WFIRST-MECH-SPEC-0128_DRAFT.pdf

Effective Date: <Date>

Expiration Date: <Date> [as required]

National Aeronautics and Space Administration

Goddard Space Flight Center Greenbelt, Maryland

WFIRST-MECH-SPEC-0128, Revision [-, A]

Wide Field Infrared Survey Telescope (WFIRST), Code 448

High Gain Antenna System

Jitter Damper

Performance Specification

(SPEC)

DRAFT

WFIRST HGAS Jitter Damper Spec WFIRST-MECH-SPEC-0128, Revision Number Draft

Check FPD BCI Document Management Guidance to verify that this is the correct version prior to use

400-FORM-0002 (4/16/2014)

<Full document title>

Review/Signature/Approval Page

Prepared by: Lia Sacks, Code 591

Approved by:

Electronic Approval available on-line in the WFIRST CM Tool https://fpdspi.gsfc.nasa.gov/sites/fpdat/BCI/SitePages/Document%20Management%20Guidance file://///gs448share/WFIRST/01.0%20Project%20Management/1.4%20Configuration-Data%20Mgmt/Templates/Document%20Templates/TDMS/Templates%20(boilerplates)/Historical/in ii

Preface

This document is a Wide Field Infrared Survey Telescope (WFIRST)

Configuration Management (CM)-controlled document. Changes to this document require prior approval of the applicable Configuration Control Board (CCB) Chairperson or designee.

Proposed changes shall be submitted to the WFIRST CM Office (CMO), along with supportive material justifying the proposed change.

In this document, a requirement is identified by “shall,” a good practice by “should,” permission by “may” or “can,” expectation by “will,” and descriptive material by “is.”

Questions or comments concerning this document should be addressed to:

WFIRST Configuration Management Office

Mail Stop 448

Goddard Space Flight Center

Greenbelt, Maryland 20771 iii

Change History Log

Revision Effective Date Description of Changes

(Reference the CCR & CCB/ERB Approval Date) iv

Table of TBDs/TBRs/TBSs [optional]

Item No. Location Summary Individual/

Organization

Actionee

Due Date v

Table of Contents

1 INTRODUCTION

1.1 Purpose

1.2 Scope

1.3 Related Documentation

1.3.1 Applicable Documents [and Forms]

1.3.2 Reference Documents

2 CONTRACT DESCRIPTION

2.1 HGAS Jitter Damper Description

2.2 Reserved

3 FUNCTIONAL/PERFORMANCE REQUIREMENTS

3.1 HGAS Jitter Damper Flight Unit Functional/Performance Requirements

3.1.1 Damping Requirement

3.1.2 Stiffness Requirement

3.2 Reserved

3.3 Reserved

3.4 Electrical Grounding

3.4.1 Reserved

3.4.2 Reserved

3.4.3 Reserved

3.4.4 Reserved

3.4.5 Reserved

3.4.6 Non-Electrical and Electro-Mechanical Bonding Resistance

3.5 Reserved

3.6 Reserved

3.7 Reserved

3.8 Reserved

4 PHYSICAL REQUIREMENTS

4.1 Interface Documentation

4.1.1 Mechanical Interface

4.1.2 Reserved

4.1.3 Reserved

4.2 Mass Properties

4.2.1 Component Masses

4.2.2 Center of Mass Location

4.2.3 Reserved

4.2.4 Reserved

4.3 Physical Envelope

4.4 Mounting

4.5 Reserved

4.6 Reserved

5 ENVIRONMENTAL REQUIREMENTS

5.1 Quasi-Static Acceleration

5.2 Frequency Requirement

vi

5.2.1 Stowed Fundamental Launch Frequencies

5.3 Vibration

5.3.1 Sinusoidal Vibration

5.3.2 Random Vibration

5.4 Shock

5.5 Reserved

5.6 Reserved

5.6.1 Operating Pressure Range

5.6.2 Maximum Depressurization Rate

5.6.3 Reserved

5.7 On-Orbit Dynamic Environment

5.8 Ground Environments

5.9 Thermal Requirements

5.9.1 Flight Interface Design Temperature Limits

5.9.2 Allocation for Spacecraft Thermal Hardware

5.10 Reserved

5.11 Static Load Requirement

6 CLEANLINESS

6.1 Surface Contamination

6.1.1 Surface Contamination Levels at Delivery

6.1.1.1 Particulate Contamination

6.1.1.2 Molecular Contamination – Exposed Surfaces

6.1.1.3 Molecular Contamination – Covered Surfaces

6.1.2 Surface Contamination Generation

6.1.2.1 Particulate Generation

6.1.2.2 Molecular Generation

Material Selection Material Selection - Silicones

Assembly Outgassing

6.1.2.3 Intentional and Unintentional Vents

6.1.2.4 Intentional and Unintentional Vents – Filters

6.1.2.5 Intentional Vents – Pressure Buildup Prevention

6.1.3 Cleanability

6.1.3.1 Cleanability – Sensitive Surfaces

6.1.3.2 Cleanability – Sensitive Surface Cleaning Methods

6.1.4 Transportation Cleanliness

6.2 Charging Mitigation

6.2.1 Conductive Surface Ground Path

6.2.2 Conductive Surface Resistivity

6.2.3 Closeout of Gaps and Apertures

6.2.3.1 Conductive Tape Surface Resistivity

6.2.3.2 Conductive Tape, Grounding

6.2.4 Exposed Harness Specific Requirements

6.2.5 Thermal Blankets

6.2.5.1 Thermal Blanket Surface Resistivity

6.2.5.2 Thermal Blanket Grounding

vii

6.2.5.3 Thermal Blanket Grounding Wire Distance

6.2.5.4 Thermal Blanket Grounding Measurement

7 DESIGN & CONSTRUCTION REQUIREMENTS

7.1 Parts, Materials & Processes (PMP)

7.1.1 Reserved

7.1.2 Materials

7.1.2.1 Material Conductivity

7.1.3 Reserved

7.2 Reserved

7.3 Reserved

7.4 Reserved

7.5 Identification and Marking

7.6 Workmanship

7.6.1 Workmanship Standards

7.6.2 Reserved

7.7 Reliability and Mission Lifetime

7.7.1 Mission Life

7.7.2 Reserved

7.8 Reserved

8 MECHANICAL DESIGN REQUIREMENTS

8.1 Mechanical Factors of Safety

8.2 Fracture and Fatigue

8.3 Reserved

8.4 Reserved

8.5 Reserved

8.6 Materials

8.6.1 Dissimilar Metals

8.6.2 Material Allowables and Stiffness

8.6.3 CTE Data

8.6.4 Stress Corrosion Cracking

8.7 Joints

8.7.1 Joint Edge Distance

8.7.2 Bonded Joint Allowable

8.7.3 Reserved

8.7.4 Fastened Joints

8.7.4.1 Fastener Locking

8.7.4.2 Fastened Joint Margin of Safety

8.7.4.3 Installation Torque Documentation

8.7.4.4 Seal Analysis

8.7.4.5 Critical Fasteners

8.8 Mechanism Design

8.8.1 Minimum Torque

8.8.2 Torque Margin Formula

8.8.3 Mechanism Stall Performance

8.8.4 Mechanism Installation

8.8.5 Deployables and Mechanism Jamming

viii

8.8.5.1 Non-Powered Restraint

8.8.5.2 Visual Indication of Caging

8.8.5.3 Confirmation of Deployment

8.8.5.4 Springs Failure Tolerant

8.8.5.5 Tolerancing

8.8.5.6 Clearances

8.8.6 Viscous Dampers

8.8.6.1 Air Entrapment

8.8.6.2 Damper Temperature Effects

8.8.7 Motors

8.8.7.1 Brush-Type Motor Avoidance

8.8.8 Bearings

8.8.8.1 Hertzian Contact Stress

8.8.8.2 Bearing Strength and Performance

8.8.9 Switches

8.8.9.1 Indicating Device

8.8.9.2 Microswitches

8.8.10 Lubricants

8.8.10.1 Lubricant Life Analysis

8.8.10.2 Dry Lubricants

8.9 Mechanism Verification Requirements

8.9.1 Mechanism Verification

8.9.1.1 Mechanism Qualification Testing

8.9.1.2 Mechanism Life Testing

8.9.1.3 Mechanism Acceptance Testing

8.9.1.3.1.1 Functional Test Structuring

8.9.1.3.1.2 Run-In Testing

8.9.1.3.1.3 Motor Characterization Testing

9 LOGISTICS

9.1 Reserved

9.2 Reserved

9.3 Reserved

10 VERIFICATION REQUIREMENTS

10.1 Verification Methods

10.1.1 Inspection

10.1.2 Analysis

10.1.3 Test

10.2 Inspection Requirements

10.2.1 Visual Inspection

10.2.2 Physical Measurement

10.2.3 Documentation Search

10.3 Analysis Requirements

10.4 Test Requirements

10.4.1 Definitions

10.4.2 Test Factors

10.4.3 Thermal Cycle Prior to Structural Testing

ix

10.4.4 Powered-on Conditions for Test

10.4.5 Proof Testing Factors

10.4.6 Test Tolerances

10.4.7 Test Restrictions

10.4.7.1 Failure During Tests

10.4.7.2 Modification of Hardware

10.4.7.3 External Adjustment

10.4.7.4 Re-Test Requirements

10.5 Required Tests

10.5.1 Performance Tests

10.5.1.1 Comprehensive Performance Test

10.5.1.2 Limited Performance Test

10.5.1.3 Reserved

10.5.1.4 Life Testing

10.5.2 Mass Properties Measurement

10.5.3 Static Loads/Strength Test

10.5.3.1 Sine Burst

10.5.3.2 Static Pull

10.5.4 Frequency Signature Survey

10.5.5 Modal Survey

10.5.6 Sine Vibration

10.5.7 Random Vibration

10.5.8 Reserved

10.5.9 Reserved

10.5.10 Shock

10.5.11 Thermal Vacuum Bake-out

10.5.12 Thermal Vacuum Test

10.5.12.1 Thermal Vacuum Test Parameters

10.5.12.2 Thermal Vacuum Test Profile

10.5.13 Thermal Balance Requirement

10.5.14 Thermal Cycling Testing - Ambient

10.5.15 Reserved

10.5.16 Reserved

APPENDIX A ABBREVIATIONS AND ACRONYMS

List of Figures

Figure 10-1 Thermal Vacuum Profile

List of Tables

Table 5-1 HGAS Jitter Damper Design Limit Loads

Table 5-2 HGAS Jitter Damper Generic Sine Vibration Environment Table 5-3 Random Vibration Limit Levels for Components Weighing Less Than 22.7 kg Table 5-4 Minimum Workmanship ASD Level for Components Weighing Less than 45.4 kg. . 10 Table 5-5 Shock Limit Levels x

Table 5-6 Temperature Limits at Damper Mounting Interface

Table 6-1 - Thermal Blanket Area vs. Grounding Tabs Table 8-1 Design Factors of Safety

Table 8-2 Minimum Edge Distance Table 8-3 Torque Margin Calculation Factors of Safety Table 8-4 Mean Hertzian Contact Stress Table 10-1 Test Factors and Durations Table 10-2 Proof Test Factors

Table 10-3 Test Tolerances Table 10-4 Thermal Vacuum Test Parameters

1 INTRODUCTION

1.1 Purpose

The Wide Field InfraRed Survey Telescope (WFIRST) is a mission responding to the 2010

National Research Council New Worlds, New Horizons (NWNH) Astronomy and Astrophysics

Decadal Survey top priority recommendation in the large space mission category. The science program includes two dedicated investigations to tackle outstanding questions in dark energy research and exoplanet exploration, and includes a substantial General Observer program to enable targeted investigations of astrophysical phenomena to advance other goals from the Decadal

Survey. A coronagraph instrument is included in the payload for purposes of advancing the present state of the art of coronagraph technology. This document defines the requirements for the HGAS jitter damper.

1.2 Scope

This specification describes the electrical, mechanical, environmental, and verification testing requirements for a space-qualified HGAS jitter damper for the NASA Goddard Space Flight

Center (GSFC) WFIRST Mission.

1.3 Related Documentation

WFIRST documents can be obtained in the WFIRST CM Tool.

1.3.1 Applicable Documents [and Forms]

The following documents and drawings in effect on the day this specification was signed shall apply to the fabrication and to the electrical, mechanical, and environmental requirements of the

HGAS jitter damper to the extent specified herein. In the event of conflict between this specification and any referenced document, this specification will govern, with the exception of the WFIRST HGAS Jitter Damper Statement of Work (WFIRST-MECH-SOW-0036), in which case the Statement of Work takes precedence.

Document Number Title

ANSI/TIA/EIA-422-B Electrical Characteristics of Balanced Voltage Digital Interface

Circuits

ANSI/TIA/EIA-644-A-

Electrical Characteristics of Low Voltage Differential Signaling

(LVDS) Interface Circuits

ASTM E-595-07 Standard Test Method for Total Mass Loss and Collected

Volatile Condensable Materials from Outgassing in a Vacuum

Environment

ECSS-E-ST-50-12A SpaceWire - Links, Nodes, Routers and Networks

EEE-INST-002 Instructions for EEE Parts Selection, Screening, Qualification, and Derating

IEST-STD-CC1246E Product Cleanliness Levels And Contamination Control Program

MIL-STD-1553B Department of Defense Interface Standard for Digital Time

Division Command/Response Multiplex Data Bus

MIL-STD-461F Military Standard, Electromagnetic Emission And Susceptibility

Requirements For The Control Of Electromagnetic Interference

(EMI)

MIL-STD-462, Notice 2 Electromagnetic Interference Characteristics, Measurement of, 1

May 1970

MSFC-STD-3029A Guidelines for the Selection of Metallic Materials for Stress

Corrosion Cracking Resistance in Sodium Chloride

Environments

NFPA 70 National Fire Protection Association National Electric Code

NASA-STD-5017A Design and Development Requirements for Mechanisms

NASA-STD-5019A Fracture Control Requirements for Spaceflight Hardware

NASA-STD-5020 Requirements for Threaded Fastening Systems in Spaceflight

Hardware

NASA-STD-8719.24 NASA Expendable Launch Vehicle Payload Safety

Requirements

GSFC-STD-7000A General Environmental Verification Standard (GEVS)

541-WI-5330.1.41 Fastener Locking Using Arathane 5753

WFIRST-SYS-PLAN-

WFIRST Contamination Control Plan

WFIRST-MECH-LIST-

WFIRST HGAS Jitter Damper Deliverable Items List and

Schedule (DILS)

WFIRST-MECH-SOW-

WFIRST HGAS Jitter Damper Statement of Work (SOW)

WFIRST-SYS-SPEC-0031 WFIRST Math Models Guidelines Document

WFIRST-SYS-SPEC-0033 WFIRST Cleanliness Specification

1.3.2 Reference Documents

The following documents are referenced herein and amplify or clarify the information presented in this document. These documents are not binding on the content of this document.

Document Number Title

2 CONTRACT DESCRIPTION

2.1 HGAS Jitter Damper Description

The HGAS jitter damper is an isolation device that is capable of reducing the transmission of excitations induced by the HGAS motion back into the spacecraft.

2.2 Reserved

WFIRST HGAS Jitter Damper Spec WFIRST-MECH-SPEC-0128, Revision Number

3 FUNCTIONAL/PERFORMANCE REQUIREMENTS

This section defines the functional and performance requirements for the HGAS jitter damper as defined in Section 3.1.

3.1 HGAS Jitter Damper Flight Unit Functional/Performance Requirements

3.1.1 Damping Requirement

The HGAS jitter damper shall reduce jitter induced by the High Gain Antenna System and maintain adequate stiffness and damping values over the specified temperature range. The

HGAS jitter damper shall provide at least 2% (TBR) damping.

3.1.2 Stiffness Requirement

Two candidate locations are identified for the HGAS jitter damper. At each of the locations, the

HGAS jitter damper shall provide the following minimum stiffness:

Root Hinge Location:

Minimum (TBR) Maximum (TBR)

SI units Imperial

Units SI units

Imperial Units

Radial Stiffness [N/m (lbs/in)] 1.88E+08 1.07E+06 3.14E+08 1.79E+06

Axial Stiffness [N/m (lbs/in)] 1.59E+08 9.08E+05 2.65E+08 1.51E+06

Bending Stiffness [N-m/rad (in-lbs/rad)] 4.40E+05 3.89E+06 7.33E+05 6.48E+06

Torsional Stiffness [N-m/rad (in-lbs/rad)] 2.38E+05 2.10E+06 3.96E+05 3.51E+06

Midboom Location:

Minimum (TBR) Maximum (TBR)

SI units Imperial

Units SI units

Imperial Units

Radial Stiffness [N/m (lbs/in)] 1.57E+07 8.98E+04 3.63E+07 2.07E+05

Axial Stiffness [N/m (lbs/in)] 1.82E+07 1.04E+05 4.20E+07 2.40E+05

Bending Stiffness [N-m/rad (in-lbs/rad)] 5.07E+04 4.49E+05 1.17E+05 1.04E+06

Torsional Stiffness [N-m/rad (in-lbs/rad)] 8.91E+04 7.88E+05 2.06E+05 1.82E+06

The HGAS jitter damper shall also maintain a deployed frequency of 2.2Hz (TBR).

Variability on any of these values can be considered on a case by case basis as long as it does not affect performance. Stiffness shall be evaluated in a fixed base configuration.

3.2 Reserved

3.3 Reserved

3.4 Electrical Grounding

3.4.1 Reserved

3.4.2 Reserved

3.4.3 Reserved

3.4.4 Reserved

3.4.5 Reserved

3.4.6 Non-Electrical and Electro-Mechanical Bonding Resistance

Conductive non-electrical and electro-mechanical components shall be bonded to the observatory chassis in such a manner as to provide DC resistances not exceeding 5 ohms between the component chassis or case and the observatory chassis

3.5 Reserved

3.6 Reserved

3.7 Reserved

3.8 Reserved

4 PHYSICAL REQUIREMENTS

4.1 Interface Documentation

The contractor shall use metric units when interfacing with NASA GSFC including any drawings, documents, models, except for the following cases:

SI units with parenthetical English units are permitted for engineering and manufacturing drawings.

Angular measurement may be expressed in degree of arc or in an appropriate subdivision of degree of arc such as minute or second of arc (arc-min or arc-sec).

Hardware that has been previously built, or new hardware of similar design heritage, may be specified in English units where use of metric equivalents would lead to additional risk and cost to the program, but interfaces with that hardware must use metric with parenthetical English units.

Hybrid SI/standard astronomical units are permitted for Astronomer User’s Manuals, user interfaces (Graphical User Interfaces and files) consistent with the Astronomer's User

Manuals, and requirements documents.

4.1.1 Mechanical Interface

The mounting interface shall be defined in the Mechanical Interface Control Drawing (MICD), which will be developed between the contractor and NASA GSFC.

4.1.2 Reserved

4.1.3 Reserved

4.2 Mass Properties

4.2.1 Component Masses

a. The mass of the HGAS jitter damper shall be less than or equal to 3 kg.

b. The mass of the HGAS jitter damper shall be measured to within 0.2%.

4.2.2 Center of Mass Location

The contractor shall define the center of mass in the Mechanical ICD.

4.2.3 Reserved

4.2.4 Reserved

4.3 Physical Envelope

The HGAS jitter damper outside dimensions, including mounting flanges and connectors, shall not exceed the volume specified in 2237261 (HGAS Jitter Damper MICD). Additional restrictions to the shape of the damper are also provided in the MICD.

4.4 Mounting

a. Mounting interface flatness, and co-planarity requirements for the component side of the interface (including brackets, if any, and shims) shall be as defined in the MICD.

4.5 Reserved

4.6 Reserved

5 ENVIRONMENTAL REQUIREMENTS

Environmental design requirements are specified in this section.

The HGAS jitter damper shall meet its performance requirements in section 5.0 during and after exposure to the environments specified in this section.

5.1 Quasi-Static Acceleration

Quasi-static acceleration represents the combination of steady-state accelerations and the low frequency mechanically transmitted dynamic accelerations that occur during launch.

The HGAS jitter damper shall be designed to withstand the quasi-static Design Limit Loads

(DLL) defined in the Mass-Acceleration Curve (MAC) shown in Table 5-1 without damage or degradation of performance.

Note:

1. For masses within the breakpoints, linear interpolation is used to determine load.

2. Loads are considered to act in any direction, one axis at a time.

Table 5-1 HGAS Jitter Damper Design Limit Loads

Component Mass (Kg) Limit Load (g)

0.5 35.9

1 35

5 30.1

5.2 Frequency Requirement

5.2.1 Stowed Fundamental Launch Frequencies

The HGAS jitter damper shall have a fundamental frequency greater than 75 Hz when hard mounted at its interface.

1. Requirements are met assuming rigid stiffness to restrained Degree of Freedom (DOF).

2. Components with first fundamental frequency greater than 75 Hz may verify through low level signature tests. Components with a frequency less than 75 Hz are required to perform modal testing and provide a test correlated FEM for dynamic analysis. Requirements for the FEM are in the SOW and discussed in Section 10.5.5.

3. Frequency requirements apply to all modes with modal effective mass fraction (MEMF)

>5% of FEM mass. MEMF is compared to the total mass of the element/subsystem/component, not against higher levels of assembly. e.g. OBS modes

MEMF is compared to OBS mass

4. For modes with MEMF between 5% and 10% that do not meet the frequency requirement(s), additional assessments can be made by the observatory systems group to determine the effects of the mode on observatory dynamics and subsystem/element design limit loads.

5.3 Vibration

5.3.1 Sinusoidal Vibration

The HGAS jitter damper shall withstand the sinusoidal vibration levels defined in Table 5-2.

1. Levels defined are acceptance levels. Analysis is conducted against acceptance with the safety factors defined in Table 8-1. Testing factors are defined in Table 10-1.

2. Peak levels at the low end of the frequency range (5 - 20 Hz) may be ramped up as needed to accommodate table limitations.

3. The sine sweep vibration levels shown in Table 5-2 are defined at the interface of the element/subsystem.

4. Input levels may be notched to limit the test specimens CG response to 1.25 times its

Design Limit Load outlined in Table 5-1.

5. Test verification is required over the range 5 to 50 Hz. Analytical verification is required from 50 to 100 Hz.

6. Elements/Subsystems/components with a first fundamental frequency equal to or greater than 75 Hz can forgo sine vibration testing from 5 to 50 Hz, while verification through analysis of the 50 to 100 Hz is still required.

7. Subsystems/components with a fundamental frequency equal to or greater than 150 Hz can forgo the sine vibration environment until higher levels of assembly upon approval by the

NASA/GSFC COR.

Table 5-2 HGAS Jitter Damper Generic Sine Vibration Environment

Frequency (Hz) Limit Level

5 to 100 10.0 g

Levels may be notched to not exceed 1.25 times the design limit load outlined in section 5.1.

Peak levels at the low end of the frequency range (5 – 20 Hz typically) may be ramped up as needed to accommodate shaker table displacement limitations.

5.3.2 Random Vibration

a. The HGAS jitter damper shall withstand the random vibration environment in Table 5-3 applied at the interface to the HGAS jitter damper.

The random vibration inputs are based on GEVS and may be notched to limit the test article’s cg response to 1.25 times DLL. Notched inputs must envelope minimum workmanship levels in order to screen for design or manufacturing flaws. A delicate optic, detector, sensor, etc., which is shown analytically to have negative margin at minimum workmanship levels may notch further at those frequency bands with project concurrence.

Table 5-3 shows the limit level random vibration environment for components with mass less than

22.7 kg. Analysis is conducted against acceptance with the safety factors defined in Table 8-1.

Testing factors are defined in Table 10-1. Table 5-4 defines minimum workmanship for components weighing less than 45.4 kg.

During testing, force limiting control is recommended and the control method must be approved by the NASA/GSFC COR.

Table 5-3 Random Vibration Limit Levels for Components Weighing Less Than 22.7 kg

Frequency (Hz) ASD Limit Level (g2/Hz)

20 0.013

20 - 50 +6 dB/oct

50 - 800 0.08

800 - 2000 -6 dB/oct

2000 0.013

Overall 10.0 grms

Table 5-4 Minimum Workmanship ASD Level for Components Weighing Less than 45.4 kg.

Frequency (Hz) ASD Level (g2/Hz)

20 0.01

20 - 80 +3 dB/oct

80 - 500 0.04

500 - 2000 -3 dB/oct

2000 0.01

Overall 6.8 grms

5.4 Shock

The HGAS jitter damper shall be designed to meet its performance requirements after being subjected to the shock environment in Table 5-5, applied at the HGAS jitter damper interface to the WFIRST spacecraft structure. Levels defined are acceptance levels. Testing factors are defined in 10.4.2.

Table 5-5 Shock Limit Levels

Frequency (Hz) Limit Load (g)

100 100

2000 2500

10000 2500

Note: A shock susceptibility and attenuation assessment is to be performed on HGAS jitter damper. This assessment can be based on past shock tests or other relevant information.

5.5 Reserved

5.6 Reserved

5.6.1 Operating Pressure Range

The HGAS jitter damper shall be designed to meet all performance requirements while operating over a pressure range of 1.08 x 105 N/m2 (813 Torr) to 1.3 x 10-12 N/m2 (1 x 10-14 Torr).

5.6.2 Maximum Depressurization Rate

The HGAS jitter damper shall be designed to meet all performance requirements after exposure to a depressurization rate of 2.48 kPa/sec (0.36 psi/sec) or less with a single brief allowable peak of up to 5.03 kPa/sec (0.73 psi/sec).

5.6.3 Reserved

5.7 On-Orbit Dynamic Environment

5.8 Ground Environments

a. The HGAS jitter damper shall meet all of their performance requirements during exposure to air temperature between +5 and +30 degrees C and relative humidity between

30% and 70%.

5.9 Thermal Requirements

5.9.1 Flight Interface Design Temperature Limits

a. The HGAS jitter damper shall be capable of surviving indefinitely when its temperatures are within the survival limits shown in Table 5-6 without damage or permanent performance degradation.

b. The HGAS jitter damper shall meet all performance requirements anywhere within the

Operational and Protoflight/Qualification limits shown in Table 5-6. If all performance requirements cannot be met over the entire range the temperature range that performance requirements can be met shall be provided along with the capability and stiffness/damping performance outside of that range shall be provided.

Table 5-6 Temperature Limits at Damper Mounting Interface

Minimum Temperature (ºC) Maximum Temperature (ºC)

Operational (In Spec) -10 +40

Protoflight/Qualification (In

Spec)

-20 +50

Survival (Unpowered) -25 +55

5.9.2 Allocation for Spacecraft Thermal Hardware

The HGAS jitter damper shall provide provisions to mount thermal hardware if thermal control is required to maintain the optimal temperature range.

5.10 Reserved

5.11 Static Load Requirement

The HGAS jitter damper shall be designed such that the following static loads may be applied simultaneously, or any possible combination of loads without degradation in performance.

Two candidate locations are identified for the HGAS jitter damper. At each of the locations, the

HGAS jitter damper shall comply with the following minimum loads:

Root Hinge Location:

Radial Load: 2.5 kN (562 lbs)

Axial Load: 5.0 kN (1,125 lbs)

Bending Load: 2.0 kN-m (17,702 in-lbs)

Torsional Load: 0.5 kN-m (4,425 in-lbs)

Midboom Location:

Radial Load: 2.5 kN (562 lbs)

Axial Load: 3.0 kN (675 lbs)

Bending Load: 2.0 kN-m (17,701 in-lbs)

Torsional Load: 2.0 kN-m (17,701 in-lbs)

Loads shall be evaluated in a fixed base configuration.

6 CLEANLINESS

The requirements in this section ensure the cleanliness of the HGAS jitter damper at delivery, so as not to adversely affect its own performance, as well as not be a source of contamination to other items, including not generating contaminants following delivery in excess of that permitted below by virtue of its design, materials of construction, or operation.

6.1 Surface Contamination

6.1.1 Surface Contamination Levels at Delivery

6.1.1.1 Particulate Contamination

The HGAS jitter damper surfaces shall meet IEST-STD-CC1246E Particulate Cleanliness Level

300 and shall also be visually inspected and meet Level VC-0.5-1000 + UV, or equivalent, when inspected with both UV and white light in a darkened room prior to be integrated to WFIRST.

6.1.1.2 Molecular Contamination – Exposed Surfaces

The HGAS jitter damper surfaces shall meet IEST-STD-CC1246E NVR Cleanliness Level R1 and shall also be visually inspected and meet Level VC-0.5-1000 + UV, or equivalent, when inspected with both UV and white light in a darkened room prior to be integrated to WFIRST.

6.1.1.3 Molecular Contamination – Covered Surfaces

a. All HGAS jitter damper surfaces not exposed to the space environment shall meet IEST-

STD-CC1246E VC-0.5-1000 + UV, or equivalent, when inspected in a darkened room with white and UV light.

b. The surfaces shall be free of molecular contamination – for example films, spots, or other.

6.1.2 Surface Contamination Generation

6.1.2.1 Particulate Generation

The HGAS jitter damper contractor shall not employ any of the following particle generating materials or processes into the HGAS jitter damper design or construction without prior approval by the NASA/GSFC COR:

Paints prone to shedding due to large paint pigment molecules, overspray, poor adhesion, etc.

Surfaces prone to corrosion or oxides because of a lack of corrosion protection or dissimilar metals in close contact.

Fabrics with brittle constituents (e.g., composites, graphite or glass).

Perforated materials when material is highly susceptible to tear propagation (e.g., multi-layer insulation (MLI)).

Metal oxides (bare [untreated] aluminum and magnesium, iron, non-corrosion resistant steel, etc.).

Braided metallic or synthetic wires, ropes, slings, etc. unless measures have been taken to contain any broken filaments or fibers (sheathing, sealing with polymers, covering, etc.).

Woven materials especially cut or unfinished ends (metal braid, EMI shielding, lacing cord, expando sleeving), unless measures have been taken to prevent fraying or generation of particles (cut with a hot knife, seal with polymer, bag, etc.).

Materials with thin films known to erode or crack or flake when subjected to normal handling (e.g., indium tin oxide [ITO] or other rigid or brittle semiconductor or ceramic coating on flexible substrates, Teflon, MLI, etc.).

Foams, highly textured materials.

Trapped debris in holes.

6.1.2.2 Molecular Generation

Material Selection

The HGAS jitter damper materials shall have a total mass loss (TML) less than 1.00% and a collected volatile condensable mass (CVCM) less than 0.10%, when measured in accordance with ASTM E-595 unless a materials usage agreement has been generated and approved by the

NASA/GSFC COR.

Material Selection - Silicones

Silicones on external (to the spacecraft) surfaces shall not be exposed to the space environment unless approved by the NASA/GSFC COR. Silicones should be avoided or minimized. It is highly recommended that silicones be baked out at a high temperature prior to integration into the system to prevent extended bakeouts of the entire assembly.

Assembly Outgassing

a. The HGAS jitter damper outgassing shall be measured in a vacuum of 1E-5 torr at the unit under test’s maximum hot survival temperature based on Table 5-6. The hot operating temperature plus 5 degrees may be used with the NASA/GSFC COR’s approval.

b. The HGAS jitter damper outgassing shall meet an outgassing rate of 4.41 E-11 g/s with the QCM at -20 degrees C. It is recommended that certification be conducted after thermal cycling to take advantage of heat exposure times.

c. The HGAS jitter damper outgassing measurements shall be made in a chamber that has been certified clean (back ground outgassing rate and free of silicones and other high molecular weight contaminants) and has been modeled by the Contamination Analyst to account for mass sinks (cold fingers, pumps, cold surfaces, etc.) that could influence the source outgassing rate. A cold finger and/or a scavenger plate shall be used in the test.

d. A cold finger and/or a scavenger plate shall be used in tests for components that will be mounted externally unless approved otherwise by the NASA/GSFC COR.

6.1.2.3 Intentional and Unintentional Vents

When located external to the spacecraft, intentional vents (dedicated ascent vents or thermal blanket vents for example) and unintentional vents (through holes, gaps at seams and faying surfaces, thermal blanket openings and other openings) shall not impinge on the surface of instruments or other contamination sensitive surfaces (star trackers, calibration standards, contamination sensitive thermal surfaces like radiators, etc.).

6.1.2.4 Intentional and Unintentional Vents – Filters

Any vents shall have filters or other means of preventing the egress of particles larger than 35 microns.

6.1.2.5 Intentional Vents – Pressure Buildup Prevention

a. Intentional vents shall be sized to prevent a buildup of pressure during ascent that may result in mechanical damage.

b. Intentional vents shall be sized to prevent a buildup of pressure during high vacuum due to outgassing that could result in discharges in higher voltage circuits.

6.1.3 Cleanability

6.1.3.1 Cleanability – Sensitive Surfaces

If any surfaces are not cleanable with Isopropyl alcohol and polyester wipes or light vacuuming, they shall be identified on the MICD.

6.1.3.2 Cleanability – Sensitive Surface Cleaning Methods

Alternate cleaning methods shall be identified and appropriate documentation provided for any surfaces that are not cleanable with Isopropyl alcohol.

6.1.4 Transportation Cleanliness

Materials and enclosure used for transportation and storage shall not generate molecular or particle contaminants or degrade the surface cleanliness of the item or adjacent items

6.2 Charging Mitigation

The following paragraphs provide requirements and guidelines for minimizing the magnitude and variations in the radiated electric field from the external surfaces of the HGAS jitter damper when exposed to the space plasma. All external Observatory surfaces that are exposed to the space plasma will be sufficiently conductive and be connected to spacecraft ground through low impedance paths.

6.2.1 Conductive Surface Ground Path

All HGAS jitter damper external conductive surfaces shall be connected to the spacecraft interface with a resistance less than 5 ohms, either through the use of ground wire(s) or through metal-to-metal mounting contact.

6.2.2 Conductive Surface Resistivity

All HGAS jitter damper external conductive surfaces shall have a resistivity less than 10^8 ohm-cm or 10^9 ohms/square.

6.2.3 Closeout of Gaps and Apertures

All gaps and apertures not required for component fields of view, deployments, or observatory venting shall be closed out with conductive tape or thermal blankets.

6.2.3.1 Conductive Tape Surface Resistivity

Conductive tapes used to closeout gaps or apertures shall be designed to meet the conductive surface resistivity requirements.

6.2.3.2 Conductive Tape, Grounding

The external surface of conductive tapes shall be connected to the spacecraft interface through the use of folded under tabs, or conductive adhesives.

6.2.4 Exposed Harness Specific Requirements

Harnesses that are exposed to sunlight or the ambient plasma shall be bundle shielded from source to destination.

6.2.5 Thermal Blankets

Include this subsection only if procuring Thermal Blankets.

6.2.5.1 Thermal Blanket Surface Resistivity

The Outer layer of multi-layer insulation (MLI) blankets surface resistivity shall not exceed 10^9 ohms/square.

6.2.5.2 Thermal Blanket Grounding

All conductive layers of multi-layer insulation (MLI) blankets shall be grounded to the spacecraft structure using low resistance wire as specified in Table 6-1.

Table 6-1 - Thermal Blanket Area vs. Grounding Tabs

Blanket Area (cm2) # Of Ground Tabs

<25 0

<25 (only if potential ESD victim within 30 cm) 2

25 - 900 2

900 – 8000 3

8000 – 16000 4

Each additional 8000 1 additional

6.2.5.3 Thermal Blanket Grounding Wire Distance

Any point on the blanket shall be no more than 1 meter from the nearest grounding wire location.

6.2.5.4 Thermal Blanket Grounding Measurement

The measured DC resistance from any point on the blanket to the spacecraft structure shall not exceed 10 ohms.

7 DESIGN & CONSTRUCTION REQUIREMENTS

7.1 Parts, Materials & Processes (PMP)

7.1.1 Reserved

7.1.2 Materials

The HGAS jitter damper will be comprised of materials and processes in accordance with the requirements in the SOW, WFIRST-MECH-SOW-0036.

7.1.2.1 Material Conductivity

All parts should be passivated and mounting surfaces on HGAS jitter damper shall be conductive as defined in Section 3.4.

7.1.3 Reserved

7.2 Reserved

7.3 Reserved

7.4 Reserved

7.5 Identification and Marking

Each unit shall be permanently marked with the part number and a unique sequential serial number in the area designated on the interface control drawing in a manner to be approved by the

NASA/GSFC COR.

All markings shall use alcohol proof ink, engraving, or laser etching.

7.6 Workmanship

7.6.1 Workmanship Standards

The workmanship standards and processes outlined in the SOW will be used.

7.6.2 Reserved

7.7 Reliability and Mission Lifetime

7.7.1 Mission Life

The HGAS jitter damper shall meet all performance specifications through three (3) years of ground testing and five (5) years of operation in space, following a three (3) month commissioning period.

7.7.2 Reserved

7.8 Reserved

8 MECHANICAL DESIGN REQUIREMENTS

For additional guidance on the design and analysis of threaded fastening systems in NASA spaceflight hardware, consult NASA-STD-5020, “Requirements for Threaded Fastening Systems

In Spaceflight Hardware”.

8.1 Mechanical Factors of Safety

Positive Margin of Safety (MS) shall be demonstrated analytically for HGAS jitter damper, including interfaces to MGSE, using the MS formula below with the appropriate Factors of

Safety (FS) defined in Table 8-1 applied to flight limit loads.

1. MS is defined as follows:

𝑀𝑆 =

𝐴𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 𝐿𝑖𝑚𝑖𝑡 𝐿𝑜𝑎𝑑 𝑜𝑟 𝑆𝑡𝑟𝑒𝑠𝑠

𝐴𝑝𝑝𝑙𝑖𝑒𝑑 𝐿𝑖𝑚𝑖𝑡 𝐿𝑜𝑎𝑑 𝑜𝑟 𝑆𝑡𝑟𝑒𝑠𝑠 ∗ 𝐹𝑆

− 1

Table 8-1 Design Factors of Safety

Type of Hardware Static /Sine Random/Acoustic 3,4

Tested Metallic Yield 1.252 1.6

Tested Metallic Ultimate 1.42 1.8

Stability/Buckling Ultimate 1.4 1.8

Beryllium Yield 1.4 1.8

Beryllium Ultimate 1.6 2.0

Composite Ultimate1 1.5 1.9

Bonded inserts/Joints Ultimate 1.5 1.9

Glass/Ceramic 3.05 3.8

Bond in Glass/Ceramic 1.5 1.9

(1) All composite structures must be tested to 1.25 x limit loads.

(2) For qualification by analysis only, positive margin must be shown with FS of 2.0 and 2.6 for metallic yield and ultimate, respectively.

(3) Factors shown are applied to statistically derived peak response based on limit/acceptance RMS level.

As a minimum, the peak response must be calculated as a 3-sigma value.

(4) Factors shown assume that qualification testing is performed at 3dB above limit/acceptance limits. If the difference between acceptance and qualification is less than 3dB then the above factors may be applied to qualification minus 3dB.

(5) For qualification by analysis only, a no-test safety factor of 5.0 may be used for glass (not ceramic), per

NASA-STD-5001B Table 3.

8.2 Fracture and Fatigue

The vendor shall evaluate all hardware to determine fracture criticality. A four-tier system is used to evaluate fracture criticality of hardware; each tier has associated mitigation requirements that shall be followed, as specified below.

Tier 1 fracture classification: Light-weighted optics, ceramic structural elements used to transfer load from one component to another, and any glass/ceramic hardware designated high risk by WFIRST shall mitigate risk of catastrophic failure due to cracks/flaws through the following requirements:

a. Proving design is fail-safe or,

a. Industry standard fracture analysis using NASGRO, Flaw Growth Analysis per NASA-STD-

5018, or other fracture analysis software demonstrating safe-life for 4 times number of mission cycles.

and,

b. Positive MS using B-basis Weibull accounting for Weibull scale effect per ASTM C1683 and,

c. Slow crack growth analysis of glass/ceramics made of materials with SiO bonds or,

a. Positive MS using B-basis Weibull accounting for Weibull scale effect per ASTM C1683

b. Proof testing with 2.0 proof test factor

For all flight hardware designated Tier 1 fracture critical, a Fracture Control Plan (FCP) shall be developed and approved by the WFIRST FCB.

Tier 2 fracture classification. All glass/ceramics not classified as Tier 1 shall mitigate risk of catastrophic failure due to cracks/flaws through the following requirements:

a. Proving design is fail-safe or,

a. Positive MS using B-basis Weibull accounting for Weibull scale effect (ASTM 1683) or

a. Industry standard fracture analysis using NASGRO, Flaw Growth Analysis per NASA-STD-

5018, or other fracture analysis software demonstrating safe-life for 4 times number of mission cycles

Tier 3 fracture classification: Metals with fracture toughness to yield strength ratio less than

0.33 (KIc/Fty < 1.66 mm1/2 (0.33 in1/2)); thin walled metallic components serving as springs or flexures; and fastened joints identified as critical, that experience unconcentrated stress at greater than 30% of Ultimate strength shall mitigate risk of catastrophic failure due to cracks/flaws through the following requirements:

a. Proving design is fail-safe or,

a. Demonstrate sufficient fatigue strength for 4 times the number of mission cycles or,

a. Prove safe-life design through industry standard linear-elastic fracture analysis for 4 times the number of mission cycles.

Tier 4 fracture classification: Fracture control requirements (per NASA-STD-5019) shall apply to the following elements only: (1) Pressure vessels, dewars, lines, and fittings (per NASA-STD

8719.24);(2) Castings (unless hot isostatically pressed and the flight article is proof tested to 1.25 times limit load);(3) Weldments;(4) Parts made of materials in Tables II or III of MSFC-SPEC-

3029A if under sustained tensile stress;(5) Parts made of materials susceptible to cracking during quenching;(6) Nonredundant, mission-critical preloaded springs loaded to greater than 25 percent of ultimate strength.

Notes for fracture/fatigue:

1. Fracture analysis is performed assuming an initial crack size. NDE or proof testing is required to verify this initial crack size assumption. If proof testing, the proof tests must be at load sufficient enough to screen for any crack size above the assumed. This often results in over-test compared to DLL.

2. If NASGRO is used for brittle component fracture analysis, the NASGL module is used.

3. If the max principle stress in the glass/ceramic containing SiO bonds in the glass with a minimum detectable crack size (a) is calculated (from KIc =σ√πa) to be within 25% of fracture toughness, then slow crack growth is not a concern.

4. A fail-safe component is a structural component in a redundant load path which after the loss of the component, the remaining load path(s) has sufficient structural capability to withstand the redistributed loads, and the loss of the component will not cause a catastrophic hazard.

Examples of redundant load paths are multiple fasteners in bolted joints, stitched welded structures, and riveted and bolted structures. A factor of safety of 1.0 shall be applied to the remaining load path(s) when demonstrating fail-safe.

5. Critical fastened joints are joints whose failure results mission ending failure. Class-C fasteners that are contained within Class-C hardware are not critical fasteners.

6. Mission cycles include ground testing and handling, transportation, launch, and on orbit loading. The load spectrum will include the load level and the accompanying number of cycles and duration (for static loading) at each level during the hardware service life. Mission cycle load spectrum is included in the FCP.

7. In cases where fracture toughness of a metal is not known, contact WFIRST project for help in fracture classification.

8.3 Reserved

8.4 Reserved

8.5 Reserved

8.6 Materials

8.6.1 Dissimilar Metals

Dissimilar materials in direct contact with each other shall be compatible as defined in Table I of

MIL-STD-889C, unless approved by the Parts, Materials and Processes Control Board.

1. Use of similar materials sealed per NASA-STD-6012 may be acceptable in some instances.

8.6.2 Material Allowables and Stiffness

Material allowables and stiffness shall be:

a) At least A-basis for metallic materials as defined in MMPDS or B-basis values tested under the appropriate environments.

b) At least B-basis for composite materials as defined in CMH-17, or B-basis values tested under the appropriate environments and representative of the processes used in the fabrication of the components while accounting for strength degradation due to thermal cycles.

c) B-basis values for glass/ceramics based on Weibull distribution, or using a test verified threshold stress, or a value of 6.9 MPa (1 ksi. Used in the absence of test data).

1. A and B basis statistics apply to material allowables only.

8.6.3 CTE Data

Coefficient of Thermal Expansion (CTE) data for materials shall be tested or obtained for the range of maximum survival temperature down to minimum survival temperature.

1. Obtained data requires project approval for use.

8.6.4 Stress Corrosion Cracking

All metallic materials shall be selected from Table I of MSFC-STD-3029, unless otherwise approved by Parts, Materials, and Processes Control Board.

8.7 Joints

8.7.1 Joint Edge Distance

The minimum bolt edge distance shall be as specified in Table 8-2 unless a detailed analysis is performed to justify otherwise.

Notes

1. Use appropriate bearing value from MMPDS for metals

2. D = Bolt hole or insert sleeve diameter, e = edge distance from center of bolt to edge of panel

Table 8-2 Minimum Edge Distance

Minimum Edge Distance (e/D)

Composite/Ceramic 2.5 min

Metallic 1.5 min

8.7.2 Bonded Joint Allowable

Bonded joint allowables shall be B-basis produced through coupons representative of flight hardware, tested under their appropriate environments, and taking into account strength degradation due to thermal cycles.

Rationale: Bond strength is dependent on materials and workmanship, e.g. surface prep. Due to scatter from the workmanship process and material variability, B basis allowables are developed for structural analysis.

Note: Bonded joints on flight hardware are proof tested to 1.25 times limit load.

8.7.3 Reserved

8.7.4 Fastened Joints

8.7.4.1 Fastener Locking

Each threaded fastening system in spaceflight hardware shall incorporate a minimum of one locking feature that does not depend upon preload to function.

Notes:

1. Locking features and their installation processes, including verification methods, should be specified in the engineering documentation.

2. Locking features should be verifiable per Section 7.6 of NASA-STD-5020.

8.7.4.2 Fastened Joint Margin of Safety

Positive MS for all threaded fastening systems shall be demonstrated for:

a) Ultimate design loads under all structural failure modes in conjunction with the applicable maximum expected range of environmental conditions without failure per the following:

1) The ultimate design load, Pu, is calculated using the following formula.

2) 𝑃𝑈 = 𝐹𝐹 ∗ 𝐹𝑆𝑈 ∗ 𝑃𝐿

i. where FF is the fitting factor, FSu is the ultimate factor of safety, and PL is the limit load.

3) The fitting factor (FF) defined in NASA-STD-5020 Appendix A.12 is used.

4) Analysis for ultimate design loads will address potential rupture in all elements of the threaded fastening system, including the fastener, the internally threaded part, such as a nut or an insert, and the clamped parts.

5) Insert pull-out strengths given in vendor documentation typically assume full bolt to insert thread engagement. An appropriate knock down in pull-out strength is included if the bolt does not fully engage the insert.

6) Ultimate strength analysis of a fastening system under applied tensile loading is performed per NASA-STD-5020, Section 6.2.1.

7) Ultimate strength analysis of a fastening system under applied shear loading is performed per NASA-STD-5020, Section 6.2.2.

8) Ultimate strength analysis of bolts under shear loading is based on the assumption that no shear load is carried by friction between the faying surfaces.

9) For fasteners under simultaneous applied tensile and shear loads, along with any applicable bending analysis will account for interaction of the combined loading per NASA-STD-5020, Section 6.2.3.

10) When possible, joints should be designed for bearing failure rather than bolt tension or shear failure.

b) Yield design loads in conjunction with the applicable maximum expected range of environmental conditions without detrimental yielding per the following:

1. If one or more of the following applies:

i. Fastener yielding causes the joint to separate under an applied tensile load that is less than the design separation load;

ii. Fastener yielding causes the joint to suffer detrimental slip under an applied shear load that is less than the applicable design shear load;

iii. Some other design-specific reason exists for why fastener yielding is detrimental (e.g., any fastener yielding that adversely affects the form, fit, or function of the design);

then fastener yielding is detrimental and analysis is performed per NASA-STD-5020, Section 6.3 to show the fastener’s total tensile load, when accounting for maximum preload and the yield design tensile load, does not exceed the allowable yield tensile load.

2. The yield design load, PY, is calculated using the following formula.

𝑃𝑌 = 𝐹𝐹 ∗ 𝐹𝑆𝑌 ∗ 𝑃𝐿

where FF is the fitting factor, FSY is the yield factor of safety, and PL is the limit load.

3. The fitting factor (FF) defined in NASA-STD-5020 Appendix A.12 will be used.

4. If MS for joint slip is shown to be positive, friction may be included as a shear load path for yield strength analysis of joint members (e.g. bearing). NASA-STD-5020 section 6.4 is used for joint slip analysis.

c) Gapping load in conjunction with applicable maximum or minimum temperatures without gapping per the following:

1) Margin of safety for gapping is defined as follows:

i) 𝑀𝑆𝑠𝑒𝑝 = 𝑃𝑝−𝑚𝑖𝑛

𝐹𝐹∗𝐹𝑆𝑠𝑒𝑝∗𝑃𝐿

- 1 where FF is the fitting factor, and Pp-min is the minimum preload.

2) Gapping factor of safety (FSsep) of 1.0 for non-gapping critical joints, FSsep=1.25 for non-catastrophic failure gapping critical joints, and FSsep=1.4 for catastrophic failure gapping critical joints is used for margin calc.

3) The fitting factor (FF) defined in NASA-STD-5020 Appendix A.12 will be used.

4) NASA-STD-5020, Section 6.5 is used to guide gapping analysis to show no separation for each threaded fastening system that is subject to applied tensile loading, with the assumption of minimum preload.

5) Analysis of threaded fastening systems will address nominal, maximum, and minimum preloads per NASA-STD-5020 Section 6.1.

See NASA-STD-5020, section 6.2 as reference.

8.7.4.3 Installation Torque Documentation

Engineering documentation shall specify the installation torque range or specify an applicable standard that defines the installation torque range.

1. The engineering documentation should clearly identify when the installation torque is the torque above running torque.

8.7.4.4 Seal Analysis

For a joint that maintains a seal (e.g., to maintain pressure or contain a fluid), the seal shall meet its requirements at the design separation load when assuming minimum preload for all fasteners in the joint.

8.7.4.5 Critical Fasteners

Fastened joints identified as critical shall be demonstrated as either safe-life or fail-safe.

1. Critical joints will be identified with project concurrence. Critical joint’s failure lead to mission ending failure.

2. A safe-life component is a structural component which can be demonstrated to have at least

4 design life cycles under all anticipated load environments, including integration, testing, ground transport, and launch. Industry standard methods such as linear-elastic fracture mechanics using NASGRO® or S-N fatigue analysis curves may be used for analytically demonstrating safe-life. NDE is required for substantiating initial crack size in linear-elastic fracture analysis.

3. A fail-safe component is a structural component in a redundant load path which after the loss of the component, the remaining load path(s) has sufficient structural capability to withstand the redistributed loads, and the loss of the component will not cause a catastrophic hazard. Examples of redundant load paths are multiple fasteners in bolted joints, stitched welded structures, and riveted and bolted structures. A factor of safety of

1.0 shall be applied to the remaining load path(s) when demonstrating fail-safe.

8.8 Mechanism Design

8.8.1 Minimum Torque

The minimum torque at the motor shaft necessary for mechanism function shall never be less than 7.06E-3 N-m (1 oz- in)

1. Mechanisms that require torque below the listed value requires project approval.

8.8.2 Torque Margin Formula

The Torque Margin (TM) shall be greater than zero and be calculated using the following formula and using FS specified in Table 8-3:

𝑇𝑀 = {

𝑇𝑎𝑣𝑎𝑖𝑙

(𝐹𝑆𝑘 ∑ 𝑇𝑘𝑛𝑜𝑤𝑛 + 𝐹𝑆𝑣 ∑ 𝑇𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒)

} − 1

Where:

Driving Torques:

Tavail = Minimum Available Torque or Force generated by the mechanism at worst case…