2006-2007 - Kennedy Space Center Technology Transfer Office

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Automated Method for Estimating Nutation Time Constant ModelParameters for Spacecraft Spinning on AxisSpacecraftNutationModelsFigure 1. DI configuration (with stand-off).Calculating an accurate nutationtime constant (NTC), or nutationrate of growth, for a spinning upperstage is important for ensuringmission success. Spacecraftnutation, or wobble, is caused by energy dissipationanywhere in the system. Propellant slosh in the spacecraftfuel tanks is the primary source for this dissipation and,if it is in a state of resonance, the NTC can become shortenough to violate mission constraints. The Spinning SloshTest Rig (SSTR), developed by NASA and SouthwestResearch Institute (SwRI), is a forced-motion spin tablewhere fluid dynamic effects in full-scale fuel tanks can betested in order to obtain key parameters used to calculatethe NTC. We accomplish this by independently varyingnutation frequency versus the spin rate and measuring forceand torque responses on the tank. This method was usedto predict parameters for the Genesis, Contour, and Stereomissions, whose tanks were mounted outboard from the spinaxis. These parameters are incorporated into a mathematicalmodel that uses mechanical analogs, such as pendulumsand rotors, to simulate the force and torque resonancesassociated with fluid slosh.Most recently, the SSTR was modified to simulate the onaxisspin motions of the centerline-mounted tanks used inthe Pluto New Horizons (PNH) and Deep Impact (DI)spacecraft (Figures 1 and 2). We varied diaphragm shapes(Figure 3), nutation frequencies (ratio of upper-motor toFigure 2. PNH configuration (withoutstand-off).Figure 3. Diaphragm shapes tested by SwRI.total revolutions per minute [RPM]), and fill levels ata constant spin rate of nearly 60.5 RPM to examinehow the various force and torque activity wouldinfluence the mechanical analog parameters. Datawas recorded while each fill level/diaphragm shapecombination underwent a nutation sweep wherespecific nutation frequencies ranged from 10 to90 percent of the total spin rate. After testing, it wasdetermined that the pendulum analog parameterscould be set to zero because very little resonanceactivity was observed in the force response along thetank wall, leaving the rotor analog available to be thesole influencer of the torque response. These ideal, ormassless, rotors have inertia only about their primaryaxis of spin. Their associated parameters includeinertia and spring/damping constants.The current method for identifying modelparameters involves laboriously hand-derivingequations of motion for both the SSTR andmechanical analogs and, by trial and error,82 Fluid System Technologies
a compatible spacecraft model where the NTCcan be calculated and compared with flight data.This proven process will be a valuable tool forquickly examining both traditional and novelmechanical fuel slosh analogs and for allowingspacecraft designers to build accurate sloshmodels early in the design phase, when potentialNTC violations can be avoided.Contacts: James E. Sudermann , NASA-KSC, (321) 867-8447; andKeith L. Schlee , AnalexCorporation, (321) 867-4186Participating Organization: Southwest ResearchInstitute (Dr. Steve Green and Russell C. Burkey)Figure 4. Overall layout of on-axis SSTR SimMechanics model.comparing their results with experimental results. Astrong desire exists to automate this method so differentanalogs can be tested quickly and the results can becompared with measured data.The method presented accomplishes this task by usinga MATLAB Simulink/SimMechanics-based simulationwhere the parameters are identified by the ParameterEstimation tool. Simulink Parameter Estimationprovides a graphical interface where several optimizationalgorithms can be selected. The simulation incorporatesthe same slosh analog used by SwRI, two torque rotorsabout the radial (x) and tangential (y) axes (Figure 4),allowing direct comparisons between the hand-derivedand automated methods. Six sets of measured data canbe supplied to the simulation for parameter estimation.These include forces (Fx/Fy) along the tank wall andtorques (MR/MT) resolved to the tank center of gravity(CG) (Figure 5), as well as the angular velocities ofthe tank CG (Ωx/Ωy) about each axis. Each nutationsweep test, usually consisting of 9 to 11 individualnutation frequencies, is supplied to the Estimator, whereits multiple dataset estimation feature can be used.Estimating to the entire set of measured data allows therotor parameters to be optimized for reproduction of thetorque resonance response over the entire range of testednutation frequencies (Figure 6).Current research efforts focus on identifying andrecording the differences between the hand-derived andSimMechanics methods, such as the effects of largerrotor inertias. Once complete, the same SimMechanicsanalog used in the SSTR model will be incorporated intoForce (lb) / Moment (in.lb) / Angular Velocity (rad/s)100806040200–20–40–60–80–10020 20.5 21 21.5 22 22.5 23 23.5 24 24.5 25Time (s)Measured FX Simulated FX Measured FY Simulated FYMeasured MRSimulated MRMeasured MTSimulated MTFigure 5. Comparison between measured and simulation dataat a nutation rate of 0.44 for typical PNH test (upper-motorRPM = 26.26, lower-motor RPM = 34.30).Phase Difference: MR–ΩY (deg)8765432100.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Nutation Frequency / Spin RateMeasuredLow Rotor Inertia Limits (lx=ly=2,750)Converged Rotor Inertias (lx=10,191, ly=10,463)SwRI Rotor Inertias (lx=1,400, ly=1,500)Medium Rotor Inertia Limits (lx=ly=4,000)Figure 6. MT-to-WY phase comparison using variousestimated parameters (inertia unit: lb.in 2 ).KSC Technology Development and Application 2006-200783
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ForewordSuccessful technology devel
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ContentsSpaceport Structures and Ma
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Contents (continued)Process and Hum
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IntroductionJohn F. Kennedy Space C
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Constellation SystemsSurfaceSystems
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Spaceport Structures and MaterialsK
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20181614∆ E1210Modified Sensor Be
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Initial results of the EDEM model o
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Contacts: Dr. Carlos I. Calle ,NASA
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Close examination of the corrosions
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Adhesion at Failure (psi)2500200015
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Figure 1. After 500 hours of salt f
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Contacts: Dr. Paul E. Hintze , NASA
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Figure 2. Repairs to various types
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on top of the cuvette contains the
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Figure 2. A corrugated NiTi sheet e
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The PLTD can be used to (1) calibra
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SEM images of neat MWNT fibers: (a)
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Contacts: Trent M. Smith
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Figure 1. An isometric cutaway view
Page 45 and 46: Figure 2. Quartz sand flowing in th
Page 47 and 48: Figure 2. Top images show how the e
Page 49 and 50: Sand volume fraction contour at t =
Page 51 and 52: Integrated LWRD/RVC engineering bre
Page 53 and 54: Mean relative percentage change in
Page 55 and 56: We compared the model’s predictio
Page 57 and 58: Figure 2. Three-dimensional simulat
Page 59 and 60: Figure 3. Camera calibration model.
Page 61 and 62: The sketch in Figure 2 shows alaunc
Page 63: Figure 2. Signal generator (right)
Page 66 and 67: Hail Size Distribution MappingA 3-D
Page 68 and 69: Launch Pad 39 Hail Monitor Array Sy
Page 70 and 71: Autonomous Flight Safety System - P
Page 72 and 73: The Photogrammetry CubeSpaceport/Ra
Page 74 and 75: Bird Vision SystemThe Bird Vision s
Page 76 and 77: Automating Range Surveillance Throu
Page 78 and 79: Next-Generation Telemetry Workstati
Page 80 and 81: GPS Metric Tracking UnitAs Global P
Page 82 and 83: Space-Based RangeSpace-Based Range
Page 85 and 86: Fluid System TechnologiesKSC Techno
Page 87 and 88: 0.900.850.80Discharge Coefficient,
Page 89 and 90: Composite seals for performance eva
Page 91 and 92: 140000120000100000Signal80000600004
Page 93 and 94: Contacts: Dr. Barry J. Meneghelli ,
Page 95: 60555045Comparative k-value (mW/m-K
Page 99 and 100: In an ongoing effort for improvemen
Page 101: Low-gravity probe prototype test.th
Page 104 and 105: Countermeasure for Radiation Protec
Page 106 and 107: Focused Metabolite Profiling for Di
Page 109 and 110: Process and Human FactorsEngineerin
Page 111 and 112: DON uses game technology to enable
Page 113 and 114: Type of mobile crane that impacted
Page 115 and 116: SALT proof-of-concept communication
Page 117 and 118: SSLM CAD model.Our design offers th
Page 119 and 120: Variables that can be integrated by
Page 121: Exploration Supply Chain Simulation
Page 124 and 125: Nanosensors for Evaluating Hazardou
Page 126 and 127: Sixty-four-Channel Inline Cable Tes
Page 128 and 129: Wireless Inclinometer Calibration S
Page 130 and 131: Generating Safety-Critical PLC Code
Page 132 and 133: Spacecraft Electrostatic Radiation
Page 134 and 135: Ion Beam Propulsion StudySpacecraft
Page 136 and 137: RT-MATRIX: Measuring Total Organic
Page 139 and 140: Appendix AKSC High-Priority Technol
Page 141 and 142: Risk Assessment ToolMission Data Fe
Page 143 and 144: Appendix BInnovative Partnership Pr
Page 145 and 146: system for the Government, using th
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tracking objects after launch, and
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2006-2007 - Kennedy Space Center Technology Transfer Office

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