Spacecraft Mechanical Sub-System Design & Manufacturing
Spacecraft Mechanical Sub-system Design & Manufacturing Introductory Course
Presented by Atipat Wattanuntachai | [email protected]
1 Acronyms
S/C = Spacecraft CAD = Computer Aided Design L/V = Launch Vehicle CAM = Computer Aided Manufacturing AIT = Assembly, Integration and Test CAE = Computer Aided Engineering (Analysis) EVT = Environment Test DR = Discrepancy Report AOCS = Attitude and Orbit Control Systems RF = Radio Frequency MGSE = Mechanical Ground Support Equipment CoG = Center of Gravity FEM = Finite Element Modelling FEA = Finite Element Analysis
2 Contents
▪ Mechanical Sub-system Introduction – Mechanical Engineering – Launch Vehicles – Satellite – Class of Satellite (by application & by mass) – Satellite Platform & Payload – Satellite Structure Feature – Satellite Structure Classification – Satellite Structure Architecture
3 Contents - Cont. ▪ Mechanical Design & Manufacturing - Requirement Gathering - Mechanical Engineer Roles - Design Consideration - How to Start Designing - Derived Requirement - Design & Manufacturing Tools - Heritage Design - Material Selection - Platform Selection - Manufacturing Technique - Project Lead-time - Design for Manufacturing - V-Diagram - Worth Mentioning Concept ▪ Procurement ▪ Inspection
4 Mechanical Engineering: ME
“Mechanical engineering is an engineering branch that combines engineering physics and mathematics principles with materials science to design, analyze, manufacture, and maintain mechanical systems. It is one of the oldest and broadest of the engineering branches..” - Wikipedia
“Mechanical Engineering takes in all built structures and moving parts flown in space, which includes automation and robotics, instruments for scientific missions as well as assessing the effects of the space environment on materials.” - The European Space Agency
5 Launch Vehicles
THEOS-2 SmallSAT Launcher (Auxiliary payload)
6 Launch Cost
7 Class of Satellite (by Mass)
Credit: https://www.nanosats.eu/cubesat Credit: Canadian Space Agency 8 Spacecraft Structure Features
Primary Features ✔ Accommodate payload, instruments, and compulsory on-board avionics ✔ Provide a mechanical interface between spacecraft & launcher ✔ Provide a sufficient stiffness to meet a natural frequency requirement of launcher and to minimize a dynamic amplification between launcher & satellite by carefully performing a modal design ✔ Provide a capability of S/C to withstand a launch environment (vibrations, high G-force, and shock event) ✔ Provide a sufficient mechanical stability to satisfy a pointing sensitive payload requirements i.e. build tolerance, alignment, micro-vibration, and thermo-elastic stability) To make sure the S/C will get into orbit in one piece!
9 Spacecraft Structure Features (Cont.)
Secondary Features ✔ Protect payloads & avionics from harsh environment in outer-space (cosmic radiation & temperature fluctuation in orbit) ✔ Protect payloads & avionics component from depressurization during launch and vacuum environment in space ✔ Provide a proper electrical grounding design for electronic and power equipment ✔ Provide mechanical ground support equipment (MGSE) interface and harness routing accessibility to accommodate AIT needs ✔ Provide an optimum assembly pattern to satisfy AIT requirement
10 Spacecraft Structure Classification
Primary Structure - Carries a majority of mechanical loading during launch - Know as “load path structure” that transmits loads from launcher interface to the rest of S/C SMART-1 S/C Primary Structure - Any failure of this structure can cause the Credit: sci.esa.int/web/smart-1 S/C to collapse which means a major loss of mission functionality - i.e. separation ring, centre tube, thrust tube, separation panel, struts (all fixing JUICE S/C Primary Structure element) Credit: sci.esa.int/web/juice
ESTCube-1 Cubesat Credit: https://en.wikipedia.org/ 11 Spacecraft Structure Classification (Cont.)
Secondary Structure: - Carry a significant mechanical loading - This structure accommodate most of equipment inside/outside S/C - Any failure of this structure can cause a partial loss of S/C mission functionality - i.e. closure panels, deployable panel & hinges
Credit: Mohamed A., Cairo University, Egypt Tertiary Structure / Non-Structural Mass: - Any component which does not carry a significant load within the structure or contribute to structural behavior / performance - i.e. small equipment, avionic modules, brackets 12 System Requirement Assembly, Requirement Gathering Integration Payload , and Test
Mechanical Radio Launch Frequency Derived vehicle Requirement
Space Power Environment THEOS (Thaichote) Attitude and Orbit Control Systems 13 Design Consideration
Derived Heritage requirement design
Platform Project lead selection time
14 Derived Requirement • Can use any tools • QFD matrix is one of the best choices (also known as House of Quality)
Customer Requirement (Mission objectives)
System Level Requirement
Sub - system Level Requirement 15 Heritage Design THEOS-2 SmallSAT: Launch expected 2022
✔ Space proven ✔ Lower development time ✔ Lower risk of schedule delay ✔ Faster integration and test (similar configuration) ✔ Economic of scale (i.e. same size module box, MGSE) ✔ Lower EVT requirement (Test only to acceptance level)
CARBONITE-1: Launched 2015 CARBONITE-2: Launched 2018
16 Platform Selection SSTL-CUBE 8U-12U CUBE SAT ✔ Lower development time (if not develop new platform) ✔ Faster integration and test (similar configuration) ✔ Economic of scale ✔ Lower EVT requirement (May not need to test for 50-150 KG SSTL-MICRO constellations) THEOS2 SMALL-SAT
SSTL- 200 KG OR MINI MORE
17 Class of Satellite (by Application)
Communication & Relay Earth Observation Scientific (Thaicom 4) (THEOS-2 SmallSat) (Hubble Space Telescope)
Meteorological (Himawari) Reconnaissance Navigation (TacSat-4) (Galileo, GPS, Beidu, GLONASS) 18 Frame-Panel Structure Type
Satellite Structure Forms
Thrust Tube Structure Type
Korean STSat-2 Credit: earth.esa.int
Monocoque Structure Type
ESA Trace Gas Orbiter (TGO) SSTL Carbonite 1 Credit: spaceflight101.com Credit: directory.eoportal.org Mass: 3.8 ton (Large-Satellite Class) Mass: 90 kg (Micro-Satellite Class)
KAIST STSat-3 Credit: kis.kaist.ac.kr 19 Project Lead Time Longer project lead time • Require less resource (design engineers) • Lower risk of late design change • Better structural performance (lower mass, easier to manufacture, easier to integrate) Shorter project lead time • Require more resource (design engineers) • Higher risk of late design change • May sacrifice structural performance • Incur higher cost (fast track manufacturing cost, overtime) Key to reduce project lead time • Design for Manufacturing principle (more on this later) • Clear and precise requirement • Development and support tool and resources 20 V-Diagram
Product Assurance & Quality Assurance In every process
Mechanical Sub-system
21 Example: THEOS2-SmallSAT
22 How to start the designing
⮚ The heart of satellite mission is “a payload”, but the payload can’t work alone without support from “various avionic sub-systems” ⮚ We design “a spacecraft (S/C) structure” to accommodate both “payloads” and “avionics” by assemble them together into one piece ⮚ We also design “the S/C structure” to make it’s compatible with “a selected launcher” ⮚ Payload & launcher requirements mainly “drives” the S/C structural design ⮚ To verify a robustness & integrity of S/C structural design, structural analysis & test shall be performed
23 Exercise: THEOS2-SmallSAT
Which are mission requirements? Which are derived requirement?
• Lower Earth Orbit Earth Observation Satellite • 3-years service lifetime • 100-kg class SSTL’s carbonite platform • Soyuz/ PSLV auxiliary bay • Featuring AIS/ADS-B secondary payload • Featuring Raspberry Pi based Third payload • One deployable panel
• No-propulsion system 24 Satellite Shape & Dimension
Things to be considered…
All avionic and payload shall be fit in this structure - Size of main payload (i.e. imager) - Amount of avionic system required - Power requirement High power consumption need more solar cell area
It must be compatible with launcher - Will it fit inside a launcher fairing? - Will it fit inside a dynamic envelope? - Will it fit with available separation system?
25 Satellite Inside Rocket Fairing
Primary Passenger Auxiliary or Secondary Passenger
Launcher: Vega Launcher: Falcon 9 Block 5 Credit: ARIANE Space Credit: https://spaceflightnow.com/
26 Structural Qualification Status List (QSL)
Equipment Heritage Required modification from Qty. Sub-system Unit Qualification Mission sub-system heritage baseline (THEOS-2 Status SmallSat) Structure General Structure Carbonite-2 C Change panel inserts technology from hot 1 bonded to cold bonded. (CAT C) Small change in dimension (CAT B) Structure Separation system Carbonite-1, A Same separation system 1 Carbonite-2 Payload Main imager payload Carbonite-2 C Change imager electronic from COTS to SSTL’s 1 Ceria camera AOCS Torque rod Carbonite-2, A Change only position on S/C 3 many others AOCS Sun sensor Carbonite-2, A Change only position on S/C 4 many others Etc.
27 Mechanical Engineer Roles
28 Mechanical Design & Manufacturing Tools
CAD: Solidworks, CATIA, NX CAD file control: Solidworks PDM, Enovia CAM*: NC Solution, Cura
29 Module Placement Example of Pleiades-HR (High-Resolution Optical Imaging Constellation of CNES), launched in 2009
https://directory.eoportal.org/web/eoportal/satellite-missions/p/pleiades
30 Structure Elements Every S/C structures, whatever how much of complexity is, they usually comprise of a following structure elements Panels: thin walls designed to Monocoque structure: thin- Trusses: a set of beams or struts enclose volumes or to provide a walled tubes (round or rectangular Beam, Bar, and Strut: connected together at angles mounting surface for spacecraft cross-section) made of composite Long component that supported which is stronger that a single equipment. Honeycomb sandwich skins with stiffener or sandwich axial and lateral loadings beam panel is the most popular usage panels
31 Material Selection
• Yield strength • Stiffness • Specific mass • Thermal expansion coefficient • Manufacturability • Shelf life • Outgassing • Non-magnetic* • Raw material cost • Order lead time
32 Manufacturing Technique
• CNC Machining • CNC Turning • Wire EDM (Wire cut) • Laser cut • 3D printing • Honeycomb sandwich panel • Injection molding
CNC – Computer Numerical Control EDM - Electrical Discharge Machine
33 Design for Manufacturing
✔ Reduce the total number of parts ✔ Develop a modular design ✔ Use of standard components ✔ Design parts to be multi-functional ✔ Design parts for multi-use ✔ Design for ease of fabrication ✔ Avoid separate fasteners ✔ Minimize assembly directions https://www.innovationservices.philips.com/looking- expertise/manufacturing-systems-industry-40/design-for- ✔ Maximize compliance manufacturing-assembly-and-testing/ ✔ Minimize handling
34 THEOS-2 SmallSAT Example
Part/Component Manufacturing Technology Material GNSS Antenna Riser CNC Turning Aluminium 7000 Series S-Band Mounting Block CNC Turning / Machining Aluminium 7000 Series X-Band Horn Antenna Wire Eroding EDM Aluminium 7000 Series Module Box CNC Machining Aluminium 7000 series Module Box Lid CNC Machining Aluminium 7000 Series Connector Bracket CNC Machining Aluminium 7000 Series Star Tracker Bracket Multiple Processes Titanium Satellite Assembly Trolley Multiple Processes Multiple Materials Deployable Panel Sandwich-structured composite CRFP skin, Perforated Aluminium Honeycomb Side Panel Sandwich-structured composite Aluminium skin, Perforated Aluminium Honeycomb Separation Plate Large CNC Machining Aluminium 7000 Series Momentum Wheel CNC Turning Aluminium 7000 Series
35 Procurement
⮚ In-house or external supplier ⮚ Procurement lead time ⮚ Compliance (export control) ⮚ Quality ⮚ Price ⮚ Minimum order quantity (MoQ) ⮚ Reliability, thrustworthy
36 Inspection
⮚ From supplier ⮚ Inspection report ⮚ Product conformance report ⮚ Discrepancy report ⮚ Inspect to drawing ⮚ May require specific inspection tools ⮚ No need to inspect every dimension ⮚ Fit-check method applies
37 THANK YOU!
38 Spacecraft Mechanical Integration, Analysis, Test, and Mechanical Related Roles Introductory Course
Presented by Panachai Santananukarn | [email protected]
39 Contents
⮚ Integration ⮚ Mechanical Analysis – Build Instruction – Launcher Environment – Drawing – Failure Mode Evaluation – Tackle Box – Analysis Tools – Build Log, Mate/De-Mate Log – S/C Structural Analysis – Discrepancy Report – Finite Element Model – Mechanical Ground Support Equipment – Mechanical Loading – Analysis Results
40 Contents - Cont.
⮚ Mechanical Testing ⮚ Other Roles in Mechanical Team – Vibration Tests – Mass Budget – Mass Property Test – Working with AIT Team – Pyro-Shock Test – Support Other Sub-Systems – Micro-Vibration Test – Material Testing ⮚ Other Potential Responsibilities - Mechanism Engineer - Propulsion Engineer
41 Mechanical Engineer Roles
42 Integration
Build Instruction Drawing Tackle Box
Build Log Discrepancy Report Mate/De-mate Log
43 Build Instruction
▪ As a step by step guideline ▪ To use in accordance to drawing and tackle box ▪ No need to strictly follow the instruction ▪ Assume fundamental mechanical and integration knowledge ▪ When in doubt, ask module owner!
44 Drawing ▪ As a overall complete build perspective ▪ To use in accordance to build instruction and tackle box ▪ Give part number as well as quantity and location ▪ Assume fundamental drawing reading knowledge ▪ When in doubt, ask module owner!
Source:https://en.wikipedia.org/wiki/Engineering_drawing#/media/File:DIN_69893_hsk_63a_drawing.png
45 Tackle Box
▪ As a handy fasteners, small bracket tray ▪ To use in accordance to drawing and tackle box ▪ Each box represent sub-assembly (i.e. Space Facing Facet, Earth Facing Facet) ▪ Give part number as well as quantity ▪ When in doubt, ask module owner!
Sorce: https://my-mould.en.made-in-china.com/productimage/wXeJdFmPrcrl-2f1j00kwTtopNJnszY/China-Multi- Compartment-Customized-Plastic-Electronic-Parts-Partition-Box.html
46 Build Log, Mate De-Mate Log
▪ To record every progress made during integration Build Detail Date Signed ▪ To record mating, de-mating of each component sequence ▪ Prevent overuse fasteners 1 Fit Space Facing Facet xx/xx/xx AW ▪ Prevent loosen fasteners 2 Fit shear walls ▪ Allow better traceability 3 Fit X-band module ▪ If find any deviation, open the discrepancy report 4
Part Date Torque Date Date Torque Date Description Signed Signed Signed Signed number mate1 (N.m) De-mate1 mate2 (N.m) De-mate2 00123 X-Band module xx/xx/xx 10.7 AW 00884 00381
47 Discrepancy Report (DR)
▪ Also known as Non-conformance report (NCR), Corrective & Preventive Action Request (CPAR) ▪ To record every non-conformance, deviation, accident occur ▪ Can be very negligible or major problem ▪ Assign to all relevant person ▪ Module review board meeting need for major DR ▪ Solution will be recorded for future build
48 Mechanical Ground Support Equipment
▪ Lifting frame ▪ Integration trolley ▪ Transit case ▪ Spacecraft rotation frame ▪ Vibration test bed adaptor ▪ Thermal test bed adaptor ▪ Mass properties test bed adaptor ▪ Electromagnetic compatibility test table
49 Structural Analysis
Structural analysis is an approach to predict a mechanical behavior of engineering product design under its application loading.
With help of a computer aided engineer (CAE) alongside with computer aided design (CAD) widely used in modern research & development (R&D) engineering, a complex product design problem can be solved quickly without creating a lot of prototypes and doing a lot of tests as previously done in the past
The main goal of structural analysis in space industry is to evaluate the robustness, integrity of S/C structural design and mechanical interaction between concerned equipment to increase a confident before manufacturing.
It can be done iteratively alongside with S/C structural designing while it’s in a designing phase to help revealing the problem and improving it earlier!
50 Launcher Environment Is the mechanical loads generated by launcher during assenting are transmitted to the passenger (satellites) through its separation ring or interface
Quasi-static acceleration (QS): Caused by a steady-state acceleration of launcher (can be up to 9 g) Dynamic loads Ares I-X Aerodynamic Transonic Soyuz Fairing Separation ⮚ Sine vibration: Credit: NASA Credit: ESA–P. Carril, 2014 Caused by a structural response of launcher body ⮚ Random vibration: Caused by aerodynamic interaction between air & rocket, engine combustion, and transmitted acoustic load through S/C mechanical interface (for <400 kg S/C class) ⮚ Vibro-acoustic: Caused by high intensity acoustic noise generated by engine combustion & aerodynamic effect that transmitted to S/C external surface by surrounding air (for ≥400 kg S/C class) Transient Load ⮚ Pyro-shock: Caused by pyro-technique device actuation (i.e. explosive boles) during a separation of rocket stages, fairing, other S/C, and S/C itself Rocket Engine Firing Credit: NASA 51 Failure Modes Evaluation on S/C Structure
Metallic Skin Insert - Core Structure Bolt Slippage Bolt Gapping Bolt Yielding Yielding Yielding Shear Metallic Panel ✔ Sandwich Panel ✔ ✔ Fasteners ✔ ✔ ✔
52 Failure Modes - Sandwich Panel
Core Shear & Face Yielding Insert - Core Shear Failure
Credit: Ralf S. and Dieter K., Numerical modelling of partially potted inserts in honeycomb sandwich panels under pull-out loading, Composite Structures, Volume 203, 2018.
Credit: https://www.hexcel.com/
Credit: Steves and Fleck, 2004; Shivakumar and Chen, 2009
53 Fastener Yielding & Rupture Failure Modes - Fastener Joints
Fastener Joints Slippage Fastener Joints Gapping
Credit: www.structuremag.org/?p=10652 Credit: www.eng-tips.com/viewthread.cfm?qid=455218 Credit: Nassar S.A., Yang X. (2013) Bolted Connections
54 Finite Element Solver Software Mechanical Analysis Tools Solve S/C mechanical analysis problem Finite Element Modelling Software Create S/C mechanical analysis model View the analysis result
Others Calculate margin of safety of S/C mechanical parts Calculate shock response spectrum to evaluate vibration test profile
55 S/C Structural Analysis
A Finite Element Analysis (FEA) is used to predict ⮚ Modal properties of S/C assembly and modules under launch configuration - Natural frequencies - Mode shapes - Modal effective mass* Uses MSC NASTRAN software to solve and calculate this problem ⮚ Base forces of S/C separation system to evaluate vibration test profile ⮚ Stress analysis of S/C primary structure parts i.e. panels, thrust tube - Under quasi-static acceleration, sine and random vibration loadings - Then calculate a margin of safety to evaluate the strength against various failure modes ⮚ Vibration transmissivity between S/C separation interface and any modules or equipment - Under 1g-sine or random vibration - Then, vibration response magnitude of each modules under any level of sine or random vibration loading can be calculated by simply multiply the input profile with transmissivity curve 56 S/C Structural Analysis Model
This analysis model is known as “a finite element model (FEM)” which is needed to be created to predict the structure behavior
1. Import the S/C CAD model design, and minimize detailed features
2. Define material & structure properties as per datasheet, supplier info, or material test result
3. Simulate S/C configuration by applying an appropriate boundary condition to S/C interface
4. Model validity checks shall be performed when FEM has been firstly created, and every time that FEM has been updated to ensure a validity of FEM before uses
Credit: Jae Hyuk Lim, A correlation study of satellite finite element model for coupled load analysis using transmissibility with modified correlation measures, Aerospace Science and Technology, 2014. 57 Mechanical Loading
Credit : Adriano C., ESA Spacecraft Structural Dynamics & Loads An Overview. 2020 58 Analysis Results Vibration Response Analysis (Predict vibration transmissivity, and vibration response of Modal Analysis modules or equipment inside the S/C in each axis to support module level development) (Predict natural frequency, mode shapes, & modal effective mass to evaluate S/C design)
Source: https://asrengineering.com/2018/12/18/how-spacecraft-survive-launch/
Credit: Israr, Asif. "Vibration and modal analysis of low earth orbit satellite." Shock and Vibration, vol. 2014, 2014. Accessed 18 Mar. 2021. 59 Analysis Results – Cont.
Stress Analysis
(Predict MAXIMUM mechanical stress under quasi-static, sine & random vibration to evaluate the robustness of designed parts before manufacturing)
Credit: Kudzanai S. & Tawanda M. Finite Element Analysis of a Cubesat, Proceedings of the 2017 International Conference on Industrial Engineering and Operations Management (IEOM). 60 Mechanical Testing
Mechanical testing is another set of activities to be performed in order to verify the mechanical sub-system requirement including
- Qualification test: to demonstrate a survivability of S/C or spaceflight hardware against mechanical loadings during launch i.e. vibration test, shock test, acoustic test. This is a mandatory test which needed to be complied as per structural verification plan and DDVP approach.
- Material test: to determine material or structural properties which can be used to support S/C structural and spaceflight hardware mechanical analysis (most reliable material properties usually get from this test) and evaluate a workmanship build of mechanical part
- S/C mass property test: to determine mandatory mass properties of S/C and supply for AOCS sub-system and launch agency needs
61 Vibration Tests
As long as people still rely on rocket technology, S/C and flight hardware vibration test is required to be done before launching the S/C into space as per following reasons
- To de-risk a structure from failure & backfire during launch which may leads the lost of mission, destroying other S/C or the whole launcher! - To increase a confident on a new S/C structure design by testing them even stronger than launcher requirement to incorporate additional margin for future development & usage
The S/C or flight hardware shall be tested on an electrodynamic shaker or equivalent as shown in right picture. Several accelerometers will be attached on test object interface to control the vibration input and on critical location in S/C to capture the vibration response Credit: Brüel & Kjær
62 Vibration Tests - Cont. Vibration test is usually performed in three orthogonal axes (X, Y, and Z) as mechanical loafing come from every direction Three types of vibration tests are regularly performed - Sine Dwell Vibration demonstrate structure survivability against quasi-static loading as this test profile is nearly equivalent to quasi- static acceleration - Sine Sweep Vibration At low level (< 0.5 g) to evaluate any structural changes or damages on each stage of vibration tests by comparing current and previous LLRS response
At high level (≥ 0.5 g) to demonstrate structure survivability Spacecraft Vibration Testing in lateral direction against sine vibration environment (10-100 Hz) Credit: NASA - Random Vibration demonstrate structure, modules, and equipment survivability against random vibration environment (10- 2000 Hz) 63 Vibration Test Result Analysis
Once the tests are done, raw data capture from each tests still can’t be used instantly and requires to do a proper post processing
For vibration test; Useful data is natural frequencies of primary structure, main payload, and other vibration sensitive equipment i.e. battery
Vibration transmissivity is another important data needed to be extracted as it can be used for predicting vibration response under higher level of vibration input
64 S/C Mass Property Test
The S/C (in flight configuration) shall receive a mass property test using a mass properties measurement machine and S/C M.o.I rig to extract mandatory information including - S/C Mass - S/C Center of Gravity (C.o.G) - S/C Moment of Inertia (M.o.I) - S/C Product of Inertia (P.o.I) - Optional
These information can be used as an input for a satellite altitude controlling system and shall be submitted to AOCS engineer straight forward.
Besides, launch agency also requires mass & C.o.G. information as well!
65 Pyro-Shock Test
Some small electronic board components i.e. atomic clock, piezoelectric crystal (and glass) are subjected to get damage by shock loading causing by pyro-technique device actuation during rocket stages, fairing separation, and S/C jettison. If new or non-heritage shock sensitive component has been introduced into an electronic board design or other instrument, pyro-shock test shall be performed (usually at module or equipment level) in a shock rig to evaluate a survivability of these component against shock loading. Credit: ESA
If it pass the test, the component will get shock If the component is found broken after test, qualification and can be used in other unit or in new part shall be replaced, or design change future mission without any further test may be introduced, then repeat the test again.
66 Pyro-Shock Test - Cont.
Pyro-shock test can be performed at S/C level as well by using an engineering model (EM) separation system which contains a set of explosive bolts.
BepiColombo Mercury Spacecraft Structural Model – Shock Test Credit: https://sci.esa.int/web/bepicolombo/-/50681- bepicolombo-composite-spacecraft-separation-shock-testing
67 Micro-Vibration Test
In some S/C that equipped with a pointing sensitive instrument i.e. imager, a vibration at very low magnitude generated by on- board mechanism can cause an instability (a small vibration) to the imager. If this happens during capturing the image, it may cause the photograph to be distorted or blurred. This phenomenon is called “a jitter effect”. With a combination of decent S/C structure, mechanism, and imager design, the micro-vibration response at the imager can be controlled in a satisfied limit. There’re only two ways to evaluate the imager micro-vibration performance, by analysis, and test. However, if the imager pointing requirement is really needed to be complied, the micro- vibration test may be performed at S/C level to predict a maximum pixel shift that could happens in orbit. Jitter Effect on Satellite Imagery Credit: Cornelius J. Dennehy, SURVEY OF REACTION WHEEL DISTURBANCE MODELING APPROACHES FOR SPACECRAFT LINE-OF-SIGHT JITTER PERFORMANCE ANALYSIS, NASA
68 Micro-Vibration Test – Cont.
To simulate in orbit configuration of the S/C as close as possible, the S/C will be slightly lifted from the ground and hanged by a springy bungee cord. Then, reaction wheels will be commanded to run in a proper approach and several accelerometers attached to the imager will capture the micro-vibration response, then the pixel shift can be predicted.
Credit: Shan-Bo C. et al., Simulating and Testing Microvibrations on an Optical Satellite Using Acceleration Sensor-Based Jitter Measurements, 2019.
69 Material Testing In some occasions, mechanical team may request some additional material testing in order to get some useful information to support their job. For example.
- Stiffness testing To extract a stiffness property of S/C component (i.e. isolation rubber mount) and update into the S/C structural analysis model (FEM) to correlate the mechanical behavior against vibration test result
- Strength testing To evaluate the workmanship build quality and performance of S/C part (i.e. sandwich panel) against potential mechanical loadings. This test requires sets of test coupons (a small piece of material which represent that S/C part, made in various forms to suit individual material test). It usually built from the same production lot of that part. The test may includes (depends on function of a parent part) Universal testing machine - a flexural strength test Credit: Wikipedia - an adhesive peel off strength - an insert pull out/shear strength 70 Other Roles in Mechanical Sub-System
71 Mass Budget • Owns by Mechanical team • Use for Structural Analysis, AOCS performance, Launch • Consistent with system level and other sub-system • Breakdown to sub assembly level • Can trace down to each module, bracket and fasteners • Contains mass, center of gravity (CoG), inertia respect to the spacecraft origin • Preliminary CAD margin 10-20% • Critical Design Review CAD margin 5-10% • Actual weighted margin 0-2%
72 Mass Budget Sub-system Unit Total mass CoG (X) CoG (Y) CoG (Z) w/t out unit Wrt. Wrt. Wrt. Total mass without unit Sub-system level margin S/C origin S/C origin S/C origin level margin [kg] [kg] (mm.) (mm.) (mm.)
AOCS 7.5 AOCS Sun-sensor-0 0.12 271.0 250.4 -15.0
Power 15.0 AOCS Sun-sensor-1 0.12 271.0 -249.4 -15.0
Communication 0.9 AOCS Gyro-0 0.15 140.6 10.2 240.5
Central processing 3.1 AOCS Wheels-0 3.1 175.1 164.3 445.2
Environment control 1.0 AOCS Wheels-1 3.1 -173.4 164.3 445.2
Structure 43.5 Structure Space Facing Facet 15
Harness 5.6 Structure Shear panel +X 5.6
Payload 23.4 Structure Shear panel -X 5.8
TOTAL MASS 100.0 Structure Shear panel -Y 6.0
73 Working with AIT Team
• Mechanic team lead the initial spacecraft integration with support from AIT team • AIT team then later prepare the spacecraft for series of test • AIT might ask for support from mechanical team i.e. to rotate the spacecraft, to integrate/ remove main payload • Every discrepancy with the spacecraft structure during AIT phase will be reported to mechanic team
74 Support Other Sub-System
• Mechanic team owns spacecraft configuration and mass budget • Mechanic team will design the spacecraft to be easy to assembly, integration and test • The component placement could change by request from sub-systems • AOCS might ask to provide images of the location of the ACOS equipment • Sub-systems might ask mechanical team to produce module box, radiation shield, extra adaptor plate, etc.
75 Other Potential Responsibility
76 Mechanism Engineer • Hinges • Focus Mechanism • Antenna Pointing Mechanism • Reaction wheels • Hold down and release mechanism
Credit: https://directory.eoportal.org/web/eoportal/satellite- missions/content/-/article/nigeriasat-2
77 Credit: https://ntrs.nasa.gov/api/citations/20150004077/downloads/20150004077.pdf Propulsion Engineer
• Propulsion budget estimation • Propulsion system selection • Propulsion system design, manufacturing, integration and test • Small thruster design • Propulsion Ground Support Equipment
Credit: https://directory.eoportal.org/web/eoportal/satellite-missions/d/dmc
78 THANK YOU!
Q&A
79