ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
340 Summary and Lessons Learned  

The initially used procedure of EDM machining of the thin flexible shutter hinges was not the appropriate  technology. It was shown that the unfavorable oxidati on affinity of titanium, which is accompanied by a  variation of the structural properties, lead to  arbitrary results and a low surface quality. 

With a revised version of the shutter, it was possi ble to manufacture the complex geometry by micromachining and an adjacent pickling procedure. The va riation of the spring constant was below ±1 N/m.  The realization as a monolithic structure offers furt her potential for miniaturization. In general, the usage  of titanium offers advantages due to the low mass, high  specific stiffness (ratio of the specific strength  and the Young’s Modulus) and high fatigue strength.   Acknowledgements   MERTIS is a joint project of the Institut für Planetologie (IfP) at the Westfälische Wilhelms-Universität (WWU) Münster and two institutes of the German Aerosp ace Center (DLR) in Berlin-Adlershof, as well as  several industrial partners, including Kayser-Threde GmbH München. The MERTIS instrument, funded by the Federal Government of Germany through the German Space Agency, is part of the scientific payload  of the BepiColombo mission to Mercury. This miss ion is developed by the Eu ropean Space Agency (ESA)  in close collaboration with Japan.   References 

[1] S.D. Lewis et al.: SPACE MECHANISM DEVELOPMENT LESSONS TO BE LEARNED – AN  INDEPENDENT VIEW. In: Proceedings of the 9th Europea n Space Mechanisms and Tribology  Symposium, 19-21 September 2001, Liège, Belgium.   [2] Theodore Nicholas: High Cycle Fatigue: A Mechanics of Materials Perspective . Elsevier Science;  ISBN-10: 0080446914, September 27, 2006  [3] MIL-HDBK-697A (NOTICE 1), TITANIUM AND TITANIUM ALLOYS  , 1 JUNE 1974     NASA/CP-2010-216272
341 Miniaturized Single-Shot Valve and its Application to the ExoMars   Pasteur Payload 

Pierre Muller*, Hartmut Henkel* and Sabine Klinkner * 

Abstract 

Hermetically sealing a gas tank and opening it into  tubing under telecommand control is a function  required in various space instruments. There are a number of space valves that are power saving,  withstand vibration, and do not cont aminate the gas. But none of them combines these features with low  mass and the ability to withstand temperatures of 130°C during the sterilization process mandatory for  planetary missions.   In this paper, a novel miniature valve is presented, whic h is particularly adapted to space applications. It  is electrically actuated, utilizing a bimetallic snap-d isc that pierces a metallic membrane by a needle pin,  thereby opening the valve. The design of this single-s hot valve is such that it allows it to withstand a  temperature of 130°C and a pressure of 50 bars. The valv e is also lightweight (6. 62 g) and it requires only  9 W to operate.  

Figure 1.  Schematic of a gas chromatograph (MOMA design).     Introduction   How to hermetically seal a high pressure tank and re motely open it in a relia ble manner? This technical  question arose within the development of the gas chromatograph of the Martian Organic Molecular  Analyzer (MOMA), a space instrument part of the ExoMars Pasteur Payload. Onboard is a gas tank, since  gas is needed to carry the substances in the ch romatographic columns. After assessing the existing  valves, the conclusion was drawn that none of thes e valves was perfectly adapted to the purpose  described above.                                                     * von Hoerner & Sulger GmbH, Schwetzingen, Germany  

Proceedings of the 40th Aerospace Mechanisms Symposium, NASA Kennedy Space Center, May 12-14, 2010  NASA/CP-2010-216272
342 Therefore other solutions were considered. A self -opening valve consists of two main elements: the  sealing element, and an actuator. All combinations of existing sealing elements and actuator were listed,  and it appeared that sealing valves is  a field that requires more explor ation. Who has ever built a sealing  valve with a piezoelectric actuator ? To the current knowledge this ha s never been done. This seems also  the case for a valve working with a bimetallic snap-disc. 

This paper first explains the motivation of this developm ent, in particular the function the valve has to fulfill  in the MOMA gas chromatograph. After this, the ba sic design and the refined design of the valve are  developed. Finally, the valve was tested and the design reviewed. 

Figure 2.  Diagram of the applications of the valve. 

Purpose   MOMA is a project of the Max Planck Institute for Solar System Research and the Laboratoire  Atmospheres, Milieux, Observations Spatiales. The MO MA objective is the analysis of the Martian soil  composition during the ExoMars mission. It consis ts mainly of a gas chromatograph and a laser  spectrometer. The gas chromatograph uses helium to carry the evolved gases from the heated soil sample to the capillary co lumns, as shown in Figur e 1. The speed of the gas flow is regulated by a  thermal regulation valve in which the flow is controll ed by a sapphire ball compressed to the aperture to a  higher or lower level. The compression of the ball is determined by the therma l expansion of the body of  the regulation valve, which is heated by a resistor. In this continuou s process the regul ation valve opens  as its temperature is increased. Here a key proble m appears, as the entire in strument is heated up during  the sterilization process required by the committee on space research for missions to the Martian surface: If no other device is hermetically closing the gas tank  during sterilization, it wo uld lose its contents. The  main focus of the development presented here is to  have a valve that truly hermetically seals the tank,  before it is opened by breaking the seal. The initial hermeticity is the key point  to select a single-shot  valve principle.  The projected valve has to be very lightweight (maximum 10 g), as the mass budget of the scientific instrument is very limited. The flow rate does not need to be very large, as the ty pical flow rate of helium  NASA/CP-2010-216272
345 where the snap-disc does not block the flow of gas:  the inlet tube and the outlet tubes will be placed at  the same side of the housing, the inlet (high pressures) at the side  and the outlet with the membrane at  the center (See Figure 3). This has also the advant age to let one side free for the placement of the  heater. A heater with a diameter 12.7 mm from th e manufacturer Minco could be found. It is an ohmic  heater that is very thin and lightwei ght that can heat up to a temperature of 200°C. The cover material of  the heater is made of Kapton .Because of its low out -gassing rate and because it remains stable in the  temperature range of -273°C to +400 °C, Kapton is a mate rial that is often used in the space industry. The  heater has a hole in the middle so that it can be reliably fixed via a screw and a custom-made washer.  As shown in Figure 3, the pin is also attached via a hole in the middle of the snap-disc and a washer. The  parts are soldered together with a 300°C melting temperature solder. The pin is gold plated and the  washer is made of brass, so it can be soldered without any problem.  The snap-disc itself is held in place by the two main parts of the housing that form the volume for the snap-disc where it cannot touch the membrane when it is not actuating. It was also verified by CAD that  the pin enters in the membrane with a reasonable margin. The snap-disc is not fully fixed to the body of the valve, but has a little play to let it bend correctly,  this also providing ther mal expansion. The snap-disc  does not separate the inside of the valve into two chambers; a little drilling is in the housing equalizes the pressures. Hence it is ensured that gas pressure cannot activate the snap-disc.  Figure 3.  3D view of the inside of the valve. 

The thickness of the housing was determined with a fi nite element analysis program. The behavior of the  housing under a pressure of 50 bars was simulated.  Resulting from the analysis, the housing was  reinforced at the fixing points of t he tubes. This resulted in a mechanica l factor of safety using the von  Mises yield criterion of 3.34.  All welds were carried out using Nd:YAG Laser technique. The process for welding the membrane to the housing needed some iteration to come to a gas-tight result, but now the process is well determined. Once the valve had been manufactured, the overall ga s tightness could be verified, and also that the  valve opens when electrically powered. 

Design Verification 

Testing a single-shot device is a critical issue, be cause repeatability has to be tested over many valves,  and therefore has to be carried out carefully.  A helium leak detector was used to test separately  the gas-tightness of the welds for mounting the  membrane within the housing. No leak could be detected after one hour at 30 bar inner pressure. The valves were tested in an oven at 130°C and it was obser ved that the valves were afterwards still gas-tight.  The opening test was also successful: in average afte r 90 s of powering the valve at 9 W, the valve at 30  NASA/CP-2010-216272
346 bar on the inlet opens and bubbles become visible if t he outlet is put in water. A test with an open valve  was also carried out, in order to observe t he hole created by the pin after actuation. 

Nevertheless, the valve is still not formally space qualified; this would imply a program with testing of a large amount of valves, including thermal cycling and vibration test.  

Conclusion 

Bimetallic thermal actuation is a very simple, rugged and widely used principle. However, its use is mainly  confined in thermal switches where the force needed is not large. In some application where a small, simple actuator, preferably without harness, is re quired, a standard snap-disc can be a good choice.   Even though single-shot devices have drawbacks concerning their testing, they provide a considerable  advantage concerning their reliability. In the specific case of MOMA wh ere a perfectly hermetical device is  required, it is safer to choose a sea ling element based on single-shot operation.   The valve built (see Figure 4) has the advantage over the previously foreseen solenoid valve to be lighter  by a factor of ten. Space qualification was taken in to account from the beginning of the design task, and  testing showed high reliability of the device.    

Figure 4.  Photo of the manufactured valves. 

References   1. http://planetary.chem.tufts.edu/Phoeni x/thermal_evolved_gas_analyzer.htm  2. http://www.conaxfl.com/Aerospace/1832205.htm 3. Edeson, Ruben, Martin Whalley, Barry Kent, Simon Canfer and Eric Sawyer. “SMA gas release  mechanism for the Rosetta Lander's Ptolemy instrument”, Acta Astronautica, Volume 58, Issue 11, June  2006, pages 576-582. 4. http://www.techbriefs.com/index.php?option=com_st aticxt&staticfile=/Briefs/Mar00/MSC22726.html  5. Bejhed, Johan, Pelle Rangsten and Johan Kaohler. “D emonstration of a single use microsystem valve  for high gas pressure applications”, Journal of Micromechanics and Microengineering , February 2007  NASA/CP-2010-216272
348 During the friction experiment, a mass spectrometer was used to measure the outgassing of the  materials. After the experiments, SEM and EDX were performed at the surface of the samples as well as  XPS analyses.  Technical data - UHV Tribometer:  Sliding mode:    reciprocating  Load:    5 mN to 5 N Stroke:    3 mm Frequency:   ca. 0.5 – 1.5 Hz Temperature:   Room temperature Residual pressure: 10 -10 - 10- 4 hPa      

Figure 1. Ultra high vac uum tribometer (UHVT) 

Table 1. Test parameters in UHV 

residual pressure  (hPa) stroke  (mm) velocity  (m/s) Load (N)   cycles  10-9 3 0.01 5; 10 500     Results   Figure 2 indicates an average friction coefficient of  0.12 – 0.15 with a maximum at 0.25 and accompanied  by stick-slip behavior under these conditions. The influence of load on the friction coefficient is not as significant in UHV as in high vacuum (Fig. 3), but t he values are somewhat smaller at 10 N than at 5 N.  The relatively higher friction coefficient in UHV at v = 0.01 m/s compared to the one obtained in high vacuum at v = 0.1 m/s could be due to the lower sliding velocity or to the fact that the end of the runningin phase in UHV was not yet achieved.   SEM images of the friction surface of the pin and flat a fter the experiment in UHV at 5 N are presented in  Figure 4. EDX analyses of the steel flat indicate that polymer was transferred to it, especially in the grooves present on the surface (Fig. 5). Since the F- map could not be distinguished from the Fe one (of  the flat), it is not shown here. MoS 2 is homogeneously transferred, but doe s not form a closed transfer film  on the steel flat. In this case, the very  low friction coefficient obtained by MoS 2 film at higher sliding speed  in high vacuum cannot be reached.  Furthermore, EDX analyses of the polymer pin indicate a MoS 2 rich surface, intermittent due to carbon  fibres (Fig. 6). The analyses revealed also that some Fe has been transferr ed from the steel to the  polymer pin. In addition, XPS analyses were performed after the experiment in UHV. Figure 7 shows the measured binding energy with the corresponding components. Beside MoS 2, the formation of  molybdenum oxides was observed, which could be form ed with the oxide layer of the steel disc. The  presence of molybdenum oxides could also explain the higher coefficient of friction, as reported in [7].   A preliminary measurement was performed to characte rize the outgassing during the friction experiment.  Figure 8 indicates that the outgassing increases du ring sliding, especially for hydrogen and nitrogen  compounds. Indeed, due to frictional heat, desorbed hydrogen and trapped gas are released during the test.   NASA/CP-2010-216272
349   Figure 2.  Friction behavior in oscillating motion in ultra-high vacuum 

   Figure 3.  Friction behavior in oscillating motion in high vacuum 

           Steel flat             Polymer pin  Figure 4.  SEM Analyses after the test in UHV at   -0.3-0.2-0.100.10.20.3 23456 distance [mm]friction coefficient 5N 10N -0.3-0.2-0.100.10.20.3 -15 -10 -5 0 5 10 15 distance (mm)Friction coefficient 1 MPa  7MPa 50 µm 50 µm  10 µm 10 µm  NASA/CP-2010-216272
350              

Figure 5.  EDX Analyses of the polymer transfer on the steel counterface after the test in UHV at  room temperature, 5 N 

Figure 6.  EDX Analyses of the polymer pin after the test in UHV at room temperature, 5 N 

Figure 7.  Mo(3d) and O(1s) spectra after the test in UHV at room temperature, 5 N Mo (3d) 1015202530 224 226 228 230 232 234 236 238 240 Binding Energy (eV)Counts (X 10²)MoS2  MoO 2   MoO 3O (1s) 152535455565 526 528 530 532 534 536 538 540 Binding Energy (eV)Counts X 10²MoO 2   MoO 3C MoCS C Mo S F OFe NASA/CP-2010-216272
351  

Figure 8.  Mass spectroscopy during friction test in UHV 

Conclusion 

This subsidiary study gives additional information concerning the tribological behavior of MoS2-filled PEEK in vacuum environment. The outstanding performa nce of this composite found in high vacuum at  v = 0.1 m/s [5, 6] is limited in UHV at low sliding speed (v = 0.01 m/s), where some static friction as well  as increased outgassing are observed. However, since the sliding velocity is an influencing factor on the  tribological behavior of pol ymer composite, further tests in UH V should be performed at higher speed and  during a longer period of time to veri fy the potential of these PEEK composites. 

References 

[1] Jones, Jr., W. R., and M. J ansen. ”Space Tribology.” NASA  report TM -2000-209924   [2] Jones, Jr., W. R., and M. Jansen . “Tribology for Space Application.” Proc. IMechE Vol. 222 Part J .  Journal of Engineering Tribology  (2008)  [3] Noshito, J., S. Watanabe, T. Sakurai, and S. Miyake. “Friction properties of co-sputtered  sulphide/DLC solid lubricating films.” Surface Coating Technol.  200 (2006) 5849-5854.  [4] Voevodin, A., J.P. Oneill and J.S. Zabinski. “Nan ocomposite tribological coatings for aerospace  applications. ” Surf. Coat. Technol.  116–119 (1999), p. 36.  [5] Theiler, G., and T. Gradt. “Inf luence of the Temperature on th e Tribological Behaviour of PEEK  Composites in Vacuum Environment.” Artikel: Journal of physics/ Conference series 100(2008)  072040, 1-4; IOP Publ.ISSN 1742-6588, 1742-6596  [6] Theiler, G., and T. Gradt T. “Tribological Behaviour of PEEK Composites in Vacuum Environment.”  12 th European Space Mechanisms and Tribology Symposium (ESMAT 2007) , September 19-21  2007, Liverpool, UK (Proceedings) 2007, 1-5; Hrsg.: European Space Agency (ESA)  [7] Martin, J.M., Th. Le Mogne, C. Grossiord, and Th . Palermo. “Adsorption and friction in the UHV  tribometer.” Tribology Letters  3 (1997) 87-94 

NASA/CP-2010-216272
353 Evolution of the IBDM Stru ctural Latch Development   into a Generic Simplified Design 

K. De Vriendt*, H. Dittmer*, D. Vrancken*, P. Urmston** and O. Gracia** 

Abstract 

This paper presents the evolution in the development of  the structural latch for the International Berthing  Docking Mechanism (IBDM, see Figure 1). It reports on  the lessons learned since completion of the test  program on the engineering development unit of the fi rst generation latching system in 2007. The initial  latch design has been through a second generation co ncept in 2008, and now evolved into a third  generation of this mechanism. Functional and structural  testing on the latest latch hardware has recently  been completed with good results.    Figure 1  The IBDM equipped with the first generation latching system      General Objective   The IBDM latching system will provide the structural  connection between two mated space vehicles after  berthing or docking. The mechanism guarantees that the interface seals become compressed to form a leak-tight pressure syst em that creates a passageway for the astronauts.  

The First Generation Latching System   Introduction

The initial latch design was driven by the r equirements of the NASA X- 38/CRV spacecraft, being the  envisaged 7-crew astronaut rescue vehicle for the ISS.  This implied that the mechanism had to be single  fault tolerant for docking (no catastrophic hazard when in LEO) and dual fault tolerant for undocking (i.e.,  release).                                                    * Verhaert Space, Kruibeke, Belgium  ** ESA/ESTeC, Noordwijk, The Netherlands 

Proceedings of the 40th Aerospace Mechanisms Sym posium, NASA Kennedy Space Center, May 12-14, 2010  NASA/CP-2010-216272
355 standard bushings with the net re sult that the load capability of  the latch/latch tab combination  was lower than anticipated.  Test conclusion: Pin and bushing failures have b een observed at a significantly lower load level  compared to the values predicted by analysis.    From a very early stage of the development, fa ctors of safety were introduced on the applied  loads. Due to the non-linear behavior of the latchi ng system due to the presence of a load-limiter  in the latch tab, the structural margin of safety on the resulting stresses are low.  

Figure 3  Theoretical (left) versus measured (right ) trajectory of the Latch onto the Latch Tab    Lessons learned from the first generation latching system

A thorough investigation of the observed anomalies resulted in a number of valuable lessons learned:   The shape of the latch tab hook has to be properly controlled by careful factoring of the relative  stiffness of the latch and the tunnel, the mountin g tolerances and differential thermal expansion.  Additionally, positive locking of the latch must be in corporated to prevent the roller interface at all  times to snap off the latch tab at (excessive) load increase.    Avoid as much as possible dual use for both the primary and the secondary drive of single  linkage joints.    Due to the exceptional characteristics of the space environment and the limitations in mass and  envelope imposed to any space equipment, the design  of structural elements, in particular pins  and bushings, cannot be done based on suppliers or textbook generic formulas. Careful estimations of stresses and deformations have to be carried out by FEM, even for simple  geometries. Material allowables must be determined by test. Breadboarding and testing of function critical or highly stre ss elements must be always carried out and results correlated with  the FEM models.   The optimal dimensional relations (i.e., small L/D ra tio) for the structural strength of the bushing  should be maintained as much as possible. Non-linear contact analysis showed that bushings with a large L/D ratio show a big variation in the stresses in the bushing liner, while this is much less for bushings with a small L/D.     Suppliers of COTS equipment may only have limited knowledge of their products, usually only  around the qualification range of the first product that used the element. It is not always an option  to design space mechanisms so they comply wi th the known environment of these COTS parts,  therefore, supplier’s calculations and analysis methods have to be carefully assessed and verified  by test under the foreseen environment and condi tions early in the project when corrective  actions or alternative designs can be considered.   Apply the structural factor of safety on the resu lting stresses instead of on the applied loads.   

  Roller path 5.566.57 0 0.5 1 1.5 2 2.5 xy NASA/CP-2010-216272
357  The load path from the interface load to the load-limiter has to be decreased as much as  possible, in order to avoid hysteres is in the load-limiter operation.  

Figure 4  Functional and structural testing of the second generation latching system 

The (Present) Third Generation Latching System   Introduction

The latest latch design is derived from the second generation latch. It maintains the hook-on-hook concept, but the kinematics are restricted to a single 4-bar linkage. The size of the latch is reduced back to that of the first generation latch (i.e., the size of the latch/latch tab, intended for an IBDM tunnel  diameter that allows astronaut passage only).   Per IBDM, 12 latches are attached in a tangential dire ction to the outside of the tunnel wall (Figure 5).  Each latch has its proper motor, gearbox and adjusta ble compliance element. The motor and the gearbox  are developed as an integrated actuator unit. Dual failu re tolerance has been established for both docking  and undocking, and inherent positive locking of the mechanism provides the guarantee against  inadvertent release.   

Figure 5  The IBDM with the third generation latching system 

 IBDM structural latch (3rd generation)  NASA/CP-2010-216272