X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

Volume I

Report of Findings

X-43A Mishap

By the 

X-43A

Mishap Investigation Board
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

ii

Volume I

Table of Contents

1 Board Charter............................................................................................................... 1

2 Signature Page ............................................................................................................. 2

3 Acknowledgments ....................................................................................................... 3

4 Board Members........................................................................................................... 4

5 Executive Summary..................................................................................................... 5

6 Hyper-X Program Overview........................................................................................ 8

7 Description of X-43A Mishap ................................................................................... 15

8 Method of Investigation, Board Organization, Special Circumstances..................... 20

9 Finding, Root Cause, Contributing Factors, Recommendations - Export Controlled 25

10 Significant Observations, Anomalies, Recommendations - Export Controlled......... 45

11 Definition of Terms and Acronyms......................................................................... 62

Table of Figures

Figure 6-1. X-43A Stack..................................................................................................... 9

Figure 6-2. B-52 Carrier Aircraft with X-43A Stack.......................................................... 9

Figure 6-3. X-43A Stack with Modifications from Pegasus............................................. 10

Figure 6-4. Altitude vs. Time............................................................................................ 11

Figure 6-5. Dynamic Pressure vs. Mach........................................................................... 11

Figure 6-6. HXLV Control System Diagram.................................................................... 12

Figure 6-7. Subsystem Models Comprising the System Level Models............................ 13

Figure 6-8. X-43A Mission Profile ................................................................................... 14

Figure 7-1. Vehicle Flight Parameters.............................................................................. 18

Figure 7-2. Control Surface Positions and Roll Rate........................................................ 19

Figure 8-1. X-43A Mishap Investigation Board Process.................................................. 21

Figure 8-2. Top Level Fault Tree...................................................................................... 23

Figure 8-3. Critical Fault Tree Branch.............................................................................. 23

Table of Tables

Table 7-1. Detailed Timeline ........................................................................................... 16.
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

iii

 Appendices

Appendix A. Fault Tree Closure Summaries – Export Controlled ................................... A-1

Appendix B. Anomalies – Export Controlled ....................................................................B-1

Appendix C. Mishap Investigation Participants ............................................................. C-1
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

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Volume II

Volume II is comprised of Appendices A, B, and C. Volume II Appendix A contains the 

fault tree used by the X-43A Mishap Investigation Board (MIB) in resolving the X-43A 

mishap. In electronic format, Volume II Appendix B contains the plans, closeout forms 

and supporting data used to disposition each fault. This appendix also contains hardcopy 

examples of a plan and closeout. In electronic format, Volume II Appendix C contains 

the MIB schedule used for planning and monitoring the MIB activities. This appendix 

also contains a hardcopy of the top level schedule.

Volume III

Volume III contains the Corrective Action Plan to be submitted under separate cover by 

the X-43 Project Office.

Volume IV

Volume IV contains the lessons learned from the X-43A Mishap Investigation. Lessons 

learned are presented in the NASA Lessons Learned Information Systems (LLIS) format 

obtained from the LLIS website. These lessons learned are provided per NPG: 8621.1 

paragraph 6.1.1 and as directed in the charter for the MIB (Volume I, Section 1).

Volume V

Witness statements and testimony taken in support of the X-43A Mishap Investigation 

are being retained by the Mishap Board Chairman. These witness statements and 

testimonies had no direct bearing on any of the contributors to the mishap.
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

1

1 BOARD CHARTER

The Associate Administrator for Aerospace Technology formally appointed the X-43A 

Mishap Investigation Board (MIB) through a letter of appointment on June 8, 2001. The MIB 

assumed responsibility for the investigation on June 5, 2001 based on verbal direction from 

the Associate Administrator.

The letter of appointment established the following charter for the MIB.

The Board will:

ß Obtain and analyze whatever evidence, facts, and opinions it considers relevant.

ß Use reports, studies, findings, recommendations, and other actions by NASA officials and 

contractors. The Board may conduct inquiries, hearings, tests, and other actions it deems 

appropriate. The Board may take and receive statements from witnesses.

ß Impound property, equipment, and records as necessary.

ß Determine actual cause(s) or if unable, determine probable cause(s) of X-43A Mishap, and 

document and prioritize their findings in terms of (a) the dominant root cause(s) of the 

mishap, (b) contributing root cause(s), and (c) significant observation(s).

ß Develop recommendations for preventive or other appropriate actions.

ß Provide a verbal report to Associate Administrator for Aerospace Technology as soon as 

possible, and a final report by August 31, 2001, in the format specified in NASA 

Procedures and Guidelines (NPG) 8621.1. (Due to the complexity of the X-43A mishap 

investigation, this date was amended by the Associate Administrator for Aerospace 

Technology to permit the board to complete its activities.)

ß Provide a proposed lessons learned summary. (Proposed corrective action implementation 

plan is to be provided by the X-43A project office.)

ß Perform any other duties that may be requested by the Associate Administrator for 

Aerospace Technology.
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

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2 SIGNATURE PAGE

___________/s/_______________ ___________/s/_______________

Robert W. Hughes Joseph J. Lackovich, Jr.

MIB Chairman MIB Executive Secretary

Chief Engineer, Space Launch Initiative Deputy Director, ELV Launch Services

Marshall Space Flight Center Kennedy Space Center

___________/s/_______________ ___________/s/_______________

Frank H. Bauer Michael R. Hannan

Chief, Guidance, Navigation & Control Center Control Systems Engineer

Goddard Space Flight Center Space Transportation Directorate

Marshall Space Flight Center

___________/s/_______________ ___________/s/_______________

Luat T. Nguyen Victoria A. Regenie

Deputy Director, Airborne Systems Competency Deputy Director, Research Engineering Directorate

Langley Research Center Dryden Flight Research Center

___________/s/_______________ ___________/s/_______________

Karen L. Spanyer Pamela F. Richardson 

Lead, Strength Analysis Group Manager, Aeronautics Mission Assurance 

Engineering Directorate Office of Safety and Mission Assurance

Marshall Space Flight Center

___________/s/_______________ ___________/s/_______________

Accept: NASA HQ / Code R Approve: NASA HQ / Code Q

Jeremiah F. Creedon Bryan D. O’Connor

Associate Administrator Associate Administrator

Office of Aerospace Technology Office of Safety and Mission Assurance

Advisors

Office of Chief Counsel: DFRC/ Chauncey Williams 

Office of Public Affairs: DFRC/ Fred Johnsen
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

3

3 ACKNOWLEDGMENTS

The X-43A MIB wishes to thank the members of the Mishap Investigation Team (MIT) and 

associated organizations for their committed efforts in the support of the X-43A MIB 

activities. Determining the cause of the X-43A mishap was a complex effort requiring a 

significant commitment of time and resources. The successful resolution of this mishap 

would have been impossible without the total cooperation, openness and commitment of the 

entire MIT. Key factors in the mishap resolution were the technical and programmatic 

competence, positive attitude and sustained support displayed by the Hyper-X Program team. 

The outstanding support provided by the expert consultants from both industry and NASA 

was equally important to understanding the complex technical issues associated with this 

mishap. 

Organizations with members who participated actively in the MIT were:

ß Dryden Flight Research Center (DFRC)

ß Goddard Space Flight Center (GSFC)

ß Kennedy Space Center (KSC)

ß Langley Research Center (LaRC)

ß Marshall Space Flight Center (MSFC)

ß Orbital Sciences Corporation (OSC)

ß Micro Craft Corporation 

The X-43A MIB would also like to recognize and thank the managers and staffs at DFRC, 

LaRC and OSC for their assistance and hospitality during the MIB residence in their facilities. 

The dedicated support from these organizations during MIB operation in their facilities was a 

major contributor to the success of the investigation.

Finally, the MIB would like to thank Jackie Sneed and Jon Rick for their outstanding support 

in the scheduling, coordination and documentation of MIB activities. The daily efforts 

provided by Jackie and Jon were the key activities that enabled the MIB to function 

efficiently.
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

4

4 BOARD MEMBERS 

 Board Position/Responsibility Function(s)

Control and Aerodynamics

Board: L. Nguyen, F. Bauer, V. Regenie

Board Consultants: C. Hall, M. Hannan

Systems and Software

Board: V. Regenie

Avionics and Electronic Systems

Board: F. Bauer

Chairperson

Board: R. Hughes

Processing and Operations

Board: J. Lackovich

Propulsion 

Board: R. Hughes

Board Consultant: B. Neighbors

Stress and Environmental Analyses

Board Consultant: K. Spanyer

Safety and Mission Assurance and

Management Processes

Ex O: P. Richardson

Executive Secretary

Board: J. Lackovich

Mechanical Systems

Board: R. Hughes

Board Organization and Report 

Development

Assoc.: J. Sneed, J. Rick

Board Organization and Implementation

Alternate Board Chairperson / 

Fault Tree Organization and Scheduling

Aerodynamics and Controls Investigation Organization 

and Implementation

Avionics and Electronics Investigation Organization 

and Implementation

Processing and Operations Investigation Organization 

and Implementation

Systems and Software Investigation Organization and 

Implementation

Mechanical Systems Investigation Organization and 

Implementation

Stress and Environmental Analyses Investigation 

Organization and Implementation

Propulsion Investigation Organization and 

Implementation

Organization of Daily Board Processes, Report 

Development and Fault Tree Control

Safety and Mission Assurance and Evaluation of 

Management Processes

Structures and Aeroelastic Effects 

Board Consultant: K. Spanyer

Structures and Aeroelastic Effects Investigation 

Organization and Implementation
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

5

5 EXECUTIVE SUMMARY

NASA initiated the Hyper-X Program in 1996 to advance hypersonic air-breathing 

propulsion and related technologies from laboratory experiments to the flight environment. 

This program was designed to be a high-risk, high-payoff program. The X-43A was to be 

the first flight vehicle in the flight series. The X-43A was a combination of the Hyper-X 

Research Vehicle (HXRV), HXRV adapter, and Hyper-X Launch Vehicle (HXLV) referred 

to as the X-43A stack. The first X-43A flight attempt was conducted on June 2, 2001. 

The HXLV was a rocket-propelled launch vehicle modified from a Pegasus launch vehicle 

stage one (Orion 50S) configuration. The HXLV was to accelerate the HXRV to the 

required Mach number and operational altitude to obtain scramjet technology data. The 

trajectory selected to achieve the mission was at a lower altitude and subsequently a higher 

dynamic pressure than a typical Pegasus trajectory. This trajectory was selected due to 

X-43A stack weight limits on the B-52. 

During the first mission, the X-43A stack was released from a B-52 carrier aircraft one hour 

and 15 minutes after takeoff. This corresponds to 0.0 seconds mission time. The HXLV 

solid rocket motor ignition occurred 5.19 seconds later and the mission proceeded as planned 

through the start of the pitch-up maneuver at 8 seconds. During the pitch-up maneuver the 

X-43A stack began to experience a control anomaly (at approximately 11.5 seconds) 

characterized by a diverging roll oscillation at a 2.5 Hz frequency. The roll oscillation 

continued to diverge until approximately 13 seconds when the HXLV rudder 

electromechanical actuator (EMA) stalled and ceased to respond to autopilot commands. 

The rudder actuator stall resulted in loss of yaw control that caused the X-43A stack sideslip 

to diverge rapidly to over 8 degrees. At 13.5 seconds, structural overload of the starboard 

elevon occurred. The severe loss of control caused the X-43A stack to deviate significantly 

from its planned trajectory and the vehicle was terminated by range control 48.57 seconds 

after release. 

The X-43A Mishap Investigation Board (MIB) was convened at DFRC on June 5, 2001.

The mission failure was attributed to the HXLV. 

Root Cause: The X-43A HXLV failed because the vehicle control system design was 

deficient for the trajectory flown due to inaccurate analytical models (Pegasus heritage and 

HXLV specific), which overestimated the system margins.

ß The key phenomenon that triggered the mishap was the divergent roll oscillatory 

motion at a 2.5 Hz frequency. 

− The divergence was primarily caused by excessive control system gain. 

ß A second phenomenon that was a consequence of the divergent roll oscillation was a 

stall of the rudder actuator that accelerated the loss of control.

ß Neither phenomenon was predicted by preflight analyses.

ß The analytical modeling deficiencies resulted from a combination of factors.

Note: Models include system architecture, boundary conditions and data.
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

6

The mishap occurred because the control system could not maintain the vehicle stability 

during transonic flight. The vehicle instability was observed as a divergent roll oscillation. 

An effect of the divergent roll oscillation was the stall of the rudder actuator. The stall 

accelerated loss of control. The loss of control resulted in loss of the X-43A stack. The 

rudder actuator stalled due to increased deflections that caused higher aerodynamic loading 

than preflight predictions. The deficient control system and under prediction of rudder 

actuator loads occurred due to modeling inaccuracies. 

Determining the cause of the X-43A mishap was a complex effort requiring a significant 

commitment of time and resources. This effort consisted of in-depth evaluations of the 

Pegasus and HXLV system and subsystem models and tools as well as extensive system 

level and subsystem level analyses. To support the analyses, extensive mechanical testing 

(fin actuation system) and wind tunnel testing (6 percent model) were required. 

The major contributors to the mishap were modeling inaccuracies in the fin actuation system, 

modeling inaccuracies in the aerodynamics and insufficient variations of modeling 

parameters (parametric uncertainty analysis). Pegasus heritage and HXLV specific models 

were found to be inaccurate. 

ß Fin actuation system inaccuracies resulted from:

− Discrepancies in modeling the electronic and mechanical fin actuator system 

components 

− Under prediction of the fin actuation system compliance used in the models. 

ß Aerodynamic modeling inaccuracies resulted from:

− Error in incorporation of wind tunnel data into the math model

− Misinterpretation of wind tunnel results due to insufficient data 

− Unmodeled outer mold line changes associated with the thermal protection 

system (TPS). 

ß Insufficient variations of modeling parameters (parameter uncertainty analysis) were 

found in:

− Aerodynamics

− Fin Actuation System

− Control System

Less significant contributors were errors detected in modeling mass properties. Potential 

contributing factors were found in the areas of dynamic aerodynamics and 

aeroservoelasticity. 

Linear stability predictions were recalculated using the corrected nominal models. Stability 

gain margins were computed for all axes. Aileron gain margin (roll axis) was examined in 

particular and showed a sizeable reduction from the 8 dB preflight prediction. Model 

corrections led to a revised prediction of less than 2 dB at nominal conditions. This was well 

below the requirement of a 6 dB gain margin. Although this reduction was very significant 

and close to instability boundaries, the revised prediction was still stable. This meant that the 

nominal model corrections alone were insufficient to predict the vehicle loss of control and 

that parameter uncertainty had to be included. Accounting for parameter uncertainties in the 
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

7

analyses replicated the mishap. This was confirmed by nonlinear time history predictions 

using the 6-degree of freedom (6-DOF) flight dynamics simulation of the X-43A stack. 

No single contributing factor or potential contributing factor caused this mishap. The flight 

mishap could only be reproduced when all of the modeling inaccuracies with uncertainty 

variations were incorporated in the system level linear analysis model and nonlinear 

simulation model. 
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

8

6 HYPER-X PROGRAM OVERVIEW

This section is written in the past tense to express the status of the Hyper-X Program and X43A mission as evaluated by the MIB. The use of past tense is not intended to reflect the 

current status of the Hyper-X Program.

6.1 Overview

The Hyper-X Program was a collaborative effort between NASA LaRC and DFRC with 

shared mission success responsibilities. To execute the program, NASA awarded industry 

contracts for the design, development and fabrication of the flight test vehicles. OSC was the 

contractor for the Hyper-X Launch Vehicle (HXLV) and Micro Craft was the contractor for 

the Hyper-X Research Vehicle (HXRV) and HXRV adapter. These contracts included 

launch services and flight test support. 

6.2 Program/Project Objectives

The Hyper-X Program was designed to be a high-risk, high-payoff program. NASA initiated 

the program in 1996 to advance hypersonic air-breathing propulsion and related technologies 

from laboratory experiments to the flight environment. The primary program goal was to 

demonstrate and flight validate analytical design tools, computational methods and 

experimental techniques required for the development of a hypersonic, air-breathing aircraft. 

Accomplishing this goal required flight data from a scramjet-powered vehicle. The scramjet 

vehicle configuration was designated the X-43A Hyper-X Research Vehicle (HXRV). The 

X-43A HXRV was designed and built to fly at hypersonic speeds (greater than Mach 5). 

Three X-43A flights, each with a non-recoverable HXRV, were planned. The first X-43A 

flight attempt was conducted on June 2, 2001. 

6.3 Configuration

The X-43A HXRV was designed to be accelerated to its operational altitude and Mach 

number using a rocket-propelled launch vehicle, designated the Hyper-X Launch Vehicle 

(HXLV). The HXRV was attached to the HXLV via the HXRV adapter. The HXRV 

adapter also provided services to maintain the desired HXRV environmental conditions 

during mated flight and to separate the HXRV from the HXRV adapter for scramjet 

operation. This combination of the HXLV, the HXRV adapter and the HXRV was 

designated the X-43A stack (Figure 6-1). The X-43A stack was integrated to the B-52 

carrier aircraft and was flown to the launch area for deployment (Figure 6-2).
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

9

Figure 6-1. X-43A Stack

Figure 6-2. B-52 Carrier Aircraft with X-43A Stack

HXLV HXRV Adapter

X- 43A

(HXRV)
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

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6.4 Description of X-43A Flight Hardware and Mission

6.4.1 B-52 Carrier Aircraft 

The carrier aircraft was the NASA DFRC B-52B (52-008). 

6.4.2 X-43A Hyper-X Research Vehicle (HXRV)

The HXRV was 12 feet long, 5 feet wide, 2 feet high, and weighed about 3,000 pounds. It 

was powered by a single hydrogen-fueled, dual-mode, airframe-integrated scramjet 

propulsion system. 

6.4.3 Hyper-X Launch Vehicle (HXLV)

The HXLV was derived from a modified Pegasus launch vehicle stage one (Orion 50S) 

configuration. Modifications to the Pegasus configuration for the X-43A mission are 

depicted in Figure 6-3. 

Figure 6-3. X-43A Stack with Modifications from Pegasus
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

11

6.4.3.1 Environments: HXLV versus Pegasus

The HXLV was launched and flown in an environment that was significantly different from 

previous Pegasus experience. At the time of failure, 13.5 seconds, the HXLV altitude was 

22,244 feet, whereas a typical Pegasus altitude for the same flight duration would have been 

approximately 40,000 feet. In addition, at Mach 1, near the failure point, the HXLV 

dynamic pressure was 650 psf whereas a typical Pegasus dynamic pressure for the same 

Mach number would have been approximately 300 psf. This increase in dynamic pressure at 

transonic conditions was a major factor in the mishap. 

0 10 20 30 40 50 60 70 80 90

0 

50,000

100,000

150,000

200,000

250,000

time (sec)

Altitude (ft)

X-43A

failure

point

Pegasus

(typical)

HXLV

0 10 20 30 40 50 60 70 80 90

0 

50,000

100,000

150,000

200,000

250,000

time (sec)

Altitude (ft)

X-43A

failure

point

0 10 20 30 40 50 60 70 80 90

0 

50,000

100,000

150,000

200,000

250,000

time (sec)

Altitude (ft)

0 10 20 30 40 50 60 70 80 90

0 

50,000

100,000

150,000

200,000

250,000

time (sec)

Altitude (ft)

0 10 20 30 40 50 60 70 80 90

0 

50,000

100,000

150,000

200,000

250,000

time (sec)

Altitude (ft)

X-43A

failure

point

Pegasus

(typical)

HXLV

Figure 6-4. Altitude vs. Time

0 1 2 3 4 5 6 7 8 9

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Mach

Dynamic Pressure (psf)

X-43A

failure

point

Pegasus

(typical)

HXLV

0 1 2 3 4 5 6 7 8 9

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Mach

Dynamic Pressure (psf)

0 1 2 3 4 5 6 7 8 9

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Mach

Dynamic Pressure (psf)

0 1 2 3 4 5 6 7 8 9

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Mach

Dynamic Pressure (psf)

X-43A

failure

point

Pegasus

(typical)

HXLV

Figure 6-5. Dynamic Pressure vs. Mach
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

12

6.4.3.2 HXLV Control System

The HXLV control system was a closed-loop feedback system (Figure 6-6). The HXLV 

control system consisted of an inertial measurement unit (IMU) that sensed the X-43A stack 

accelerations and rates; an autopilot that translated the output from the IMU into steering 

commands; an electronic control unit (ECU) that translated the autopilot commands into fin 

(elevons and rudder) position commands; and an electromechanical actuator (EMA) that 

rotated the fins to the commanded positions. A sensor measured fin actuator position that the 

ECU used as feedback for servo control. The ECU also filtered the sensed actuator position 

and transmitted it to the autopilot (talkback). The ECU and the EMA comprised the Fin 

Actuation System (FAS). 

Figure 6-6. HXLV Control System Diagram

IMU

Autopilot

ECU Actuator

Fin Actuator

Commands

Fin Actuator

Positions

Talkback

Fin Actuator

Positions

Accelerations, rates, 

velocities, positions

Fin 

Commands

Fin Actuation System (FAS)

IMU

Autopilot

ECU Actuator

Fin Actuator

Commands

Fin Actuator

Positions

Talkback

Fin Actuator

Positions

Accelerations, rates, 

velocities, positions

Fin 

Commands

Fin Actuation System (FAS)
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

13

6.4.3.3 HXLV Control System Modeling

The analysis of the HXLV control system was performed using two systems level models: 

ß The linear analysis model 

ß The 6-degree of freedom (6-DOF) nonlinear simulation model. 

These systems level models were developed from multiple supporting models (Figure 6-7). 

Three of the supporting models (FAS, aerodynamics, mass properties) were determined to be 

contributors to the mishap.

Figure 6-7. Subsystem Models Comprising the System Level Models

Longitudinal Axis Autopilot

Lateral Directional Autopilot

Guidance

Mass Properties

Fin Actuation System

(FAS)

Environment

Aerodynamics

Propulsion

Plant Dynamics

Sensor (IMU)

Longitudinal Axis Autopilot

Lateral Directional Autopilot

Guidance

Mass Properties

Fin Actuation System

(FAS)

Environment

Aerodynamics

Propulsion

Plant Dynamics

Sensor (IMU)
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

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6.5 Mission Profile

Figure 6-8 shows the planned mission profile with flight events for the X-43A mission.

Figure 6-8. X-43A Mission Profile

6.6 Mission Operations

All flight operations in the Pacific Sea Range were conducted in accordance with U.S. Navy 

requirements per RCC319-92 and met DFRC/Air Force Flight Test Center Range Systems 

Safety Office requirements.

Drop

Hyper-X Free Flight
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

15

7 DESCRIPTION OF X-43A MISHAP

7.1 Captive Carry 

At 12:28 p.m. PDT on June 2, 2001, the X-43A stack (HXLV, HXRV and HXRV adapter) 

was attached to the DFRC B-52 (008) and carried to the Point Mugu sea range. The captive 

carry of the X-43A stack on the B-52 was nominal, with the exception of an alternator on the 

B-52 that failed prior to take-off. The two F-18 chase planes, 846 and 852, followed the B52, operating per standard procedures throughout the flight. Chase plane 846 provided live 

video, while chase plane 852 provided still photos. 

7.2 Release and Flight 

A detailed timeline is presented in Table 7-1. This table indicates the times that data for 

events were received on the ground. Critical event times that were used in the analysis 

(including time histories) of the mishap were adjusted for data latencies. The adjusted times 

are denoted with an asterisk (*). Also listed in the table are anomalies recorded during the 

investigation of the mishap. These anomalies are discussed in Volume I Appendix B.

The following paragraphs describe the events of the release and flight until the time of data 

loss. 

The X-43A stack was released from the B-52 one hour and fifteen minutes after takeoff. 

This corresponded to 0.0 seconds mission time. The HXLV autopilot was enabled at 0.38 

seconds. The HXLV solid rocket motor ignition occurred 5.19 seconds mission time. These 

events were nominal and occurred as planned. 

Between 6.23 seconds and 7.1 seconds, the HXRV adapter gaseous nitrogen (GN2) pyro 

valve opened. The regulator malfunctioned and uncontrolled GN2 venting began. This 

uncontrolled venting incident was recorded as an anomaly but determined to have no 

contribution to the mishap. At 10.18 seconds, the HXLV path steering guidance was 

engaged. During the pitch-up maneuver, at approximately 11.5 seconds, a divergent 

oscillation primarily in the roll axis was observed at a 2.5 Hz frequency. At 13.02 seconds, 

the rudder actuator reached its current limit of -36.7 amps and no longer responded to 

commands, indicating a rudder actuator stall. Shortly after the rudder actuator stalled, the 

starboard fin departed from the vehicle, quickly followed by the port fin, then the rudder and 

wing. 

The HXRV left wing linkage failed at 18.84 seconds. At 20.87 seconds, the HXLV 

telemetry stream was lost and one minute later the HXRV telemetry data was lost. At 48.57 

seconds, the flight termination system (FTS) was initiated. Flight termination was successful 

and the vehicle stayed within the Point Mugu range. 
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

16

Table 7-1. Detailed Timeline

Anomaly

No.

Mission Time:

Time from 

Separation 

(sec)

*Adjusted for 

Latencies

Event

Description

A-10 -1:57 B-52 loss of alternator (right forward)

-0.33 Pylon adapter pushrods begin to move

A-09 -0.25 Hook movement has released preload, stack load still present. 

~B-52 launch lock indication loss

-0.23 Stack begins to drop from B-52

0.00 Physical separation of umbilical connectors

0.03 B-52 release sense by the flight management unit 

0.16 HXLV flight computer separation sense

0.18* HXLV sequencer reset

0.34* Initialize HXLV autopilot filters (phase count=24)

0.38* Enable HXLV autopilot (phase count=25)

5.19 Motor ignition

A-06 5.22 HXLV motor start debris

A-07 5.24 Change in HXRV vertical/lateral accelerometer

A-04 6.23 HXRV adapter GN2 pyro valve opened (SV-19)

A-05 7.10 GN2 venting due to pressures exceeding relief valve setting

10.18* Enable HXLV path steering guidance (phase count=31)

11.50* Divergent roll oscillation begins

A-02 13.02* HXLV rudder actuator reaches current limit 

(-36.7 A)

A-01 13.30 Starboard fin shaft strain gauge goes to positive maximum value 

indicating broken gauge wiring

13.46 Starboard actuator motor temperature value goes to maximum, 

indicating broken gauge wiring

13.48 Starboard fin leading edge temperature value goes to maximum, 

indicating broken gauge wiring

13.62* Starboard actuator position value goes to zero, indicating broken 

actuator wiring

13.70 Port actuator motor temperature value goes to maximum, indicating 

broken gauge wiring

13.74* Rudder actuator begins to be back driven, as indicated in position and 

current monitor changes from stall

13.78* Port actuator position value goes to zero, indicating broken actuator 

wiring
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

17

Anomaly

No.

Mission Time:

Time from 

Separation 

(sec)

*Adjusted for 

Latencies

Event

Description

13.80 Port fin shaft strain gauge value goes to positive maximum, indicating 

broken gauge wiring

13.83 Rudder shaft left side strain gauge value goes to positive maximum, 

indicating broken gauge wiring

13.85 Rudder shaft right side strain gauge value goes to positive maximum, 

indicating broken gauge wiring

14.26 Rudder right side temperature value goes to maximum, indicating 

broken gauge wiring

15.00 Wing leading edge compression strain gauge value goes to maximum, 

indicating broken gauge wiring

15.65 LBIT1010 failure - PPT B3 power-up failure

15.65 LBIT1011 failure - PPT B4 power-up failure

17.57 LBIT1005 failure - PPT A3 power-up failure

18.84 HXRV left wing failure

20.87 Loss of HXLV data stream

45.37 HXRV adapter H2O pyro valve opened (SV-15)

48.57 FTS

49.31 HXRV separation from HXRV adapter

49.63 Aft S-band come on

58.85 LBIT 0101 failure - U-gyro reasonableness fail

75.17 LBIT 0107 failure - U-gyro dither gain fail

75.17 LBIT 0115 failure - U-gyro health status fail

77.57 Loss of HXRV data stream
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

18

7.3 Flight Data 

Figure 7-1 shows vehicle flight parameters [Mach, angle of attack (alpha), sideslip (beta) and 

dynamic pressure (q)] for the time period between 9 and 14 seconds. Also denoted on this 

figure are the key phenomena that triggered this mishap. The first phenomenon was the 

divergent roll oscillatory motion that started at approximately 11.5 seconds. The second 

phenomenon was the rudder actuator stall at approximately 13 seconds. Data shown in 

Figure 7-1 for Mach, angle of attack (alpha) and dynamic pressure (q) indicate that these 

parameters remained nominal until after the rudder actuator stalled at 13 seconds. Sideslip 

(beta) was within the expected range until 12.5 seconds but began a rapid divergence at 13 

seconds when rudder actuator stall occurred.

Vehicle Flight Parameters

1.1

0.7

0.8

0.9

1

Mach

12

14

16

alpha (deg)

-2

0

2

4

6

8

beta (deg)

9 9.5 10 10.5 11 11.5 12 12.5 13.0 13.5 14

300

400

500

600

700

q (psf)

time (sec) Rudder Actuator 

Stalls

Divergent Oscillation 

Begins

Vehicle Flight Parameters

1.1

0.7

0.8

0.9

1

Mach

12

14

16

alpha (deg)

-2

0

2

4

6

8

beta (deg)

9 9.5 10 10.5 11 11.5 12 12.5 13.0 13.5 14

300

400

500

600

700

q (psf)

time (sec) Rudder Actuator 

Stalls

Divergent Oscillation 

Begins

Figure 7-1. Vehicle Flight Parameters
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

19

Figure 7-2 shows the control surface positions (rudder and elevon) and vehicle roll rate for 

the time period between 9 and 14 seconds. The data for rudder deflection (rudder), and 

differential elevon deflection (elevon) and roll rate remained within the expected range until 

11.5 seconds when the divergent oscillation began. At that point, rudder deflection, 

differential elevon deflection and roll rate began an oscillatory increase at 2.5 Hz. At 

approximately 13 seconds, rudder actuator stall occurred and differential elevon and roll rate 

increased dramatically. At approximately 13.5 seconds the starboard elevon departed from 

the vehicle.

Control Surface Positions and Roll Rate

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14

-5

0

5

10

Rudder (deg)

9 9.5 10 10.5 11 11.5 12 12.5 13.5 14

-10

-5

0

5

10

Aileron (deg)

9 9.5 10 10.5 11 11.5 12 12.5 13.0 13.5 14

-20

0

20

40

time (sec)

Roll Rate (deg/s)

Divergent Oscillation

Begins

Rudder Actuator

Stalls

13

Elevon

Control Surface Positions and Roll Rate

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14

-5

0

5

10

Rudder (deg)

9 9.5 10 10.5 11 11.5 12 12.5 13.5 14

-10

-5

0

5

10

Aileron (deg)

9 9.5 10 10.5 11 11.5 12 12.5 13.0 13.5 14

-20

0

20

40

time (sec)

Roll Rate (deg/s)

Divergent Oscillation

Begins

Rudder Actuator

Stalls

13

Elevon

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14

-5

0

5

10

Rudder (deg)

9 9.5 10 10.5 11 11.5 12 12.5 13.5 14

-10

-5

0

5

10

Aileron (deg)

9 9.5 10 10.5 11 11.5 12 12.5 13.0 13.5 14

-20

0

20

40

time (sec)

Roll Rate (deg/s)

Divergent Oscillation

Begins

Rudder Actuator

Stalls

13

Elevon

Figure 7-2. Control Surface Positions and Roll Rate
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

20

8 METHOD OF INVESTIGATION, BOARD 

ORGANIZATION, SPECIAL CIRCUMSTANCES

The Associate Administrator for Aerospace Technology formally appointed the X-43A 

Mishap Investigation Board which assumed responsibility for the investigation on June 5, 

2001. The basic guidance used in implementing and executing the X-43A mishap 

investigation was per NPG: 8621.1, NASA Procedures and Guidelines for Mishap Reporting, 

Investigating, and Record Keeping, dated June 2, 2000. The investigation implementation 

was adjusted as required to reflect the situations and conditions specific to the MIB. The 

intent of NPG 8621.1 was met.

A special circumstance associated with the X-43A mishap investigation was:

ß The X-43A mishap resulted in the physical evidence from the flight vehicle being 

dropped into the Pacific Ocean in approximately 1,200 feet of water. No attempt was 

made to recover physical evidence from the flight hardware. 

The initial MIB meetings were conducted at the DFRC from June 5, 2001 through June 23, 

2001. Data reviews were held daily as the flight data was processed and interpreted. The 

MIB relocated to Orbital Sciences Corporation in Chandler, Arizona from June 23, 2001 

through August 31, 2001 to focus on the HXLV failure scenarios of the investigation. The 

MIB relocated to the LaRC from September 10, 2001 through December 7, 2001 to support 

wind tunnel testing. The final efforts of the investigation were completed through 

teleconferences and electronic communications. The verbal report for the X-43A mishap 

was presented to the Associate Administrator for Aerospace Technology on February 7, 2002 

and the Report of Findings was submitted to NASA Headquarters for approval in March, 

2002.

8.1 Methodology

A fault tree-based investigation methodology was chosen for the X-43A mishap. The basis 

for this choice was the complexity of the X-43A physical and functional systems, the multiorganizational character of the X-43A team, the availability of fault trees used in risk 

assessments by the X-43A Project and the familiarity of the MIB with the fault tree 

investigation process. 
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

21

8.2 Process

The MIB followed a rigorous process during investigation of the X-43A mishap (Figure 8-1). 

* Corrective Actions are to be developed by the Project

Figure 8-1. X-43A Mishap Investigation Board Process

8.3 Board Organization

The MIB consisted of those individuals formally appointed by the Associate Administrator, 

expert consultants and administrative support personnel. The MIB was organized to permit 

the MIB members to support the fault tree based investigation in their specific areas of 

expertise. Technical teams were formed to support the MIB in the investigation. These 

technical teams were formed in conjunction with the existing integrated product teams (IPTs) 

of the X-43A Project and were supplemented by independent experts from NASA Centers 

and contractor organizations. The MIB and the technical teams collectively formed the MIT.

Secure Premises/Data

Obtain Witness Statements

Establish Team

Obtain X-43A 

Familiarization Overview / 

Inspections / Tours

X-43A Mission

HXRV Vehicle

HX Adapter

HXLV

B-52

Facilities

Operations 

Data / Data Sources

Coordinate Facilities and 

Support

General Data

Gathering/ Fact Finding

Determine Root Cause / 

Contributing Cause

Develop Failure Scenarios

Develop Corrective 

Actions

Determine Technical Cause

Develop Fault Trees

Develop Detailed Data / 

Timeline / Understanding 

of Conditions (FACTS) 

Refine and Analyze Data 

Develop Lessons Learned

Add New Fault Trees / 

Close Inapplicable Fault 

Trees /Establish Anomalies

X-43A Mishap

Refine Failure Scenarios

Perform needed analyses / 

testing / evaluations

Publish Report

Develop Fault / Anomaly 

Closure Action Plans

*
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

22

8.4 Board Operation

The general operation of the MIB encompassed three basic responsibilities: Overall planning 

and management, technical investigation and presentation and report formulation. 

The overall planning and management was the exclusive function of the MIB. This function 

was implemented through daily MIB sessions where the investigation process, planning, 

scheduling and execution strategy were decided. 

The management of the technical investigation was accomplished through daily team 

meetings with the MIT where status reports of the ongoing activities were provided. 

Presentations that included supporting analyses and data were provided to assess fault tree 

scenarios. In addition, the MIB held periodic data reviews, which summarized the multidisciplined fault tree analyses, performed to support possible failure scenarios. 

Monthly status reports were provided throughout the investigation. Presentation and report 

formulation included the interim report to management, a formal presentation and the final 

report of findings. 

8.5 Implementation

The implementation of the fault tree investigation involved the identification of potential 

mishap faults or causes. Initially, this was done at a high level based on assessments of the 

physical, functional, engineering, and operational characteristics of the X-43A program in 

relation to the data from the mishap. This effort involved the MIB and the MIT leads. When 

high level faults were deemed credible, lower level or subtier faults that might have 

precipitated the higher level fault were developed. These lower level faults were developed 

using potential scenarios for the specific high level fault. No fault was added or removed 

from the fault tree without MIB review and approval. 

Technical evaluation of each lower level fault constituted the building blocks of the 

investigation and yielded the information that, when assessed in a total systems environment, 

permitted understanding of the mishap. 

The result of each lower level fault evaluation was a determination of the potential for the 

individual fault to have contributed to the final mishap. A color-code was assigned to each 

fault based on the potential of that fault to have contributed to the final mishap. The key to 

the color-code is as follows:

ß Green (G) - A confirmed non-contributor

ß Yellow (Y) - A potential contributor that cannot be assigned a confirmed quantifiable 

contribution

ß Red (R) - A contributor with a confirmed quantifiable contribution

The top level fault tree developed for the X-43A mishap is shown in Figure 8-2. A total of 

613 faults were evaluated. Of these, eleven were determined to be direct contributors to the 

mishap and three were determined to be potential contributors. The entire fault tree used in 

this investigation is shown in Volume II Appendix A. 
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

23

Figure 8-2. Top Level Fault Tree 

The critical branch of the fault tree is shown in Figure 8-3. 

Figure 8-3. Critical Fault Tree Branch

Top

Hyper-X

Mishap

1.0

Loss of B-52

Flight Safety

2.0 3.0 5.0 6.0 7.0

Loss of X-43

Stack

Failure to

Drop / Ignite

Fail to Reach

Desired

Separation Point

Unsuccessful

HXLV / HXRV

Separation

Unsuccessful

Free Flight

Ground Ops

Stack 

Damage

4.1.3

Aerodynamic

/Control Motor

4.1.4

Avionics

4.1.5

Structures

4.1.2

External

Disturbances

4.1.1

4.1

Loss of

Control Structural

4.2

FTS

Initiation

4.3

Fire/

Explosion

4.4

Collision

with

Air Vehicle

4.5

Loss of

HXLV

Data

4.6

4.0

(G) (G) (G) (R) (G) (G) (G)

(R) (G) (G) (G) (G) (G)

(G) (G) (R) (G) (G)

(R)

confirmed non-contributor

potential contributor to the mishap that cannot be assigned a confirmed quantifiable contribution

contributor to the mishap with a confirmed quantifiable contribution

(G)

(Y)

(R)

Top

Hyper-X

Mishap

1.0

Loss of B-52

Flight Safety

2.0 3.0 5.0 6.0 7.0

Loss of X-43

Stack

Failure to

Drop / Ignite

Fail to Reach

Desired

Separation Point

Unsuccessful

HXLV / HXRV

Separation

Unsuccessful

Free Flight

Ground Ops

Stack 

Damage

4.1.3

Aerodynamic

/Control Motor

4.1.4

Avionics

4.1.5

Structures

4.1.2

External

Disturbances

4.1.1

4.1

Loss of

Control Structural

4.2

FTS

Initiation

4.3

Fire/

Explosion

4.4

Collision

with

Air Vehicle

4.5

Loss of

HXLV

Data

4.6

4.0

(G) (G) (G) (R) (G) (G) (G)

(R) (G) (G) (G) (G) (G)

(G) (G) (R) (G) (G)

(R)

Top

Hyper-X

Mishap

1.0

Loss of B-52

Flight Safety

2.0 3.0 5.0 6.0 7.0

Loss of X-43

Stack

Failure to

Drop / Ignite

Fail to Reach

Desired

Separation Point

Unsuccessful

HXLV / HXRV

Separation

Unsuccessful

Free Flight

Ground Ops

Stack 

Damage

4.1.3

Aerodynamic

/Control Motor

4.1.4

Avionics

4.1.5

Structures

4.1.2

External

Disturbances

4.1.1

4.1

Loss of

Control Structural

4.2

FTS

Initiation

4.3

Fire/

Explosion

4.4

Collision

with

Air Vehicle

4.5

Loss of

HXLV

Data

4.6

4.0

(G) (G) (G) (R) (G) (G) (G)

(R) (G) (G) (G) (G) (G)

(G) (G) (R) (G) (G)

(R)

confirmed non-contributor

potential contributor to the mishap that cannot be assigned a confirmed quantifiable contribution

contributor to the mishap with a confirmed quantifiable contribution

(G)

(Y)

(R)

confirmed non-contributor

potential contributor to the mishap that cannot be assigned a confirmed quantifiable contribution

contributor to the mishap with a confirmed quantifiable contribution

(G)

(Y)

(R)

4.1.3

Aerodynamic

/Control

4.1.3.1

Autopilot

Design

4.1.3.2

Autopilot

Implementation

4.1.3.3

Structural

Dynamics

Modeling

4.1.3.4

Mass

Properties

Modeling

4.1.3.5

Aerodynamic

Modeling

4.1.3.6

Vehicle

Configuration

4.1.3.7

Fin Actuation

System

4.1.3.8

Aeroelastic

Effects

(G) (G) (G) (R) (R) (R) (R) (Y)

(R)

confirmed non-contributor

potential contributor to the mishap that cannot be assigned a confirmed quantifiable contribution

contributor to the mishap with a confirmed quantifiable contribution

(G)

(Y)

(R)

4.1.3

Aerodynamic

/Control

4.1.3.1

Autopilot

Design

4.1.3.2

Autopilot

Implementation

4.1.3.3

Structural

Dynamics

Modeling

4.1.3.4

Mass

Properties

Modeling

4.1.3.5

Aerodynamic

Modeling

4.1.3.6

Vehicle

Configuration

4.1.3.7

Fin Actuation

System

4.1.3.8

Aeroelastic

Effects

(G) (G) (G) (R) (R) (R) (R) (Y)

(R)

4.1.3

Aerodynamic

/Control

4.1.3.1

Autopilot

Design

4.1.3.2

Autopilot

Implementation

4.1.3.3

Structural

Dynamics

Modeling

4.1.3.4

Mass

Properties

Modeling

4.1.3.5

Aerodynamic

Modeling

4.1.3.6

Vehicle

Configuration

4.1.3.7

Fin Actuation

System

4.1.3.8

Aeroelastic

Effects

(G) (G) (G) (R) (R) (R) (R) (Y)

(R)

confirmed non-contributor

potential contributor to the mishap that cannot be assigned a confirmed quantifiable contribution

contributor to the mishap with a confirmed quantifiable contribution

(G)

(Y)

(R)

confirmed non-contributor

potential contributor to the mishap that cannot be assigned a confirmed quantifiable contribution

contributor to the mishap with a confirmed quantifiable contribution

(G)

(Y)

(R)
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

24

8.6 Data Sources

Data used by the MIB was taken from monitoring sources on board the B-52 carrier aircraft; 

sites receiving flight downlink from the X-43A stack; data developed during the preflight 

manufacture, test and checkout of the X-43A stack; postflight testing of X-43A stack 

software and hardware; postflight evaluation of the FAS/Fin (elevon(s) and/or rudder) 

system; postflight aerodynamics testing of the X-43A stack; postflight evaluation of X-43A 

analytical models, systems, subsystems and processes; and special analyses performed in 

support of the investigation. 

8.7 Other Data Sources

The MIB used other sources to improve their understanding of the X-43A mishap.

These other sources included applicable failure reports and anomaly reports from previous 

Pegasus missions. The WIRE mission flown from Vandenburg Air Force Base on March 4, 

1999 was used as a benchmark. During the transonic flight regime (approximately 6-12 

seconds after release from the carrier aircraft, Mach 0.9-1.2, approximately 40,000 feet) a 

significant attitude disturbance was observed in which the vehicle experienced large sideslip 

and bank excursions. The excursions began in roll, and then quickly coupled into yaw and 

finally pitch. As the vehicle left the transonic region it recovered from the disturbance and 

the WIRE mission successfully achieved the proper orbit. Following this anomaly, changes 

to the autopilot, improvements in aerodynamic modeling and upgrades to fin actuation 

system modeling were implemented. The significantly higher launch altitude and reduced 

dynamic pressure was a key difference between all other Pegasus flights and the X-43A 

trajectory.

Subsequent Pegasus missions with these modifications were successful. 

As a part of this investigation, failures of vehicles related to the X-43A (Pegasus and Taurus) 

were evaluated for applicability to the mishap.
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

25

9 FINDING, ROOT CAUSE, CONTRIBUTING FACTORS, 

RECOMMENDATIONS - EXPORT CONTROLLED
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

45

10 SIGNIFICANT OBSERVATIONS, ANOMALIES, 

RECOMMENDATIONS - EXPORT CONTROLLED
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

62

11 DEFINITION OF TERMS AND ACRONYMS

6-DOF 6 Degree of Freedom

A, Amps. Amperes

AIT Aircraft Integration Trailer

Alpha, α Angle of Attack

ATP Acceptance Test Procedure

Backlash Total rotational and radial motion (stop-to-stop) that occurs in the 

output gear of the FAS gear train when the input gear is held fixed

BET Best Estimated Trajectory

Beta, β Angle of Sideslip

B/AM Ballast/Avionics Module

CAD Computer Aided Design

CFD Computational Fluid Dynamics

CG Center of Gravity

Chm Hinge moment coefficient

Clda, Clδa Rolling moment coefficient due to aileron (differential elevon) 

deflection

Clp Rolling moment coefficient due to roll rate (roll damping derivative)

Clr Rolling moment coefficient due to yaw rate

CM Configuration Management

Cnp Yawing moment coefficient due to roll rate

Cnr Yawing moment coefficient due to yaw rate (yaw damping 

derivative)

CPU Central Processing Unit

δelv Elevon deflection

δr Rudder deflection

dB Decibels

Deg Degrees

DFRC Dryden Flight Research Center

DR Discrepancy Report

ECU Electronic Control Unit

ELV Expendable launch vehicle 

EMA Electromechanical Actuator

ERB Engineering Review Board

EXP Experiment

FAS Fin Actuation System

FEM Finite Element Model

Fin Elevon(s) and/or rudder

FTS Flight Termination System

G Green – Non-contributor to the mishap

GN2 Gaseous Nitrogen

GN&C Guidance, Navigation, and Control
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

63

GSFC Goddard Space Flight Center

GVT Ground Vibration Test

H2O Water

HQ NASA Headquarters

HXLV Hyper-X Launch Vehicle

HXRV Hyper-X Research Vehicle

Hz Hertz

IMU Inertial Measurement Unit

INS Inertial Navigation System

IPT Integrated Product Team

KSC Kennedy Space Center

LaRC Langely Research Center

LBIT Latched Built-in-Test

LFRC Load Friction 

LOS Loss of Signal

M Mach

MassProp Mass Properties

MDL Mission Data Load

MIB Mishap Investigation Board

MIT Mishap Investigation Team

MOI Moment of Inertia

MSFC Marshall Space Flight Center

MST Mission Sequence Time

NASA National Aeronautics and Space Administration

NPG NASA Procedures and Guidelines 

NRTSim Non-Real-Time Simulation

OD Outer Diameter

PID Parameter Identification

PPT Precision Pressure Transducer

PR Pressure Regulator

PSS Premature Separation Sense

PWM Pulse Width Modulation

q Dynamic Pressure

QA Quality Assurance

R Red – Contributor to the mishap

RCC Range Commanders’ Council

RTCL Real Time Closed Loop

RTS Ready-To-Separate

RV Relief Valve

Sigma, σ Sigma (Standard Deviation)

SNI San Nicolas Island

SPR Software Problem Report

SRS Software Requirements Specification

SV Servo Valve

SWAS Sub-millimeter Wave Astronomy Satellite

TM Technical Memorandum
X-43A Mishap Investigation Board Approved 5/8/03

Submittal Draft 3/8/02 Accepted Draft 9/6/02

64

TO Technical Order

TPS Thermal Protection System

VDD Version Description Document

WIRE Wide-Field Infrared Explorer

Y Yellow – Potential Contributor to the mishap