_MSR-CCRS-SYS-SPEC-0004-DRAFT.pdf

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

National Aeronautics and Space Administration

Goddard Space Flight Center Greenbelt, Maryland

MSR-CCRS-SYS-SPEC-0004, Revision -

Capture, Containment and Return System (CCRS) Project

NASA/GSFC Code 430

CCRS Mechanical and Mechanism

Design Specification

MSR-CCRS CMO

<Date>

DRAFT

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

Mechanical and Mechanism Design Specification MSR-CCRS-SYS-SPEC-0004, Revision DRAFT

Effective Date: XX/XX/XXX

[Disclosure notice belongs here.]

CCRS Mechanical and Mechanism Design Specification

Signature/Approval Page

Prepared by:

Joseph Schepis Date Son Ngo Date

CCRS Mechanisms Systems CCRS Structure & Deployables

Code 544 Code 543

Reviewed by:

Chanel Duncan Date

CCRS Chief Safety & Mission

Assurance Officer

Code 383

Fernando Pellerano Date

CCRS Senior Tech Leader

Code 590

Brendan Feehan Date

CCRS Mission Systems Engineer

Code 599

Approved by:

David Littmann Date

CCRS Project Manager

Code 458

*** Electronic signatures are available on-line at: https://ipdtdms.gsfc.nasa.gov*** https://ipdtdms.gsfc.nasa.gov/

Preface

This document is a Mars Sample Return (MSR) Capture, Containment and Return System

(CCRS) Project configuration control board (CCB) controlled document. Changes to this document require prior approval of the CCB Chairperson or designee. Proposed changes shall be submitted in the Technical Data Management System (TDMS) via a configuration change request (CCR) along with supportive material justifying the proposed change. Changes to this document will be made by complete revision.

All of the requirements in this document assume the use of the word "shall" unless otherwise stated.

Questions or comments concerning this document should be addressed to:

CCRS Configuration Management Office

Mail Stop: 435

Goddard Space Flight Center

Greenbelt, Maryland 20771

Change History Log

Revision Effective Date Description of Changes

(Reference the CCR & CCB/ERB Approval Date)

Released per CCRS-CCR-XXXX

Table of TBDs/TBRs/TBSs [optional]

Action Item

No.

Location Summary Individual/

Organization

Actionee

Table of Contents

1 INTRODUCTION

1.1 Purpose

1.2 Scope

1.3 CCRS Mission Overview

1.4 Terminology Definition

Statement of Fact Hard Requirement Statement of a Goal Permission To Be Reviewed To Be Determined Component

2 Applicable Documents

2.1 Governing Documents

2.2 Reference Documents

2.3 Acronyms

3 Mechanical Design Requirements

3.1 Fastening Systems

Fastener Performance Analysis Fastener Locking and Retention Fastened Joints Criteria

3.2 Mechanism Design

Torque/Force Margins Binding/Jamming/Seizing Lubrication Deployables Springs Viscous Dampers Motors Bearings Gears

Mechanical Stops Pulleys Switches Retaining Rings Set Screws

3.3 Mechanism Performance and Strength Analysis

3.4 Mechanism Installation

3.5 Structural Requirements

Finite Element Modeling Component Fatigue Fracture Control Requirements

3.6 Verification Requirements

Mechanism Verification

3.7 Ground Support Equipment

3.8 Mechanical Ground Support Equipment (MGSE)

1 INTRODUCTION

1.1 Purpose

This Capture, Containment, and Return System (CCRS) Mechanical and Mechanism Design

Specification (MMDS) specifies Level 3.5 requirements for the design and implementation of the CCRS.

1.2 Scope

This document establishes general mechanical/mechanism design and implementation requirements and guidelines for the CCRS mission. CCRS performance requirements are covered in other documents.

The requirements in this document are design requirements, and, as such, do not all require the same level of rigor in their verification. The requirements that require verification down to the test or analysis report, work order event or other specific document containing the measured value of the met requirement are marked with “Verification document required” in parentheses after the requirement statement. For all other requirement statements not marked in this manner, it is expected that at every major review, any expected or possible exceptions to these design requirements be presented, and compliance with the other requirements be acknowledged.

It is the responsibility of the Product Design Lead (PDL) to ensure that those values are flowed down correctly to all lower levels of assembly. For the requirements listed “Verification document required” the Performance Verification Matrix will refer to the document containing the relevant verification information, and a copy of the verification information will be available in the CCRS TDMS systems. For other requirements, the verification matrix reference should simply refer to the product End-item delivery package, which will document compliance and lists exceptions to this design specification as specified above.

An equivalent document for Jet Propulsion Laboratory (JPL) provided flight hardware may be used in place of this document with approval from CCRS.

1.3 CCRS Mission Overview

The Mars Sample Return (MSR) Campaign is an international collaboration between the National

Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) to bring back the first samples from Mars to Earth. The MSR campaign involves the following flight projects: Perseverance (previously known as Mars 2020), Sample Return Lander (SRL), the ESA-provided Earth Return Orbiter (ERO), which includes the NASA-provided Capture, Containment and Return System (CCRS), and the Sample Retrieval Facility (SRF). The JPL-led Perseverance

Project, which launched in July 2020, will collect and cache samples on Mars for future return.

The JPL-led SRL Project will launch in 2026, collect the cached samples and use a Mars Ascent

Vehicle to launch contained samples into Mars Orbit. The ERO with CCRS, which will also launch in October 2026, captures samples in Mars orbit and returns them to Earth, while meeting backwards planetary protection requirements.

The ERO is an ESA-contributed spacecraft that contains a chemical propulsion module, the main return module, which includes electric and chemical propulsion, a rendezvous sensor system, and the NASA-provided CCRS. CCRS includes a Capture and Containment System (CCS and Earth

Return Module (ERM), which includes the Earth Entry System (EES). The EES is passive, with no sensors or propulsion capability. The CCS has sensors, robotics, and mechanisms to capture, contain and sterilize an orbital sample (OS) container with Mars material samples, while in Mars orbit, and transfer the contained OS to the Earth Entry System. The CCS is also responsible for providing secondary containment of the OS. The ERM (TBR) includes a deployable micrometeoroid protection system to mitigate damage to the EES in transit to and from Mars.

To reduce the mass that the ERO is required to return to Earth, the CCS is jettisoned while in

Mars orbit.

The CCRS project is being implemented as a directed Project, led by Goddard Space Flight

Center, in partnership with JPL, Langley Research Center (LaRC) and Ames Research Center

(ARC).

1.4 Terminology Definition

Statement of Fact

A “Will” statement defines a fact and does not require verification.

Hard Requirement

A “Shall” statement defines a hard requirement that requires formal verification.

Statement of a Goal

A “Should” statement defines a goal and does not require verification.

Permission

A “May” or “Can” statement implies permission.

To Be Reviewed

To Be Reviewed or (TBR) denotation signifies that the requirement value is not yet firm.

To Be Determined

To Be Determined or (TBD) denotation signifies that the referenced text is in development.

Component

A “Component” is defined as any element of the payload.

2 APPLICABLE DOCUMENTS

2.1 Governing Documents

The following are higher-level documents. In cases of conflict between this document and the higher level documents, the higher level documents will take precedence.

Table 2.1-1 Governing Documents

MSR-CCRS-SMA-REQ-0003 Capture, Containment and Return System (CCRS) Mission

Assurance Requirements (MAR)

MSR-CCRS-SMA-PLAN-

CCRS Safety Mission Assurance Plan (SMAP)

MSR-CCRS-SYS-REQ-0001 Capture Contain and Return System (CCRS) Systems

Requirements Document

MSR-CCRS-SYS-REQ-0002 Capture Contain and Return System (CCRS) Environmental

Requirements Document (ERD)

GSFC-STD-1000 Rules for Design, Development, Verification and Operations of Flight Systems

NASA-STD-5019 Fracture Control Requirements for Spaceflight Hardware

2.2 Reference Documents

In cases of conflict between this document and the reference documents, this document will take precedence.

Table 2.2-1 Reference Documents

540-PG-8700.2.1 Design of Dollies, Stands, and Spacecraft Shipping

Containers

540-PG-8719.1.1 Lift Sling Design

541-WI-5330.1.41 Fastener Locking Using Arathane 5753

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

Hardware

540-PG-8072.1.2 Mechanical Fastener Torque Guidelines

541-PG-8072.1.2 GSFC Fastener Integrity Requirements

2.3 Acronyms

The acronyms used in this document are defined in Appendix A (Table of Acronyms).

3 MECHANICAL DESIGN REQUIREMENTS

3.1 Fastening Systems

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.

Fastener Performance Analysis

3.1.1.1 Factors of Safety

MM1 Factors of safety for fastener strength analysis shall be as specified in MSR-

CCRS-SYS-REQ-0002, CCRS Environmental Requirements Document.

3.1.1.2 Supplemental Factor

MM2 A supplemental factor, referred to as a fitting factor (greater than or equal to

1.0), shall be applied. See NASA-STD-5020, section 4.1(b) as a reference.

3.1.1.3 Ultimate Design Loads

MM3 All threaded fastening systems shall withstand ultimate design loads in conjunction with the applicable maximum expected range of environmental conditions without rupture.

3.1.1.4 Yield Design Loads

MM4 All threaded fastening systems shall withstand yield design loads in conjunction with the applicable maximum expected range of environmental conditions without detrimental yielding. Detrimental yielding is yielding that affects the fit, form, function, or integrity of the structure. See NASA-STD-

5020, section 6.3 as reference.

3.1.1.5 Design Separation Load

MM5 Mechanical joints using threaded fastening system hardware shall withstand the design separation load in conjunction with applicable maximum or minimum temperatures without separation, using a separation factor of safety

(FSsep) of 1.0 for non-separation critical joints, FSsep=1.25 for non-catastrophic separation critical joints, and FSsep=1.4 for catastrophic separation critical joints. See NASA-STD-5020, section 4.3 for reference.

NOTE: A separation critical joint is one that would not function properly if separated; e.g., a fluid or gas would penetrate a seal at an unacceptable rate, or an instrument would fail to perform properly due to misalignment.

Further, ‘catastrophic’ here refers to risk/loss of human life, such as could occur if a pressurized component failed or released a toxic substance due to joint separation.

NASA-STD-5020 Section 6.5 provides criteria for separation analysis and guidance for fitting factor application.

Fastener Locking and Retention

3.1.2.1 Locking Features

3.1.2.1.1 Locking Feature Minimum

MM6 Regardless of the magnitude of preload, each threaded fastening system in spaceflight hardware shall incorporate a minimum of one locking feature that does not depend upon preload to function.

Note: Devices such as jam nuts may not be suitable locking features to satisfy this requirement if they require preload to function effectively, or if a change in preload could compromise the locking performance. A redundant locking feature may be advisable for some joints as described in Federal Aviation Administration Advisory Circular (AC) 20-

71, “Dual Locking Devices on Fasteners".

3.1.2.1.2 Locking Feature Verification

MM7 Locking features shall be verifiable per Section 7.6 of NASA-STD-5020.

3.1.2.1.3 Locking Feature Installation

MM8 Mechanical locking features such as cotter pins, safety wire, and safety cable, shall be installed per National Aerospace Standard NASM 33540, “Safety Wiring, Safety Cabling, Cotter Pinning, General Practices for”.

3.1.2.1.4 Snap Ring & Cotter Pin Use and Limitation

MM9 Snap rings and cotter pins shall not be used where other acceptable retention methods are possible.

MM10 Where use of snap rings or cotter pins cannot be avoided, new snap rings or cotter pins shall be used once the previous snap ring or cotter pin is removed.

3.1.2.1.5 Liquid Locking Compounds

MM11 When a liquid locking compound is used, it should be applied using a formal, validated process that addresses, where appropriate, the following link layer component (LLC) sensitivities:

a. quantity and coverage of LLC,

b. fastener and joint material,

c. thread size,

d. fastener preload,

e. all environmental conditions,

f. specified process for cleaning threads,

g. specified process for application of primer to threads,

h. specified process for applying LLC to threads, and

i. break-torque strength in comparison with LLC’s manufacturer-stated capability.

3.1.2.2 Locking Features Verification

3.1.2.2.1 Visual Inspection

MM12 Mechanical locking features, such as cotter pins, safety wire, and safety cable, shall be verified by visual inspection after installation. Proper installation processes are located in specifications, such as National

Aerospace Standard NASM 33540, “Safety Wiring, Safety Cabling, Cotter

Pinning, General Practices for”, and Society of Automotive Engineers

International SAE AS567, “Safety Cable, Safety Wire, Key Washers, and

Cotter Pins for Propulsion Systems, General Practices for Use of”.

3.1.2.2.2 Torque Measurement

MM13 Prevailing torque features, such as deformed thread features, pellets, strips, or patches, shall be verified by torque measurement during the installation process.

3.1.2.2.3 Witness Coupons and Cure Samples

MM14 Adhesive locking features dependent upon substrate and/or configuration for cure, such as anaerobic liquid locking compounds, shall be verified by torque measurements on witness coupons that are representative of and processed with the hardware being verified.

MM15 All other adhesive locking features shall be verified using cure samples processed at the time of application/processing.

3.1.2.3 Locking Features

MM16 Locking features and their installation processes, including verification methods, shall be specified in the engineering documentation.

MM17 When using locking adhesives, whether as thread-locking compounds or staking materials, installation processes shall be developed and validated prior to implementation to ensure adhesives cure, adhere, and function as expected; see 541-WI-5330.1.41 for specific instructions.

It should be recognized that some locking features are not a means of maintaining preload, but rather are safety devices principally intended to resist rotational loosening and prevent loss of fasteners. Examples of the selection of locking features are provided in Appendix B of NASA-STD-

3.1.2.3.1 Installation Torque Specification and Control

MM18 The engineering documentation shall specify the installation torque range or specify an applicable standard that defines the installation torque range.

MM19 The engineering documentation shall clearly identify when the installation torque is the torque above running torque.

Fastened Joints Criteria

3.1.3.1 Minimum and Maximum Preload

MM20 Analysis of threaded fastening systems shall address maximum and minimum preloads per NASA-STD-5020 Section 6.1.

3.1.3.2 Analysis Addressing Potential Rupture

MM21 Analysis for ultimate design loads shall 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.

Additional explanation can be found in NASA-STD-5020, Section 6.2.

3.1.3.3 Ultimate Strength Analysis

MM22 Ultimate strength analysis of a fastening system under applied tensile loading shall be performed per NASA-STD-5020, Section 6.2.1.

3.1.3.4 Applied Shear Loading

MM23 Ultimate strength analysis of a fastening system under applied shear loading shall be performed per NASA-STD-5020, section 6.2.2.

3.1.3.5 Shear Loading

MM24 Ultimate strength analysis of bolts under shear loading shall be based on the assumption that no shear load is carried by friction between the faying surfaces.

3.1.3.6 Simultaneous Applied Tensile and Shear Loads

MM25 For fasteners under simultaneous applied tensile and shear loads, along with any applicable bending, analysis shall account for interaction of the combined loading. See the equations contained in NASA-STD-5020, section

6.2.3 for reference.

3.1.3.7 Allowable Yield Tensile Load

MM26 Analysis shall be 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 if one or more of the following applies:

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

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

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)

3.1.3.8 Separation Analysis

MM27 Analysis shall be performed per NASA-STD-5020, Section 6.5 showing no separation for each threaded fastening system that is subject to applied tensile loading, with the assumption of minimum preload.

3.1.3.9 Seal Analysis

MM28 For a joint that maintains a seal (e.g., to maintain pressure or contain a fluid), analysis shall show that the seal meets its requirements at the design separation load when assuming minimum preload for all fasteners in the joint.

3.1.3.10 Fail Safe

MM29 Bolted joints shall be designed to be fail safe where practical. All fasteners shall meet the GSFC fastener integrity 541-PG-8072.1.2.

3.2 Mechanism Design

Torque/Force Margins

MM30 The minimum torque at the motor shaft shall never be less than 7.06E-3 N-m

(1 oz-in)

MM31 Sufficient torque or force margins will be provided to assure reliable mechanism operation over the life of the mission (8 years).

a. Margins shall be determined using worst-case credible combination of conditions and include all flight drive electronics effects and limitations.

b. Torque margin shall be verified using data acquired from unit qualification or acceptance level operational testing.

MM32 Torque margin shall be greater than zero and be calculated using the following formula:

𝑇𝑜𝑟𝑞𝑢𝑒 𝑀𝑎𝑟𝑔𝑖𝑛 = 𝑇𝑎𝑣𝑎𝑖𝑙

∑ 𝐹𝑆𝑓𝑖𝑥 ∙ 𝑇𝑓𝑖𝑥 + ∑ 𝐹𝑆𝑣𝑎𝑟 ∙ 𝑇𝑣𝑎𝑟

− 1

Where:

Origin of Factor Kfix Kvar

Value Obtained via Theory or Analysis 1.5 3.0

Value Obtained via Test of Flight-Like Hardware 1.25 2.0

Value for One-Spring-Out Case 1 1.0 1.0

1Spring-driven mechanisms that utilize multiple springs nominally working together to provide torque may utilize a minimum Kfix and Kvar of 1.0 for the cases in which one of those springs fails. Prior to failure, the nominal (non-failure) factors still apply.

For linear devices, “Force” replaces “Torque” in the above equations and descriptions.

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 shall be determined at the output of the motor, not including gear heads or gear trains at its output based on minimum supplied motor voltage. Tavail similarly applies to other actuators such as springs, pyrotechnics, solenoids, heat actuated devices, etc.

Resistive Torques:

ΣTfix = Sum of the fixed torques or forces that are known and quantifiable such as accelerated inertias and not influenced by friction, temperature, life, etc. A constant factor of safety is applied to the calculated torque.

ΣTvar = Sum of the torques and 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.

MM33 Where mechanisms are driven by electric motors, a torque-versus-current relationship for each motor under minimum, maximum, and ambient thermal conditions shall be established.

MM34 For servomechanism applications, performance margins shall be documented and verified.

MM35 Stroke margin shall be greater than zero and be calculated using the following formula:

𝑆𝑡𝑟𝑜𝑘𝑒 𝑀𝑎𝑟𝑔𝑖𝑛 =

𝑂𝑢𝑡𝑝𝑢𝑡 𝑠𝑡𝑟𝑜𝑘𝑒 𝑜𝑓 𝑎𝑐𝑡𝑢𝑎𝑡𝑜𝑟

𝑆𝑡𝑟𝑜𝑘𝑒 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝑡𝑜 𝑎𝑐ℎ𝑖𝑒𝑣𝑒 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑓𝑢𝑛𝑐𝑡𝑖𝑜𝑛 𝑥 1.1 − 1

All stroke margins shall account for worst-case credible combinations of the following:

a. Environmental conditions.

b. Thermally induced distortions.

c. Load-induced distortions.

d. Mounting alignments.

e. Tolerances.

Binding/Jamming/Seizing

3.2.2.1 Clearances

MM36 Static and dynamic clearances between the mechanism and any other structure, component, thermal covering, and FOV shall be established and maintained during all phases of the mission. The established clearance requirements shall account for the following (Critical Envelope/Clearances -

CCRS-MECH-REQ-TBD, contains the requirements for monitoring, tracking and verifying all clearances on CCRS):

a. Manufacturing, assembly, and alignment tolerances,

b. Bulk Temperature,

c. Temperature gradients,

d. Vibration, and

e. Operational loads.

3.2.2.2 Tolerancing

MM37 Dimensional tolerances on all moving parts and intentional interference-fit parts shall be established and documented via a tolerance stack-up/clearance analysis to ensure that proper functional performance is maintained under all natural and induced environmental conditions and configurations.

Lubrication

3.2.3.1 Lubricant Compatibility

MM38 Lubricants used in the mechanism shall be compatible with the following:

a. Interfacing materials (including components and fluids),

b. Other lubricants used in the mechanism,

c. All natural and induced environments encountered by the mechanism,

d. Outgassing/creep requirements (e.g., for nearby optical surfaces), if applicable, and

e. Hydroscopic requirements, if applicable.

3.2.3.2 Lubricant Life

MM39 The selection of lubricant for use in the mechanism shall be based upon development tests or other heritage use of the lubricant that demonstrate its ability to provide adequate lubrication under all specified operating conditions over the design lifetime.

MM40 An evaporative loss analysis shall be performed for any liquid lubricant application, subject to depletion, to show that there is an adequate amount of lubricant in the system (not including degradation) for the duration of the mechanism’s operational life with a margin greater than 10.

3.2.3.3 Solid Lubrication

MM41 If solid lubrications are used, specific written procedures shall control the method of application, subsequent handling and ground testing of the components and assemblies to avoid exposure to moisture or humidity.

Deployables

MM42 Separation systems utilizing separation nuts or frangible nuts shall extract the bolt without reliance upon preload or gravity.

MM43 All interfaces in deployment and jettison mechanisms designed to separate in service shall use kickoff springs to ensure first motion.

MM44 All pyrotechnic (or “ordinance”) devices shall comply with AIAA S-113-

2005 “Standard: Criteria for Explosive Systems and Devices On Space and

Launch Vehivles”.

3.2.4.1 Caging of Deployables

MM45 Mechanisms that require restraint during launch shall not require power to maintain the restrained condition.

MM46 All mechanisms requiring restraint shall be designed for a positive visual indication of proper restraint.

3.2.4.2 Indication of Deployment/Release Status

MM47 All movable/deployable mechanisms shall include in telemetry a positive indication that the mechanism has achieved its desired position or else it shall be possible to directly ascertain from telemetry that the mechanism has released and deployed adequately.

Springs

MM48 Springs shall be failure tolerant unless spring failure can be shown to be non-credible.

Viscous Dampers

MM49 Piston dampers shall be used in place of diaphragm damper.

MM50 All viscous dampers shall be vacuum filled to preclude entrapment of air.

MM51 Viscous dampers shall be vacuum tested to verify no leaks.

MM52 Viscous dampers shall not be used in any application which require operation after continued exposure to vacuum for greater than six (6) months.

Motors

MM53 Designs shall not include brush-type motors for critical applications with very low relative humidity or for vacuum operations. Excluded from this rule are contacting sensory and signal power transfer devices such as potentiometers and electrical contact ring assemblies (slip rings, roll rings, etc.).

MM54 For applications where the motor performance is critical to the mission success, the design shall be based on a complete motor characterization at the minimum and maximum voltages from the Spacecraft bus and motor driver.

MM55 Each commutated brushless motor shall have the following characteristics determined:

a. Rotor inertia

b. Torque versus current relationship.

c. Motor constant (Km).

d. Powered torque versus angle.

e. Unpowered parasitic torques (i.e., detent torque and torque ripple) versus angle.

f. Torque versus speed (including no-load speed and stall torque).

g. Phase resistances.

MM56 For applications where the motor is integrated into a higher assembly (i.e., assembled with gear head), the motor characterization shall be performed at the motor level prior to the integration.

Bearings

MM57 Bearings shall not be used for ground current return paths or to carry electrical current.

MM58 Bearings shall meet Annular Bearing Engineering Council (ABEC) 7, 7P, or

7T tolerances (or better) in accordance with Anti-Friction Bearing

Manufacturing Association (AFBMA) standards. Nonstandard bearings or thin sectioned bearings where AFBMA tolerances do not apply shall have the manufacturer’s precision level most nearly equivalent to ABEC 7.

MM59 The mean Hertzian contact stress in a bearing shall not exceed the appropriate values in Table 4.2.6-1 when subjected to the yield load.

Table 4.2.6-1 Mean Hertzian contact stress

Bearing Material, Typical Hardness Range

Mean Hertzian Contact Stress—

High Precision, Low Torque Ripple

Applications

Mean Hertzian Contact Stress—

Other Applications

440C Steel, 58-62 HRC 2310 MPa (335 ksi) 2760 MPa (400 ksi)

52100 Steel, 60-63 HRC 2480 MPa (360 ksi) 2960 MPa (430 ksi)

M50 Steel, 62-64 HRC 2480 MPa (360 ksi) 2960 MPa (430 ksi)

VIM CRU20 Steel, 66

HRC minimum 3790 MPa (550 ksi) 4070 MPa (590 ksi)

MM60 Rolling element bearings shall have a minimum hardness as given in Table

4.2.6-1.

MM61 Bearing fatigue life analysis shall be based on a minimum survival probability of 99.95% (L0.05) when subjected to maximum time varying operational loads under worst-case environmental conditions.

MM62 All ball bearings shall be preloaded with the following exceptions:

a. Four-point (gothic arch) bearings,

b. deep groove ball bearings for which it can be shown that the absence of preload on the deep groove ball bearing is not detrimental to the performance of the mechanism

MM63 If axial sliding of a bearing ring is required to maintain preload, sliding shall be facilitated by methods such as a tribological coating or a lubricated sleeve.

MM64 Mechanisms utilizing guides or linear bearings shall use a length-to-width ratio of 2:1 or greater, unless it can be shown by analysis that a length-to-width ratio of less than 2:1 will not cause the mechanism to bind or undergo stick-slip motion taking into account the following:

a. Possible friction coefficients

b. Contact forces

c. Actuating forces

d. Dynamically induced forces

e. Misalignments

f. Eccentric loading

Gears

MM65 Gear trains shall have analysis demonstrating positive margins of safety for strength and wear, accounting for the following conditions:

a. Tooth pitting, brinelling, and bending stresses under nominal and peak operating loads.

b. Impact tooth loads from maximum combined axial, radial, and moment loads sustained during the full life cycle of the mechanism.

c. Backlash.

d. Effects of temperature and temperature gradients on quality of lubrication and gear contact pattern.

e. Effects of tooth geometry.

f. Undercutting and tooth profile modifications.

g. Gear mounting, misalignment, and face load distribution.

h. Variation in operating center distance.

Mechanical Stops

MM66 Non-jamming end-of-travel stops shall be incorporated into mechanisms to prevent mechanism motion beyond design travel limit.

MM67 Mechanical stops or shoulders and associated attachments shall be designed to a structural yield factor of safety of at least 2.0 and an ultimate factor of safety of 3.0 based on static analysis for maximum impact loads that occur upon full extension, actuation, or stopping of the Moving Mechanical

Assembly.

MM68 Impact loads shall account for uncertainties in model parameters, analysis methodology, and any other effects, such as amplified inertia loads that may be transmitted through gear trains.

MM69 The design shall ensure that the stop transients do not overstress gear teeth or drive mechanisms. A snubbing arrangement that dissipates energy may be provided where necessary to reduce the impact forces.

Pulleys

MM70 All pulleys shall use pulley guards that extend to the tangency points of the cable.

Pulley Guard Illustration

Switches

MM71 When switches are used as indicating devices for mechanisms, the design of the switch mounting and the switch orientation shall be such that improper installation of the switch shall not physically impede mechanism travel.

MM72 The use of mechanically activated microswitches shall be limited to the indication of status conditions in telemetry and is prohibited in logic or command circuits.

MM73 The worst-case maximum travel of switch actuating mechanisms shall not damage the switch.

Retaining Rings

MM74 All retaining rings used shall be multiple-turn spiral-wound retaining rings.

Set Screws

MM75 Set screws shall not be used to transmit torque between a shaft and a component mounted on the shaft.

3.3 Mechanism Performance and Strength Analysis

MM76 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.

MM77 Bearings shall have analysis demonstrating acceptable material, mounting, preload, performance, and structural integrity, accounting for the following conditions:

a. Maximum combined axial, radial, and moment loads sustained during ground handling, launch, on-orbit, or other operational modes

b. System stiffness requirements

c. Effects of temperature, temperature gradients, fits, tolerances and initial preload on torque, stiffness, and life

d. Lubrication

e. Wear

f. Friction torque, considering breakaway and running, in the installed state

g. Reliability and life

h. Effects of alignments, fits, tolerances, thermal, and load-induced distortions on preload, stress, and bearing shoulder height requirements.

3.4 Mechanism Installation

MM78 Mechanisms shall either be designed to preclude installation in an incorrect orientation or else be clearly labeled in a manner that indicates proper installation orientation and prevents improper installation.

3.5 Structural Requirements

MM79 The CCRS component shall be capable of withstanding all worst-case load conditions to which it may be exposed, without requiring additional recalibration or realignment and by maintaining structural integrity (i.e., positive structural margins). This includes handling and transportation, test, pre-launch operations, launch, and on-orbit operations. Sections TBD through TBD of the CCRS Environmental Requirements Document (ERD), MSR-CCRS-SYS-REQ-0002, describe the environmental loads.

Finite Element Modeling

MM80 Components required by the ERD to submit finite element models (MSR-

CCRS-SYS-REQ-0002) to the CCRS shall submit model documentation that describes the following:

a. The version of the model, including date of creation.

b. A list of element, node, property, and material identification (ID) numbers.

c. A description of the nonstructural mass represented on each property card.

d. A description of units.

e. A description of the local reference coordinate system.

f. The results of satisfying the following model validity checks.

1. Equilibrium/grounding

2. Free-free dynamics (showing rigid body modes)

3. Unit gravity loading (each axis)

4. Enforced displacement/rotation (all 6 degrees-of-freedom)

5. Unit increase temperature (if required)

g. Mass Properties (CG location, Inertias, and total model mass).

Components required by the ERD to submit finite element models (MSR-

CCRS-SYS-REQ-0002) to the spacecraft shall adhere to the following:

a. Model submitted as a MacNeal Schwendler Corporation (MSC)/

NASA Structural Analysis (NASTRAN) data deck.

b. All model property and material cards have descriptive names.

c. Models submission is "full" model with no symmetry assumptions made to reduce model size.

d. Model includes no "Super Elements".

e. Model submission includes an explicit Single Point Constraint set.

f. Until actual hardware mass properties are verified and final, the finite element model is adjusted to the maximum allocated mass for each subsystem and component.

Component Fatigue

MM81 Thin-walled, highly loaded metallic CCRS components serving as springs, flexures and other compliance devices under cyclic loading shall show sufficient fatigue strength for 4 times the number of mission cycles

(including ground testing, launch and on-orbit loading).

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.

MM82 If materials are used for structural applications that are not listed in Table 1 of MSFC-SPEC-3029A, a Materials Usage Agreement (MUA) shall be negotiated with the project office.

MM83 Fracture control requirements (per NASA-STD-5019A) shall apply to the following elements only:

a. Pressure vessels, dewars, lines, and fittings (per NASA-STD

8719.24);

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

c. Weldments;

d. Parts made of materials in Tables II or III of MSFC-SPEC-3029A if under sustained tensile stress;

e. Parts made of materials susceptible to cracking during quenching;

f. Nonredundant, mission-critical preloaded springs loaded to greater than 25 percent of ultimate strength.

MM84 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.

3.6 Verification Requirements

Mechanism Verification

MM85 All mechanisms, including deployment and latching, devices shall be tested to demonstrate adequate functioning following exposure to the environments in the CCRS Environmental Requirements Document (ERD), MSR-CCRS-

SYS-REQ-0002, following NASA-STD-5017.

3.6.1.1 Mechanism Qualification Testing

MM86 Each mechanism shall undergo qualification testing to assure that its design margin meets all performance and safety requirements in all environments and situations that the mechanism may reasonably expect to encounter during its service life.

The mechanisms shall be qualification tested in their launch, on-orbit, and other operational configurations at the appropriate corresponding environmental extremes and in their appropriate passive or operating state during the launch or on-orbit operational phases.

MM87 Qualification testing of mechanical systems shall be conducted with the appropriate mounting interface, boundary conditions, including stiffness/flexibility, mounting alignment tolerances, thermal and load-induced distortions to ensure mechanical system structural integrity and performance.

MM88 Inspection and functional tests shall be performed both before and after qualification tests. The inspection and pass-fail criteria for the functional tests shall be established prior to the qualification test.

3.6.1.2 Mechanism Life Testing

MM89 Life testing shall be performed on all mechanism functions to verify that all design life requirements have been met. Life tests shall achieve no less than two times (2x) the total of all operational cycles plus ground cycles, with a goal of completing 1x cycles by Critical Design Review.

MM90 Life testing shall include a number of cycles at the expected operating environmental extremes, loads, and speeds that is representative of the number of cycles at those conditions expected in the service life of the mechanism.

MM91 The life test shall include operating bearings under the maximum predicted operational contact stress for the number of cycles predicted in flight multiplied by the appropriate life test factor. Note that differences between life-test drive electronics and flight electronics (e.g., voltage, current, duty cycle, etc.) could affect mechanism operating life and should be considered in the life test set-up.

MM92 If mechanical stops are contacted in the normal operation of the mechanism, life testing shall include testing of the mechanical stops by intentionally running the mechanism into the stops during each test cycle.

MM93 A performance test shall be conducted during both the first and last cycles of the life test. Inspection procedures and pass-fail criteria for life test and pre-and post-performance tests shall be established prior to the start of life testing.

3.6.1.3 Mechanism Acceptance Testing

MM94 All mechanisms shall be subjected to acceptance testing, which incorporates functional, run-in, and environmental testing structured to detect workmanship defects that could affect operational performance.

MM95 Mechanical stops shall be tested by intentionally running the mechanism into the stops whether or not the mechanism has limit switches or other design features to prevent contacting the stops in normal operation.

3.6.1.3.1 Functional Test Structuring

MM96 Functional tests shall be structured to demonstrate that the mechanism is operating correctly in order to verify all performance requirements.

MM97 All mechanism functions shall be exercised during mechanism functional testing.

MM98 Each mechanism designated as a flight or qualification test article shall undergo an initial functional test prior to undergoing any other acceptance or qualification testing.

MM99 Functional tests that exercise all mechanism functions shall be performed both before and after environmental tests in order to establish whether damage or degradation in performance has occurred.

3.6.1.4 Run-In Testing

MM100 A run-in test shall be performed on each mechanism after initial functional testing and prior to being subjected to further acceptance testing unless both of the following are true:

a) It can be shown that this procedure is detrimental to performance and would result in reduced reliability, and

b) The appropriate technical authority of the governing program grants a waiver for the run-in test prior to the start of acceptance testing.

MM101 The run-in test shall be conducted for a minimum of 50 hours except for items where the number of cycles of operation, rather than hours of operation, is a more appropriate measure of the capability to perform in a consistent and controlled manner. For these mechanisms, the run-in test shall be for at least 15 cycles or 5% of the total expected life cycles; whichever is greater for these mechanisms.

MM102 The run-in test conditions shall be representative of the operational loads, speed, and environment.

MM103 During the run-in test, periodic measurements shall be made to indicate what conditions may be changing with time and what wear rate characteristics exist.

3.7 Ground Support Equipment

MM104 Design and certification of dollies, stands and shipping container GSE shall follow the requirements outlined in 540-PG-8700.2.1.

MM105 Shipping containers for CRSS elements and GSE shall have features that permit the use of a forklift.

MM106 Lift sling design and certification shall follow the requirements outlined in

540-PG-8719.1.1.

3.8 Mechanical Ground Support Equipment (MGSE)

MM107 MGSE shall support performance verification of CCRS functionality, with specific MGSE used for alignment, vibration, thermal, and Instrument calibration activities.

MM108 CCRS lifting fixture shall be used to transfer the CCRS from the dolly to the

Spacecraft during CCRS installation.

MM109 CCRS MGSE shall have the capability of rotating the CCRS into the necessary orientations (e.g., 2-axis rotation, 0-180 degrees at 15 degree increments) for the integration and testing of Instrument components.

MM110 MGSE installed on CCRS shall have common ground with CCRS and

Spacecraft via mounting hardware or ground straps.

Appendix A Abbreviations and Acronyms

ABEC Annular Bearing Engineering Committee

AFBMA American Bearing Manufacturers Association

ARC Ames Research Center

CCB Configuration Control Board

CCR Configuration Change Request

CCRS Capture, Contain and Return System

CG Center of Gravity

EAR Export Administration Regulations

ESA European Space Agency

GSE Ground Support Equipment

GSFC Goddard Space Flight Center

GSFC Goddard Space Flight Center

HRC Rockwell Hardness C-Scale

ITAR International Trade in Arms Regulation

JPL Jet Propulsion Laboratory

KSI Thousand Pounds per Square Inch

LaRC Langley Research Center

LLC Link Layer Components

MGSE Mechanical Ground Support Equipment

MMDS Mechanical and Mechanism Design Specification

MPa Million Pascal

MSC MacNeal-Schwendler Corporation

MSR Mars Sample Return

MUA Material Usage Agreement

NASA National Aeronautics and Space Administration

NASTRAN NASA Structural Analysis

OS Orbiting Sample

PDL Product Design Lead

SBU Sensitive But Unclassified

SRF Sample Retreival Facility

SRL Sample Retrieval Lander

TBD To be determined

TBR To be revised

TDMS Technical Data Management System