Richard C. Oeftering, Martin A. Bradish, Jeffrey R. Juergens, Michael J. Lewis, and Daniel R. Vrnak

Glenn Research Center, Cleveland, Ohio

Component-Level Electronic-Assembly Repair 

(CLEAR) System Architecture

NASA/TM—2011-216956

January 2011

CLEAR–DOC–008
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Richard C. Oeftering, Martin A. Bradish, Jeffrey R. Juergens, Michael J. Lewis, and Daniel R. Vrnak

Glenn Research Center, Cleveland, Ohio

Component-Level Electronic-Assembly Repair 

(CLEAR) System Architecture

NASA/TM—2011-216956

January 2011

CLEAR–DOC–008

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
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7115 Standard Drive

Hanover, MD 21076–1320

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NASA/TM—2011-216956 iii

Executive Summary

This document intends to capture the system architecture for a Component-Level ElectronicAssembly Repair (CLEAR) capability. This architecture, hereafter referred to as the CLEAR system 

architecture, can be applied to electronic repair needs of the Constellation Program (CxP) in missions in 

Earth orbit and the Moon, and extendable to Mars. The CLEAR system architecture may be considered a 

precursor to a system functional requirements document and is intended to define the functions required 

to respond to the “Component-Level Electronic-Assembly Repair (CLEAR) Operational Concept” 

(CLEAR–DOC–007). The operational concept was developed to respond to the “Component-Level 

Electronic-Assembly Repair (CLEAR) In-Space Electronic Diagnostics and Repair Needs Assessment”

(CLEAR–DOC–006), and “Component-Level Electronic-Assembly Repair (CLEAR) Analysis of ISS 

On-Orbit Electrical Systems Problem Reporting and Corrective Actions,” (CLEAR–DOC–005), which 

both use the existing International Space Station (ISS) as an analogy for the types of electronics used in 

spacecraft and the types of problems encountered. 

The problem of electronics repair cannot be resolved by a simple monolithic solution. Instead, a 

solution must exploit existing capabilities while building new capabilities. This document considers the 

evolution or incremental growth in capability. The CLEAR system architecture is a semiautomated

system, capable of the complete repair cycle that includes diagnostic, repair, and test processes. This 

architecture considers the role of ground support, teleoperations, and the information infrastructure 

required to achieve its capability. 

A basic assumption is that the CLEAR repair process deals with flight hardware that is removed from 

the system as an orbital replaceable unit (ORU) and has been replaced with a spare ORU. The CLEAR 

strategy is to repair the faulty ORU and return it to service in the system or as a functioning spare.

The CLEAR system architecture is composed of four primary systems that have interactions with 

elements of the overall CxP architecture. Each system can be considered to involve both a Space segment 

and an Earth segment. The four systems for CLEAR are (1) Teleoperations, (2) Control and Data, (3) 

Diagnostics and Test, and (4) Repair Apparatus.

The CLEAR Teleoperations (CTO) system architecture is closely coupled with the CxP Command, 

Control, Communications, and Information (C3I) infrastructure. Repair involves problem diagnostics, the 

physical repair materials and processes (M&P), and functional test capabilities. CLEAR is highly 

dependent on detailed and complex information that requires specialized knowledge in a wide array of 

disciplines. The knowledge base exceeds that of our highly trained flight crews. Historically, the National 

Aeronautics and Space Administration (NASA) has augmented the flight crew by employing extensive 

telemetry, communications, and monitoring of systems by mission operations centers. Science payloads 

have been supported by remote payload operations centers that provide user access to science instruments 

and experiment payloads, without adding a burden on the primary flight system operations. CTO is an 

extension of this payload capability. 

The CLEAR Control and Data (CC&D) system architecture serves as the data backbone of the Space 

segment. The CC&D system must provide for incremental development of the repair-related technologies. 

It must be established early and yet resist obsolescence. A local-area network (LAN)-based architecture is 

inherently an open architecture, less restrictive than proprietary architectures, and considered the best 

option for long-term stability. The LAN-based data backbone is consistent with a plug-and-play approach 

that provides ease of integration and incremental growth. To assure high performance, the project is 

adopting the Institute of Electrical and Electronics Engineers (IEEE) 1588 “Standard for a Precision 

Clock Synchronization Protocol for Networked Measurement and Control Systems” (IEEE–1588) for 

precision synchronization of instruments, robotics, and machine control. This standard is already 

incorporated in Orion’s primary control architecture. 

The CLEAR Diagnostics and Test (CD&T) system architecture addresses the instrumentation of two 

repair-related activities. Diagnostics is used to determine and isolate a system malfunction to the 

component level and determine the root cause. Testing (functional) is aimed at verifying that the repair 

has restored full function and verifying that the repaired assembly is suitable to return to service. 

Although diagnostics and test are different activities, they often use similar functions and the same 
NASA/TM—2011-216956 iv

instruments. Thus, diagnostic functions and test functions are considered different applications of a single 

CD&T system. 

For diagnostics, CLEAR will adopt characterization techniques employed by the U.S. Navy that rely 

on “known-good” circuit signatures as a means of quickly isolating circuit faults. Functional tests require 

external power and emulation of external system interfaces. Emulation, along with a wide array of 

measurements, drives complexity and test system mass. To address the need for compact light equipment 

and the need for simple crew operation, the CD&T system will exploit the synthetic instrument (SI) 

approach. Synthetic instrumentation exploits advances in reconfigurable electronics and the ability to 

synthesize instruments on demand. Synthetic instrumentation is also consistent with the CTO approach.

The CLEAR Repair Apparatus (CRA) system architecture addresses the repair processes that are 

beyond the capability of manual tools and the crew skill level. Repair is driven by the design, materials, 

and fabrication processes used in the original circuit fabrication. Advanced high-density component 

technologies involve process cycles with control parameters and requirements that are beyond the 

capability of manual methods. Furthermore, spacecraft electronics require conformal coatings and 

conductive cooling features that impede the repair process. Fortunately, nearly all component replacement 

can be done by modern reflow techniques. The CRA system will employ flexible, programmable 

equipment that can be configured for each application. These repair processes will be validated on Earth 

before repairs are executed on critical flight hardware in space. Properly programmed and validated 

robotics control of thoroughly developed processes will create in situ repair capability for nearly all 

spacecraft circuit repair applications.
NASA/TM—2011-216956 v

Contents

Executive Summary.....................................................................................................................................iii

1.0 Introduction ..........................................................................................................................................1

2.0 Documents............................................................................................................................................2

2.1 Reference Documents.................................................................................................................2

2.2 Applicable Documents................................................................................................................2

3.0 CLEAR System Architecture ...............................................................................................................3

3.1 Overview.....................................................................................................................................3

3.2 Assumptions................................................................................................................................3

3.3 Partitioning Into Segments..........................................................................................................5

3.3.1 Space Segment .............................................................................................................. 5

3.3.2 Earth Segment............................................................................................................... 5

3.4 CLEAR Systems.........................................................................................................................5

3.4.1 CLEAR Teleoperations System Architecture ............................................................... 5

3.4.2 CLEAR Control and Data System Architecture ........................................................... 6

3.4.3 CLEAR Diagnostics and Test System Architecture ..................................................... 6

3.4.4 CLEAR Repair Apparatus System Architecture........................................................... 6

4.0 CLEAR Teleoperations System Architecture ......................................................................................7

4.1 Overview.....................................................................................................................................7

4.2 Teleoperations Approach............................................................................................................7

4.3 Teleoperation Segments..............................................................................................................8

4.3.1 Space Segment: CLEAR SARADA Teleoperations..................................................... 8

4.3.2 Earth Segment: CLEAR TEST Teleoperations............................................................. 8

4.3.3 Communications Between Space and Ground Segments ............................................. 8

4.3.4 Teleoperation Computer Software ................................................................................ 9

4.3.5 CLEAR Teleoperations Data Transactions................................................................... 9

4.4 CLEAR Diagnostic, Repair, and Test Application Development.............................................12

4.4.1 Merging System Information with Development Tools ............................................. 12

4.4.2 Spacecraft Design Data............................................................................................... 13

4.4.3 System Problem History (PRACA Database)............................................................. 13

4.4.4 CLEAR Reference Database....................................................................................... 13

4.4.5 CLEAR Process Library ............................................................................................. 13

4.4.6 CLEAR Application Development Tools................................................................... 14

4.4.7 CLEAR Integrated Validation Tools........................................................................... 16

4.4.8 CLEAR Repair Process and Uplink Products............................................................. 16

5.0 CLEAR Control and Data System Architecture.................................................................................17

5.1 Overview...................................................................................................................................17

5.2 CLEAR Control and Data Approach ........................................................................................17

5.3 CLEAR Data Backbone: IEEE–1588 Enhanced Ethernet........................................................18

5.4 CLEAR Control and Data Unit.................................................................................................20

5.4.1 Crew Interface............................................................................................................. 20

5.4.2 CLEAR Imaging Controller........................................................................................ 20

5.4.3 CLEAR Diagnostic and Test Controller ..................................................................... 20

5.4.4 CLEAR Repair Apparatus Control ............................................................................. 22

6.0 CLEAR Diagnostics and Test System Architecture...........................................................................25

6.1 Introduction...............................................................................................................................25

6.2 Examination by Imaging Functions..........................................................................................25

6.2.1 Imagers........................................................................................................................ 25

6.2.2 Optics and Illumination............................................................................................... 26

6.2.3 Nonvisible Examination Technology (Ultraviolet, Infrared, and X-ray).................... 26

6.3 Compact Conventional Instruments Functions.........................................................................27
NASA/TM—2011-216956 vi

6.3.1 Meters.......................................................................................................................... 27

6.3.2 Oscilloscopes .............................................................................................................. 27

6.3.3 Signal Generators........................................................................................................ 27

6.3.4 Analyzers .................................................................................................................... 27

6.4 CLEAR Diagnostics by Characterization .................................................................................27

6.4.1 Analog Signature Analysis Function .......................................................................... 27

6.4.2 Complex Signature Analysis Functions...................................................................... 29

6.5 CLEAR Synthetic Instrument Architecture ..............................................................................30

6.5.1 Conventional Automatic Test Equipment Functions.................................................. 30

6.5.2 CLEAR Synthetic Instrument Functions..................................................................... 31

6.5.3 Allocating Space and Earth Synthetic Instrument Functions...................................... 32

6.5.4 Synthetic Instrument Functions and Technology Options.......................................... 33

7.0 CLEAR Repair Apparatus Architecture.............................................................................................38

7.1 Overview...................................................................................................................................38

7.2 Repair Apparatus Robotic Functions........................................................................................38

7.2.1 Robotic Motion ........................................................................................................... 38

7.2.2 Robotic Motion Parameters......................................................................................... 38

7.2.3 Robotic Operating Environment Constraints.............................................................. 39

7.3 Repair Process Functions..........................................................................................................40

7.3.1 Reflow Soldering Process........................................................................................... 40

7.3.2 Repair Process Containment ....................................................................................... 41

7.4 Staging and Handling Functions of Tools, Components, and Materials...................................42

7.4.1 Resource Staging......................................................................................................... 42

7.4.2 Diagnostic Probe Handling ......................................................................................... 42

7.4.3 Imager Handling ......................................................................................................... 42

7.4.4 Tool Handling ............................................................................................................. 42

7.4.5 Reflow Hardware Handling ........................................................................................ 43

7.4.6 Component Staging..................................................................................................... 43

7.4.7 Process Material Dispensing....................................................................................... 44

8.0 Concluding Remarks..........................................................................................................................45

Appendix.—Acronyms and Abbreviations.................................................................................................47

References...................................................................................................................................................49
NASA/TM—2011-216956 1

Component-Level Electronic-Assembly Repair (CLEAR) 

System Architecture

Richard C. Oeftering, Martin A. Bradish, Jeffrey R. Juergens, Michael J. Lewis, and Daniel R. Vrnak

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

1.0 Introduction

The Component-Level Electronic-Assembly Repair (CLEAR) task is part of the NASA Exploration 

Technology Development Program (ETDP) Supportability Project. CLEAR’s objective is to develop 

technologies that enable a capability for future space-flight crews to perform in situ repairs of electronic 

hardware at the component level (Ref. 1). This document, which is one of many documents produced by 

the CLEAR task (see Section 2.0), identifies a proposed architecture concept for how to perform 

component-level repair of electronics within a spacecraft or habitat. This architecture is based on a 

documented diagnostic and repair needs assessment (CLEAR–DOC–006) and operational concept 

(CLEAR–DOC–007).

The CLEAR task responds to the general need to reduce the upmass of spare hardware and to 

empower the crew to respond to problems without dependence on a robust and timely logistics system.

The CLEAR task has chosen to approach enabling component-level repair of electronics without 

expanding crew size or dramatically expanding flight crew training. This task has adopted a strategy to 

exploit teleoperations as a means of augmenting the flight crew with ground-based support on an asneeded basis. Previous documents (Refs. 1 and 2) have described this strategy.
NASA/TM—2011-216956 2

2.0 Documents

The following documents contain supplemental information related to the CLEAR task. 

2.1 Reference Documents

Document number Document title

CLEAR–DOC–005 Component-Level Electronic-Assembly Repair (CLEAR) Analysis of ISS OnOrbit Electrical Systems Problem Report and Corrective Actions

CLEAR–DOC–006 Component-Level Electronic-Assembly Repair (CLEAR) Assessment of 

Constellation Program In-Space Electronic Diagnostics and Repair Needs

CLEAR–DOC–007 Component-Level Electronic-Assembly Repair (CLEAR) Operational Concept

2.2 Applicable Documents

Document number Document title

CLEAR–ANA–001 Component-Level Electronic-Assembly Repair (CLEAR) Life-Cycle Cost 

Impacts of Different Approaches for In Situ Maintenance of Electronics 

Hardware

CLEAR–ANA–002 Component-Level Electronic-Assembly Repair (CLEAR) Noncontact Coupling 

Techniques for Performing Signature Analysis

CLEAR–DOC–001 Component-Level Electronic-Assembly Repair (CLEAR) Component Repair 

Exp-1 (CRE–1) Flight System Requirements Document

CLEAR–DOC–002 Component-Level Electronic-Assembly Repair (CLEAR) Component Repair 

Exp-1 (CRE–1) Concept and Hardware Summary

CLEAR–DOC–003 Component-Level Electronic-Assembly Repair (CLEAR) Recommendations for 

the Design of Electronic Assemblies for NASA's Exploration Program

CLEAR–DOC–004 Component-Level Electronic-Assembly Repair (CLEAR) Trade Study: Current 

Technologies and Instruments for Electronic Fault Diagnosis and Repair

CLEAR–DOC–005 Component-Level Electronic-Assembly Repair (CLEAR) Analysis of ISS OnOrbit Electrical Systems Problem Report and Corrective Actions

CLEAR–DOC–006 Component-Level Electronic-Assembly Repair (CLEAR) Assessment of 

Constellation Program In-Space Electronic Diagnostics and Repair Needs

CLEAR–DOC–007 Component-Level Electronic-Assembly Repair (CLEAR) Operational Concept

CLEAR–DOC–009 Component-Level Electronic-Assembly Repair (CLEAR) Recommendations for 

Enabling Manual Component-Level Electronic Repair for Future Space 

Missions

CLEAR–RPT–001 Component-Level Electronic-Assembly Repair (CLEAR) Component Repair 

Exp-1 (CRE–1) Systems Requirements Review (SRR) Panel Report

CLEAR–RPT–002 Component-Level Electronic-Assembly Repair (CLEAR) Soldering in Reduced 

Gravity (SoRGE) Mission Test Report

CLEAR–RPT–003 Component-Level Electronic-Assembly Repair (CLEAR) Analog Signal and 

Complex Signature Analysis Test Report

CLEAR–RPT–004 Component-Level Electronic-Assembly Repair (CLEAR) Synthetic Instrument 

Capabilities Assessment and Test Report
NASA/TM—2011-216956 3

3.0 CLEAR System Architecture

3.1 Overview

The CLEAR system architecture is an organized functional system structure that establishes primary 

elements, the functional hierarchy, and dependencies of a system to meet the operational needs of the 

CLEAR concept of operations. The CLEAR architecture serves as a guide for the development and 

design of the actual system.

The CLEAR system architecture is intended to cover the complete system from ground-user 

interfaces to flight hardware and crew. Since the capability is aimed at supporting flight systems, there 

are many aspects of both ground and flight operations that must be considered. Where possible, the 

project intends to exploit existing ISS infrastructure or planned Constellation Program (CxP)

infrastructure. This includes existing organizational capabilities that currently support the ongoing space 

shuttle and International Space Station (ISS) operations. 

The overall architecture, as outlined in the CLEAR Operational Concept (CLEAR–DOC–007), is 

split into an Earth segment and a Space segment. The Earth segment involves information and database 

management, operational planning, and robotic and automated equipment programming and validation.

The Space segment involves all the in-space equipment including diagnostic and test instruments, 

robotics, and repair process equipment with related controllers and crew interfaces. 

This document defines three major system architectural elements, the teleoperations, the diagnostics

and test, and the repair apparatus subsystems. As described in CLEAR–DOC–007, CLEAR depends on 

teleoperations to perform complex tasks with minimum impact on crew time and training. CLEAR 

Diagnostics and Test (CD&T) functions are performed by an integrated set of highly reconfigurable 

equipment. The CLEAR Repair Apparatus (CRA) includes the materials and processes (M&P) of repair 

and the robotic elements required to automate the processes. Each CLEAR subsystem has a distinct role,

and this document describes functions and relationships between subsystems and users.

3.2 Assumptions

CLEAR is a task under the supportability project for CxP’s ETDP office. Since much of the CxP

architectures are still being formulated, the CLEAR team must make assumptions about future 

capabilities that will be provided by the program. Many assumptions are extrapolations of space shuttle 

and ISS capabilities. The CLEAR team acknowledges that assumptions are will be inherently inaccurate,

and the architecture is expected to be revised and updated as program changes and new information 

becomes available. 

Assumption.—The command, control, communications, and information (C3I) infrastructure is 

provided by CxP.

Rationale.—CLEAR is not responsible for developing independent C3I. The design will, however, 

be compatible with the C3I infrastructure provided.

Assumption.—The spacecraft systems for CxP will utilize a modular orbital replaceable unit (ORU)

design philosophy similar to that used in the ISS. 

Rationale.—Component-level repair does not negate the need for ORUs. ORUs make it feasible to 

quickly remove and replace malfunctioning hardware and return systems to full operation. Componentlevel repair affects how an ORU is processed once it has been removed from the system.

Assumption.—Removal and replacement of an ORU is handled by operations. CLEAR controls the 

hardware once an ORU has been disassembled or a faulty intermediate-level assembly has been removed 

from the ORU. 
NASA/TM—2011-216956 4

Rationale.—CLEAR relies on spacecraft operations to perform ORU remove-and-replace operations 

and any deintegration required to access electronic (intermediate-level) subassemblies. CLEAR 

diagnostics, repair, and test activities will be used to repair subassemblies by removal and replacement of 

components. Components will be repaired or reworked depending on the complexity of the tasks and the 

available M&P.

Assumption.—Communications for CLEAR equipment are handled as a payload rather than a 

spacecraft system.

Rationale.—This relaxes certain safety, reliability, and security requirements that are normally 

needed for real-time interaction with flight critical systems. It provides greater latitude in CLEAR 

equipment control. It also implies that CLEAR would be communicating through a payload host center 

that would handle the communications exchanges between the CLEAR Earth segment and the CLEAR 

Space segment.

Assumption.—A CxP logistics depot or equivalent logistics center will provide the main source of 

engineering support and management for the CLEAR Teleoperations Support Team (TEST) center.

Rationale.—Logistics depots provide ongoing support for on-orbit operations, including processing 

of hardware prior to flight integration and servicing ORUs. These depots are equipped to diagnose, 

repair, and test ORUs in preflight operations or as part of processing ORUs returned from orbit.

Expertise and skills are distributed throughout the Agency and its contractors. A depot serves as the

center for organizing the detailed responses to system hardware problems. It is assumed that such a depot 

would take ownership once the capability is developed.

Assumption.—The C3I infrastructure will expand the capabilities beyond that currently employed 

for the space shuttle and ISS.

Rationale.—According to the C3I CxP 70022: Constellation Program Command, Control, 

Communication, and Information (C3I) Interoperability Standards Book, Volume 1: Interoperability 

Specification, the system will be upgraded to better exploit existing legacy capability and incorporate 

non-Government assets. The routing of messages and data will employ an Internet-like protocol; 

therefore, CLEAR uplink and downlink transactions may be more like Internet transactions.

Assumption.—CLEAR will be operated as an independent payload; thus, a CLEAR TEST will be 

provided with communications interfaces and communications software development kits that will 

simplify teleoperations development. 

Rationale.—To avoid the interference with primary spacecraft operations and allow the payloads to 

operate freely within a predefined envelope, the ISS program established separate communications 

channels. For ISS payloads, command and data communications between payloads and payload users, 

such as science experiments, are accommodated by the Huntsville Operations Support Center (HOSC)

(based at the NASA Marshall Space Flight Center). The HOSC also provides a Telescience Resource Kit

(TReK) to assist payload developers and users in developing an interface that will provide access to 

payload data and command uplink. A similar arrangement is assumed for CxP operations.

Assumption.—CLEAR hardware will be accommodated in a payload or multipurpose facility.

Rationale.—CLEAR repair operations will use techniques, materials, and processes that should be 

isolated from the crew’s cabin environment. For CxP lunar surface operations, the repair apparatus and 

containment enclosure may share resources with science payloads. This would include utilities that 

support atmosphere containment, inert atmosphere supply, and a means of exhaust venting.

For the shuttle and ISS, many small microgravity experiments are performed in a small, rack-mounted 

facility called microgravity science glovebox. CLEAR assumes that CxP will provide functionally 

similar accommodations on the lunar surface.
NASA/TM—2011-216956 5

3.3 Partitioning Into Segments

CLEAR will comprise an Earth segment referred to as “CLEAR TEST” (Teleoperations Engineering 

Support Team) and a remote (on-orbit) segment, referred to as semiautomated repair and diagnostics 

apparatus (SARADA).

3.3.1 Space Segment

CLEAR SARADA is a system that will operate in a manner similar to an experiment payload.

Payloads often are supported with a mix of voice, video, and data communications. SARADA provides 

for both manual operations involving direct action of the crew and automated operations under the direct 

control of the CLEAR TEST team. SARADA will provide diagnostic, repair, and test equipment suited 

for isolating faults, performing repairs, and performing functional tests. 

 SARADA will support both a manual diagnostic and test capability and a teleoperated 

automated diagnostic and test capability.

 SARADA will provide specialized equipment to support manual operations, such as removal of 

intermediate-level assemblies from ORUs and simple component-level repairs.

 SARADA will provide the specialized equipment and material handling capabilities needed to 

support the M&P required for automated component-level repair. 

CLEAR SARADA integrates many discrete functions. It encompasses the flight CC&D system, 

CD&T system, and the CRA system.

3.3.2 Earth Segment

The ground-based CLEAR TEST center will be similar in concept to the Glenn Telescience Support 

Center (TSC) used to support science payload operations. Payload teleoperations allow NASA centers 

and institutions to interact with their payloads without posing a risk to the primary flight systems.

The CLEAR TEST concept will be consistent with the NASA logistics and repair depot system used 

for the space shuttle and ISS. Flight electronics problems will be tracked with the existing Problem 

Reporting and Corrective Action (PRACA) system, and flight system information will be accessible 

through the Vehicle Master Database (VMDB). By exploiting existing problem tracking and design 

information infrastructure, CLEAR can expand capabilities with minimum impact to current operations.

The CLEAR TEST center also will develop and validate diagnostic and test procedures, process kits, 

and software code required for performing the physical repairs. The CLEAR TEST center will develop 

and maintain a CLEAR library containing validated procedures and programming code for reuse in 

future applications.

3.4 CLEAR Systems

CLEAR involves four interdependent systems with their own architectures: the CLEAR 

Teleoperations (CTO), CLEAR Control and Data (CC&D), CD&T, and CRA systems.

3.4.1 CLEAR Teleoperations System Architecture

Regardless of the repair method (manual or automated), it is essential to define space and groundbased activities related to the repair process and the telecommunications infrastructure that links them. In 

many ways, repair is an off-nominal or contingency operation, and there may be considerable risks to the 

crew and mission. The wide diversity of systems makes it impractical to have each crew member 

familiar with the level of detail required to diagnose and repair flight hardware. The crew must be 

backed by ground-based expertise and a knowledge base capable of resolving the problem, creating and 

coordinating crew procedures, and programming equipment to execute corrective actions.
NASA/TM—2011-216956 6

As described in the CLEAR Operational Concept (CLEAR–DOC–007), teleoperation involves 

people, information, and information and development tools. Section 4.0 will outline what information is 

acquired, what actions are formulated, and type of commands and information that pass between the 

ground and flight segments.

3.4.2 CLEAR Control and Data System Architecture

The CC&D system links directly to the spacecraft’s onboard command and data system. The CC&D 

system serves as the Space segment of the overall CLEAR architecture and is the primary controller for 

the SARADA subsystems including the CD&T system and CRA system.

3.4.3 CLEAR Diagnostics and Test System Architecture

The CD&T architecture is tightly coupled with the overall teleoperations via the CC&D system.

CD&T data will be passed from flight equipment to the Earth segment. The goals of diagnostic and 

functional test measurements have distinctly different objectives, but the measurement instruments are 

often the same. Therefore, diagnostics and test are considered to be different functional applications of a 

single architecture. At the component level, CD&T requires planning and is highly dependent on 

acquiring specific measurements, locating the specific measurement nodes, and properly setting up both 

target device and measurement instruments. All of these activities require planning and preparation prior 

to measurements and detailed examination of the resulting data.

3.4.4 CLEAR Repair Apparatus System Architecture

Component-level repair may be performed manually and will always be an option when human 

crews are available. However, many operations are best handled by dedicated preprogrammed 

equipment designed to reproduce many of the conditions used in manufacturing. Most high-density 

devices and particularly, modern grid array devices, require a solder reflow capability that is beyond the 

reach of simple manual soldering irons. One of the overlooked parameters associated with solder repairs 

is process timing. Since reflow processes have specific temperature profiles with heat ramp and soak 

periods, special programmable closed-loop controllers are required. The actual profile may have been 

developed by analysis or by actual experiments.

In low or zero gravity, normal heat convection currents are suppressed, which means heated objects 

will become hotter more rapidly. Overheating components is the main hazard in component repairs.

Therefore, a manufacturer’s heat profile cannot be used without accounting for gravity. The effect of low 

gravity on convective cooling requires adjusting profiles based on gravity models. For robotic 

component removal and replacement, a motion-control sequence must be programmed. Therefore, 

apparatus programming must be performed and validated offline before teleoperations.

Since repair may require removal of conformal coatings and application of flux and cleaning fluids,

the repair apparatus must provide methods of containing vapors, liquids, and debris. Many process steps 

are easier to accomplish with simple crew intervention. Like CD&T, the actual CRA architecture is

intimately tied to the CTO architecture via the CC&D system.
NASA/TM—2011-216956 7

4.0 CLEAR Teleoperations System Architecture

4.1 Overview

CLEAR intends to provide a capability to perform in situ repairs of electronic hardware at the 

component level. CLEAR responds to the need to reduce the upmass of spare hardware and to empower 

the crew to respond to problems without dependence on a robust and timely logistics system. The 

CLEAR project has determined that this must be accomplished without expanding crew size or 

dramatically expanding flight crew training. The project has adopted a strategy to exploit teleoperations 

as a means of augmenting the flight crew with ground-based support on an as-needed basis. The previous 

CLEAR white paper, the CLEAR project plan, and CLEAR–DOC–007 described this strategy. 

This section defines the role of teleoperations in the diagnosis, repair, and functional test of 

electronic hardware in future missions, defines the roles of various elements in the program, and 

identifies computer software components needed to create teleoperations.

4.2 Teleoperations Approach 

CLEAR will be composed of the CLEAR TEST Earth segment and the remote (on-orbit) CLEAR 

SARADA segment. The ground-based CLEAR TEST center will be similar in concept to the Glenn TSC 

used to support science payload operations. Data communications and transfer rates given here are based 

on those available between the TSC and the ISS. The makeup of the CLEAR TEST will be consistent 

with the NASA depot system used for the space shuttle and ISS.

CLEAR is designed to keep the crew workload to a minimum. The key is to link the diagnostic and 

repair process to knowledgeable and skilled engineering staff through teleoperations. However, this 

support should not become a burden to the program by requiring a dedicated staff to perform repair and 

diagnostic teleoperations. The preferred approach is to provide a capability that can be called upon as 

needed.

The CLEAR concept is intended to minimize dependency on real-time interaction. Real-time 

interaction is possible and feasible for some operations. The process of diagnosing faults, testing, and 

setting up a repair is prone to long pauses while support staff assess data and consider the next step.

Considering the frequent loss-of-signal events and the high value of both crew time and 

communications, it is more practical to perform as much of the process offline as possible. To 

accomplish this, CLEAR considers both NASA practices and industry practices in regards to automated 

operations.

From manufacturing, CLEAR borrows the approach used by relatively small or short-run 

manufacturing operations. To compensate for the high cost of labor, manufacturers will leverage 

engineering and machinist skills by capturing machine operating parameters in software data files. An 

early example was the development of computer numerical control (CNC) techniques where simple and 

compact machine “G-codes” are used to program and execute machine tool operations. Similarly, 

microgravity experiments aboard the space shuttle and ISS were extensively preplanned and automated 

with optional breakpoints in the experiment procedures to accommodate changes based on near real-time 

assessment of experiment data.

To provide efficient preprogrammed control and to accommodate flexibility, CLEAR TEST 

engineers will develop and verify pre-scripted diagnostic and repair routines that may include decision 

branches at key points. The process may employ manual crew operations in combination with a robotic 

mechanism. 

CLEAR SARADA will be designed to accommodate both manual and automated operations. For the 

most part, CLEAR SARADA will not operate under remote real-time control. Programming and 

subsequent verification will be performed offline and will avoid unnecessary consumption of crew and 

teleoperations time.
NASA/TM—2011-216956 8

Figure 1.—CLEAR is composed of an Earth segment and Space segment that is linked via 

Constellation Command, Control, Communications and Information (C3I) infrastructure.

4.3 Teleoperation Segments

As described in the introduction, CLEAR is composed of two segments. For this document, the 

Earth segment is referred to as CLEAR TEST. The Space segment is referred to as the CLEAR 

SARADA. The following subsections delineate the roles of each segment (Figure 1).

Teleoperations must bridge these segments by relying on program assets, such as the deep space 

network and the tracking and data relay satellite system. As CxP evolves, new capabilities may be added 

to the system. Teleoperations must be transparent to the flight-hardware and ground-based users.

4.3.1 Space Segment: CLEAR SARADA Teleoperations

CLEAR SARADA represents the Space segment of CTO. SARADA’s internal command and data 

system interfaces with the spacecraft Command and Data Handling (C&DH) system. The CLEAR 

command and data backbone supports teleoperations within the SARADA hardware.

4.3.2 Earth Segment: CLEAR TEST Teleoperations

CLEAR TEST represents the Earth segment of CTO. TEST is composed of people and the tools they 

employ for developing and validating repair operations. It also includes the information libraries 

required to support CLEAR and to capture and archive teleoperations

4.3.3 Communications Between Space and Ground Segments

Table I indicates the average and maximum data file sizes for diagnostic and repair operations. The 

files required to control the diagnostic and repair system are uplinked via the C3I system to CLEAR 

SARADA. The data are parsed out to the final subsystem controllers. The data downlinked will include 

diagnostic and test data files, digital images, and high-definition digital video.
NASA/TM—2011-216956 9

TABLE I.—CLEAR PRELIMINARY FILE SIZE ESTIMATESa

File type Maximum size,

MB

Average size,

MB

Uplink/

downlink

Comment

Huntron test file

(includes CAD files)

50 25 Uplink Compressed

Separate printed circuit board

CAD files (Gerber format)

10 2 Uplink Compressed

Functional test files 

(ref. LabView)

25 10 Uplink Uncompressed

Acquired functional data files 

(DSO, etc.) 

100 25 Downlink Eight high-speed

channels

(compressed)

Still image files 

(lossless JPEG2000)

4 3 Downlink 2000- by 2000-pixel

resolution

Motion image files 

(MPEG–4)

150 60 Downlink 60-s HDTV resolution

a

File size depends heavily on board size and complexity. These estimates are conservative and assumed a multilayer, 6U-size board.

4.3.4 Teleoperation Computer Software 

Teleoperation is software-intensive. Conversely, software development is highly constrained by the 

communication and security protocols imposed by spacecraft telecommunications. As noted in the 

assumptions, CxP will provide separate telecommunications channels to be used in the same manner that 

the ISS handles science payloads. In this way, CTO poses a minimum risk to flight system operations.

For ISS, a payload developer or user may interact with their payload using local ground facility that is 

certified and linked to the HOSC, which provides telemetry services.

Teleoperation software will need to support the CD&H for diagnostics, repair, and functional tests.

Major software functions are called computer software components (CSCs). CLEAR CSCs for 

diagnostic, repair, and test activities are tailored to each specific ORU application. Figure 2 illustrates 

some of the potential CSCs. Each CSC will have distinct development and validation requirements. To 

facilitate rapid development and validation, special software tools will be needed. For ISS, a TReK is 

provided to assist payload developers in developing a user interface that will provide access to payload 

data and command uplink.

4.3.5 CLEAR Teleoperations Data Transactions 

Figure 3, which is based on the scenarios outlined in CLEAR–DOC–007, shows the data 

transactions that occur between elements of the Earth and Space segments. The figure is a diagram that 

is often referred to as a “swim lanes diagram” by software architecture designers. System elements are 

illustrated as lanes that represent elements domain. Rounded bubbles represent data, and rectangular 

blocks represent operations or processes. Each element owns certain processes and data libraries. Data 

files generated may require input data from other elements, and dependencies are illustrated. 

In the illustration, information from VMDB and PRACA databases is used to help create diagnostic 

strategies. The programming of diagnostics also requires information regarding diagnostic capabilities. 

The data product is a diagnostic routine that was developed and validated for uplink to the Space 

segment. If synthetic instrument (SI) technology is employed, the code required to synthesize an 

instrument is included in the diagnostic routine. Any new code developed will also be sent to update the 

CLEAR library.
NASA/TM—2011-216956 10

Figure 2.—CLEAR CSC using the International Space Station payload operation 

center model.
NASA/TM—2011-216956 11

Figure 3.—Swim lanes model of the CLEAR data transactions.

As shown, the Space segment is composed of the crew and the CLEAR apparatus. Note that the 

Space segment activity is directly related to setup and execution of the diagnostic and repair operations.

The time-consuming processes of creating and validating diagnostic and repair procedures, equipment 

control, and data processing routines are all done offline. This minimizes crew time and training 

requirements. 
NASA/TM—2011-216956 12

4.4 CLEAR Diagnostic, Repair, and Test Application Development

4.4.1 Merging System Information with Development Tools

Effective response to problems requires access to detailed design information and an understanding 

of the system history and its current configuration. The response also requires the ability to access, 

understand, and use the technical repair tools. The TEST will need an array of information and an array 

of technical options to formulate corrective action.

As illustrated in Figure 4, diagnostic, repair, and test operations will involve details provided by a 

complete set of drawings and documents. The emphasis on teleoperations and remote control will require 

special tools, particularly if robotic equipment is used. The following sections describe the database, 

library, and development tools required.

Figure 4.—CLEAR diagnostic, repair, and test application development.
NASA/TM—2011-216956 13

4.4.2 Spacecraft Design Data

For shuttle and ISS, design details are captured in a design database called the VMDB. Diagnostic, 

repair, and functional tests will require detailed design and configuration information. 

The design data must provide the following design information:

 Functional design requirements

 Assembly and component details (circuit-card assembly (CCA) digital drawing files)

 Fabrication details including materials and process information

 Software specifications

 Built-in test (including Joint Test Action Group (JTAG) tests)

 Accept test specifications

To facilitate diagnostics, repair, and functional tests, the VMDB can be expanded to include as-built

and as-repaired configurations.

4.4.3 System Problem History (PRACA Database)

The PRACA system provides information regarding ongoing open-problem reports and historical 

closed-problem reports. The recent review of ISS PRACA reports in CLEAR–DOC–005 shows

electrical systems problem reports were reviewed. The analysis was launched as part of an overall needs 

assessment for on-orbit electrical repair. The analysis indicated that roughly 42 percent of electrical and 

electronic system problems are ultimately resolved with component-level repairs.

The same report indicated that the existing telemetry and built-in tests are inadequate to resolve 

many problems. The “root cause unknown” statement in many electrical PRACA reports is an indicator 

of a need for greater diagnostics to resolve problems below the ORU level. The PRACA reports often 

refer to failure analysis reports that may involve a very detailed investigation and examination of a 

problem’s root cause.

The PRACA system is very important not only as a problem archive but as a problem-reporting and 

tracking tool. The first time a problem is detected, a problem report is activated. From a CxP perspective, 

a problem report initiation will be the first indication that a CLEAR diagnostic repair and test process is 

needed. The problem report closeout will be the final indication that the CLEAR process is complete.

4.4.4 CLEAR Reference Database

The CLEAR reference database is composed of information not found in the design database or 

spacecraft problem reports. For example, circuit cards characterization information for “known-good”

boards.

The CLEAR reference database will contain information unique to CLEAR operations and design 

capabilities. 

 Analog signature analysis (ASA) and complex signature analysis (CSA) characterization data

 SI capabilities 

 Test functions

 Repair process parameters 

 Repair materials properties 

 Repair apparatus functions and capabilities 

4.4.5 CLEAR Process Library

The CLEAR process library represents the accumulated knowledge for the diagnostics, repair, and 

test of circuits. Unlike other databases, this library is intended to contain reusable control codes and 
NASA/TM—2011-216956 14

setup parameters. Much like an industrial CNC library, it will contain the programming code and 

parameters for specific component-repair operations. 

Diagnostic Routines.—The developed diagnosis of a specific fault of a specific circuit will be stored 

in this library. Because diagnostic processes search for an undetermined cause, a variety of diagnostic 

routines may be used to determine a specific fault. Over the life of the circuit design, multiple 

independent faults may occur. Therefore, we expect to accumulate a large library of diagnostic routines.

Repair Procedures.—For any given circuit, a procedure may be needed for every component type.

Therefore, like diagnostics, a significant library of repair procedures can be accumulated. It would be 

useful to have a template process that covers setup operations and contains commonly used processes.

Functional Test Procedures.—A delta (subset) of acceptance test procedures will be used to verify 

that the circuit has been successfully repaired. CLEAR will use the SI approach to synthesize interfaces 

required for a functional test.

4.4.6 CLEAR Application Development Tools

Diagnostic and Test Programming Tools.—These tools are aimed at programming the Space 

segment to perform various diagnostic and test functions for specific circuit applications. Since 

diagnostics and functional testing involve many of the same instruments, they will use the same tools. In 

some cases, the programming involves purely electronic functions while others, such as automated 

probing, involve robotic motion control.

Diagnostic and test functions often rely on basic conventional instruments, such as multifunction

meters, oscilloscopes, and signal generators. A new generation of “panel-less instruments” minimizes 

space and weight by eliminating displays and adjustment knobs and by employing a common laptop 

computer as the user interface. Setup of instrument parameters and coordination between stimulus 

signals and signal measurement must be programmed into the hardware. Instrument vendors can provide 

the programming and interface software. Coordination will require programming of diagnostic and test 

controllers that will use an IEEE–1588 instrument triggering standard. 

Imaging tools provide the ability to manipulate imaging cameras that are part of the flight apparatus.

A remotely controlled digital camera will be used in visual examination and will provide imaging for 

both flight crew and CLEAR TEST. These tools will provide camera resolution, frame rate, and optical 

settings suited for circuit board examination. These tools also define the data processing and 

compression techniques.

The robotics programming tools will be used to preset the positions of imaging devices that are 

manipulated robotically. The positioning will be based on circuit computer-aided design (CAD) data for 

component location and identification and to locate registration points for the repair process. This same 

data will support advanced examination tools like infrared imaging or x-ray.

For safe operation, CLEAR will employ robotic motion validation tools, assuring collision-free 

motion control to minimize risk to hardware and crew.

Analog Signature Analysis and Complex Signature Analysis Programming.—ASA and CSA both 

rely on data from “known good boards” (Gold Boards). Similar to the U.S. Navy “gold disk” program, 

these “gold signatures” will be needed to support the diagnostics. If not available, a library of gold 

signatures will be acquired through actual tests of good circuits performed at a ground-based depot.

These will be added to the CLEAR reference library for future reference. 

Synthetic Instrument Programming.—SI technology provides a highly capable, but generic 

instrument, front end. This is described further in the diagnostics and test architecture. In many ways,

synthetic instrumentation is based on the premise that many instrument functions are digital or can be 

performed by digital circuits, which implies that instrument functions can be operated as software. To 

achieve instrument-level performance, it is necessary to embed software into field-programmable gate 

array (FPGA) that allows designers to exploit data pipelines, parallel processes, and other signal 

processing techniques that give conventional instruments their high performance. A set of tools will be 
NASA/TM—2011-216956 15

needed to create an instrument model and then perform the hardware programming. Ground-based 

simulators of the flight hardware will be needed to develop and validate the code.

FPGA programming has a specific programming language called VHDL. VHDL is a compound 

acronym where V is VHSIC (very high-speed integrated circuit) and HDL is hardware description 

language. The Department of Defense (DOD) developed the VHDL language for logic synthesis 

applications. IEEE–1076 is the main standard governing the VHDL language syntax. Higher-level and 

easier-to-use tools have been developed that simplify the programming process. Products like MatLab

(The MathWorks, Inc.) and LabVIEW (National Instruments) can generate VHDL code. Tools are 

available the can model and validate the VHDL code prior to committing it to hardware. To assure high 

performance, the code must be programmed and tested in real hardware before it is uplinked to the 

CLEAR SARADA’s SI system.

Repair Material and Processes Modeling Tools.—Certain processes may have a significant 

dependence on gravity. In microgravity, voids in metal solder joints are more prevalent than 1-g and 

require certain adjustment to the process. Microgravity tools take the setting used for normal solder 

processes and compensate them for microgravity effects.

Solder reflow is used for removing components and installing new components. The process 

typically employs a solder paste with heat-activated flux. A predefined temperature profile is required to 

ensure proper flux activation and solder reflow, yet it minimizes the excess temperatures that may 

damage the circuit.

Many circuits are conductively cooled with integrated heat sinks that make reflow processes more 

difficult to achieve. Reflow process models will incorporate thermal models of each circuit card and will

account for microgravity effects. The models will be used to adjust preheat cycles and component 

heating profiles to assure a reliable repair and prevent damage due to excessive heating. The final output 

is a reflow process profile that specifies the heat flux and wattage of each heating element along the 

timed reflow profile.

Apparatus Control Programming Tools.—The repair apparatus requires control software to perform

robotic motion control functions and control the reflow process. There are several forms of robotics for 

general-purpose movement and manipulation of objects. The simplest and most widely used is a 

Cartesian or Gantry robot. This mechanism moves through space along three orthogonal axes and is 

often used in CNC machining centers where rotary tools carve complex shapes from simple base stock.

The simple coordinate system gave rise to simple-to-use programming languages. The common 

International Organization of Standardization (ISO) standard uses the CNC G-code. G-codes are simple 

character codes that defined a specific point-to-point motion along with a specific motion or tool 

parameter, such as rotation rate, or feed rate. G-code was intended to be a compact text code that would 

be simple enough for a machinist with no computer background to program.

Sophisticated programs are now available that can model three-dimensional motion and can even 

show the process and an animation. These more advanced programming tools produce G-code as their 

primary output because most CNC machines have G-code interpreters that convert the code into motion 

control parameters. The motion controllers coordinate the motion along multiple axes simultaneously so 

that they can perform complex motion.

Like CNC, the CLEAR apparatus must be protected from motion-control errors that could result in 

hardware collision or potentially harm a crew member. Thorough code validation can be performed by 

industry-standard three-dimensional validation tools that check the robotic motion paths for collisions or 

process sequence errors. For Cartesian-style robotics, there is a wide range of programming and 

validation tools available.

Reflow process control programming would normally be developed by experiment. However the 

influence of the low-gravity environment makes it impossible to accurately duplicate the process in 

Earth’s 1-g environment. M&P low-gravity models are, therefore, essential to creating an appropriate 

process heat profile. The criticality of the flight hardware and consequences of damage to the circuit are 

too great to allow a loosely controlled process.
NASA/TM—2011-216956 16

4.4.7 CLEAR Integrated Validation Tools

Before complex commands are uplinked to the Space segment, the code must be validated. The 

complex interactions among the instruments, robotic hardware, flight crew, and repair targets involve so 

many details that it is easy to overlook a detail that results in damage to hardware or injury to a crew 

member. As described in the previous section, industry uses development tools that can also perform 

simulation and serve as an initial validation of the process. However, the interaction between robotics, 

instruments, and crew members will require a simulation of the overall process. Motion control may be 

performed by three-dimensional animation of the process as used by industry for robotic and CNC 

operations. If substantial crew interaction is required, then a live simulation using a high-fidelity mockup 

of the system will be needed. The simulator and/or trainer would support this simulation and also serve 

as a trainer for flight crews.

4.4.8 CLEAR Repair Process and Uplink Products

The final products of the CLEAR development and validation effort are primarily software to 

configure, control and acquire data. The products will also involve repair process M&P kits needed to 

perform the repair. 

 CLEAR Diagnostics Software and Procedures 

 CLEAR Repair Apparatus Software and Procedures 

 CLEAR Functional Test Software and Procedures 

 CLEAR Repair M&P kits

The content of the products, the software programs, and kits are further described in later sections. 
NASA/TM—2011-216956 17

5.0 CLEAR Control and Data System Architecture

5.1 Overview

CLEAR system architecture attempts to create a unified strategy that can also accommodate 

incremental growth. There are many individual operations associated with the diagnosis, repair, and 

testing of flight hardware. These operations must be sequenced and coordinated and must not demand 

excessive crew time. Such a system must also tolerate communications interruptions and maintain 

control, regardless of external events.

The CC&D system architecture is intended to serve as a backbone to which discrete functional 

elements are integrated into a fully teleoperational and semiautomated system. This architecture is also 

intended to accommodate incremental growth capability while averting hardware obsolescence. The 

CC&D system must provide the flexibility to accommodate new functions as they are developed. 

5.2 CLEAR Control and Data Approach

Figure 5 illustrates a simplified hierarchy of the CC&D system, and Figure 6 shows many major 

CLEAR SARADA functions. The figure also illustrates the interconnections where commands, data, and 

power flow. The CC&D controller is both the main controller and master of the data network or data 

backbone of the system. This backbone function is essential to the incremental development strategy and 

must be defined explicitly prior to incremental hardware development. 

The CC&D controller is the master control of the SARADA. It serves as the primary interface with 

the equipment, crew, and spacecraft. It is also the gateway for CLEAR teleoperations. Each block in 

Figure 6 has a smart subsystem controller that also provides network interfaces to the block above and 

below it in the system hierarchy. Ideally, the blocks would provide a plug-and-play capability that would 

allow additional blocks to be added without requiring a massive reconfiguration of the system. The best 

way to accommodate plug-and-play is with LAN protocols.

Spacecraft Interface.—The CC&D controller is linked with the spacecraft’s C&DH network. For 

ISS, the connection would be a MIL–STD1553 serial bus. For CxP, the time-triggered gigabit Ethernet 

(TTGbE) would be the likely interface and incorporates features of the recently established IEEE–1588 

instrument network standard. The channel on the spacecraft side would be the branch of the C&DH 

system that supports payloads. Using payload, instead of primary system channels, eliminates the 

concern that CLEAR transactions would consume bandwidth needed for mission support. Since the 

payload command and data channels pose no risk of system hardware interference, the CLEAR TEST 

center can operate independently.

Figure 5.—CLEAR data backbone is a common Ethernet extension with IEEE–1588 protocols to 

make it deterministic and suited for high-speed instrumentation and robotics networking.
NASA/TM—2011-216956 18

Figure 6.—CLEAR semiautomated repair and diagnostics apparatus (SARADA).

5.3 CLEAR Data Backbone: IEEE–1588 Enhanced Ethernet

Several architectures are considered to be part of the CLEAR data backbone. For a number of 

reasons, a high-speed serial network that also supports precise triggering is the preferred approach. The 

data backbone architecture will be based on a variant of the ubiquitous Ethernet. Ethernet is a LAN 

protocol and is the world’s most widely supported standard. An unmodified Ethernet, based on network 

time protocol, is not normally considered to be adequate to support real-time control. However, industry 

has recently enhanced Ethernet to make it more “deterministic” and suited for systems with critical 

timing. 
NASA/TM—2011-216956 19

Enhanced Ethernet has been adopted in three relevant applications:

 Constellation.—TTGbE is the current standard for Orion. CxP originally considered STD 1553 

and 1394B before selecting TTGbE.

 Instrumentation.—LAN extension for instruments (LXI) is an Ethernet-derived instrument 

network promoted by several instrument makers, including Agilent.

 Industrial Motion Control.—New Ethernet derivatives have appeared in industrial equipment 

applications, particularly, for multiaxis motion controllers like robotics and CNC.

The adoption of IEEE–1588 has been essential in making Ethernet viable for these applications. The 

protocol makes Ethernet deterministic; that is, it makes the timing and response of the equipment fast 

and predictable. It is even possible to employ universal time clock transmissions provided by the global 

positioning system. The IEEE–1588 relies on a master clock and synchronization protocol to keep 

various devices in sync and deterministic.

Military Analogy.—If a general is preparing a synchronized attack by multiple armed forces, all 

subordinate commanders synchronize their clocks to the general’s master clock. Each commander is 

issued specific orders to execute at a precise time. When the internal clocks reach that precise point in 

time, each commander executes the assigned orders. The result is an attack that is coordinated,

simultaneous, and not dependent on further signals. Likewise, the IEEE–1588 master unit can use the 

Ethernet to command actions of subordinate units without special external trigger lines. This also implies 

that subordinate or slave units are both “smart” and are equipped with accurate “slave clocks.”

IEEE–1588 Synchronization Process.—Figure 7 shows how the network master device clock 

synchronizes a number of slave device clocks. The master and slave devices perform a series of message 

transactions that are intended to measure innate delays in the network and intervening connections. A 

precise characteristic delay is calculated and recorded by the slave device. When the master issues a 

“The time is now,” the slave device knows that the time received needs to be adjusted by the calculated 

characteristic delay and adjusts its own internal clock accordingly. With each device precisely 

synchronized, the master can download specific instructions to each slave device to be executed at a 

specific time.

Figure 7.—Message transactions used to synchronize slave clocks with the master clock.
NASA/TM—2011-216956 20

The master clock and network controller roles are performed by the CC&D controller. All other 

units within SARADA are slave units. The crew interface and the spacecraft payload data interface are 

external units and will have override authority. This is to assure that the flight crew and CLEAR TEST 

engineers can halt SARADA for safety.

5.4 CLEAR Control and Data Unit

This unit will perform the command and data handling functions.

 Mastering LAN

− Master clock 

− Synchronization management.

 Command and data multiplexing and demultiplexing for uplink and downlink 

 Command and data buffering

 Mass data storage 

 Data compression and formatting

 System health and safety monitoring

 Manage external interfaces 

− Crew interface 

− Spacecraft payload interface

 Manage CLEAR SARADA subsystems 

− Image controller 

− Diagnostics and test controller

− Repair apparatus controller

5.4.1 Crew Interface

The crew will interface the system through a Government-furnished laptop computer. The crew 

interface may be used for monitoring the CLEAR process, archiving instrument data, and performing 

data processing required to analyze and display data. The crew interface will provide the graphics 

display for CLEAR process setup and operating procedures. The crew interface will provide a CLEAR 

process library that will include background information and refresher training for the crew.

The crew interface also will provide the crew with an override authority to interrupt or halt CLEAR 

processes and will provide a software E-stop function for the crew.

5.4.2 CLEAR Imaging Controller

Imaging is essential for examination, process control, and postrepair evaluation. Imaging data 

usually demands high data rates and mass storage. As a separate controller, it provides dedicated circuits 

that minimize the impact on control loops and other instrumentation. Although there are a variety of 

imaging devices from visible light to infrared (IR) and even x-ray, the images can be converted to a 

common digital format.

Although the IEEE–1588 extended Ethernet bus is the primary conduit of data, specialized highspeed serial ports with plug-and-play capability, such as universal serial bus (USB) and 1394 FireWire 

may also be included for high-speed digital image transfers.

The high-speed bus may also pass imaging camera parameters such as frame rate, resolution, and 

exposure settings. Optical zoom and focus can also be performed by the controller. Crew access images 

can be passed to the crew interface via the CC&D controller or via a separate 1394B bus.

5.4.3 CLEAR Diagnostic and Test Controller

Diagnostic and test functions will require many of the same instruments particularly where SI

technology is employed. The diagnostic and test functions will employ a mix of instruments linked by 
NASA/TM—2011-216956 21

the IEEE–1588-compliant networks. This provides a stable data environment that accommodates 

incremental growth in capability over several years. Individual complex multicard analyzers or SIs may 

employ backplane interconnections. However, backplane designs will likely become obsolete more 

rapidly than network links. Whenever possible, IEEE–1588-compliant network buses will be used.

The CD&T controller will manage the ASA/CSA characterization instruments (see Figure 8). It will 

house the setup parameters for the instruments and initiate any instrument triggering, if needed. 

Data passed from the instrument will be buffered in the CD&T controller and transmitted to the main 

CC&D unit for further processing. Reference known-good data will be housed in the CC&D unit or in 

the crew interface for real-time diagnostic display. Similar functions will be provided for any IEEE–

1588-compliant handheld equipment and high-speed data bus analyzers.

Figure 8.—Imaging control and diagnostics and test control functions (analog signature analysis (ASA) and 

complex signature analysis).
NASA/TM—2011-216956 22

The CD&T controller will control the synthesizing process for synthetic instrumentation. The CD&T 

controller will program the FPGA, load software, and will manage the overall configuration and 

coordination of multiple SIs. The CD&T will act as the IEEE–1588 master clock unit for instrument 

triggering and synchronization. In addition, it will buffer and correlate instrument data prior to 

forwarding it to the CC&D unit for further processing, downlink, or crew display. 

For automated diagnostic probing, the CD&T controller interacts with the CLEAR repair apparatus 

controller (CRAC). The CD&T passes node XYZ location coordinates to the CRAC via the CC&D

controller or by direct network link. Automated probing of the circuit card will require manual setup by 

the crew. A card-specific setup routine would be executed to capture registration points and adjust the 

system alignment to assure that each diagnostic node is accurately located.

The imaging system may also support the alignment exercise. All alignment information is stored in 

the CD&T controller and merged with diagnostic node test parameters.

5.4.4 CLEAR Repair Apparatus Control

The repair apparatus involves robotic motion control for a variety of automated mechanical 

functions and process control for reflow and related processes (Figure 9). Motion control and process 

control will be handled by separate controllers. The CRAC will determine if there are any safety 

conflicts, such as open enclosure switches, which may indicate that the crew is not clear of the apparatus.

The CRAC will not permit process operation unless all inhibit functions and safety limits are cleared.

Motorized robotics requires coordination of multiaxis motors to move a payload through a 

predefined motion path. A responsive closed-loop control is needed to assure that each axis accurately 

tracks its position and speed profile to achieve the needed complex motion. This is an example of a 

deterministic system where each axis must be at a specific location at a specific time. As noted earlier,

Ethernet-derivative networks are being adopted in industrial systems partly because they are low-cost 

and partly because they modularize the functions so that the system can be easily expanded. IEEE–1588-

compliant networks may provide sufficient deterministic control to support both motion control and 

process control.

Motorized robotic motion is usually provided by stepper motors or servo motors. Each motor type 

requires a distinctly different motor-drive modulation and feedback scheme. Many motion control 

architectures separate the high-power motor-drive electronics from the controllers, creating distinct drive 

modules tailored to the motor type. This modularization also allows a single controller to manage a 

variety of motor types.

Tool handler control is needed when general-purpose robotics are coupled with special functions 

such as material dispensing, component pick-and-place, and special tool handling, each requiring unique 

control. These devices at the tool end of the robotic apparatus are often referred to as end-effectors. Endeffectors may include grippers and vacuum pick up tools, paste-dispensing syringes, and coating 

applicators. Feedback signals may be required for closed-loop control that may include temperature 

sensors, position sensors, and pressure sensors. 

End-effectors, such as vacuum-dispensing tools, depend on both pneumatic supplies and valves for 

actuation. Pneumatic actuation is considered to be an alternate method of delivering actuation power.

Grippers may be either motorized or pneumatically actuated. Pneumatic actuators will still require a 

motorized vacuum pressure pump. Like the motor drives for motion control, these ancillary devices must 

have separate drive units. Pneumatic actuation will require flexible feedlines routed similarly to the 

electrical lines.

End-effector tools are interchangeable and may be changed manually or by automated means. To 

accommodate quick and simple tool changes, a standardized tool handler is needed. This device not only 

holds a particular tool, but it may also conduct power and provide an interface for special devices and 

sensors. All potential end-effectors and their related power and control-loop requirements must be 

considered to define the tool handler requirements.
NASA/TM—2011-216956 23

Figure 9.—Repair apparatus control functions.

Reflow Process Control.—Reflow heat may be delivered as hot gas or as IR radiation. Some circuitcard fabrication facilities use a combination of hot gas and IR. A conventional industrial temperature 

control is usually employed in rework stations. Because spacecraft circuits are often conductively 

cooled, the cards may have added metal layers to enhance conductivity. The added metal will make 

localized heating of the components more difficult. Therefore, the circuits must be preheated to reduce 

the heat loss during reflow.

The reflow process will need a closed-loop control, and thus temperature readings may be needed on

the circuit card, the component, and the reflow hardware.
NASA/TM—2011-216956 24

Repair Process Containment Control.—Process containment and its related control functions 

depend on the process and on the accommodations provided. If a general-purpose glovebox is available

with purge and vent capability, then the CLEAR repair apparatus will be designed to operate in the 

provided accommodations. However, if no glovebox is provided, then CLEAR will need to develop a 

containment enclosure that captures vapor, liquid, and particle debris.
NASA/TM—2011-216956 25

6.0 CLEAR Diagnostics and Test System Architecture

6.1 Introduction 

The CD&T system is perhaps the most ambitious in terms of reducing a complex system down to a 

light, compact, and simple-to-use system. Diagnosing and testing complex flight systems demand an 

understanding of the internal details of the system. In effect, diagnostics and testing require expertise in 

both the device under test and the test equipment.

When electrical problems occur in the field (or in space), the first process is to isolate the problem to 

specific hardware. System telemetry can locate a specific ORU. Furthermore, telemetry combined with 

built-in tests, can refine the isolation down to a specific CCA. Isolating a problem down to a single 

component usually requires external diagnostic equipment. 

Visual examination or imaging equipment can reveal physical flaws like broken leads, bad joints, or 

damaged components. The U.S. Navy (Naval Sea Systems Command (NAVSEA)) considers visual 

inspection a simple and effective initial screening method. Image examination techniques are described 

in Section 6.2.

The U.S. Navy has successfully simplified component-level diagnostics in the field by employing 

comparative characterization techniques. ASA, developed by Huntron, Inc., allows a relatively unskilled 

user to distinguish good circuits from faulty circuits by using a side-by-side comparison. For CLEAR,

this approach can be used as a screening technique that may be sufficient to isolate components in many 

situations. This and more advanced techniques are described in Section 6.4.

For complex devices like microprocessors and high-density integrated circuits, special methods are 

needed to access internal features. When systems involve software, the ambiguity between software and 

hardware behaviors further obscures the root cause of problems. This means special access ports, such as 

JTAG ports, and boundary scan techniques are needed.

Often emulation of a circuit’s external interfaces is needed to reveal subtle transient problems or 

errors in software or communications protocols. Techniques that involve emulation of functions are 

described further in Section 6.5.

To isolate the root cause of a component fault, the CLEAR team may need special diagnostic testing,

and the component may need to be placed under operating stress to expose the root cause. Circuit stress 

under power loading is often required to expose power supply instability, radiofrequency (RF) tuning 

problems, or heat-related problems.

The incorporation of all these techniques in a weight- and volume-constrained environment,

compounded by low crew availability, is driving the architecture toward a highly reconfigurable SI 

architecture.

6.2 Examination by Imaging Functions

Imaging provides direct data or supporting information throughout the repair process. A good visual 

examination can eliminate substantial diagnostic setup and programming. High-resolution closeup 

imaging can reveal subtle problems like corrosion and contamination that may not show up with 

electrical diagnostics. A visual inspection that discovers frayed lead wires, cracking solder joints, or tin 

whisker growth can preempt a developing problem or isolate frustrating transient problems.

6.2.1 Imagers 

Image processing is easily handled by the crew interface computer. High-resolution images will 

create large files and may be time consuming for downlink operations. A field of view of a few 

millimeters and a 2000- by 2000-pixel imager array, shown in Figure 10, is expected to satisfy most 

imaging needs.
NASA/TM—2011-216956 26

Figure 10.—A digital camera with integrated illumination is mounted along with a probing device on a 

robotic carriage. The camera provides inspection and verifies registration and process 

monitoring.

Lossless compression will be used to reduce file size and bandwidth while maintaining image 

quality. 

The widespread adoption of digital high-definition television (HDTV) may provide a low-cost 

commercial-off-the-shelf (COTS) solution. HDTV has multiple resolution modes. The 1080- by 1920-

pixel resolution mode will suffice for most imaging applications.

The 30-frame/s rate of HDTV may pose a problem for downlink data transmission. This frame rate 

is not necessary for most applications, and the transmission rate needs may be reduced by using a 

reduced frame rate or employing a still frame mode. HDTV employs lossy compression techniques, and 

HDTV camera performance should be evaluated to determine if the loss is significant.

6.2.2 Optics and Illumination 

Imager optics will have a zoom and field of view of a few millimeters, equivalent to a microscope 

used in circuit fabrication and inspection. The 24-bit color will be standard, but conversion to grayscale 

may be used to reduce memory and bandwidth when necessary.

Although general lighting will be available, an adjustable high-intensity lamp will be used for very 

close work. In some cases, imaging is enhanced by polarization of the light source and the camera optics.

The lighting should be positioned separately from the camera in order to optimize reflections for the 

clearest image and best contrast.

6.2.3 Nonvisible Examination Technology (Ultraviolet, Infrared, and X-ray)

Nonvisible radiation can provide information beyond visible methods. 

Infrared imaging.—IR emissions from a circuit can diagnose thermal problems on operating 

circuits. The weight and complexity varies with wavelength. For imaging temperature, profiles on 

circuits a mid-range IR unit with internal cooling is required. IR imaging may also support the repair 

process if IR radiant heat is used in reflow operations.
NASA/TM—2011-216956 27

Ultraviolet imaging.—Ultraviolet (UV) is used for certain types of conformal coatings, such as 

Paralene, that may be too thin to detect visually. Normally a strong UV light source is used for visual 

inspection, which can harm the user’s unprotected eyes. A UV-range camera may be used to detect 

fluorescence using a much weaker UV light source. 

X-ray.—The electronics industry is increasing its reliance on x-ray for diagnosis of ball grid array 

(BGA) and land grid array (LGA). The recent CLEAR program needs assessment determined that the 

BGA and LGA will likely replace many surface-mount technology integrated circuit (IC) packages in 

future avionics. For BGA and LGA devices, x-ray inspection may be the only viable technique.

A number of ISS electronics problem reports also included x-ray examinations to reveal critical 

circuit flaws. X-ray applications range from full-size circuit boards to small hybrid assemblies. Some xrays use x-ray fluorescence techniques, whereas others use very small scanning x-ray point sources 

suited to a two-axis scanning method.

6.3 Compact Conventional Instruments Functions

6.3.1 Meters

After visual examination, many simple problems are isolated by a simple handheld multimeter. The 

most common measurement is to test continuity in a connector or cable harness. Voltage and current 

measurements can quickly determine if power is reaching the faulty component and if shorts or open 

circuits exist.

6.3.2 Oscilloscopes

Oscilloscopes require greater operator knowledge to setup and are often very difficult to interpret.

Recently industry is tending toward panelless instruments. The user controls and display functions have 

been offloaded to a laptop computer, and the instrument is reduced to a simple box with connectors and a 

data port. The unit weight may be reduced by half. Since a panelless instrument is already networked, it 

is simple to extend the data flow to include uplink and downlink functions.

6.3.3 Signal Generators

Many diagnostic and test techniques require injecting a stimulus signal-to-target circuit and 

observing its response. For example, ASA requires a small signal injection. The trend is toward direct 

digital synthesis, where single-chip devices are used to synthesize signals from high-frequency clocks.

Direct digital synthesis is a suitable application for synthetic instrumentation. 

6.3.4 Analyzers

Generally an analyzer is a compound instrument that incorporates a specific stimulus signal, a 

response measurement, and signal processing and display function. The Huntron ASA and the CLEAR 

CSA techniques can both be described as analyzers. Many of these analyzer functions could be 

synthesized by SIs.

The most effective compact stand-alone analyzers are used for diagnosing high-speed networks, 

such as Ethernet LANs, RF cables, and optical networks. Although very specialized, they are often 

handheld and simple to operate, making them an attractive option.

6.4 CLEAR Diagnostics by Characterization 

6.4.1 Analog Signature Analysis Function

A power-off technique called ASA was developed by Huntron (see Figure 11) as a simple but 

effective form of diagnostics, based on comparison with a known-good board. It provides the advantage 

of diagnosing a circuit in the power-off condition, which negates the need for power supplies and the 

risk posed by powering up a faulty circuit.
NASA/TM—2011-216956 28

Figure 11.—Analog signature analysis (ASA) relies on measuring the response to 

very low-power sine wave signal, I–V, current-voltage.

Figure 12.—Analog signature analysis (ASA) characterization may involve several individual devices contributing 

to the node’s characteristic signature. A fault in any one of them alters the signature.

The ASA technique applies a current-limited sine-wave voltage to an unpowered circuit or electronic 

component (Figure 12). The resulting current (I) and voltage (V) characteristic (analog signature) is then 

stored and displayed for comparison with signatures of a known-good circuit card or electronic 

component. Thus, circuit cards and electronic components can be diagnosed without applying external 

power.

A single component that can be isolated provides a very predictable curve. Circuits usually have 

multiple devices on each node; thus, a node will have a signature that is a composite of multiple devices.
NASA/TM—2011-216956 29

As long as the settings and probe positions are consistent, the signature should accurately duplicate the 

known-good-board signature.

A personal computer (PC) workstation with ASA software graphically displays the analog signature.

This approach can be applied to any type of passive component like a resistor, capacitor, or inductor. It 

can also be applied to solid-state semiconductor components like a diode, a transistor, a siliconcontrolled rectifier, digital, analog, or mixed-signal IC. 

Alternatively, the signature can be compared with “known node faults,” where individual 

components with various fault modes can be precharacterized, providing a more precise diagnosis. A 

skilled user that is familiar with the circuit design and each component’s function, may use the signature 

to determine exactly which component is faulty. If the user is not skilled and no known-good reference is 

available, the results will be ambiguous. 

6.4.2 Complex Signature Analysis Functions

CSA is an extension of ASA that uses capability a vector network analyzer. Not to be confused with

network protocol analyzers, a vector network analyzer tests networks of components in high-frequency 

alternating current (AC) signal circuits. Vector network analyzers share certain capabilities with a 

spectrum analyzer. These devices are generally used for high-frequency or RF circuits, where operating 

frequencies can range from 10 kHz to 110 GHz.

A vector network analyzer measures the frequency domain properties of component networks rather 

than single components. It injects a signal into the network and measures the signal reflecting back from 

the circuit and the signal transmitted through the circuit. These analyzers are commonly used to test 

high-frequency amplifiers, filters, and tuning networks and can also test piezoelectric devices like crystal 

resonators. They operate at very low wattage and inject signals into passive networks or active devices 

like amplifiers.

For CLEAR, the vector network analyzer provides a complex impedance measurement. Network 

analyzers make their measurements relative to a reference impedance value (typically 50 Ω for RF 

systems). The scale can be very large; a log scale is used, and impedance ratio (expressed in dB) is 

displayed. 

Complex impedance Z is a complex value; that is, it is composed of a real value R and an imaginary 

value X.

Z = R + Xi

The resistance term (R) is measured with a common direct current (DC) resistance meter. The reactance 

term (X) typically involves inductors or capacitors and is only meaningful for AC signals. Beyond this,

the explanation involves amplitude and phase relationships, which are difficult to grasp. Complex 

impedance measured over a frequency sweep reveals resonant behaviors for both the entire network and 

individual component resonance. By performing a wide sweep, one can identify specific components. By 

comparing the sweep signature to a known-good or gold signature, one can quickly spot a failed 

component. As shown in the plot, the data may be very difficult to interpret directly, but it provides a 

very distinct, unique signature. 

As shown in Figure 13, a filter composed of several LC (inductor capacitor) nodes has a distinct 

resonant condition for each node. The plots produced by the network analyzer could be used to 

characterize the network. The actual measurement can be taken at the input or output end.

In Figure 13, note that markers 1 through 5 indicate distinct nodes and each node’s contribution to 

the characterization curve. Therefore, it is possible to characterize the network without measuring every 

node. This is particularly useful when parts of a circuit are inaccessible. The measurement is taken from 

the signal injection side of the circuit rather than from the output side. In Figure 13, the blue trace is the

characterization of a known-good reference network. The red trace is a test trace from a network where 

node 2 has a faulty component.

This illustrates that any device fault will appear as a distortion of the curve at that point.
NASA/TM—2011-216956 30

Figure 13.—Each marker indicates a normal resonance of a “knowngood” network composed of five components. The red trace 

indicates that element 2 of the test circuit has a faulty component 

and therefore does not match up with the expected known-good 

trace.

6.5 CLEAR Synthetic Instrument Architecture

The motivation behind synthetic instrumentation is the need to reduce the size and weight of 

instruments and related hardware used in the diagnosis and test of electronics. It is not uncommon for a 

specific ORU to require multiple racks of equipment. DOD studies consider automatic test equipment 

(ATE) as a primary contributor to the high life-cycle cost of avionics equipment. ATE life-cycle cost can 

become an increasingly expensive part of avionics cost over time as hardware becomes obsolete. The 

studies also determined that test software is a major component of avionics and test equipment cost.

Hardware and software obsolescence also tends to drive up cost, particularly for proprietary systems.

These DOD studies prompted development of nontraditional concepts for ATE to keep life-cycle cost 

down. SIs are conceived as a way to make ATE equipment more universal and easier to update remotely.

6.5.1 Conventional Automatic Test Equipment Functions

To define the CLEAR SI functions, it is essential to first define the basic capabilities of a 

conventional ATE for functional test. Simple measurements are inadequate to fully diagnose or 

functionally test complex systems that are distributed over many circuit cards. 

Generation of Stimulus Signals.—Diagnostic and test equipment generally requires a stimulus 

signal injected into the test target. For ASA or CSA diagnostics, injecting a signal is an essential step in 

characterization. The response is measured on the same line as the injected signal. The characteristics of 

the injected signal must be identical in the known-good circuit reference and the test target, otherwise the 

method is unreliable. 
NASA/TM—2011-216956 31

Functional tests require a variety of stimulus signals.

 Input clock for clocking or triggering digital functions

 Signals from sensors and transducers

 RF communications signal

 Parallel and serial data bus signals 

 Analog signals from the audio through the RF range 

 Amplitude modulation (AM), frequency modulation (FM), frequency shift keying, pulse-width 

modulation, and other modulation methods

 Analog feedback signals in control loops

Capture of Response Signals.—For every stimulus signal there is a circuit with a like output signal.

Diagnostic and test equipment must match signal generation with similar signal capture capability.

Overall, this implies that the signal-generation channel count should match the captured-signal channel 

count.

Monitoring Measurements.—Diagnostic instruments are mounted to serve as a nonintrusive or 

transparent monitor of circuit behavior or signal traffic. Secondary effects, such as heat generation 

during various operating modes, are also monitored to locate heat-related problems.

Emulation of Interfaces.—For electronic circuits that are part of a much larger system, the largest 

consumer of capability is the need to emulate external circuits. This can involve emulating hundreds of 

individual signal channels. Emulators often serve as indirect points for stimulus signal injection or 

provide breakout channels for receiving and collecting system data.

Spacecraft Power Simulator.—A power supply that emulates the spacecraft power is needed to 

perform functional tests. Spacecraft power can be the source of many problems in avionics. Functional 

testing often includes testing the ability of a circuit’s internal power supply to tolerate occasional 

spacecraft power system transients. The power supply needs to be programmable to simulate these 

transients.

Power Load Simulator.—Power systems and RF systems cannot be fully tested without external 

loads to absorb power. These loads stress the test circuit so the components are tested in actual 

conditions. 

6.5.2 CLEAR Synthetic Instrument Functions

Figure 14 illustrates the complexity of a test setup required to fully functionally test a circuit. It 

shows how emulation requirements drive the scale of ATE. A conventional system intended to perform 

automated functional tests can result in a multirack system too massive for space applications. Likewise, 

the software code developed to exercise and coordinate various test functions is usually much larger than 

the code installed in the flight avionics.

A system is needed that can be configured to diagnose and test virtually any form of electronics on 

the spacecraft and fit within the small accommodations. Furthermore, the system must not create a 

substantial workload for the flight crew or significantly increase training requirements. So far, the SI

concept appears to be the best approach.

CLEAR SI strategy involves

 Partitioning the functions between Space and Earth segments

 Allocating (offload) data processing and analysis functions to the Earth segment

 Employing analog front-end hardware with greatest possible range and bandwidth

 Exploiting digital functions instead of analog functions where possible

 Employing FPGA technology to synthesize the digital functions

 Employing signal routing capability to match instruments to specific circuit connections
NASA/TM—2011-216956 32

Figure 14.—Conventional automatic test equipment functional test systems involve interface 

emulators, data loggers, signal monitors, signal stimulus sources, measurement instruments, 

power supplies, and load simulators (with cooling).

6.5.3 Allocating Space and Earth Synthetic Instrument Functions

As described in CLEAR–DOC–007, CLEAR is composed of a Space and an Earth segment for both 

hardware and software. CLEAR synthetic instrumentation is also partitioned in that manner. The intent 

is to provide the essential signal capture and generation capability on orbit and to offload the signal 

processing related to analysis and display to the Earth segment.

Earth segment functions are already described in the teleoperations architecture. The Earth segment, 

or CLEAR TEST center, processes the raw data sent by the Space segment and performs the analyses, 

assessment, decision making, and action planning for the next phase of the process (see Figure 15). This 

segment is well within the current technology base.

Earth Segment Functions

 Data processing and storage

 Data analysis 

 Data assessment 

 SI control programming

 SI library (database management)
NASA/TM—2011-216956 33

Figure 15.—The synthetic instrument (SI) architecture is partitioned into Space and Earth segments.

The Space segment can be considered the front end of a diagnostic and test system, providing the 

interface with the test target and acquiring the raw data. For a complete solution including the postrepair 

functional tests, the Space segment will need to provide the supporting emulation capability. 

Space Segment Functions

 Measurement capture including signal conditioning, analog-to-digital conversion (ADC)

 Stimulus generation including digital-to-analog conversion (DAC) filtering

 Timing and triggering

 Input/output (I/O) interface emulation

 Signal routing

 Crew and spacecraft interfaces

6.5.4 Synthetic Instrument Functions and Technology Options

Flight Segment Analog Front End.—Although SI technology relies on exploiting digital domain 

capabilities, instrumentation and measurements are started in the analog domain. Analog hardware is the 

primary restriction on SIs, and the sooner signals are converted to digital, the easier it is to exploit 

synthetic instrumentation. The analog front end refers to both analog input and output. For an all-purpose 

system, these devices must have an inherent ability to be configured over a wide range of parameters.

When a specific application cannot be accommodated by a reconfigurable or programmable device,

then add-on modules may be inserted into the system as a temporary means of extending capability.

Generally, the add-on approach is how variations of physical contact or sensors are handled. For 

example, a high-voltage measurement that is beyond the safe range of the analog front end may be 

required for a specific instance. An add-on solution would be to provide a high-voltage probe that 

preconverts the voltage down to a safe level. Similarly, it is common to use RF upconverters and 
NASA/TM—2011-216956 34

downconverters to convert extremely high RFs to a range that common equipment can handle and to 

avoid extremely expensive RF instruments (Figure 16 and Figure 17).

Analog Signal Conditioning.—Signal conditioning involves the analog manipulation of the signal 

to make it suitable for measurement by electronic devices. Raw signals may include low-voltage 

thermocouple measurements, high-voltage power measurements, high-impedance logic, or 50-Ω

impedance-frequency RF signals. Each type of measurement requires specific input conditions to prevent 

signal distortion or damage to the instruments. The input signal must be preconditioned for the 

measurement instrument. Signal conditioning involves signal amplification or attenuation and filtering.

For flexibility, the instruments must have a fully programmable signal-conditioning section.

Signal amplification improves the signal-to-noise ratios of measurements and increases the 

resolution and sensitivity of measurements by matching signal magnitudes to the acquisition ranges.

Signal filtering will allow signal shaping and rejection of unwanted noise from power lines and prevents 

signal aliasing. In many cases, signal isolation may be built in to remove common-mode voltage errors 

caused by differences in grounding potentials. The sample-and-hold function will be the last point where 

the signal is analog. This function will sample the continuous signal and hold it, upon triggering, at a 

steady value so that the ADC can read it in and convert it to digital. Once the sample is read into the 

converter, the sample and hold circuit will be retriggered to capture another sample.

Analog to Digital Conversion.—The analog-to-digital converter will receive the preconditioned 

signal and perform a conversion to digital data. The digital word generated will depend on the device,

but is typically 8-, 10-, 12-, or 16-bit word. The word size will define the resolution of the measurement.

Once converted to digital format, the remaining processes will be handled in the digital domain. 

Digital Signal Processing.—Data can be stored in both raw form and in a processed form. Storing 

raw unprocessed data is important since there may be many alternate ways of processing data to reveal 

different signal properties. For conventional instruments, considerable computational power is dedicated 

to processing and presenting the data to the user in an understandable format. For CLEAR, most of this 

will be deferred by the Space segment and performed by the Earth segment. This will allow the flight 

system to focus on controlling the analog section, routing signals, and packaging and transmitting raw 

diagnostic data.

On the ground, data analysis will involve processing and presenting diagnostic data for the CLEAR 

TEST team. This is also where the TEST team can employ analysis tools to extract characteristics not 

easily visible in the raw data.

Digital Control of Analog Function.—There are several instances where a digital device can 

enhance the range and function of a dedicated analog device.

 Amplifier gain and attenuation control 

 Absolute voltage and differential voltage

 Input impedance

 Temperature compensation

 Voltage reference (calibration)

 Input filter frequency band

 Sample rate, sample resolution, and sample hold time

 Signal multiplexing control

 Trigger source, trigger delay, and trigger level 

Virtually any adjustment that can be made on the front panel of an instrument can be handled by 

digital control of an analog device. In some cases, an analog function can be replaced completely by a 

digital function. For example, certain forms of digital filtering can eliminate equivalent analog filters.

The digital filter may actually be a mathematical algorithm that filters digitized data in a digital signal 

processor. Again, CLEAR would handle this digital process on the ground.

Digital Input/Output and Interfaces.—Most avionics ORUs have a mix of analog and digital I/O 

signals. At the ORU level, the digital signals may take the form of a serial data bus. For ISS, the standard 
NASA/TM—2011-216956 35

is the STD 1553 bus that was developed and deployed in the 1970s for aircraft avionics and fly-by-wire

control systems. For CxP, the current data bus is a LAN known as the TTGbE, which is described in 

Section 5.0. These interfaces, although physically simple, have complex protocols and driver software. A

specialized TTGbE digital network analyzer with preprogrammed test functions may be the simplest 

option.

At the shop replaceable unit or circuit-card level, digital interfaces are more likely to require large 

backplane connections with dozens of data, address, and I/O lines. These connections employ parallel

data bus architecture. This is an application where SIs can be most effective. Digital instruments do not 

need analog signal conditioning and only require digital buffers or isolators to protect the instrument 

from circuit faults. The SI can bypass the analog section and link directly to the digital test target.

Figure 16.—Signal capture (analog-to-digital conversion (ADC) and multiplexer (MUX)).

Figure 17.—Signal generation.
NASA/TM—2011-216956 36

SIs can be setup as traditional logic analyzers to test digital I/O. The most common application will 

likely be to serve as a digital emulator. The emulator can be programmed to interact with the target by 

emulating a device that would be attached to the target in normal operations. Emulators are frequently 

used in embedded computer development. The emulator transmits signals and interacts like the original 

device, but it has added instrument capabilities to capture detailed measurements. This technique can 

capture timing and triggering errors down to nanosecond resolution. It can capture handshake or protocol 

errors, and detect abnormal transients or slow I/O faults. 

Stimulus Signal Generation.—For every signal type used, there is a signal-generation need. Signals 

are generally categorized as analog, digital, or RF. Digital signals are based on binary logic state 

voltages, nominally 0 to 5 V for transistor-transistor logic. Analog signals can range from simple AC 

waves to waves with complex amplitude and frequency content such as audio. RF signals are analog 

signals with high enough frequency to be effectively transmitted via antenna. Each signal type has its 

own signal modulation techniques and impedance characteristics.

SI can produce digital and analog signals, as shown in Figure 18. RF signals are more difficult to 

measure and produce because of the extremely wide range of frequency and power levels. RF systems 

employ antenna technology to transmit across space where voltage and current measurements are 

meaningless. 

Field Programmable Gate Array Technology.—In SI, the FPGA is an enabling capability because it 

provides the user a “sea” of available logic gates that can be programmed to synthesize the desired 

digital functions. Because these logic gates can be arranged to provide highly parallel pipeline 

processing, they can achieve very high performance. In contrast, a PC microprocessor-controlled data 

acquisition instrument performs many sequential functions and must perform memory fetches and must 

also support operating system overhead. As a result, microprocessor-controlled instruments usually have 

poor performance. The FPGA can provide signal processing performance near that of a benchtop 

instrument. 

Ultimately, the SI will support low- to moderate-frequency or baseband analog signals, highfrequency or RF analog signals, and digital signals. For RF, the frequency required for radio 

transmission is normally well beyond the internal data rates, and it is normal to use RF upconversion and 

RF downconversion. 

Figure 18.—Routing signals from various test targets may be accomplished by combined internal 

signal routing matrix and intermediate hardwired signal routing connector adapter.
NASA/TM—2011-216956 37

Signal Routing.—The signal router will route all signals going to and from the test target. It is a 

means in which signals will be aligned to pin outs of each target. This routing function is needed to 

accommodate large ORU connectors and circuit-card backplane connectors. Unless the target circuit is 

part of a standard backplane assembly, each target is expected to have unique pin-out arrangements that 

may mix input, output, analog, digital, and power in a single connector.

In conventional automatic test systems, it is common to employ special test cables that mate with the 

ORU connector but attach to multiple instruments. A similar scheme can be employed for CLEAR, but 

there are crew time and stowage penalties for this approach. The analog section limits the routing 

flexibility. Unlike digital circuits, where bidirectional buffers can change direction on command, analog 

input and output circuits are distinctly different. Therefore, routing analog input and output requires 

external routing capabilities. 

Analog switches can be used to route a signal to the appropriate analog input or output. Digital 

timing and control logic can configure the analog front end and switching to reassign channels. The 

generic SI block diagram includes a signal routing connector adapter and a front signal routing matrix.

Recent studies regarding plug-and-play satellites indicate that microelectromechanical-systems-based

reconfigurable manifolds may be best suited for flexible signal routing.

Alternatively, FPGAs with large-field open gates, can provide an option to relocate or resynthesize 

an SI into a location that is more accessible for a given signal channel.
NASA/TM—2011-216956 38

7.0 CLEAR Repair Apparatus Architecture

7.1 Overview

The CRA borrows heavily from industry experience with automated and robotic technology.

Industrial robots, unlike NASA robots, are typically stationary and focused on moving hardware instead 

of robot mobility (see Figure 9). The distinction between robots and automated equipment is the need for 

flexibility in motion and function. Automated equipment tends to involve a series of simple devices that 

perform only one task, where robots are complex and perform a series of tasks. Robot flexibility is 

extended by interchangeable end-effector tools. Robot motion ranges in complexity from simple 

Cartesian (XYZ) robots to complex multiple joints with multiple degrees of freedom.

All robots must be programmed, but in recent years the availability of three-dimensional programs 

and simulation tools has made it much easier to both program and validate the robot motion-control 

system. Three-dimensional computer programs allow the user to execute a robot program in a virtual 

three-dimensional environment to reveal errors and hazards. This reduces the risk of program errors 

causing collisions that damage hardware and harm workers. These programs also can predict the effect 

of different tools.

Because CLEAR repair involves materials and a variety of processes in a space environment, 

process modeling must be employed to convert 1-g processes to low-gravity applications. Materials must 

be properly staged in an area accessible to the robot. Once again, low-gravity will affect how materials 

are staged and dispensed. As with many repair processes, debris, vapors, and liquid byproducts may be 

produced, and these must be contained. Therefore, the repair apparatus architecture includes process 

containment.

7.2 Repair Apparatus Robotic Functions

7.2.1 Robotic Motion

Robots for semiautomated repair and diagnostics can be categorized as an industrial robot. ISO 

defines an industrial robot as an “automatically controlled, reprogrammable, multipurpose manipulator 

programmable in three or more axes.”

For fabrication and repair operations, robotic motion can be accomplished by various configurations.

The simple Cartesian robot (Gantry robot) illustrated in this document is akin to flat-bed plotters and 

CNC machining centers. The Cartesian robot translates on three orthogonal linear axes to achieve a full 

range of motion. Two other common robot types include the selective compliant articulated robot arm 

(SCARA) and articulated (arm) robots. The SCARA uses a combination of rotary joints and linear 

telescoping slides. The articulated arm has compound rotary joints that tend to emulate the motion of a 

human arm. The remote manipulator arms used on the space shuttle and ISS are articulated arm robots.

Another class is the anthropomorphic robot, which is intended to emulate the motion of a human and 

have at least two arms. These are most useful when used by a remote human operator often using haptic 

(touch) feedback. NASA’s Robonaut is an anthropomorphic robot. 

Cartesian and the SCARA robots are effective for motion that is simple, planar, and repetitive. These 

robots are widely used in pick-and-place operations for electronics assembly. Articulated arm robots are 

more effective when long complex paths are required such as spray paint and welding applications.

Articulated arm robots are more likely to be used when multiple robots are used in a cooperative 

arrangement.

7.2.2 Robotic Motion Parameters 

Tradeoffs to consider for robotic motion include the following: 

 Degrees of Freedom.—For CLEAR, the repair target normally will be a planar circuit card and 

three translation degrees of freedom will suffice. 
NASA/TM—2011-216956 39

 Working Envelope.—The planar circuit card will have a simple envelope; however, access to 

multiple tool, component, and material pallets will expand the needed envelope.

 Kinematics.—The combination of linear and rotary degrees of freedom and the length of each 

arm between joints will define the possible motion paths. Robot kinematics becomes important 

when complex motion paths are required, such as reaching into a constrained space or around 

obstructions.

 Payload, Speed, and Acceleration.—In low gravity, payload inertia is a primary concern.

Minimizing speed and acceleration requirements minimizes motor horsepower and braking 

requirements. Inertia is a major factor in motion overshoot, vibration, and the required damping 

in a control system. It is also why industrial Cartesian pick-and-place robots require massive 

bases. Lightweight payloads (tools), in combination with low accelerations, minimize the overall 

system mass for CLEAR.

 Accuracy and Repeatability.—Accuracy refers to how precisely a robot will move to a 

commanded position. Repeatability refers to how consistently the robot achieves the same 

intended position. For CLEAR, accuracy and repeatability must be consistent with industrial 

electronics assembly equipment. Compound kinematics and cantilever beam segments make

articulated robots the most prone to accuracy and repeatability problems. Simple kinematics and 

an end-supported beam structure make Cartesian robots the most accurate and repeatable. 

 Backlash and Compliance.—Backlash is the natural play in mechanical gears and drive screws 

in motorized motion and directly affects accuracy and repeatability. True zero backlash in 

conventional drives is nearly impossible. Compliance is the natural deflection of the robot beam 

structures. The combination of backlash and compliance define the inherent rigidity of the 

apparatus. For CLEAR, probing, pick-and-place, and dispensing will not be dramatically 

affected by backlash and compliance as long as absolute position feedback is used to 

compensate for these effects. Rotary cutting and grinding tools will require substantial stiffness 

to prevent tool chatter and vibration throughout the system. 

 Tool Handling End-Effectors.—The ability to accommodate a wide range of end-effectors 

provides a wide range of utility. Mechanical end-effectors are constrained by the supporting 

lines for power, control, and instrumentation. Routing of these lines is simpler in rotary joints.

The pure translational motion of a Cartesian robot means electrical lines need to be housed in a 

folding cable tray or to employ a cable suspension system.

7.2.3 Robotic Operating Environment Constraints

For CLEAR applications, there are further operational and environment tradeoff considerations. 

 Heat Tolerance.—It will be difficult to avoid exposing the apparatus to heat during solder 

reflow cycles, particularly if the component handling (pick-and-place) and solder reflow 

functions are combined. The robotic mechanism, particularly the tool handler, must be heat 

tolerant. Furthermore, moderately high heater current must be conducted through the tool 

handler’s electrical interface. 

 Atmosphere.—The robotic apparatus may be exposed to multiple atmospheric environments.

Normally, a rework station operates at normal atmosphere; however, it is not uncommon to use 

inert nitrogen atmospheres to reduce oxidation, which in turn reduces the need for flux and 

improves quality. For CLEAR, an inert atmosphere may be employed to reduce solder porosity 

and the need for flux fume containment. The robotic apparatus may need to tolerate vacuum 

venting as a means of evacuating process vapors.

 Payload Mass and Volume.—Weight is important from an initial launch weight consideration.

The unit must minimize volume, particularly when not in use. A unit that can be reduced to a 

very small stowed volume is very desirable. 
NASA/TM—2011-216956 40

7.3 Repair Process Functions

7.3.1 Reflow Soldering Process 

The solder reflow process is the most likely method of repair beyond simple soldering iron repairs.

The process will have to apply heat carefully in a series of ramp-and-hold steps, where the heating rate 

and hold times are established to prevent thermal stress damage.

Figure 19 illustrates a representative reflow temperature profile. An initial ramp-up is used to heat 

the circuit followed by a stabilizing soak that assures a uniform temperature. The solder flux is activated 

during the second ramp-up, and then the solder is reflowed. Reflow dell time is enough to assure 

thorough melting but to minimize excessive intermetallic growth in the solder joint and minimize circuit 

card material degradation. Blowers may be used to accelerate the cooling-down process until the soak 

temperature is reached again.

Compared with the reflow process used in the original manufacture of the circuit, reflow connected 

with repair or rework is more complex. In repair, the reflow process occurs twice, once to remove the 

component and a second time to install the new component. Another problem is the need to restrict the 

heating so that reflow only affects the component being replaced. Most circuit boards are designed to 

tolerate one or more rework cycles.

Reflow heat may be delivered as hot gas or as IR radiation. Hot gas requires a pneumatic supply or a 

motorized blower. Generally, a specific nozzle that restricts the hot gas flow to the desired component is 

selected. IR heaters also can be used, and they provide a standoff distance that makes it easier to view 

the process. IR heat sources do not readily form square or rectangular heat zones without optical 

masking on either the IR source or the target circuit. The mask may be simple custom-cut foils. Many 

industrial rework stations use a combination of IR and hot gas. Figure 20 illustrates a reflow system 

integrated into a Cartesian robot.

Figure 19.—Reflow temperature profile.
NASA/TM—2011-216956 41

Figure 20.—Reflow repair with process containment.

7.3.2 Repair Process Containment

Throughout the repair process, there are operations that create debris, vapor, and smoke. The basic 

glovebox containment will suffice for most applications. The containment shown in Figure 20 also will 

include glove ports for manual operations. On ISS there are existing facilities, such as ISS microgravity 

science glovebox. CLEAR SARADA could be simplified to fit into the glovebox and reduce the overall 

upmass required. It is likely that the lunar facilities also will have glovebox containment systems 

available.

An important CLEAR M&P objective is to develop technologies that make in situ repair more viable 

through elimination of unique consumables. The process containment of debris and vapor hazards also 

provides an opportunity to control the process environment. An inert atmosphere process environment is 

known to improve reflow solder processes by eliminating atmospheric oxidation and dross buildup.

Because oxidation is eliminated, less solder flux, and thus less cleanup is needed. It may be possible to 

use light abrasives to mechanically remove any existing oxides and further reduce the need for flux 

agents.

The majority of solid debris and vapors can be controlled by circulating the air through filters. Filters 

are consumables, so processes must minimize debris and vapors. Containment of the small amount of 

cleaning and rinsing liquids can be controlled by using saturated wipes.
NASA/TM—2011-216956 42

7.4 Staging and Handling Functions of Tools, Components, and Materials

7.4.1 Resource Staging

Repairs performed by manual or automated means will benefit from proper staging of the hardware.

Tools used by the tool-handling robotic mechanism need to be staged in preassigned positions so that a 

robotic mechanism (or human) can quickly locate them. Unneeded items will have to be kept clear of the 

workarea. Since space will be limited, components, tools, and materials should be palletized so that they 

can be placed in the workarea quickly and removed quickly.

Palletized Items

 Diagnostic probes

 Imagers

 Tools (manual and motorized)

 Reflow hardware

 Repair consumables

− Components

− Process materials

7.4.2 Diagnostic Probe Handling

Automated tool handling includes the manipulation of diagnostic probes. In some cases, probes may 

need to operate in concert with imaging cameras. The probes may be passive meter or scope probes or 

they may be actively injecting signals for ASA and/or CSA applications. In addition, special probes may 

be needed for high voltage and high frequency. As noted earlier, the tool handler may provide wiring and 

connectors for common electrical and instrument needs. If additional conductor cables are required, then 

special flexible cable ways would be needed to keep them clear of mechanisms. Probes may be manually 

mounted or automatically mounted by the tool handler.

7.4.3 Imager Handling

Imaging cameras will support visual examination and process monitoring needs. The imagers will be 

used in setup to locate key registration points and check the alignment of the target circuit with the repair 

apparatus. This will require the camera to ride along on the tool handler as seen in commercial probing 

stations and certain pick-and-place machines. Using the vertical Z-axis with and fixed focal length is a 

noncontact method of measuring height. This will be used to check the level and flatness of the circuit 

and to check the clearance height of potential obstructions like circuit wiring or instrument cables.

Imagers may be manually or automatically mounted.

7.4.4 Tool Handling

Many of the tasks and tools used in manual repair will need to be duplicated for semiautomated 

operations. Many motorized rotary tools for drilling, cutting, grinding, and cleaning are safer and more 

precise if performed robotically. The human arm-hand system is simply too unsteady and compliant to 

rigidly grip high-speed tools. Small rotary tools are best handled by a rigid robotic carriage that resists 

tool torque, the tendency to climb the work, bounce, and chatter effects. For example, using rotary tools 

to remove conformal coatings without damaging the underlying circuit requires a rigid tool handling 

carriage and precise depth control. Semiautomated motorized rotary tools may support automated cutting 

of component leads. The same rotary tool using an abrasive disc or drum may remove coatings and 

prepare PC board surfaces for solder reflow. This type of tooling is consistent with CNC machine tool 

operations. Linear actuated tools driven by electric solenoids could provide pick-and-place along with 

pulling and cutting.
NASA/TM—2011-216956 43

Figure 21.—Robotic tool handling requires tool, component, and materials staging. Palletizing keeps hardware 

organized and accessible (infrared (IR), plated through hole (PTH), integrated circuit (IC), surface-mount 

technology (SMT), ball grid array (BGA), analog signature analysis (ASA), and complex signature analysis 

(CSA)).

7.4.5 Reflow Hardware Handling

The solder reflow process hardware will be the most bulky and power-consuming element of the 

robotic system (Figure 21). Commercial rework stations use varied combinations of motion and heat 

application to assure proper alignment and reflow of complex ICs. Some systems move the component 

independently of heat sources, whereas others move the heat sources into and out of position as needed. 

In some instances, the pick-and-place device and component heater are integrated. CLEAR will seek an 

appropriate combination to assure the most reliable process within the constraints.

7.4.6 Component Staging 

In circuit manufacturing, automated pick-and-place is essential to accurate high-speed placement of 

components. Component feeders in the form of tape reels, feed tubes, and pallets present the components 

for easy pickup by the pick-and-place component handler. Controlling small components and preventing 

dropped or lost components means that each component must be properly retained until needed. In 

space, there is no gravity to aid in containing materials and parts. On the lunar surface the low gravity 

will make it easier to control components, but there is some risk of contamination because of the lunar 

dust environment. 

For specific ORU and subassemblies, palletized repair component kits could be preassembled and 

stored in stowage. Most repairs will consume only a few pieces of any repair kit and could be 

replenished on an as-needed basis.
NASA/TM—2011-216956 44

7.4.7 Process Material Dispensing

Solder pastes, adhesives, and coatings each have special dispensing and application techniques. Most 

materials are in liquid or paste form and are typically applied by masking techniques to control 

distribution.

For short-run production or rework, small Cartesian robots with pneumatically driven dispensing 

syringes are employed. This type of dispensing could provide suitable accuracy for solder-paste 

dispensing. Conformal coatings are sprayed or dipped, which is not well suited for robotics. Thus, we 

expect manual brush-on dispensing to be the best option for coating materials. As an alternative, CLEAR 

is considering the development of special tapes as a replacement for conformal coatings and their 

dispensing. 

Materials should be staged as premeasured packages, to minimize waste and the subsequent cleanup 

process. Many of the materials have a short shelf life (6 to 12 months). Methods to extend shelf life 

include minimizing exposure to light, packing in an inert atmosphere, and refrigeration. Note that 

refrigeration implies that a preheat or thaw cycle must be included in repair procedures.
NASA/TM—2011-216956 45

8.0 Concluding Remarks

This architecture document was developed as a response to Component-Level Electronic-Assembly 

Repair (CLEAR) Operational Concept (CLEAR–DOC–007). The architecture is defined in the context 

of the overall Constellation Program and organizes the various functions identified in the operational 

concept. Also, the architecture establishes the relationships between crew, ground support, flight 

equipment, and ground development with validation equipment. Finally, the architecture is defined to

minimize the payload mass of the equipment, minimize logistic resources, and minimize the time and 

skill requirements of the flight crew. 

The teleoperation and automated capabilities outlined in this document are intended to let the ground 

engineers and technical experts reach out and interact with the physical hardware while offloading timeconsuming crew labor. By leveraging teleoperations, the ground crew, in effect, augments the flight 

crew. This support of the flight crew is essential for lunar surface operations where the vast distance and 

extreme payload constraints make it critical that every physical resource be fully exploited. 

The architecture is also intended to provide flexibility and permit incremental growth. The initial 

modest capability is expected to expand over a number of missions spanning several years. It is 

particularly important that electronic equipment does not become obsolete during that period. To prevent 

obsolescence CLEAR will exploit modular equipment that is linked by a long life network that is 

upgradeable yet tolerant of legacy hardware. For CLEAR, a hardened network employing the IEEE–

1588 standard is deemed the standard of choice. 

Teleoperation and command and data handling requirements must flow down to the lowest levels so 

that ground crews can have complete control of the equipment. The architecture, however, is not 

intended to be exclusively dependent on real-time control by ground-based operations. Rather, the 

CLEAR approach allows the crew to operate the system independently in the event that communications 

is lost. The processes will be automated and specific diagnostic, repair, and test programs will need to be 

developed and fully validated in ground tests and simulations. A library of validated control programs 

can be uplinked and stored at the lunar site and loaded by the crew as needed. The CLEAR

Teleoperations Engineering Support Team (TEST) center provides the development and validation tools 

in a dedicated support facility. The CLEAR TEST facility may be housed in existing NASA logistics 

depot or operations facility.

The CLEAR semiautomated repair and diagnostics apparatus (SARADA) will provide diagnostics, 

physical repair, and functional test capability for the crew. The equipment is semiautomated so that 

certain operations that are easily performed by the crew can be performed and reduce the complexity of 

the apparatus. Once set up by the crew, the SARADA performs the tedious diagnostic probing 

operations. The SARADA crew also performs automated repair operations such as reflow solder of large 

integrated circuits that cannot be done manually. 

To distill the vast number of test instruments normally required for avionics testing to a minimum 

set, CLEAR will employ the synthetic instrument approach, which relies on very flexible measurement 

and signal routing technology and the flexibility and performance of field-programmable gate array

devices. Synthetic instrumentation will support the diagnostic measurements and provide the emulation 

of external hardware that is essential for functional tests. 

To quickly determine the location of a faulty circuit and reduce the complexity of test procedures 

related to power-on testing CLEAR will exploit diagnostics based on circuit characteristics in an 

unpowered state. Analog signature analysis and complex signature analysis will be used to inject signals 

into unpowered circuits and compare the response with “known-good signatures.” This form of analysis 

is very simple for a crew member to perform and interpreting the results does not require electronics 

expertise.

Based on Constellation Program needs, the limits in logistics, equipment accommodation, and crew 

time, the CLEAR system architecture based on the technologies described will make component-level 

repair of spacecraft electronics viable for lunar missions and beyond.

NASA/TM—2011-216956 47

Appendix.—Acronyms and Abbreviations

AC alternating current

ADC analog-to-digital conversion

AM amplitude modulation

ASA analog signature analysis

ATE automatic test equipment

BGA ball grid array

C&DH Command and Data Handling

CAD computer-aided design

CCA circuit-card assembly

CC&D CLEAR Control and Data

CD&T CLEAR Diagnostics and Test

CLEAR Component-Level Electronic-Assembly Repair

CNC computer numerical control

COTS commercial-off-the-shelf

CRA CLEAR repair apparatus

CRAC CLEAR repair apparatus controller

CRE–1 Component Repair Experiment 1

CSA complex signature analysis

CSC computer software components

CTO CLEAR Teleoperations

CxP Constellation Program

C3I Command, Control, Communications, and Information

DAC digital-to-analog conversion

DC direct current

DOD Department of Defense

ETDP NASA Exploration Technology Development Program

FM frequency modulation

FPGA field-programmable gate array

HDTV high-definition television

HOSC Hunstville Operations Support Center

I/O input/output

IC integrated circuit

IEEE Institute of Electrical and Electronics Engineers

IF intermediate frequency

IR infrared

ISO International Organization of Standardization

ISS International Space Station

JTAG Joint Test Action Group

LAN local-area network

LGA land grid array
NASA/TM—2011-216956 48

LXI LAN extension for instruments

M&P materials and processes

MUX multiplexer

NASA National Aeronautics and Space Administration

NAVSEA Naval Sea Systems Command

ORU orbital replaceable unit

PC personal computer

PGA pin grid array

PRACA Problem Reporting and Corrective Action

PTH plated-through-hole

RF radiofrequency

SARA semiautomated repair apparatus

SARADA semiautomated repair and diagnostics apparatus

SCARA selective compliant articulated robot arm

SI synthetic instrument

SMT surface-mount technology

SoRGE Soldering in Reduced Gravity Experiment

SRR Systems Requirements Review

TDRSS tracking data relay satellite system

TEST Teleoperations Engineering Support Team

TReK Telescience Resource Kit

TSC Telescience Support Center

TTGbE time-triggered gigabit Ethernet

USB universal serial bus

UV ultraviolet

VHDL very high-speed integrated circuit hardware description language

VHSIC very high-speed integrated circuit

VMDB Vehicle Master Database
NASA/TM—2011-216956 49

References

1. Struk, P.M., et al.: Semi-Automated Diagnosis, Repair, and Rework of Spacecraft Electronics, 46th 

AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV (AIAA–2008–1130) 2008.

2. Struk, P.M.; Pettegrew, R.D.; and Oeftering, R.C: Repair of Electronic Equipment for Manned 

Space Exploration: A Whitepaper, submitted to NASA’s Exploration Technology Development 

Program, Apr. 2007.
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This document captures the system architecture for a Component-Level Electronic-Assembly Repair (CLEAR) capability needed for 

electronics maintenance and repair of the Constellation Program (CxP). CLEAR is intended to improve flight system supportability and 

reduce the mass of spares required to maintain the electronics of human rated spacecraft on long duration missions. By necessity it allows 

the crew to make repairs that would otherwise be performed by Earth based repair depots. Because of practical knowledge and skill 

limitations of small spaceflight crews they must be augmented by Earth based support crews and automated repair equipment. This system 

architecture covers the complete system from ground-user to flight hardware and flight crew and defines an Earth segment and a Space 

segment. The “Earth Segment” involves database management, operational planning, and remote equipment programming and validation 

processes. The “Space Segment” involves the automated diagnostic, test and repair equipment required for a complete repair process. This 

document defines three major subsystems including, tele-operations that links the flight hardware to ground support, highly reconfigurable 

diagnostics and test instruments, and a CLEAR Repair Apparatus that automates the physical repair process. 

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