Special Coverage

Technique Provides Security for Multi-Robot Systems
Bringing New Vision to Laser Material Processing Systems
NASA Tests Lasers’ Ability to Transmit Data from Space
Converting from Hydraulic Cylinders to Electric Actuators
Automating Optimization and Design Tasks Across Disciplines
Vibration Tables Shake Up Aerospace and Car Testing
Supercomputer Cooling System Uses Refrigerant to Replace Water
Computer Chips Calculate and Store in an Integrated Unit
Electron-to-Photon Communication for Quantum Computing

Implementing a Digital Phasemeter in an FPGA

Firmware for implementing a digital phasemeter within a field-programmable 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- equal-frequency heterodyne signals generated by two interferometers. In that application, zero-crossing 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 time-averaged estimate of the difference between the phases of the two pulse trains.

Posted in: Briefs, TSP, Software, Architecture, Computer software and hardware, Integrated circuits

Post-Flight 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.

Posted in: Briefs, Software, Measurements, Antennas, Computer software and hardware, Spacecraft

Post-Flight 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 time-series data on distances, measured by two range finders at different positions on one structure, to a corner-cube 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.

Posted in: Briefs, Software, Mathematical models, Antennas, Computer software and hardware, Spacecraft

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 power-management system that enables simulation of openor closed-loop engine operation over a wide range of thrust levels throughout the full range of flight conditions.

Posted in: Briefs, TSP, Software, Computer simulation, Turboprop engines

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 Active-Magnetic-Bearing Thrust-Measurement System” (SSC- 00177-1), 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 fringing-magnetic- field model that increases accuracy beyond that offered by the other AMB-design software.

Posted in: Briefs, Software, CAD, CAM, and CAE, Magnetic materials, Bearings

Computational Simulation of a Water-Cooled Heat Pump

A Fortran-language computer program for simulating the operation of a water-cooled vapor-compression heat pump in any orientation with respect to gravity has been developed by modifying a prior general-purpose heat-pump design code used at Oak Ridge National Laboratory (ORNL). Al - though it is specific to the design of a high-temperature-lift heat pump for the International Space Station, this program could serve as a basis for development of general-purpose computational software for designing and analyzing liquid-cooled heat-pumps. The ORNL program contained models of refrigerant-fluid-to-air heat exchangers; the main modification consisted in replacing those models with models of plate-type heat exchangers utilizing water as both the cooling and the heating source liquid.

Posted in: Briefs, TSP, Software, Computer simulation, Water, Heat exchangers, Cooling

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 heat-rejection performance of coolant loops and radiators, respectively, in the active thermal-control systems of the International Space Station (ISS). SCRAM Lite is a derivative of prior versions of SCRAM but is more robust.

Posted in: Briefs, TSP, Software, Computer simulation, Heat transfer, Thermodynamics, Performance upgrades, Spacecraft

Optimization of Angular-Momentum 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 low-speed range, where elasto-hydrodynamic 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 low-speed threshold.

Posted in: Briefs, TSP, Software, Wheels, Optimization, Computer software and hardware, Spacecraft guidance, Lubricants

Short- and Long-Term 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 Long-Term Orbit Predictor (POLOP), the Planetary Observer Post Processor (POPP), and the Planetary Observer Plotting (POPLOT) program.

Posted in: Briefs, Software, Computer software and hardware, Spacecraft guidance

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.

Posted in: Briefs, Software, Computer simulation, Lightning, Risk assessments

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