NASA/TM_2001-210879

High-Speed Observer: Allt:omated Streak

Detection for the Aerospi_:e Engine

T.J. Rieckhoff

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

M.A. Covan and J.M. O'Farrell

United Space Alliance, Huntsville, Alabama

June 2001
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NASA/TM--2001-210879

High-Speed Observer: Automated Streak

Detection for the Aerospike Engine

T.J. Rieckhoff

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

M.A. Covan and J.M. O'Farrell

United Space Alliance, Huntsville, Alabama

National Aeronautics and

Space Administration

Marshall Space Flight Center ,, MSFC, Alabama 35812

June 2001
Acknowledgments

The authors would like to acknowledge the assistance of Phil Best and John Suter at Marshall Space Flight Center "c,r their

support and funding of development of the High-Speed Observer (HSO) program with the aerospike engine and r,,!:chael

Ladner and Brian Sproles at Stennis Space Center for their continued support of the HSO program. We wish to lh,_.nk

William Doss and Kay Glover, editors, and Janine Roskowski, illustrator, Marshall Space Flight Center,

Scientific and Technical Publication, for their insightfid comments and expert help in preparation of this document.

TRADEMARKS

Trade names and trademarks are used in this report for identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National Aeronautics and Space Administration.

Available from:

NASA Center fi)r AeroSpace Information

7121 Standard Drive

Hanover, MD 21076-1320

(301) 621-0390

National Technical Inlbrmation Service

5285 Port Royal Road

Springfield, VA 22161

(703) 487-4650
TABLE OF CONTENTS

1. INTRODUCTION ............................................................................................................................. !

2. HIGH-SPEED OBSERVER SYSTEM ............................................................................................. 2

2.1 High-Speed Observer Hardware Upgrades ............................................................................... 3

2.2 High-Speed Observer Software and Evaluation Model Modifications ..................................... 4

3. AEROSPIKE STREAK DETECTION ALGORITHM .................................................................... 5

4. AEROSPIKE ENGINE RAMP CHARACTERISTICS ................................................................... 9

5. CATEGORIES OF HIGH-SPEED OBSERVER OBSERVED

AEROSPIKE ENGINE EVENTS ..................................................................................................... 10

6. CHARGE-COUPLED DEVICE BLOOM MITIGATION ............................................................... 12

7. RESULTS .......................................................................................................................................... 14

A1X019 ................................................................................................................ 14

A 1X020 ................................................................................................................ 14

AIX021 ................................................................................................................ 14

A 1X022 ................................................................................................................ 14

A 1X023 ................................................................................................................ 15

A 1X024 ................................................................................................................ 17

A 1X025 ................................................................................................................ i 7

A 1X026 ................................................................................................................ 17

A 1X027 ................................................................................................................ 17

A 1X028 ................................................................................................................ 17

A 1X029 ................................................................................................................ 18

A 1X030 ................................................................................................................ 18

AIX031 ................................................................................................................ 18

7.1 Engine Test

7.2 Engine Test

7.3 Engine Test

7.4 Engine Test

7.5 Engine Test

7.6 Engine Test

7.7 Engine Test

7.8 Engine Test

7.9 Engine Test

7. !0 Engine Test

7.11 Engine Test

7.12 Engine Test

7.13 Engine Test

8. DISCUSSION ................................................................................................................................... 20

BIBLIOGRAPHY ................................................................................................................................. 21

,°.

111
LIST OF FIGURES

,

a..,

,

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

HSO camera and aerospike engine at SSC .......................................................................... 2

HSO hardware configurations ............................................................................................. 3

Control value intensity determination for an image frame .................................................. 6

Candidate streak selection ................................................................................................... 6

Streak growing algorithm .................................................................................................... 7

Streak confirmation ............................................................................................................. 8

Aerospike ramp temperature-dependent lines and streak growth ........................................ 9

Categories of HSO observed events .................................................................................... 11

Growth of bloom during test A 1X026 ................................................................................. 12

Growth of bloom during test A 1X027 ................................................................................. 13

Growth of bloom during test A I X030 ................................................................................. 13

Streak detection: test AIX023/frame 3021 .......................................................................... 15

Intensity values used to determine a streak ......................................................................... 16

Power level and mixture ratio changes ................................................................................ 19

Plume streaks ....................................................................................................................... 19

Glowing area on ramp and flex seal material ...................................................................... ! 9

LIST OF TABLES

Streaks detected in test A 1X023 .......................................................................................... 15

iv
LIST OF ACRONYMS

CCD

fps

FS

GB

HSO

I/O

IRIG

LH.,

lox

MB

MSFC

RAID

SSC

SSME

charge-coupled device

flames per second

fuel side thruster

gigabyte

High-Speed Observer

input/output

interrange instrumentation group

liquid hydrogen

liquid oxygen

megabyte

Marshall Space Flight Center

redundant array of inexpensive disks

Stennis Space Center

Space Shuttle main engine

V

TECHNICAL MEMORANDUM

HIGH-SPEED OBSERVER: AUTOMATED STREAK

DETECTION FOR THE AEROSPIKE ENGINE

1. INTRODUCTION

During Space Shuttle main engine (SSME) firing, in both test and flight, visual streaking in

engine plumes has been observed. Under normal circumstances, combustion of liquid hydrogen (LH 2)

and liquid oxygen (lox) yields nearly transparent plumes. Bright, distinguishable streaks in engine

plumes are possible indicators of abnormal events. The High-Speed Observer (HSO) concept

demonstrator program began with the goal of demonstrating that SSME engine streaks, which might

indicate engine malfunction, could be detected using video and automating the detection process. The

program was extended to include development of an expert system that detects, quantifies, and reports

anomalous streaks in the SSME plumes.

The HSO technology, developed for detecting and differentiating SSME plumes, has been

extended to incorporate detection and differentiation of anomalous plume streaking for the aerospike

engine structure and plume characteristics. In changing from SSME to aerospike plume analysis

operation, both hardware and software upgrades were necessary. This memorandum documents

upgrades to the HSO system and results of HSO monitoring of aerospike engine tests on the test stand

A1 at Stennis Space Center (SSC).
2. HIGH-SPEED OBSERVER SYSTEM

The basic HSO system uses a 200-frames per second (fps), 256 x 256 pixel DALSA ® CCD a3:cay

camera to generate 8-bit gray scale digital images. This camera is mounted inside a PELCO ® EHXr-I 2

explosion-proof housing for protection against the rugged environment experienced during testing. The

HSO camera position at SSC used for single-engine testing is shown in figure 1. The current HSt) system

uses a dual Intel Pentium ® Pro 200-MHz computer running Microsoft Windows ® NT with a BitFlow_ Inc.

Road Runner frame capture board to process images in real time. Each image frame is encoded with

interrange instrumentation group (IRIG) timing and recorded on a 17.2-gigabyte (GB) redundant array of

inexpensive disks (RAID) system. After testing, images are stored on an 8-mm Exabyte ® tape and shipped

to Marshall Space Flight Center (MSFC) for posttest analysis.

Figure 1. HSO camera and aerospike engine at SSC.

The aerospike engine configuration differs significantly from that of an SSME. Modifications to

the method of operation of the HSO were made to accommodate engine differences. At present, only one

side of a single module of the engine (cover photo) is being monitored for anomalous plume streaking

with only one operational camera (HSO lI) as shown in figure 2. Another camera (HSO III) will be

added when the full-up configuration of the aerospike engine (two of the modules shown in the cover

photo) is tested.

2
'.s'S'an0A1 I [

Leve, 4 [ CameraHS0'" ]

@

IH ol Camera

I

Copper Cable--.......__:.f

........... i_ax(_u;_'_e;a;at;ono( .... "1".... "_

40 ft From Computer to Camera) ,_

HSOII

Server Computer

i

A1 Hardcore I "

I

C/')

o

--q.

4

Facility

Autosequence

Start Signal. I Test C°ntAl°l Center

T

_-r

o 0

Q --.

o_

_3Q-

_a.__

_ t2"_ m

_- Distance >1,000 ft _ _ g

Figure 2. HSO hardware configurations.

2.1 High-Speed Observer Hardware Upgrades

Hardware upgrades to the HSO system included (1) installation of an input/output (I/O) board and

communications link to detect test initiation and shutdown, (2) repositioning of the HSO client system

and camera, and (3) a new replacement RAID disk system for the HSO server.

(1) Installation of an I/O board and communications link to detect test initiation and shutdown--

A communication link was established to allow the HSO system access to the test start and

test cutoff signals.

(2) Repositioning of the HSO server system and camera--The HSO camera position at SSC for

aerospike engine tests has been changed from the position of the last series of SSME tests.

The ideal camera position on the test stand would be perpendicular to the line of combustors

and on or slightly above a plane horizontal with the midpoint between combustor exit planes

and the edge of the ramp. Although, the view angle from the camera to the combustors is not

a right angle, making a head-on view unavailable, it is sufficient to provide separation of

combustor plume areas. The height positioning of the camera provides the necessary single

line of reference at the combustor exit plane for the region of interest.
(3) A new replacement RAID disk system for the HSO server--The previous 9-GB RAID

system used to store images failed and a new disk system was necessary. The new system

can store --17 GB and transfer data at 40 megabytes (MB)/sec compared to the old 9-GB

system that had a 15-MB/sec data transfer rate. This provides additional capability for

camera operation at maximum frame acquisition speed.

2.2 High-Speed Observer Software and Evaluation Model Modifications

Initial software upgrades to the HSO system included ( 1) an HSO server routine to monitor test

status and initiate camera functions, (2) modification to region of interest, (3) elimination of quality

region; subsequent changes in software included (4) a new streak detection algorithm.

(!) Routine to monitor test status and initiate camera functions--A software routine was written

for the HSO server to monitor the test status communications link and initiate camera

operation upon receipt of the test initiation signal. The software also stops camera operation

and initiates backup procedures when the test cutoff signal is received.

(2) Modifications to the region of interest--Each side of the aerospike engine is composed

of a set of combustors, each producing a plume to be monitored. As with the SSME plume

monitoring setup, the region of interest was broken into separate columns, each column

evaluating the plume of one combustor. There were ten such columns, with each column

composed of three tiles. There were no overlapping tiles in the setup for monitoring this

engine.

(3) Elimination of the quality region--The quality region, centered on the Mach disc of an

SSME plume, had been used as an intensity control area. An image was assumed to be

valid if the quality region intensity remained above a threshold value. The aerospike engine

has no such stable gray-scale value region readily available. At present, all images are

assumed valid from engine start to cutoff, unless they are totally black.

As the testing program progressed, more software changes were necessary. The algorithm

to detect streaks was determined to be inadequate to resolve the type of streaking observed

in test A I X023. Whereas SSME plume streaks are broad and generally increase brightness

over a large area, aerospike plume streaks observed tend to be thin and do not necessarily

increase the brightness level significantly. A new algorithm was implemented to detect

streaks.

(4) Development of new streak detection algorithm--A new algorithm to detect streaks was

developed. This algorithm searches a path parallel to the ramp edge, looking for intensity

changes indicative of streaks. Upon finding such intensity changes, an attempt is made to

grow a path of pixels with similar intensity values from that point to a point near the

thrusters on the opposite side of the ramp. If such a path can be found, the path is ,judged

to be a streak.

4
3. AEROSPIKE STREAK DETECTION ALGORITHM

The SSME streak detection algorithm was found to be inadequate for detecting streaks in plumes

produced by an aerospike engine. The SSME algorithm employed a threshold tile algorithm to detect

streaks. The arrangement of aerospike thrusters required reassessment of column structure for detecting

brightness increases:

l° Over time, aerospike plumes generate an intensity profile with both high and low average

levels. By setting a general, static streak, intensity threshold, as with the SSME streak detection algorithm, either many possible streaks were removed from consideration or during

certain time periods everything was considered a streak.

2. The aerospike cooling ramp induced bright areas having many characteristics of plume

streaks. There was no such structure needing compensation with SSME plume analysis.

3. Whereas SSME streaks are often broad and provide substantial brightness increases in

plumes, aerospike streaks are thin and do not significantly raise overall brightness levels.

. An additional problem, which became apparent when streaks were present, was water on the

camera faceplate. Because of the thin nature of the aerospike plume streaks, a droplet of water

on the camera facep[ate can cause a dark area in the image and streaks that cross into this area

appear to be discontinuous across the plane of the ramp.

To account for these differences, a new streak detection algorithm was created. First, a control

intensity value _br streak detection is determined for each frame (fig. 3):

1. A column of pixels midway down the ramp from the thrusters to the end of the ramp is chosen

to be a control column.

2. An average of the pixel intensity values along the column, which are less than the "wash-out"

intensity of a bloom region, is obtained.

3. A maximum of the pixel intensities, which are less than the wash-out intensity of a bloom

region, is also obtained.

4. The control intensity value for detecting streaks is determined as 80 percent of the difference

from the average to the maximum intensity.

5
/

Plume

Flow

Ramp

PixelColumnMidway

DownRamp

MaximumIntensity

/

80 goo iference in ntensities

/ _ V'_/"_ "_"_Averagelntensity

AerospikePhysicalCharacteristics IntensityValuesofMidwayPixelColumn

Figure 3. Control value intensity determination for an image frame.

Next, candidate streak seed points are chosen from local maxima along a row of pixels at the

edge of the ramp (fig. 4):

l. Along the column of pixels at the end of the ramp area, local maxima are consecutively

selected and tested.

2. If a local maximum value is not greater than the control intensity, it is not considered as a

candidate for a streak.

3. If a local maximum value is greater than the control intensity, a streak growth algorithm,

using local greatest intensity values is initiated.

¢.o

PixelColumn

atEndof Ramp

Streak

Plume

Flow

Ramp

Figure 4. Candidate streak selection.

Candidate streaks are grown from local intensity value maxima in the pixel column at the end of

the ramp (fig. 5):

I. Local maximum intensity values above the control intensity value provide initial seeds for the

growth algorithm.

6
.

3.

,

.

Three adjacent pixels in the streak growth direction; i.e., toward the thrusters, are tested.

The pixel with the highest value within 15 percent or above the control intensity value is

chosen as the next seed pixel.

If all three pixels have intensity values <15 percent of the control value, the next three adjacent

pixels are tested. This process is repeated up to five times. If no seed pixel is detected, the

streak growth is ended and the next local maximum in the pixel column at the end of the ramp

is inspected.

If the column of pixels near the thrusters is encountered, the algorithm labels the starting local

maximum as a streak generating pixel.

Pixel Column at

Beginning of Ramp

: Streak

I 1[ A,00r,thm 0irecti0n

[_.___J Ramp

Aer0spikePhysicalCharacteristics

CandidatePixels

for Next Pixel

Elementof Streak

°

r,¢--

"5 NewSeed for ,_

-= GrowingStreak

 nnn nn

= Growing Streak / =

_ Look AheadFive Local Maximum:

_- Pixel Columns for Seedfor Streak

PossibleSeed Growth Algorithm

Figure 5. Streak growing algorithm.

The streak length and streak growth direction confirm candidate streaks (fig. 6):

I. Each thruster provides a lane for growth of a streak; i.e., a streak should not enter the plume of

two thruster plumes. There are 10 thrusters on the aerospike panel and the number of pixels in

a column covering a single plume area averages =1 I0. Therefore, no streak should grow in the

column direction more than 11 pixels from the starting pixel column location.

2. The pixel distance from the end of the ramp to the beginning of the ramp near the thrusters

averages 120 pixels, a growing-slope ratio of = 10 percent.

3. A growing-slope ratio bound of = 15 percent, evaluated as the streak is growing, serves to keep

the streak growth reasonably within a plume. This check is initiated only after the streak has

grown by 10 pixeis.

4. If a growing path reaches the pixel column at the beginning of the ramp, this indicates a

reportable streak was found.

7
Pixel Column at

Beginning of Ramp

Streak

StreakGrowth

-,4

Algorithm Direction

Plume Flow

Ramp

Aerospike Physical Characteristics

el:

-g

1.1_1

==

m

o

iT_.

Pixel Column at

Beginning of Ramp

Streak

Not Streaks /

Ramp lengt,h .

Height/Length Ratio >15%

EliminatesCandidateStreaks

E

E

.--

Figure 6. Streak confirmation.

This streak detection algorithm was tested and found to recognize streaks in aerospike engine

plumes. It can discriminate many of the near streak-type events from true streaks and deal with certain

types of anomalous events which prevent contiguous pixels in a streak from being illuminated: i.e.,

water droplets on the camera faceplate. This algorithm was first implemented on aerospike engine test

A 1X023 data.
4. AEROSPIKE ENGINE RAMP CHARACTERISTICS

The ramp of the aerospike engine is cooled much like the nozzle bell of the SSME. Several

temperature-dependent areas on the ramp produce light colored areas that often appear in the same

intensity range and run in the same directions as streaks (fig. 7). The streak growth algorithm attempts

to take this into account as it traverses the path of the suspected streak.

Figure 7. Aerospike ramp temperature-dependent lines and streak growth.

Note that true engine streaks are usually visible from the end of the ramp up to the thruster

nozzle exit area. Because of the higher average intensity value of pixels in the nozzle exit area, the

differences in intensity of streak pixels to pixels surrounding the streak in the thruster nozzle exit area

are consequently a little less.

If an engine streak exists and a growth path reaches one of the temperature-dependent streak

patterns of the ramp near the nozzle exit area, it is probable that the growth algorithm will complete the

path and a streak will be reported, since the intensity of the streak and the temperature dependent area

become very similar. Conversely, if a streak does not exist, it is entirely possible that a partial streak

growth path matches with one of the temperature dependent high intensity areas and the streak growth

algorithm will push forward to the beginning part of the ramp and report a streak.

The 80-percent value between the maximum and the average value for a pixel row midway

between the dark end section of ramp area and lighter nozzle exit area portions of the ramp will exclude

many false streaks that would grow along a ramp temperature induced intensity line since intersections

with these lines are included in the average calculation. However, close-in to the thruster nozzle exit

planes, nearly all streak candidates will finish their growth paths. Most incomplete growth paths are

weeded out early and certainly before 90 percent of a complete streak path is final.
5. CATEGORIES OF HIGH-SPEED OBSERVER OBSERVED

AEROSPIKE ENGINE EVENTS

Several types of events have been observed during aerospike engine testing. None have led to

catastrophic failure; therefore, none are judged to be critical. Some have, however, been associated with

damage to thrusters. Most of these events (shown in fig. 8) are plume fluctuations that have not been

correlated to any specific event. These events do produce spikes in the average intensity data calculated

across one row of pixeis parallel to the lower edge and in the midsection of the ramp.

10
Category

CCDBloom

Description

Maximum intensity region, derived

from CCDpixel voltage overflow. All

pixel values in this region have

numeric value 255.

Examples

Light Intensity

Linear Plume

Anomaly

Very diffuse streak-type phenomenon.

Boundary not well defined. Insufficient intensity to be considered a

streak.

Strong

Intensity Linear

Plume Anomaly

Boundary not well defined. Sufficient

intensity to be considered a streak.

Startup Pop

Debris Induced

Streak

Engine

Produced

Streak

Strong intensity linear phenomenon,

extending from thruster nozzle exit

plane to midramp area. Occurs during

startup.

Linear plume phenomenon caused by

debris hitting the plume. Starts from a

position below the thruster nozzle exit

planes.

Well defined border. Intensity much

greater than surrounding pixels. Starts

from thruster nozzleexit planes.

Figure 8. Categories of HSO observed events.

11
6. CHARGE-COUPLED DEVICE BLOOM MITIGATION

Blooming (a voltage well of a pixel fills, spilling charge into adjacent pixels) has become a

problem for capturing data near the outboard side of the present aerospike engine configuration. An

ablative layer was applied to the outboard side of the engine ramp. This layer glowed brightly during

engine firing and produced substantial blooming in the DALSA Camera CCD. The intensity of the

outboard ramp edge overfills pixel charge wells and large areas of the ramp can be obscured due to the

bloom. No significant information can be gained from this area.

Blooming on the HSO DALSA camera spills charge directionally along a column of pixels. On

tests A 1X024-A 1X026, the charge spilling direction of the camera was directed onto the ramp area from

the edge (fig. 9). To mitigate the effects of blooming on the HSO camera, the camera was turned 180

degrees. Since the bloom originated near the edge of the ramp, this reversal of charge spilling direction

within the camera allowed the charge to drain away from the ramp area.

Figure 9. Growth of bloom during test A 1X026.

Turning the DALSA camera 180 degrees in its mount partially mitigated the blooming problem.

As shown in figure 10, the direction of blooming moved away from the origination area on the ramp

toward the frame edge. Note the bloom direction travels in the opposite direction from that in figure 9.

A wraparound effect, however, continued the bloom and made it reappear on the opposite side of the

frame. At 100-percent power level, the bloomed area entered the ramp area from the side of the frame

opposite the area where the bloom initiated and eventually touched the area where the bloom had initiated. Even at power levels < 100 percent, it appeared the distance from the bloom initiation point to the

frame edge was not sufficient to absorb enough energy to prevent the wraparound blooming effect.

12
Figure 10. Growthof bloomduringtestAIX027.

Sincethebloomoriginatedin anareaat thesideof theramp,turningthecamera,sothatthe

bloomproceededparallelto theplumeflow acrosstheramp,allowedthecameraCCD to bloom,yet

preservedmuchof theimagefor streakanalysis.Figure 11illustratesthegrowthof thebloom.Only

theregiondirectly belowor abovetheglowingablativelayeris affectedby thebloom,permittingstreak

analysisof mostof thethrusterexhaustplumearea.

_i ̧ ii_

Figure 11. Growth of bloom during test A 1X030.

13
7. RESULTS

Data from thirteen aerospike engine tests at SSC, A1X019-AI X031, have been obtained and

processed. The following section includes the analysis and results of that HSO data. Engine test A1X023

motivated the change in streak detection algorithm. Tests preceding A 1X023 were reevaluated using the

newer streak detection algorithm.

In addition to the streak algorithm being tested on data from each test, each data set was observed visually and observations recorded. This was done to check the accuracy of the streak detection

algorithm. It is sometimes difficult to determine exactly on which thruster an event occurred and the

event from the designated thruster may have occurred on the adjacent thruster plume boundary. The best

estimate of the origin of the event is listed.

7.1 Engine TestA1X019

This aerospike engine test was performed at SSC on test stand A I on Wednesday, November 17,

09:41:43, 1999. No substantial streaks were observed by the HSO system and visual inspection of data

revealed no significant streaks.

7.2 Engine Test A1X020

This aerospike engine ignition test was performed at SSC on test stand AI on October 27, 1999,

at 6:20 p.m. No substantial streaks were observed by the HSO system and visual inspection of data

revealed no significant streaks.

A series of small diffuse anomalies occurred between 300:18:20:26.619 and 300:18:20:26.642

c.s.t. Another very diffuse streak-like anomaly occurred at 300:18:20:25.372 c.s.t.

7.3 Engine Test A1X021

This aerospike engine test was performed at SSC on test stand A I on November 1I, 1999, The

test ran the planned 10 sec. No substantial streaks were observed by the HSO system and visual inspection of data revealed no significant streaks.

There were numerous small diffuse streaks observed on this test. Sixteen of the anomalous events

were on fuel side thruster No. 1 (FS-I), four were on FS-3, three were on FS-6, one was on FS-5, and

one on FS-8.

7.4 Engine Test AIX022

This aerospike engine test was performed at SSC on test stand A l on November 22, 1999. No

substantial streaks were observed by the HSO system and visual inspection of data revealed no significant streaks.

14
7.5 Engine Test AIX023

This aerospike engine test was performed at SSC on test stand A i on December 18, i 999.

Planned duration of the test, 10 sec, was achieved.

The streak detection algorithm detected streaks in frames 2998, 3003-3005, 3021-3027, and

3169. Visual inspection of image data revealed streaks observed in frames 2997-2999, 3003-3005,

3019-3027, 3111, and 3169-3172 at thruster FS-4. Posttest inspection of the hardware revealed erosion

in this thruster.

Table 1 lists the flames where a streak was reported by the new streak detection algorithm. The

older streak detection algorithm had failed to detect any streaks during this test. Also listed in table I are

the 80-percent level intensity control value, the intensity value observed for the local maximum which

was selected as the seed point for growing possible streak, and the location of the seed point for growing

the streak path. Figure 12 illustrates the type of streak observed during test A 1X023.

Table I. Streaks detected in test Al X023.

Frame 80%

2998 32

3003 37

3004 38

3005 36

3021 57

3022 56

3023 67

3024 65

3025 41

3026 32

3027 42

3169 32

SeedValue Location

32 (114, 70)

4O (114, 69)

41 (114, 70)

41 (114, 69)

71 (114, 70)

64 (114, 70)

88 (114, 70)

79 (114, 70)

50 (114, 69)

43 (114, 69)

60 (114, 69)

38 (114, 70)

tA

L.

-..1

,J_

I.-,,-

Pixel Column at End of Ramp

Observed Streak_

Plume

Flow

Ramp

_(114,70)

Figure 12. Streak detection: test A1X023/frame 3021.

15
The streaks noted in test A 1X023 are long and thin; they begin at the thruster exit plane and

extend past the ramp. The boundaries of the streaks are well defined with intensity levels within the

streaks much greater than the average intensity of the surrounding pixels.

Figure 13 illustrates the operation of the streak detection algorithm. The three intensity values,

the mean intensity of a column, the maximum intensity of the pixels in a column, and the control intensity used to determine a threshold value for local maxima selected as seed pixels, are shown in the figure

from 0 to 4200 frames. A closeup of the region from frames 2990 to 3040 shows the pixels chosen as

seed points and their relation to the control intensity.

Frames0-4200 80

7O

6O

5O

j 40

=

30

2o '

l I I I I ,I I I I I I I t I I | I I I 1 I I I l I l I I I I I I I I I

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

8O

Maximum

I 60 Control

. Maximum

_ "" I 50

-3o _ '_-'-'__

20, _:..____.--. _ ..... :__ 5E.__--- .-v_

t_ "1" ?"'_' 1(}; Fi.sllll:_O...3040

_" Control 0 , ........ I ...................................

,n ,_l_i[ T_ 2,990 3,000 3,010 3,020 3,030 3,040

;, Average

ir m.

....._,_

Frame

Figure 13. Intensity values used to determine a streak.

Streaks are usually the brightest elements in a frame and are therefore related to the maximum

intensity. The streak intensity value changes along the length of the streak path and a range of values

must be allowed to admit enough values along the streak path for the streak path to reach the nozzle exit

plane. The average intensity provides a floor for the intensity values along a column. The intensity of

this floor changes with each frame. In figure 13, near frame 1750 the average intensity is -=40, whereas

near frame 3250 the average intensity is =20, indicating an overall average brightness change of =20

units between control columns in the two frames. The nonnormalized intensity value of =75 near frame

1750 does not indicate a streak when normalized with the high average column intensity, whereas the

nonnormalized intensity value of 79 at frame 3024 normalized against the control intensity of =20,

indicates a possible streak.

16
7.6 Engine Test A1X024

Aerospike engine test A IX024 was performed on test stand A 1 at SSC on Friday, January 21,

2000, at 10:09 p.m, c,s.t, The test ran the planned 60 sec. No substantial streaks were observed by the

HSO system and visual inspection of data revealed no significant streaks.

7.7 Engine Test A1X025

The aerospike engine test Al X025 occurred at SSC on Thursday, February 3, 2000, at 16:50 p.m.

c.s.t. Planned duration of the test, 125 sec, was achieved.

Video real-time observation by test stand operators indicated three significant streaks from the

thrusters. Preliminary inspections showed several of the base flex seal straps to be broken and several

burnthrough areas in the base flex seal covering. Tactile inspection of the thrusters indicated a coolant

channel burnthrough in two thrusters.

Due to blooming, no substantial streaks were observed by the HSO system and visual inspection

of data was unable to reveal significant streaks.

7.8 Engine Test A1X026

The aerospike engine test A I X026 occurred at SSC on Wednesday, February 16, 2000, at 4:27 p.m.

c.s.t. Planned duration of the test, 175 sec, was achieved.

HSO operated from T-5 seconds until the end of test as programmed, recording 30,800 images for

an average run speed of--170 fps. No substantial streaks were observed by the HSO system and visual

inspection of data revealed no significant streaks. However, blooming effects as shown in figure 9, such as

experienced during the last tests, precluded detection of engine streaks over a large section of the ramp.

7.9 Engine Test AIX027

The aerospike engine test A1X027 occurred at SSC on Thursday, March 9, 2000, at 3:26 p.m.c.s.t.

Planned duration of the test was 220 sec. The test was terminated at 75.44 sec by the Fuel Pump Discha_e

Pressure Control Qualification limit. This was the first engine redline system cutoff.

The HSO system operated from T-7 sec until engine shutdown, recording 14,174 irnages for an

average run speed of = 173 fps. No substantial streaks were observed by the HSO system. Several flashes

were observed during the test. These flashes were not considered anomalous.

7.10 Engine Test AIX028

The aerospike engine test A 1X028 occurred at SSC on March 22, 2000, at =7:00 p.m.c.s.t. The

test duration was =225 sec.

The HSO system began operation at T-7 sec (82:19:00:00.470 c.s.t.), recording 38,498 images for

an average camera speed of--170 fps. No substantial streaks were observed by the HSO system. However,

several flashes were observed near the FS-3 and FS-4 thruster locations during the test.

17
7.11 Engine Test A1X029

The aerospike engine test A1X029 occurred at SSC on April 6, 2000 at =10:27 p.m.c.s.t.

The test duration was =235.0 sec.

The HSO system began operation at T-7 sec (97:22:26:57.299 c.s.t.), recording 44,098 images

for an average camera speed of --180 fps. No substantial streaks were observed by the HSO system.

One faint flash was observed. This flash was not considered anomalous and was probably a debrisinduced streak. However, bloom was still a problem, with at least 50 percent of the ramp area obscured

by bloom during portions of the test.

7.12 Engine Test A1X030

The aerospike engine test A 1X030 occurred at SSC on May 2, 2000, at =4:00 p.m.c.s.t.

The test duration was -_250 sec.

The HSO system began operation at T-7 sec (123:16:55:59:986 c.s.t.), recording 46,538

images for an average camera speed of = 173 fps. No substantial streaks were observed by the HSO

system. However, several small flashes were observed during the test. One faint flash at

123:16:57:37.838 c.s.t., another flash at 123:16:58:15.002 c.s.t., and a third very faint flash at

123:16:59:40.708 c.s.t. Rotation of the camera allowed the bloom to proceed vertically, providing a

minimal area obscured by the bloom.

7.13 Engine Test A1X031

The aerospike engine test AIX031 was conducted at the SSC on May 12, 2000, at =4:30 p.m.

c.s.t.. The test was terminated at =290 sec by the test conductor due to a flex seal burnthrough.

The HSO system began operation at 133:16:49:13.247 c.s.t, and ended operation at

133: !6:54:09.290 c.s.t., recording 50.738 images over 296.043 sec for an average camera speed of

= 171 fps. No substantial streaks were observed by the HSO system.

Changes to the fuel mixture ratio and power level were evident in the aerospike engine plumes

in the area just beyond the ramp. Figure 14 illustrates a narrowing of the bright area of the plume

below the ramp, which corresponds to the change to a 63-percent power level and mixture ratio of 5.

Prior to the flex seal burnthrough, a number of streaks were observed in the plumes below the

ramp. Figure !5 illustrates several such streaks. The streaks occurred in the region where the

burnthrough was noted.

A glowing area appeared at the edge of the ramp, shown in figure 16, in the region of the

burnthrough, well before the thermal protective flex seal material became evident as it dropped into

the plume.

18
133:16:53:42.991 133:16:53:42.997 133:16:53:43.002

Figure 14. Power level and mixture ratio changes.

133:16:53:43.008

133:16:53:43.941 133:16:53:44.004

Figure 15. Plume streaks.

133:16:53:44.089

133:16:53:53.031 133:16:54:05.474

Figure 16. Glowing area on ramp and flex seal material.

19
8. DISCUSSION

The HSO system has shown the ability to monitor SSME and aerospike engine tests and quickly

report the occurrence of anomalous engine streaking. The hardware and software systems are easily reconfigurable with off-the-shelf hardware and software and can provide streak data for health monitoring

of LH.,-lox engines. Additionally, the HSO system can be used for indepth posttest analysis of all plume

events. Reported events can be evaluated against hardware inspection results and correlated with

hardware failure.

From the testing accomplished using the new streak detection algorithm, major streaks were

correctly distinguished from the myriad of minor fluctuations that occur during engine test. This

technique is not limited to the aerospike engine characteristics and can be applied to the SSME plumes

to detect streaks as well. Adaptation of the algorithm to streak detection in SSME plumes at the launch

site is the next step in evolution of the HSO project.

Due to the wide range of intensities encountered in the aerospike engine plume images, it was

natural to encounter bloom. The only possibilities for bloom mitigation for the DALSA camera presently

used are reduction of the light entering the camera aperture or orientation of the camera so that bloom

proceeds away from the area being investigated. The gray-scale intensity of light (0-255) in the areas

not being affected by bloom averaged between l0 (dark areas) and 50 (near thruster exit planes) as

compared to areas affected by bloom which had values >255, creating spillover to adjacent pixels.

Solutions to bloom mitigation that reduced the intensity of light were not the most favored solutions.

Such solutions would also reduce the ability of the system to accurately distinguish streaks, since the

margin of error on streak intensity detection would be increased corresponding to the amount of light

reduction. Fortunately, bloom mitigation was accomplished by orientation of the camera in a direction

so that the bloom did not encroach upon the ramp area. In the future, the DALSA cameras employed

will be upgraded to include antibloom technology.

20
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1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

June 2001 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

High-Speed Observer: Automated Streak Detection

for the Aerospike Engine

6, AUTHORS

T.J. Rieckhoff, M.A. Covan,* and J.M. O'Farrell*

7.PERFORMINGORGANIZATIONNAMES(S)ANDADDRESS(ES)

George C. Marshall Space Flight Center

Marshall Space Flight Center, AL 35812

9.SPONSORING/MONITORING AGENCYNAME(S)ANDADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

8. PERFORMING ORGANIZATION

REPORT NUMBER

M- 1005

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA/TM--200 i-210879

11. SUPPLEMENTARY NOTES

Prepared for Vehicle and Systems Development Department, Space Transportation Directorate

*United Space Alliance

12a. DISTRIBUTION/AVAII._BILI'rY STATEMENT

Unclassified-Unlimited

Subject Category 35

Nonstandard Distribution

12b. DISTRIBUTION CODE

13. ABSTRACT (Max/mum 200 words)

A high-frame-rate digital video camera, installed on test stands at Stennis Space Center (SSC),

has been used to capture images of the aerospike engine plume during test. These plume images

are processed in real time to detect and differentiate anomalous plume events. Results indicate

that the High-Speed Observer (HSO) system can detect anomalous plume streaking events that

are indicative of aerospike engine malfunction.

14. SUBJECT TERMS

high-speed photography, photographic analysis,

aerospike, engine streaks, image processing

17.SECURITYCLASSIFICATION 18.SECURITYCLASSIFICATION

OFREPORT OFTHISPAGE

Unclassified Unclassified

NSN 7540-01-280-5500

15. NUMBER OF PAGES

28

16. PRICE CODE

19. SECURITY CLASSIFICATION 20, UMITATION OF ABSTRACT

OF ABSTRACT

Unclassified Unlimited

Standard Form 298 (Rev. 2-89)

PrescribedbyANSIStd 239-18

298 102
BIBLIOGRAPHY

°

°

"Engine 0523 Test Failure: January 25, 1996: At Stennis Space Center," Board of Investigation

Report, Marshall Space Flight Center, Alabama, March 1996.

Rieckhoff, T. J.; Covan, M.; and O'Farrell, J.M.: "High-Speed Observer: Automated Streak Detection in SSME Plumes," NASA/TM, Marshall Space Flight Center, January 2001.

21

National Aeronautics and

SpaceAdministration

AD33

George C. Marshall SpaceFlight Center

Marshall SpaceFlight Center,Alabama

35812