AMS02 Structural Analysis Overview

1

• AMS-02 Structural Analysis Overview
• Carl Lauritzen
• Jacobs Engineering
• May 22, 2007

2
Introduction

• Structural Analysis Requirements
• Structural Analysis Approach
• Design Loads
• Math Models
• Shuttle Cargo Compatibility Assessment
• Loads Analysis
• Stress Analysis
• Fracture Analysis

3
Structural Analysis Requirements

• Space Shuttle Program strength and frequency
• NSTS-14046 Rev. E, Payload verification
  Requirements
• NSTS-37329B, Structural Integration Analyses
  Responsibility Definition for Space Shuttle
  Vehicle and Cargo Element Developers
• NSTS-1700.7B, Safety Policy and Requirements for
  Payloads Using the Space Transportation System
• International Space Station strength and
  frequency
• SSP-57003, Attached Payload Interface
  Requirements Document
• NSTS-21000-IDD-ISS, International Space Station
  Interface Definition Document
• NSTS-1700.7B, Safety Policy and Requirements for
  Payloads Using the International Space Station
• SSP-52005, Rev. C, ISS Payload Flight Equipment
  Requirements and Guidelines for Safety Critical
  Structures
• Fracture Control
• JSC-25863, Rev. A, Fracture Control Plan for JSC
  Flight Hardware
• NASA-STD-5003, Fracture Control Requirements for
  Payloads Using the Space Shuttle
• SSP-30558C, Fracture Control Requirements for
  Space Station
• Fastener Analysis
• NSTS-08307A, Criteria for Preloaded Bolts
• Alpha Magnetic Spectrometer (AMS-02) Project
• JSC-28792, Rev. E, AMS-02 Structural
  Verification Plan for the Space Transportation
  System and the International Space Station
• Reviewed by AMS-02 Configuration Control Board
• Approved by the NASA Structures Working Group and
  NASA OB ISS Structures Team

4
Structural Analysis Approach for AMS-02

• A finite element model (FEM) of the full payload
  has been used to characterize the overall
  structural behavior of the system.
• The large AMS-02 component are modeled explicitly
  in the full payload model with detailed
  structural representations
• Structural analyses of these components are
  performed using stand-alone models of the
  component using load conditions derived from the
  full payload model.
• Smaller components that are not affected by the
  global response of the structure are represented
  as a rigid body with the appropriate mass and
  center of gravity.
• Structural analyses of these smaller components
  are performed using stand-alone models of the
  component with load factors

5
Design Loads for AMS-02 Primary Structure

• Primary structure is defined as the structure
  that provides the primary load path for the
  entire payload
• Design load factors were generated using Space
  Shuttle math models and launch/landing load cases
• Derived from a design coupled loads analysis
  (DCLA)
• Dynamic analysis that represents excitations and
  responses as a function of time
• Performed in 1999 using preliminary math models
  of the payload
• Performed for a generic manifest configuration
• An uncertainty factor of 1.5 was included in the
  resulting load factor

• These load factors have been approved by the NASA
  Structures Working Group
• These load factors were used in nonlinear, static
  analyses with a math model of the full payload to
  derive internal loads for detailed design and
  stress analyses of the USS, vacuum case, and the
  magnet support system.

6
Design Loads for AMS-02 Mated Configuration on
ISS

• Primary structure design loads for ISS attached
  payloads (defined in SSP 57003 Rev A, Table
  3.1.1.2.3-2 )
• Represent worst case loads due to berthing and
  ISS re-boost events
• These interface loads were used to design the
  AMS-02 payload attach system (PAS)

7
Design Loads for Large AMS-02 Components

• As part of an effort to reduce the weight of the
  payload, less conservative load factors were
  developed for some of the large components of the
  payload
• Performed a second Design Coupled Loads Analysis
  (2003)
• Used updated math models of the AMS-02 payload
• Incorporated the nonlinear effects of the magnet
  support straps
• Used updated Shuttle math models and forcing
  functions from Boeing
• Used math models for the cargo elements
  associated with UF-4 flight
• These load factors include an uncertainty factor
  of 1.25

• These load factors have been approved by the NASA
  Structures Working Group
• These load factors were used in combination with
  component interface displacements to design and
  assess the large payload components not
  considered primary structure (radiators, RICH,
  upper and lower TOF, and the TRD)

8
Design Loads for AMS-02 Secondary Structure

• Design load factors for AMS-02 secondary
  structure
• Secondary structure is defined as components that
  are not part of the primary load path and can be
  treated as independent entities for analysis
  purposes
• Components weighing less than 500 pounds use
  simplified design load factors (Simplified
  Design Options for STS Payloads, JSC-20545A,
  April 1988).
• The factors are applied simultaneous in three
  axes directions
• 100 of load factor is applied in primary axis
  direction
• 25 of load factor is applied in remaining two
  orthogonal axes

9
Acoustic Design Loads for AMS-02

• Experiment components with large panels were
  assessed for acoustic loads
• Responses computed using the Statistical Energy
  Analysis method(VAPEPS and AutoSEA software)
• The total component load is determined by
  combining the static design load factor with the
  specified acoustic load factor

10
Additional Design Loads for AMS-02

• Magnet forces and eddy current induced loads
• Assessment has shown that these only critical for
  the magnet structure.
• EVA related loads for all external items that
  have potential EVA access
• Crew kick loads, hand hold loads, crew-actuated
  tool loads
• Shuttle RMS and Space Station RMS grapple fixture
  loads
• Orbiter emergency landing loads
• Defined in NSTS-21000-IDD-ISS
• Bounded by primary structure design load factors
• Quasi-static load conditions for Shuttle ascent
  and Orbiter entry
• Defined in NSTS-37329
• Consists of 2064 deflection cases from
  mechanical, thermal, and pressure loading
  conditions
• Helium slosh loads are combined with the helium
  tank design load factors for contingency landing
  cases
• Ground and air transportation loads
• Ground handling loads

11
Math Model for AMS-02 Loads Analysis

• Math models are based on CAD models and drawings
  from designers
• High level of fidelity for all major components
• USS and vacuum case
• Magnet, helium tank
• Selected experiments (upper/lower TOF, TRD, TRD
  gas supply, ECAL, radiators, RICH)
• Nonstructural items that are relatively rigid are
  modeled as lumped masses (e.g., electronic boxes)
• Nonstructural items that have a low stiffness are
  modeled as distributed mass (cables, pipes, etc)
• Model mass properties reflect current assessment
  from all component developers
• Current loads model for the full payload is in
  excess of 500,000 DOF
• Nonlinear model of magnet support straps
• Modeled using tension-only elements with a
  defined stress-strain relationship
• Stress-strain relationship in math model is based
  on physical force-displacements for each strap
  configuration
• Stress-strain relationship accounts for
  temperature conditions (cryogenic environment vs.
  room temperature)

12
AMS-02 Finite Element Loads Model
13
AMS-02 Finite Element Loads Model
14
Magnet Support Strap Representation for Loads
Model

• Warm strap model used for assessment of
  configurations that assume helium tank is empty
• 1-D strap test, STA sine sweep test, modal test,
  and static test
• Cold strap model used for assessment of
  configurations that assume helium tank is full
• Liftoff and abort landing

15
Compatibility Assessment for Shuttle Cargo
Integration

• Primary trunnion xo 1163.40, Stabilizer
  trunnion xo 1242.07, Keel trunnion xo 1175.20
• Satisfies ROEU compatibility requirements
  extension to be made 6.07 inches longer
• AMS-02 interface loads are within the Orbiter
  attach point capability
• Clearances with ISS payload envelope and Orbiter
  hardware have undergone preliminary assessment

16
AMS-02 Orbiter Clearance Assessment

• Clearance assessment performed by Boeing
  engineers in 2003(AMS-02 and Orbiter Payload
  Bay Static and Dynamic Clearance Assessment by
  Karen Bellard, Gilmar Gonzalez, and Charles
  Hethcoat of Boeing, April 29, 2003)
• AMS-02 cargo bay location based on ROEU
  compatibility assessment by Gilmar Gonzalez,
  Boeing
• Assumptions for dynamic clearance assessment
• Manufacturing tolerance of 0.1 inch
• Thermal growth of 0.5 inch
• Relative dynamic motion of 3.0 inch at all
  locations except scuff plates
• All items show acceptable clearance except for
  PAS guide pins which show close clearance
• Dynamic clearance will be reassessed when
  displacement data is available from dynamic
  analyses

17
AMS-02 Structural Analyses

• Primary analyses
• Nonlinear static for loads generation and
  strength assessment (FEA, hand calculations)
• Nonlinear transient for loads generation (FEA)
• Quasi-static loads analysis for deflection and
  clearance assessment (FEA)
• Buckling analysis for vacuum case and helium tank
  design verification (FEA)
• AMS-02 load factors are obtained using results
  from nonlinear Design Coupled Loads Analysis
  (DCLA)
• Design cycle load factors include an uncertainty
  factor of 1.25 and have been coordinated with the
  Structures Working Group (SWG) and ISS Structures
  Team
• Modal analysis of nonlinear, preloaded model
  (FEA)
• Assess frequency requirements for components and
  full payload
• Dynamic correlation of payload model
• Acoustic analysis of components with large
  honeycomb panels (statistical energy analysis)
• Fracture mechanics and fatigue crack-growth
  analyses (NASGRO)
• Fastener analysis (per NSTS-08307)

18
Stress Analysis Overview

• Stress analysis of all components are performed
  per JSC-28792 (AMS-02 Structural Verification
  Plan)
• Appropriate Factors of Safety have been used as
  presented in Appendix A of JSC-28792 (AMS-02
  Structural Verification Plan)
• For combined loading conditions, interaction
  formulas are used based on stress ratios for each
  loading condition
• Material properties for metallic materials are
  taken from MIL-HDBK-5H and temperature reduction
  factors are applied, if required
• Fitting factors, joint separation factors, and
  uncertainty factors are used for fastener
  analysis
• Margins of safety for all structural components
  are greater than zero for all combined load
  conditions
• An exception is a non-failure condition for joint
  separation
• A detailed margin of safety summary is provided
  in the Hazard Report AMS-02-F01

19
Fracture Control Assessment

• Fracture control requirements of the AMS-02
  payload components have been established in
  accordance with Space Shuttle and International
  Space Station requirements
• The objective is to ensure safety of the crew,
  Orbiter, and ISS such that failure of any
  structure will not result in a catastrophic
  hazard
• Combined fatigue loading spectrum have been used
  for fracture analysis
• Spectrum includes air transport, truck transport,
  launch/landing, and on-orbit loading events
• STA vacuum case (flight backup) also includes
  sine sweep test and acoustic test spectrums
• Scatter factor of 4 is used for design safe life
  analysis
• The flight hardware has been reviewed and the
  fracture critical components have been
  identified.
• Appropriate inspections, analyses, and controls
  have been implemented
• A detailed summary of the fracture classification
  for the payload components is provided in Hazard
  Report AMS-02-F01.

20
Fracture Critical Components

• Safe-life analysis is performed using the NASGRO
  program
• Size of flaw used in the analysis is based on the
  appropriate NDE techniques or on proof testing
• All fracture critical components will be NDE
  inspected per standard aerospace quality
  procedures (as referenced in JSC-25863, Rev. A)
• Composite materials will be classified low risk
  per the specifications of section 5.2 d of the
  Fracture Control Plan (JSC 25863, Rev. A)

21
Pressurized Components

• Composite over-wrapped pressure vessels (COPV)
  follow the guidelines of ANSI/AIAA S-081
• Stainless steel pressure vessels  follow the
  guidelines of ANSI/AIAA S-080
• Designed to have a non-hazardous
  leak-before-burst (LBB) mode of failure
• Cracks through the thickness with a length 10
  times the wall thickness will not result in
  unstable fracture
• Components, lines, and fittings comply with burst
  and proof factors of safety as defined in NSTS
  1700.7B and the ISS Addendum
• Minor exceptions to this will be discussed in
  more detail in a separate presentation on the
  pressurized components.

22
Conclusion

• An approved plan is in place to satisfy all
  structural analysis requirements for the AMS-02
  payload
• There are no significant open issues related to
  structural analysis.