The Role of Bearing and Scan Mechanism

Life Testing in Flight Qualification of

the MODIS Instrument

NASA/TM—2001-210896

April 2001

Steven G. VanDyk

Raytheon Systems Company, Santa Barbara, California

Brian J. Dietz

Moog, Inc., Chatsworth, California

Kenneth W. Street and William R. Jones, Jr.

Glenn Research Center, Cleveland, Ohio

Mark J. Jansen

AYT Corporation, Brook Park, Ohio

Michael J. Dube

Nye Lubricants, Inc., New Bedford, Massachusetts

Rajeev K. Sharma and Roamer E. Predmore

Goddard Space Flight Center, Greenbelt, Maryland
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National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

35th Aerospace Mechanisms Symposium

cosponsored by the Lockheed Martin Missiles and Space and the

Aerospace Mechanisms Symposium Committee

Mountain View, California, May 9–11, 2001

The Role of Bearing and Scan Mechanism

Life Testing in Flight Qualification of

the MODIS Instrument

NASA/TM—2001-210896

Steven G. VanDyk

Raytheon Systems Company, Santa Barbara, California

Brian J. Dietz

Moog, Inc., Chatsworth, California

Kenneth W. Street and William R. Jones, Jr.

Glenn Research Center, Cleveland, Ohio

Mark J. Jansen

AYT Corporation, Brook Park, Ohio

Michael J. Dube

Nye Lubricants, Inc., New Bedford, Massachusetts

Rajeev K. Sharma and Roamer E. Predmore

Goddard Space Flight Center, Greenbelt, Maryland
Acknowledgments

J. Uber, S. Cicchelli, and M. Roberto, NASA Goddard Space Flight Center. A. DeForrest, Raytheon Systems

Company, Santa Barbara Remote Sensing. L. Alegre, S. Natvipada, D. Owens, T. Phan, P. Tokeshi and

 H. Tsui, Moog SMD. N. St. Pierre and M. LaRochelle, Nye Lubricants.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

This report is a preprint of a paper intended for presentation at a conference. Because

of changes that may be made before formal publication, this preprint is made

available with the understanding that it will not be cited or reproduced without the

permission of the author.

Trade names or manufacturers’ names 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 electronically at http://gltrs.grc.nasa.gov/GLTRS
NASA/TM2001-210896 1 

THE ROLE OF BEARING AND SCAN MECHANISM LIFE TESTING IN 

FLIGHT QUALIFICATION OF THE MODIS INSTRUMENT 

Steven G. VanDyk 

Raytheon Systems Company 

Santa Barbara Remote Sensing 

Santa Barbara, CA 

Brian J. Dietz 

Moog, Inc. 

Schaeffer Magnetics Division 

Chatsworth, CA 

Kenneth W. Street and William R. Jones, Jr. 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, OH 

Mark J. Jansen 

AYT Corporation 

Brookpark, OH 

Michael J. Dube 

Nye Lubricants, Inc. 

New Bedford, MA 

Rajeev K. Sharma and Roamer E. Predmore 

National Aeronautics and Space Administration 

Goddard Space Flight Center 

Greenbelt, MD 

ABSTRACT

This paper describes the results of accelerated 

and operational life tests on bearings for the 

Moderate Resolution Imaging Spectroradiometer 

(MODIS). It also describes the post test analysis 

of the disassembled bearings. Analysis was 

performed using micro-Raman, micro-FTIR, Xray Photoelectron Spectroscopy (XPS), 

Scanning Electron Microscopy (SEM), and Size 

Exclusion Chromatography (SEC). In general, 

the three sets of bearings in each of three test 

stations were in very good condition after 

accumulating 68, 144, and 209 million cycles, 

respectively. Some of the bearings exhibited 

lubricant degradation, indicated by viscous 

lubricant deposits on the cage and raceways. 

INTRODUCTION 

The Moderate Resolution Imaging 

Spectroradiometer (MODIS) is an instrument 

aboard the Terra (EOS AM-1) satellite and has 

been operating successfully since December 

1999. The MODIS instrument’s mission is to 

view the entire Earth’s surface, gathering data to 

better understand the global dynamics and 

processes occurring on land, in the oceans, and 

in the lower atmosphere. All observations are 

made through an extremely high resolution, 

optically and mechanically precise, scan-mirror 

motor/encoder assembly. The reliable 

performance of this assembly depends on two 

duplex bearing pairs lubricated with PennzaneTM 

SHF-X-2000, a synthetic hydrocarbon, 

formulated with lead naphthenate. 

As with most long-life lubricated mechanisms, 

lubricant life, bearing precision, and dynamic 
NASA/TM2001-210896 2

performance are the critical factors in the 

operation of the scan motor/encoder. As a first 

phase of lubricant selection for MODIS, bearings 

were tested with several candidate lubricants, 

accelerated life tests performed, and results 

evaluated. A synthetic hydrocarbon, Pennzane 

SHF-X-2000 with 2.5% lead naphthenate and 

0.6% antioxidant additives, was selected. Phase 

one results have not been reported. The second 

phase of lubricant testing consisted of three 

bearing life tests. The results were reported in 

Ref. 1 and in this paper. The third phase was 

the successful qualification life test of the scan 

motor/encoder mechanism. 

Each MODIS instrument contains a scan 

motor/encoder mechanism that has two duplex 

bearing pairs that are driven by a brushless dcmotor. To mitigate instrument risk, both 

accelerated and operational speed, lubricant life 

tests were conducted in parallel with the 

mechanism design and fabrication. This was 

done to verify the life early enough in the 

program to switch lubricants if accelerated 

testing revealed early anomalies. 

At the onset of the MODIS development, 

Pennzane had not been flown on Goddard long 

life lubricated space mechanisms. Both 

accelerated and real-time life tests were 

conducted on MODIS scan bearings to 

demonstrate that Pennzane would successfully 

lubricate the mechanism for the 5-year (57 

million cycle) life. Accelerated testing was 

achieved by increasing speed while increasing 

temperature to maintain a constant film 

thickness. Three stations were setup to test the 

bearings at various temperatures and speeds. A 

long-term test was also conducted on a full-scale 

motor/encoder, termed the life test unit (LTU). 

Short-term tests were also done using an 

engineering model (EM). Both units were flight 

quality. 

Three more flight quality motor/encoder units 

were constructed. One was flown in the MODIS 

instrument on the TERRA satellite. Another will 

be flown in the MODIS instrument on the AQUA 

satellite later this year. The final mechanism 

remains as a spare. 

Six months before launch of the Terra satellite 

(Dec 99), one of the accelerated life test stations 

was disassembled and two of the three bearing 

sets were found to be severely worn (Ref. 1). 

These results raised doubts about 

flightworthiness of the MODIS instrument. 

Fortunately, the LTU had been tested for almost 

five years at that time. Comparisons of torque 

margins and operating parameters between the 

EM scan mechanism, with only a few months of 

operating time, and the LTU mechanism showed 

no torque variation or operating parameter 

variation. From these measurements, it was 

concluded that no measurable bearing wear or 

lubricant degradation occurred during the longterm life test and that TERRA/MODIS instrument 

was safe to fly. 

This paper describes the bearing wear and 

lubricant degradation and distribution after the 

accelerated bearing life tests and the real time 

life test (LTU). 

EXPERIMENTAL 

LIFE TEST STATIONS 

Three test stations (II, III, IV) were setup for 

testing the bearings at various conditions. The 

test station is illustrated as Figure 1. Within each 

station, three flight quality, 440C steel, 66.675 

mm (2.625 inch) outer diameter, 50.800 mm (2 

inch) inner diameter, DF duplex pair bearings 

with a 165 N (37 pound) preload were mounted. 

The bearings, phenolic laminate retainers, and 

sintered nylon reservoirs were lubricated in 

accordance with flight requirements. 

Each bearing pair was contained in its own 

clamp/housing. The housings also contained 

lubricant reservoirs. Station II and III housings 

were fitted with inner and outer race heaters. A 

strain gauge was mounted on a cantilever beam 

supporting each bearing enclosure to measure 

the torque. The inner races of three duplex pairs 

were driven by a common drive shaft. One 

telemetry platinum resistance thermometer 

(PRT) was mounted to each bearing outer race 

housing. Two control PRTs (Stations II and III 

only) were also mounted to each bearing 

housing (one for the outer race and one for the 

inner race). All testing was performed under 

vacuum. 

Instantaneous torque readings were recorded 

every 15 minutes. The monthly average of these 
NASA/TM2001-210896 3

readings was plotted over the life of the test (see 

Figure 2). 

Three sets of duplex MODIS bearings were 

tested in each station (for a total of nine duplex 

pairs) at the conditions listed in Table 1. 

Accelerated testing was achieved by increasing 

the shaft speed. The temperature was also 

increased to maintain a similar calculated 

specific film thickness (λ) in all three-test 

stations. This method was used as an arbitrary 

way of creating an accelerated lubrication life 

test. 

Table 1 – Operational test station conditions 

Station 

Temp 

(°C) 

Speed 

(RPM) 

Total 

Cycles 

(x106

) 

II 45 72.0 209 

III 37 50.0 144 

IV 23 20.3 68 

ENGINEERING MODULE (EM) AND LIFE TEST 

UNIT 

Evaluation of the life test bearings from Station 

III had shown severe degradation (Ref. 1). To 

regain confidence in the MODIS scan 

mechanism before the launch of 

TERRA/MODIS, a performance evaluation was 

conducted on the like-new engineering model 

(EM) and the qualification life test mechanism 

after 4.7 years of testing. 

The performance of the two test units was 

measured by evaluating the motor drag torque 

and phase error signals. The EM scanner had 

seen a few hundred thousand cycles whereas 

the LTU has completed more than one mission 

lifetime, approximately 58 million cycles, in 

vacuum testing. 

Both scanners tested had their spin axis vertical 

with an equivalent inertia disk attached to 

represent the scanner mirror at the top end of 

the drive system shaft. The hardware used to 

record the drag torque and phase error signals 

was a portable data acquisition system running 

LabVIEW software and all data was recorded 

at 250 samples per second. 

RESULTS 

STATION II 

Station II was an accelerated life test running at 

72 RPM and 45°C. The original plan specified a 

life test duration of 57 million revolutions. After 

the bearing life tests successfully achieved the 

required 57 million revolutions, the test torque 

data was reviewed and it was concluded that 

there was no indication of failure so the tests 

were allowed to continue. 

Average torque data is shown in Figure 3 for 

Station II. Intermittent jittering of the upper 

bearing pair housings was observed toward the 

end of testing. Torque characterization with and 

without visible vibration is shown in Figures 4 

and 5. 

STATION III

Bearing life test Station III (50 RPM and 37°C) 

results were reported at the 34th Aerospace 

Mechanisms Symposium (Ref. 1). Bearings in 

this station indicated consistent operation well 

past 57 million revolutions until a suspected 

heater malfunction occurred at 88 million cycles 

(Figure 2). The test continued until 144 million 

revolutions were achieved. 

STATION IV 

Station IV operated for 68 million cycles at 20.3 

RPM, which is the speed for satellite operation. 

This station operated at room temperature 

(23°C) and exhibited vibration that randomly 

affected the bearings at different times. The 

vibration was visible and varied with intensity. At 

times there was no vibration noted on any of the 

bearings. Torque history for all bearing pairs 

appears in Figure 6. 

STATION DISASSEMBLY 

The decision to disassemble two of the test 

stations was finally made after station IV 

surpassed 57 million cycles. At the time of 

disassembly, station II had accumulated 209 

million cycles while station IV had achieved 68 

million cycles. 
NASA/TM2001-210896 4

Upon disassembly some lubricant discoloration 

was observed, but none of the bearings had 

visible damage. The bottom bearings of each 

pair had more lubricant and a stickier feel than 

the upper bearings. Bearing torque remained 

well below the operational requirements of the 

system (18 oz-in drag torque) throughout the life 

test. 

Photographs were taken throughout the 

disassembly and inspection process. A test 

station prior to disassembly is shown in Figure 7. 

The complete shaft and all bearing components 

were removed from the test station and 

transported to a class 100 flow bench in a class 

100,000 clean room for further inspection. 

One of the disassembled bearings (4-012) is 

shown in Figure 8. Although not easily seen in 

the macro photograph (Figure 8), dark viscous 

deposits were observed on the cage and 

raceways. A higher magnification photograph 

(Figure 9) shows an example of these deposits 

in a raceway. Two other photographs showing 

the variation and distribution of lubricant within 

the raceways appear in Figures 10 (greater 

amount of lubricant) and Figure 11 (lesser 

amount of lubricant). 

Station II

Upon inspection, it was noted that some oil crept 

into the support cups. The oil was black and 

viscous and all balls, retainers and races were 

wetted, small meniscuses of oil were at the ball 

race junctions, and very limited wear was 

observed on the balls and races. Dark deposits 

of lead or lead naphthenate were not visible, 

indicating the lead naphthenate remained 

dissolved in PennzaneTM. This formulation of 

PennzaneTM performed very well at high 

temperature and in the boundary lubrication 

regime. 

Station III

When station III was disassembled, two of the 

three bearing sets were found to be severely 

worn. This is believed to be because of the 

heater malfunction (Ref. 1). 

Station IV

As with station II, upon disassembling station IV 

it was noted that part of the oil had crept into the 

support structure. Again, the oil color was dark 

amber and the viscosity unchanged. All balls, 

retainers, and races were wetted and contained 

oil meniscuses. Almost no wear was observed 

on the balls or races. 

The lubricant and bearing surfaces have been 

analyzed using micro-Raman, micro-FTIR, X-ray 

Photoelectron Spectroscopy (XPS), Scanning 

Electron Microscopy (SEM) and Size Exclusion 

Chromatography (SEC) and the results 

summarized later in this paper. 

Comparison of the bearing wear and the 

lubricant degradation after life testing at 23°C 

and 45°C, clearly demonstrated that the severe 

bearing damage found in the 37°C accelerated 

life test originated from a thermal control failure 

that drove the bearing test temperature well 

above 90°C, as suggested in Reference 1. 

EM AND LTU 

The steady state drag torques measured on the 

MODIS EM and LTU scanner units were 

approximately 9.4 and 12.2 oz.-in. respectively, 

indicating a beginning-of-life and a end-of-life 

torque margin of greater than 20. The more 

important parameter of margin on phase lock for 

both units is a healthy 200 percent. Because of 

the design similarities between the EM and LTU 

scanner units and the MODIS scanners that are 

in flight or scheduled for flight, it was concluded 

that the flight unit MODIS scanners have 

sufficient margin for a five-year mission life on 

the Terra and EOS-PM programs. A more 

detailed description of the comparison appears 

later in this paper. 

ANALYTICAL RESULTS 

In general, the results showed the balls, 

retainers, and races were still lubricated and in 

good condition at the end of test. The top 

bearing assemblies had the least lubricant of the 

three bearing pairs in both stations II and IV and 

bottom bearing assemblies had a thicker greasetype residue. There was no sign of dry debris in 

any of the bearing assemblies. The oil had 

darkened significantly and was more viscous, 
NASA/TM2001-210896 5

almost like honey. Wear paths were seen in the 

races and on some of the balls. There was no 

sign of elongation in the retainer pockets. 

However, some slight metallic debris was 

observed on some of the retainers. The metallic 

debris was noticed only on station IV. 

Raman and Infrared analyses of the lubricant 

indicated the standard signature for nondegraded PennzaneTM. XPS, SEM, and EDAX 

showed the normal elemental composition for 

440C steel. The most striking demonstration of 

lubricant degradation was observed in some 

bearings as a thickened lubricant deposit with a 

grease-like consistency. These deposits 

occurred on both races and on the cage. For the 

Size Exclusion Chromatography (SEC) analysis, 

the cages were all weighed and then extracted 

using tetrahydrofuran (THF). The solution was 

concentrated and injected into a size exclusion 

chromatograph. An example from bearing 4-012 

appears in Figure 12. Detector signal is plotted 

as a function of molecular weight (MW). Several 

peaks are evident. The negative peaks at low 

MW are injection peaks. The peak at 195, which 

occurs in all samples, is an artifact from a 

preservative in the mobile phase (THF). The 

next peak represents the disubstituted 

PennzaneTM compound. The higher MW peak, 

at about 1,300, represents the primary 

PennzaneTM material as well as a contribution 

from the lead naphthenate. The broad high MW 

peak, centered about 18,000, represents 

polymerized lubricant. This high MW peak does 

not occur in unused samples. 

The weight of extracted lubricant from the cages 

varied from bearing to bearing with the smallest 

amount being about 9 mg from cage 4-015 to 49 

mg from cage 4-002A. This compares to the 

nominal amount of 75 mg impregnated at build 

up. In addition, dark residues were observed on 

cages 4-002A, 4-005A, 4-006A and 4-015A. 

Photographs for these two cages after THF 

extraction appear in Figures 13a and 13b. 

PERFORMANCE MEASUREMENT TEST 

Performance tests on the MODIS engineering 

model (EM) and life test unit (LTU) scanners 

were made to determine the changes in 

performance over the expected on-orbit life of 

the flight unit. Scan motor drag torque and 

phase error signal performance from both test 

units was measured, recorded and evaluated. 

The EM scanner had seen a few hundred 

thousand rotation cycles whereas the LTU had 

completed more than one mission lifetime and 

about 58 million cycles in vacuum testing. 

Figure 14 documents the running or steady state 

drag torque of the EM scanner, which had an 

average value of .067 N-m (9.4 oz-in). During 

this test, the EM unit maintained the required 

rotation rate of 20.3 rpm with phase-lock control. 

The beginning-of-life requirement for this value 

was 0.11 N-m (15 oz-in), which was met. This 

represents a beginning of life torque margin 

greater than 20. 

Figure 15 documents the measured phase error 

signal of the EM scanner under turn ON and 

steady state conditions. When the scanner was 

initially turned on, there was a large error signal 

generated between the commanded rate and the 

actual rate, shown by the indicated spike shortly 

after turn-on. The phase-lock circuitry was 

designed to reduce the error between the 

commanded rate and the actual rate over a 

given time, therefore the error signal reduced 

shortly after turn-on to a value of approximately 

1 volt peak-to-peak. This was equivalent to a 

phase error of approximately 20 micro-radians 

under steady state scanner rotation. 

Figures 16 and 17 show an attempt to bring the 

EM scanner out of phase lock by increasing the 

external drag torque on the drive system. Due to 

the limitation of the test setup, the external drag 

was increased manually while monitoring the 

system till the scanner was out of phase lock. 

The two figures also show maximum drag torque 

when the scanner went out of phase lock. The 

drag torque was compared to the maximum 

available torque of the scanner motor and the 

torque margin established. When the transient 

drag torque events on Figures 16 and 17 were 

omitted and the maximum drag from the eight 

attempts averaging, the drag torque when the 

scanner phase lock was lost occurred at about 

0.71 N-m (100 oz-in). This represents a margin 

on phase lock of about 200% at the beginningof-life. 

Figure 18 documents the steady-state drag 

torque of the LTU scanner. After completing 

more than 58 million cycles in vacuum, the LTU 

has an average value of 0.086 N-m (12.2 oz-in). 
NASA/TM2001-210896 6

The measurement indicated that at the end of 

one mission life, the torque margin for the 

scanner was greater than 20. 

Figure 19 documents the measured phase error 

signal of the LTU scanner under turn ON and 

steady state conditions. Similarly as with the EM 

unit system, when the LTU scanner was initially 

turned on, there was a large error signal 

generated between the commanded rate and the 

actual rate, shown by the indicated spike shortly 

after turn-on. The phase-lock circuitry was 

designed to reduce the error between the 

commanded rate and the actual rate over a 

given time; therefore there was a reduction in 

error signal shortly after turn-on to a value of 

about 0.5 volt peak-to-peak. This was 

equivalent to a phase error of about 10 microradians under LTU scanner steady-state 

rotation. 

Due to the LTU scanner test vacuum apparatus, 

it was not possible to perform the phase lock 

tests for comparison to the EM data. 

Nonetheless, based on phase error and drag 

torque measurements there was good 

confidence that the life test unit, after greater 

than one mission life, had no significant 

difference in measurable parameters and 

therefore has good correlation in margin for 

phase lock equivalent to the EM unit measured 

data. 

CONCLUSIONS 

The steady state drag torques measured on the 

MODIS EM and LTU scanner units were 

approximately 0.067 N-m (9.4 oz-in) and 0.087 

N-m (12.2 oz-in) respectively, indicating a 

beginning-of-life and a end-of-life torque margin 

of greater than 20. Phase lock margin, the more 

important parameter, for both units was a 

healthy 200 percent. Because of the design 

similarities between the EM and LTU scanner 

units and the flight scanners, it was concluded 

that the flight scanners had sufficient margin for 

the five-year mission. 

LESSONS LEARNED 

Since a worn slip ring was the cause of heater 

loss in the accelerated test station, it was shown 

that the test equipment must be more robust 

than the hardware being tested. Also, in the 

presence of gravity, considerations for the 

orientation of test samples should be given. 

Where feasible, rotation of the samples should 

be performed to counter the effects of gravity. 

The labyrinth seal should match that of the flight 

configuration. And lastly, when testing 

mechanical systems, consider the frequency of 

the test apparatus. In this test it was noted that 

jitter, seen during life testing, was likely due to 

the cantilevered test arm resonating or coupling 

with the rotational speed of the bearings. 

REFERENCES 

1. Brian J. Dietz, Steven G. VanDyk and Roamer E. 

Predmore, “Earth Scanner Bearing Accelerated 

Life Test”, 34th Aerospace Mechanisms 

Symposium, May 2000, pp. 303–316. 
NASA/TM2001-210896 7

Figure 1 – Test Station 

0.00

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0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Revolutions (Millions)

Torque (N-m)

GAUGE III2 GAUGE III3 GAUGE III1

Figure 2 – Torque vs. revolutions for upper pair bearings (III1), middle bearings (III2), and lower bearings (III3) 
NASA/TM2001-210896 8

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Figure 3 – Torque vs. revolutions for upper pair bearings (II1), middle bearings (II2), and lower bearings (II3) 

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Figure 4 – Torque characterization for Station II upper bearing pair with visible vibration 
NASA/TM2001-210896 9

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Figure 5 – Torque Characterization for Station II Middle Bearings without Vibration 

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Figure 6 – Torque vs. revolutions for station IV upper pair bearings (IV1), middle bearings (IV2), and lower bearings (IV3) 
NASA/TM2001-210896 10

Figure 7 – Test station prior to disassembly 
NASA/TM2001-210896 11

Figure 8 – Disassembled MODIS 4-012 bearing 

Figure 9 – Darkened lubricant deposit 
NASA/TM2001-210896 12

Figure 10 – One bearing from station II with a greater amount of lubricant 

Figure 11 – One bearing from station II with a lesser amount of lubricant 
NASA/TM2001-210896 13

 

Figure 12 – Size exclusion chromatogram from extracted lubricant from cage 4-012 

 (a) (b) 

Figure 13 – Photograph of extracted cage from 4-002A (a) and 4-015A (b) 

Molecular Weight: 43,000 2,610 472 92 
NASA/TM2001-210896 14

0 5 10 15

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Time (seconds)

Drag Torque (N-m)

MODIS EM Scanner Drag Torque Measurement, Mean Drag= 0.067 N-m

Figure 14 – MODIS EM Scanner Steady State Drag Torque 

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MODIS EM Scanner Phase Error

Figure 15 – MODIS EM Scanner Phase Error 
NASA/TM2001-210896 15

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MODIS EM Scanner Phase Lock Test, 5 Attempts

Figure 16 – MODIS EM Scanner Phase Lock Test 1 

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MODIS EM Scanner Phase Lock Test, 3 Attempts

Figure 17 – MODIS EM Scanner Phase Lock Test 2 
NASA/TM2001-210896 16

0 5 10 15 20 25 30 35 40 45

0.05

0.06

0.07

0.08

0.09

0.1

0.11

0.12

Time (seconds)

Drag Torque (N-m)

MODIS LTU Scanner Drag Torque Measurement, Mean Drag= 0.086 N-m

Figure 18 – MODIS LTU Scanner Steady State Drag Torque 

0 2 4 6 8 10 12

-1

0

1

2

3

4

5

6

7

8

9

Time (seconds)

Phase Error (Vdc)

MODIS LTU Scanner Phase Error

Figure 19 – MODIS LTU Scanner Phase Error 
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

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22

The Role of Bearing and Scan Mechanism Life Testing in Flight

Qualification of the MODIS Instrument

Space mechanisms; Lubricants

Unclassified -Unlimited

Subject Category: 27 Distribution: Nonstandard

Prepared for the 35th Aerospace Mechanisms Symposium cosponsored by the Lockheed Martin Missiles and Space and the Aerospace Mechanisms

Symposium Committee, Mountain View, California, May 9–11, 2001. Steven G. VanDyk, Raytheon Systems Company, Santa Barbara Remote Sensing,

Santa Barbara, California; Brian J. Dietz, Moog, Inc., Schaeffer Magnetics Division, Chatsworth, California; Kenneth W. Street and William R. Jones, Jr.,

NASA Glenn Research Center; Mark J. Jansen, AYT Corporation, 2001 Aerospace Parkway, Brook Park, Ohio 44142; Michael J. Dube, Nye Lubricants,

Inc., New Bedford, Massachusetts; and Rajeev K. Sharma and Roamer E. Predmore, Goddard Space Flight Center, Greenbelt, Maryland. Responsible

person, Kenneth W. Street, organization code 5140, 216–433–6051.

Steven G. VanDyk, Brian J. Dietz, Kenneth W. Street, William R. Jones, Jr.,

Mark J. Jansen, Michael J. Dube, Rajeev K. Sharma, and Roamer E. Predmore

This paper describes the results of accelerated and operational life tests on bearings for the Moderate Resolution Imaging

Spectroradiometer (MODIS). It also describes the post test analysis of the disassembled bearings. Analysis was performed

using micro-Raman, micro-FTIR, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and

Size Exclusion Chromatography (SEC). In general, the three sets of bearings in each of three test stations were in very

good condition after accumulating 68, 144, and 209 million cycles, respectively. Some of the bearings exhibited lubricant

degradation, indicated by viscous lubricant deposits on the cage and raceways.