Presently, the evaluation of the health of space propulsion systems includes obtaining and analyzing limited flight data and extensive post flight performance, operational and inspection data. This approach is not practical for deep-space missions due to longer operational times, lack of in-space inspection facility, absence of timely ground commands and very long repair intervals. This paper identifies the on-board health- management/inspection needs of deep-space propulsion and thermodynamic power-conversion systems. It also describes technologies that could provide on-board inspection and more comprehensive health management for more successful missions

Barkhoudarian, Sarkis

NASA Technical Reports Server

Real-Time On-Board HMSDnspection Capability 
For Propulsion and Power Systems 
Sarlus Barkhoudarian 
Rocketdyne Propulsion and Power Division, Canoga Park, California 91 309 
Presently, the evaluation of the health of space propulsion systems includes obtaining and 
analyzing limited flight data and extensive post flight performance, operational and 
inspection data. This approach is not practical for deep-space missions due to longer 
operational times, lack of in-space inspection facility, absence of timely ground commands 
and very long repair intervals. This paper identifies the on-board health- 
management/inspection needs of deep-space propulsion and thermodynamic power- 
conversion systems. It also describes technologies that could provide on-board inspection 
and more comprehensive health management for more successful missions. 
I. Introduction 
A. Current Health Management Approach 
Current space-propulsion system on-board Health Management Systems (HMS) provides partial data about 
the health of liquid-propellant propulsion systems in real time. This data is telemetered to earth for real-time review 
and immediate shutdown commands during approximately 500 seconds of engine operation. Additional HMS data is 
obtained after the return to earth. In addition, extensive post-flight manual inspections are performed, requiring 
removal of engines from the vehicle and disassembly of the engines. These inspections require complex tools and 
elaborate disassembly and reassembly, followed by leak tests, binding-torque measurements, etc. They check the 
internal erosion, corrosion, chipping, rotary system rubbing and radiallaxial plays, etc. Present space-propulsion 
engines need ground commands for safer operation during the launch. Current on-board controllers use two control 
variables in real time and shut the engine down when a predetermined parameter, e.g. temperature, pressure or RPM, 
exceeds its threshold level. They typically can not respond to multiple failures. As can be seen, current 
controllerIHMSlinspection cannot meet the requirements of deep-space propulsion or thermodynamic power- 
conversion systems. 
B. Modern HMSlInspection Needs 
The HMS for deep-space propulsion and power-conversion systems will require very intelligent and 
autonomous engine controllers that function for a much longer operational time, while performing real-time 
automated inspection and fault mitigation. They must provide early life assessment, and diagnostic and prognostic 
information, based upon the engine performance and hardware degradation in real time. They will need adaptive 
control capability to optimize performance and mitigate operational anomalies and hardware degradation. The 
failure symptoms must be detected when the failure is in very early stages of development. This will require novel 
sensor technologies capable of rapidly providing increased awareness of the entire propulsion and power-conversion 
system health. It will also require advanced algorithms that can be used to detect the symptoms, predict 
consequence of the failure, and mitigate faults in real time. Ideally, modem HMS will require an active health- 
control manager that can in real time provide automated diagnostics, prognostics, optimiziation, and repair. 
Furthermore, it will require collection of real-time data that should be processed dynamically, resulting in more 
rapid identification of off-normal conditions and enabling reliable corrective actions to ensure mission success and 
safety. It will also require on-board plant archived data to better diagnose problems before they become critical. 
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https://ntrs.nasa.gov/search.jsp?R=20050207551 2019-08-29T20:47:55+00:00Z
11. Solution 
Comprehensive fault-detecting and fault-mitigating propulsion and power-conversion systems are needed. 
Ideally, all hardware degradation types must be identified, monitored and mitigated. They include fatigue, wear, 
erosion, corrosion, leakage, rotary component run-outs, rubbing, fluid and dynamic instabilities, etc. In addition, 
multidimensional mapping of exterior surface anomalies such as strain, vibration, and temperature are needed to 
provide comprehensive knowledge of the health of the hardware, rather than just single-point information. 
Advanced sensors are needed capable of monitoring these degradations and provide multidimensional 
measurements. Advanced algorithms are needed to process and fuse the data; diagnose, prognose and mitigate the 
failures; and prevent catastrophes. Such advanced integrated HMS/control systems provide additional tiers of health 
assessment far beyond the present shut-down or throttle-down systems. 
111. Approach 
New sensors are being developed for rocket engines to enable automated health assessment and 
management instead of traditional manual inspections. In addition, intelligent engine algorithms are being 
developed. These technologies must be developed to an acceptable level of readiness. Through the use of advanced 
sensors and algorithms, the life of critical hardware could be measured and significantly prolonged and mission 
success improved, while reducing the maintenance/inspection cost. Examples of these advanced technologies are 
described below. 
IV. Advanced Technology Description 
A. Measurement Technologies 
Advanced measurement technologies must be, as much as possible, nonintrusive, remote, multifunctional 
and multidimensional to minimize interference with the operation of the propulsion and power-conversion systems. 
These features will increase the reliability of sensors and allow comprehensive assessment of the health of the entire 
system. Furthermore, direct-monitoring, rather than inferred, must be used as much as possible. They monitor the 
phenomenon directly and reduce false alarms due to inaccurate inference. They will provide more robust 
HMMnspection systems, capable of handling even multiple-failure anomalies. 
Multiparametric sensors provide information of more than one parameter, using only one sensor and cable. 
They provide more intelligent and robust measurement systems, while saving cable weight and hardware 
complexity. Multidimensional sensors provide 2-D or 3-D information of the plant exterior. They, similarly 
eliminate the need of numerous single-point sensors and their cables. They provide more information with less 
hardware. 
Non-intrusive sensors are beneficial for monitoring the internal component structural and operational 
parameters. They do not require holes through the housing. This eliminates parasitic pressure drops, the potential for 
sensor port leaks and catastrophic sensor fractures. Nonintrusive sensors improve the safety and performance of 
propulsion and power-conversion systems. The nonintrusive sensors eliminate the need of leak and FOD 
inspections of sensor ports, which enhances the operability and reduces the maintenance of the system. 
1.  Nonintrusive Magnetic Sensors 
conductive blade is passing in front of them, as shown in Fig 1. 
Nonintrusive variable-reluctance magnetic sensors generate an electric signal when an electrically 
Figure 1. Unamplified signal from Delta I1 engine turbine. 
3/21/2005 2 
. .  
I '  .. . 
%-inch diameter 
Blade vibration also generates a signal but at much higher frequency. 
Robust, high- temperature, high-frequency, high-sensitivity and miniature 
sensors have been developed at Rocketdyne. Figure 2 shows a %-inch 
diameter, 400-F, 1 00-KHz all-metal housing Rocketdyne-developed variable- 
reluctance sensor. 
Figure 2. Rocketdyne developed 
1/4-inch diameter sensor. 
This technology provides direct blade-by-blade resonance data, 
allowing the user to isolate the fault to an individual blade. This type of 
sensors were used to obtain blade-tip resonance amplitude and frequency 
data at Rocketdyne Whirligig Facility, as shown in Figure 3, without 
contacting the blades. The blisk, consisting of the disc and blades, is shown 
in Figure 4. 
Figure 3. 50-KRF'M whirligig. 
Figure 4. Test blisk with three sensors. 
The data was compared with the measurement of individual blade strain, using epoxied intrusive strain 
gauges and fiagile rotary slip rings. The results were almost identical. Both techniques indicated approximately 300 
microstrains in a blade in the same revolutions per minute (RPM) range. See Figure 5.  
Blade 4 u.4 pJe 4 
Mil 0.2 deflection 
O 
w 
Blade 4 
strain 
4m 
,"m 
Microstrain f m  
rm 
0 
Turbine Figure 5. Individual Blade Stress and Deflection. 
This capability allows calculation of fatigue life by combining the resonant frequency, amplitude and 
duration data. In addition, it has experimentally been demonstrated that seeded flaws in blades cause changes in the 
frequency and amplitude of resonance. This information could also be used for life determination, prediction and 
confirmation. The same sensor could also be used for RPM and blade-gap measurements, providing multifunctional 
data. Furthermore, additional variable-reluctance magnetic sensors can also measure radial and axial turbopump 
runouts, torque and horsepower. They could eliminate the need of intrusive inspection of the turbine/pump 
bladeshmpellers. 
2. Multidimensional Remote Sensors 
Remote sensors could be used to provide 3-D information of the exterior of propulsion and power- 
conversion systems. Today, only single-point measurements are obtained. The remote sensors eliminate parasitic 
pressure drops, the potential for sensor port leaks and catastrophic fractures; thus, improving the safety and 
performance of the propulsion and power-conversion systems. 
3/2 1/2005 3 
An example of such a technology is fiberoptic (FO) 
spectrometry. It provides an overall health assessment means of the 
internal components. Commercial off-the-shelf (COTS) fiberoptic 
spectrometers, as shown in Fig 6, contain a diffraction grating and 
4096-diode linear-array photodetector. The grating diffracts the light 
transmitted by FO cable to different colors at different angles. The 
photodetector array, placed in front of the difGacted light, measures the 
amplitude of each color simultaneously. An electronic multiplexer 
provides consecutive electrical spectra in only five milliseconds, 
covering 300 to 800 nanometers. The spectral wavelengths are an 
indication of the combusting element types and the intensity of each 
wavelength is a measure of the amount of that element. 
~i~~~~ 6. Fiberoptic spectrometer. 
A spectrometric system was developed at Rocketdyne using a robust probe, 
shown in Fig 7, 1004 long FO cable, shown in Fig 8, and ruggedized COTS FO 
spectrometers. The spectrometer probe, located at the bottom lip of Space Shuttle 
Main Engine (SSME) nozzle is oriented in a direction that detects plume optical 
intensity above the shock diamond, eliminating shock-diamond mechanical tracking 
complexities. 
Figure 7. Rocketdyne-developed fiberoptic 
spectrometer probe. 
Figure 8. Fiberoptic cable routing on 
Space Shuttle Main Engine. 
These systems detected simultaneously Ni, Cr, and Fe elements from Inconel-powder-containing uralite 
paste, applied to the inner wall of the SSME nozzle, almost instantaneously. Fig 9 shows the spectra of a seeded and 
unseeded SSME plume. 
f AIO%6Ol.hot 352-0783 3520783 -4- A1096301.hol 352-0783 352.0783 
-*%- A1096601.hot 357-0806 357.0806 */ A1096301.hol 357-0806 357.0806 
8 A1096601.hd 372-0917 372.0917 5- A1096301.hol 372-0917 372.0917 .I 
13wO- 
1 2 5 70W ~ 4 
Seconds from STMT 
Figure 9. Seeded and unseeded SSME plume spectra. 
3/2 1/2005 4 
3. Other Multidimensional Remote Sensors 
Rocketdyne has also developed remote external-leak imaging techniques, optically monitoring the leak 
using special cameras. Leaks as small as a fkaction of a standard cubic inch of H2, N2, 02 ,  H20, and C02 have 
already been mapped in 2-D, in a laboratory environment. These leaks could simultaneously be imaged, using only 
one camera. 
B. Algorithms 
There are many powerful algorithms that can be useful for better control, health-monitoring and real-time 
inspection of deep-space propulsion and power-conversion systems. They could provide information for reliable 
long-duration missions. They include multivariable, adaptive, ac-component-based derivative, data-fusion 
algorithms, etc. 
An application of adaptive-control algorithms could be the 
detection of resonant blade anomalies. If a blade resonates violently at 
a given RPM, the rotary speed can be changed to detune that blade 
resonance. This may cause resonance of another blade that hopefully 
has not operated in resonant mode extensively. This self-repairing 
approach increases the over-all life of the blisk, allowing successful 
completion of long-duration missions. In the tests conducted at 
Rocketdyne Whirligig Facility, at least 8 times higher deflection 
amplitude was observed at resonant fiequency. Fig 10 shows blade #13 
deflecting up to 0.4 mils at approximately 21,540 WM, whereas at 
only 30 RPM higher or 20 RPM lower operation, the deflection is 
almost zero. 
I 
0.2 
0 
21.4 21.45 21 6 
- - ~  
Figure 10. Resonance amplitude variation at 
different RF'M. 
It might also be needed to constantly dither the RPM. This type of algorithm could, for example, reduce the 
dwell time of each blade in its resonant fiequency and extend the life of the blisk. 
V. Conclusion 
Advanced measurement, algorithm and control technologies are needed for safer deep-space on-board 
propulsion and power-conversion HMShnspection systems. Comprehensive autonomous HMS/inspection systems 
are needed to reduce the life cycle cost of propulsion and power conversion systems. Presently, these technologies 
are not at Technology Readiness Level ( T U )  six. Measures must be taken soon to develop these technologies for 
long-duration space-exploration missions. These technologies require extensive testing to generate confidence in the 
designers to incorporate them in deep-space propulsion and power-conversion systems. 
New nonintrusive, multidimensional, direct, multifunctional and robust sensors are needed for these 
systems. Furthermore, novel technologies such as nanosensors, lasers, microprocessors, ultrasonics, optical, 
electromagnetic, etc, should also be thoroughly evaluated and promising ones developed immediately to a TRL of 
six before the design of the hardware starts. These measurement technologies should collectively be able to monitor 
all potential failure modes of propulsion and power-conversion systems with very high sensitivity and speed to 
allow early detection and timely fault mitigation for these demanding missions. 
Advanced multivariable, data-fusion, dithering and adaptive control/HMS algorithms must also be tested 
extensively under adverse extreme cases in simulation laboratories. By injecting faults and improving the validity of 
the response, the confidence in their stability and utility will increase. This type of control system has never been 
used in aerospace applications. 
3/2 1/2005 
VII. Acknowledgments 
5 
, 
The author would like to thank Jerry Jackson for supporting the development of these technologies and Mr. Raffi 
Ohanians and Kelly Stallmo for their assistance in preparing this paper. 
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Ezell, W., S. Barkhoudarian, and G. Gross, “Health monitoring of reusable rocket engines,” SAE, Aerospace 
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Delcher, R., A. Dergevorkian, and S. Barkhoudarian, “Fiberoptics for liquid propellant rocket engine environments,” 
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based reusable rocket engines,” AIAA-88-3 1 13, AIAAIASMEISAEIASEE Joint Propulsion Conference, Boston, 
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Randall, M. R., S. Barkhoudarian, J. J. Collins, and A. Schwartzbart, “Noncontacting measurement technologies for 
space propulsion condition monitoring,” Joint Army-Navy-NASA-Air Force Interagency Propulsion Committee, 
Propulsion Meeting, San Diego, California, December 15-1 7, 1987. 
Maram, J., and S. Barkhoudarian, “Progress toward an advanced condition monitoring system for reusable rocket 
engines,” Joint Army-Navy-NASA-Air Force Interagency Propulsion Committee, Propulsion Meeting, San Diego, 
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Alabama, 1986. 
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Winter Annual Meeting, New Orleans, Louisiana, December, 1984. 
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Real-Time On-Board HMS/Inspection Capability for Propulsion and Power Systems

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