NASA/TM--2002-211706

In-Situ,

System

On-Demand Lubrication

for Space Mechanisms

Mario Marchetti, William R. Jones, Jr., and Stephen V. Pepper

Glenn Research Center, Cleveland, Ohio

Mark J. Jansen

SEST, Inc., Middleburg Heights, Ohio

Roamer E. Predmore

Goddard Space Flight Center, Greenbelt, Maryland

July 2002
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NASA/TM--2002-211706

In-Situ,

System

On-Demand Lubrication

for Space Mechanisms

Mario Marchetti, William R. Jones, Jr., and Stephen V. Pepper

Glenn Research Center, Cleveland, Ohio

Mark J. Jansen

SEST, Inc., Middleburg Heights, Ohio

Roamer E. Predmore

Goddard Space Flight Center, Greenbelt, Maryland

Prepared for the

2002 Annual Meeting

sponsored by the Society of Tribologists and Lubrication Engineers

Houston, Texas, May 19-23, 2002

National Aeronautics and

Space Administration

Glenn Research Center

July 2002
Acknowledgments

This work was performed while the main author held a National Research Council Research Associateship Award

in the Tribology and Surface Science Branch, NASA Glenn Research Center. The authors respectfully acknowledge

the help and the work of Gary S. Kostyack, NASA Glenn Research Center, for the metallic coatings.

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.

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Available from

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Available electronically at http: / / gltrs.grc._aasa.gov/GLTRS
In-Situ, On-Demand Lubrication System for Space Mechanisms

Mario Marchctti,* William R. Jones, Jr., and Stephen V. Pepper

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Mark J. Jansen

SEST, Inc.

Middlcburg Heights, Ohio 44130

Roamer E. Prcdmorc

National Aeronautics and Space Administration

Goddard Space Flight Ccnter

Greenbelt, Maryland 20771

ABSTRACT

Many of today's spacecraft have long mission lifetimes. Whatever the lubrication

method selected, the initial lubricant charge is required to last the entire mission. Fluid

lubricant losses are mainly due to evaporation, tribo-degradation, and oil creep out of the

tribological regions.

In the past, several techniques were developed to maintain the appropriate amount

of oil in the system. They were based on oil reservoirs (cartridges, impregnated porous

parts), barrier films, and labyrinth seals. Nevertheless, all these systems have had limited

success or have not established a proven record for space missions.

The system reported here provides to the ball-race contact fresh lubricant in-situ and

on demand. The lubricant is stored in a porous cartridge attached to the inner or the outer

ring of a ball bearing. The oil is released by heating the cartridge to eject oil, taking

advantage of the greater thermal expansion of the oil compared to the porous network. The

heating may be activated by torque increases that signal the depletion of oil in the contact.

The low surface tension of the oil compared to the ball bearing material is utilized and the

close proximity of the cartridge to the moving balls allows the lubricant to reach the ball-race

contacts. This oil re-supply system can be used to avoid a mechanism failure or reduce

torque to an acceptable level, and extend the life of the component.

I- Introduction

1- Overview

Many moving mechanical assemblies (MMA) for space mechanisms rely on liquid

lubricants to provide reliable, long-term performance. The proper performance of the MMA

is critical in assuring a successful mission. Historically, mission lifetimes were short and

MMA duty cycles were minimal. As mission lifetimes were extended, other components,

such as batteries and computers, failed before lubricated systems. However, improvements

in these ancillary systems over the last decade have left the tribological systems of the MMAs

as the limiting factor in determining spacecraft reliability.

* National Research Council_NASA Research Associate at Glena Research Ce*_ter.

NASA/TM--2002-211706 1
Typically,MMAsareinitiallylubricatedwith a smallcharge(mg)thatis supposedto

last the entiremissionlifetime,often well in excessof five years.In manycases,the

prematurefailureof alubricatedcomponentcanresultinmissionfailure[1-3].

Tribologicalfailureof MMAs occurswhenthelubricantdegradesor evaporatesand

thereforelosesits abilityto lubricaterubbingsurfaces,beatingballscontactingracewaysfor

example.SincetheMMA is stillmechanicallyintactwhenthelubricantdegrades, if lubricant

couldbere-suppliedto thecontact,thelifeof theMMA couldbeextended.Onemeansof

lubricantre-supplyhasbeenprovidedby lubricantreservoirs,but they arebulky,add

complexity,and cannot be activatedwhen needed.Rather,they continuouslysupply

lubricantto thecontact,oftenleadingto anexcessof lubricantsuppliedto theMMA.Some

ballbeatingshaveholesdrilledin theracewaysnextto thecontactarea[4],butthisdesignis

moreadaptedto largeballbeatings.

2-Backgroundof in situ-lubricationandporousreservoirs

To supplyfluid lubricantandto assureatleasta 5-yearmission,porousreservoirs

wereextensivelyemployedin ballbearingssincethe 1960's[5,6]. Overthepast40years,

numerousstudieswereundertakenon impregnatedporousmaterialsandtheir behavior

(evaporation,capillaryeffectson oil release,oil circulation,etc.)[5-11].Porousmaterials,

mainly in the form of retainers,were employedin severalspacemechanisms

[12-20].Oil flowandcirculationin porousbeatingshavebeenwidelystudiedsincetheearly

fiftiesby MorganandCameron[11].Fully describedin openliterature,thistopichasnow

reacheda goodunderstandinglevel[21].But theireffectremainedlimited asshownby

Marchettietal.[22,23]

One of the waysfor oil to be releasedfrom a porousreservoiris to raiseits

temperature. As aconsequence, threedifferentphenomenawouldoccurandhaveanimpact

onthelubricationof spacemechanisms.

The frrst oneis a differencebetweenthe thermalexpansionsof the fluid andthe

porousmatrix.Theoil hasagreaterexpansionwhenheatedthantheporoussolidnetwork

[10, 14,24, 25]. Thus,the oil is "ejected"from the reservoir.The differentialthermal

expansionforcesthefluidto be"squeezedout."Jamison[24]gaveanexpressionaboutthe

quantityof oil ejected,assumingthe porosityis isotropic(Dupuit'slaw).A systemwas

attachedto aninertialwheel[14]butit wasneveractivatedandnoevidenceof its efficiency

given.

ThesecondphenomenonistheMarangonieffect,whereachangein thetemperature

modifiesthe surfacetensionof the fluid [10,26-32].A temperaturegradientcausesa

correspondingsurfacetensiongradient,andsoanassociatedstress.The fluid thenmoves

from thecoldzonetowardthewarmzone.Thespeedof thefluidis parallelto thethermal

gradient.ThetemperaturegradientPrat[31]usedwas6.4°C.cm-I, asrepresentativeof the

oneexistingin ballbeatings,whileForeetal.[10,26-29,32]basedtheirstudyongradients

between0.5and2°C.cm-I.

Thelastphenomenoninvolvestheevaporationof thelubricant,thevaporpressure

of a materialbeingincreasedwith the temperature.Kato et al. first introducedthe idea

[33-36]ona systemto combattheproblemof solidcoatingwear.Thesystemdepositeda

solidfilm lubricantinto acontactzoneduringsliding(pin-on-disk)throughevaporation.As

frictionincreased, thesystemcouldbereactivatedandanewcoatingdeposited,thusyielding

a virtuallylimitlesslifetime.Termed'tribo-coating,'thissystemdemonstratedthe abilityto

re-lubricateacontactin-situ.Adachiet al.[36] attemptedtwotypesof in-situcoatingusing

thesolidlubricantindiumandapin-on-disktestdevice.Thefirstwasto depositacoatingon

NASA/TM--2002-211706 2
the partsbeforerunningthetest.Thiswastermed'vapor deposition.' The second was to

deposit the coating while the system was operating. This is called 'tribo-coaring.' It was

observed that tribo-coaring had lower friction and longer life than a vapor deposited coating.

Tests conducted on a Spiral Orbit Tribometer have shown that a similar mechanism was

able to induce the recovery of the system [371.

3- Objective of the study

In-situ, on-demand lubrication provides a step between having no additional

lubricant and large lubricant reservoirs. The in-situ, on-demand lubrication device is a small

reservoir that can be remotely activated to provide a minimal charge of lubricant near the

contact zone. It is based on the three physical phenomena described above: Marangoni

effect, thermal expansion and evaporation. A sensor attached to the MMA monitors its

health, as the beating torque for example, and, when needed, activates the lubricator. The

objective of this work was to test the feasibility of using an in-situ, on-demand system with a

liquid lubricant under ultra-high vacuum and in a boundary lubricated, rolling contact. The

method of lubricant delivery to an unlubricated ball beating, and the re-lubrication of the

mechanism were studied.

II- Experimental

1- Test rig

The GOES rig used for these experiments was first introduced by Jansen et al. [38]

and is shown in Figure 1. The system is designed to operate at pressures below 5×10 -(' tort

and between temperatures of 23 ° to 100°C. The device has a computer data acquisition

(DAQ) and control system based upon LabVIEW ®. The DAQ monitors beating

temperature, torque, load, cross-bearing electrical resistance, and rotational speed. Motion is

provided by a computer controlled stepper motor and ferrofluidic feedthrough. The system

allows either a constant rotational speed between 0 and 1000 RPM or a precise dither at a

desired angle. The rig uses a soft, dead weight loading system. A heating unit can maintain

the bearing at a constant temperature between ambient and 100°C or impose a temperature

ramp.

Cross-bearing electrical resistance is monitored throughout the test. The inner race is

electrically isolated from the rest of the rig. The outer race is grounded. A 1.5-volt supply is

provided at the inner race though a 1.5 tCQ resistor. The voltage at the inner race is

measured to obtain the voltage drop across the bearing. The cross-bearing resistance can be

calculated from the voltage drop. From the resistance data, the lubrication regime can be

determined. A low contact resistance indicates operation in the boundary or mixed regime.

A high or infinite resistance indicates either operation in the elastohydrodynamic lubrication

0EHL) regime or the build up of an electrically insulating friction polymer [39].

The system uses a single angular contact bearing. It is mounted within a fixture, also

shown in Figure 1, which holds the inner race fixed and rotates the outer race. A

thermocouple is mounted touching the inner race and measures bearing temperature.

Torque is monitored using an in-line torque meter.

NASA/TM--2002-211706 3
2-Preparationof thetests

Cleaning

Theball bearingsusedwereMPB 1219,angularcontactbearingsfrom MPB,Inc.

Theyweretakenapartandtheretaineremoved.Ballswereaddedto theballbearingto cope

withtheabsenceof cage,reachingatotalof 24balls.Thisretainerlessdesignhasbeenused

in somepreviousstudy[40,41].Parts,madewith 440Cstainlessteel,werethencleaned

withhexaneanddeionizedwaterfor 10mineachwith ultrasonicassistance. Theywerethen

subjectedto UV-ozonefor 15min.No lubricantwasaddedto theballbeatingbeforeor

afterthein-situ,on-demandlubricationsystemwasattachedto the ballbearing.Thus,an

earlyfailureof thebeatingwaslikelyto occurandtheefficiencyof there-lubricatingsystem

would be evaluated.The bearingwith the in-situ, on-demandlubricatingsystemis

representedinFigure2.

Priorto anytreatment,theporousringsweremeasured,thencleanedin a Soxhlet

extractorwithmethanol(HPLCgrade)for atleasteighthours,andweighed.Theywereput

in a vacuumovenovernightandstoredin aninert atmospherebeforeimpregnation.The

poroustingswerethenweighedandtheirporositywasdetermined.Thetingsweremade

withpolyimide,anditsmaincharacteristicsarepresentedinTable1.

Lubricantsusedforimpregnation

TheoilsconsideredhereweretheKrytox143AB,aperfluoropolyalkylether, andthe

NYE 2001,a multiplyalkylatedcyclopentanewith additives.Both arecommonlyusedto

lubricatespacemechanisms, andsomeof theirpropertiesaregiveninTable2.

Theporousringswereimpregnatedwith theoil by immersingthemundervacuum

for at leastfour consecutivedays.The lubricantswerekeptwarm (-_40°C)to makethe

impregnationeasier.To avoidaspreadingexcessoil fromtheporousringontheballbeating

duringtheassembly,the impregnationwasdeliberatelychosento belessthan100%.An

impregnationbetween70and80%wasselected,meaningthe outersurfaceof theporous

structurewas"dry" beforebeingattachedto theballbeating.

3-In-situ,on-demandlubricationsystemandassembly

Theoil reservoirwasmadewithporouspolyimide.Thismaterialwasdevelopedearly

in theseventies[42],andsinceusedin spacemechanismsasretainersin ballbearingsor as

staticreservoirs[18,19,43, 44]. This materialhasanimportantopenporosity(Table1)

comparedto theusualphenolicresin,andhasself-lubricatingproperties[45].

Thethermalexpansionof theoil wasobtainedby attachinga heaterontheporous

reservoircontainingthelubricant.Theheaterconsistedof ametalfilm depositedonaface

of thering,afractionof amicrometerthick.Thefilm actedasanelectricalresistanceheater.

Thetemperaturereachedis directlyproportionalto the currentpassingthroughthe film.

Themainideawasto useaslittlecurrentaspossibleto reachanoptimaltemperature. The

temperaturehad to be high enoughto allowthe releaseof the oil, but alsobe within

reasonablelimits,which arethe temperaturea ball beatingis usuallyfacingin a space

mechanisms.A thermocouplewas attachedclose to the lubricator to monitor its

temperature.

Thein-situ,on-demandlubricatorwasattachedto theinnerringof theballbeating,

verycloseto theballsandtherace.No directcontactoccurredbetweentheballsandthe

lubricator.With the currentsystem,the retainerwasremoved,but the systemcouldbe

adaptedto anyconventionalballbeating.Theelectricalconnectionsof thelubricatorwere

linkedto apowersupply.It wasalwaysturnedonbutarelayallowedthecurrentto activate

NASA/TM--2002-211706 4
thelubricatorwhenthe torquereachedanupperthreshold,andto terminateit whenthe

torquewentbelowalowertorquelimit.Thestatusof thelubricatoranditstemperaturewere

continuouslymonitoredduringthe test.A secondconditionwas setup to stopa test.

Indeed,as the ball bearingstartedrunningwithout any oil, and becauseof thermal

conductivityof thedifferentelementsin contactto eachother,thetemperatureof theball

bearingincreased.Testswererunundervacuum,sotherewasnoconvectionto dissipatethe

heatgenerated.Thissecondconditionmustthenberelatedto thetemperature.Indeed,the

lubricatorbecameuselesswhentheballbearingtemperaturehascompletelyovertakenthat

of the lubricatorsincethe temperaturecannotbe controlledanymore.The temperature

thresholdof the ball bearingwassetat 50°C.Hereagain,the computerdataacquisition

(DAQ) and control systembasedupon LabVIEW ® was in charge of activating and

deactivating the in-situ, on-demand lubricator automatically.

The test was run at a speed of 200 RPM, with an axial load of 20 lb (89 N) in the

case of the NYE 2001. With Krytox 143AB, the selected speed was 420 RPM. These

conditions must be considered as very severe. Indeed, the ball bearing started operating

without any oil and without retainer. This last choice has created conditions of zero

entrainment velocity (ZEV) between some balls [46].

III- Results

1- Torque response

An initial test with an unlubricated ball bearing, and no lubricator was run as a

reference. It clearly appeared that the bearing was unable to last long in such severe

conditions. The torque trace is shown in Figure 3. The time allowed for the in-situ, ondemand lubricator to correct the failure clearly depends on the values of the thresholds to

activate and deactivate it. The higher the threshold to activate the lubricator, the less the

time left before failure, ranging between a few seconds, and almost one minute.

The test with the Krytox 143 AB showed that the cartridge was able to stabilize the

torque and to avoid the failure (Figure 4). The design of the lubricator was not optimum.

Indeed, the test had to be stopped because the ball bearing temperature reached the limit. In

this case, several points have contributed to have this test stopped: the design of the

lubricator was not correct, the speed was too high, and the upper torque limit (5 inch.oz) did

not allow enough time to the lubricator to be activated to correct the impending failure.

A second test was performed with the NYE 2001 oil. The design of the lubricator

was improved in this test. The speed was reduced to 200 RPM, allowing more time to the

lubricator to correct the failure (upper torque limit 2 inch.oz). As shown in Figure 5, the

torque remained stable and low enough to allow a modification of the limits to activate and

deactivate the lubricator, and showing that some oil had reached the ball bearing. The

lifetime compared to the unlubricated ball bearing was improved by a factor 10. While the

test was running, an attempt was made to show how efficient the lubricator was. The power

supply was voluntarily shut down for almost two hours. The torque progressively increased

(Figure 6) and became more and more unstable. Then the power supply was turned on again

and the lubricator active again. An immediate drop in the torque was observed. The torque

became stable immediately.

NASA/TM--2002-211706 5
2-Oil released

Theballbearingswereweighedbeforeandafterthetest.Thisgivesusanindication

onhow muchoilwastransferredfrom thelubricator.Theresultsaregivenin Table3.The

ballbearinggainedweight,andsometracesof oil werefoundontheringsandballsof the

mechanismafterthetest.Thein-situ,on-demandlubricatoris basedonapolyimideporous

structure.Becausethe humiditycouldnot be controlledduringthe testandcouldbe a

sourceof errorsin theweighingsof suchstructures[471, the weights of the lubricator before

and after the tests are not reported in this paper.

IV- Discussion

1- Physical phenomena

As shown in previous studies quoted in the paragraph 1-2 of this paper, the capillary

effects maintaining the oil within the pores of any porous reservoirs are usually strong

enough to avoid any release. One of the main differences between the in-sire, on-demand

lubricator system, compared to previous reservoirs developed for space mechanisms, is its

proximity to the tribological areas. Moreover, it appeared clear that some energy had to be

provided to the system to have the lubricant ejected.

The method chosen was the differential thermal expansion, because of its efficiency

and its ease of set up. The conductive metallic layer had a very high resistivity. The

knowledge of the current and the voltage applied allowed for the determination of the

energy provided, as well as the temperature reached. Since the lubricants and the porous

material have totally different thermal expansion coefficients, the quantity of oil removed

from the pores could be calculated. Moreover, the polyimide is not a good thermal

conductor compared to the oil. The oil was heated more quickly than the porous network

was. The lubricator was not activated all the time, so its temperature was not steady and the

in-situ, on-demand lubricator was allowed to cool down between cycles.

According to Figure 6, after 1000 s of test, the difference of temperature between the

oil and the ball bearing is nearly 10°C. We are assuming that the temperature of the ball

bearing is the same as the one of the porous network in which the oil is stored. This

assumption is based on the low thermal conductivity of both 440C stainless steel and of

porous polyimide, compared to the one of a fluid, and on the fact that the porous reservoir

is directly attached to the ball bearing. The oil volume "squeezed out" of the pores is given

by the following expressions:

goil = gpolyimid ....... ir'_'0 + (Xoil "AT) (1)

gp .... = gpolyimid ....... ir'0 q- O_polyimide .ATy mp°lyimid ....... ir (2)

P polyimide

AV T = Voi 1 - Vp .... (3)

Voil is the volume the oil occupied within the pores of the reservoir. Vpolyimid .......... ir is the

volume of the porous reservoir, defined by its geometrical dimensions. Vp ..... is the volume

occupied by the pores in the porous reservoir. The term mpolyimid........... ir is the mass of the

clean and dry porous reservoir before being impregnated with oil. AT is the expression of

temperature difference between the oil and the porous reservoir when the lubricator is

NASA/TM--2002-211706 6
activated.Onlyonefaceout of thefourfacesof theporousreservoiris heated,sowecould

considerthatonlyonefourthof theoil givenbytheequation3 aboveisreallyejectedfrom

thepores.Consideringa differencetemperatureof roughly10°C(Figure7), andusingthe

valuesfromTables1and2, thevolumeof oil releasedisnearly5.8mgin thecaseof theoil

NYE 2001.Thisvalueisextremelyhighcomparedto themassgainof theballbearinggiven

inTable3.Nevertheless, thisoil isnotanymorestoredintheporesandisnowavailableand

verycloseof therollingelements.

The first aspecto consideris the temperatureincrease.The ballbearingstarted

withoutanylubricant,soits temperaturenaturallyincreased.Thistemperatureincreasewas

transmittedto thelubricatorattachedto theballbearing,causingareleaseof oil,implying

thatthein-situ,on-demandlubricatoris self-sufficientin someway.Unfortunately,leaving

thesystemoperatingthiswaycouldcauseseveredamageto ballsandraces.

Thelubricatoris directlyattachedto theballbearing.It is clearthattheactivationof

thelubricatorwouldcauseanincreaseof thetemperatureof theballbearingandtheoilinit.

Whenthetesthasstarted,therewasnooil in theballbearing.Thus,thetorquestabilization,

observedin Figures4 to 6, is mainlydueto thereleaseof oil within themechanism.Not

much oil was released,explainingwhy the lubricatoris continuouslyactivatedand

deactivated(Figure6, lubricatorstatus).An explanationof the torquereductionwhenthe

lubricatoris activatedcouldbealsoa reductionof theoil viscositydueto thetemperature

increase.Nevertheless, accordingto theFigure7,thetemperatureof theballbearingwasin

a5°Crangeduringthetest,if wedidnottakeinto accounthebeginningof thetest.Sucha

variationof temperaturewill notcausealargechangein theviscosity.

Oncetheoil wasreleasedfromthepores,thereareseveralmeansto allowit to reach

thetribologicalareas.Firstisby evaporationandcondensation. In spiteof theirlow vapor

pressure,spaceoils evaporatea little, and their vapor pressureis greaterat higher

temperature. At thetemperaturethelubricatoreached,thereleasedoil temperatureishigher

thantheoneof theracesandtheballsaccordingto thetemperaturemonitoredin theball

bearing(Figure7).So,acondensationof vaporwasmorelikelyto occur.Furthermore,since

the porouscartridgeis very closeto the balls,condensationon othernon-tribological

surfacescouldbeavoided.

The secondpoint is the capillaryeffect.Oncethe oil is ejected,it will spreadand

reachaplacesuchasacornerwhereit will betrapped.In theconfigurationpresentedinthis

study,theonlyplacewheretheoil couldgois theplacetheporouscartridgeis attachedon

theinnerring.Theoil thenformsareservoirof lubricantandspreadslowlyon theraces.

This aspectcouldbea criticism,statingthatwhenthe heateris off, theporouscartridge

couldabsorbthelubricantpreviouslyejected,i.e.aporoussystemactingasa "well of oil,"

i.e., "a sponge" as quoted in the literature. This remark is valid only for the oil in the

immediate vicinity, or touching the cartridge. But it is less likely to occur to the oil on the

balls and on the races, which is moving. Nevertheless, if mechanisms had to face this

problem, with the consequences of a starvation regime and of an increase of torque, the

lubricator would be then activated and would correct the failure to come.

The wettability of the 440C stainless steel surface also helped spreading of the oil.

Both oils have a very low surface tension (Table 2), and the surface energy of the 440C

stainless steel is generally very high (2400 mN.m-' for pure iron) [48]. These values imply

that once the oil is in contact with a polished 440C stainless steel surface, spontaneous

spreading could be expected.

NASA/TM--2002-211706 7
Thelastphenomenoninvolvedto "drive"the oil towardtheballsandracesis the

Marangonieffect[25,26, 30, 31,49, riO],consistingof lubricantmigrationcausedby a

temperaturegradient.Indeed,sincetherigwasoperatingwithoutanylubricantontheballs

andtheraces,anincreaseof temperaturein thebearinghappens.But,oncethelubricatoris

activated,thetribologicalareasarecoolercomparedto it. Theoil is locatedin thewarmer

areaof atemperaturegradient.Thiscausesagradientin thesurfacetensionof thelubricant,

whichtendsto causeamigrationof oil to thecoolerarea.Generally,thiseffectisveryslow.

But comparedto mechanismswheretheracesaregenerallythe"warm" part of the gradient,

the in-situ on-demand lubricator causes an inversion of the thermal gradient. And what was

formerly a burden, and a cause of oil loss and starvation of the contact, the thermal gradient

is now driving the lubricant toward the tribological area.

In each of the last three situations described before, the lubricant is poured slowly

and in small quantity into the contacts, avoiding torque peaks.

2- Extension of the lifetime. Power consumed

All the phenomena described before occurred simultaneously and contributed to

providing the ball beating with oil in the tribological area when the mechanism was

approaching failure. They helped to maintain the torque at an acceptable level. Figure 6

shows that the lubricator was able to create a torque reduction when activated. It has also

demonstrated that in the case of a lubricated ball beating progressively reaching failure, the

mechanism could be returned to normal status. Compared to an unlubricated ball bearing,

there is obviously a gain in lifetime.

The test with the oil NYE 2001 was stopped manually after 5 hours, while the torque

was stable. It corresponded to an increase in lifetime of a factor 45 compared to the

unlubricated ball bearing. The test conducted with Krytox 143AB has led to an increase in

lifetime of nearly a factor 5.

Another factor is the power consumed by the in-situ, on-demand lubricator. This

parameter is critical in a spacecraft where the available power is always limited. The system

operated at a potential around 35 V and a current around 30 mA. This represents a total

power consumption of roughly 1.0 W. In the case of the test with the oil NYE 2001, the

lubricator was activated during a total duration of nearly 2200 s, corresponding to 0.61 W.h.

V- Conclusion

An in-situ, on-demand lubrication system was developed. The system was able to

correct a mechanism before failure occurred under conditions where the failure was more

likely to be fatal to the mechanism. The system, designed mainly for space applications, is

neither volume nor power intensive. The system can be easily extended to conventional ball

bearings used in applications where lubrication failure is a main concern.

The main objective is either to have a lubricant reservoir in a retainerless ball beating,

or a back-up system in a more conventional mechanism. Indeed, there is usually an initial

charge of lubricant in any mechanical assembly. A potential failure is generally very

progressive and can be detected. The in-situ, on-demand lubricator could be used in a critical

system to maintain the mechanism operational, and so extend its lifetime.

NASA/TM--2002-211706 8
References

1 Shapiro W., Murray F., Howarth R., Fusaro R. "Space Mechanisms Lessons Learned Study. Volume 1:

Summary". Cleveland (Ohio): National Aeronautics and Space Administration, 1995. 227 p. NASA TM

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2 Shapiro W., Murray F., Howarth R., Fusaro R. "Space Mechanisms Lessons Learned Study. Volume 2:

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3 Jones, W. R. Jr., Jansen, M. J. "Space Tribology", Modern TriboloD_ Handbook Vol. II, pp 1159 1181, CRC

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6 Zaretsky E. V. "Liquid Lubrication in Space". Tribology International, volume 23, n°2, April 1990. pp. 75 93.

7 Carr_ D. J. Proceedings of the 8th European Space Mechanisms and Tribolog T Symposium, Toulouse, 29

September 1st October 1999. Noordwijk (Netherlands): ESA Publications Division, 1999, pp. 29 33.

8 Bertrand P.A., Carr_ D.J., Bauer R. Tribology Transactions, vol. 38 (1995), n ° 2, pp. 342 352.

9 Bertrand P.A., Carr_ D.J. Tribology Transactions, vol. 40 (1997), n ° 2, pp. 294 302.

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11 Morgan V. T., Cameron A. "Mechanism of Lubrication in Porous Metal Bearings". Proceedings of

Conference Lubrication and Wear. London (England), October 1957. pp. 151 157.

12 Schulien H. E. "Skylab Control Moment Gyro: a Description of the Inner Gimbal and Rotor Assembly and

its Lubrication System". Proceedings of the International Bail Bearings Symposium, Cambridge

_[assachusetts), 5 7 June 1973. pp. 1 27.

13 Rockhower B. "Centrifugal Wiper Lubrication of Full Complement Ball Beatings". Proceedings of the

International Ball Bearings Symposium, Cambridge (Massachusetts), 5 7 June 1973. Article E 2776.

14 Sturtivant G. J. "Results of a 10 Nms Reaction \Vheel Test Program, Including Tests on a Nylon Pore

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Meersburg (Germany), 9 11 October 1985. Noordwijk (Netherlands) :ESA, 1985. pp. 273 279.

15 Granzow M. "Tribological Design of Medium Speed Mechanism (MSM) for Despin Antennas". Proceedings

of the 1_*European Space Tribology Symposium, Frascati, Italy, 9 11 April 1975. pp. 351 356.

16 Glassow F. A. "Despin Bearing Technology and Applications for Communications Satellites". 3"dConference

of American Institute of Aeronautics and Astronautics (Communications Satellite Systems), Los Angeles

(California,), 6 8 April 1970. pp. 129 150.

17 Allen T. "Optical Chopper Assembly for the Mars Observer". Proceedings of the 2_ h Aerospace Mechanisms

Symposium, Moffet Field (California), 12 14 May 1993. pp. 165 173.

18 Voss T. Lt., Singer H. B. "G 200 Bearing TechnoloDT Improvement Program". Proceedings of the

International Ball Bearings Symposium, Cambridge (Massachusetts), 5 7 June 1973. Article E 2764.

19 Kissel J. W., Snediker D K. "A Study of Friction Characteristics of Some Porous Bearing Cage Materials".

ASLE Transactions, 1978, volume 21, n ° 4, pp. 307 314.

20 Christy R. I., Meeks C. R. "Polyurethane Retainers for Bail Bearings". Proceedings of the International Ball

Bearing Symposium, Cambridge _[assachusetts), 5 7 June 1973. pp. 1 21.

21 Meurisse M. H., Giudicelli B. "A 3D Conservative Model for Sel£Lubricated Porous Journal Bearings in a

Hydrodynamic Steady State". Journal of TribologT, 1999, volume 121, n ° 3, pp. 529 537.

22 Marchet6 M.,. Meurisse M. H, Vergne P., Sicre J., Durand M. Proceedings of the 26th Leeds Lyon

Symposium, Leeds, 5 8 Sept. 1999, pp. 777 786

23 Marchet6 M., Meurisse M. H. Vergne P., Sicre J., Durand M. Proceedings of the International Tribology

Conference, Nagasaki, 29 Oct. 2 Nov. 2000, pp. 1427 1432.

24 Jamison W. E. "Applications of Microporous Polymer Lubricants". Lul)rication Engineering, 1982, volume

38, n°12, pp. 758 761.

25 Liu Jianhai, Fan Youwen, Wen Shizhu. "An Experimental Study on Oil Supply in a Space Bearing with an Oil

Impregnated Retainer". Wear, 1993, volume 165, n ° 2, pp. 193 196.

NASA/TM--2002-211706 9
26 FoteA.A."SfigrationofApiezonConMetalSubstrates undertheInfluenceofTemperature Gradients:

Mathematical Model".E1Segundo(California). TheAerospaceCorporation, 1975.25p.Reportn°ADA

019665.

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Migration". E1 Segundo (California). The Aerospace Corporation, 1977.14 p. Report AD A 048716.

29 Fote A. A., Slade R. A., Feuerstein S. "Surface transport of Oil in the Presence of Nylasint and Micro Well

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31 Prat P. "Rapport de Synth&se. Etude Bibliographique: R_alimentation de M_canismes LubrifiEs en Ambiance

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32 Slade R. A., Fote A. A., Feuerstein S. "Thermally Induced _figration of Apiezon C. The Effects of Vacuum

and Surface Finish". E1 Segundo (California). The Aerospace Corporation, 1976. 31 p. Report n°AD A

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35 Kato, K., Kim, H., Adachi, K., Furuyaman, H. "Basic Study of Lubrication by Tribo Coating for Space

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36 Adachi, K., Kato, K., Oyamada, T. "Tribo Coating for Friction Control in Ultra High Vacuum". Inter. Symp.

For High Perf. Tribo., Taegu, Korea, pp 61 65, May 29 30, 1998.

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Mechanisms". (TM to be published)

38 Jansen, M. J., Jones, w. R., Jr., Pepper, S. V., Predmore, R. E., Shogrin, B. A., "EHL Transition Temperature

Measurements on a Geostationa U Operational Environmental Satellite (GOES) Filter Wheel Beating",

NASA TM 2001 210670, January 2001.

39 Konchits, V. V., Myshkin, N. K., "Evaluation of the Interface at Boundary Lubrication Using the

Measurement of Electric Conductivity". Wear, 172, 29 40, 1994.

40 Kingsbury E. P. "Ball Ball Load Carrying Capacity in Retainerless Angular Contact Bearings". J. of Lub.

Tech. 104, (1982), pp. 327 329.

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22 24 April 2002, pp. 86 93.

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Cambridge (Massachusetts). The Charles Stark Draper Laborato_-, 1973.25 p. Report MITE 2767.

43 Powers C. E. "The Advanced Microwave Sounding Unit A, Antenna #2 Bearing Assembly Life Test".

Proceedings of the 31 _ Aerospace Mechanisms Symposium, Huntsville (Alabama), 14 16 May 1997.

pp. 71 83.

44 Prat P., Suzuki M., Matsumoto K. "Outgassing and lifetime Performance of Bearings Impregnated with Space

Lubricants". Proceedings of the Japanese Spring Meeting for TriboloDT, Tokyo, Japan, 11 13 May 1998.

pp. 505 507.

45 Singer I. L. "Solid Lubrication Processes", pp. 237 261, in "Fundamentals of Friction: Macroscopic and

Microscopic Processes", edited by Singer I. L., Pollock H. M., NATO ASI Series, Series E: Applied Science

Vol. 220.

46 Shogrin B. A., Jones W. R., Jr., IZingsbu_- E. P., Jansen M. J., Prahl J. M. "Experimental Study of Load

Carrying Capacity of Point Contacts at Zero Entrainment Velocity". Cleveland (Ohio): National Aeronautics

and Space Administration, October 1998. 12 p. Report NASA TM 1998 2088650.

47 Bertrand P. A. "Absorption of Water and Lubricating Oils into Porous Nylon". E1 Segundo (California). The

Aerospace Corporation, 1995. Report n ° NASA CR 197344.

48 IsraelachviliJ. N. "Intermolecular and Surface Forces". Orlando: Academic Press Inc., 1985, 450 p.

49 Prat P. "Contribution 5 l'Etude de la Lubrification Fluide en Ambiance Spatiale. Approche Exp&imentale de

la Rfialimentation". Thesis: Institut National des Sciences Appliqufies de Lyon (France), 14 Februa_- 1997.

169 p. (n ° 97 ISAL0018).

NASA/TM--2002-211706 10
50 MarchetdM."Aspectsglobauxetlocauxdelamiseenoeuvre de la lubrification fluide en ambiance spatiale".

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(n ° 00 ISAL0082).

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Inc., 1972. 764 p. ISBN 0 486 65675 6.

52 Space Tribolog T Handbook, European Space Tribology Laboratory (s.1.) editor, 1997.

Table 1: Properties of the pot(

average pore radius (grn)

,us polyimide [50]

0.5

porosity _ (%) -_ 25

permeability (m 2) 2.1.10-15 * [51]

density ppolyimide (g.cm -3) -_ 1.5

thermal expansion coefficient

_,polyimide (°C-l) 4"2"10-5

reservoir volume

Vpolyimid ....... ir (cm 3) -_ 0.375

mass of the clean and dry reservoir

-_ 0.428

mpolyimid ....... ir (g)

• value obtained using the l<ozeny (2arman expression of the _ermeability

viscosity (Pa.s)

Table 2: Properties of the lubricants

NYE 2001 [521

0.270 (20°C)

0.090(38°c)

1.4.10 -4 (100°C)

Kryox 143AB [52]

vapor pressure (Pa)

surface tension (mN.m -1) -_ 31.0 -_ 21.0

thermal expansion

._ 2.6.10-2 ._ 9.5.10-3

coefficient {]{oil (°C-1)

0.230 (20°C)

0.085(38°c)

5.0.10 -4 (38°C)

oil tested

Krytox

143AB

Table 3: Mass evolutions of the ball beating

before the test

mass of the dry

and clean ball

bearing (g)

14.07342

mass of ball

bearing (g)

14.07610

after the test

mass of oil

gain (btg)

+268

cause of the

end of the test

ball beating

temperature

exceed 50°C

manual

Nye 2001 14.07250 14.07331 +81 shutdown

NASA/TM--2002-211706 11
Drive

Slip Ring

Assembly

Test Section

.d

In-Line

Torque Meter

nd Bearing

Figure 1: GOES rig

full complement ball-bearing

heater position (lower surface)

Figure 2: Lubricator attached to the inner ring of a full-complement ball bearing

NASA/TM 2002-211706 12
©

.d

¢.)

<D

2

11

10

9

8

7

6

5

4

3

2

liner to activate tile lubri_m¢ = 5 illeh.oz

o _ ' ' time (s)

0 100 200 300 400

-- torque

Figure 3: Torque trace of a non lubricated ball bearing and time left for the in-sltu, on-demand

lubricator to correct the failure (load: 20 lb, speed: 200 RPN D

NASA/TM 2002-211706 13
12

©

_d

¢.)

<D

2

11

10

9

off

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

time (s)

--torque ,, lubricator status

Figure 5: Torque trace of ball bearings (load: 20 lb, speed: 200 RPN D with in-situ, on-demand

lubricator with NYE 2001

©

_d

¢.)

<D

2

11 ......

10 ......

supply c

9

8

7

6

5

4

3

2

1

0 : : i i , off

13000 14000 15000 16000 17000 18000 time (s)

--torque ,, lubricator status

Figure 6: Torque trace of ball bearings (load: 20 lb, speed: 200 RPN D with reactivation of the

in-situ, on-demand lubricator with NYE 2001

NASA/TM 2002-211706 14
C

8

<D

50

40

30

20

10

/\ •

/ "%,i ........

• • ,, • •

• , .

power supply >ff

--: _xxxxxxxxxxxxxxxxxxx off

5000 10000 15000 20000

time (s)

--ball bearing temperature ....... lubricator temperature ,, lubricator status

Figure 7: Temperature of the lubricator and of the ball bearing during the test

with the oil NYE 2001

NASA/TM 2002-211706 15
Form Approved REPORT DOCUMENTATION PAGE

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

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

July 2002 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

In-Situ, On-Demand Lubrication System for Space Mechanisms

6. AUTHOR(S)

Mario Marchetti, William R. Jones, Jr., Stephen V. Pepper, Mark J. Jansen, and

Roamer E. Predmore

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

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135-3191

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

National Aeronautics and Space Administration

Washington, DC 20546-0001

WU-274-00-00-00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-13454

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--2002-211706

11. SUPPLEMENTARY NOTES

Prepared for the 2002 Annual Meeting sponsored by the Society of Tribologists and Lubrication Engineers, Houston,

Texas, May 19-23, 2002. Mario Marchetti, William R. Jones, Jr., and Stephen V. Pepper, NASA Glenn Research Center;

Mark J. Jansen, SEST, Inc., Middleburg Heights, Ohio 44130; Roamer E. Predmore, Goddard Space Flight Center,

Greenbelt, Maryland 20771. Responsible person, Mario Marchetti, organization code 5960, 216-433-5843.

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category: 27 Distribution: Nonstandard

Available electronically at http:/Igltrs.grc.na_sa.gov/GEI'RS

This publication is available from the NASA Center for AeroSpace Information, 301-621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Many of today's spacecraft have long mission lifetimes. Whatever the lubrication method selected, the initial lubricant

charge is required to last the entire mission. Fluid lubricant losses are mainly due to evaporation, tribo-degradation, and

oil creep out of the tribological regions. In the past, several techniques were developed to maintain the appropriate amount

of oil in the system. They were based on oil reservoirs (cartridges, impregnated porous parts), barrier films, and labyrinth

seals. Nevertheless, all these systems have had limited success or have not established a proven record for space missions.

The system reported here provides to the ball-race contact fresh lubricant in-situ and on demand. The lubricant is stored in

a porous cartridge attached to the inner or the outer ring of a ball bearing. The oil is released by heating the cartridge to

eject oil, taking advantage of the greater thermal expansion of the oil compared to the porous network. The heating may

be activated by torque increases that signal the depletion of oil in the contact. The low surface tension of the oil compared

to the ball bearing material is utilized and the close proximity of the cartridge to the moving balls allows the lubricant to

reach the ball-race contacts. This oil resupply system can be used to avoid a mechanism failure or reduce torque to an

acceptable level and extend the life of the component.

14. SUBJECT TERMS

Space mechanisms; Lubrication

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

NSN 7540-01-280-5500

15. NUMBER OF PAGES

21

16. PRICE CODE

18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

OF THIS PAGE OF ABSTRACT

Unclassified Unclassified

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102