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Implementing a Digital Phasemeter in an FPGA
Firmware for implementing a digital phasemeter within a fieldprogrammable gate array (FPGA) has been devised. In the original application of this firmware, the phase that one seeks to measure is the difference between the phases of two nominally equalfrequency heterodyne signals generated by two interferometers. In that application, zerocrossing detectors convert the heterodyne signals to trains of rectangular pulses (see figure), the two pulse trains are fed to a fringe counter (the major part of the phasemeter) controlled by a clock signal having a frequency greater than the heterodyne frequency, and the fringe counter computes a timeaveraged estimate of the difference between the phases of the two pulse trains.
PostFlight Estimation of Motion of Space Structures: Part 1
A computer program estimates the relative positions and orientations of two space structures from data on the angular positions and distances of fiducial objects on one structure as measured by a targettracking electronic camera and laser range finders on another structure. The program is written specifically for determining the relative alignments of two antennas, connected by a long truss, deployed in outer space from a space shuttle.
PostFlight Estimation of Motion of Space Structures: Part 2
A computer program related to the one described in the immediately preceding article estimates the relative position of two space structures that are hinged to each other. The input to the program consists of timeseries data on distances, measured by two range finders at different positions on one structure, to a cornercube retroreflector on the other structure. Given a Cartesian (x,y,z) coordinate system and the known x coordinate of the retroreflector relative to the y,z plane that contains the range finders, the program estimates the y and z coordinates of the retroreflector.
Simulating Operation of a Large Turbofan Engine
The Commercial Modular Aero Propulsion System Simulation (CMAPSS) is a computer program for simulating transient operation of a commercial turbofan engine that can generate as much as 90,000 lb (≈0.4 MN) of thrust. It includes a powermanagement system that enables simulation of openor closedloop engine operation over a wide range of thrust levels throughout the full range of flight conditions.
Automated Assistance for Designing Active Magnetic Bearings
MagBear12 is a computer code (see figure) that assists in the design of radial, heteropolar active magnetic bearings (AMBs). MagBear12 was developed to help in designing the system described in “Advanced ActiveMagneticBearing ThrustMeasurement System” (SSC 001771), which appears in NASA Tech Briefs, Vol. 32, No. 9 (September 2008), p. 61. (See the Mechanics/Machinery section in the accompanying issue of NASA Tech Briefs). Beyond this initial application, MagBear12 is expected to be useful for designing AMBs for a variety of rotating machinery. This program incorporates design rules and governing equations that are also implemented in other, proprietary design software used by AMB manufacturers. In addition, this program incorporates an advanced unpublished fringingmagnetic field model that increases accuracy beyond that offered by the other AMBdesign software.
Computational Simulation of a WaterCooled Heat Pump
A Fortranlanguage computer program for simulating the operation of a watercooled vaporcompression heat pump in any orientation with respect to gravity has been developed by modifying a prior generalpurpose heatpump design code used at Oak Ridge National Laboratory (ORNL). Al  though it is specific to the design of a hightemperaturelift heat pump for the International Space Station, this program could serve as a basis for development of generalpurpose computational software for designing and analyzing liquidcooled heatpumps. The ORNL program contained models of refrigerantfluidtoair heat exchangers; the main modification consisted in replacing those models with models of platetype heat exchangers utilizing water as both the cooling and the heating source liquid.
Computational Model of Heat Transfer on the ISS
SCRAM Lite (“SCRAM” signifies “Station Compact Radiator Analysis Model”) is a computer program for analyzing convective and radiative heat transfer and heatrejection performance of coolant loops and radiators, respectively, in the active thermalcontrol systems of the International Space Station (ISS). SCRAM Lite is a derivative of prior versions of SCRAM but is more robust.
Optimization of AngularMomentum Biases of Reaction Wheels
RBOT [RWA Bias Optimization Tool (wherein “RWA” signifies “Reaction Wheel Assembly”)] is a computer program designed for computing angular momentum biases for reaction wheels used for providing spacecraft pointing in various directions as required for scientific observations. RBOT is currently deployed to support the Cassini mission to prevent operation of reaction wheels at unsafely high speeds while minimizing time in undesirable lowspeed range, where elastohydrodynamic lubrication films in bearings become ineffective, leading to premature bearing failure. The problem is formulated as a constrained optimization problem in which maximum wheel speed limit is a hard constraint and a cost functional that increases as speed decreases below a lowspeed threshold.
Short and LongTerm Propagation of Spacecraft Orbits
The Planetary Observer Planning Software (POPS) comprises four computer programs for use in designing orbits of spacecraft about planets. These programs are the Planetary Observer High Precision Orbit Propagator (POHOP), the Planetary Observer LongTerm Orbit Predictor (POLOP), the Planetary Observer Post Processor (POPP), and the Planetary Observer Plotting (POPLOT) program.
Monte Carlo Simulation To Estimate Likelihood of Direct Lightning Strikes
A software tool has been designed to quantify the lightning exposure at launch sites of the stack at the pads under different configurations. In order to predict lightning strikes to generic structures, this model uses leaders whose origins (in the x–y plane) are obtained from a 2D random, normal distribution. The striking distance is a function of the stroke peak current, which is obtained from a random state machine that extracts the stroke peak current from a lognormal distribution. The height in which the leaders are originated is fixed and chosen to be several “strike distances” greater than the tallest object under study.
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