ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Measured Initial Harmonic Drive Stiffness  Rotation Angle  Figure 15. Typical Harmonic Gear Assembly Stiffness  Note two regions of stiffness: low near zero torque and larger at high torques.  The following figures are from measured data on the fliaht harmonic aear assemblies:  (Note: the following figures' axes are rotated relative to Figure 15)  .,~ __-......._.I *_. . :, r. . ,. . .. . . . . . . . . . . . .. . , ..  I  Applied Torque Applied Torque  Figure 16. Stiffness Curve Showing  Low Stiffness Region Figure 17. Stiffness Curve with Minimal  Low Stiffness Region  49
ji  Applied Torque Applied Torque  Figure 18. Next Larger Plug Size Over Figure 17 Figure 19. Next Larger Plug Size Showing  Showing a Small Change in Shape Showing Little Change  Conclusions and Lessons Learned  The most significant result of the failure investigation was determining that the internal stresses due to the  preload and the cable harness loading caused the premature failure of the EDU harmonic gear assembly.  In order to maintain reliability for long life applications, increasing the wave generator plug size (a service  provided by the harmonic drive vendor) is an acceptable technique up to the point where the low stiffness  region is eliminated. This is the maximum stiff ness enhancement achievable without compromising the  reliability of the gear assembly for long life. Any further increase in the wave generator plug size will  increase the stiffness at the cost of reducing the life of the unit. For minimal life applications, increasing  the stiffness beyond this point may still be acceptable.  Stiffness enhanced harmonic gears are very sensitive to the externally applied load and test environment.  Since the failure mode is galling, the presence of any gas (nitrogen, for example) severely compromises  the test results. Life capabilities from previous heritage programs had been successful and so the initial  gear material for the MRO gimbal actuators was considered acceptable and robust. However, some of  the heritage operation had been performed in nitrogen, instead of vacuum. When enhanced stiffness is  required in a harmonic gear application and it is not being used in a preload configuration represented by  Figure 16, the situation is sensitive to possible galling of the harmonic gear teeth. Performing harmonic  gear component operation at loads above the planned level to increase the tooth contact stresses should  be considered. This will demonstrate if internal stress margin exists in the hardware. Also note that  running a harmonic gear at a high input speed to reduce the operating time is not adequate. The high-  speed condition may function with no incidents while low speed operation may catastrophically quit  functioning. Finally, operating a unit at nominal contact stress levels to a larger number of revolutions  than planned is a necessary, but not complete, margin demonstration program. A catastrophic failure may  be lurking just a few megapascals away from the nominal value.  References  Harmonic Drive, LLC web site, www.harmonic-drive.com/suppor-t/principals.htm, description of harmonic  gear assembly operation  Acknowledgements  This work was performed at Lockheed Martin Space Systems, Denver, Colorado under a spacecraft  system contract to the Jet Propulsion Laboratory, California Institute of Technology, under a contract with  the National Aeronautics and Space Administration. Reference herein to any specific commercial product,  process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its  endorsement by the United States Government, the Jet Propulsion Laboratory, Pasadena, California, or  Lockheed Martin Space Systems, Denver, Colorado.  50
Stacer Driven Deployment: The Stereo Impact Boom  Robert Ullrich’, Jeremy McCauley*, Paul Turin*, Ken McKee* and Bill Donokowski*  Abstract  The Impact’ Booms carry 3 scientific instruments each on the twin NASA Stereo2 satellites. When stowed  for launch the boom is 1.54 m in length, when deployed the boom extends to 5.80 m. The boom consists  of 5 concentric graphite epoxy (GlE) tubes extended by the spring force of a Stacer. The Stacer is  fabricated from a flat strip of Elgiloy spring material, rolled with a constant diameter and fixed helix angle.  It supplies the motive force for deployment, and requires no external power once released. The deployed  boom exhibits excellent rigidity, the natural frequency first mode occurring at 1.96 Hz. Discussed is the  implementation of a Stacer to deploy the 5 segment telescoping boom and some of the activities  performed during its design, qualification and testing.  Mission Introduction  The NASA Stereo mission consists of twin, three-axis stabilized satellites orbiting and viewing the Sun in  the plane of the ecliptic at -1 AU. Spacecraft A (Ahead) will be sent into an Earth preceding path with an  Earth-Sun-Spacecraft angle increasing at e rate of 22’ per year, while Spacecraft B (Behind) is sent into  an Earth lagging orbit, also at a rate of 22 per year. The imagers on board will yield true ‘stereoscopic’  views of coronal mass ejections, while other instruments perform concurrent in-situ measurements of a  large portion of the electro-magnetic spectrum. The telescoping boom was conceived to interface 3  instruments from the Impact suite: the Magnetometer (Mag), the Solar Wind Electron Analyzer (SWEA),  and the Supra-Thermal Electron - Downward looking instrument (STE-D) to the Stereo spacecraft. The  program requirements demanded a new concept, as existing hardware was deemed too expensive or  unsuitable. The boom was initially developed via three ‘proof of concept’ models for the tube locking  mechanism, and a final mock up using the Stacer to deploy four concentric, telescoping graphitejepoxy  tubes from the center of the fixed 5th tube. An engineering model (EM) was then built to verify end to end  design via qualification testing. The challenge for this mechanism was demonstrating that the design met  the requisite GEVS SE3 force (torque) margin. Two flight models (FMs) were then produced, with the EM  being refurbished as a flight spare. The FMs are currently mounted to the spacecraft and mission I & T is  progressing. Launch is scheduled for May 2006 from Cape Kennedy on a Delta II.  Figure 1 Magnetometer, SWEA and STE-  D mounted on the end of the Istowed) Figure 2. Magnetometer  ’ Space Sciences Lab, University of California, Berkeley, CA  ’ In-situ Measurements of Particles And Coronal mass ejection Transients  * Solar - TErrestrial RElations Observatory ’ See References Section  Proceedings of the 3dh Aerospace Mechanisms Symposium, Langley Research Center, May 1 7- 19,2006  51
e  Figure 4. Solid Model Section View of Stowed Impact Boom  Impact Boom Mechanism  The Impact Boom consists of five concentric Gr/E Tubes, ranging from 50 mm to 210 mm in diameter,  with a pair of aluminum rings bonded to each end. Each ring pair contains three lock pins, pointing  outward at the Sun-ward end, and inward pointing at the release mechanism end, and three sockets, in  their corresponding orientations. The pins are spring loaded, and have rollers mounted in their tips. When  released, the Stacer spring extends the tubes until the end of travel where the pins drop into sockets,  locking the assembly rigid. The mounting feet are integral to the outermost rings on the 0210-mm tube.  There is a spool for the electrical harness while stowed, a flyweight brake to govern the deployment  speed, a shape memory alloy release mechanism with pretensioning adjustment, deployment assist rods  and kick springs to initiate the deployment. Combs at each end hold the tubes in alignment prior to  deployment, and during vibration/launch. A provision for individually adjusting the combs to remove any  play in the stowed tubes due to fabrication tolerances is also provided. The design was performed in  SolidworksTM, utilizing its 3-dimensional solid modeling and multiple configuration capabilities.  Tube Details  q-  .I I The use of telescoping concentric tubes is not a new idea. Each telescope  application brings its own set of challenges however. For the Impact  Boom, the tubes needed loose tolerances on their cylindricity callout to  allow for simple tube manufacture. The deployment / locking scheme  required compliance regarding the inter-tube fit since there is a relatively  low force available from the Stacer. The boom needed to be very rigid  when deployed, so locking pins were utilized at end of travel, rather than  relying on spring force to hold them in place. The tubes have three  longitudinal concave grooves equispaced  about their circumference, running their  length, with a precise profile that doesn’t jam  the rollers. These grooves kept the pins on  track to be aligned with the sockets at the far  end of the tube. The tubes are a five-layer  Gr/E composite ~ designed to be quasi-  isotropic: three 0 -90 layers interleaved with  two 45’ layers of 0.1 2-mm woven epoxy pre-impregnated material (Fiberite  Hy-E 1034C prepreg). The tubes were fabricated by Vision Composites of  Signal Hill, California on internal mandrels, with a slight taper to enhance  ease of extraction after cure. The cure regimen was specified to be ‘dry’: the  ratio of epoxy to carbon filament was held to a minimum to ensure low  surface resistance. This was achieved by using a higher autoclave pressure  with a slower ‘warm up to cure’ temperature ramp and a thick layer of  absorbent over the bleeder sheet. The process determination was somewhat  lengthy, however, the final result met requirements. ’  Figure 5. Tube  End Detail  Figure6 Partially  Deployed Tubes  53
At both ends of each tube there are inner and outer interlocking aluminum rings that ‘sandwich’, and are  bonded to, the Gr/E. After an extensive search, Loctite Hysol 9309NA was used to form the bond. The  thermal environment for the boom is rather severe: it will be in the shadow of the spacecraft for all of the  science activity; thermal analysis estimates put the operating low temperature at 30K. There is very little  data for epoxies at this temperature, so we performed an FEA for the bond between the aluminum and  the Gr/E to establish what parameters minimized the stresses in the glue, the weakest part. Several  cases for the glue design were examined: thickness of the bond, edge conditions of the bond and effects  of the aluminum ring thickness (internal and external) on the joint stresses. Optimized, the glue line was  1 vo. mue. 1 vo. YUU  Figure 7. FEA of Aluminum Ring - Glue Line - Gr/E - Glue Line - Aluminum Ring  chosen to be -0.4-mm thick, with a fillet onto a tapered aluminum ring edge. This best case predicted a  stress value of 11OvMPA (16 k~i)~, which exceeded the glue published maximum stress value of 38 MPa  (5.5 ksi)’.  There was concern that the joint would not be sound after exposure to the thermal gradient, so an actual  test was needed. A test GR/E tube / aluminum ring  assembly was fabricated, with a large cantilever  mass attached at the extremity providing -2X  expected loads for this test. This test ‘tube’  assembly was installed in a cryogenic liquid  helium chamber, which was then installed into a  cryogenic liquid nitrogen chamber in turn was  placed inside of a refrigerated chest. We  performed a multiple cycle thermal test (in a dry air  environment), utilizing four candidate gl!es. The  cold temperature was set to 25K (-248 C), and  nominally, with no crazing or cracking and was warm was 150K (-1 23’C). The 9309 performed  accepted for use. As a side note, only one of the tested epoxies exhibited any signs of thermal distress.  As a hedge against exceeding our thermal predicts, small solar absorbers were attached to the two joints  in the mid boom. These little flags raise the expected temperature by -5 degrees, buying some margin for  the assembly (Figure 6). I  Figure 8’ Epoxy Thermal Test Chamber  Besuner Consulting, Madera, CA 93638  Loctite Hysol Applications Note, April 101, Loctite Aerospace, Bay Point, CA 94565 4  54
At deployment, the formation of the Stacer starts with the initial coil winding out of the storage canister  onto a cylindrical tip piece, which is slightly larger than the free coil diameter of the Stacer. Thus the  Stacer grabs the tip piece tightly, and the subsequent coils ‘stack’ up on the prior, producing the  characteristic spiral appearance. The typical helix angle provides for significant overlap, such that a  section taken at any point along the Stacer would yield at least two thicknesses of strip material. Since  the ‘outer’ layer of strip is rolled to the same diameter as the inner layer, the outer grips the inner with a  force normal to the surface. So between layers, significant inter-coil friction exists and prevents inter-coil  slipping for small disturbances. This gives the Stacer one of its more useful properties: it behaves as a  thin walled tube for small displacements, with similar bending strength and stiffness. If a larger  displacement occurs, the coils slip, dissipating the strain energy, serving as a friction damper. The  damping ratio value is typically 5 - 15% for the non-slipping regime, and can reach 30 - 40% with the  slipping. Of course, the displacement limit is buckling, as any tube would experience when taken beyond  its yielding strength.  As described, the motive force for the deployment is a Stacer. When compressed (stowed) it is a very  compact package: it fits in a cylinder 050 X 130-mm long. When the Stacer is stowed, the strip is flexed  into the canister, laying each coil inside its predecessor, and wound tightly to the outside of the can.  When released, this stored strain energy is reclaimed, giving the motive effort needed to move the tubes  along their path. The Stacer generates a higher force at the beginning of stroke, -46 N for this  application, and the force curve dropped to 1 N at the end of stoke (this was an isolated minimum value  obtained from one force test). The force that the Stacer provides is shown in the polynomial fit curve in  Figure 13.  Impact Boom Stacer Push Force  50  25  20 3 0 1 2 3 4 5  Deployed Length (m)  Figure 13. Stacer Force  57
I Impact Magnetometer Alignment  0.090  0.085  0.040 0.045 0.050 0.055 0.060 0.065 0.070 0.075  -1 Average Deviation in the X-Y Plane (degrees)  Circle Diameter = Std. Deviation  Figure 17. Magnetometer Alignment Error  For the final determination of pointing error, the root of the sum of the squares was calculated to give the  magnitude of the deviation (the directiqn is not of interest as long as the specification is met), Flight Model  1 measured deviation "used up" 0.10 of its allowable 0.88O margin, while FM2 used 0.11 . The Impact  Boom deploys accurately, repeatably, and exceeds requirements by a large margin.  Lessons Learned  Desian for test.  The final validation of any design is complete when the device performs as expected in its orbital  environment. GEVS SE gives guidelines, developed over many programs, as to what tests must be run,  and how much extra (or over-) testing is needed. For the boom to be tested, a vacuum chamber was  required to be built in a vertical orientation. The initial plan had been to use a horizontal track, using an  existing facility. This plan did not give sufficient demonstration of the booms ability to deploy in a straight  line as the track would have given alignment to the sections through out their travel. Additionally, the drag  induced by the lock pin rollers when the tubes deploy horizontally far exceeded the Stacer deploy force.  At the time the decision was made to go vertical, the Stacer should have been sized to allow a non-  counterweighted deployment. There would have been a mass hit, but being able to leave off the gantry  would have been a great savings, as the chamber would not have had to be as tall.  Safetv  One person was iniured durina initial installation of the stacer into its canister. As the final Dortion was  stowed, the safety ietaining pinwould not fit into the hole provided for it. When additional force was tried,  the operator lost control of the stacer and it deployed in an uncontrolled manner to -1 m, when it was  grabbed, cutting their finger deeply through two sets of latex gloves.  Some points arose from the review of the accident:  a) Check fit all safety related parts, sub-assemblies and fixtures. The size + tolerance of the hole  for the safety pin were too small after plating to allow the pin to be inserted. This would have been an  easy test, prior to assembly.  b) Have back up hardware and personnel: the operator was working virtually alone, and had no  back up person there to hold the stacer while the pin was being inserted. After the finger was cut, a  colleague from another part of the lab had to run to help control the stacer and finger damage. Another  61
point for spring loaded deployables: don’t rely on a single safety path. A lock down plate in front of the  stacer assembly would have caught the stacer, preventing damage. These recommendations have been  implemented in the procedures, and stowing fixture used now: the stowing procedure has a minimum  requirement of two persons to proceed.  Materials SDecifications  Often materials can be useful beyond supplier’s data, one only needs to verify what limits to the previous  testing exist. The search for a cryogenic temperature suitable glue was fruitless. In the end a test was  performed to establish suitability, after much effort. The question to add after “At what temperatures does  the product perform satisfactorily?” is “Has it been tested beyond that?” A fair number of days could have  been saved by realizing the manufacturers don’t have all the information.  Marain  While most programs have a margin requirement, it is good to carry some margin for additional mass  demands while designing. This is almost rhetorical. The proposal mass for the instruments at the end of  the boom was 1.2 kg. After deliberation, it was determined that the data would be significantly better if  pre-processing were done closer to the detector, so additional circuit boards were added out at the end,  raising the deployed end mass to 2.2 kg. This drove the size of the release mechanism from being ‘off the  shelf‘ to a new, custom version, requiring additional testing, with the usual learning curve associated with  new mechanisms. The entire structure needed ‘beefing up’ to accommodate the added loads.  Summary  The Impact Boom has completed qualification and acceptance verification for use in flight for the NASA  Stereo mission. This application has shown the use of a Stacer spring can be implemented for major  deployables as a motive force, not only as a sensor or sensor support. This represents a major cost  savings from traditional motor driven deployables, with their associated high cost electronics. Currently,  the launch is planned for 26 May 2006, with deployment of the boom occurring within a 3 - 30 day window  after launch.  Acknowledgements  Thanks go to Dr. Janet Luhmann, Principle Investigator for the Impact Suite, and the entire Impact Boom  Team at the University of California Berkeley, the Space Sciences Lab. Also to NASA Goddard Space  Flight Center for working with us to get this new hardware off the ground, and to all the reviewers whose  inputs and criticisms helped make the boom robust enough to survive qualification. Thanks also go to the  Stereo crew at APL for their continued support for the program.  62
I .-  Figure 18. Stereo “B” Spacecraft: Impact Boom location  References  Space System Reliability and Safety Office, Code 302; “General Environmental Verification Specification  for STS and ELV, Rev A; (June 1996), National Aeronautics and Space Administration, Goddard Space  Flight Center, Greenbelt, MD 20771; June, 1996; 32.4.5.3 - 2.4.6.2  Appendix A  1543.1 [60.757 Overall inc Blanket at each end  Figure 19. Impact Boom ICD Detail: “B” Stowed  63
4260 [I 67.72-1  (Deployment Travel)  r SWEA Deployed Position m ‘i  2 r ” r SWEA Stowed Position  +X ___)  - 1267.4 [49.907  (from Boom 4299.5 Origin [I to 69.272 Magnetometer) ------I - 5803.1 1228.477 (Overoll incl Blankets at each end) -1  DETAIL B  Boom Origin  (Bottom of Insulator Pad)  Figure 20. Impact Boom ICD Detail: “B” Deployed  64
cools, a Push Piston return spring resets the actuator for further ground testing. Resetting of the cover  and Latch Arm is manually performed.  Latch Mechanism  Cover 7  Hinge  Mechanism 7  Energy  Absorber  Mechanisms  Energy  Absorber  Structure Figure 1. Cover Deployment  L and Latch Cover Ring  Magnets  Instrument  Canister  Microswitches  -  LatchArm - 1  Figure 2. Latch mechanism and Cover/Cover Ring  66
Hinge Mechanism  The Hinge mechanism works by means of two sets of nested compression springs acting against a lead  screw / carrier nut combination. A clever and complex design, the Hinge is fully single fault tolerant. For  some failure modes, such as the loss of a spring, the Hinge is two-fault tolerant. A graphic of the Hinge  mechanism is presented in Figure 5 and a cross section is shown in Figure 6.  In the cover-closed position, the compressed springs react against the Hinge mid section and the spring  support end, which are restrained from rotation by shoulder screws and rollers running in slots in the  housing. Attached to the spring support end is the lead screw, which is also restrained from rotation. The  lead screw passes though a carrier nut, which is constrained from translation, but allowed to rotate. As  the lead screw translates, the carrier nut rotates. The cover is attached to the clevis, which in turn is fitted  on roller bearings on the carrier nut. Pins fixed in the carrier nut and clevis engage during rotation, driving  the cover open. Each side of the hinge mechanism works independently of the other. If one side jams, the  Clevis rotates freely on the bearings. If a Clevis bearing freezes, the carrier nut and Clevis can rotate on  the inner bearing.  rn Should screw /  Rollers  Spring Support End  Housing L  Clevis Translating  Rotating  Fixed I Lead Screw  Figure 6. Hinge mechanism cross section  Energy Absorber Mechanism  The GALEX Energy Absorber used a compression spring in combination with a ratcheting plunger. Once  the plunger was pushed in, the ratchet held the plunger and compressed spring fixed. Hall effect sensors  imbedded in the striker and magnets mounted on the cover provided telemetry of a deployed cover. The  cover magnets also served to latch the cover open. One disadvantage of the GALEX design was that  after each cover deployment test, the Energy Absorber had to be disassembled to be reset. It was  requested by the project to simplify the GALEX Energy Absorber design with replaceable, crushable  honeycomb.  We desired to keep the new energy absorber function as similar as possible to the GALEX mechanism  due to the support structure design. The housing and Hall effect sensor striker were left relatively  unchanged, but the compression spring and ratcheting device were replaced with crushable honeycomb  core. The honeycomb core is bonded to a simple disposable aluminum plate which is attached to the  plunger. The push rod and Hall effect sensor striker are then attached to the plunger, creating the plunger  subassembly. As the magnets mounted on the Cover impact the striker during a deployment, the core is  crushed against the Energy Absorber End Cap. See Figure 7 for an exploded view of the crushable  honeycomb Energy Absorber mechanism and Figure 8 for a graphic of the Plunger subassembly.  The Energy Absorber honeycomb core is replaced after each cover deployment. The Push Rod is  segmented in two pieces with a left-hand thread so that the Hall effect sensor striker and front segment  68