Attachment_B,_WFIRST-ACS-SPEC-0050_A.pdf

Effective Date: April 18, 2019

National Aeronautics and Space Administration

Goddard Space Flight Center Greenbelt, Maryland

WFIRST-ACS-SPEC-0050, Revision A

Wide Field Infrared Survey Telescope (WFIRST), Code 448

Reaction Wheel Assemblies

Performance Specification

(SPEC)

GSFC WFIRST CMO

April 18, 2019

Released

WFIRST Reaction Wheel Performance Specification WFIRST-ACS-SPEC-0050, Revision A i

Reaction Wheel Assemblies

Performance Specification

(SPEC)

Review/Signature/Approval Page

Prepared by:

Edward Davis

Approved by:

Betsy Forsbacka 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 CIR/CCR Approval Date)

Rev - March 26, 2019 Initial Release per WFIRST-CIR-09310

Rev A April 18, 2019 Per WFIRST-CCR-0003 Added Reaction Wheel

Specification numbers to each of the SPEC "shall" statements to make it easier to track proposals for compliance. Also bolded several of the "shall" words to match the rest of those in the document. Also, Document

No. changed from: WFIRST-SPEC-11751 TO: WFIRST-

ACS-SPEC-0050 due to the migration from Windchill to

TDMS.

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 RESERVED

2 CONTRACT DESCRIPTION

2.1 Reaction Wheel Assembly Description and Definitions

2.1.1 Description

2.1.2 Definitions

3 FUNCTIONAL/PERFORMANCE REQUIREMENTS

3.1 Reaction Wheel Assembly Flight Unit Functional/Performance Requirements

3.1.1 Torque/Momentum

3.1.2 Torque Noise

3.1.3 Critical Frequency

3.1.4 Static Imbalance

3.1.5 Dynamic Imbalance

3.1.6 Cogging Torque

3.1.7 Ripple Torque

3.1.8 Tachometer Sensor Knowledge

3.1.9 Overspeed

3.1.10 Viewing Window

3.1.11 Phasing

3.2 Resource Allocations

3.2.1 Mass Allocation

3.2.2 Nominal Power Allocation

3.2.3 Peak Power Allocation

3.3 Power

3.3.1 Primary (Unregulated) Power Input Requirements

3.3.1.1 Operating Voltage Range

3.3.1.2 Abnormal Voltages

3.3.1.3 Voltage Ripple

3.3.1.4 Voltage Transients

3.3.1.5 Sudden Removal of Power

3.3.1.6 Polarity Reversal Protection

3.3.1.7 Over-Current Protection

3.3.1.8 Primary Power Return Ground

3.3.1.9 Power Wiring Redundancy

3.3.2 Load Induced Noise Requirements

3.3.2.1 Turn-on Current Transients

3.3.2.2 Operational Current Transients (one time)

3.3.2.3 Low Frequency Repetitive Transients (during nominal operation)

3.4 Electrical Grounding

vi

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

3.4.7 RESERVED

3.4.8 Connector and Back-Shell DC Resistance

3.5 Signal and Data Interfaces

3.5.1 Active Analog Telemetry

3.5.1.1 Reserved

3.5.1.2 Active Analog Telemetry Short Circuit Protected

3.5.1.3 Active Analog Telemetry Source and Load Resistance

3.5.1.4 Active Analog Telemetry Voltage Range

3.5.2 Passive Analog Telemetry

3.5.2.1 Passive Analog Telemetry Interface

3.5.2.2 Passive Linearizing Resistor

3.5.2.3 Thermistor Resistor Conditioning

3.5.3 RESERVED

3.5.4 Data and Clock Signals

3.5.4.1 Data and Clock Signal Interface

3.5.4.2 RS-422 Interface

3.5.4.3 Reserved

3.5.4.4 1553 Bus Interface

3.5.4.5 Reserved

3.5.4.6 Reserved

RESERVED

3.6 Operating Modes

3.7 RESERVED

3.8 RESERVED

3.9 Box Watt Density

3.10 Box Heat Sink

4 PHYSICAL REQUIREMENTS

4.1 Interface Documentation

4.1.1 Mechanical Interface

4.1.2 Electrical Interface

4.1.3 Data Interface

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

4.4 Mounting

4.4.1 Box Flatness

vii

4.5 RESERVED

4.6 Spin Axis Alignment

5 ENVIRONMENTAL REQUIREMENTS

5.1 Quasi-Static Acceleration

5.2 Frequency Requirement

5.2.1 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 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 of Spacecraft Monitored Temperature Sensors

5.10 Charged Particle Radiation Requirements

5.10.1 Definitions

5.10.2 Total Ionizing Dose

5.10.2.1 Minimum TID Tolerance for EEE Parts and Materials

5.10.3 Displacement Damage Dose

5.10.4 Single Event Effects

5.10.4.1 Destructive Events (SELs)

5.10.5 All devices shall have Linear Energy Transfer (LET) thresholds for Single Event

Latchup (SEL) greater than 37 MeV-cm2/mg. If between 37 and 75 MeV-cm2/mg there must an evaluation of likelihood & mission impact, and (possibly) circumvention circuitry

6 CLEANLINESS

6.1 Surface Contamination

6.1.1 Surface Contamination Levels at Delivery

6.1.1.1 Particulate Contamination

6.1.1.2 RESERVED

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 Reserved

6.1.2.4 Intentional and Unintentional Vents – Filters

6.1.2.5 Intentional Vents – Pressure Buildup Prevention

viii

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

Connector Specifications External Box Power Connectors

Contact Derating Redundant Contact Derating

7.2.2.2 Signal Segregation

7.2.2.3 Test and Flight Signal Isolation

7.2.2.4 Test Interfaces

Facility-Induced Noise Facility-Induced ESD GSE Malfunction 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

Bulk Resistivity Charge Bleed-Off

7.3 Safety

7.4 Electromagnetic Compatibility

7.4.1 Conducted Emissions

7.4.1.1 Applicability of Conducted Emissions

7.4.1.2 CE101 – Differential Mode Current Emission Limits

7.4.1.3 CE102/03 – Differential Mode Current Emission Limits (RF Frequency) .. 33

7.4.1.4 Common Mode Current Emissions Limits

7.4.1.5 Conductive Emission Measurement Bandwidths

7.4.2 Conducted Susceptibility

7.4.2.1 Applicability of Conducted Susceptibility

7.4.2.2 CS101 – Power Leads, 30 Hz to 150 kHz Limit

7.4.2.3 CS02/CS114 – Power Leads, 150 kHz to 50 MHz Limit

7.4.2.4 CS106 - Transients

7.4.3 Radiated Emissions

7.4.3.1 RE102 - Electric Field Emissions

ix

7.4.4 Radiated Susceptibility

7.4.4.1 RS103 - Electric Field

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

Connector Uniqueness

Connector Facing Connector Keying Accessibility Connector Gender

7.6.2.3 Test Connectors

7.6.2.4 Connector Identification

7.6.2.5 Protection of Unused Test Connectors

7.7 Reliability and Mission Lifetime

7.7.1 Mission Life

7.7.2 Operating Time

7.7.2.1 Total Time

7.7.2.2 Failure Free Time

7.8 Ground Handling

7.8.1 Ground Support Equipment (GSE) Design

7.8.2 Lifting Hardware

7.8.3 Dollies, Stands, Shipping Containers

7.8.4 Reserved

7.8.5 Reserved

7.8.6 Reserved

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 Component Fatigue

8.3 Fracture Control Requirements

8.4 Electronics Box Minimum Vent Area

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

8.6 Joints

8.6.1 Joint Edge Distance

8.6.2 Bonded Joint Allowable

8.6.3 Joint Creep

8.6.4 Fastened Joints

x

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 RESERVED

8.8 RESERVED

9 LOGISTICS

9.1 RESERVED

9.2 RESERVED

9.3 Transportation Equipment

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 Reserved

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 Test

Considerations Prior to the Life Test

Considerations During the Life Test Considerations After the Life Test

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

xi

10.5.4 Frequency Signature Survey

10.5.5 Modal Survey

10.5.6 Sine Vibration

10.5.7 Random Vibration

10.5.8 ReservedRESERVED

10.5.9 Shock

10.5.10 Thermal Vacuum Bake-out

10.5.11 Thermal Vacuum Test

10.5.11.1 Thermal Vacuum Test Parameters

10.5.11.2 Thermal Vacuum Test Profile

10.5.12 RESERVED

10.5.13 RESERVED

10.5.14 RESERVED

10.5.15 EMI/EMC Tests

10.5.15.1 Conducted Emissions Tests

10.5.15.2 Conducted Susceptibility Tests

APPENDIX A ABBREVIATIONS AND ACRONYMS

List of Figures

Figure 5-3: Shock Response Spectra for Assessing Component Test Requirements ............ Error!

Bookmark not defined.

Figure 7-1: CE101/CE03 Differential Mode Current Emission Limits

Figure 7-2: Common Mode Current Emission Limits Figure 8-2 Common Mode Current Emission Limits

Figure 7-3: CS06/106 Transient Waveform Figure 11-1 Thermal Vacuum Profile

List of Tables

Table 5-1 Design Factors of Safety ............................................... Error! Bookmark not defined.

Table 5-2 RWA Design Limit Loads Table 5-3 RWA Sine Vibration Environment Table 6-4 RWA Random Vibration Environment, (22.7 kg, or less) Table 5-6 Qualification Level Shock Response Spectrum

Table 5-7 Flight/Acceptance Level Acoustic Environments ......... Error! Bookmark not defined.

Table 5-8 Protoflight/Qualification Level Acoustic Environments ............. Error! Bookmark not defined.

Table 5-9 Transportation Loads ..................................................... Error! Bookmark not defined.

Table 5-10 Temperature Limits at Reaction Wheel and Reaction Wheel Electronics Box

Mounting Interface Table 7-1 Limited materials for debris casualty area ..................... Error! Bookmark not defined.

Table 7-2 Emission and Susceptibility Requirements Table 7-3 : Receiver Notch RE102 Test Limit Levels (TBR) Table 7-4: RS103 Radiated Susceptibility Levels

Table 10-1 Test Factors and Durations xii

Table 10-2 Test Tolerances

Table 10-3 Thermal Vacuum Test Parameters

1 INTRODUCTION

1.1 Purpose

This specification describes the electrical, mechanical, operating environment, and verification testing requirements for space-qualified, Reaction Wheel Assemblies for a Goddard Space Flight

Center (GSFC) payload, the Wide Field Infrared Survey Telescope.

1.2 Scope

This specification describes the electrical, mechanical, environmental, and verification testing requirements for a space-qualified Reaction Wheel Assemblies for the NASA Goddard Space

Flight Center (GSFC) WFIRST Mission.

1.3 Related Documentation

The latest versions of all documents below should be used. WFIRST documents can be obtained from URL: https://gddms.gsfc.nasa.gov/Windchill/app/.

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

Reaction Wheel Assemblies 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 Reaction Wheel Assemblies Statement of Work (WFIRST-SOW-11752), 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

FAA AC 20-71 Federal Aviation Administration Advisory Circular (AC) 20-71, “Dual Locking Devices on Fasteners".

IEST-STD-CC-1246E Product Cleanliness Levels And Contamination Control Program

MIL-A-8625F Anodic Coatings for Aluminum and Aluminum Alloys

MIL-DTL-5541 Chemical Conversion Coatings on Aluminum and Aluminum

Alloys

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

Division Command/Response Multiplex Data Bus https://gddms.gsfc.nasa.gov/Windchill/app/

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

NASM 33540 Safety Wiring, Safety Cabling, Cotter Pinning, General Practices for

NFPA 70 National Fire Protection Association National Electric Code

SAE AS567 Safety Cable, Safety Wire, Key Washers, and Cotter Pins for

Propulsion Systems, General Practices for Use of

NASA-HDBK-7005 Dynamic Environment Criteria

NASA-STD-5001B Structural Design And Test Factors Of Safety For Spaceflight

Hardware

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-6016 Standard Materials and Processes Requirements for Spacecraft

NASA-STD-7001 Payload Vibroacoustic Test Criteria

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-LIST-11753 WFIRST Reaction Wheel Assembly Deliverable Items List and

Schedule (DILS)

WFIRST-REQT-05819 WFIRST Mission Assurance Requirements

WFIRST-SOW-11752 WFIRST Reaction Wheel Assembly Statement of Work

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 Assembly Description and Definitions

2.1.1 Description

The Reaction Wheel Assembly (RWA) is one of six units used to accumulate disturbance produced spacecraft momentum and thereby keep the spacecraft pointed toward given targets with high accuracy.

2.1.2 Definitions

The Reaction Wheel Assembly (RWA) designates a single device, with an external electronics box, if one is required. Reaction Wheel Assemblies (RWA’s) refers to more than one device.

RW designates just the Reaction Wheel without its accompanied electronics. The rotor designates all the rotating components, flywheel, conical support, shaft, bearings, and rotating part of the motor.

The Reaction Wheel Assembly is an electromechanical flywheel device that is one of six units used to accumulate disturbances that produces spacecraft momentum and thereby keep the spacecraft pointed toward given targets to with high accuracy.

WFIRST Reaction Wheel Assembly Spec WFIRST-ACS-SPEC-0050, Revision A

3 FUNCTIONAL/PERFORMANCE REQUIREMENTS

This section defines the functional and performance requirements for each Reaction Wheel

Assembly as defined in Section 3.1.

3.1 Reaction Wheel Assembly Flight Unit Functional/Performance Requirements

3.1.1 Torque/Momentum

RWA-SPEC-001: At nominal 32 volts the RWA shall provide a constant net acceleration torque of 0.45 Nm or greater from zero momentum to 100 Nms @ 2400 RPM (revolutions per minute) or less.

3.1.2 Torque Noise

RWA-SPEC-002: The torque noise shall be less than 5E-4 Hz

Nm over the frequency range of 0.1 to 1.0 Hz.

3.1.3 Critical Frequency

RWA-SPEC-003: The rotor shall not have a critical (first modal) frequency below 60 Hz.

3.1.4 Static Imbalance

RWA-SPEC-004: The rotor static imbalance shall not exceed 1.14 g-cm.

3.1.5 Dynamic Imbalance

RWA-SPEC-005: The rotor dynamic imbalance shall not exceed 41.54 g-cm2.

3.1.6 Cogging Torque

RWA-SPEC-006: Each RW shall have a cogging torque less than 3 mN-m, RMS.

3.1.7 Ripple Torque

RWA-SPEC-007: Each RW shall have a ripple torque magnitude less than 10% of the commanded torque.

3.1.8 Tachometer Sensor Knowledge

RWA-SPEC-008: As a cost option, for each RW, the tach sensor location shall be calibrated to better than 0.1 degrees.

3.1.9 Overspeed

RWA-SPEC-009: The RWA shall operate properly without stress or degradation over all speed ranges including simultaneous full speed and full torque commands.

RWA-SPEC-010: The RWA shall meet safety requirements through the use of single fault tolerant controls or demonstrate sufficient margin to prevent wheel destruction under any combination of external inputs and conditions. Safety must be maintained under a sustained full torque command at full speed in the presence of a single wheel failure.

3.1.10 Viewing Window

RWA-SPEC-011: Each RWA shall have a viewing port for visual observation of wheel rotation.

3.1.11 Phasing

RWA-SPEC-012: Positive wheel rotation shall be defined as counter-clockwise (CCW) rotation as viewed looking down at the top cover (opposite side from base).

3.2 Resource Allocations

3.2.1 Mass Allocation

RWA-SPEC-013: Total as delivered RWA mass shall be less than or equal to 22 kg per wheel.

This value includes the mass of a separate electronics box, if one is required, but does not include the harness between the wheel and electronics box. Section 4.2.1 contains more requirements on mass properties and individual component mass.

3.2.2 Nominal Power Allocation

RWA-SPEC-014: The RWA shall have a nominal (no torque) power consumption of less than or equal to 50 W.

3.2.3 Peak Power Allocation

RWA-SPEC-015: The RWA shall have a peak power consumption of less than or equal to 200

W when at max torque and maximum wheel speed of 2400 RPM over bus voltage range of 22 V to 35 V .

3.3 Power

3.3.1 Primary (Unregulated) Power Input Requirements

3.3.1.1 Operating Voltage Range

RWA-SPEC-016: The RWA shall be designed to operate over the bus voltage range of +22 to

+35 VDC at their primary power inputs during all normal mission phases and for all expected load conditions (except when turned off).

3.3.1.2 Abnormal Voltages

RWA-SPEC-017: The RWA shall survive without performance degradation after indefinite exposure to an anomalous voltage range of 0 to +40 VDC. This requirement is to be verified by analysis or test of a non-flight unit.

3.3.1.3 Voltage Ripple

RWA-SPEC-018: The RWA shall be designed to meet its performance requirements in the presence of low and RF frequency ripple voltage specified in paragraphs 7.4.2.2 and Error!

Reference source not found., respectively.

3.3.1.4 Voltage Transients

RWA-SPEC-019: The RWA shall be designed to meet its performance requirements in the presence of transient voltages specified in the CS106 requirements in paragraph 0.

3.3.1.5 Sudden Removal of Power

RWA-SPEC-020: The RWA shall meet its performance requirements without degradation after exposure to an abrupt, unannounced removal of power.

3.3.1.6 Polarity Reversal Protection

The RWA should have built-in protection to prevent damage due to polarity reversal at the power inputs (up to -35V), where feasible.

3.3.1.7 Over-Current Protection

RWA-SPEC-021: The RWA should not use non-resetting over-current protection (i.e., fuses) internal to the unit, but if they are required by the contractor to isolate an internal fault, prior approval shall be obtained from the NASA/GSFC Contracting Officer’s Representative (COR).

3.3.1.8 Primary Power Return Ground

RWA-SPEC-022: RWA shall provide a dedicated Primary Power return in the same connector as the primary power.

3.3.1.9 Power Wiring Redundancy

RWA-SPEC-023: The RWA shall provide the redundant power interface.

3.3.2 Load Induced Noise Requirements

3.3.2.1 Turn-on Current Transients

RWA-SPEC-024: The amplitude and duration of in-rush currents, at both initial application of prime power and subsequent component turn-on, shall be per the following:

<10 microseconds: 10 times of max steady state or 10A whichever is larger

Between 10 microseconds and 10 milliseconds: 3 times of max steady state or 3A whichever is larger

>10 milliseconds: not to exceed max steady state

The compliance of this requirement can be demonstrated using a solid-state power switch with the similar turn on characteristics as the flight power control switch.

3.3.2.2 Operational Current Transients (one time)

a. RWA-SPEC-025: The RWA operational current transients shall be less than or equal to

5A above the steady state current for a period of less than 1 millisecond.

b. RWA-SPEC-026: The rate of change of the current shall be less than or equal to 20 milliamperes/microsecond.

3.3.2.3 Low Frequency Repetitive Transients (during nominal operation)

RWA-SPEC-027: Any repetitive current transients, in the frequency range between 1 Hz to 200

Hz, shall not exceed 0.8 A peak-to-peak.

This measurement will be performed with an oscilloscope current probe in time domain.

3.4 Electrical Grounding

3.4.1 Primary Power DC Isolation

RWA-SPEC-028: At the RWA 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

RWA-SPEC-029: 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

RWA-SPEC-030: 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

RWA-SPEC-031: 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 Mechanical Interface Control Document (MICD), the use of a ground strap is necessary.

3.4.6 Ground Strap, Non-Conductive Surface

RWA-SPEC-032: The RWA 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

RWA-SPEC-033: 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.

3.4.7 RESERVED

3.4.8 Connector and Back-Shell DC Resistance

RWA-SPEC-034: Component connectors including the EMI back-shells shall be electrically connected to chassis ground with a DC resistance less than or equal to 100 mΩ.

3.5 Signal and Data Interfaces

RWA-SPEC-035: The RWA shall provide at a minimum, the following telemetry from the

RWA:

Tachometer/Speed/Momentum Data

Spin Direction Data

Motor Current

Motor Power Status

Wheel Bearing/Motor Temperature

Electronics Temperature

3.5.1 Active Analog Telemetry

3.5.1.1 Reserved

3.5.1.2 Active Analog Telemetry Short Circuit Protected

RWA-SPEC-036: The sources of active analog signals shall be short circuit protected.

3.5.1.3 Active Analog Telemetry Source and Load Resistance

RWA-SPEC-037: The source and load resistances (at the source and destination, respectively) shall be documented in the RWA Electrical Interface Control Document (EICD) such that the overall system compatibility of the telemetry signal is reviewed and controlled.

3.5.1.4 Active Analog Telemetry Voltage Range

RWA-SPEC-038: The active analog telemetry voltage range shall be within 0 to +5.12 VDC.

3.5.2 Passive Analog Telemetry

3.5.2.1 Passive Analog Telemetry Interface

RWA-SPEC-039: If the RWA 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 Passive Linearizing Resistor

The linearizing resistor for the thermistors, if required, will be located with the temperature sensor conditioning circuit in the Spacecraft avionics.

3.5.2.3 Thermistor Resistor Conditioning

Temperature sensors will 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.

3.5.3 RESERVED

3.5.4 Data and Clock Signals

3.5.4.1 Data and Clock Signal Interface

3.5.4.2 RS-422 Interface

RWA-SPEC-040: The RS-422 interface circuit and line termination shall be documented in the

RWA Electrical ICD, using ANSI/TIA/EIA-422-B, Electrical Characteristics of Balanced

Voltage Digital Interface Circuits as a guide.

Signals that use RS-422 interface should be designed to minimize the chassis ground current loop. The chassis current due to the line imbalance of the 3.3V CMOS interface should be less than 30 micro-amps.

3.5.4.3 Reserved

3.5.4.4 1553 Bus Interface

RWA-SPEC-041: Any 1553 Bus interface shall be designed per MIL-STD-1553B, Digital Time

Division Command/Response Multiplex Data Bus.

3.5.4.5 Reserved

3.5.4.6 Reserved

RESERVED

3.6 Operating Modes

RWA-SPEC-042: The RWA shall support three operating modes

1. Off

2. Electronics Powered

3. Motor and Electronics Powered

3.7 RESERVED

3.8 RESERVED

3.9 Box Watt Density

RWA-SPEC-043: The maximum watt density of electronics boxes shall not exceed 1.55 W/cm2 on the box baseplate, analyzed at least every 2.5cm.

3.10 Box Heat Sink

RWA-SPEC-044: No less than 95% of electronic box generated heat shall be dissipated at the baseplate.

4 PHYSICAL REQUIREMENTS

4.1 Interface Documentation

RWA-SPEC-045: The contractor shall use metric units when interfacing with NASA GSFC including any drawings, documents, models, except for the following cases:

Heritage Component: Components that has been previously qualified, or of similar design heritage, may be specified in English units where use of metric equivalents would lead to additional cost to the program.

Fasteners: Although bolt patterns will be defined using metric dimensioning, use of

English fasteners (with hole dimensioning and tolerancing) is permitted.

Angular Measurement: Angular measurement may be expressed in degree of arc or in an appropriate subdivision of degree of arc such as second of arc (arc-sec) when advantageous to application.

4.1.1 Mechanical Interface

RWA-SPEC-046: The mounting interface shall be defined in the Mechanical Interface Control

Drawing (MICD), which will be developed by the contractor.

4.1.2 Electrical Interface

RWA-SPEC-047: The electrical interface shall be defined in the Electrical Interface Control

Document (EICD), which will be developed by the contractor.

4.1.3 Data Interface

RWA-SPEC-048: The data interface shall be defined in the Data Interface Control Document, which will be developed by the contractor.

4.2 Mass Properties

4.2.1 Component Masses

a. RWA-SPEC-049: The total mass of the RWA (excluding any interconnect harness if the

RW and RWE are separate) shall be less than or equal to 22 kg.

b. RWA-SPEC-050: The mass of each RWA component shall be measured to within 25 g.

4.2.2 Center of Mass Location

RWA-SPEC-051: The contractor shall define the center of mass in the Mechanical ICD.

4.2.3 Center of Mass Accuracy

RWA-SPEC-052: The center of mass of the RWA components shall be determined to within

±10 mm relative to an external reference.

4.2.4 Determination of Moments and Products of Inertia

RWA-SPEC-053: The final moments of inertia of the RWA shall be calculated to within 1%.

RWA-SPEC-054: The final products of inertia of the RWA shall be calculated to within 5%.

4.3 Physical Envelope

RWA-SPEC-055: The RW shall occupy a space of less than:

Height: 190 mm

Diameter: 500 mm

RWA-SPEC-056: If the RWA contains a separate electronics box its maximum dimensions shall be ≤240 mm length, by 180 mm width, and 130 mm height. Length and width determine mounting base, and height and length determine location of connectors as defined in the Mechanical ICD.

4.4 Mounting

RWA-SPEC-057: The RWA will be hard-mounted on a mechanical surface of the Reaction

Wheel Isolator system. Proper fit/alignment of the RWA to the structure shall be inherent in its design, fabrication, and assembly to the structure, through the use of close dimensional control in the location of mounting holes and the use of correct mounting hardware. If a separate electronics box is required, its mounting tolerance is not critical.

RWA-SPEC-058: The mounting interfaces of both shall be defined in the Interface Control

Document.

4.4.1 Box Flatness

RWA-SPEC-059: Electronics boxes shall be flat to within 0.15mm over 305mm.

4.5 RESERVED

4.6 Spin Axis Alignment

RWA-SPEC-060: The spin axis shall be normal to the mounting surface to within 5 arcminutes.

5 ENVIRONMENTAL REQUIREMENTS

Environmental design requirements for the spacecraft components are specified in this section.

RWA-SPEC-061: The RWA 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.

RWA-SPEC-062: The RWA 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. The design loads shown below will be updated based on the results of coupled loads analysis.

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.

3. DLLs are intended to cover only the low frequency launch environment and must be used in conjunction with the random vibration environments to assess structural margins.

Table 5-1 RWA 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

5.2 Frequency Requirement

5.2.1 Fundamental Launch Frequencies

RWA-SPEC-063: The RWA shall have a fundamental frequency greater than 60 Hz when hard mounted at its interface.

RWA-SPEC-064: The external electronics-box, if included, shall have a fundamental frequency greater than 100 Hz when hard mounted at its interface.

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

2. RWA-SPEC-065: A test correlated FEM shall be supplied 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

RWA-SPEC-066: The RWA shall withstand the sinusoidal vibration levels defined in Table 5-2.

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

2. The sine sweep vibration levels shown in Table 5-2 are defined at the interface of the element/subsystem. These preliminary values are intended to minimize risk of under-designing hardware and are not necessarily intended for test.

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

Design Limit Load outlined in section 5.1.

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

5. 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.

6. 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 RWA 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. RWA-SPEC-067: The RWA components shall withstand the random vibration environment in Table 5-3 applied at the interfaces to the RWA component.

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 22.7 kg, relief can be provided in accordance with

Error! Reference source not found.. Error! Reference source not found. defines minimum workmanship for components weighing less than 45.4 kg. For components weighing more than

45.4 kg, relief can be provided in accordance with Error! Reference source not found.. 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 RWA Random Vibration Environment, (22.7 kg, or less)

Frequency ASD Level (g2/Hz)

(Hz) Qualification Acceptance

20-50

50-800

800-2000

0.026

+6 dB/oct

0.16

-6 dB/oct

0.026

0.013

+6 dB/oct

0.08

-6 dB/oct

0.013

Overall 14.1 Grms 10.0 Grms

This environment will be updated with random vibration analysis. Note for lightweight RWA, the highest design loads may be from this random vibration environment.

b. RWA-SPEC-068: The contractor shall provide random vibration analysis along with static loads analysis. Please see NASA-HDBK-7005 and NASA-STD-7001 for more information.

During the test, the test input level will be reduced (notched) at critical frequencies, if required, to limit the random vibration loads and/or acceleration responses to 3 dB above design limit levels.

c. RWA-SPEC-069: Notching shall be limited to -12 dB of the original input and to a bandwidth of less than 100 Hz to limit the random vibration responses to 3dB above design limit levels. Notching beyond these limits will require NASA/GSFC COR approval.

5.4 Shock

a. RWA-SPEC-070: The RWA shall be designed to meet its performance requirements after being subjected to the shock environment in Table 5-4, applied at the RWA interface to the RW Isolator system.

Table 5-4 Qualification Level Shock Response Spectrum

Internal

Source

Internal

Source

Freq (Hz) Limit Level 100 34 g

100 - 2150 6.5 dB/oct 2150 - 10000 919 g

RWA-SPEC-071: A shock susceptibility and attenuation assessment shall be performed on the RWA, based on its susceptibility to the shock environment provided in Table 5-6.

RWA-SPEC-072: The results of this assessment shall be provided to the NASA/GSFC

COR for review, and the COR will decide whether a shock test can be deferred to the observatory level.

b. RWA-SPEC-073: Analysis supporting this conclusion (i.e. deferral of shock testing) shall be provided to the NASA/GSFC COR for review.

c. RWA-SPEC-074: Any component determined to be susceptible to the shock environment shall have shock testing performed at the component level (preferably on a qualification unit).

d. RWA-SPEC-075: Component self-induced shock testing shall be accomplished by two actuations at the component level for each self-induced shock source (in order to account for the scatter associated with the actuation of the device) for the first flight unit, and a single actuation on subsequent units.

5.5 Reserved

5.6 Pressure

5.6.1 Operating Pressure Range

RWA-SPEC-076: The RWA 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

RWA-SPEC-077: The RWA shall be designed to meet all performance requirements after exposure to a maximum depressurization rate of 5033 Pa/sec experienced during launch and ascent.

Note: Electronic boxes which meet the requirements of Electronic Box Minimum Vent Area of

Section 8.4 may waive maximum depressurization rate analysis.

5.6.3 RESERVED

5.7 On-Orbit Dynamic Environment

RWA-SPEC-078: The RWA shall meet all requirements while subjected to loads resulting from the following rate and accelerations:

Angular acceleration = 4.5 E-3 rad/sec^2, per axis

Angular velocity = 3.5 E-3 rad/sec, per axis

Lateral acceleration = 0.0035 m/sec^2, per axis

Axial acceleration = 0.045 m/sec^2, thrust direction (+X)

1. Angular rates and accelerations are about the Observatory CG

2. These loads are to be combined with other loads (thermal, etc.).

3. Angular velocity is applied so that centripetal force adds to the lateral or axial load applied.

5.8 Ground Environments

a. RWA-SPEC-079: The RWA 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%.

b. RWA-SPEC-080: After being powered “OFF” and exposed to air temperatures of +5 to

+30 degrees C and relative humidity of 0 to 70%, the RWA shall meet all of its performance requirements.

5.9 Thermal Requirements

5.9.1 Flight Interface Design Temperature Limits

a. RWA-SPEC-081: When powered “OFF”, the RWA shall be capable of surviving indefinitely when its temperatures are within the survival limits shown in Table 5-5 without damage or permanent performance degradation.

b. Cold-start capability will be demonstrated at the end of survival soak. Performance will not be assessed until operational temperatures are met.

c. RWA-SPEC-082: The RWA shall meet all performance requirements when powered

“ON” anywhere within the Operational and Protoflight/Qualification limits shown in

Table 5-5.

d. RWA-SPEC-083: The RWA shall demonstrate turn on at the Minimum and Maximum

Protoflight/Qualification (in spec) limits shown in Table 5-5.

Table 5-5 Temperature Limits at Reaction Wheel and Reaction Wheel Electronics Box

Mounting Interface

Minimum Temperature (ºC) Maximum Temperature (ºC)

Operational (In Spec) -20 +60

Protoflight/Qualification (In

Spec)

-30 +70

Survival (Unpowered) -30 +70

5.9.2 Allocation of Spacecraft Monitored Temperature Sensors

RWA-SPEC-084: Each Reaction Wheel (RW) unit shall be outfitted with 2 temperature sensors

(thermistors) external to the RW, and 1 sensor (thermistor) internal to the RW.

RWA-SPEC-085: Each Reaction Wheel Electronics (RWE) unit shall be outfitted with 2 temperature sensors (thermistors) internal to the WDE. The spacecraft will monitor temperature sensors on the panel adjacent the WDEs.

5.10 Charged Particle Radiation Requirements

Components containing electronic parts will be exposed to a natural space radiation environment that consists of: (1) trapped particles which include electrons, protons, and heavier ions; (2) particles from solar events (coronal mass ejections and flares); and (3) galactic cosmic ray particles.

5.10.1 Definitions

Total Ionizing Dose (TID) - the mean energy deposited by ionizing radiation in a device region divided by the mass of the region. This is often given in units of rad(Si), where 1 rad(Si) = 100 erg deposited per gram of silicon.

Radiation Design Margin (RDM) - the ratio of the derated hardness capability of the part to the estimated dose at the part location.

Enhanced Low Dose Rate Sensitivity (ELDRS) - used to refer to a part that shows enhanced radiation-induced damage at dose rates below 50 rad(Si)/s. The enhancement is the result of true dose rate effects.

Displacement Damage Dose (DDD) - the mean energy deposited by ionizing radiation in a device region that goes into atomic displacements divided by the mass of the region. There is no official unit for DDD. One such unit is MeV/g

Non-Ionizing Energy Loss (NIEL) - a measure of the rate of energy loss due to atomic displacements as a particle traverses a material.

Single Event Effect (SEE) - any measurable effect to a circuit due to an ion strike. This includes, but is not limited to, single event upsets (SEUs), single event transients (SETs), single hard errors (SHEs), single event latchups (SELs), single event functional interrupts (SEFIs), single event burnouts (SEBs), single event gate ruptures (SEGRs), and single event dielectric ruptures

(SEDRs).

Single Event Upset (SEU) - a change of state or transient induced by an energetic particle such as a cosmic ray or proton in a device. This may occur in digital or analog, circuits and may have effects in surrounding interface circuitry (a subset known as SETs). These are “soft” errors in that a reset or rewriting of the device will usually return the device to normal behavior thereafter.

The general goal for non-destructive events such as SEUs or SETs is not to avoid them completely, but to manage their impact through robust circuit design, automatic correction, and/or operational activities based on knowledge from ground radiation tests and circuit/system analysis.

Single Hard Error (SHE) - a SEU that causes a permanent change to the operation of a device.

An example is a stuck bit in a memory device.

Multiple Bit Upset (MBU) - an event induced by a single energetic particle such as a cosmic ray or proton that causes multiple upsets or transients during its path through a device or system in a single logical structure (ex., 2 bits affected in a single 16-bit word).

Single Event Functional Interrupt (SEFI) - a condition that causes loss of device functionality due to a single event in a control portion of a device. It generally requires a device reset or a re-initialization to resume normal device operations, but, for some devices, a power cycle is necessary to resume normal device operations. The general goal for non-destructive events such as SEFI is to avoid them, however, managing their impact through robust circuit design, automatic correction, and/or operational activities may be considered.

Single Event Latchup (SEL) - a condition that may cause device failure due to a single event induced high current state. A SEL may or may not cause permanent device damage, but requires power cycling of the device to resume normal device operations. In addition, susceptible devices have the concern for latent damage (device does not fail from the immediate single particle event, but reliability is degraded and premature failure may occur).

Single Event Burnout (SEB) - a condition that can cause device destruction due to a high current state in a power transistor.

Single Event Gate Rupture (SEGR) - a single ion induced condition in power MOSFETs that may result in the formation of a conducting path in the gate oxide.

Linear Energy Transfer (LET) - a measure of the energy deposited per unit length as an energetic particle travels through a material. The common LET unit is MeV*cm2/milligram (mg) of material.

Threshold LET (LETth) - the maximum LET at which no SEE is observed at a particle fluence of

107 ions/cm2.

5.10.2 Total Ionizing Dose

5.10.2.1 Minimum TID Tolerance for EEE Parts and Materials

RWA-SPEC-086: All EEE parts shall tolerate a minimum Total Ionizing Dose (TID) of 22.3 krad (Si).

This value is based on radiation analysis data in the WFIRST radiation analysis using the Total

Ionizing Dose 95% confidence level curve with an equivalent of 2.54 mm (100 mils) of Aluminum shielding and factoring for extended mission considerations as seen below in Table 5-10.

Table 5-6 Dose (including x2 margin) as a Function of Shielding

Aluminum Shield

Thickness

(krad-

Si)

C = 95% (mm): (mils): (g/cm2):

0.026 1.024 7.017E-03 1.03E+03

0.033 1.299 8.906E-03 8.46E+02

0.041 1.614 1.107E-02 7.24E+02

0.052 2.047 1.403E-02 6.06E+02

0.063 2.480 1.700E-02 5.25E+02

0.082 3.228 2.213E-02 4.43E+02

0.100 3.937 2.699E-02 3.75E+02

0.126 4.961 3.401E-02 3.13E+02

0.159 6.260 4.291E-02 2.63E+02

0.200 7.874 5.398E-02 2.24E+02

0.256 10.079 6.909E-02 1.82E+02

0.319 12.559 8.609E-02 1.53E+02

0.404 15.906 1.090E-01 1.26E+02

0.508 20.000 1.371E-01 1.02E+02

0.637 25.079 1.719E-01 8.58E+01

0.804 31.654 2.170E-01 6.83E+01

1.012 39.843 2.731E-01 5.47E+01

1.275 50.197 3.441E-01 4.51E+01

1.604 63.150 4.329E-01 3.57E+01

2.019 79.488 5.449E-01 2.84E+01

2.542 100.079 6.861E-01 2.23E+01

3.198 125.906 8.631E-01 1.75E+01

4.024 158.425 1.086E+00 1.34E+01

5.069 199.567 1.368E+00 1.03E+01

6.380 251.181 1.722E+00 7.75E+00

8.033 316.260 2.168E+00 5.85E+00

10.112 398.110 2.729E+00 4.35E+00

12.731 501.220 3.436E+00 3.16E+00

16.025 630.906 4.325E+00 2.31E+00

20.175 794.291 5.445E+00 1.65E+00

25.399 999.961 6.855E+00 1.18E+00

5.10.3 Displacement Damage Dose

The displacement damage dose or non-ionizing dose is the mean energy deposited in a material that goes into atomic displacements divided by the mass of the material. It is analogous to the ionizing dose except that the energy considered produces displacements in a semiconductor lattice.

RWA-SPEC-087: The silicon and gallium arsenide EEE parts susceptible to displacement damage degradation shall be able to tolerate a minimum DDD of 5.84 x 108 MeV/g (or a 10

MeV equivalent proton fluence of 7.40×1010 cm-2 ) and 4.81 x 108 MeV/g (or a 10 MeV equivalent proton fluence of 7.30×1010 cm-2 ), respectively.

This meets the DDD exposure for a 5.25-year mission with orbit about the Sun-Earth second

Lagrange point, L2, at the 95% confidence level and nominal 100 mils of aluminum shielding.

Dose

(mm): (mils): (g/cm2): (krad-Si):

0.002935 0.115532 0.000792 7.98E+03

0.004039 0.159003 0.00109 5.56E+03

0.005521 0.217353 0.00149 3.96E+03

0.007596 0.299042 0.00205 2.94E+03

0.010412 0.409907 0.00281 2.28E+03

0.014302 0.563075 0.00386 1.74E+03

0.019601 0.771675 0.00529 1.34E+03

0.0269 1.059047 0.00726 1.05E+03

0.036941 1.454366 0.00997 8.06E+02

0.050761 1.998477 0.0137 6.12E+02

0.069658 2.742436 0.0188 4.54E+02

0.095595 3.763556 0.0258 3.38E+02

0.131165 5.163948 0.0354 2.58E+02

0.180073 7.089488 0.0486 1.91E+02

0.246767 9.715225 0.0666 1.38E+02

0.339027 13.34749 0.0915 9.40E+01

0.466857 18.38015 0.126 6.32E+01

0.637297 25.09037 0.172 4.16E+01

0.87443 34.42632 0.236 2.66E+01

1.204194 47.40913 0.325 1.70E+01

1.64882 64.91404 0.445 1.10E+01

2.263885 89.12916 0.611 7.28E+00

3.108674 122.3885 0.839 5.40E+00

4.260995 167.7554 1.15 4.14E+00

5.854237 230.4813 1.58 3.22E+00

8.040313 316.5471 2.17 2.54E+00

11.04154 434.7053 2.98 2.06E+00

15.15432 596.6257 4.09 1.65E+00

20.78625 818.3545 5.61 1.32E+00

Aluminum Shield Thickness

5.10.4 Single Event Effects

a. RWA-SPEC-088: The RWA shall be designed to avoid or tolerate errors due to non-destructive Single Event Effects (SEE).

b. RWA-SPEC-089: The integral galactic cosmic ray and solar heavy ion linear energy transfer spectrum in

c. Figure 5-1 ( d.

e. Table 5-7) and Figure 5-2 (Table 5-8), respectively, shall be used for prediction of heavy ion-induced single-event effects.

Note: CREME96 may be used to generate the environments, provided that the

CREME96 calculations are shown to match the referenced figures and tables.

f. RWA-SPEC-090: The RWA shall meet the WFIRST Observatory performance requirements for the background environment.

g. RWA-SPEC-091: The RWA shall survive the peak proton flux of a worst-case solar flare.

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

0.1 1 10 100

F lu x

L E

T

/c m /d a y

LET (MeV-cm2/mg)

WFIRST

Galactic Cosmic Ray LET Spectra

Solar Minimum

Solar Maximum

Figure 5-1 Integral LET Spectra for Galactic Cosmic Ray Ions for 100 mils of Aluminum

Shielding

Table 5-7 Integral LET Spectra for Galactic Cosmic Ray Ions

LET

(MeV-cm2/mg):

Flux > LET (#/cm2/day): LET

(MeV-cm2/mg):

Flux > LET (#/cm2/day):

Solar

Maximum

Solar

Minimum

Solar

Maximum

Solar

Minimum

1.01E-01 8.74E+02 2.23E+03 7.78E-01 8.95E+01 2.27E+02

1.15E-01 6.22E+02 1.76E+03 8.84E-01 8.11E+01 2.02E+02

1.30E-01 5.15E+02 1.49E+03 1.00E+00 7.22E+01 1.79E+02

1.48E-01 4.62E+02 1.32E+03 1.14E+00 6.41E+01 1.57E+02

1.68E-01 4.19E+02 1.17E+03 1.30E+00 2.66E+01 9.43E+01

1.91E-01 3.68E+02 1.02E+03 1.47E+00 1.52E+01 6.73E+01

2.17E-01 3.39E+02 9.16E+02 1.67E+00 1.00E+01 5.04E+01

2.47E-01 2.93E+02 7.97E+02 1.90E+00 6.91E+00 3.83E+01

2.80E-01 2.50E+02 6.86E+02 2.16E+00 4.86E+00 2.92E+01

3.18E-01 2.23E+02 6.03E+02 2.45E+00 3.46E+00 2.23E+01

3.62E-01 1.71E+02 4.89E+02 2.79E+00 2.49E+00 1.70E+01

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

0.1 1 10 100

F lu x

L E

T

/c m /d a y

LET (MeV-cm2/mg)

WFIRST

Galactic Cosmic Ray LET Spectra

Solar Minimum

Solar Maximum

4.11E-01 1.49E+02 4.23E+02 3.16E+00 1.81E+00 1.29E+01

4.67E-01 1.31E+02 3.66E+02 3.59E+00 1.32E+00 9.77E+00

5.30E-01 1.20E+02…