ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
The P5 Truss is structurally attached to two other in tegrated trusses of the ISS on either side; the P3/P4  and the P6 truss segments. The purpose of the P5 truss is to separate the trusses that contain the solar  power modules and arrays. These trusses produce power from large photovoltaic solar cells. The location  of the P5 Truss on the port side of the ISS is shown in Figure 3.  

ITS P1   (11A ) ITS P3 /P4  (12A)P5 Short  Spacer  (12A.1) P6 (Relocated  on 13A.1 ) MT/MBS (9A/11A o n) Figure 3.  P5 Truss Location on the ISS 

The P5 truss weighs approximately 1225 kg (2700 lb) and is composed of tubular aluminum members.  These members are arranged so that one end is open and the other end provides a square planar  arrangement. The truss can fit in a cubical space that  measures approximately 4.6 m (15 ft) a side. The  structure has a set of trunnions that interface with  the Space Shuttle and serv e the purpose of carrying  the structural launch and emergency landing (if required) loads. 

The P5 Truss has three interfaces of interest for this study. These structural and mechanical interfaces  are shown in Figure 4. For clarity purposes, the figur e does not show Multi Layer Insulation blankets that  provide thermal protection5 for the truss during on-orbit operations. 

On one end, the P5 truss interfaces with the P3/P4 truss segment through the MRTAS berthing  mechanism, the focus of this study. On the other end, it interfaces with the P6 truss segment via another  berthing mechanism, the Rocketdyne Truss Attachment System. Thirdly, the truss also has a Flight  Releasable Grapple Fixture. Unlike other grapple fixtur es on the ISS trusses, this grapple fixture is  releasable, and as its name implies, it will be remov ed from the P5 truss after the berthing operation has  been completed.    The grapple fixture allows the SSRMS to grasp or grappl e the P5 truss to first remove it from the cargo  bay, and then to translate it through space to the point  of assembly with the ISS. Nominally, the SSRMS  translates payloads in the berthing corridor at speeds  between 0.3 to 0.9 cm/sec (0.01 to 0.03 ft/sec). 

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P5 to P4  Interface P5 to P6  InterfaceITS P5 PVRG F & OSE Figure 4.  P5 Truss w ith Structural and Mechanical Interfaces 

Figure 5.  MRTAS Soft Dock Capture  Mechanism    The MRTAS mechanism is composed of two  subsystems. The capture or soft dock  mechanism and the fine alignment bolts and  nuts6. The capture mechanism uses a set of four  slotted stingers called coarse cones that push  aside a set of four spring-loaded pins that  subsequently lock into the slots in the stingers.  The coarse cones also serve the function of  coarse alignment during the initial phase of  capture. The coarse cones can be discerned in  Figure 5.  Once all the coarse cones and all the springloaded pins have engaged, the P5 truss is  considered to be “soft-docked” to the P3/P4  truss. During the berthing operation, the SSRMS  positions the P5 in the trajectory for these  stingers to acquire the circular housing on the  P3/P4 side of the interface that houses the  spring-loaded pins. As the stingers slide into the  housing, and seek to push the spring-loaded  pins, capture resistive forces arise. These forces  are due to friction and due to the load in the pin  springs.  During the capture phase, there is an embedded functi on. At the same time the coarse cones are  attempting to engage the soft dock pins, a fine alignment function is taking place through the fine  alignment mechanisms on the bolt side and the nut side. Details of this mechanism are shown in Figure  6. Since perfect alignment of these two interf aces cannot be guaranteed, due to SSRMS or operator  errors, these features must serve to align the bolt and nuts on the trusses for them to be successfully P5 So ft Docking Capture MechanismP5 So ft Docking Capture Mechanism 319
bolted together. For successful alignment to take pl ace, a feature called shear cylinder, which surrounds  the primary bolt, must acquire the floating primary nu t. Once the shear cylinders are fully seated into the  floating nut primary cavity, the trusses are now ready to bolt. 

The MRTAS P3/P4 side of the truss also has four distinct corners. One corner is fix ed; that is to say, the  primary nut is not allowed any movement. The other three corners have “floating” primary nuts; where  each is allowed to slide in a particular direction.  Of these three corners, one corner has one degree of  freedom in the direction of ISS X-axis. The other two corners have two degrees of freedom, in the X and  Z-axes of ISS coordinate system. These degree- of-freedom allocations not only assure proper  engagement of the fine alignment featur es during the capture and fine alignm ent process, but also assure  the structure will carry the on-orbit loads appropriately following bolt up. 

P5 P4Contingen cy BoltPrimary Bo lt Contingency SpacerShear Cylinde r Floating Primary N ut Floating Co ntingenc y Nut Coar se ConeCoarse Cone   HoleSoft Dock Spring Loade d Pin Pin & Cone S lot gapCoar se ConeCoarse Cone   HoleSoft Dock Spring Loade d Pin Pin & Cone S lot gap

Figure 6.  MRTAS Details of the Capture M echanisms and Fine Alignment Sub-Sy stem 

The fine alignment features also contribute to the ov erall allocation of the forces that must be accounted  for. Several surfaces contribute to the capture and soft dock forces via friction. These must be accounted  for accurately to compare the total sum to the SSRMS capability. Should this exceed the push force  capability of the SSRMS, the mating could stall prior to  capture complete. The contact dynamic simulation  first, will consider the mechanism as-designed with tolerances. Later  on, as field measurements are  taken, these will allow considering the as-built c ondition of the trusses. In addition, as ISS on-orbit  integrated thermal analysis is completed, thermal deflections also will be considered to represent the  hardware interacting as close as po ssible to the on-orbit environment.  

Methodology  

The contact dynamic model of the MRTAS was built  using MSC/ADAMS multi-body dynamics tool. The  elements that come into contact during the berthing operation - capture pin to coarse alignment cone,  coarse alignment cone to housing, and fine alignment nut to shear cylinder – are modeled in detail based  on the final design drawings (Figure 7). While such detail is required for accurate results, complex  320
geometry can lead to long simulation times. The time required to retrieve contact intersection information  from the geometric modeler is directly related to the complexity of the gi ven geometry. Rather than  importing the geometry from CAD models,  they were built up from primit ives such as cylinders, spheres,  boxes and frustums. These shapes branch into much faster calculation algorithms in ADAMS. 

Capture  Pin Housi ng (P4)Alignment Cone (P5 ) Fine Al ignment  Nut ( P4)Shear C ylinder (P5)Capture  Pin Housi ng (P4)Alignment Cone (P5 ) Fine Al ignment  Nut ( P4)Shear C ylinder (P5)

Figure 7.  MRTAS Contact Features 

The MRTAS model includes two tight dock and two easy dock corners (Figure 8) which are essentially  identical except for one major difference; the eas y dock coarse alignment cones are longer and extend  farther out from the interface plane than the corres ponding tight dock cones. During a “perfectly aligned”  berthing event, the easy dock cones will pass through the corresponding coarse guide receptacles in the  housing first, and engage the capture pins. The captur e pins are spring mounted on the housing with a  stiffness coefficient of 4.4 N/cm (2 .5 lb/in) and pre-load of 0.75 kg (1 .65 lb). The fine alignment nut is  connected to the housing by a spherical joint and is free to swivel in all directions. Mechanical stops that  restrict the rotation to ±0.5 degree are modeled usi ng the ADAMS bi-stop function. The shear cylinder  that mates with the fine nut is fixed to the coarse alignment cone with the correct geometric offset. This  modular construction allows easy modification of the m odel to account for “as-built” and thermal effects in  future analyses.  

The four corners of the MRTAS model are connected to the SSRMS grapple fixture location fixture by a  NFORCE element representing the fl exibility of the P5 truss. This element is formed from a 24 x 24  stiffness matrix that was generat ed from a test verified finite element model of the P5 truss2. The mass of  the truss is lumped at its center of gravity (CG) location. A bushing element was introduced at the grapple  fixture location to represent the SSRMS flexibility. Stiffness values were obtained from an ADAMS model  of the SSRMS2 configured in the P5 truss ready-to-berth position.   321
P5  Mass lu mped at cg Grappl e Fixture Corner 1 (& 4): Ti ght dock Corner 3 (& 2): Easy dock  P5  Mass lu mped at cg Grappl e Fixture Corner 1 (& 4): Ti ght dock Corner 3 (& 2): Easy dock 

Figure 8.  MRTAS Soft Docking features 

For contact model geometry verification, the AD AMS MRTAS model geometry was output to another  format readable by the Unigraphics CAD programs.  The CAD analysis team imported the ADAMS  geometry into Unigraphics and compar ed the geometry of the course and fine alignment features, as well  as the soft-dock mechanisms, to the validated as- designed CAD model geometry for both the P4 and P5  truss elements. This comparison verified that the ADAMS model geometry was essentially identical to  that of the CAD models, which were built from the final design drawings.  This provided confidence in the initial ADAMS study results, which primarily dealt with the forces required  to achieve “soft-dock” condition when the P5 element is  mated to P4. Again, current plans call for the P5  element to be mated robotically to P4 with the SSRMS  which will push P5 into P4 until the four soft-dock  mechanism pins on P4 engage corresponding slots on P5. The SSRMS has limited push force capability,  depending on the arm geometry for a giv en operation, so analysis is required to verify the robot can  successfully mate the element, even with less than the expected perfect ali gnment between the initial  aligning features on either  side of the interface.  Once the ADAMS model geometry was verified, we c ould proceed to berthing simulation correlation with  the NASA engineering team. They had generated their ow n multi-body dynamic MRTAS simulation in the  JSC-common simulation environment, TRICK. This model  was planned to be used in the real-time robotic  simulation training facility used by the astronauts for crew  training. In that facility they incorporate these  contact models of the Space Station elements to be berthed with the latest real-time simulations of the  SSRMS, controlled by flight-like robot ic control consoles, running the actual flight control software. In  these simulations the crew can practice piloting t he P5 into the soft-dock condition with P4 using the  SSRMS, and can view the operation through graphics si mulating the camera views they would have onorbit. Therefore this planned correlation consideri ng the critical MRTAS berthing contact geometry,  interface stiffness, and sliding friction coeffici ents between the NASA simulation and the Boeing “truth”  model in ADAMS was essential.  322
Results 

Analysis Results   Four berthing cases are selected for ADAMS and TRIC K simulation correlation to verify the adequacy of  the TRICK simulation for real-time studies by NASA JSC engineers to later on be used in simulations with  crew performing the berthing operation in comm and of the SSRMS. The cases presented are time  histories of the P5 berthing operation in the ADAM S contact dynamic simulation realm and exercised the  various coarse and fine alignment features leading to a successful soft dock configuration with all four  soft dock pins engaged. A description of each case follows.  

Case 1 Results   The P5 element is flown in with an initial velocity of 3 cm/sec (1.2 inch/sec) with no misalignments. For  this simulation, the SSRMS spring is disabled and the truss is constrained to move in ISS y-direction  (closing direction). Friction effects are not modeled. T he effects of varying the c ontact force parameters of  the contact model were studied using the following relationships:  F=K* δexp from their baseline values  K= 1.0E5 lb/in  exp=2.1  Figure 9 (Case1a) shows the forces in the spring- loaded capture pin as it engages the alignment cone.  Initial contact occurs at the easy-dock corners (2&3 ). As the berthing operation proceeds and the capture  pins are pushed up, the pin-cone z-c ontact force balances force in the capture-pin springs. After capture  is completed and the pins have clicked in their respec tive slots, the spring forces return to the 7.3-N  (1.65-lb) preload level.  

Figure 9.  Berthing Case 1a: Forces In The Spring-Loaded Capture Pin  Figure 10 (case1b, 1c) shows the y-component of the pi n-cone contact forces. Sinc e there is no friction,  the y-component of the pin-cone contact is zero as  the pin rides along the cylindrical portion of the  alignment cone. After capture pins click in, P5 rebounds  as the shear cylinder hits the fine alignment nut,  and additional impacts occur between pin and cone as it is trapped inside the slot.    323
Figure 10.  Berthing Case 1b,1c: Y-Com ponent Of The Pin-Cone Contact Forces  Figure 11 shows the effect of changing the contact param eter exponent from 2.1 to 1.5. The result is to  stiffen the spring and increase the peak load (green curv e).  This is the global view of the event. The  circled portion of Figure 11 is shown on different scale in Figure 10. 

Figure 11.  Berthing Case 1c: Y-Compone nt Of The Pin-Cone Contact Forces  Figure 12 (case1d) shows the y-component of the fine alignment nut-shear cylinder contact. Impact at  corners 1and 2 are higher than 3 and 4 due to their proximity to the grapple fixture location. 

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Figure 12.  Berthing Case 1d: Y-Component Of The  Fine Alignment Nut-Shear Cy linder Contact  Case 2 Results   Case 2 of the analysis performed is identical to Ca se 1 except that fricti on effects (coefficient of  friction=0.1) are now included at all contacting surfac es and joints. The initial velocity had to be increased  to 3.8 cm/sec (1.5 in/sec) to accomplish captur e and Figure 13 (case 2a) shows the capture-pin spring  forces.   

Figure 13.  Berthing Case 2a: Capture Spring Forces 

The effect of friction can be seen in Figure 14 (cas e 2b). The pin-cone contact force has a non-zero ycomponent as the pin rides along the cyli ndrical portion of the alignment cone.  325
Figure 14.  Berthing Case 2b: Capture Spring Forces w ith Friction Effects  Figure 15 shows that after the capture-pins have clicked in, multiple pin-cone impacts occur as the pin  rattles in the slot. The impacts occur at t he tight-dock corners 1 and 4 (Fig case 2c). 

Figure 15.  Berthing Case 2c: Impacts Inside Cone Alignment Feature 

Figure 16 for the berthing Case 2d shows the y-co mponent of the fine alignment nut-shear cylinder  contact forces. Impact at corners 1and 2 are higher than 3 and 4 due to their proximity to the grapple  fixture location.   326
Figure 16.  Y-Component Of The Fine A lignment Nut-Shear Cy linder Contact Forces 

Case 3 Results   Case 3 includes the SSRMS attached at the grapple lo cation on P5 as a spring to better represent the  behavior of the berthing system. Friction effects are not included. The base of the SSRMS is constrained  to move in ISS Y direction with a constant velocity  of 3 cm/sec (1.2 in/sec). The sprung P5 is not  constrained, so its velocity deviates from the enf orced value at the SSRMS base during the capture  operation. This is shown in Figure 17, case3a. The sp ring forces show the capture pins click in and then  return to the preload value of 7.3 N (1.65 lb). 

Figure 17.  Berthing Case 3a: Soft Dock Spring Forces w ith SSRMS as a Spring  Figure 18, case 3b shows that the SSRMS spring forces (in x and z directions) and moments are  balanced by the constraint forces in the bas e translation joint, where motion is enforced. 

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Figure 18.  Berthing Case 3b: Soft Dock Spring Forces w ith SSRMS as a Spring  The SSRMS spring y-forces during the capture operat ion are shown in Figure 19, case3c. This is a  measure of the push force required for berthing and its ma ximum of 23 N (5.2 lb) for this case is less than  the SSRMS capability of approximately 151 N (34 lb). 

Figure 19.  Berthing Case 3c: SSRMS Spring Y Forces During The Capture  The effect of adding friction is seen in Figure 20,  case3d. The maximum SSRMS spring y force during  capture has increased to 30.7 N (6.9 lb).  328
Figure 20.  Berthing Case 3d: SSRMS Spring Y Force During Capture w ith Friction 

Case 4 Results   This analysis case is similar to Case 3 except for a small misalignment in the initial berthing configuration.  The P5 element is offset in +z direction by 6.3 mm (0.25 in). It is shown in Figure 21, case 4a, that this  causes a relative shift in the initial contact time of the capture pins  to coarse cone. Spring forces at  corners 1 and 3 are smaller due to the offset. Once capt ure pins have clicked in, spring forces return to  their preload value of 7.3 N (1.65 lb). 

Figure 21.  Berthing Case 4a: Contact Time  Of The Capture Pins To Coarse Cone  Figure 22, case 4b, shows the SSRMS spring force Y fo rce during capture operation. As in case 3, these  forces increase when friction effects are included. 

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Figure 22.  Berthing Case 4b: SSRMS spring force Y force during capture operation 

Figure 23, case 4c, shows the shear cylinder to fi ne nut contact force. Corners 1 and 2 have higher peaks  due to the proximity of grapple fixtur e. As the enforced motion continues to drive the SSRMS forward, the  SSRMS spring forces are essentia lly reacted at corners 1 & 2. 

Figure 23.  Berthing Case 4c: Shear Cy linder To Fine Nut Contact Force  330
Discussion Of Results 

The analysis performed for the Cases 1 through 4 served the purpose to understand the sensitivities of  the contact dynamic model to friction, SSRMS interaction and misalignments. The initial ADAMS  simulation appears to indicate that the forces to “soft dock” do not exceed the SSRMS force capability.  These results were also compared to the NASA simulation and they appear to be consistent for  correlation purposes. This was one of the principal objectives of the analyses. It is also noted that the  ADAMS simulation will be further modified and utilized to refine the set of analyses that will provide the  final verification the MRTAS mechanism. 

The modified ADAMS simulation will include all the contact surfaces that contribute to the total “soft dock”  and seating force as well as the different degrees of freedom the MRTAS mechanism possesses at each  of the corners. These steps are necessary to refine the knowledge that the alignment and soft-docking  forces are within the SSRMS capability. More detail ed contact surfaces may add to the total the current  analysis has yielded. It is foreseen that the total fo rce, once a detailed model has been constructed, will  be higher. 

The ADAMS simulation will also include a more deta iled geometric model, since field measurements of  the flight hardware will have been validated and availabl e to be incorporated to the model. In addition,  deflections due to the on-obit thermal environment w ill also be incorporated. At each phase the results  will be assessed and compared to the previous set of  analyses, to achieve the goal of quantifying the  total force to “soft dock” and seat the interface. Thes e results will be also correla ted, as previously stated  with NASA’s models. 

References 

1. Boeing in Brief. [On-line]. Available: http://www.boeing.com/companyoffices/aboutus/brief.html  (2000,  April)  2. Bruner, Wesley  "SSRMS ADAMS Simulation Models." Boeing Technical Mem orandum  J332-2002134, (November 2002), pp. 1-2.  3. Department of the Air Force. Space Environm ent for USAF Space Vehicles  (MIL-STD-1809 (USAF).  Los Angeles, CA: Author (1991)  4. Housner, J.  Recent developm ents in deploym ent analysis simulation using m ulti-body com puter  code .  In J. Stroud, Computational Methods for structural mechanics and dynamics (p. 435).  Hampton, VA: NASA (1985)  5. Jacobson, C., Price, M., & Rudd, R. Space station on-orbit t herm ostructural analysis . American  Institute of Aeronautics and Astronautics Journal , AIAA-97-1040, 157-158, (1997).  6. Katell, G., & As ato, K. Rocket dyne t russ at tachment system fine alignm ent bolt/nut misalignm ent  qualification test report  (ETD-PQ4-C01189). Canoga Park, CA: The Boeing Company. (1999).  7. Lauer, M., & Gustavino, S. Design of EVA-assem bled utility connec tion system s for the international  space station . American Institute of Aeronautics and Astronautics, AIAA-98-1934, 1877. (1998).  8. Nagy, K.  Pre-integrated truss space station and m ethod of assem bly [Abs tract]. American Ins titute of  Aeronautics and Astronautics . (1992, December). 

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Figure 1.  Test bearin g with toroid b all separa tors 

Table 1.  An gular Con tact Ball Be aring Paramete rs  Parameter Typical Fligh t Bea ring Life Tes t Bearing  Type Angu lar Co ntact, Duple x, Tube T ype Same  AFBMA Precision ABEC Grade 7  or Better Same  Mount Back-to-Back Same  Bore x OD x W idth 39.68 75 x 50.8  x 6.35 mm   (1.562 5 x 2. 000 x 0.2 50 inch) Same  Preload 67 ± 9 N (15 ± 2 lb) 200 ± 13 N (45  ± 3 lb)  Max. Co ntact Stres s 758 MPa (1 10 ksi) 1130 Mp a @ 200 N   (164 k si @ 45 lb)  Ball N umber / Diamet er /  Grade 34 ba lls / 3.175  mm (0.125 inc h)  diam eter / Grade 3 Same  Contact Ang le 20 ± 3 de g Same  Race C onformi ty 52 to 53% Same  Lubric ant Grease Oil  Angu lar Ru nout, pair < 20 arcsec Same  Radial Runout, pair < 152 nm (60 microinc h)  (non-r epeat < 100 (4 0)) Same  Lube  Weight per Row 160 – 1 90 mg  (≈15% fill) 30 – 50 mg1  Race Mater ial AISI 440-C per  AMS 5630 (E SR) Same  Ball Mater ial AISI 440-Cper AMS 5618 (CE VM) Same  Ball T reatmen t Passi vated Same & T iC Coating  Toroids PTFE, alternating Same  Running Torque Variati on ± 20% ma x. Same  Max. W eight per Pair 54 g (0.12 l b) Same  160 to 80 mg fo r Bra yco 815Z 

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Test Conditio ns  The b earing pairs were m ounted i nto a cartridg e and then hard prelo aded, wi th the inn er bearin g race s  clamp ed on a geared sha ft (Figure 2 ). The ca rtridges were then i nstalle d into one of Lo ckheed Ma rtin’s  45.7-cm (18-i nch) diam eter vacu um bell jar life test st ations (Figu re 3), whi ch was then pumped do wn to   10-6 Torr ran ge. A compu ter cont rolled  motor locate d external to  the bell jar drives a central bull gea r,  which in turn  drive s up to twelve te st beari ng pairs  concurrently . The o uter b earin g cup is mounte d in  flexures, so that the b earing’s to rque can be  mea sured via  the te st compute r using a strain  gage d torque   reaction ele ment. 

The be arings were continu ously cycled at a stroke of ± 12 d egree s at a spee d of 2.5 cycles per second.  The stroke d oes n ot allow for compl ete rewetting of t he co ntact, b eing sli ghtly greate r than th e inner race  ball tra ck overlap but le ss than one complete b all rotation. Peri odic fu nctio nal tests were perfo rmed   approximatel y every five million cy cles, in ord er to ascertain  bearing he alth. Du ring the se functional te sts,  the bea ring oscillation was stopp ed and the be arings we re imm ediately rotated three revoluti ons i n each  direction at a rate of 60  deg/s. Th e resul ting torq ue signature wa s plotted for co mpari son with prior health  check results.   Bearin g Test  Cartridge 

Figure 2.  Be aring life tes t fixtu re with indiv idual strain gaged b earing car tridges 

Motor Control ler and  Data Acq uisition System Bell Jar Figure 3.  Be aring Life Te st Setu p  336