ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
145 -20246810 0 100 200 300 400Arc minutes DegreesRadial Misalignment Accuracy Test fo r Single Speed VRR offset by 0.001" Delta Accuracy Readingaccuracy requirement of 30 arc-minutes. Following the initial accuracy test, various tests were  conducted for different parameters to locate which were the greatest contributors to the accuracy of the resolver. The numerous tests included recordings of the signal outputs of the resolver from radial misalignment testing, axial misalignment testing, stator core alignment and repeatability testing. It was established that the stator core alignment had the greatest contribution to the accuracy. See Table I for accuracy readings obtained after the stator core alignment was improved with a significant increase in accuracy from 85 arc-minutes to approximately 48 arc-minutes. For rotor misalignment, the radial misalignment was found to be of higher contribution to the accuracy than axial misalignment with a deviation in the accuracy reading of approximately 9 arc-minutes at the off-set position of 25 µm (0.001 in) as seen in Figure 7.    Table I –Accuracy Test Results of Single Speed VRR  Angle (degree) 0 20 60 100 140 180 220 260 300 340 360 Initial Accuracy Test  (arc-min) 0.0 -5.9 -17.8 17.5 44.2 84.4 -40.4 42.6 -48.0 -9.6 0.0 Accuracy after Stator Core Alignment (arc-min) -0.3 -6.6 -13.1 -2.4 20.1 43.6 47.6 36.3 24.3 7.7 0.3 2nd Gen VRR Accuracy Test (arc-min) 0.0 -9.0 -14.9 -3.4 1.6 -5.3 -9.1 -7.7 6.3 5.6 0.0               

Figure 7. Radial misalignment test result    Lessons learned from the first generation Single Speed VRR  The observations made and the lessons learned from the manufacturing and initial testing of the single  speed VRR were the following:   Excessive machining of the rotor core assembly was causing de-lamination of the rotor core and  needed to be dimensioned such as to minimize the machining required to achieve final  dimensions.   Based on the stator core alignment test, it became apparent that the variation in the insulation  thickness affected the accuracy significantly; therefore it was found that masking the stator core surface at the outer edge prior to applying insulation was critical.   Lastly, a final grinding of the O.D. of the rotor core assembly was observed to be necessary to  increase concentricity since the accuracy was found to be greatly affected by radial misalignment.  Design improvements for the second generation single speed VRR  The lessons learned from the first generation were implemented in the next generation single speed VRR  through the following design modifications:
147 FeF 3 Catalytic Influence on PFPE Lubricant’s Lifetime   under Loaded Conditions 

Lionel Gaillard*, Antoine Mariot**, Catalin Fotea* and Roland Holzbauer+ 

Abstract 

A Perfluoropolyalkylether (PFPE) oil was heated in an inert atmosphere under dynamic temperature control. The temperature profile allowed precise determination of the degradation onset temperature. The degradation temperature appears to be lower than literature values under the conditions used for this investigation. Other samples of PFPE oil were later tested with a Pin on Disk Tribometer under different temperature and loading conditions. 

Introduction 

While PFPE lubricants are widely used in mechanisms designed for aerospace industry because of their numerous advantages, it is known that they degrade quickly and heavily under boundary lubrication conditions, especially when in contact with 440C or 52100 stainless steels.  Numerous authors (1) (2) (3) (4) (5) (6) in the past decades suggested that degradation of PFPE oils under boundary lubrication conditions was catalyzed by the Lewis acid FeF 3 (Iron fluoride III). Some  authors (3) even proposed the degradation mechanism was autocatalytic, which means it could continue for a while after the mechanical stress ceases.  In 1991, David J. Carré (2) proved indeed that PFPE does degrade in the presence of FeF 3 by reacting a  branched PFPE and FeF 3 in a nickel-lined autoclave under inert atmosphere at high temperatures. The  reaction is triggered in this instance at a temperature approximately 30°C below thermal degradation; however, high mechanical stress could have contributed to the high temperature excursions (7).  The recent experiment, on the other hand, has dealt specifically with the degradation temperatures and more importantly to precisely assess the triggering temperature for PFPE degradation. This is the first experiment that combined the precise temperature control for the heating ramp by using a state of the art Netzsch Simultaneous Thermal Analyser (STA) while monitoring the discrete changes that occur within the PFPE/FeF 3 mixture using Fourier Transform Infra-Red (FTIR) and a mass spectrometer. Furthermore,  the experiment would provide further insight into the autocatalytic mechanisms as suggested by (3). 

Experiment 

The Netzsch STA consists of a dynamic temperature controlled furnace coupled with a Fourier Transform Infrared Spectroscopy and Mass Spectrometry (Figure 1 and Figure 2). The instrument is vacuum tight by design, the furnace is evacuated first at pressures of ca. 10 -2 mbar and is continuously purged with N 2 gas  therefore the pressure inside the furnace is atmospheric during continuous operation.                                                              * European Space Agency, Noordwijk, The Netherlands  ** École Nationale Supérieure d'Arts et Métiers ParisTech, Lille, France  + Aerospace & Advanced Composites GmbH, Seibersdorf, Austria 

Proceedings of the 41st Aerospace Mechanisms Symposium, Jet Propulsion Laboratory, May 16-18, 2012
148   Figure 1. Furnace (left) and mass spectrometer (right). 

Figure 2. FTIR facility.  The fact that we were working at a more or less ambient pressure should not be an issue since even in  high vacuum both FeF 3 and PFPE oil are expected to be present as a condensed form. In this case, the  pressure dependence of the Arrhenius equation is low.  Approximately 5 mg of FeF 3 powder were mixed with ca. 100 mg of Fomblin Z25 PFPE lubricant in an  aluminum crucible. Fomblin Z25 is a base oil used in various Maplub and Braycote greases. These quantities of FeF 3 were intentionally high to ensure that iron fluoride would be in excess. It was feared  that the reaction rate with “realistic” amounts of FeF3 (which is supposed to form as a near-monomolecular layer on real-life mechanisms (3)) would be too slow to be measured during a reasonable timespan. A “witness” cup containing only Z25 oil was also prepared.  The temperature profiles used for this exercise are shown in (Figure 3).
149   Figure 3. Temperature profiles.  At the time of writing this paper, the following tests were completed:  1. Neat Fomblin Z25 was heated to 1300°C using a 10 K/min ramp to assess the degradation  temperature of the lubricant.  2. A mixture of Fomblin Z25 and FeF 3 was heated to 300° using a 10 K/min ramp.  3. A mixture of Fomblin Z25 and FeF 3 was heated to 300°C using a 10 K/min ramp and cooled  down to 40°C using a -10 K/min ramp.  4. A mixture of Fomblin Z25 and FeF 3 was heated to 300°C using a 10 K/min ramp and cooled  down to 40°C using a -10 K/min ramp, then maintained at 40°C for one hour. 

The FeF 3 has never been clearly identified in an actual mechanism or test apparatus, even if its presence  is very likely. Consequently, additional tests on a tribometer were run. The aim was to observe the gaseous compounds coming out of the degradation reaction. Although it would not be a definitive proof, finding the same degradation products and behavior as in the STA facility would greatly increase the 0 Time (hours) Temperature (°C) 10 K/min  40 1300  1 2 0 Time (min) Temperature (°C) 10 K/min  40 300  10 25 5 15 20  0 Time (min) Temperature (°C) 10 K/min  40 300  10 50 30 40 20 - 10 K/min  0 Time (hours) Temperature (°C) 10 K/min  40 300  2 1 - 10 K/min
150 likeliness of the hypothesis. A Pin-on-Disc (PoD) tribometer was used in a high-vacuum chamber under  temperature control, along with mass spectrometer analysis. 

Results and discussion 

The heating of neat lubricant to 1300°C determined the thermal degradation onset temperature of the Fomblin Z25 oil. Very precise onset points for the lubricant mass loss and the FTIR Gram-Schmidt reconstruction readings were observed. Figure 4 presents the temperature profile (red curve), the total mass loss of the oil (green curve), the differential scanning calorimetry (DSC) reading (blue curve), and the FTIR Gram-Schmidt reconstruction (black curve). The thermal degradation occurs at ca. 400°C.   

Figure 4. PFPE run to 1300°C.
151   Figure 5. Z25 sublimation test under high vacuum.  Observation: the experiment was run at an ambient pressure, which means that under vacuum,  sublimation will occur before the oil reaches 400°C. This was shown by a sublimation test run by AAC GmbH (Figure 5). Given those results, it was not necessary to go above the thermal degradation temperature, which led us to choose a 300°C maximum limit.   The second (PFPE and FeF 3 mixture heated to 300°C using a 10 K/min ramp) and third test (mixture of  Fomblin Z25 and FeF 3 heated to 300°C using a 10 K/min ramp and cooled down to 40°C using a   -10 K/min ramp) showed that some degradation was occurring at a much lower temperature. Figure 6 shows an onset point for the mass loss (green curve), FTIR Gram-Schmidt reconstruction (black curve) and mass spectrometer readings (dotted curves). Thus, the degradation appears to be triggered at ca. 220°C. Figure 6 presents the different gaseous products detected by the mass spectrometer as follows: the main peaks were observed at atomic mass units (amu) 19, 44, 47, 66 and 69. The 19 amu trace can be attributed either to electron-stimulated desorption (along with 1 and 16 peaks, not shown) (8) or to fluorine radicals coming out. The other traces are 44 amu: CO 2, 66 amu: COF 2 and its ionization product  47 amu: COF, all of them being predicted by the theory of FeF 3/PFPE reaction (3).
152   Figure 6. Second run with associated mass spectrometry data. 

The final experiment used a mixture of Fomblin Z25 and FeF 3 heated to 300°C using a 10 K/min ramp  and cooled down to 40°C using a -10 K/min ramp, then maintained at 40°C for one hour. We could not see any measurable decrease once the temperature dropped below 260°C, which makes us think that no catalytic reaction takes place at ambient temperature, or that its rate does not allow one to see it with the experiment/equipment used and the time spent.  The experiment has been made somewhat more difficult because of the absence of vacuum: gaseous compounds were noted to “contaminate” the test chamber, leading to sometimes false spectrometer readings. Moreover, some chemical species seem to be able to “stick” to the chamber from one test to another. This behavior has already been experienced within other test facilities such as the spiral orbit tribometer, even under a high vacuum.   Given the complex spectra of the studied compounds, it was difficult to identify each species. Care should be taken during mass spectrometer analysis to know in advance what are the expected compounds and to have a reference spectrum for each of them, especially when their spectra are overlapping (which was the case here).  The goal of the Pin-on-Disc experiments was to evaluate the influence of loading and temperature on the degradation mechanism. A total of 8 different experiments were conducted as shown in Table 1, using both temperature and mean Hertzian pressure as parameters.  Figure  presents the results of one particular test run at a 1200 MPa mean Hertzian pressure and at a 120 °C temperature. Notably, traces at 28 amu: CO and 47 amu: COF (not shown) were noted accordingly to the degradation mechanism theory (3). Interestingly, there was a continuous increase of these traces during the rotation of the tribometer.
153 However, it has not been possible to compare the mass intensity of these traces between each  experiment. Because of the presence of moisture inside the test chamber, the mass spectrum associated with water was exceeding the range of the mass spectrometer, thus rendering other readings inaccurate. Future tests should therefore carefully use amplification settings that do not make water traces exceed the range of the instrument.    Table 1. List of conducted PoD experiments.     Test 1  560 MPa, 20 °C Test 2  560 MPa, 80 °C Test 3  560 MPa, 120 °C  Test 4  850 MPa, 20 °C  Test 5  850 MPa, 120 °C  Test 6  1200 MPa, 20 °C  Test 7  1200 MPa, 120 °C  Test 8  1900 MPa, 20 °C   

Figure 7. Example of MS readings from a Pin-on-Disc test (red curve: 28 amu, blue curve: 47 amu). 

  0.00E+005.00E-051.00E-041.50E-042.00E-042.50E-043.00E-04 0.10.150.20.250.30.350.4 -1.00 1.00 3.00 5.00 7.00 9.00 11.00 intensityFriction coefficient duration [h]Friction coefficient 28
162   Figure 1. Shape Memory Alloy phases [1] 

SMA2C press fitting  Assembly begins with a load cell in order to measure the amount of stress incurred on the NiTi during  press fit. The outer bushing is placed inside the cradle and a little Isopropyl alcohol is dropped inside in order to clean and act as a lubricant during the press fit. The remaining cradle is then placed on top followed by the NiTi ring on the press pin. The press pin is then forced down causing the NiTi ring to be forced into the steel bushing as the load cell records the amount of force being asserted by the press pin. Figure 2 depicts the press fit assembly.    

Figure 2. SMA2C Press fit [2]  SMA2C holding force  As mentioned above, the amount of stress induced between the Twinned and Detwinned Martinsite phase is directly correlated to the the amount of strain (expansion) that the NiTi undergoes. This
163 expansion affects the amount of holding force when inside the bushing. In order to demonstrate this  relationship, four different sample sets of NiTi rings were used with different outer diameters. They were each press fitted into a bushing of a certain diameter. The outcome was four sample sets, each with different interference measurements (difference between the outer radius of the NiTi ring and inner radius of the bushing). The sample with the greatest interference required greater force when press fitting the two pieces together, therefore increasing the stress induced. Because of this increased stress, the NiTi expands, leading to a greater force required to separate the two. Figure 3 plots the four different samples with varying interference and the amount of force needed to separate the NiTi ring from the bushing.  

Figure 3. SMA2C holding force [2]    SMA 2C assembly  After the NiTi ring has been press fitted into the bushing, a polyethermide isolation washer is placed through the bushing in order to thermally isolate it from the remaining assembly and the CubeSat. The bushing is wrapped with a Kapton foil heater and this assembly is then inserted into the outer housing. A push plate and spring are inserted on the other end. This push plate will provide the little push required to separate when the NiTi is heated in a zero gravity environment. Figures 4 and 5 depict the final assembly.  00.511.522.5 012345Force (kN) Displacement (mm)Press-Fit Removal Forces for "G" Type SMA Rings Press-Fit Specimen #1   13 µm (0.0005” )  Press-Fit Specimen #4  76 µm (0.003” )   Press-Fit Specimen #3  51  µm (0.002” )   Press-Fit Specimen #2  25 µm (0.001” )
164   Figure 4. SMA2C final assembly [2] 

Figure 5. SMA2C assembled [2] 

SMA2C release  The SMA2C housing would be secured to the bottom of the CubeSat. A retaining bolt would be inserted  through the bushing and NiTi ring with the head of the bolt resting on the NiTi ring, and the other end secured to the solar panel. When commanded, current is sent to the Kapton foil heater, which then heats the SMA 2C micro coupling. Once heated, the NiTi will shrink allowing it to be released from the steel  bushing. The push plate and spring would help nudge the NiTi ring along with the bolt out of the bushing.    

Figure 6. SMA2C release [2]
165 Conclusion 

CubeSats, and other small satellites, require a mechanism to secure and to control the release of their solar panels and other deployables. One common practice is to use fishing wire to secure the deployable and cut it thermally at the desired time on-orbit to release it. Due to the limitation of the fishing wire’s strength and reliability, especially during vibration testing, other release methods may be useful.  SMAs, when pressed fitted into another metal, provide a strong holding force which can be released with the addition of heat. The amount of holding force can be modified by simply adjusting the difference between the outer diameter of the SMA ring and the inner diameter of the bushing. Once heat is added to the bushing, the SMA contracts allowing the SMA and the bolt to release from the bushing.   References 

[1] D. C. Lagoudas – Editor, Department of Aerospace Engineering Texas A&M, Shape Memory Alloys  Modeling and Engineering Applications ; Published by Springer Science + Business Media, LLC ©  2008.  [2] Crane, William Mike. Development of a Nano-Satellite Micro-Coupling Mechanism with  Characterization of a Shape Memory Alloy Interference Joint.  MS thesis. Naval Postgraduate School,  Monterey, 2010. Print
167 Development and Testing of a High Compact  Stepper Motor Mechanism 

Jörg Schmidt* and Greg Wright** 

Abstract   The Laboratory for Atmospheric and Space Physics (LASP) has developed for the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission an Imaging Ultraviolet Spectrometer (IUVS) instrument. A grating flip mechanism (GFM), inside the IUVS instrument, is based on a highly compact and innovative stepper motor solution to drive an optic in two precise, bi-stable positions. Rotation angle between positions was 90°. This paper discusses major design restrictions, unique design characteristics and lessons learned from the development up through environmental and performance testing.                                 Figure 1. IUVS mechanism overview                                                     * Phytron Elektronik GmbH, Grabenzell, Germany  ** Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 

Proceedings of the 41st Aerospace Mechanisms Symposium, Jet Propulsion Laboratory, May 16-18, 2012
168 Introduction 

Function of the GFM consists of turning a grating assembly inside two hard end stops. The position accuracy defines the systemic grating position. Very restrictive geometrical boundary conditions limited the degree of freedom for an actuator solution – especially with respect to axial length and diameter for the actuator. Standard components or “of the shelf” products were not applicable.  Low weight, high rigidity and functional safety were fundamental design criteria. The long-term cleanliness of the grating represents a systemically size for the spectroscope. To keep the probability and the various ways of grating surface contamination in a very low level, an effective design strategy had to meet all these criteria. This risk mitigation was the key point in the complete design concept. A much more compact construction had to be developed.  Mounted on the cover was the grating assembly with the counter balance mass. The rotation angle was 90°. Two hard end stops on both sides limit the rotation angle. Electrical limit switches detect both end positions. To facilitate the bi-stable positioning we added a flexible coupling between cover and planetary gear shaft. Our purpose was to turn the grating assembly very smoothly in to the end positions. A torque preload should hold the grating in the end position under unenergized conditions via detent torque. Motorization was done by a special modified hybrid stepper motor size VSS 25.200.0,1-X from Phytron.                                Figure 2. Integrated stepper motor mechanism         planetary  gear cover flexible coupling  double row hybrid  bearing  (instrument main  bearing)  stepper motor central   housing
170 Final Concept Approach 

Flexible Titanium Coupling  To get enough safety margins in the flexible coupling design, following the wisdom “expect the unexpected”, we start with some different designs.              Figure 3. Evolution steps flexible coupling    Nearly 30 different models were calculated to find an optimal flexure structure. The stiffness was defined and the dimensions very hard restricted. Material stress reduction and the radial and axial dimensional  changes were limited, too. We could reduce the internal stress from 724 MPa down to 54 MPa (= ~8%).  Both parties recalculated the final FEM model. LASP with ANSYS, Phytron used COSMOS. The results  correlated in the stress and dimensional changes very exact.   To reduce any risk in the later assembling and test phase, we decided to produce three different flexure structures in the couplings. So, three versions were manufactured and tested respective to the torsional stiffness. Calculated and final measured stiffness values were different. Similar results were found in [1].                     Figure 4. Structure of flexible couplings    Intensive studies of comparable flexible structures, which were used in other mechanisms e.g., titanium butterfly pivots [2] and their final tested characteristics, creates a higher confidence level for our design approach.
171 Central Housing Structure  The only constructive way to be able to press many requirements in a small space was to use a well  coordinated conceptual design in hybrid joining technology. The central housing used all the advantages of the accuracy of CNC machines. At the same time, it represents the basic structure without soft joints.   To achieve excellent out gassing properties, the cover envelops the entire internal structure on 3 sides. Desorbing products will be dissipated controlled in one direction.                   Figure 5. Main structural titanium parts and complete mechanism     Final Grating Flip Stepper Motor   To obtain detailed performance data from each assembly phase, several tiered test sequences have been defined. The performance data were therefore known at any time. The irreversibility of some assembly processes requires a precise line of action with parts which must absolutely comply with the requirements.                    Figure 6. Final tested motor assembly