem Design Design YamSat

37 Home work for Final Report 1. Define main load path of your structure, i.e. how the loads transfer through the structure to the supporting points. 2. Determine preliminary sizing of main structure elements for your Picosat design and estimate the total weight. 3.Construct a finite element model and determine natural frequencies of your Picosat design using the preliminary sizing derived from HW#2.(Bonus Exercise) YamSat