ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
387 Conclusion 

The radiometric performance of the BESST instrument  meets the science requ irements for SST studies  for a much lower cost and with better spatial resolution. The accuracy of the mi crobolometer temperature  readings are 0.09° C and the accuracy of the overall instrument is 0.3 °C for individual pixels. The  temperature accuracy and spatial re solution can be traded off:  more pixels can be averaged to achieve  better accuracy, but at the cost of lower spatial resolution. This is done during post-processing of the data  and will be explored further as part of continued scientific demonstrations.   Laboratory and flight testing of the BESST radiometer have show n it to be a valuable complement to shipborne SST instruments. In addition to performing calibration / validation activities for satellite SST sensors, BESST can perform measurements with higher spatial resolution and repeat area coverage than currently available instruments. The lightweight, modula r design is responsible for these advantages as it  allows the instrument to be deployed on a UAV platfo rm in a configuration suitable to each mission.   

Acknowledgements   The authors wish to acknowledge the help and suppor t of Ray Demara, Paula Wamsley, Shelley Petroy  and the Airborne Initiative group at Ball Aerosp ace. Also the hard work of numerous engineers,  technicians and interns including Paul Kaptchen, Raymund To, Tony Lin and James Lasnik as well as Brian Johnson, Michele Kuester, Jennifer Turner-Val le, Kartik Ghorakavi and Julie Sandberg. A special  thanks to Dr. William Emery of the University of Co lorado for scientific guidance with respect to SST  measurements and requirements.   References 

Brunke, M.A., X.B. Zeng, V. Misra, and A. Beljaar s, 2008: Integration of a prognostic sea surface skin  temperature scheme into weather and climat e models. J. Geophys. Res., 113, D21117.   Fairall, C.W., E.F. Bradley, D.P. R ogers, J.B. Edson, and G.S. Young,  1996: Bulk parameterization of airsea fluxes for TOGA COARE. J. Geophys. Res., 101, 3747-3767.  Fairall, E.F. Bradley, J.S. Godfrey, J.B. Edson, G.S. Young, and G.A. Wick, 1996: Cool skin and warm  layer effects on the sea surface temperat ure. J. Geophys. Res., 101, 1295-1308.   Fairall, C. W., E. F. Bradley, J. E. Hare, A. A. Grac hev, and J. B. Edson, 2003: Bulk parameterization of  air-sea fluxes: Updates and verification for the COARE algorithm. J. Clim., 16, 571-591.   Zeng, X.B., and A. Beljaars, 2005: A prognostic scheme  of sea surface skin temperature for modeling and  data assimilation. Geoph ys. Res. Lett., 32, L14605.     NASA/CP-2010-216272
389 Development of an Actuator for Ambient to Cryo Application  

Karen Menzel*, Hans Jürgen Jung* and Jörg Schmidt** 

Abstract 

During the qualification campaign of the NIRSpec In strument Mechanism, the ac tuator could not achieve  the expected life time which was ex tended during the development phase. The initial design could not be  adapted to the requested number of  revolutions during that phase.   Consequently the actuator needed to be modified such that the function of the mechanism would not be  endangered and thus the overall function of the NIRS pec instrument. The modification included the  change of the overall actuator design - internal dimensions, tolerances, materials, lubrication and  assembly process - while keeping the inte rface to the mechanism, mass, and function.   The lessons learned from the inspection of the failed actuator have been implem ented in order to ensure  the development and qualification succe ss. The initially available time for this activity was in the range of  6 months to meet the overall program schedule. 

Introduction 

The actuator consists of a three-stage gearbox fl anged to a stepper motor. A lever connected to the  actuator by an eccentric mechani sm moves the upper sled of the Refocusing Mechanism Assembly  (RMA), an optical NIRSpec subunit carrying highly sensitive mirrors (see Figure 1).   

Figure 1: Refocusing Mechanism Assembly   The high non-operational temperature range of 296K as  well as the low operational temperature of 30K  requires a special design considering the great ther mal expansions between 27K and 323K as well as a  proper material selection that deals with the change  of mechanical properties at cryogenic temperatures.  Both the new material concept and the molybdenum disulfide (MoS 2) lubrication coating confronted the  engineers with unexpected effects                                                     * EADS Astrium GmbH Satellites , Friedrichshaf en, Germany  ** PHYTRON-Elektronik GmbH, Gröbenzell, Germany 

Proceedings of the 40th Aerospace Mechanisms Symposium, NASA Kennedy Space Center, May 12-14, 2010  NASA/CP-2010-216272
391      

   Figure 3: Lubrication failure of first actuator after life test1 

 Motor current measurements during the life test dem onstrated that the actuator lubrication would have  survived the nominal life time but due to life time extension, the results as  described above have been  obtained.  Similar actuators have been successfully used in gr ound-based cryo applications, but in areas where an  exchange of a failed actuator can be performed at any time.  

Design of the New Actuator   Figure 4 represents the new actuator in cross section, the main design was kept in general but the rear  motor bearing was substituted by larger duplex beari ngs. The rotor axial pre-load spring was moved from  the front duplex to the rear bear ing. Ideally the front duplex bearin gs of the motor should have been  arranged in 0-orientation to allow a limited rotation of t he rotor axis (iso-static support conditions). Due to  assembly constraints, an X-arrangement had to be sele cted in combination with an increased play of the  rotor axis rear bearing. The planetary gear with  three stages still has a gear ratio of 184:1.                                                    1 Visible corrosion results from the exposure of the blank metal to air after disassembly of the actuator.  NASA/CP-2010-216272
392    Figure 4: New Design RMA Actuator 

The material concept was changed significantly to a CTE-consistent design as increased friction and raised bearing loads are supposed to be at least part of the reason for the first actuator’s failure.   As Figure 5 illustrates, all motor and gearbox parts except the sc rews are manufactured of either  hardened Cronidur ® (X30) or titanium, the higher CTE of t he screws only results in behavior comparable  to extension bolts, and the machining of well known ma terial for these critical functional components  minimizes risks.  

Figure 5: New Material Concept 

Coating for Solid Lubrication 

After the failure of the Dicronite co ating during life test, a solid lubricant  concept had to be selected that is  well known for space applications due to the short time frame of development. Sputtered molybdenum disulphide (MoS 2) seemed to be the most suitable lubricant as it has proven its reliability in numerous  space applications. In order to have a backup soluti on during the development program, a lead lubricated  breadboard model was set up, tested and compared to the MoS 2-coated model before starting the  Qualification program - this developme nt approach is explained later on.  NASA/CP-2010-216272
394 Pre-QM1 is MoS 2 lubricated and contains bushings of Vespel SP1, Torlon and planet axes without  bushings according to Figure 6. Pre-QM2 is lead lubric ated with bushings of lead bronze assembled or no  bushings, respectively (Figure 7). If no bushing is as sembled on one of the planet axes, a distance ring is  necessary to prevent the appropriate planet gear from moving along the axis. 

     Figure 6: Pre-QM1 design (MoS 2 lubricated) 

Figure 7: Pre-QM2 design (Lead lubricated) 

These breadboard models have been manufactured first and the FM1 production has been started during their test campaign as displayed in Figure 8. Indee d the FM1 has been assembled into the subunit at a  time the actuator has not been fully qualified – as the Pre-QM1 and FM1 are not assembled completely  identical and the Pre-QM life test was in some ways simplified but equivalent at the best.  

Figure 8: Development concept and success oriented approach     Life Test Pre-QMs   As the Pre-QMs had to be life tested without being int egrated into the RMA, an equivalent test set-up had  to be designed in order to load the actuators correctly.  Springs connected to a disc (Figure 9) load the act uators with the torque corresponding to the load the  real blades are generating in the RMA mechanism. Figure 9 illustrates that the maximum torque at 120°  from launch position and the load represented by the spring set-up is very accurate. 

NASA/CP-2010-216272
395      Figure 9: Pre-QM Life Test (left), Load appli cation during life test by spring assembly (right) 

The cryogenic temperature during Pre-QM life test wa s not 30K (liquid helium) but 80K (liquid nitrogen)  due to facility reasons. This temperature is justified by the fact that neither the shrinking nor the change in material properties between these two temperatures is high compared to their absolute values.  

Figure 10: Results of Pre-QM life test 

     Figure 11: MoS 2 Gearbox inspection after life test   The expected life time of the RMA actuator is about 400,000 motor revolutions including ECSS margins. As Figure 10 illustrates, in the case of Pre-QM1 the so called success current - indicating the friction –  does decrease during life time up to the end of life test at about 430,000 motor revolutions. The MoS 2  coating seems to be properly run in at this time . Lead coated Pre-QM2 showed some degradation starting  between 320,000 and 380,000 motor revolutions, but is still within the ECSS success criteria at end of  0100200300400500600 0 20 40 60 80 100 120 140 160 180 200 ϕ [°]Torque [mNm]Life-Test-Torque required Torque (Spring) Pre-QM1 life test success current 051015202530354045 I [mA] 050100150200250300350400450 k-cycles current [mA] amb current [m A] cryo k-cyclesPre-QM2 life test success current 010203040506070809010 0 I [mA] 05010 015 0200250300350400450 k-cycles current [mA] amb current [m A] cryo k-cycles NASA/CP-2010-216272
396 life. The detailed visual inspection of the bushings (Figure 12  and Figure 13) did not show significant  differences in abrasion on bushings made of Vespel SP1 and Torlon.  

   Figure 12: Pre-QM1 Vespel SP1 Bushing and Distance Washer after life test 

   Figure 13: Pre-QM1 Torlon Bushing and Distance Washer after life test   These test results provide high confidence in the selected material co mbination. Flakes of coating have  been delaminated during vibration (this issue is explained later in detail) from gear teeth on planets, suns  and hollow wheel. This damage did not affect the gear-box’s performance, the su rfaces look smooth and  properly run in after life test (Figure 11) and XRF measurement at ESTL revealed a remaining MoS 2 layer  of at least 0.14 microns.   The visual inspection of the lead-coated Pre-QM 2 gearbox revealed as well a good condition with no  evidence of metallic wear of the steel surfaces. XRF measurements confirmed that lead remained on the gear teeth but that in several areas it was extremely thin. Examination of the thickness values show that  in all but one case the minimum thickness was less than 0.1 µm, being as low as 0.03 µm in one case. However, it should be stressed that ve ry little lead is required – particularly on polished steel surfaces - to  provide effective lubrication.       Figure 14: Lead-coated gearbox and lead-bronze bushing after life test 

As with the MoS 2-lubricated gears, the wear of the lead coatings was uneven across the teeth. This is  illustrated in Figure 15 for a planetary gear from Stage 3 where it can be seen that the lead coating in the center of the tooth is virtually unw orn whereas elsewhere wear of the lubricant has clearly taken place.  NASA/CP-2010-216272
397   Figure 15: Uneven distribution of remain ing lead coating on the planet teeth 

It was also apparent that lead had transferred during tooth-to-tooth contact leaving patches where the  thickness of the lead was greater than the thickness of the coating as initially applied. This effect  accounts for the relatively large patch width (>2 mm)  occasionally observed. It should be noted that lead  transfers more efficiently than MoS 2 – a fact consistent with the observation that no anomalously high  coating thicknesses were observed for the MoS 2-lubricated gears. 

Technical Difficulties and Challenges   Planet carriers and gearbox housing

The initial approach was a design containing some  parts made of unhardened Cronidur®, namely the  planet carriers and th e gearbox housing. It is impossible to shrink-fit hardened pins onto hardened  carriers and the risk of deformation due to hardening of the hollow wheel ( → ovalization) was supposed to  be too high. But Cronidur® is not corrosion-resi stant in the unhardened c ondition and therefore a  substitution of the material or heat treatment had to be considered.   

Figure 16: Failed pressing trial results   To replace the Cronidur ® the planet carriers have been manufacture d from titanium and extensive trials  have been performed in order to identify the necessa ry oversize for press fit to transmit the required  torque loading to the sun wheel on the one hand but not to exceed the ultimate strain of about 7% of titanium (Figure 16 and Figure 17). In the case of  the gearbox housing, a material substitution has been  widely discussed with many experts but the number of materials in the same CTE range of Cronidur ® is  very limited.  

Figure 17: Passed pressing trial results with 40 µm oversize  NASA/CP-2010-216272
398 Using titanium for the gearbox housing is out of the question as the gear supplier is not able to cut the  internal gear from titanium. The steel 17-4PH has been considered to be an alternative but due to its  sensitivity against stress corrosion cracking its us age would have required advanced fatigue analyses.    Sticking to the previo us concepts still offers tw o opportunities:  harden the en tire gearbox housing (Figure  18 right) or manufacture a hollow wheel ring from Cronidur ® (Figure 18 left), harden it and assemble it in  an integrated design to a titanium housing (Figure 18 middle). Both methods have been tested; entire  gearbox and hollow wheel ring have been hardened and 3D-measured afterwards with the following result: the hollow wheel was ova lized but the gearbox stayed stable! 

Figure 18: Hollow wheel ring and integrated design vs. gearbox housing completely   made of Cronidur®    Influence of surface quality on coating adhesion 

As indicated previously, both Pre-QM1 and FM1 showed signs of coating delamination on the gear teeth  of planets, sun wheel and gearbox housing after vibration test, which was detected during subsequent inspection (Figure 19). This finding raised two main questions:   1. Does a remaining layer of MoS 2 still exist on the gear teeth and is therefore the lubrication  sufficient?  2. How can the generated particle s be prevented from emerging fr om the gearbox and possibly  contaminating optical equipment on the instrument? 

Figure 19: Coating damage after vibration   Investigations at ESTL revealed a minimum MoS 2 layer of 0.14-micron thickness existing on the affected  surfaces and the successful Pre-QM1 life tests supports the confiden ce in the coating quality. But  nevertheless an investigation has be en started in order to find out whether the chosen pre-treatment  electropolishing and the defined surface roughness represent indeed the ideal parameters.    Samples have been manufactured with varying surface qualities between 0.1 micron and 0.5 micron as well as electropolished / not electropolished. The deflat ing conclusion of the pin-on-disc test following the  NASA/CP-2010-216272
401 Development and Acceptance Testing of the Dual Wheel Mechanism for the  Tunable Filter Imager Cryogenic Instrument on the JWST 

Martin Leckie* and Zakir Ahmad 

Abstract 

The James Webb Space Telescope (JWS T) will carry four scientific instruments, one of which is the  Tunable Filter Imager (TFI), which is an instrument  within the Fine Guidance Sensor. The Dual Wheel  (DW) mechanism is being designed, built and tested by COM DEV Ltd. under contra ct from the Canadian  Space Agency. The DW mechanism includes a pup il wheel (PW) holding se ven coronagraphic masks  and two calibration elements and a filter whee l (FW) holding nine blocking filters.     The DW mechanism must operate at both room temperature and at 35K. Successful operation at 35K comprises positioning each optical element with the required repeatability, for several thousand occasions  over the five year mission.     The paper discusses the results of testing geared mo tors and bearings at the cryogenic temperature. In  particular bearing retainer design and PGM-HT mate rial, the effects of temperature gradients across  bearings and the problems associated with cooli ng mechanisms down to cryogenic temperatures. The  results of additional bearing tests are described that  were employed to investigate an abnormally high  initial torque experienced at cryogenic temperatures. T he findings of these tests, was that the bearing  retainer and the ball/race system could be adversely affected by the large temperature change from room temperature to cryogenic temperature and also the temperature gradient across the bearing. The DW  mechanism is now performing successfully at both r oom temperature and at cryogenic temperature. The  life testing of the mechanism is expected to be completed in the first quarter of 2010.   

Introduction 

The TFI, which includes the DW mechanism, is shown in Figure 1 (labelled “Filter Wheel Assembly”). The TFI has been designed to provide infra-red narrow band imaging in the 1.5 to 5 micrometer wavelength range. In order to make these observations, it  has stringent temperature requirements. The TFI  temperature is approximately 35K for JWST science observations.       The role of the DW mechanism is to place optical el ements into the optical path, in any combination of  corona graphic mask and blocking filter. The optical elements must be placed accurately and in a highly  repeatable manner.   The paper discusses the following topics. First, the desi gn of the DW is described in some detail so that  the function of each component is clarified for the r eader. Secondly, the test results of component parts  and the DW assembly are described in more detail.  The geared motor test results are described first and the bearing tests second. The bearing tests revealed an abnormally high start up torque, at cryogenic temperatures, which led to an in depth investigation of this issue.                                                        * COM DEV Ltd., Cambridge, Ontario, Canada 

Proceedings of the 40th Aerospace Mechanisms Symposium, NASA Kennedy Space Center, May 12-14, 2010  NASA/CP-2010-216272
402                     Figure 1. Fine Guidance Sensor – TFI Side 

The high initial start up torque at 35K of the bearing s was attributed to three causes. The first cause was  mitigated by a retainer design change. The sec ond and third causes have been investigated and  understood, such that confidence in the flight de sign is high. The results of the investigation are  presented, together with the lessons learned from the problem. Finally, the results of the flight model  testing are discussed.  

Design Description 

A general arrangement of the DW mechanism is shown in Figure 2. The main components are the pupil  and filter wheels, bearings, gears, static hub, motor/ resolver support plate and the support bracket. The  DW mechanism also includes geared stepper motors, re solvers and variable reluctance sensors. A cross  section of the DW mechanism is shown in Figure 3.  Each wheel (approximately 280-mm diameter) rotates  on a duplex pair of angular contact preloaded bearings.   A stepper motor is used to drive each wheel, through a reduction gear train. The stepper motor has been  geared down to enable the positional accuracy requirements for each optical element to be met. A resolver provides feedback to confir m that each wheel is in the correct position. Flight software uses the  resolver reading to calculate a position adjustment to bring the wheels to the correct position.   All moving parts are lubricated with MoS 2 dry lubricant to be compatible with the cryogenic temperature  requirements. The wheels (the bearing housing) and the hub (the bearing shaft) were machined from titanium Ti-6Al-4V. The selection of titanium alloy was dictated by a requirement for low mass and also to closely match the coefficient of thermal expansion (C TE) of the 440C stainless steel bearings.      The bearings were manufactured by ADR of France, with the MoS 2 dry lubricants and the PGM-HT  retainer added by ESR Technology in the UK. The bear ings are located at the center of gravity of each  wheel in order to reduce the bending moments acting on the bearings during launch. The bearing size, ball diameter, and preload are designed to balance the critical requirements – high enough preload to meet the stiffness requirement, but still low eno ugh to allow low running torques and stresses.       NASA/CP-2010-216272
403               

        Figure 2. Dual Wheel Mechanism – General Arrangement 

Each bearing is secured in place with clamping nuts.  Each nut includes a flexure, which is preloaded by  the action of torquing the nuts into place. The flexur es maintain the preload on the bearings, despite the  slight difference in the coefficient of therma l expansion between the 440C bearings and titanium  housings. The PW bearing installation is shown in det ail in Figure 4. The FW bearing installation is  similar.    The bearing “fits” to the wheel and hub are sized so t hat a line on line to a clearance fit is obtained at the  mechanism operating temperature range of 35K. The se lection of a small clearance fit at the cryogenic  temperature, necessitates that an interference fit between the bearings and shafts exist at room  temperature, at the outer diameter. The use of a clearance fit at the cryogenic temperatures is to  eliminate bearing race distortion, which could cause va riations in bearing preload. The bearing fits were  verified using a bread board model (BBM) filter wheel mechanism, tested at 35K. The BBM also served to determine bearing torque at 35 K and to determine a suitable baseline for the motor drive current.   The PW and the FW wheel are each rotated via a pinion and ring gear. The pinion gears are made from stainless steel 13-8 PH and the ring gears are m ade from stainless steel 17-4 PH. Both gears are  lubricated with MoS 2 dry lubricant. The gear tooth size was evaluated using AGMA standards for tooth  contact stress and tooth bending stress.   Resolver –  Pupil Wheel Filter Wheel  Geared Motor -  Pupil Wheel Pupil Wheel  Resolver – Filter Wheel  Geared Motor –  Filter Wheel  NASA/CP-2010-216272
404 Filter Wheel  Pupil Wheel Ring  Gear  Filter Wheel  Ring Gear Pupil Wheel Pupil Wheel Variable Reluctance Sensor   Pupil Wheel Geared Motor  Filter Wheel Resolver Filter Wheel  Variable Reluctance   Sensor    (Filter Wheel)  Filter Wheel Duplex Bearing Pupil Wheel Duplex Bearing  

           Figure 3. Dual Wheel Mechanism – Cross Section 

The gear ratios were selected to give the desired si ze of granularity of movement of the PW and FW  wheel and to reduce same tooth encounters between the pinion gear teeth and the ring gear teeth. 

Each wheel is driven by a geared motor. The geared moto r drives a pinion gear, which meshes with each  ring gear. The geared motor was procured from CDA Intercorp and is comprised of an 8 pole, 3 phase stepper motor, having a 15° step angle and a planetar y gear stage having a ratio of 9.6:1. The geared  motor bearings and planetary gears were lubricated with Ball Aerospace MoS 2 lubricant.      NASA/CP-2010-216272