November 2010 

NASA/TM-2010-216870 

NESC-RP-10-00635 

 

Independent Peer Review of Communications, 

Navigation, and Networking re-Configurable 

Testbed (CoNNeCT) Project Antenna Pointing 

Subsystem (APS) Integrated Gimbal Assembly 

(IGA) Structural Analysis 

Ivatury S. Raju/NESC 

Langley Research Center, Hampton, Virginia 

Curtis E. Larsen/NESC 

Johnson Space Center, Houston, Texas 

Joseph W. Pellicciotti/NESC 

Goddard Space Flight Center, Greenbelt, Maryland 
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November 2010 

NASA/TM-2010-216870 

NESC-RP-10-00635 

 

Independent Peer Review of Communications, 

Navigation, and Networking re-Configurable 

Testbed (CoNNeCT) Project Antenna Pointing 

Subsystem (APS) Integrated Gimbal Assembly 

(IGA) Structural Analysis 

Ivatury S. Raju/NESC 

Langley Research Center, Hampton, Virginia 

Curtis E. Larsen/NESC 

Johnson Space Center, Houston, Texas 

Joseph W. Pellicciotti/NESC 

Goddard Space Flight Center, Greenbelt, Maryland 
Available from: 

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7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

The use of trademarks or names of manufacturers in the report is for accurate reporting and does not 

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National Aeronautics and Space Administration. 
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Technical Assessment Report

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NESC-RP10-00635

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Title:

Independent Review of CoNNeCT Antenna IGA Model and 

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NESC Request No.: TI-10-00635

Independent Peer Review of Communications, Navigation, and 

Networking re-Configurable Testbed (CoNNeCT) Project Antenna 

Pointing Subsystem (APS) Integrated Gimbal Assembly (IGA) 

Structural Analysis 

October 21, 2010 
NASA Engineering and Safety Center 

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Approval and Document Revision History 

NOTE: This document was approved at the October 21, 2010, NRB. This document was 

submitted to the NESC Director on October 26, 2010, for configuration control. 

Approved

Version:

Original Signature on File 10/27/10

1.0 NESC Director Date

Version Description of Revision Author Effective Date

1.0 Initial Release Dr. Ivatury Raju, NASA 

Technical Fellow for 

Structures, and Joseph 

Pellicciotti, NASA Technical 

Fellow for Mechanical 

Systems

10/21/10
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Table of Contents 

Volume I: Technical Report 

1.0 Authorization and Notification ............................................................................ 4

2.0 Signature Page ....................................................................................................... 5

3.0 Team List ............................................................................................................... 6

4.0 Executive Summary .............................................................................................. 7

5.0 Problem Background and Approach .................................................................. 8

6.0 Data Analysis ....................................................................................................... 10

6.1 SNC Structural Analysis ....................................................................................... 11

6.2 NESC Team Model Review Comments ............................................................... 20

7.0 Findings, Observations, and NESC Recommendations .................................. 21

7.1 Findings................................................................................................................. 21

7.2 Observations ......................................................................................................... 22

7.3 NESC Recommendations...................................................................................... 22

8.0 Definition of Terms ............................................................................................. 22

9.0 Acronyms List ..................................................................................................... 23

List of Figures

Figure 5.0-1. Testbed mounted onto ExPA AFRAM (Prior to Redesign) ................................... 8

Figure 5.0-2. APS ......................................................................................................................... 9

Figure 5.0-3. APS Base (Left) and Nose (Right) Range of Motion ........................................... 10

Figure 5.0-4. Gimbal Restraint Mechanism ............................................................................... 10

Figure 6.1-1. APS NASTRAN Model ........................................................................................ 11

Figure 6.1-2. APS NASTRAN Analysis Results for Free-Free Vibration ................................. 12

Figure 6.1-3. Modal Effective Mass Participation for First 50 Modes ....................................... 13

Figure 6.1-4. Mode Shapes for Modes 8 and 34 – Modes with Most Modal Mass 

Participation .......................................................................................................... 14

Figure 6.1-5. APS Random Vibration Environment .................................................................. 15

Figure 6.1-6. Gimbal Actuator Capacity (excluding Torsion Limit).......................................... 17

List of Tables

Table 6.1-1. Loads in the 3 kinematic pins and their allowables (Coefficient of Friction = 0.05, 

Angle = 60 degrees) .............................................................................................. 16

Table 6.1-2. Forces in the Actuators and Comparison with Allowables ................................... 17

Table 6.1-3. Stresses in Various Components of the Model and the Computed Margins for 

Yield and Ultimate Strengths ................................................................................ 19

Volume II: Appendices 

A. APS Model Review Questions and Answers 
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Volume I: Technical Report 

1.0 Authorization and Notification 

This activity is in response to the effort requested by Glenn Research Center (GRC) to conduct 

an independent review of the structural analysis and modeling of the Communications, 

Navigation, and Networking re-Configurable Testbed (CoNNeCT) Project Antenna Pointing 

Subsystem (APS) Integrated Gimbal Assembly (IGA). The IGA Project has completed its CDR 

and the GRC Chief Engineer and the CoNNeCT Chief Engineer requested an independent 

assessment to assure the soundness of the modeling and analysis effort. Mr. Sam Hussey (APS 

Lead) served as CoNNeCT’s point of contact for the effort. CoNNeCT provided the structural 

model and analysis to the NESC team. 

The key stakeholders for this assessment include the Mr. Michael Barrett, GRC Chief Engineer; 

Ms. Ann Over, GRC CoNNeCT Project Manager; Mr. Glen Horvat, GRC Acting Center Chief 

Engineer; and Mr. Jim Free, GRC Director of Spaceflight Projects.
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2.0 Signature Page 

Submitted by: 

Team Signature Page on File – 11/19/10 

Dr. Ivatury S. Raju Date Dr. Curtis E. Larsen Date 

Mr. Joseph W. Pellicciotti Date 

Signatories declare the findings and observations compiled in the report are factually based from 

data extracted from Program/Project documents, contractor reports, and open literature, and/or 

generated from independently conducted tests, analysis, and inspections. 
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3.0 Team List 

Name Discipline Organization/Location

Core Team

Dr. Ivatury Raju

NASA Lead, Technical Fellow for 

Structures LaRC

Joseph Pellicciotti

NASA Lead, Technical Fellow for 

Mechanical Systems GSFC

Dr. Curtis Larsen

NASA Technical Fellow for Loads and 

Dynamics JSC

Ken Hamm Engineer ARC

Tom Irvine Dynamic Concepts MSFC

Pete Mule Aerospace Engineer GSFC

Linda Anderson MTSO Program Analyst LaRC

Support

Erin Moran Technical Writer LaRC, ATK

Tina Dunn-Pittman Project Coordinator LaRC, ATK
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4.0 Executive Summary 

In June 2010, Mr. Michael Barrett, from the Glenn Research Center (GRC) Chief Engineer’s 

Office requested an independent review of the structural analysis and modeling of the 

Communications, Navigation, and Networking re-Configurable Testbed (CoNNeCT) Project 

Antenna Pointing Subsystem (APS) Integrated Gimbal Assembly (IGA). At this time, the IGA 

had completed its critical design review (CDR).

The charter of the team was clarified to be a peer review of the NEi-NASTRAN1 model of the 

APS Antenna, and not a peer review of the design and the analysis that had been completed by 

the GRC team for CDR. Thus, only a limited amount of information was provided on the 

structural analysis. However, the NASA Engineering and Safety Center (NESC) team had 

difficulty separating analysis concerns from modeling issues. The team studied the NASTRAN 

model, but did not fully investigate how the model was used by the CoNNeCT Project and how 

the Project was interpreting the results. The team’s findings, observations, and NESC 

recommendations are based on the clarified peer review effort. 

The NESC team received the NASTRAN model on July 14, 2010 and performed a review 

providing comments and questions to the CoNNeCT Project. These comments ranged from 

model-specific concerns and system analyses questions. The prime contractor for this 

subsystem, Sierra Nevada Corporation (SNC), provided responses and the team followed up with 

a teleconference to address them. Generally, the team was comfortable with the model 

developed by SNC. However, due to the lack of information regarding the detailed system 

analyses, it was difficult to comment on the adequacy of the design to meet the mission 

requirements. A comparison of the hardware build to the model development (i.e., constrained 

and released degrees of freedom) was not made in the time available, but it was confirmed with 

the Project that this comparison was covered in the CDR. 

The model developed by SNC is a good representation of the CoNNeCT Antenna IGA. The 

responses to the issues raised by the NESC team were adequately answered by SNC. The 

contractor is in the process of implementing the team’s suggestions and correcting the identified 

model deficiencies. After the model is revised, the new margins of safety (MOS) need to be 

evaluated and verified that they are satisfactory. 

 

1

NASTRAN is a registered trademark of NASA. NEi is a trademark of NEi software, Inc. 
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5.0 Problem Background and Approach 

The CoNNeCT will investigate reprogrammable (software defined) radio technology for use 

during space exploration missions. This investigation will advance a common, Software Defined 

Radio (SDR) architecture standard for future use on long duration space exploration missions. 

CoNNeCT will demonstrate communications from the International Space Station (ISS) to the 

Tracking and Data Relay Satellite (TDRS) constellation at Ka-band frequency (20 - 30 gigahertz 

(GHz)); and Global Positioning Satellite (GPS) signals will be received and processed at current 

and future frequencies comparing performance and integrity. 

The Mechanical subsystem includes the support structure for mounting of hardware components. 

Figure 5.0-12

illustrates the testbed components and Figure 5.0-2 illustrates the APS. All Flight 

System components are mounted to the Enclosure, which is attached to the EXPRESS Pallet 

Assembly Flight Releasable Attachment Mechanism (ExPA/FRAM) adapter plate. All Flight 

System components are mounted inside the Enclosure except for the APS, the 18 inch diameter 

dish Ka-Band high gain antenna (HGA), the S-Band medium gain antenna (MGA), the two SBand low gain antennas (LGAs), and the L-Band LGA. The APS as shown is mounted off a 

structural pedestal. This mounting configuration changed after preliminary design review (PDR) 

as discussed further.

Figure 5.0-1. Testbed mounted onto ExPA AFRAM (Prior to Redesign) 

 

2

All the figures except Figure 6.1-6 were extracted from documentation provided by GRC or SNC.
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Between PDR and CDR, the two axis gimbal assembly was redesigned. The PDR design was 

such that the nose axis articulation was 180 degrees to get out of the launch locks and position 

the gimbal in its operational range. This generated a potential catastrophic hazard by 

illuminating the ISS structure with Ka band radio frequency (RF). The redesign for CDR limited 

the nose articulation and implemented hard stops to control the illuminating hazard (see Figure 

5.0-3). In addition, the CoNNeCT Project adopted the philosophy of Design For Minimum Risk 

(DFMR) with zero fault tolerance. 

Figure 5.0-2. APS 
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Figure 5.0-3. APS Base (Left) and Nose (Right) Range of Motion 

The redesign caused the launch loads on the gimbal assembly to increase, resulting in negative 

MOS. Restraint modifications and the gimbal mounting scheme were changed and the loads 

were reduced into an acceptable range, although with small positive MOS in some cases. Figure 

5.0-4 illustrates the restraint mechanism design. 

Figure 5.0-4. Gimbal Restraint Mechanism 

The result of this redesign activity was the origin of the request from the GRC Chief Engineer’s 

Office to the NESC for an independent review of the APS model to verify that the analysis was 

sufficiently conservative, and there were not significant deficiencies that could cause negative 

MOS or a test/flight anomaly. 

6.0 Data Analysis 

The NESC team received the CoNNeCT Antenna IGA model from SNC. The model was a NEINASTRAN finite element model (FEM). GRC and SNC independently developed the models. 
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SNC performed structural analysis with their model and developed MOS of various components. 

In this section, this analysis is presented, first. Then the team’s review of the model is discussed. 

6.1 SNC Structural Analysis 

The model consists of the IGA major structural components: Base (part number (P/N): 38544), 

Arm (P/N: 38553), Biaxial bracket (P/N: 37184), S-band support bracket (P/N: 38558, Bolt 

catcher base, Actuators (upper and lower), kinematics pins (also called Launch Restraints or 

Kinematic Launch snubbers or Locks – see Figure 5.0-4) and plates, S-band antenna, and KaBand antenna. Figure 6.1-1 shows several views of the NASTRAN model. The FEM was 

exercised and free-free vibration verification was performed. Figure 6.1-2 shows the results of 

this analysis. As expected, there are six rigid body modes3(modes 1 through 6 with near zero or 

zero Eigen values). 

Figure 6.1-1. APS NASTRAN Model 

 

3

In all NASTRAN runs the T1, T2, T3, R1, R2, R3 correspond to the translations along and rotations about the three orthogonal coordinates 

directions.
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Figure 6.1-2. APS NASTRAN Analysis Results for Free-Free Vibration

The modal effective mass was examined next to determine which modes would participate most 

significantly to a random base drive excitation. As shown in Figure 6.1-3, the highest modal 

mass participation in the X- and Y-axes comes from mode 8 at about 198 Hz, and for the Z-axis 

from mode 34 at 443 Hz. The shapes for these two modes are shown in Figure 6.1-4. The model 

was analyzed next for response to base drive random vibration (RV) excitations at maximum 

expected fight levels (MEFL) + 3 decibel (dB). The RV environments as a function of the 

frequency and the damping used are shown in Figure 6.1-5. These data were provided by GRC. 
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Figure 6.1-3. Modal Effective Mass Participation for First 50 Modes 
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Figure 6.1-4. Mode Shapes for Modes 8 and 34 – Modes with Most Modal Mass Participation 

Undeformed Mode 8 (198Hz) Deformed

Undeformed

Mode 34 ( 443Hz) Deformed
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Figure 6.1-5. APS Random Vibration Environment 

The reaction forces in the three kinematic pins and loads in both the actuators are critical forces 

and were scrutinized. The loads in the pins are compared to the allowables in Table 6.1-1. For 

this environment the response forces are acceptable (i.e., are less than the allowable). However, 

analysis of the launch restraint system appears to be incomplete. The following are suggestions 

for the analyses: 

(a) Lateral loads on sloped surfaces and geometric layout of the restraints need to be 

properly accounted for when determining external load on Qwknut and needed 

pre-load for gapping. 

(b) External loads on the Qwknut restraint need to be properly combined with preload. With no Bellville washers or other measures to make it a constant-force 

interface, the external loading would add to the pre-load. One would expect the 

pre-load to be something just above the expected external load so the restraint 

$ CoNNeCT Random Vibration Damping Schedule (20-100 Hz 2%, 100.1-200 HZ 3%, 200.1-2000 Hz 4%)

$ John Shaker June 10, 2010

$

TABDMP1 20 CRIT + 

+ 20. .02 100. .02 100.1 .03 200. .03+ 

+ 200.1 .04 2000. .04ENDT
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would need to handle double the preload. 

(c) Moments into the Qwknut, due to misalignments, mechanical shifts, launch loads, 

or thermal effects need to be properly accounted. The restraint arm is fixed at the 

Qwknut and pinned at the antenna bracket. 

Table 6.1-1. Loads in the Three Kinematic Pins and Their Allowables (Coefficient of Friction = 

0.05, Angle = 60 degrees) 

Pins

(Figure 5.0-4)

Load set -1 (X)

(lbf)

Load set -2 (Y)

(lbf)

Load set -3 (Z)

(lbf)

 Allowable

(lbf)

S-Band 303 228 480 578

Ka-Band 464 514 650 826

Front 1440 767 778 1949

The actuator forces and moments are presented in Table 6.1-2. Load set 1 produces torsion in 

the upper actuator near the allowable torque, while the other cases result in torsion in either the 

upper or lower actuators below the allowable. Load set 1 applied torque during launch (249 inlbs) is close to the unpowered holding torque on the actuators (250 in-lbs). Although the 

actuators can be backdriven without damage according to the vendor, there are secondary 

concerns for the system if this occurs. Backdriving the actuator could result with a rotor in a 

position where there is now stored energy or windup of the harmonic drive. The NESC team’s 

concern with this condition is that once the launch restraints are released and the APS is free, that 

stored energy could release and the APS will shift, potentially causing a deployment hang-up or 

damage. 

The other forces and moments in the actuators were compared to capability in Figure 6.1-6. In 

this figure, radial load is plotted against the moment. The two straight lines represent the failure 

boundary that is determined by the combination of axial, radial, and moment loads on the main 

bearings so as to not affect actuator life. Hence these lines represent the capability limit for that 

particular value of the axial load in the actuator. The upper line corresponds to a capability limit 

for an axial load less than or equal to 1,000 pounds (lbs). The lower line corresponds to an axial 

load of 1,500 lbs. If the axial load is greater than 1,500 lbs, then the actuator will have a 

negative MOS on some component (probably a bearing). 

All points below the lines in this figure represent combinations of radial loads and moments for 

safe operations (i.e., positive MOS). The root mean square (RMS) values for the radial loads and 

corresponding moments shown in Table 6.1-2 are plotted on Figure 6.1-6 with black symbols for 

the upper actuator and blue symbols for the lower actuator. From this figure, there is significant 

positive MOS for these actuators for a 1,500 lbs axial load capability. 
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Table 6.1-2. Forces in the Actuators and Comparison with Allowables 

Forces and Moments Load Set 1 Load Set 2 Load Set 3 Allowable (Torque)

in-lbs.

Upper Actuator

Radial X, lbs. 276 192 147

Axial Y, lbs. 123 183 147

Radial Z, lbs. 141 213 228

Moment X, in-lbs. 267 288 285

Torsion Y, in-lbs. 249 147 96 250

Moment Z, in-lbs. 387 231 123

RMS Values - Radial, Moment 310, 470 287,370 270,310

(lbs., in-lbs.)

Lower Actuator

Radial X, lbs. 153 84 42

Radial Y, lbs. 135 192 99

Axial Z, lbs. 180 285 609

Moment X, in-lbs. 507 528 312

Moment Y, in-lbs. 726 462 192

Torsion Z, in-lbs. 135 87 87 250

RMS Values - Radial, Moment 204, 886 210, 702 108, 366

(lbs., in-lbs.)

Figure 6.1-6. Gimbal Actuator Capacity (excluding Torsion Limit) 

Upper Actuator

Lower Actuator

Radial Load (lbs.)

Capability

(1500 lb. axial Load)

Capability

( 1000 lb. axial Load)

Moment (in-lbs.)
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The maximum stresses in the arm, biaxial bracket, base, and the S-Band bracket due to the RV 

environment and the associated MOS for yield and ultimate are presented in Table 6.1-3. A 

factor of safety (FOS) of 1.4 on yield and 2.0 on ultimate are used in computing the MOS. In 

this table, the MOS in fasteners in the model are also included and grouped by bolt type. The 

margins are calculated using: 

 (EQ. 1) 

In some cases it appears that the MOS is calculated using a FOS applied to the qualification 

loads instead of being applied to the design limit loads as defined in NASA-STD-5001A. It is 

the review team’s opinion that this is overly conservative. 

In Eq. 1, the allowable stress is either the yield or ultimate stress, and maximum stress is the 

maximum 3σ von Mises stress. Both 1σ and 3σ stresses are presented in Table 6.1-3. The 

margins are, however, calculated for the 3σ von Mises stress values. All of the calculated MOS 

are positive suggesting that various structural components are safe. 

The assumption that 3σ loading is the worst case may be unconservative, particularly for brittle 

(low elongation) materials. Systems subjected to RV environments can experience excitations 

higher than 3σ if the system is subjected to the environment for long enough duration. However, 

imposing a 4.5σ load requirement in this case appears to be excessive due to multiple apparent 

conservatisms in the modeling and analysis. 

In addition, random loads were applied one axis at a time and analyzed separately. Combined 

load analyses were not performed. Although such analyses may not be a requirement for this 

project, the practice is unconservative. Furthermore, it was also not clear if the restraint preload 

was included in a combined loading analysis. 

1

FOS*StressMax.

AllowbleStress MOS = –
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Table 6.1-3. Stresses in Various Components of the Model and the Computed Margins for Yield 

and Ultimate Strengths 
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6.2 NESC Team Model Review Comments 

The SNC IGA FEM was reviewed by the NASTRAN experts in the NESC team

4

. A number of 

issues were raised by this subteam and they are presented in Appendix A. SNC responded to 

each of the issues. This section summarizes the issues and the corresponding SNC responses. 

1. Minor issues: Several minor book-keeping inconsistencies were found in the model: (a) 

Coefficients of thermal expansions of materials with identification numbers 3 and 5 and 

the corresponding reference temperatures are not assigned, (b) Some 279 nodes have no 

associated elements, loads, or constraints associated with them, and (c) PID 40006 is not 

used. 

 SNC: As thermal analysis is not being performed, issue (a) is not pertinent. 

Dummy node numbers exist in the model and they do not participate in the 

analysis. PID 40006 is not used and is a remnant of previous analysis, and thus 

items (b) and (c) are benign. 

2. Fastener Modeling: Holes for fasteners (assumed as fasteners) as small as 0.125 inch 

were modeled with local refined meshes. But these round holes appears as hexagon areas 

in the mesh. It is not clear why features of this size were modeled into a dynamic model. 

 SNC suggested that these features were modeled to accommodate other 

components not in the primary load path. These other components will be added 

as the system design/model is finalized. The mesh around the mentioned areas is 

mainly to provide attachment points for the other hardware. This type of modeling 

is not expected to lead to or cause stress issues in these regions. 

3. Base Plate Boundary Conditions: There is a large RBE2 (rigid element connections) on 

the base plate that attaches the bolt holes to a central point where a large mass is located. 

This RBE2 specification effectively rigidly ties these bolt holes together. Thus, when 

free-free vibration analysis modes are performed, the effect is to rigidize the base plate. 

It is not clear if this is a desired condition. This boundary condition implementation 

appears to be in the model to utilize the prior "large mass" method of inducing base 

acceleration. Current versions of NASTRAN allow direct input of applied acceleration 

without having to resort to the use of the large mass method. 

 SNC: The “large mass” method is a widely accepted and historically used method 

of performing random response analysis. This method is typically used by SNC. 

 SNC: The RBE2 constraints on the nodes on the base plate to connect to the node 

where the mass is located will rigidize the base plate. In reality the base plate is 

effectively rigid along that interface due to the large number of 0.250-28 fasteners 

used to secure the base plate. 

 

4 Ken Hamm –ARC and Pete Mule –GSFC
NASA Engineering and Safety Center 

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 SNC: In the free-free mode analyses the RBE2 constraints would tie the plate 

together and may miss some “free” elements. Therefore, SNC performed the freefree analyses again to demonstrate that no “free” elements exist and that the 

previous free-free modes analysis is valid. (See Appendix A). 

4. Gussets: There are what appear to be gussets or stiffeners plates under the base plate. 

However, the meshes do not line up so there is no connectivity between the base plate 

and the stiffener in that area. Is this is an error or is the modeling intentional? 

 SNC will examine this region to determine if there is a connectivity issue in those 

local areas. The modal analysis will then be updated and the results scrutinized. 

5. Interfacing linear and quadratic elements: The current IGA model had areas where Quad 

8 elements (8-node quadrilateral elements with corner and mid-side nodes) are directly 

connected to Quad 4 elements (4-node quadrilateral elements with corner nodes) or Tria 

3 elements (3-node triangular elements). Quad 8 elements have quadratic shape 

functions while Quad 4 elements and Tria 3 elements have linear shape functions. 

Recommended modeling practice is to interface Quad 8 elements with other Quad 8 

elements or other quadratic elements such as Tria 6 elements, and not Quad 4 or Tria 3 

elements (i.e., so corner nodes are connected to corner nodes, and mid-side nodes to midside nodes). Mixing Quad 4 and Tria 3 elements with Quad 8 elements is not 

recommended as compatibility across the inter-element boundaries cannot be maintained. 

 SNC is aware of these modeling issues. Apparently, this situation occurred when a 

local area of the mesh was updated after the majority of the mesh is completed. In 

the next model revision, all Quad 4 and Tria 3 will be updated to Quad 8 and Tria 

6 elements with proper connectivity. 

 SNC agreed to revise the model according to the team’s suggestions and will be 

providing the new margins to the CoNNeCT Project. 

7.0 Findings, Observations, and NESC Recommendations 

7.1 Findings 

The following findings are made: 

F-1. There appears to be considerable amount of conservatism in the design and analysis. 

F-2. The NASTRAN FEM is overall a good representation of the CoNNeCT Antenna IGA. 

F-3. SNC provided satisfactory explanations or agreed to make appropriate corrections to the 

FEM issues identified. 

F-4. Gimbal actuator analytical applied torque during launch is approximately same as the 
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unpowered, 249 and 250, respectively. 

7.2 Observations 

The following observations are made: 

O-1. The assumption that 3loading is the worst case may be unconservative. 

O-2. Analysis of the launch restraint system appears to be incomplete. 

O-3. Application of FOS to qualification level loads appears to be redundant. 

O-4. Load combinations used in the margin calculations need to be reported (including 

restraint pre-load). 

7.3 NESC Recommendations 

The following NESC recommendations are directed to the CoNNeCT Project: 

R-1. The IGA FEM should be exercised using combinations of nominal and zero for actuator 

rotational stiffness to bound the possible response. (F-3)

R-2. Evaluate if the IGA FEM hardware is mounted to a 0.5 inch radiator panel to determine if 

some of the loads are missing due to the flexibility of the mounting structures. 

(F-3 and O-2)

R-3. Verify positive MOS following incorporation of IGA FEM updates. (F-3)

R-4. Incorporate a FOS for the gimbal actuator (250 in-lbs) unpowered torque value and 

update the analysis to ensure a positive MOS. (F-4)

8.0 Definition of Terms 

Corrective Actions 

Changes to design processes, work instructions, workmanship practices, training, inspections, 

tests, procedures, specifications, drawings, tools, equipment, facilities, resources, or material that 

result in preventing, minimizing, or limiting the potential for recurrence of a problem. 
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Finding 

A conclusion based on facts established during the assessment/inspection by the investigating 

authority. 

Lessons Learned 

Knowledge or understanding gained by experience. The experience may be positive, as in a 

successful test or mission, or negative, as in a mishap or failure. A lesson must be significant in 

that it has real or assumed impact on operations; valid in that it is factually and technically 

correct; and applicable in that it identifies a specific design, process, or decision that reduces or 

limits the potential for failures and mishaps, or reinforces a positive result. 

Observation 

A significant factor established during this assessment that supports and influences the 

conclusions reached in the statement of Findings and Recommendations. 

Problem 

The subject of the independent technical assessment/inspection. 

Recommendation 

An action identified by the assessment/inspection team to correct a root cause or deficiency 

identified during the investigation. The recommendations may be used by the responsible 

C/P/P/O in the preparation of a corrective action plan. 

Root Cause 

Along a chain of events leading to a mishap or close call, the first causal action or failure to act 

that could have been controlled systemically either by policy/practice/procedure or individual 

adherence to policy/practice/procedure. 

9.0 Acronyms List 

APS Antenna Pointing Subsystem 

ARC Ames Research Center 

CDR Critical Design Review 

CoNNeCT Communications, Navigation, and Networking re-Configurable Testbed 

dB decibel 

DFMR Design For Minimum Risk 

ExPA EXPRESS Pallet Assembly 

FEM finite element model 
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FOS factor of safety 

FRAM Flight Releasable Attachment Mechanism 

GPS global positioning satellite 

GRC Glenn Research Center 

GSFC Goddard Space Flight Center 

HGA high gain antenna 

Hz hertz 

IGA Integrated Gimbal Assembly 

ISS International Space Station 

JSC Johnson Space Center 

LaRC Langley Research Center 

LGA low gain antennas 

MEFL maximum expected fight levels 

MGA medium gain antenna 

MOS margins of safety 

MTSO Management and Technical Support Office 

NASA National Aeronautics and Space Administration 

NESC NASA Engineering and Safety Center 

NRB NESC Review Board 

P/N part number 

PDR Preliminary Design Review 

RF radio frequency 

RMS root mean square 

RV random vibration 

SDR Software Defined Radio 

SNC Sierra Nevada Corporation 

TDRS Tracking and Data Relay Satellite 

Volume II: Appendices 

A. APS Model Review, July 21, 2010 
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Appendix A. APS Model Review, July 21, 2010 
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REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Independent Peer Review of Communications, Navigation, and 

Networking re-Configurable Testbed (CoNNeCT) Project Antenna 

Pointing Subsystem (APS) Integrated Gimbal Assembly (IGA) Structural 

Analysis

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Raju, Ivatury S.; Larsen, Curtis E.; Pellicciotti, Joseph W.

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

 8. PERFORMING ORGANIZATION

 REPORT NUMBER

L-19949 NESC-RP-10-00635

10. SPONSOR/MONITOR'S ACRONYM(S)

NASA

13. SUPPLEMENTARY NOTES

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category 17-Space Communications, Spacecraft Communications, Command and Tracking

Availability: NASA CASI (443) 757-5802

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

Glenn Research Center Chief Engineer's Office requested an independent review of the structural analysis and modeling of the 

Communications, Navigation, and Networking re-Configurable Testbed (CoNNeCT) Project Antenna Pointing Subsystem 

(APS) Integrated Gimbal Assembly (IGA) to be conducted by the NASA Engineering and Safety Center (NESC). At this time, 

the IGA had completed its critical design review (CDR). The assessment was to be a peer review of the NEi-NASTRAN1 

model of the APS Antenna, and not a peer review of the design and the analysis that had been completed by the GRC team for 

CDR. Thus, only a limited amount of information was provided on the structural analysis. However, the NESC team had 

difficulty separating analysis concerns from modeling issues. The team studied the NASTRAN model, but did not fully 

investigate how the model was used by the CoNNeCT Project and how the Project was interpreting the results. The team's 

findings, observations, and NESC recommendations are contained in this report. 

15. SUBJECT TERMS

Antenna Pointing Subsystem; Integrated Gimbal Assembly; NASA Engineering and Safety Center; Communications, 

Navigation, and Networking re-Configurable Testbed

18. NUMBER

 OF 

 PAGES

62

19b. TELEPHONE NUMBER (Include area code)

(443) 757-5802

a. REPORT

U

c. THIS PAGE

U

b. ABSTRACT

U

17. LIMITATION OF 

 ABSTRACT

UU

Prescribed by ANSI Std. Z39.18

Standard Form 298 (Rev. 8-98)

3. DATES COVERED (From - To)

June 2010 - October 2010

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

869021.05.07.07.99

11. SPONSOR/MONITOR'S REPORT

 NUMBER(S)

NASA/TM-2010-216870

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01- 11 - 2010