ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Digital Signal Processing— All digital signal processing is performed in the FPGA. The serial outputs from  the two A/D converters in each sensor head are applied to the FPGA through RS-422 receivers. This  FPGA applies gain, offset, and phase correction, interpolates the signals from each of the sensor heads  to 14 bits (1.22 nm), counts fringes, defines the home position from the index window, formats the output signals and provides timing signals.  Cyclic Error— For gain, offset, and phase (GOP) correctio n, the system uses a patented GOP correction  algorithm that iteratively reduces gain, offset, and phase errors by sensing the respective GOP errors and  adding correction coefficients to the sine and cosine signals.   Once the correction factors are fully reduced, they are fixed so that the encoder position is repeatable, as  shown in Figure 6 and Figure 7.   The Lissajous is a graphical depiction of sine versus cosine. Lissajous roundness is used to measure  cyclic error along with encoder position verses reference. Note that a change in the vector length of the  Lissajous does not result in a position change. 

Figure 6.  Typical MII Lissajous roundness cyclic error correction 

   Figure 7.  Typical MII Lissajous FTT cyclic error correction  A/D conversion and interpolation— To ensure proper fringe counting, the A/D conversion and interpolation  rate is considerably high. The highly effective ca libration/correction algorithm developed by MicroE  provides extremely high accuracy (see the Accuracy Section below).   196
Radiation— MicroE uses radiation-hardened integrated circuits for the encoder electronics. Due to the  inherent radiation hardness of GaAs, radiation environments do not present a problem for the VCSELs in  the encoder. Data shows that the primary effect of high dose  radiation on VCSELs is a moderate  reduction in output power. The encoder design accommodates these levels of changes. The VCSEL driver design utilizes AGC to maintain a constant output power further mitigating the effects of radiation.  Conclusions   The Mercury II Aerospace Encoder prov ides many advantages ove r standard encoders:  /g120 Small, low-mass sensor with ultra low Z-height fits in compact motion systems  /g120 Superior resolution and accuracy - resolutions up to 1.22nm (linear), 268M CPR (rotary); interpolation  accuracy of /g148 30 nm mean, std. dev. 4 nm (linear glass scales); up to ± 1 /g151m (linear glass scales up  to 130-mm long)  /g120 High-speed operation - up to 2.5m/s at 0.1-/g151m resolution  /g120 Versatility - one sensor works, linear or rotary glass scales  /g120 Broad sensor alignment tolerances, built-in red/yellow/green setup LEDs, and pushbutton setup make  sensor, index and limit setup fast and eliminate ancillary setup instruments  /g120 Large alignment tolerances   /g120 Large range of thermal performance  /g120 Proven solid history as reliable and dependable  /g120 Robustness features include all differential digital outputs, all digital signals from the sensor, and  double-shielded cabling for superior EMI/RFI immunity; scale contamination resistance insures  encoder operation even with fingerprints, oil, dust and other forms of contamination  References   [1]  Emil Wolf, Editor, Progress in Optics, Volume XXVII North Holland, Publisher, 1989  

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A Novel Grabbing/Latching Mechanism Without Moving Parts  Brian W. Gore* and Gary F. Hawkins*  Abstract A preliminary design concept and prototype hardware have been developed for a grabbing/latching  mechanism that uses no moving parts. The mechanism uses an innovative material named a M achine  Augmented C omposite (MAC), or MACterial, in a female configuration to accept a male bar or rod with  almost imperceptible resistive force. However, when a reversing force  is applied to disengage the bar/rod,  it is virtually impossible to remove it due to the increasingly applied holding force. In other words, the  higher the removal force applied, the higher the clam ping force to resist it. The theory and physics behind  this and other MACterial concepts are presented herein, as well as several potential applications that  have been defined; surely there are many other applications only limited by one’s imagination.  Introduction – or, How Does it Work?  A “machine” is defined in the Merriam-Webster dictionary as  Machine n, An instrument (as a lever) designed to … modify the  application of force, power, or energy.   The Aerospace Corporation’s Dr. Gary Hawkins has developed a material dubbed a Machine Augmented  Composite, or MACterial, which uses tiny machines, or flexures, embedded within a softer matrix material  to give the composite unique prop erties. For example, when one ap plies a compressive force to a sample  of MACterial, the sample deflects as if it is in shear. Conversely, if one applies a shear force, the material  can either compress or elongate, depending on the direction  of the shear force applied. Figure 1  illustrates a simple 4-bar linkage machine used in a typical MACterial and its resulting stress/strain  response.  Figure 1.  Example Of A Machine To Be Placed Into Composite Material  When a series of these machines, placed in a row or in a 2-dimensional array as in Figure 2, are  embedded into a matrix material such as silicone, graphite epoxy, or any other suitable material (see  Figure 3), the material takes on the properties of the machine when subjected to external loads.                                                    * The Aerospace Corporation, El Segundo, CA  Proceedings of the 39th Aerospace Mechanisms Symposium, NASA Marshall Space Flight Center, May 7-9, 2008  199
Figure 2.  Extruded Nylon Simple Machine (Left); 100 Machines In 2-D Arrangement Before Matrix  Infiltration 25.4 mm (1 in)  Figure 3.  One Ply Of Machines Inside Matrix Material  With a bulk material made up of many little embedded machines, or even a material made up of a few  number of larger ones, one can construct a combination of material and mechanism to accomplish interesting tasks. Figure 4 shows a simple example of a one-layer MAC and an engaged slider bar that  can be measured for push-in or pull-out forces. In this example, pushing the slider bar to the left is  considered the “easy” direction, and pulling it to the right is considered the “hard” direction, since that is the direction with the tendency of the MAC to grab or latch onto the slider bar, much like the common  “Chinese finger puzzles” in which the harder one pulls, the more tightly the subject is constrained.  Layers of Machines   Axial Direction  Lateral Direction Slider Bar   Figure 4.  Grabbing Mechanism Prototype, With Slider Bar Engaged  Theory – or, Why Does It Work?  It is all about friction. The explanation starts with the classical friction equation,   f = /g80/g3* N,        (1)  200
where f is the force required to break static friction and generate motion. A typical plot of this relationship  is shown in Figure 5a, in which several values of /g80 are shown.  (a) (b)  Figure 5.  Classical Friction Relationships  In Figure 5b, F is plotted against the quantity /g80 * N, so one can see that if F is above the dotted equality  line (in the green zone), motion will occur, and vice-versa for the red zone below the equality line.  Normally this relationship is true for the classical block-on-an -inclined-plane example, but this application,  with the schematic shown in Figure 6, is a bit different.    N = Compressive force N        on MAC  f = Friction on MAC  (both act opposite on bar)f /g52/g3 fF N/g803/g802/g801F /g80/g3* N   45o Pull = /g54/g3f Figure 6.  Schematic Of Grabbing Mechanism Prototype, With Slider Bar Engaged  We can also break down the schematic into a more simplified model of what is occurring, as illustrated in  Figure 7.  /g80/g15/g3Ni/g52/g3 /g52/g3 N = F*tan /g52C = F/cos /g52 F F Figure 7.  Force Model for Bar Retraction Case  Assuming there is a small compressive preload, N i, between the gray MAC member(s) and the bar, and if  one begins to pull the bar out of the device (to the right, as in Figure 6), friction between the bar and the  MAC member creates a compressive force, C, in the MAC members which, in turn, increases the Normal  force, N, between the MAC member and the bar. It is now clear that, unlike the classical example, N is a  function of F such that  201
Horizontal vs Vertical Deflection  (3 MACs) 0.01.02.03.04.05.0 0.0 2.0 4.0 6.0 8.0 Vertical Deflection (mm)Horizontal  Deflection (mm ) w/o matrix w/ matrix Figure 9.  Matrix Material Has Little Effect On Bulk Behavior  The next investigative study compared similar results as above for different geometric configurations of  the machines. Samples were con structed with 45-, 60-, and 75-degree  machines in them, and the same  horizontal-vs.-vertical deflection tests were run. It was shown, as in Figure 10, that the “grabbing” efficiency can easily be affected by the design of the machines. For both the 60- and 75-degree  machines, there is more than a one-to-one effect between shear and axial displacement, indicating very  desirable potential applications that can exploit this mechanical advantage.  Figure 10.  Geometric Effects Of Different Angled Machines  Compressive displacement (mm)Shear displacement (mm) In addition, a similar laboratory experiment was con structed to measure the transfer of force from a  compressive direction to a transverse direction, using MACterials. Figure 11 depicts the experimental setup, and Figure 12 displays the force relationship da ta. One can see that the force relationship in Figure  12 is very similar to the displacement relationship in Figure 10 for the same MAC design, with the 45degree machines producing a relationship slope in both cases of slightly less than one.  Figure 11.  Measuring The Relationship Between Compressive And Shear Forces  203
Figure 12.  Effect Of Instron Applied Load On The Lateral Load Caused By MAC Movement  Next, getting back to the type of MAC device discussed in the theory section, Figure 13 shows axial and  lateral force measurements that were made using this setup while sliding the bar in the “easy” and “hard” directions.    Sliding in the “Easy” Direction Sliding in the “Hard” Direction  Lateral Load (lb) Figure 13.  Experimental Data From Insertion/Retraction Test  When sliding in the easy direction, the data in the plots moves from the upper/left direction, where axial  load applied to the bar is zero, and the finite values of lateral load are the initial compressive preload, N i. As axial load is applied and increased, moving to the right, the lateral – or pinching – force gets reduced until the slider bar breaks free. Conversely, when sliding in the hard direction, the data starts out in the  lower/left corner with no axial load applied, bu t with a finite lateral preload, N i. As retraction force is  increased the lateral, or pinching, load moves upward with an increasing slope as the resultant lateral load seizes it.  Data from these measurements can also be shown to be well correlated with ABAQUS finite element  analyses, from which a sample finite element model (FEM) is shown in Figure 14.    Figure 14.  Sample Abaqus Finite Element Model Slider Breaks Free Instron Applied Load (lb)Lateral Load (lbs)MAC Prototype (5 cell)  20 lb preload Lateral Load (lb)Lateral Load (lb) Axial Load (lb) Axial Load (lb) 204
Using a FEM for a sample with a 60o MAC angle, Figure 15 shows one case of measured and  experimental data, and how well they typically agree. Having a well-correlated FEM is very important and  convenient so as to not have to make many differ ent variations of hardware prototypes for testing.  Figure 15.  Correlation Between Analysis And Experiment For MAC Displacement  So far, this paper has discussed the static behavior of MACs, but there has also been a significant  amount of effort expended to study the dynamic response of these MACterials. Specimens can be designed to drastically alter the behavior of impacting bodies, redirecting energy and stresses in ways  that cannot be achieved with standard materials. For example, the use of a material that modifies forces  may provide new methods for energy control in vehicles that can minimize impact dama ge to people or  property. Also being explored is this material’s potential use in ballistic applications, such as bulletproof  vests and armor.  For more information on the dynamic behavior of MACs, see Reference 2.   Conclusion – or, Can it Work FOR YOU?  Machine Augmented Composites have been developed in the Space Materials Laboratory (SML) at The  Aerospace Corporation and have been shown to have the potential of achieving fascinating results. With  the ability to change the direction of force, displacement, shock, or rotation, or act as a one-way retention  mechanism without moving parts, MACs could provide unique and innovative solutions to a wide variety  of problems. By presenting the work done by SML, perhaps it will resonate with one or more members of  the space mechanisms community to solve a particular issue which has eluded a more conventional solution.    Alternatively, devices utilizing this concept, perhaps even in conjunction with current device technology  could be newly developed and used by the industry. Being able to design from the start using MACs  could lead to more efficient designs and better performance, with lower risk. An increased robustness as  a result of a lack of moving parts, pyrotechnics, or other weaknesses in contemporary mechanical assemblies is a driving factor and a worthwhile goal.  There are varied space-related static applications that have been identified thus far for which this concept  could be useful. Some examples include release devices, end-of-travel retention devices, electronic  board clamps, or zero-in sertion force electrical connector inte rfaces. Besides being useful for static  applications, dynamic studies have also led to other investigations, both theoretical and practical, in widely varying areas such as hard-stop load re-distribution, shock attenuation, even sporting goods and  body armor protection. Other space (or non-space) related applications are only limited to the engineer’s  imagination.  205
Acknowledgements – or, Who Did the Work?  The authors wish to acknowledge The Aerospace Corporation’s Independent Research & Development  Program, whose support made this development work, as well as its continued refinement, possible. Michael O’Brien and Tony Tang created the ABAQUS models and ran the drop tower tests, and Rafael  Zaldivar, Juliet Schurr, Dhruv Patel, and James Yamasaki were instrumental in constructing the  experiments, performing the laboratory measurements, and collecting data.  References  1. Hawkins, G. F., O’Brien, M. J., Tang, C.-Y., Von Bremen, H. F., Theoretical And Finite-Element  Modeling Of The Z-Macs , Aerospace Technical Report ATR-2003(8810)-3, September 30, 2003.   2. Tang, C.-Y., O’Brien, M. J., Hawkins, G.F., “Embedding Simple Machines to Add Novel Dynamic  Functions to Composites,” Journal of Materials , March 2005.  3. Zaldivar, R. J., O’Brien, M. J., Schurr, J. N., Yamas aki, J. T., Hawkins, G. F., The Load-Load  Characteristics Of Z-Shaped Machines , Aerospace Technical Rep ort ATR-2003(8810)-2, September  10, 2003.  4. Zaldivar, R. J., Yamasaki, J. T., Schurr, J. N., Hawkins, G. F., The Fabrication And Mechanical  Behavior Of Z-Shaped Machine-Au gmented Composites , Aerospace Technical Report ATR2002(8810)-1, March 5, 2002.  206
Docking System Mechanism Utilized on Orbital Express Program  Scott Christiansen* and Troy Nilson* Abstract Autonomous docking operations are a critical aspect of unmanned satellite servicing missions. Tender  spacecraft must be able to approach the client spacecraft, maneuver into position, and then attach to facilitate the transfer of fuel, power, replacement parts, etc. The philosophical approach to the docking system design is intimately linked to the overall servicing  mission. The docking system functionality must be compatible with the maneuvering capabilities of both of the spacecraft involved. This paper describes significant features and functionality of the docking system that was eventually chosen for the Orbital Express (OE) mission. Key analysis efforts, which included extensive dynamic modeling, are also described. Zero-g simulation tests were performed to validate the dynamic analyses.  The docking system was flown and operated on the Orbital Express mission. The system performed as  intended and has contributed to demonstrating the feasibility of autonomous docking and un-docking of independent spacecraft. Introduction Once on orbit, typical spacecraft have limited lives. The harsh environment and lack of access make any  type of external support or maintenance nearly impossible. Anything from simply running out of fuel to failure of a significant component can end the life of an otherwise useful spacecraft. If some type of servicing capability were possible, flight operators could potentially get more out of their flight systems. While limited servicing capability has been available through the Space Transportation System, or  Shuttle, high cost has limited its use to very expensive systems within the Shuttle’s orbital reach, notably  the Hubble Space Telescope. Over the past decade there has been a push to develop the capability of  autonomous servicing of orbiting spacecraft. The intent is to create autonomous, un-manned, tender spacecraft that might provide services such as spare propellant, or new or replacement parts to already orbiting client spacecraft.   Several practical needs can be met through autonomous servicing  • Extension of the life of spacecraft due to propellant replenishment • Replacement of components that are obsolete or have failed • Capture and move spacecraft to more effective orbit • Recovery of a spacecraft with a failed deployment by assisting deployment • Examination of a spacecraft to determine cause of failure  The company began working on a docking mechanism concept and prototype docking system on an Air  Force Research Laboratory (AFRL) Small Business Innovative Research (SBIR) program in 1999. As the docking mechanism design matured, the Orbital Express program was developing requirements for  docking hardware. These eventually converged and our docking system was chosen for the flight demonstration. * SpaceDev, Louisville, Colorado  Proceedings of the 39th Aerospace Mechanisms Symposium, NASA Marshall Space Flight  Center, May 7-9, 2008  207
establishing a rigid interface. Release of the structure would be achieved by reversing these steps, with  separation velocity provided by the spring loaded kinematic mounts. Construction on the prototype developed under the Phase I SBIR was completed in the early part of 2000. Figure 2 shows a picture of the completed design.  Figure 1: SRC grappling concept   Figure 2: SRC prototype  Prototype Testing Beginning in early 2000, SRC began extensive testing on the prototype hardware in order to evaluate its  effectiveness and limitations. The test program included two significant components:  /g120 In-house off-load testing: An off-load fixture was designed and manufactured to assist in  understanding various dynamics of docking as well as to prove system ability to dock and  transfer cryogenic fluids (LN2).  /g120 Micro-gravity flight: A test plan was developed and executed to test the prototype in a microgravity environment.  Counter Balanced Off-load Testing In order to gain a general understanding of the docking system dynamics, a test was constructed using a  simulated inertia mass and cable/pulley system. Figure 3 shows the system with the prototype mounted  in the lower left hand corner. The passive side was mounted to an adjustable tip/tilt fixture allowing tests to be performed in various misalignment configurations. Adjustment of the cable attachment point (universal joint) and offload weights provided an approximation of a zero-g environment. During development, more than 200 mechanical mate/de-mate cycles were successfully completed.  209
Figure 3:  Off-load setup   Figure 4: Micro-g flight  Micro-gravity Testing The second component of testing included a flight on NASA’s modified KC-135 aircraft flown from  Ellington Field near Johnson Spaceflight Center (JSC), Houston (Figure 4). The experiments focused on  the grappling and capture events that could be accomplished within the 25-second micro-g window each  parabola. The experiment was designed to have two separate, free-floating simulators that represent the relative mass and inertia of a client and a servicing satellite (approximately 2:1, client to servicing). The active and passive halves of the prototypes were each mounted to their respective mass/inertia simulator. With JSC crew assistance, the two halves were positioned within capture range. The active docking mechanism was immediately powered in an attempt to demonstrate “zero” gravity docking. Because of the limited time in micro-gravity, consecutive phases of the docking sequence were performed throughout  a series of parabolas. Despite these limitations, the micro-gravity tests proved instrumental in  demonstrating the mechanism behavior. The basic functionality of the docking system was demonstrated.  Observations of dynamic behavior during the test led to improvements of the design prior to the next prototype build.  Development of 2 nd Prototype and Orbital Express Flight Design  The OE program was intended to develop an industry-wide standard architecture to perform cost effective  autonomous satellite servicing. To demonstrate the technology, OE planned to use two spacecraft:  the client vehicle, referred to as NEXTSat, and the servicing vehicle, referred to as ASTRO. An illustration of the OE vehicles is shown in Figure 5. The demonstration mission launched both vehicles together and performed a series of mating and servicing operations on-orbit. Orbital Express and the Phase II SBIR A major criterion for autonomous docking success is the reliability of the capture system. SRC already  had developed and tested a functional prototype, and the capture requirements were well suited to the SRC design. OE was still in the proposal stage and the design of the mechanical docking system (MDS) [this was the second generation prototype/engineering unit] was proceeding under AFRL funding. It therefore became necessary to balance the design objectives of OE within the practical limits of the SBIR scope. At the onset of the MDS design effort, SRC worked closely with Boeing, who was providing much of the initial insight into the technical requirements. 210