Attachment_B,_WFIRST-PROP-SPEC-0052-.pdf

Effective Date: May 30, 2019

National Aeronautics and Space Administration

Goddard Space Flight Center Greenbelt, Maryland

WFIRST-PROP-SPEC-0052, Revision -

Wide Field Infrared Survey Telescope (WFIRST), Code 448

Latch Valve Specification

GSFC WFIRST CMO

June 10, 2019

Released

WFIRST Latch Valve Spec WFIRST-PROP-SPEC-0052, Revision -ii

Latch Valve Specification

Review/Signature/Approval Page

Prepared by:

Dina Hoffman

Approved by:

Betsy Forsbacka 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 - May 30, 2019 Initial Release per WFIRST-CCR-0004 v

Table of TBDs/TBRs/TBSs [optional]

Item No. Location Summary Individual/

Organization

Actionee

Due Date vi

Table of Contents

1 INTRODUCTION

1.1 Purpose

1.2 Scope

1.3 Related Documentation

1.3.1 Applicable Documents [and Forms]

2 CONTRACT DESCRIPTION

2.1 Latch Valve Description

3 FUNCTIONAL/PERFORMANCE REQUIREMENTS

3.1 Latch Valve Flight Unit Functional/Performance Requirements

3.1.1 Pressure

3.1.1.1 Maximum Expected Operating Pressure

3.1.1.2 Maximum Pressure Exposure

3.1.1.3 Proof Pressure

3.1.1.4 Burst Pressure

3.1.1.5 Interface Tube Design Pressure

Proof Pressure

Burst Pressure

3.1.1.6 Flow Rate and Pressure Drop

3.1.1.7 Back Relief Pressure

3.1.2 Leakage

3.1.2.1 Internal Leakage

3.1.2.2 External Leakage

3.1.3 Response Time

3.1.4 Position Indication

3.1.5 Coil Redundancy

3.1.6 Cycles

3.1.7 Filtration

3.2 Resource Allocations

3.2.1 Mass 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 Sudden Removal of Power

3.3.1.4 Operational Current Transients (one time)

3.4 Electrical Grounding

3.4.1 Primary Power DC Isolation

3.4.2 Mechanical Contact Resistance

3.4.3 Mating Method

4 PHYSICAL REQUIREMENTS

4.1 Interface Documentation

4.1.1 Mechanical Interface

4.1.2 Electrical Interface

vii

4.2 Physical Envelope

4.3 Mounting

4.3.1 Fastener Accessibility

4.3.2 Interface Tube

4.3.2.1 Dimensions

4.3.2.2 Material

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 Pressure

5.5.1 Operating Pressure Range

5.6 Ground Environments

5.7 Thermal Requirements

5.7.1 Flight Interface Design Temperature Limits

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

6.1.1.4 External Cleanliness

6.1.1.5 Internal Cleanliness

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

6.1.3 Cleanability

6.1.3.1 Cleanability – Sensitive Surfaces

6.1.3.2 Cleanability – Sensitive Surface Cleaning Methods

6.1.4 Transportation Cleanliness

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

7.1.2.2 Material Cleanliness

7.2 Electrical

7.2.1 Coil Resistance

viii

7.2.2 Interface Requirements

7.2.3 Wires

7.2.3.1 Wire Specifications

7.2.3.2 Minimum Wire Size

7.2.3.3 Wire Derating

7.2.3.4 Wire Composition

7.2.3.5 Wire Twists

7.2.4 Connector Selection

7.2.4.1 Connector Specifications

7.2.4.2 External Box Power Connectors

7.2.4.3 Contact Derating

7.2.5 Dielectric Structures

7.2.5.1 Bulk Resistivity

7.2.5.2 Charge Bleed-Off

7.3 Identification and Marking

7.4 Workmanship

7.4.1 Workmanship Standards

7.4.2 Welding

7.5 Reliability and Lifetime

7.5.1 Mission Life

7.5.2 Shelf Life

7.5.3 GSE Cleanliness

7.6 Interchangeability

8 MECHANICAL DESIGN REQUIREMENTS

8.1 Mechanical Factors of Safety

8.2 Fracture Control Requirements

8.3 Fastening Systems

8.3.1 Fastener Locking

8.3.2 Fastened Joint Margin of Safety

8.3.3 Installation Torque Documentation

8.3.4 Seal Analysis

8.3.5 Critical Fasteners

8.4 Mechanism Design

8.4.1 Torque Margin Formula

8.4.2 Mechanism Stall Performance

8.4.3 Deployables and Mechanism Jamming

8.4.3.1 Springs Failure Tolerant

8.4.3.2 Tolerancing

8.4.4 Switches

8.4.4.1 Microswitches

8.4.5 Lubricants

8.4.5.1 Lubricant Life Analysis

8.4.5.2 Dry Lubricants

9 VERIFICATION REQUIREMENTS

9.1 Verification Methods

9.1.1 Inspection

ix

9.1.2 Analysis

9.1.3 Test

9.2 Inspection Requirements

9.2.1 Visual Inspection

9.2.2 Physical Measurement

9.2.3 Documentation Search

9.3 Analysis Requirements

9.4 Test Requirements

9.4.1 Definitions

9.4.2 Test Factors

9.4.3 Thermal Cycle Prior to Structural Testing

9.4.4 Proof Testing Factors

9.4.5 Test Tolerances

9.4.6 Test Restrictions

9.4.6.1 Failure During Tests

9.4.6.2 Modification of Hardware

9.4.6.3 External Adjustment

9.4.6.4 Re-Test Requirements

9.5 Required Tests

9.5.1 Mass Properties Measurement

9.5.2 Static Loads/Strength Test

9.5.2.1 Sine Burst

9.5.2.2 Static Pull

9.5.3 Sine Vibration

9.5.4 Random Vibration

9.5.5 Shock

9.5.6 Thermal Vacuum Bake-out

9.5.7 Thermal Vacuum Test

9.5.7.1 Thermal Vacuum Test Parameters

9.5.8 Thermal Vacuum Test Profile

9.5.8.1 Thermal Cycling Testing – Ambient

9.5.9 Continuity/Hi-Pot Tests

9.5.10 Proof Pressure Test

9.5.11 Flow/Pressure Drop Test

9.5.12 Back Pressure Relief Test

9.5.13 Internal Leakage Test

9.5.14 External Leakage Test

9.5.15 Response Time Test

APPENDIX A ABBREVIATIONS AND ACRONYMS

x

List of Figures

Figure 1. Thermal Vacuum Profile

List of Tables

Table 1. Latch Valve Design Limit Loads Table 2. Latch Valve Generic Sine Vibration Environment Table 3. Latch Valve Random Vibration Environment, (22.7kg, or less) Table 4. Minimum Workmanship ASD Level for Components Weighing Less than 45.4 kg

Table 5. Internal and External Shock Source Limit Levels Table 6. Temperature Limits at Box Mounting Interface Table 7. Design Factors of Safety

Table 8. Torque Margin Calculation Factors of Safety Table 9. Test Factors and Durations Table 10. Proof Test Factors

Table 11. Test Tolerances Table 12. 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 latch valve.

1.2 Scope

This specification describes the electrical, mechanical, environmental, and verification testing requirements for space-qualified latch valves for the NASA Goddard Space Flight Center

(GSFC) WFIRST Mission. The WFIRST Propulsion Subsystem requires eight (8) latch valves.

1.3 Related Documentation

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

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 latch valve 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 latch valve Statement of Work (WFIRST-PROP-SOW-0016), 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

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

Corrosion Cracking Resistance in Sodium Chloride

Environments https://ipdtdms.gsfc.nasa.gov/

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-6016 Standard Materials and Processes Requirements for Spacecraft

NASA-STD-8719.24 NASA Expendable Launch Vehicle Payload Safety

Requirements

NASA-STD-8739.4 Workmanship Standard for Crimping, Interconnecting Cables, Harnesses, and Wiring

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-PROP-LIST-

WFIRST Latch Valve Deliverable Items List and Schedule

(DILS)

WFIRST-PROP-SOW-

WFIRST Latch Valve Statement of Work

AMS5569 REV. B Steel, Corrosion and Heat Resistant, Seamless and Welded

Hydraulic Tubing 19Cr - 9.5Ni - 0.03C max Cold Drawn, 1/8

Hard Temper

AMS5647 REV. K Steel, Corrosion-Resistant, Bars, Wire, Forgings, Mechanical

Tubing, and Rings 19Cr - 9.5Ni Solution Heat Treated

2 CONTRACT DESCRIPTION

2.1 Latch Valve Description

The propulsion subsystem latch valve is a latching type device that regulates the supply of propellant by electromagnetically opening and closing the valve. Power is only required for valve open, valve close, and position indicator. Once either opened or closed, the latch valve shall maintain its position without applying further power.

The WFIRST Propulsion Subsystem shall use eight (8) latch valves.

Each latch valve design shall either have been qualified for space flight or the vendor shall designate one (1) unit as protoflight to test at the qualification levels listed in this document.

Latch valve designs that have been qualified previously shall include qualification documentation as described in the Latch Valve SOW WFIRST-PROP-SOW-0016.

3 FUNCTIONAL/PERFORMANCE REQUIREMENTS

This section defines the functional and performance requirements for the latch valve as defined in Section 3.1.

3.1 Latch Valve Flight Unit Functional/Performance Requirements

3.1.1 Pressure

3.1.1.1 Maximum Expected Operating Pressure

The latch valve shall have a Maximum Expected Operating Pressure (MEOP) value of 400 psia.

Maximum expected operating pressure is the maximum pressure to which the latch valve is subjected under nominal operating conditions.

3.1.1.2 Maximum Pressure Exposure

Due to back pressure relief, the latch valve may encounter pressure as high as 550 psia. The latch valve shall withstand, in both open and closed latching positions, the maximum pressure exposure without increased leakage or damage

3.1.1.3 Proof Pressure

The latch valve shall be capable of withstanding, in both open and closed latching positions, proof pressures of no less than 825 psia without permanent physical deformation, yielding, or cracking. This is (MEOP + back pressure relief) x 1.5 proof factor.

3.1.1.4 Burst Pressure

Burst pressure of the propellant latch valve shall be at least 1375 psia. Burst pressure is the pressure (2.5 x maximum pressure exposure) that, once applied to the latch valve, results in exceeding its ultimate strength.

3.1.1.5 Interface Tube Design Pressure

Proof Pressure

The interface tube design proof pressure capability shall be at least 825 psia. This is (MEOP + back pressure relief) x 1.5 proof factor.

Burst Pressure

The interface tube design burst pressure capability shall be at least 2200 psia. This is a burst pressure capability of 4.0 x maximum pressure exposure.

3.1.1.6 Flow Rate and Pressure Drop

The latch valves shall have a maximum pressure drop of 10 psid at 0.0408 kg/s for hydrazine

(0.0406 kg/s for water). These requirements shall apply for when the inlet filters are clean.

Pressure drop and flow rate shall be quantified for the case of filtration capacity being reached.

3.1.1.7 Back Relief Pressure

The latch valve shall have a back relief pressure less than or equal to 150 psid. Back relief pressure is the pressure differential between the downstream and the upstream fluids required to force the latch valve open to relieve downstream pressure.

3.1.2 Leakage

3.1.2.1 Internal Leakage

Leakage past the closed latch valve shall be no greater than 5 standard cubic centimeters per hour (scch) of Gaseous Helium (GHe) with the valve’s inlet at MEOP and the valve’s outlet at atmospheric pressure.

3.1.2.2 External Leakage

Each latch valve shall demonstrate a total external leakage rate of no greater than 1 x 10-6 standard cubic centimeters per second (sccs) of GHe at the valve’s MEOP over the operational temperature range. Leakage shall be verified by test at ambient temperature. The test data will be used to analytically extrapolate the leakage rate at the maximum and minimum temperature limits by NASA to verify the maximum leakage rate.

3.1.3 Response Time

The opening and closing response time for each latch valve shall be less than 120 ms at the

MEOP given in Section 3.1.1.1 throughout the input voltage range specified in Section 3.3.

3.1.4 Position Indication

The latch valve shall have at a minimum a single position indicator which gives positive confirmation that the valve is either open or closed.

The position indicator shall consist of closed, open, and common leads.

3.1.5 Coil Redundancy

The latch valve shall have redundant drive coils for opening and closing. Each coil (primary open, primary close, redundant open, and redundant close) shall include independent power lines.

3.1.6 Cycles

The latch valve shall be qualified for at least 2000 functional cycles while maintaining all performance requirements. One cycle is defined as the valve position moving from closed to open to closed. These cycles shall be performed at atmospheric internal pressure.

3.1.7 Filtration

The latch valve shall have an inlet filter with a filtration rating of greater than or equal to 30 microns. The inlet filter shall be sized properly to provide adequate protection for the latch valve seat.

3.2 Resource Allocations

3.2.1 Mass Allocation

The latch valve shall have a mass of less than or equal to 0.9 kg. This mass shall include the valve and all electrical lead wires.

3.3 Power

3.3.1 Primary (Unregulated) Power Input Requirements

3.3.1.1 Operating Voltage Range

The latch valve shall be designed to operate over the bus voltage range of +24 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

The latch valve shall survive without electrical overstress after exposure to an anomalous voltage range of 0 to +40 VDC and input power short or open. This requirement shall be verified by analysis or test of a non-flight unit.

3.3.1.3 Sudden Removal of Power

The latch valve shall meet its performance requirements without degradation after exposure to an abrupt, unannounced removal of power.

3.3.1.4 Operational Current Transients (one time)

a. The latch valve operational current transients shall be less than or equal to 5A, not exceeding 1 milli-second.

b. The rate of change of the current shall be less than or equal to 20 milliamperes/microsecond.

3.4 Electrical Grounding

3.4.1 Primary Power DC Isolation

At the latch valve 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 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.

3.4.3 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.

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:

Heritage Hardware: Hardware 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

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

4.1.2 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.

4.2 Physical Envelope

The physical envelope of the latch valve shall be less than 2.75” X 4.25” X 9” (6.88cm X

10.80cm X 22.90cm) not including electrical lead wire length.

4.3 Mounting

The latch valve shall accommodate being hard-mounted with mechanical fasteners on a single mechanical surface of the spacecraft structure.

4.3.1 Fastener Accessibility

The latch valve shall be designed such that it can be fastened or removed by accessing fasteners from above without any disturbance.

4.3.2 Interface Tube

4.3.2.1 Dimensions

Each latch valve shall have interface tube with the dimension of 0.375±0.003 inches OD with a

0.028±0.003 wall thickness and a length of no less than 1.5±0.06 inches.

4.3.2.2 Material

The interface tube shall be SS 304L per AMS5647 and AMS5569.

5 ENVIRONMENTAL REQUIREMENTS

Environmental design requirements are specified in this section.

The latch valve shall meet its performance requirements in Section 3 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 latch valve shall be designed to withstand the quasi-static Design Limit Loads (DLL) defined in the Mass-Acceleration Curve (MAC) shown in Table 1 without damage or degradation of performance.

Note:

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

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

Table 1. Latch Valve Design Limit Loads

Component Mass (Kg) Limit Load (g)

0.5 35.9

1 35

5.2 Frequency Requirement

5.2.1 Stowed Fundamental Launch Frequencies

The latch valve 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. Components/subsystems verification is required through low level signature tests.

3. Failure to meet frequency requirement requires a test correlated Finite Element Model

(FEM) be supplied for dynamic analysis. Requirements for the FEM are in the SOW, Section 3.5.

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

5.3 Vibration

5.3.1 Sinusoidal Vibration

The latch valve shall withstand the sinusoidal vibration levels defined in Table 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 2 are defined at the interface of the element/subsystem.

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.

7. Levels defined represent limit level. Analysis is conducted against limit level with FS defined in section 8.1. For testing factors see section 9.4.2.

Table 2. Latch Valve Generic Sine Vibration Environment

Frequency (Hz) Flight, Acceptance level

5- 20 0.50 in (double amplitude)

20-100 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

The latch valve shall withstand the random vibration environment in Table 3 applied at the interface to the latch valve.

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

22.7 kg. Table 4 defines minimum workmanship for components weighing less than 45.4 kg.

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.

Levels defined represent limit level. Analysis is conducted against limit level with FS defined in section 8.1. For testing factors see section 9.4.2.

Table 3. Latch Valve Random Vibration Environment, (22.7kg, or less).

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

Frequency (Hz) ASD Level (g2/Hz)

20 0.01

20 - 80 +3 dB/oct

80 - 500 0.04

500 - 2000 -3 dB/oct

2000 0.01

Overall 6.8 grms

5.4 Shock

The latch valve shall be designed to meet its performance requirements after being subjected to the shock environment in Table 5, applied at the latch valve interface to the WFIRST spacecraft structure. This shock environment may be updated based on testing of shock sources located near the latch valve.

Table 5. Internal and External Shock Source Limit Levels

Component Frequency (Hz) Limit Level

Latch Valve

100 34g

100 – 2150 6.5 dB/oct

2150 – 10000 919g

A shock susceptibility and attenuation assessment is to be performed on the latch valve. 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 latch valve. If the environment is low risk, then the shock test may be deferred to the Observatory level with concurrence from the NASA/GSFC COR. Levels defined represent limit level.

Analysis is conducted against limit level with FS defined in section 8.1. For testing factors see section 9.4.2

5.5 Pressure

5.5.1 Operating Pressure Range

The latch valve 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 Ground Environments

a. The latch valve 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. After being powered “OFF” and exposed to air temperatures of +5 to +30 degrees C and relative humidity of 0 to 70%, the latch valve shall meet all of its performance requirements.

5.7 Thermal Requirements

5.7.1 Flight Interface Design Temperature Limits

a. The latch valve shall be capable of surviving indefinitely when its temperatures are within the survival limits shown in Table 6 without damage or permanent performance degradation.

Table 6. Temperature Limits at Box Mounting Interface

Minimum Temperature (ºC) Maximum Temperature (ºC)

Operational (In Spec) +10 +50

Protoflight/Qualification (In

Spec)

+10 +50

Survival (Unpowered) +8 +60

6 CLEANLINESS

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

6.1 Surface Contamination

6.1.1 Surface Contamination Levels at Delivery

6.1.1.1 Particulate Contamination

The latch valve shall meet IEST-STD-CC1246E VC-0.5-1000 + UV, or equivalent, when inspected with both UV and white light in a darkened room.

6.1.1.2 Molecular Contamination – Exposed Surfaces

If the latch valve has surfaces exposed to the space environment, all such surfaces shall meet a molecular surface cleanliness level of IEST-STD-CC1246E R3.3E-1 on all external and critical surfaces, when tested in accordance with IEST-STD-CC1246E VC-0.5-1000 + UV, or equivalent.

6.1.1.3 Molecular Contamination – Covered Surfaces

a. All latch valve surfaces not exposed to the space environment shall meet IEST-STD-

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

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

6.1.1.4 External Cleanliness

All hardware surfaces shall be verified to be “visibly clean, highly sensitive” per JSC-SN-C-

0005C or equivalent, prior to delivery to NASA/GSFC. This is accomplished by maintaining all hardware in a double bag for storage.

6.1.1.5 Internal Cleanliness

The propulsion components, lines, and fittings shall be cleaned, and verified internally clean, to level 100R1 per IEST-STD-CC1246E (as modified by the following: no metal particles allowed above 25 um) prior to integration in the system.

6.1.2 Surface Contamination Generation

6.1.2.1 Particulate Generation

The latch valve contractor shall not employ any of the following particle generating materials or processes into the latch valve design or construction without prior approval by the NASA/GSFC

COR:

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

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

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

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

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

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

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

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

Foams, highly textured materials.

Trapped debris in holes.

6.1.2.2 Molecular Generation

Material Selection

The latch valve materials shall have a total mass loss (TML) less than 1.00% and a collected volatile condensable mass (CVCM) less than 0.10%, when measured in accordance with ASTM

E-595 unless a materials usage agreement has been generated and approved by the NASA/GSFC

COR.

Material Selection - Silicones

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

Assembly Outgassing

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

b. The latch valve outgassing will be measured and recorded for informational purposes under test’s mass that is condensable on a Quartz Crystal Monitor (QCM) operated at -20 degrees C. The measurement will be made in a chamber that has been certified clean

(back ground outgassing rate and free of silicones and other high molecular weight contaminants) and has been modeled by the GSFC Contamination Analyst to account for mass sinks (cold fingers, pumps, cold surfaces, etc.) that could influence the source outgassing rate.

6.1.3 Cleanability

6.1.3.1 Cleanability – Sensitive Surfaces

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

6.1.3.2 Cleanability – Sensitive Surface Cleaning Methods

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

6.1.4 Transportation Cleanliness

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

7 DESIGN & CONSTRUCTION REQUIREMENTS

7.1 Parts, Materials & Processes (PMP)

7.1.1 EEE Parts

The latch valve contractor’s Quality Assurance system for EEE parts will be in accordance with the requirements in the SOW, WFIRST-PROP-SOW-0016.

7.1.2 Materials

The latch valve will be comprised of materials and processes in accordance with the requirements in the SOW, WFIRST-PROP-SOW-0016.

7.1.2.1 Material Conductivity

All parts should be passivated and mounting surfaces on the latch valve shall be conductive as defined in Section 3.4.

7.1.2.2 Material Cleanliness

The latch valve surface shall be free of surface contamination generation as defined in Section

6.1.2.

7.2 Electrical

7.2.1 Coil Resistance

The electrical resistance of the valve opening and closing measured across the leads shall be no less than 21 ohms at 68°F. When open and when closed, the latch valve shall only require power for the position indication micros-witches

7.2.2 Interface Requirements

The latch valve shall be delivered with either:

a. A one (1) meter minimum flying lead harness length for the entire bundle (and no connector); Or,

b. A mating connector

7.2.3 Wires

7.2.3.1 Wire Specifications

All internal wire types shall meet the Wire and Cable Requirements in Section W1 of EEE-

INST-002.

7.2.3.2 Minimum Wire Size

No wire smaller than AWG #26 shall be used.

7.2.3.3 Wire Derating

The current carrying capacity of the wires shall be derated for continuous operation at the required current levels in a vacuum, as defined in Section W1 of EEE-INST-002.

7.2.3.4 Wire Composition

Wire conductors shall be copper or a copper alloy. The wires shall be plated with suitable materials except nickel or other magnetic materials.

7.2.3.5 Wire Twists

Power wires shall be twisted with their power return wires and signal wires shall be twisted with their signal return wires.

7.2.4 Connector Selection

7.2.4.1 Connector Specifications

a. Selected connector types shall meet the Connector and Contact Requirements defined in

Section C2 of EEE-INST-002.

b. Environmental seals shall not be used in connectors especially if made from silicone without the explicit approval by the NASA/GSFC COR.

7.2.4.2 External Box Power Connectors

The use of micro-miniature D connectors shall be prohibited for unregulated bus power interfaces as defined in Section 3.3.1.

7.2.4.3 Contact Derating

The current carrying capacity of the contacts shall be derated for continuous operation at the required current levels in a vacuum, as defined in Section C2 of EEE-INST-002.

7.2.5 Dielectric Structures

7.2.5.1 Bulk Resistivity

Dielectric structures shall have a bulk resistivity less than 1012 ohm-cm.

7.2.5.2 Charge Bleed-Off

All dielectric structures shall have a charge bleed path to the spacecraft interface, designed to route the discharge into the spacecraft structure in a controlled fashion.

7.3 Identification and Marking

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

NASA/GSFC COR.

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

The latch valve shall be marked to include but not limited to the following,

a. Vendor Part number

b. Vendor Name

c. Vendor Serial Number

d. Indication of Flow Direction (Arrow)

7.4 Workmanship

7.4.1 Workmanship Standards

The workmanship standards and processes outlined in the SOW, WFIRST-PROP-SOW-0016 will be used.

7.4.2 Welding

All weld procedures and weld inspection procedures shall be approved by NASA/GSFC and in compliance with SOW, WFIRST-PROP-SOW-0016.

Test records such as dye penetrant, x-rays, etc. shall all be retained.

7.5 Reliability and Lifetime

7.5.1 Mission Life

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

7.5.2 Shelf Life

The latch valve shall not suffer any degradation in performance when stored for five (5) years either on the S/C or in bonded storage.

7.5.3 GSE Cleanliness

All Ground and Test support equipment shall be compatible with the flight component and the environment where the flight component or test component will reside (cleanroom, thermal vacuum chamber, vibration cell, etc.)

7.6 Interchangeability

The latch valve shall be directly interchangeable in form, fit, and function with other latch valves of the same part number.

8 MECHANICAL DESIGN REQUIREMENTS

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

In Spaceflight Hardware”.

8.1 Mechanical Factors of Safety

Positive Margin of Safety (MS) shall be demonstrated analytically for the latch valve, including interfaces to MGSE, using the MS formula below with the appropriate Factors of Safety (FS) defined in Table 7 applied to flight limit loads.

1. MS is defined as follows:

𝑀𝑆 =

𝐴𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 𝐿𝑖𝑚𝑖𝑡 𝐿𝑜𝑎𝑑 𝑜𝑟 𝑆𝑡𝑟𝑒𝑠𝑠

𝐴𝑝𝑝𝑙𝑖𝑒𝑑 𝐿𝑖𝑚𝑖𝑡 𝐿𝑜𝑎𝑑 𝑜𝑟 𝑆𝑡𝑟𝑒𝑠𝑠 ∗ 𝐹𝑆

− 1

2. Positive MS in joints that are both bonded and fastened is demonstrated assuming only the bond carries the load, only the bolt carries the load, or if the capability of the joint requires both the bond and fasteners, a detailed analysis is performed.

a. The adhesive portion of the joint is usually the stiffest load path and thus carries most of the load. In this scenario, the full strength of the bolted interface is not realized until after the failure of the adhesive.

3. Positive MS is demonstrated for adhesively bonded joints for all potential failure modes under all loading conditions and temperatures.

a. Failure modes may include cohesive failure in the adhesive, failure at the adhesive to adhered interface, and adherent failure. Composite adherent failure modes may include in-plane tension/compression, in-plane shear, peel, interlaminar shear, and interactions between failure modes.

b. Fiber orientation should be considered in the computation of strength for a bonded joint where one or more of the adherends are made of composite material.

c. Interaction between adhesively bonded joints in close proximity should be included when analyzing bonded joints.

d. Temperature stresses in bonded joints and sandwich panels should consider bond and consolidation cure temperatures.

e. Adhesive bond fillets and bondline thickness should be considered in bonded joint design and analysis under temperature loading.

Table 7. Design Factors of Safety

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

Tested Metallic Yield 1.252 1.6

Tested Metallic Ultimate 1.42 1.8

Stability/Buckling Ultimate 1.4 1.8

Beryllium Yield 1.4 1.8

Beryllium Ultimate 1.6 2.0

Composite Ultimate1 1.5 1.9

Bonded inserts/Joints Ultimate 1.5 1.9

Glass/Ceramic 3.0 3.8

Bond in Glass/Ceramic 1.5 1.9

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

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

(3) Factors shown should be applied to statistically derived peak response based on Acceptance RMS level. As a minimum, the peak response must be calculated as a 3-sigma value.

8.2 Fracture Control Requirements

The use of materials that are susceptible to brittle fracture or stress-corrosion cracking require development of, and strict adherence to, special procedures to prevent problems.

If materials are used for structural applications that are not listed in Table 1 of MSFC-STD-3029, a Materials Usage Agreement (MUA) shall be approved by the NASA/GSFC COR.

Fracture control requirements (per NASA-STD-5019) shall apply to the following elements only:

(1) Pressure vessels, dewars, lines, and fittings (per NASA-STD 8719.24)

(2) Castings (unless hot isostatically pressed and the flight article is proof tested to 1.25 times limit load)

(3) Weldments

(4) Parts made of materials on Tables II or III of MSFC-STD-3029 if under sustained tensile stress

(5) Parts made of materials susceptible to cracking during quenching

(6) Nonredundant, mission-critical preloaded springs loaded to greater than 25 percent of ultimate strength

All glass elements that are stressed above 10% of their ultimate tensile strength shall also be shown by fracture analysis to satisfy "Safe-life" or "Fail-safe" conditions or be subjected to a proof loads test at 1.0 times limit level.

8.3 Fastening Systems

8.3.1 Fastener Locking

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

Notes:

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

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

8.3.2 Fastened Joint Margin of Safety

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

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

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

2) 𝑃𝑈 = 𝐹𝐹 ∗ 𝐹𝑆𝑈 ∗ 𝑃𝐿

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

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

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

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

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

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

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

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

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

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

1. If one or more of the following applies:

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

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

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

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

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

𝑃𝑌 = 𝐹𝐹 ∗ 𝐹𝑆𝑌 ∗ 𝑃𝐿

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

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

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

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

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

i) 𝑀𝑆𝑠𝑒𝑝 = 𝑃𝑝−𝑚𝑖𝑛

𝐹𝐹∗𝐹𝑆𝑠𝑒𝑝∗𝑃𝐿

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

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

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

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

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

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

8.3.3 Installation Torque Documentation

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

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

8.3.4 Seal Analysis

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

8.3.5 Critical Fasteners

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

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

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

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

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

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

8.4 Mechanism Design

8.4.1 Torque Margin Formula

The Torque Margin (TM) shall be greater than zero and be calculated using the following formula and using FS specified in Table 8. Torque Margin Calculation Factors of Safety

𝑇𝑀 = {

𝑇𝑎𝑣𝑎𝑖𝑙

(𝐹𝑆𝑘 ∑ 𝑇𝑘𝑛𝑜𝑤𝑛 + 𝐹𝑆𝑣 ∑ 𝑇𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒)

} − 1

Where:

Driving Torques:

Tavail = Minimum Available Torque or Force generated by the mechanism at worst case environmental conditions at any time in its life. If motors are used in the system, Tavail is determined at the output of the motor, not including gear heads or gear trains at its output based on minimum supplied motor voltage. If the unit is procured as an actuator (motor, gear head, resolver, etc. assembly), qualified and acceptance tested to a purchase specification, Tavail will be determined at the output of the assembly. Tavail will be based on minimum supplied motor voltage and current. Tavail similarly applies to other actuators such as springs, pyrotechnics, solenoids, heat actuated devices, etc.

Resistive Torques:

ΣTknown = Sum of the fixed torques or forces that are known and quantifiable such as accelerated inertias (T=Iα) and not influenced by friction, temperature, life, etc. A constant

FS is applied to the calculated torque.

ΣTvariable = Sum of the torques or forces that may vary over environmental conditions and life such as static or dynamic friction, alignment effects, latching forces, wire harness loads, damper drag, variations in lubricant effectiveness, including degradation or depletion of lubricant over life, etc.

Table 8. Torque Margin Calculation Factors of Safety

Program Phase Known Torque Factor of

Safety (FSk)

Variable Torque

Factor of Safety (FSv)

Preliminary Design Review (PDR) 2.0 4.0

Critical Design Review (CDR) 1.5 3.0

Acceptance/Qualification Test 1.25 2.0

1. Positive torque margin is demonstrated using worst-case operational and environmental conditions and include all flight drive electronics effects and limitations. It is recommended that the following considerations be included in margin calculations as they reflect phenomena that are frequently found to cause problems in margin calculation:

Environmental conditions.

Frictional effects.

Possible changes in static and dynamic friction due to storage time.

Alignment effects.

Wire harness and blanket loads.

Damper drag.

Thermally induced distortions.

Load-induced distortions.

Variations in lubricity.

Fluid pressure on the elastomers in viscous dampers.

Supply voltage, motor, and controller parameters.

Acceleration due to vehicle motion or maneuvers that can retard motion.

Loading due to vibroacoustic environment.

8.4.2 Mechanism Stall Performance

Mechanism components and linkages shall have sufficient strength to tolerate an actuation force/torque stall condition at any point of travel and still maintain a positive margin of safety with the ultimate factor of safety applied.

8.4.3 Deployables and Mechanism Jamming

8.4.3.1 Springs Failure Tolerant

Springs shall be failure tolerant unless spring failure can be shown to be non-credible.

1. There are two ways to achieve redundancy in a spring, as follows:

a. A second spring can be used that allows the mechanism to have positive torque or force margin for a one-spring-out case based on combining worst-case conditions

b. Use of a spring that retains functionality after one coil or element of the spring

(e.g., a single conical spring in a stack) is fractured or otherwise compromised.

Determining that a spring failure is not credible requires demonstrating that adequate life and stress margins exist on the part. This can be accomplished with a combination of stress analysis, fatigue analysis, fracture control methods, and testing. However, given the size of many springs used in mechanisms, fracture approaches are often not feasible and other steps have to be taken to demonstrate reliability.

8.4.3.2 Tolerancing

Dimensional tolerances on all moving parts and intentional interference-fit parts shall be established via a tolerance stack-up/clearance analysis to ensure that proper functional performance is maintained under all natural and induced environmental conditions and configurations.

1. The dimensional analysis accounts for the following:

Manufacturing, assembly, and alignment tolerances.

Temperature.

Temperature gradients.

Vibration.

Deflections due to external loads.

Deflections due to operational loads.

Adjustability and rigging of the mechanism parts.

8.4.4 Switches

8.4.4.1 Microswitches

The use of micro switches shall be limited to the indication of status conditions in telemetry and is prohibited in logic or command circuits.

8.4.5 Lubricants

8.4.5.1 Lubricant Life Analysis

Lubricants shall be proven to lubricate the system under all specified…