ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
The vibration test consisted of a pre low level sine sweep, a 14.1-grms GEVS specification random  he thermal vacuum test was run as follows:   a hard vacuum; the valves were cycled 5 times at each  /g120  + 225°C in a CO 2 atmosphere at 10 kPa (100 mBar); the valves were  he failure with the position sensor was discovered during the TV testing, so the life test was not run on   second batch is about to begin its qualification testing as soon as possible. This batch will undergo the  dditionally, a multitude of component testing was perform ed over the last two years, including, but not  Conclusion  he Microvalve has gone from a research and development effort to a flight design in the past three and a  Acknowledgements  he author would like to acknowledge Marvin Noreiga, Bob Abell, Brett Louis, Yury Flom, Russell Rowles, vibration, a 60-g sine burst, and a post low level sine sweep.  T /g120 Eight cycles from -60°C to + 225°C at extreme and leak testing  Eight cycles from -60°C to cycled 5 times at each extreme and leak testing  T this batch of valves.  A full suite of tests, including life testing. The random vibration levels will be higher since the test levels have been updated by the project, but the increased energy is at frequencies low enough not to be a  concern.  A limited to: thermal cycling of the solenoi ds followed by high pot testing, life testing of the bellows, pressure  testing of the bellows, life testing of the disc springs, thermal cycling followed by strength testing of the  brazed joints, strength testing of weld samples for all welded joints.  T half years. The first 19 flight valves have already been welded into flight manifolds, and the remaining 25  will be assembled over the next two months. The qualification program has been successful to this point,  and additional testing will begin as soon as possible. The failure of the position sensor was a  disappointment, but the project considered the loss acceptable. More work needs to be done to either fix the current position sensor design or come up with a new method of position knowledge for future use of  the Microvalve. T Dan Harpold, John Bischell, Steve Price, Donneise Briscoe, Carl Strojny, Charlie Fleetwood, Dan  Carrigan, Armando Morell, and Lee Niemeyer, as well as the entire SAM team at NASA Goddard Space  Flight Center. Without all of their assistance the development of the in-house Microvalve would not have  been possible.  58
First Part: Development of a New Stack Bonding Process  Technical context  A laminated stator (Figure 1) generally consists of a thin sheet stacking (ferromagnetic material) with  notches designed for windings (Figure 2). The central opening of the ring is intended to house the rotor.  The resins used for bonded stacking are often winding impregnation varnishes and in all cases synthetic resins with very low viscosity.  Low viscosity is a necessary chara cteristic because it facilitates sheet capillary impregnation and stack  pressing. In addition, these resins correspond to the electric motor industry’s standard norms both in  thermal and dielectric terms. However, these resins have adhesive and mechan ical properties often  unsuited to stator bonding and to its mechanical environment.  Figure 1. Brushless DC motor stator : 18001-2  (SOTEREM)Figure 2. Thin sheet stacking with notches  Sometimes, delamination of the metal stack may occur either du ring motor manufacturing or handling, in  general because of excessive stress or shock. Delamination may also be due to defective adhesion or  lack of adhesive. During stack pressing, for example, disparities of sheet thicknesses and of oxidation  treatment can create localized contact points between sheets where fluid resin is pressed out. Lack of  adhesive is, of course, related to the intensity of applied pressure and to affinities between ferromagnetic  sheets and resin (viscosity and wettability).  Sheet stack bonding is one of the main improvements in stator manufacturing. Using structural bonding  for stack assembling can reduce the risk of delamination through mechanical or thermal constraints or shocks. It also means that stacking reinfor cements, such as housing, bolting or welding are no longer  necessary. Furthermore, rigidified stacki ng is much more machinable.  Screen printing  Screen printing is a printing method that can also be used to deposit all types of resins and, in particular,  structural adhesives with high mechanical properties within a wide range of viscosities and tacks (1 to 400  000 mPa). Adhesive is pushed through a silkscreen (Figures 3 & 4). The screen consists of a fabric tightened over a rigid framework. The characteristics of the taffeta scree ning depend on thread diameter  and spacing. Screening is selected according to rheological adhesive characteristics and required  adhesive volume.  62
Figure 3. Screen printing method Figure 4. Depositing of thin adhesive film   Deposited adhesive films are very thin (from 1 to 20 micro ns), regular and repeatable. Thickness  adjustment is very precise (±3%).  Adhesive selection depends on the ferromagnetic material that is to be assembled and on the life  constraints of the product. The resin chosen for the serigraphy of the electric motors is a structural  adhesive with high shear and peeling strength (rigidity and adherence).  Initially, sheets have a simple annular shape. They are screen printed then piled on top of each other with  a pressing tool, which guarantees precise assembly height (Figure 5).  Figure 5. Sheets are piled on top of each other  Due to the thinness of the adhesive film, the stack has a very good iron / [iron + insulator] ratio (nearly  97%). For this application, the selected adhesive, which has a strong viscosity and a high tack, does not  flow easily between sheets. So, the interlaminary space thicknesses are very homogeneous and regular.  In addition, lack of adhesive due to air bubble s or sheet defects does not occur.  The "Structural adhesive bonding" of sheets with the silkscreen method a ims to give them improved  rigidity and make them machinable, without any risk of delamination. Moreover, stack machining precision  is better than the precision of already machined assembled sheets. Good electro-magnetic performance  results from good geometry.  Stack machining  When the stacking is polymerized, it can be machined. The machining method used is wire electroerosion, which is a precise and safe technology. Indeed, notches are well aligned and assemblies are not  at all stressed.  While the use of structural adhesives is a benefit to final stator rigidity and machining, the insulator layers  are a problem for electro-erosion machining. Electro-erosion is based on capacitor discharges between an electrode wire and the part being machined. Each plate must be connected to the generator. The  discharges generate micro-plasmas (locally about 10000°C) and sublimate all the materials (ferromagnetic and synthetic resin).  63
The technique, used to make electro-erosion compatible with sheet stacking, consists of coating inner  and outer slices with an electro-conductive resin to ensure that all metallic sheets have the same  potential. Electro-erosion does not create degradation of the structural adhesive joints. The resulting geometry of  the stack is very precise; inner and outer diameters are coaxial, notches are aligned, and their geometry  is symmetrical (Figure 6).  Figure 6. Stack Geometry Second Part: New Bonded Stator Assembling and Validation Testing  To check the impact of the structurally bonded stack on motor performance, the second phase of  development consisted of the following steps:   - manufacturing of a fully wound stator based on the structurally bonded stack  - testing a frameless motor, consisting of the bonded stack stator and an associated rotor,  through a complete validation test sequence.  - for comparison, testing of a similar space-qualified motor.  Stator manufacturing  The structurally bonded stack presented in the first part has been designed and manufactured in order to  replace an existing space stator with the same stator geometrical dimensions and interfaces based on the same lamination sheet materials and design. It has been equipped with exactly the same windings as the  existing referenced stator. However, it has been impregnated with a varnish that complies with space  outgassing standards. Figure 1 shows the finished stator manufactured with the bonded stack. Figure 7 shows the existing referenced stator and the structurally bonded stack. Figure 8 shows a detail of the  existing referenced stator.  Figure 7. Existing Referenced Stator and the Structurally Bonded Stack  64
Figure 8. A Detail of the Existing Referenced Stator  The differences between both stators are summarized in Table 1   Table 1.  Stator Differences  Existing space stator Structurally bonded stack  stator  Lamination sheet Same material  Same design  Stack Synthetic resin bonded stack Structurally bonded stack  Coils Same wires  Same windings  Coating and finish Resin compound molding in  order to protect windings, and  increase stator rigidity Varnish impregnation  One of the specificities of these stators, driven by the space application, is that fixation onto the  equipment is done directly on the stack; this implies that the stack outer diameter must be designed with  very stringent tolerances (diameter ±0.02 mm and concentricity tolerance in the range of 0.02 mm). Such  constraints explain why the qualified stator had been designed with a rigid compound, which guarantees efficient winding protection, but also drastically increases mass.  For the new structurally bonded stator, and thanks to its good mechanical properties, development has  been oriented towards a lighter version without any co mpound. This raises potential criticalities with  regards to stator flexibility and to winding protection. To take into account the high flexibility of the nonmolded stator, the development effort required adaptation of existing processes and the introduction of stiffening tools. The finished stator had a small ovalization, which was easily corrected by a shaping tool,  making the average diameters and concentricity fully compliant with the required tolerances.  Stator Testing and Characterization  The stator is a part of a brushless frameless motor (DC three-phased motor). The other part is a rotor  equipped with permanent Samarium Cobalt magnets. For characterization of the new developed stator  and in order to compare with existing space referenced stator, both stators associated with the same rotor  have been successively submitted to the same complete test sequence (Figure 7). The tested environmental conditions are those which are required for a space application on a satellite platform at  qualification level. From the test results, the main characteristic variations between the two stators are  given in Table 2.  65
Initial performance - dielectric rigidity  - resistance insulation - inductance, capacity  - mass dimensions  - time constant - speed / torque characteristics  - wave shape, frequencies  - torque constant, back emf constant - motor constant  - iron friction (constant and viscous), cogging   /g200 Vibrations Sine vibration: (level 40 g at 100 Hz)  Random vibration (21.4 grms )     in all 3 axes  /g200 Post vibration performance Ditto initial  /g200 Thermal cycling 6 cycles between -50°C and 80°C  /g200 Final performance Ditto initial  Figure 7. Test Sequence  Table 2.  Stator Test Results  Existing space stator  (A) New structurally  bonded stator (B) Variation (B) / (A)  Torque constant 4.24 Nm/A 4.27 Nm/A +0.8 %  Back EMF constant 4.18 V/rad/s 4.24 V/rad/s +1.4 %  Dry iron losses 0.0301 Nm 0.0158 Nm -47.5 %  Viscous iron losses 0.0008 Nm.s/rad 0.0013 Nm.s/rad + 62.5 %  Cogging 0.0621 Nm 0.0257 Nm - 58.6 %  Motor constant 0.888 Nm/ /g151w 0.897 Nm/ /g151w +1 %  Mass 1820 g 1484 g -18.5 %  66
It can be seen that:   - the general performance (torque constant, motor constant) is equivalent; no significant  variation. - dry friction and cogging are lower; this might be the result of better insulation between the iron  sheets and to the good final geometry quality of the new bonded stator.  - drastic mass reduction, due to the suppression of the molded compound, which results from  the better mechanical behavior of the structural bonding.  Conclusion  Stack structural bonding is possible using the screen printing method. The goal of this type of bonding is  to rigidify stackings and improve their cohesion. Serigraphy also guarantees optimal insulation between  sheets. It makes it possible to machine stacks with electro-erosion, which gives them a precise and stable  geometry.  Many advantages result from this process:  - Stiffness / geometry stability /g198 better electro-magnetic performance, less dry iron losses (around  50% of friction reduction), weak cogging  (around 60% of cogging reduction).  - Rigidity /cohesion /g198 no reinforcement: lightness (around 20% of mass reduction), compactness,  reduction in number of parts, protection against delamination.  - Sustainability / reliability /g198 constancy of performan ce, protection of insulating layers.  Figure 8. Thin Sheet Stacking with Structural Bonding  Process patented under patent n°: FR 2888390, EP 06778850.5  67
were identified as the highest risk components as they saw the most severe combination of loading  conditions and stress cycles.   

Table 1: MER RAT & MSL SRT Desired Performance   MER RAT MSL SRT  Minimum Grinding Operations 3 > 80  Grind Area (min. diameter) 45 mm 35 mm  Grinding Bit Speed 3000 rpm 750 rpm  Grinding Bit Torque 28 mNm 140 mNm  Grinding Bit Down Force 20 N 100 N  Grinding Operation Duration (max) 3 hr 4 hr  Mass 685 grams < 3.5x RAT  Volume 1463 cu. cm. < 3.5x RAT  PF Min. Operating Temperature -70 C -135C  PF Max. Operating Temperature +30 C + 70C 

This paper describes the MSL SRT grinding bit bearing design and the measures taken to reduce the risk  associated with this component. The early part of the SRT design phase was spent developing the grinding bit and in turn deriving requirements for the drive train components including loads, speeds, and  maximum allowable size. Once these basic grinding bit bearing requirements stabilized, attention turned  to selecting the specific bearing geometry, material and lubricant. After surveying the literature, consulting experts in the field and performing many analysis iterations, a final bearing design was selected. The final  design featured New Hampshire Ball Bearing (NHBB) 19-mm angular contact bearings (DB configuration)  made from SAE 52100 steel with cotton phenolic retainers. The bearing pair was lubricated with a combination of perflouropolyether (PFPE) based oil and grease (specifically, Castrol Brayco 815Z oil and  Braycote micronic 601EF grease) – the recipe is described later in the paper. To verify the design, a test  program was conducted which successfully demonstrated a 3x life capability under Mars conditions.    Bearing Design and Lubricant Selection  

The SRT grinding bit bearing configuration is shown in Figure 1. When grinding, the bearing pair must  react cutting forces and loads imparted at the gear mesh. Requirements analysis yielded six distinct SRT  operating modes to be considered.  These six modes, shown in Table 2, had varying durations, speeds  and loads totaling ~20 x 10 6 bearing revolutions (~60 x 106 stress cycles) at 1x life. The bearing design  would need to survive 3x life to pass qualification test requirements.     Grinding  Bit Grinding BitBearing  PairDrive  Gear

Figure 1: Grinding Bit Bearing Configuration 

Grinding operations accounted for more than 75% of the bearing revolution s and early analysis using  COBRA EHL indicated that mean Hertzian stress levels would approach between 1.38-2.06 GPa (200300 ksi) during the grinding mode. While this satisfied standards for allowable bearing material contact  70
stress (e.g., AIAA S-114-2005), it posed a concern from a lubricant degrada tion perspective as the  contact stress levels appeared to  be beyond the published capability of viable spacecraft lubricant  options.     

Table 2: SRT Operating Modes  Operating Mode 3x Ops.  Required 3x Life  (hours) Bit Load      (N, mNm) Bit Speed  (rpm) 3x Bit Bearing  Revolutions  Grinding: Difficult Rock 90 360 100, 143 750 16.2 x 106 Grinding: Medium Rock 36 144 50, 76.5 750 6.5 x 106 Grinding: Easy Rock 126 504 25, 43 750 22.8 x 106 Brushing Rock 600 150 10, 10 1500 13.5 x 106 Seek-Scan (locates surface)  852 85 10, 10 60 0.3 x 106 Calibration (homes device)  852 85 0, 0 60 0.3 x 106

The specifications for the selecte d grinding bit bearing are shown in  Table 3. This represented the largest  bearing that could be accommodated by the design. A partial ball complement was chosen over a full  complement in order to keep parasitic friction as low as possible. Just as important, this bearing was available in quantity from a distributor with a lead time that met the schedule.   

There was a concern that grinding chatter might damage the bearing if the balls were allowed to become unloaded during the grinding process. Thus, a 124.6 N (28 lbf) preload was selected for the duplexed  (back-to-back) pair so that all balls would remain loaded under worst case grinding conditions. With this  preload, analysis showed that the maximum mean contact stress in the bearing pair ranged from 1.28 GPa (during Calibration mode) to 1.59 GPa (during Grinding Difficult Rock). 

Table 3: SRT Grind Bit Bearing Specifications  Specification Value  Manufacturer NHBB  Part Number MER-1960SD501 DB  Type Angular contact  Configuration Inner-race relieved  Outer Diameter 19 mm  Inner Diameter 6 mm  Width 6 mm  Ball Diameter 3.572 mm  Ball Complement 8  Initial Contact Angle 15  Total Raceway Curvature 0.08  Tolerance Level ABEC 7  Ball & Raceway Material SAE 52100 Steel  Cage Type Full-enclosed  Cage Material Cotton-phenolic 

Allowable Parasitic Torque   The total bearing drag at the beginning life was expected to be less than 14 mNm. The SRT grind actuator was sized with enough torque margin to handle parasitic drag up to 28 mNm from the grinding bit  bearings during the grinding mode towards the end of life.     Lubricant Considerations

Figure 2 shows how the SRT grinding bit bearing contact stress and stress cycle requirements stack up  relative to several examples of common spacecraft dry and wet lubricant performance. The chart was created using data from [2][7][8][9][10][15]. It is clear that even at 1x life and at the lower end of the  contact stress range, the SRT grinding bit bearings are operating in a regime beyond the known capability  of these lubricants. One caveat is that this is a two-dimensional chart that does not consider drag torque  or speed. Also, in the case of the Brayco 815Z, the chart reflects testing done with 440C or 52100 steel  71
bearings with phenolic cages – thus Brayco 815Z performance with ceramic (S 3N4) or ceramic coated  (TiC) balls or additives, which is known to be improved, is not shown. Finally, failure criteria vary.  Polymerization of the PFPE lubricant does not necessarily constitute a failure for the SRT bearings if  there is an adequate reservoir for re-supply of the contact zone with unaltered oil. Likewise, with regard to the MoS 2-Ni data, a 40x increase in torque also might not constitute failure for the SRT bearings  depending on the running torque at the beginning of life. It does convincingly show however, that both  lubricant systems will undergo significant degradation before the SRT achieves 1x life.   The preference was to be capable of operating the SRT at -135° C without the use of heaters, although  “heat-to-use” was an option. To enable operations at the cold end of the temperature range, dry-film lubricant options were considered. In addition to much lower drag at cold temperatures, other benefits of  using a dry-film lubricant include negligible vapor pressure, little surface migration, and valid acceleratedlife testing [4]. Specifically, the design team considered coating the balls and races with molybdenum  disulfide co-sputtered with nickel (MoS 2-Ni) and replacing the phenolic retainer with one made of  reinforced, MoS 2-containing PTFE (Rulon® AMR). However, MoS 2-Ni dry film coatings were ruled out for  the following reasons:  /g120 Relevant existing research indicates that SRT bearing contact stresses significantly exceed the  known capability of MoS 2-Ni coatings. It seemed likely that the initial surface coating on the balls  and races would quickly be worn away.  /g120 Unlike a wet lubricant (grease), dry film coatings possess a very limited ability for lubricant  replenishment in the contact zone  for rolling-element bearings once the initial coating has worn  away. Some replenishment may occur as wear particulate from the retainer migrates to the contact zone. By contrast, when mixed to the proper ratio, the grease thickener will not migrate  excessively and over the life of the component it will slowly rele ase oil to the contacting metal  parts. 

00.511.52 1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09 1.0E+10 Life, stress cyclesMean Contact Stress (GPa)Bray-815Z Bray-815Z Polymerized MoS2 MoS2 40x Torque Increase 1x 3x SRT Castrol recommended  max. for Bra y-815Z0.15 μm  thick MoS2 wear life  Nishimura et al.  19991.0 μm  thick

Figure 2: SRT Grind Bearing Contact Stress & Stress Cycle Requirement 

For these reasons, it was decided to adopt a “heat-to-use” approach and use a wet lubricant (grease).  During surface operations, heaters would warm the mechanism to -55° C if necessary before turning on  the SRT actuators. However, the protoflight test program would require the mechanism to be demonstrated at -70° C. A PFPE lubricant (Brayco 815Z oil-based grease) was selected over MAC-based  72