Attachment B WFIRST-ACS-SPEC-0073-ReleasedWFIRSTDoc.pdf

Effective Date: March 16, 2020

National Aeronautics and Space Administration

Goddard Space Flight Center Greenbelt, Maryland

WFIRST-ACS-SPEC-0073, Revision -

Wide Field Infrared Survey Telescope (WFIRST), Code 448

WFIRST Reaction Wheel Isolation

System (RWIS)

Performance Specification (SPEC)

GSFC WFIRST CMO

March 16, 2020

Released

WFIRST RWIS SPEC WFIRST-ACS-SPEC-0073, Revision -

Effective Date: March 12, 2020 ii

Reaction Wheel Isolation System Performance Specification

Review/Signature/Approval Page

Prepared by:

Allison Evans

Approved by:

Jason Hylan

Electronic Approval available on the WFIRST CM Tool iii

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 iv

Change History Log

Revision Effective Date Description of Changes

(Reference the CCR & CCB/ERB Approval Date)

Revision - March 12, 2020 Initial release of document per WFIRST-CCR-0163 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 Reaction Wheel Isolation System Description

3 FUNCTIONAL/PERFORMANCE REQUIREMENTS

3.1 Reaction Wheel Isolation System Flight Unit Functional/Performance Requirements

3.1.1 Isolator Design – Baseline

3.1.1.1 Isolator Transmissibility (Baseline)

3.1.1.2 Isolator Resonant Mode Frequency (Baseline)

3.1.1.3 Isolator Resonant Mode Damping (Baseline)

3.1.2 Isolator Design – Option 1

3.1.2.1 Isolator Transmissibility (Option 1)

3.1.2.2 Isolator Resonant Mode Frequency (Option 1)

3.1.2.3 Isolator Resonant Mode Damping (Option 1)

3.1.3 Isolator Transmissibility Test Configuration

3.1.4 Isolator Lateral and Internal Modes

3.1.4.1 Isolator Lateral and Local Vibration Modes - Frequencies

3.1.4.2 Isolator Lateral and Local Vibration Modes - Damping

3.1.5 Isolator Model Correlation

3.1.5.1 Isolator Model Correlation - Frequency

3.1.5.2 Isolator Model Correlation - Criteria

3.1.6 Magnetic Field Information

3.1.7 RW Mass Simulators

3.1.8 Launch Restraint Performance Requirements

3.1.8.1 Launch Restraint Shock Loading

3.1.8.2 Launch Restraint Reset/Refurbishment

3.1.8.3 Visual detection of Launch Restraint Locked or Unlocked Position

3.1.8.4 Electrical Detection of Launch Restraint Locked or Unlocked Position

3.1.8.5 Launch Restraint Function without Power

3.1.8.6 Launch Restraint Redundancy

3.1.8.7 Minimum Number of Launch Restraint Cycles

3.1.8.8 Dimensional Repeatability

3.1.8.9 Launch Restraint Mission Time Prior to Actuation

3.1.8.10 Launch Restraint State

3.1.8.11 Launch Restraint Clearance

3.2 Resource Allocations

3.2.1 Mass Allocation

3.2.2 Electrical Allocation

3.3 Electrical Requirements

vi

3.3.1 Voltage Supplied to Heaters on Isolator

3.3.2 Launch Lock

3.3.2.1 Launch Lock Current

3.3.2.2 Launch Lock Impedance

3.3.2.3 Launch Lock Current vs Time Curve

3.3.2.4 Launch Lock Release Confirmation

3.3.2.5 Launch Lock Time Required to Unlock

3.3.2.6 Release Initiation Circuit

3.3.2.7 Resistance Test Signal and Duration

3.3.2.8 No Initiation Current

3.3.3 Wiring Requirements

3.3.3.1 Wire Sizing

3.3.3.2 Wire Materials

3.3.3.3 Wire Labeling

3.3.4 Soldered and Wire Connections

3.3.5 Wiring/Harness Configuration

3.3.6 Harness Connection Provisions

3.4 Electrical Grounding

3.4.1 Primary Power DC Isolation

3.4.2 Internally Generated Secondary Returns

3.4.3 Internally Generated Secondary to Primary DC Isolation

3.4.4 Mechanical Contact Resistance

3.4.5 Mating Method

3.4.6 Ground Strap, Non-Conductive Surface

3.4.6.1 Ground Lug Contact Area

3.4.6.2 Internal Charging

3.4.6.3 Ground Isolation

3.4.6.4 Dielectric Strength

3.4.6.5 Insulation Resistance

3.4.6.6 Non-Electrical and Electro-Mechanical Bonding Resistance

3.4.7 Ground Straps, Hinged Joints

3.4.7.1 Ground Straps, Resistance across Hinged Joints

3.4.7.2 Ground Straps, Physical Properties

3.4.8 Connector and Back-Shell DC Resistance

3.5 Signal and Data Interfaces

3.5.1 Reserved

3.5.2 Passive Analog Telemetry

3.5.2.1 Passive Analog Telemetry Interface

3.5.2.2 Reserved

3.5.2.3 Thermistor Resistor Conditioning

3.5.2.4 Reserved

3.5.3 Reserved

3.5.4 Reserved

3.5.5 Reserved

3.5.6 Reserved

3.6 Reserved

vii

3.7 Reserved

3.8 Reserved

4 PHYSICAL REQUIREMENTS

4.1 Interface Documentation

4.1.1 Mechanical Interface to the Panel

4.1.1.1 Integration Access

4.1.1.2 Interface Restrictions

4.1.2 Electrical Interface

4.1.3 Reserved

4.2 Mass Properties

4.2.1 Component Masses

4.2.2 Center of Mass Location

4.2.3 Center of Mass Accuracy

4.2.4 Determination of Moments and Products of Inertia

4.3 Physical Envelope

4.3.1 Volume Constraint

4.3.1.1 Wheel Drive Electronics

4.3.1.2 Reaction Wheel Harness

4.3.1.3 Thermal Strap

4.3.2 Reserved

4.4 Mounting

4.5 Reserved

4.6 Alignment

4.6.1 Alignment Knowledge Accuracy: RWIS to RWA Mounting

4.6.2 Alignment Knowledge Accuracy: RWIS Mounting to S/C Panel

4.6.3 Alignment Stability

5 ENVIRONMENTAL REQUIREMENTS

5.1 Quasi-Static Acceleration

5.2 Frequency Requirement

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 Pressure

5.6.1 Reserved

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 of Spacecraft Monitored Temperature Sensors

5.10 Reserved

viii

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

6.1.2.3 Material Selection

6.1.2.4 Material Selection - Silicones

6.1.2.5 Assembly Outgassing

6.1.2.6 Intentional and Unintentional Vents

6.1.2.7 Intentional and Unintentional Vents – Filters

6.1.2.8 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 Reserved

7 DESIGN & CONSTRUCTION REQUIREMENTS

7.1 Parts, Materials & Processes (PMP)

7.1.1 EEE Parts

7.1.2 Materials

7.1.2.1 Material Conductivity

7.1.3 Reserved

7.2 Electrical

7.2.1 Test Sensors

7.2.2 Interface Requirements

7.2.2.1 Connector Selection

7.2.2.1.1 Connector Specifications

7.2.2.1.2 External Box Power Connectors

7.2.2.1.3 Contact Derating

7.2.2.1.4 Redundant Contact Derating

7.2.2.2 Signal Segregation

7.2.2.3 Test and Flight Signal Isolation

7.2.2.4 Test Interfaces

7.2.2.5 Facility-Induced Noise

7.2.2.6 Facility-Induced ESD GSE Malfunction

7.2.2.7 Facility-Induced GSE Malfunction

7.2.3 Mitigation of Internal Charging

7.2.3.1 Mitigation Strategies for Internal Charging

7.2.3.2 Floating Conductors

7.2.3.3 Dielectric Structures

7.2.3.4 Bulk Resistivity

7.2.3.5 Charge Bleed-Off

ix

7.3 Safety

7.3.1 Fluid Damping

7.4 Reserved

7.5 Identification and Marking

7.6 Workmanship

7.6.1 Workmanship Standards

7.6.2 Connector

7.6.2.1 GSE Cable Connectors

7.6.2.2 Prevention of Connector Mismating

7.6.2.3 Connector Uniqueness

7.6.2.4 Connector Facing

7.6.2.5 Connector Keying

7.6.2.6 Accessibility

7.6.2.7 Connector Gender

7.6.2.8 “Scoop-Proof”

7.6.2.9 Test Connectors

7.6.2.10 Connector Identification

7.6.2.11 Protection of Unused Test Connectors

7.7 Reliability and Mission Lifetime

7.7.1 Mission Life

7.7.2 Reserved

7.8 Ground Handling

7.8.1 Ground Support Equipment (GSE) Design

7.8.2 Reserved

7.8.3 Lifting Capability

7.8.4 Lift Point Capability

7.8.5 Lift Point Locations

7.8.6 Lift Point Proof Testing

7.8.7 GSE Cleanliness

7.8.8 GSE Bakeout

7.8.9 Test Harness

8 MECHANICAL DESIGN REQUIREMENTS

8.1 Mechanical Factors of Safety

8.2 Fracture and Fatigue

8.2.1 Tier 1 fracture classification:

8.2.2 Tier 2 fracture classification

8.2.3 Tier 3 fracture classification:

8.2.4 Tier 4 fracture classification:

8.2.5 Notes for fracture/fatigue:

8.3 Reserved

8.4 Reserved

8.5 Materials

8.5.1 Dissimilar Metals

8.5.2 Material Allowables and Stiffness

8.5.3 CTE Data

8.5.4 Stress Corrosion Cracking

x

8.6 Joints

8.6.1 Joint Edge Distance

8.6.2 Bonded Joint Allowable

8.6.3 Reserved

8.6.4 Fastened Joints

8.6.4.1 Fastener Locking

8.6.4.2 Fastened Joint Margin of Safety

8.6.4.3 Installation Torque Documentation

8.6.4.4 Seal Analysis

8.6.4.5 Critical Fasteners

8.7 Mechanism Design

8.7.1 Minimum Torque

8.7.2 Torque Margin Formula

8.7.3 Mechanism Stall Performance

8.7.4 Mechanism Installation

8.7.5 Deployables and Mechanism Jamming

8.7.5.1 Non-Powered Restraint

8.7.5.2 Visual Indication of Caging

8.7.5.3 Confirmation of Deployment

8.7.5.4 Springs Failure Tolerant

8.7.5.5 Tolerancing

8.7.5.6 Clearances

8.7.6 Viscous Dampers

8.7.6.1 Air Entrapment

8.7.6.2 Damper Temperature Effects

8.7.7 Mechanical Stops

8.7.8 Switches

8.7.8.1 Indicating Device

8.7.8.2 Microswitches

8.7.9 Lubricants

8.7.9.1 Reserved

8.7.9.2 Dry Lubricants

8.8 Mechanism Verification Requirements

8.8.1 Mechanism Verification

8.8.1.1 Mechanism Qualification Testing

8.8.1.2 Mechanism Life Testing

8.8.1.3 Mechanism Acceptance Testing

8.8.2 Functional Test Structuring

8.8.3 Reserved

8.8.4 Reserved

9 LOGISTICS

9.1 Reserved

9.2 Ground Support Equipment

9.2.1 GSE Definition

9.2.2 GSE Cleanliness

9.3 Transportation Equipment

xi

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

10.4.4 Powered-on Conditions for Test

10.4.5 Reserved

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 Abbreviated Functional Test

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 Reserved

10.5.14 Thermal Cycling Testing - Ambient

10.5.15 Reserved

xii

10.5.16 Reserved

10.5.17 Transmissibility and Induced Vibration Characterization with Reaction Wheels

(Option 2)

APPENDIX A ABBREVIATIONS AND ACRONYMS

List of Figures

Figure 3-1 RW Isolator’s Lateral Force Transmissibility Requirement (Baseline) Figure 3-2 RW Isolator’s Axial Force Transmissibility Requirement (Baseline)

Figure 3-3 RW Isolator’s Lateral Moment Transmissibility Requirement (Baseline) Figure 3-4 RW Isolator’s Lateral Force Transmissibility Requirement (Option 1) Figure 3-5 RW Isolator’s Axial Force Transmissibility Requirement (Option 1) Figure 3-6 RW Isolator’s Lateral Moment Transmissibility Requirement (Option 1)

Figure 10-1 Thermal Vacuum Profile

List of Tables

Table 5-1 Reaction Wheel Isolator Design Limit Loads Table 5-2 Item Name Generic Sine Vibration Environment Table 5-3 Random Vibration Limit Levels for Components Weighing Less Than 22.7 kg Table 5-4 Random Vibration Limit Load Reduction for components Weighing More than or equal to 22.7 kg Table 5-5 Minimum Workmanship Level for Components Weighing Less than 45.4 kg

Table 5-6: Minimum Workmanship Level Reduction for components weighing more than or equal to 45.4 kg

Table 5-7 Shock Source Limit Levels Table 5-8: Temperature Limits at Mounting Interface Table 8-1 Design Factors of Safety

Table 8-2 Minimum Edge Distance Table 8-3 Torque Margin Calculation Factors of Safety

Table 10-1 Test Factors and Durations Table 10-2 Test Tolerances Table 10-3 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

Reaction Wheel Isolation System (RWIS).

1.2 Scope

This specification establishes the functional, performance, and testing requirements for the space-qualified Reaction Wheel (RW) Mechanical Isolation System and associated Reaction

Wheel Mounting Brackets for the NASA Goddard Space Flight Center (GSFC) WFIRST

Mission.

This document defines the performance requirements for the WFIRST Reaction Wheel Isolation

System (which shall include any associated reaction wheel and deck mounting brackets, heaters, ground straps, and launch restraints), henceforth known as “Reaction Wheel Isolators,” “RW

Isolators,” or “RWIS.” The RWIS shall be used to provide structural support and vibration attenuation for six WFIRST Reaction Wheels. The RWIS can consist of one or more separate pieces of hardware that isolate one or more reaction wheels each. The entire set shall be considered one Reaction Wheel Isolation System.

1.3 Related Documentation

The latest versions of all documents below should be used. WFIRST documents can be obtained from 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

RWIS and possible launch restraint mechanisms 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 RWIS Statement of Work (WFIRST-ACS-SOW-0021), 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-ACS-LIST-0031 WFIRST Reaction Wheel Isolation System (RWIS) Deliverable

Items List and Schedule (DILS)

WFIRST-ACS-SOW-0021 WFIRST Reaction Wheel Isolation System (RWIS) Statement of

Work (SOW)

2221056 Drawing - Reaction Wheel, Volume, SC Bay 4

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

None

2 CONTRACT DESCRIPTION

2.1 Reaction Wheel Isolation System Description

The RWIS is a mechanical isolation device capable of partially or fully mechanically isolating the reaction wheels from other spacecraft systems. The RWIS includes tuned stiffness and internal damping characteristics.

The RWIS fixes the six reaction wheels to the spacecraft RWA deck and provide mechanical vibration isolation between the RWA housing and the spacecraft bus structure.

It is an option to have the reaction wheel assemblies (RWA’s) pre-integrated with the RWIS and tested before delivery if the RWA’s are available a reasonable amount of time before the delivery date.

WFIRST RWIS Spec WFIRST-ACS-SPEC-0073, Revision Number

3 FUNCTIONAL/PERFORMANCE REQUIREMENTS

This section defines the functional and performance requirements for the RWIS as defined in

Section 3.1.

3.1 Reaction Wheel Isolation System Flight Unit Functional/Performance Requirements

The proposed design shall meet the baseline requirements (Section 3.1.1) with an option to switch to Option 1 requirements (Section 3.1.2).

3.1.1 Isolator Design – Baseline

3.1.1.1 Isolator Transmissibility (Baseline)

The RW isolator will provide vibration isolation from lateral force (x, y), axial force (z), and lateral moment (x, y) disturbances induced at RW’s center of mass (see attached drawing

2221056 for RW coordinate system definition).

The RW Isolator’s force and moment transmissibility as a function of vibration frequency shall be less than the RW Isolator’s transmissibility requirement specified in Figure 3-1 through

Figure 3-3 over the operating temperature range stipulated in Section 5.9.

Figure 3-1 RW Isolator’s Lateral Force Transmissibility Requirement (Baseline) freq (Hz) trans (N/N)

0.1 2

1.5 2

2.5 17

6 17

9 0.8

110 0.004

300 0.004

350 0.02

1000 0.02

Figure 3-2 RW Isolator’s Axial Force Transmissibility Requirement (Baseline)

Figure 3-3 RW Isolator’s Lateral Moment Transmissibility Requirement (Baseline)

Transmissibility is defined as the ratio of output forces and moments at the base of the “RW mass simulator (see mechanical properties of RW mass simulator in drawing 2221056) + RWIS” system to the input forces and moments applied at the RW center of gravity (CG).

Note: see Section 3.1.3 for schematic of transmissibility test configuration.

freq (Hz) trans (N/N)

0.1 2

2 2

3 22

7 22

11 0.8

100 0.008

200 0.008

350 0.03

1000 0.03 freq (Hz) trans (Nm/Nm)

0.1 2

1.5 2

2.5 25

6 25

8 0.7

80 0.01

300 0.01

350 0.05

1000 0.05

3.1.1.2 Isolator Resonant Mode Frequency (Baseline)

The fundamental modes (axial, lateral translation, and lateral bending) of the RW Isolator shall be within a frequency range of 2.5-7 Hz, over the operational temperature range as specified in

Section 5.9.

3.1.1.3 Isolator Resonant Mode Damping (Baseline)

The fundamental modes (axial, lateral translation, and lateral bending) of the RW Isolator shall achieve a damping level of 6-12% critical, over the operational temperature range as specified in

Note:

The fundamental mode frequencies and damping levels will be evaluated utilizing RW mass simulator and RW Isolation System (RWIS)

This requirement does not include any shunt path (i.e. RW harness, heat strap, etc.)

bridging the isolator.

3.1.2 Isolator Design – Option 1

3.1.2.1 Isolator Transmissibility (Option 1)

The RWIS will provide vibration isolation from lateral force (x, y), axial force (z), and lateral moment (x, y) disturbances induced at RW’s center of mass (see attached drawing 2221056 for

RW coordinate system definition).

The RWISs force and moment transmissibility as a function of vibration frequency shall be less than the RWISs transmissibility requirement specified in Figure 3-4 through Figure 3-6 over the operating temperature range stipulated in Section 5.9.

Figure 3-4 RW Isolator’s Lateral Force Transmissibility Requirement (Option 1)

Figure 3-5 RW Isolator’s Axial Force Transmissibility Requirement (Option 1)

Figure 3-6 RW Isolator’s Lateral Moment Transmissibility Requirement (Option 1)

Transmissibility is defined as the ratio of output forces and moments at the base of the “RW mass simulator (see mechanical properties of RW mass simulator in drawing 2221056) + RWIS” system to the input forces and moments applied at the RW CG.

Note: see Section 3.1.3 for schematic of transmissibility test configuration.

3.1.2.2 Isolator Resonant Mode Frequency (Option 1)

The fundamental modes (axial, lateral translation, and lateral bending) of the RW Isolator shall be within a frequency range of 4-11 Hz, over the operational temperature range as specified in Section

5.9.

3.1.2.3 Isolator Resonant Mode Damping (Option 1)

The fundamental modes (axial, lateral translation, and lateral bending) of the RW Isolator shall achieve a damping level of 5-15% critical, over the operational temperature range as specified in

The fundamental mode frequencies and damping levels will be evaluated utilizing rigid

RW mass simulator and RW Isolator system

This requirement does not include any shunt path (i.e. RW harness, heat strap, etc.)

bridging the isolator.

3.1.3 Isolator Transmissibility Test Configuration

The requirements stated in sections 3.1.1 and 3.1.2 shall be verified with a simulated RW having mass properties as specified in the attached drawing 2221056.

The mass-simulated RW will be mounted to the RW Isolator while the base of the isolator

(interfaces to spacecraft side) is attached to a large rigid mass. The transmissibility requirement will be verified through the ratio of output forces/moments measured at the base of the isolator to the input lateral/axial forces and lateral moments applied to the CG of the RW mass simulator, in the RW local coordinate system (see attached drawing 2221056 for RW coordinate system definition). Gravity offload of the RW mass simulator to simulate on-orbit condition of test article during transmissibility testing is allowed. The transmissibility requirement will apply for input magnitudes below those levels sufficient to initiate isolator’s hard-stop contact. The test will be performed at a range of input loads from below to above flight operational load levels to confirm linearity.

3.1.4 Isolator Lateral and Internal Modes

3.1.4.1 Isolator Lateral and Local Vibration Modes - Frequencies

All lateral or local mode frequencies of the Isolator shall be evaluated by WFIRST using Isolator dynamic models at nominal temperature and temperature extremes provided by the Contractor.

The contractor shall also provide isolator dynamic models with properties tuned to be accurate at

200 – 400Hz.

The Contractor will address the design as needed to minimize dynamic coupling between isolator modes and the jitter sensitive modes of the WFIRST Observatory (215 Hz +/- 5% and 366 Hz +/-10%) to the degree to be determined between the Contractor and WFIRST.

All lateral or local mode frequencies of the Isolator will be evaluated when the ends are fully constrained in translation and rotation at the interface.

The Isolator dynamic models provided by the Contractor will be used for the system level assessment performed by WFIRST.

3.1.4.2 Isolator Lateral and Local Vibration Modes - Damping

The Contractor will attempt to maximize the damping of all lateral modes of vibration where practical. This includes internal modes of the Isolator as well as lateral modes of the Isolator, including flexures.

3.1.5 Isolator Model Correlation

The Contractor will provide a correlated Isolator finite element model based on measured data from Isolator’s axial dynamics test. The Isolator finite element model will meet the model requirements specified in WFIRST-ACS-SOW-0021.

3.1.5.1 Isolator Model Correlation - Frequency

The model correlation shall be valid from 0.1 to 400 Hz and over the operational temperature range.

3.1.5.2 Isolator Model Correlation - Criteria

The transmissibility characteristics of the correlated Isolator model shall yield frequencies and resonant peaks to within 5% of the measured frequencies and response amplitudes.

3.1.6 Magnetic Field Information

This section applies only if magnetic damper is used in the design.

The contractor shall provide the residual field strength vs distance of any magnetic damper.

Residual being the field outside the gap the moving element resides in.

The contractor shall also state whether or not the magnetic field of any magnetic damper is canceled out by shielding within the isolation system itself.

3.1.7 RW Mass Simulators

RW Mass Simulators shall be manufactured by the contractor for use during dynamic testing.

The mass properties per wheel are given in the attached drawing (2221056), along with the acceptable tolerance levels for the mass simulator. The CG location is relative to the center point of the RWA mounting interface. The X-axis is in the direction of the sight glass and the Z-axis is along the RWA spin axis with +Z defined toward the top of the wheel housing.

3.1.8 Launch Restraint Performance Requirements

Launch locks or snubbers/bumpers may be used with the isolators during launch if required. If they are provided in the design they shall accommodate the isolation scheme used, whether it is a per-wheel isolation design or a wheel platform isolation design.

3.1.8.1 Launch Restraint Shock Loading

The launch restraint mechanism shall not have a shock load above the values listed in Table 5-7.

The shock load imparted from the isolators to the spacecraft shall not exceed the shock load imparted from the spacecraft to the isolators.

3.1.8.2 Launch Restraint Reset/Refurbishment

The Launch Restraint device shall be resettable or refurbishable. “Resettable” indicates that the

Launch Restraint device can be returned to the locked condition meeting all ICD requirements without disassembly. “Refurbishable” means that the Launch Restraint device can be returned to the locked condition meeting all ICD requirements with limited disassembly and inspection. It is preferred that the Launch Restraint device be resettable while installed, but bench top resettable or refurbishable at GSFC is also acceptable.

3.1.8.3 Visual detection of Launch Restraint Locked or Unlocked Position

The Launch Restraint device shall include provisions for a positive visual indication of proper locking and a means to easily detect, from several orientations around the Launch Restraint device, visibly whether the Launch Restraint device is in the locked or unlocked state.

3.1.8.4 Electrical Detection of Launch Restraint Locked or Unlocked Position

The Launch Restraint device shall include provisions for redundant electrical indication of locked or unlocked state with electrical requirements per Section 3.3.

3.1.8.5 Launch Restraint Function without Power

The Launch Restraint device shall maintain its locked state in the absence of externally applied power.

3.1.8.6 Launch Restraint Redundancy

Electrical elements required to actuate the Launch Restraint device, including heaters, thermostats, fusible links, and other items as applicable, shall be redundant and redundantly powered.

3.1.8.7 Minimum Number of Launch Restraint Cycles

The Launch Restraint device shall be capable of a minimum of seven (7) unlock/lock cycles following delivery to GSFC. It shall meet all requirements after this number of cycles.

3.1.8.8 Dimensional Repeatability

The Launch Restraint device interface dimensions between interfaces shall not change more than

0.05 mm (0.002”) in hole location and more than 0.025 mm (.001”) in parallelism as a result of being reset or refurbished.

3.1.8.9 Launch Restraint Mission Time Prior to Actuation

The Launch Restraint device shall actuate and meet all performance requirements after being in the locked configuration for the ground testing life (Section 7.7.1) followed by a minimum of 3 months at the survival temperatures.

3.1.8.10 Launch Restraint State

The launch restraint device, once released, shall maintain its unlocked state in the absence of externally applied power.

3.1.8.11 Launch Restraint Clearance

The launch restraint shall have sufficient stroke during applications of the on-orbit dynamics environment (section 5.7) to not violate isolator transmissibility, resonant mode frequency, and resonant mode damping requirements.

3.2 Resource Allocations

3.2.1 Mass Allocation

The Reaction Wheel Isolation System shall have a total mass of less than or equal to 112 kg.

This total mass value includes the mass of any associated launch locks/snubbers. This mass allocation does not include the mass of the RWA or dummy mass used with the RWIS for testing.

3.2.2 Electrical Allocation

A maximum of six separate electrical release devices (with electrical redundancy, for a total of twelve electrical signals) shall be used on the RWIS.

3.3 Electrical Requirements

3.3.1 Voltage Supplied to Heaters on Isolator

Heaters, if required on the RWIS, shall meet all performance requirements when supplied with the unregulated input voltage range from 30 to 35 VDC.

3.3.2 Launch Lock

This sub section describes electrical requirements of either of the following two basic types of release devices:

a) Device actuated by heaters, i.e. shape memory alloy or similar

b) Device actuated by short duration high current pulse, i.e. NEA or similar

Alternate means of powering the release device must be compatible with the spacecraft design and must be negotiated with WFIRST.

3.3.2.1 Launch Lock Current

The Launch Lock Release mechanism shall be capable of actuating with a minimum current of

3.0 amperes without degradation in performance under any of the operational environment conditions specified herein.

3.3.2.2 Launch Lock Impedance

The Contractor shall provide the nominal, maximum, and minimum impedance of the Launch

Lock initiation circuit as measured for each launch lock at the electrical interface defined on the contractor supplied ICD with a calibrated ohmmeter using a test signal of 10 milliamps, or less.

3.3.2.3 Launch Lock Current vs Time Curve

The Contractor shall provide data for the relationship between actuation time versus current over the operational temperature range.

3.3.2.4 Launch Lock Release Confirmation

The Launch Lock shall provide the means for redundant remote confirmation in telemetry that the Launch Lock is in the locked or unlocked position. The confirmation shall read via a two wire connection and be greater than 1 MegaOhms when in the unlocked position and less than 1

Ohm in the locked position (or vice versa).

3.3.2.5 Launch Lock Time Required to Unlock

If the Launch Lock resistance is equal to or greater than 5 Ohms, then it shall release within 10 minutes of the initial receipt of the electrical release initiation signal at the minimum current, under any operational environment condition specified herein.

If the Launch Lock resistance is less than 5 Ohms, then it shall release within 200 milliseconds of the initial receipt of the electrical release initiation signal at the minimum current, under any operational environment condition specified herein.

3.3.2.6 Release Initiation Circuit

The release initiation circuit is defined as the electrical current carrying components of the release initiation system, in addition to any wire harness leading to, and including, the connector

(if applicable).

3.3.2.7 Resistance Test Signal and Duration

For devices actuated by heater, the Contractor shall define a resistance test signal that will be used for electrical verification of the state of the launch lock. The individual launch lock shall withstand 20 applications of the Contractor specified test signal for a duration of 60 seconds each for each release initiation system without performance degradation and without unlocking.

3.3.2.8 No Initiation Current

For devices actuated by heater, the Launch Lock shall not unlock when preloaded to its minimum preload, or suffer performance degradation, when the release initiation circuit is subject to a maximum current of 0.2 Amps for a minimum of 5 minutes with the Launch Lock in vacuum at the hot survival temperature limit or a maximum current of 0.5 Amps for a minimum of 5 minutes with the Launch Lock at ambient temperature and pressure.

3.3.3 Wiring Requirements

3.3.3.1 Wire Sizing

All wires shall accommodate peak operating current and remain within the derating guidelines of

EEE-INST-002, however, no wire shall be less than 20 AWG.

3.3.3.2 Wire Materials

All wiring shall be fabricated from low outgassing, non-flammable or self-extinguishing, material for use in the environments specified herein in accordance with EEE-INST-002. The wiring insulator shall be rated for a temperature of 200ºC at a minimum.

3.3.3.3 Wire Labeling

All wires shall be clearly color coded and marked with labels of flightworthy material. If connectors are supplied, they shall be clearly marked with labels of flightworthy material.

3.3.4 Soldered and Wire Connections

All soldered joints and wire connections shall conform to IPC J-STD-001FS and/or

IPC/WHMA-A-620B-S and shall be inspected by the Contractor as defined in WFIRST-SOW-

13052.

3.3.5 Wiring/Harness Configuration

The wiring configuration shall be negotiated between the Contractor and WFIRST.

Possible configurations include a) flying leads and b) complete harness with connector. Length of wires or harness and all pertinent details shall be described in the contractor supplied ICD.

3.3.6 Harness Connection Provisions

The Unit shall include provisions for mechanical support (strain relief) of the harness and electrical connection of harness shield. The details of these interfaces shall be described in the contractor supplied ICD.

3.4 Electrical Grounding

3.4.1 Primary Power DC Isolation

At the RWIS primary power interfaces, primary power and primary power returns shall be isolated from signal grounds and from the component chassis by a DC resistance of greater than or equal to 1 MΩ.

3.4.2 Internally Generated Secondary Returns

Secondary returns (power and signal grounds) shall be referenced to the component chassis ground by connecting them at one or more places.

3.4.3 Internally Generated Secondary to Primary DC Isolation

Secondary power (or signal) inputs shall be isolated from primary power by a DC resistance of greater than 1 MΩ.

3.4.4 Mechanical Contact Resistance

The DC resistance of the mechanical contact between two conductive mating surfaces (internal to the component) shall be less than or equal to 2.5 mΩ DC resistance.

3.4.5 Mating Method

The primary mating method for a WFIRST component is metal-to-metal contact between component mounting feet (or base plate) and the spacecraft structure. When the use of this method is not possible as determined by the contractor’s Mechanical Interface Control Document

(MICD), the use of a ground strap is necessary. See Drawing 2221056 for mechanical mounting interface.

3.4.6 Ground Strap, Non-Conductive Surface

The RWIS shall contain provisions for a grounding strap to be attached from the component chassis for connection to the spacecraft conductive structure.

3.4.6.1 Ground Lug Contact Area

The grounding lug location on the component chassis or the tie points in contact with the ground strap shall have a minimum contact area of 80 mm². The ground lug contact area must remain free of any material finish that may affect the reliability of the ground connection and be shown in the MICD.

3.4.6.2 Internal Charging

Ungrounded (floating) conductors shall not be present in the RWIS, except as approved by

WFIRST.

3.4.6.3 Ground Isolation

Unit power and return harness and circuitry shall be isolated from signal and chassis ground by greater than 2 MegaOhm at a test voltage of 500 VDC.

3.4.6.4 Dielectric Strength

Dielectric material between mutually isolated electrical circuits shall withstand a test voltage of at least 200 VAC at 60 Hz for 60 seconds without exceeding a current of 1.0 mA.

3.4.6.5 Insulation Resistance

The insulation resistance between mutually isolated electrical circuits, excluding harness, shall be at least 2 MegaOhms at a test voltage of at least 500 VDC for 60 seconds minimum.

3.4.6.6 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

3.4.7 Ground Straps, Hinged Joints

Ground straps shall be used to connect hinged joints.

3.4.7.1 Ground Straps, Resistance across Hinged Joints

When ground straps are required across hinged joints, the DC resistance across the hinge shall be less than or equal to 2.5 mΩ DC.

3.4.7.2 Ground Straps, Physical Properties

All ground straps shall have a length-to-width ratio of less than 5 to 1, be made of copper at least

1 mil thick, and still be flexible enough to allow for bending to occur.

3.4.8 Connector and Back-Shell DC Resistance

Component connectors including the EMI back-shells shall be electrically connected to chassis ground of the electronics box with a DC resistance less than or equal to 100 mΩ.

3.5 Signal and Data Interfaces

3.5.1 Reserved

3.5.2 Passive Analog Telemetry

3.5.2.1 Passive Analog Telemetry Interface

If the RWIS is supplied with passive internal temperature sensors, they shall be #311P18-

02A101 thermistor parts, with a resistance of 2252 ohms at 25 degrees C.

3.5.2.2 Reserved

3.5.2.3 Thermistor Resistor Conditioning

Temperature sensors shall be conditioned to provide a voltage range which represents a temperature range that includes a margin of greater than or equal to 5 degrees C beyond the unit qualification or non-operational survival limit, whichever is worse.

3.5.2.4 Reserved

3.5.3 Reserved

3.5.4 Reserved

3.5.5 Reserved

3.5.6 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 to the Panel

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

4.1.1.1 Integration Access

The RWIS shall be able to be integrated onto the spacecraft avionics panel with the reaction wheels already attached to the RWIS.

4.1.1.2 Interface Restrictions

The RWIS interface shall not depend on friction as a method of creating stability.

4.1.2 Electrical Interface

The electrical interface shall be defined in the Electrical Interface Control Document (EICD), which will be developed between the contractor and NASA GSFC.

4.1.3 Reserved

4.2 Mass Properties

4.2.1 Component Masses

a. The total mass of the RWIS shall be less than or equal to 112 kg.

b. The total mass of the RWIS 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 Center of Mass Accuracy

The center of mass of the RWIS shall be determined to within +/- 5% or ±5 mm, whichever is greater, relative to an external reference.

4.2.4 Determination of Moments and Products of Inertia

The final moments of inertia of the RWIS shall be calculated to within 1%.The final products of inertia of the RWIS shall be calculated to within 5%.

4.3 Physical Envelope

The RWIS outside dimensions, including mounting flanges and connectors, shall not exceed the volume envelope defined in the attached drawing 2221056.

4.3.1 Volume Constraint

The RWIS shall comply with the volume constraints as defined in the attached drawing 2221056.

4.3.1.1 Wheel Drive Electronics

The RWIS shall provide space for six wheel drive electronics on the conductive mechanical mounting interface as defined in drawing 2221056.

4.3.1.2 Reaction Wheel Harness

The RWIS shall accommodate routing the harness between the wheel units and the wheel drive electronics with a maximum harness length of 3.048 m (10 feet).

4.3.1.3 Thermal Strap

The RWIS shall accommodate routing the thermal strap between the wheel units and conductive mechanical mounting interface as defined in drawing 2221056.

4.3.2 Reserved

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.

b. The RWIS shall have a flatness of 0.15 mm from any 2 points on the mounting interface over 305 mm

c. The RWIS shall be designed to mount to the RW mounting surface as described in the attached drawing (2221056).

d. The RWIS shall be designed to mount to the spacecraft deck mounting surface as described in the attached drawing (2221056).

4.5 Reserved

4.6 Alignment

The RWIS will be mounted to the spacecraft panel with the Reaction Wheels (x6) mounted on the isolator.

4.6.1 Alignment Knowledge Accuracy: RWIS to RWA Mounting

Knowledge of the alignment between the RWA mounting and the RWIS shall be to 0.7 deg or better in the RWA spin axis.

The mounting surface shall be defined in the MICD.

4.6.2 Alignment Knowledge Accuracy: RWIS Mounting to S/C Panel

The RWIS mounting system shall maintain the mechanical frame within 180 arc-seconds of its original placement with respect to the mounting surface, over environments.

4.6.3 Alignment Stability

Throughout environments, the RWIS shall not shift the RWA spin axes by more than 234 arc-seconds.

5 ENVIRONMENTAL REQUIREMENTS

Environmental design requirements are specified in this section.

The RWIS 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 RWIS 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. This loading shall include the mass of the RWIS and the mass of RWA(s) mounted on the RWIS.

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.

3. For any system that has a mass above 225 kg use 9.5 g’s for the limit load. If 9.5g’s is too high, contact the COR for an extended specification.

Table 5-1 Reaction Wheel Isolator Design Limit Loads

Component Mass (Kg) Limit Load (g)

0.5 35.9

1 35

5 30.1

10 26.5

20 22.4

40 18.2

60 15.9

80 14.3

100 13.2

125 12.1

150 11.2

175 10.6

200 10

>= 225 9.5

5.2 Frequency Requirement

5.2.1 Stowed Fundamental Launch Frequencies

The RWIS plus the reaction wheel shall have a fundamental isolation frequency greater than 55

Hz when hard mounted at its interface. This requirement is for the first mode of the assembly that is not dominated by the reaction wheel’s fundamental rocking modes of 65 Hz. This first isolation mode should be sufficiently separated from the reaction wheel rocking modes to avoid modal coupling. These frequency requirements apply for the launch temperature range.

If the minimum isolation frequency of 55 Hz cannot be attained, then reduced frequencies may be acceptable with approval from the NASA GSFC COR.

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. Failure to meet frequency requirements may result in higher DLL than specified herein.

5.3 Vibration

5.3.1 Sinusoidal Vibration

The RWIS 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 Item Name 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 RWIS shall withstand the random vibration environment in Table 5-3 applied at the interface to the RWIS.

b. The components for random vibration testing shall include the RWIS plus the dummy mass(es) for the RWA.

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. For components weighing more than or equal to 22.7 kg, relief can be provided in accordance with Table 5-4. 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.

Table 5-5 defines minimum workmanship for components weighing less than 45.4 kg. For components weighing more than or equal 45.4 kg, relief can be provided in accordance with Table

5-6. Random vibration specs may be updated based on acoustic analysis.

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 Random Vibration Limit Load Reduction for components Weighing More than or equal to 22.7 kg

ASD Limit Load Reduction for Flight Hardware Weighing

More Than 22.7 kg(1, 2, 3) dB reduction =10 log(W/22.7)

ASD (50 - 800 Hz) = 0.08 x (22.7/W)

(1) W represents weight.

(2) Slopes are maintained at plus and minus 6dB/oct for components weighing up to 59kg.

Above 59 kg, slopes are adjusted to maintain an ASD level of 0.01 g2/Hz at 20 and 2000Hz.

(3) For components weighing more than 182 kg, levels are maintained at the 182 kg level.

Table 5-5 Minimum Workmanship 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

Table 5-6: Minimum Workmanship Level Reduction for components weighing more than or equal to 45.4 kg

ASD Minimum Workmanship Reduction for Flight Hardware

Weighing More Than 45. kg(1, 2, 3) dB reduction =10 log(W/45.4)

ASD (50 - 800 Hz) = 0.04 x (45.4/W)

(1) W represents weight.

(2) Sloped portions of the spectrum are maintained at plus and minus 3/dB/oct.

(3) Workmanship spectrum must be equal to or greater than 0.01 g2/Hz, i.e., for components whose weight is greater than 182kg, the workmanship spectrum is 0.01g2/Hz from 20 to 2000

Hz.

5.4 Shock

The RWIS shall be designed to meet its performance requirements after being subjected to the shock environment in Table 5-7 applied at the RWIS interface to the WFIRST spacecraft structure. Levels defined are acceptance levels. Testing factors are defined in 10.4.2.

Table 5-7 Shock Source Limit Levels

Component

Shock Level

Frequency (Hz) Limit Level

RWIS

100 50 g

100 - 1595 6.5 g

1595 - 10000 980 g

Note: A shock susceptibility and attenuation assessment is to be performed on the RWIS. This assessment can be based on past shock tests or other relevant information. The shock assessment will be used to determine whether the shock environment is low risk for the RWIS.

If the environment is low risk, then the shock test may be…