ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
82   Figure 11. Tilted and blocked Tension Tube.  

Design and process improvements  

The blocked Preload Jaw in the HDRM was a critical and unexpected failure.  The problem was on the  critical path of the project . The design needed to be improv ed and the test campaign had to be continued.  The design changes  could not be  too deep in order not to affect the design of  the rest of the boom: the   LP-PWI was in the midst of a qualification test campaign,  and any major changes could challenge the  validity of the previous QM tests. Additionally, most  of the flight parts had already  been manufactured,  hence the quantity of the modified parts had to remain as few as possible.   The i mprovements focused on:   - Control ling the friction coefficient between the Tension Clamp  and the T ube Interface.   - Lower ing the risk of remaining the residual vibration loads in the Preload Jaw.   - Improv ing the relation of motorization margin to the preload force.   - Better control  of the preload adjustment .  The LP -PWI qualification model QM- 1 with the following modifications is called QM -bis in the next chapters.  

Design changes   As mentioned above,  the modification had to be conservative and affect as few parts as possible. First , the  Tension Clamps were redesigned ( Figure 12). They were widened to protrude from the Tube Interface and  the edges were manually rounded. More attention was put on the surface finish.  The inclination  angle  was  increased to 15 deg. Applyi ng a higher angle was not possible as it resulted in  too high loads on the levers  and could have led to an inadvert ent opening during vibration.  

The V -shape spring was also widened. The previous spring’s model was optimized to withstand the preload  and keep a low mass. The modified spring increased the bending force at the expense of  the mass budget .
83   Figure 12. Tension Clamp  design changes  

The change of the Tension Clamp led to  the modification of the T ube Interface. The titanium part of the  interface was already attached to the CFRP tube and replacing them was not possible. Only the Vespel  SP1 overlay could have been replaced.  Because the Clamp  angle had been changed , the overlay needed  to be adjust ed as well. The simplest  solution was to round the contact surface of the overlay  and create a  linear contact with the Tension Clamp (Figure 13). This solution also had other benefits. In  the previous  design,  the contact  area between the Clamp and the T ube Interface was  random. The manufacturing  tolerances of the parts did not allow for perfect surface- to-surface contact. As a consequence,  the Clamp  pressed  the overlay  in random point s under not necessarily a correct  angle. Rounding of the overlay   improve d the control over the contact area and inclination angle . The disadvantage of this solution included  higher  Hertzian stresses of  the linear contact , but it remained within  accepted range. As a plastic material ,  Vespel SP1  can be easily deformed under pressure without risk of breaking. In this case,  after exceeding  the Hertzian stresses , the overlay simply adjust s its shape to the Tension Clamp  and creates the  sufficient   surface to surface contact  area.  

Figure 13. Vespel  SP1 overlays modification  

Change of the preload application process   The process of preload adjust ment  in the HDRM was also improved. The load was applied with a mass  attached to the tension tube, similarly as in the  BBM . During the process the boom was put in a vertical  position, hence the HDRM’s walls did not have to be screwed to the integration plate. T hanks to this , the  HDRM walls were not rigidly fixed and a clearance  remained  between them and the  Tension Tube. The  tube was able to move freely  without the risk of tilting and blocking. The position of the T ension Tube was   observed from the beginning of preloading to the blocking by the  screws.  A lot of effort  was put  to ensure
84 that the final position of  the tension tube is parallel. After constraining the tube in HD RM, its exact position  was measured with the accuracy of 0.01 mm. The measurements were taken on both sides of the T ension  Spring. All deviations of readings higher than 0.05 mm meant it was neces sary to re apply the preload. This  inspection assured that the tube was not tilted by more than 0.15 deg. 

Test Campaign Continuation  

All design changes were focused on improv ing the motori zation margin of the P reload Jaw. Figure 14  presents  the comparison between the motori zation of the Preload Jaw in QM- 1 and in QM-bis. The increase  of the Tension Clamp ’s inclination angle and the modification of the V-shape spring made the HDRM much  more independent from the preload and friction coefficient changes. The wi dening of the Tension Clamp   and rounding of its edges excluded the possibility of  the titanium edge sticking  into the Vespel SP1.  A wellfinished surface of the overlays  and the C lamps assured as low friction coefficient as possible.  The margin  of safety for the HDRM working point was significantly increased .   

Figure 14. Motorization of Preload Jaw – QM-bis (α=15 deg; FB=8 N; μ=0.22 ) 

The modified qualification model (QM- bis) was vibrated once again in accordance with the same test  specification.  During the  vibration s, it was apparent that the applied changes improved the mechanism. The  comparison of modal  responses (performed before and after the nominal random vibration test) from the  accelerometer placed on the lever was more accurate than it was in the QM-1 (Figure 15). Previously , a  major increase of the modes ’ frequencies  and a great difference of the  modes at  frequencies above 800 Hz  were observed . In the QM-bis the first mode decreases its frequency after the test. It can be explained by  the initial setting of the mechanism. For higher frequencies  the resonance characteristics  remained similar   before and after random vibration. Any major shift was not observed,  and the main mode is almost identical.
85 Figure 15. Resonance response of the lever in Base HDRM before vibration and after in Z -axis for QM- bis 

The QM-bis passed  the vibration test  – the modal responses were very similar.  For most of the parts it was  the second vibration with the qualification level  which additionally proved the endurance of the boom. The  limited release just after the vibrations was successful  as well -  both HDRMs  were opened.  The qualification  campaign c ould resume.  All other tests , including  full deployments and shocks, were completed   successfully. The LP-PWI was fully deployed over 50 times during the qualification test campaign (QM-1:  8 deployments; QM- bis: 49 deployments ). In the end,  the LP -PWI reached TRL7.  

Conclusions  and Lessons Learned   The experience from the qualification campaign of LP -PWI is essential and can be used for other project s.  Several lessons learned were  extracted:   Great heritage and successful breadboarding does not guarantee  reliability of the mechanism.    Several issues were neglected at the beginning of the project. The first motorization model  of the Preload  Jaw was too optimistic . The preload value was simply scaled from another instrument without confronting  it with the real loads acting  on the unit. These steps were taken due to the lack of a good analysis in the  early phase of the project, but also due to strong faith in the reliability of the mechanism. The good heritage  of HDRM and successful breadboard campai gn discouraged implementation of any improvements.   In simulations and mathematical models, the most conservative approach should be considered as  the baseline .  The analysis of the behavior of the Preload Jaw was neglected in the project . The i nability  to build a detailed  mathematical model was replaced with an optimistic approach. The mechanism was considered unlikely to  block. If a sufficiently detailed mathematical model is too complicated  to achieve , the most conservative  approach should always be used. In addition, in the early design process , the mechanism shall demonstrate  clearly defined constraints and parameters that are verifiable and controllable during the manufacturing,  assembly and testing process. When the project constraints appear, the design compromises are  embedded and sufficient level of risk awareness needs to be tracked and not forgot ten.  The harder material should  always protrude from a softer  one.  One of the basic mistakes in the design was the decision to make the Tube holders wider than the Tension   Clamp . In consequence,  the edges of the Clamp  could wedge into the tube holders’ overlays. The overlays  made of Vespel  SP1 are much softer than the nitride titanium Clamp . The wedged edge of the Clamp   generates much higher Hertzian stresses and deforms  the overlay. In the connections where one material  is much softer than the other one,  a contact of the hardest edges shall be avoided.
86 Parts inspection   The inspection  and rejection of the par ts with questionable quality at an early stage is critical.  The project  was under high time pressure. The risk of using several parts with surface or shape defects was  underestimated. Not enough attention was put on the surface finishing and rounding of the parts’ edges.  The accepted parts were not in a bad condition and they passed the standard acceptance criteria, however,  the standard inspection did not consider their specific application. In some cases, the parts were not  properly  finished. The elements  that are part of the interface or a component of the friction pair should  always have excellent surface finish and the inspection shall assume their future function. In addition, if the  quality of the critical parts r aises any question, the risk of accept ing them may lead to costs much higher   than those resulting from the delays or production of new ones.  

Acknowledgments  

The work described in this article was performed under a c ontract with the European Space Agency’s   Prodex  No. 4000119065/16/NL/JK. The  Primary Investigator of the project is IRF Uppsala led byJan- Erik  Wahlund (PI), Jan Bergman (Instrument manager), Victoria Cripps and Sara Gomis (Instrument Product  Assurance Manager s). The project is supervised by ESA’s  expert Ronan Le Letty.  Astronika’s  engineers   who also participated in the research and development activity  described herein  are: Tomasz Kuciński   (project managers at initial stage of the conntract ), Kamil Bochra,  Mateus z Duda,  Michał Bogoński , Mateusz  Grzyb, Karol  Jarocki,  Łukasz Bereś,  Filip Szymański, Paweł  Miara,  Henryk Gut . The authors would like to  thank the above mentioned  for their support.  

References  

1. M. Borys, L. Wiśniewski,  J. Grygorczuk,  et al.  ‘’LP-PWI deployable boom for JUICE mission – innovative  features and breadboard model development ’’ 17th European Space Mechanisms and Tribology  Symposium (ESMATS), Hatfield, UK, September 20- 22, 2017   2. A.Sjögren, ‘’Modelling of Rosetta Langmuir Probe Measurements’’ UPTEC F09 063, Uppsala, Sweden,  Octo ber, 2009   3. K.S. Jacobsen a,, J. -E. Wahlund b , A. Pedersen, ‘’Cassini Langmuir probe measurements in the inner  magnetosphere of Saturn’’, Planetary and Space Science 57 (2009) 48– 52  4. Grygorczuk, J., Banaszkiewicz, M., Seweryn, K., Spohn, “MUPUS Insertion dev ice for the Rosetta  mission” Journal of Telecommunications and Information Technology (1/2007), pp50- 53.  5. M Dobrowolski, J Grygorczuk, B Kędziora, M Tokarz, M Borys  ‘’DRAGON- 8U Nanosatellite Orbital  Deployer ’’; Proceedings of the 42nd Aerospace Mechanisms S ymposium; NASA/CP -2014- 217519;   487-496  6. J. Grygorczuk, M. Dobrowolski, L. Wisniewski, “Advanced Mechanisms and Tribological Tests of the  Hammering Sampling Device CHOMIK ” 14th European Space Mechanisms and Tribology Symposium  (ESMATS), Constance, Germany, September 28- 31, 2011
88 The REACT design employs  a segmented nut configuration, where the load is connected with a standard  threaded interface. The nut is  split in 3 segments. The mechanism is based on an over -center configuration.  The thread segments are connected by link bars to a third element, called the external ring, which has a  single degree of freedom in the longitudinal axis. The external ring is blocked in the preload or reset  configuration by a set of balls, maintaining the nut segment s closed and therefore supporting the external  load. Once a trigger element, motorized by means of SMA initiators, unblocks the balls, the external ring is  moved to a second position by internal springs. At this position, the nut segments are open and the load is  released.  

The new mechanism allows its reset by simple manual operations from the interface plane, by returning the  external ring to the reset position with a simple tool. This reduces the complexity of AIT operations, reducing  costs and improving system operations.  

Figure 1. REACT QM Models. Different sizes and mechanical interfaces.  

Development of Shape Memory Alloy Technologies for High Temperature Environments  

REACT actuator uses a trigger system based on a SMA wire, which at the environment temperature is in  the low temperature phase called martensite. When heat ed, this SMA fibre contracts by shape memory  effect once its transformation to the high temperature phase (austenite) is reached. During this contraction,  the SMA fibre pro duces a force high enough to trigger the mechanism.  

Two different SMA can be used in REACT. A commercial NiTi alloy is used for operation temperatures  below 65ºC. Another High Temperature Cu- based SMA, SMARQ, is mounted in REACT allowing operating  temper atures up to 125ºC because it has actuation temperatures over 140ºC. In Figure 2a, the thermal  transformation of the SMARQ alloy is plotted, showing the small thermal hysteresis between cooling (direct  transformation, in blue) and heating (reverse transfor mation, in red), obtained by integration of differential  scanning calorimetry measurements. The last part of the direct thermal transformation during cooling  extends along a broad temperature range, because the martensite plates have to nucleate against the  internal stresses created during the progress of the transformation. However, it is enough to apply an  external stress to promote the nucleation of the oriented martensites, getting a large transformation strain.  In Figure 2b, a transformation strain close to 8% is measured for a stress of 23 MPa. This curve represents  the thermal transformation under a constant load and is representative of the behavior of the material in a  situation similar to the working condition of REACT. This kind of experiments wer e performed in a specific  test setup working in an ultra-high vacuum (UHV) of 2∙ 10-8 mbar [1], and many measurements were  performed at different temperatures in such an UHV environment, showing that the SMARQ material  exhibits a good reliability in the space environment.
89   Figure 2. Behavior of SMARQ fibres used in the REACT extended temperature range. (a) Thermal  transformation cycle without load. (b) Thermal transformation cycle under 23 MPa load.  

Two examples of SMA fibre activation under UHV are presented in Figure 3, for two different environment al  conditions and activation parameters. In Figure 3a, the fibre was under  UHV inside a cryostat at -110ºC,  working against a load or 62 MPa, and in this case the electrical current on the heater surround ing the SMA  fibre was a pulse of 3 A with an increasing ramp of 0.5 s, a constant current time of 6 s and a decreasing  ramp of 0.5 s (curve red). The delay of the response of the triggering SMA fibre is rather long (about 5 s)  because of the very low initi al temperature of the SMA fibre, requiring to be heated above 125ºC before  actuation. However, once the actuation starts, the complete strain contraction of 3.5 % (limited by a sensor)  was accomplished in 1 s (curve blue). In the second example of Figure 3b, the SMA fibre was in UHV at  125ºC working against the same load of 62 MPa. Nevertheless, in this case, although the current pulse  sent to the heater has the same profile than before, a lower maximum current is used, 1.5 A. The delay to  start the respons e was shorter, as expected from the higher environment temperature, but the actuation  time was longer, as a consequence of the lower heating current. In both cases (a) and (b), four cycles are  plotted superimposed to show the reproducibility of the actuati on process. The parameters of the activation  current pulse can be easily tunned in order to get the response required by the customer.  

Figure 3. Plots of the activation current pulse (red), and strain- time response of the SMARQ fibres,  measured in UHV of 2 ∙ 10-8 mbar. (a) Cryogenic test at - 110ºC. (b) High- temperature test at 125ºC.
90 Analysis of L ubrication  

A set of tribological test activities were performed at ESTL with the following objectives:   • to carry out testing at a fundamental (pin on disc) level to evaluate and compare candidate lubricants.   • to carry out testing on sub- assemblies equivalent to t he Qualification Models.  

Five lubricants were applied to EN31 steel disks and Ti -alloy disks and they were evaluated in the pin- ondisk tests. Testing was carried out in air and in vacuum:    • Sputtered MoS 2 – applied by ESTL using PVD process.   • Everlube 620C – bonded lubricant applied by Arquimea.   • Molykote D321R -  bonded lubricant applied by Arquimea.   • Molykote D106 –  water -based bonded lubricant applied by Arquimea (note that this is a different  product from Molykote 106).   • X54 – PTFE based lubrican t. 

The test program was completed and the results are summarised in Figure 4.  

Table 1. Pin on D isc Test Conditions   Motion type  Reciprocating   Motion cycle  static, +5mm/s, static, - 5mm/s (TBC)   Stroke length  10 mm  Number of cycles  250 in air, followed by 250 in vacuum   Test Temperature  Laboratory ambient  

Figure 4. Pin -on-Disk Results on EN310 S teel and Ti -Alloy 

Based upon the results from this tribometer test program together with existing flight heritage and test data  for Molykote 106 (solvent -based, butyl alcohol), it was agreed that this lubricant was the preferred candidate  for the REACT application and it was therefore selected.   

Three REACT units were tested, one of each size, defined as 5kN, 15kN and 35kN units and equivalent to  the Qualification Models. The assemblies were tested under the following conditions:   1. Air at ambient temperature (ISO 7 Class Cleanroom: 55% ± 10% RH, 22°C ± 3°C).   2. Vacuum (target 1x10- 5 mbar or less) at ambient temperature (22°C ± 3°C).   3. Vacuum (target 1x10- 5 mbar or less) at 120°C.   4. Vacuum (target 1x10- 5 mbar or less) at - 90°C.  

Each test comprised a single actuation driven by a stepper motor and the actuation torque was measured.  The results are provided in Figure 5.
91 The three units, 5kN, 15kN and 35kN, all actuated successfully at each of the test temperatures. The results  indicated that the temperature and environment did not have a significant effect on the actuation torque. A  post-test examination revealed that although the Molykote 106 lubricant was worn, it was still present and  protecting the critical sliding surfaces (examples are illustrated in Figure 6).  

Figure 5. Actuation Torques Measured in the T hermal Vacuum Tests 

Figure 6. Comparison of S liding Interface with S teel Ball Before (left) and After Testing (right)
92 REACT Qualification C ampaign  

A complete qualification campaign has been defined for each model and temperature variant, for a total of  6 campaigns. Eac h campaign includes 3 different units covering different mechanical interfaces for the  customers. Figure 7 summarizes the qualification campaign sequence for each variant.  

Figure 7. REACT Qualification Campaign  

The qualification campaigns of the REACT 5kN and 15kN Standard Temperature  units  have already been  completed, while the rest of campaigns are on- going. The main results and findings are:   • The units are being qualified to a lifetime over 50 cycles, which enables for at least 10 cycles on  ground and one in orbit, according to ECSS. Extension to 70 cycles during qualification to enable up  to 15 on ground uses is being implemented on new campaigns. REACT 15kN Standard temperature  has already completed its qualification for 70 cycles.   • All the units withst ood their proof load (6.5 kN, 19 kN and 43.5 kN, respectively) with high stiffness  and were able to release even under  such preloads. Axial stress tests have shown that the strength  of each unit are well above the specification values . REACT 5kN has shown a strength over 18 kN,  where the test resulted in external bolt fracture without any sign of damage to the device, which was  still showing normal behavior actuating in nominal conditions. The REACT 15kN test r esulted in the  breakage of the external bolt at 45 kN and the device show ed nominal behavior after the test. In the  case of REACT 35kN,  a maximum preload of 100 kN  was reached, at which point  the interface  between the bolt and the tensile machine was broken. The unit was still fully  operative after such  load. These values show the robustness of the design and a high confidence in the device mechanical  strength due to the application of design margins.   • Vibration and shock environment s were succesfully applied to  all the models, show ing that the device  holds the rated  load without issues.   • The units were subjected to 6 thermal cycles over the operating range, followed by actuations at low  and high temperature extremes . The devices showed good behavior during the cycling and actuated   successfully.   • Misalignment and creep tests were  performed to characterize the devices . The results during  misalignment tests show ed that the units were able to accomodate half-cone angles of more than  4.5º during integration and release. Creep tests were run for more than 6 months succesfully, showing  very low initial preload loss followed by stabilization . Nominal actuation has been achieved after the  test. Creep test s are being extended to 12 months.   • Force margin tests have been completed by assembli ng SMA initiators with  a fraction of the nominal  cross- section, and therefore a fraction of the available output force. This way, the force margins of