Results for “duty cycle” — Page 13

NASA NTRS1983

Auxiliary propulsion requirements for large space systems

An insight into auxiliary propulsion systems (APS) requirements for large space systems (LSS) launchable by a single shuttle is presented. In an effort to scope the APS requirements for LSS, a set of generic LSSs were defined. For each generic LSS class a specific structural configuration, representative of that most likely to serve the needs of the 1980's and 1990's was defined. The environmental disturbance forces and torques which would be acting on each specific structural configuration in LEO and GEO orbits were then determined. Auxiliary propulsion requirements were determined as a function of: generic class specific configuration, size and openness of structure, orbit, angle of orientation, correction frequency, duty cycle, number and location of thrusters and direction of thrusters and APS/LSS interactions. The results of this analysis were used to define the APS characteristics of: (1) number and distribution of thrusters, (2) thruster modulation, (3) thrust level, (4) mission energy requirements, (5) total APS mass component breakdown, and (6) state of the art adequacy/deficiency.

Maloy, J. E.↗

NASA NTRS1983

Auxiliary propulsion requirements for large space systems

An insight into auxiliary propulsion systems (APS) requirements for large space systems (LSS) launchable by a single shuttle is presented. In an effort to scope the APS requirements for LSS, a set of generic LSSs were defined. For each generic LSS class a specific structural configuration, representative of that most likely to serve the needs of the 1980's and 1990's was defined. The environmental disturbance forces and torques which would be acting on each specific structural configuration in LEO and GEO orbits were then determined. Auxiliary propulsion requirements were determined as a function of: generic class specific configuration, size and openness of structure, orbit, angle of orientation, correction frequency, duty cycle, number and location of thrusters and direction of thrusters and APS/LSS interactions. The results of this analysis were used to define the APS characteristics of: (1) number and distribution of thrusters, (2) thruster modulation, (3) thrust level, (4) mission energy requirements, (5) total APS mass component breakdown, and (6) state of the art adequacy/deficiency. Previously announced in STAR as N83-26922

Maloy, J. E.↗

NASA NTRS1983

On searches for periodic pulsed emission - The Rayleigh test compared to epoch folding

The Rayleigh test has been recently invoked as a method of searching a time series for periodic pulsations. In this paper, this technique is discussed and compared to epoch folding, a technique which has had widespread use in X-ray astronomy. It is found that the Rayleigh test provides a more sensitive approach to the search for periodic pulsations when the pulses are sinusoidal or of broad duty cycle, such as those typical of the pulsing X-ray sources. Epoch folding, on the other hand, is more sensitive to the narrow pulses typical of radio pulsars.

Leahy, D. A.↗

NASA NTRS1983

Lightweight, high-frequency transformers

The 25-kVA space transformer was developed under contract by Thermal Technology Laboratory, Buffalo, N. Y. The NASA Lewis transformer technology program attempted to develop the baseline technology. For the 25-kVA transformer the input voltage was chosen as 200 V, the output voltage as 1500 V, the input voltage waveform as square wave, the duty cycle as continuous, the frequency range (within certain constraints) as 10 to 40 kHz, the operating temperatures as 85 deg. and 130 C, the baseplate temperature as 50 C, the equivalent leakage inductance as less than 10 micro-h, the operating environment as space, and the life expectancy as 10 years. Such a transformer can also be used for aircraft, ship and terrestrial applications.

Schwarze, G. E.↗

NASA NTRS1983

Study of auxiliary propulsion requirements for large space systems. Volume 1: Executive summary

An insight into auxiliary propulsion systems (APS) requirements for large space systems (LSS) launchable by a single shuttle is presented. In an effort to scope the APS requirements for LSS, a set of generic LSSs were defined. For each generic LSS class a specific structural configuration, representative of that most likely to serve the needs of the 1980's and 1990's was defined. The environmental disturbance forces and torques which would be acting on each specific structural configuration in LEO and GEO orbits were then determined. Auxiliary propulsion requirements were determined as a function of: generic class specific configuration, size and openness of structure, orbit, angle of orientation, correction frequency, duty cycle, number and location of thrusters and direction of thrusters and APS/LSS interactions. The results of this analysis were used to define the APS characteristics of: (1) number and distribution of thrusters, (2) thruster modulation, (3) thrust level, (4) mission energy requirements, (5) total APS mass component breakdown, and (6) state of the art adequacy/deficiency.

Smith, W. W.↗

NASA NTRS1983

Input filter compensation for switching regulators

A novel input filter compensation scheme for a buck regulator that eliminates the interaction between the input filter output impedance and the regulator control loop is presented. The scheme is implemented using a feedforward loop that senses the input filter state variables and uses this information to modulate the duty cycle signal. The feedforward design process presented is seen to be straightforward and the feedforward easy to implement. Extensive experimental data supported by analytical results show that significant performance improvement is achieved with the use of feedforward in the following performance categories: loop stability, audiosusceptibility, output impedance and transient response. The use of feedforward results in isolating the switching regulator from its power source thus eliminating all interaction between the regulator and equipment upstream. In addition the use of feedforward removes some of the input filter design constraints and makes the input filter design process simpler thus making it possible to optimize the input filter. The concept of feedforward compensation can also be extended to other types of switching regulators.

Kelkar, S. S.↗

NASA NTRS1984

Three phase power factor controller

A power control circuit for a three phase induction motor is described. Power factors for the three phases are summed to provide a control signal, and this control signal is particularly filtered and then employed to control the duty cycle of each phase of input power to the motor.

Nola, F. J.↗

NASA NTRS1984

Transverse flat-plate heat pipe experiment (S1005)

The objective of this experiment is to evaluate the zero-g performance of a number of transverse flat plate heat pipe modules. Performance will include the transport capability of the pipes, the temperature drop, and the ability to maintain temperature over varying duty cycles and environments. Additionally, performance degradation, if any, will be monitored over the length of the Long Duration Exposure Facility (LDEF) mission. This information is necessary if heat pipes are to be considered for system designs where they offer benefits not available with other thermal control techniques.

Owen, J. W.↗

NASA NTRS1984

Antenna tracking mechanism for geostationary satellites

The design and development of a continuous duty cycle antenna tracking mechanism (ATM) for geostationary communications satellites is described. The FACC requirements for an ATM and description of the development mechanism designed and built for the program are presented. The mechanism mechanical configuration and component performance is documented along with its launch and operational constraints. The proposed development tests and the results of computer simulations are discussed. The advantages of this mechanism are its simplicity with inherent reliability, low mass, high stiffness, and ability to accurately point a wide range of antenna sizes.

Francis, C. M.↗

NASA NTRS1983

Complementary code and digital filtering for detection of weak VHF radar signals from the mesoscale

The SOUSY-VHF-Radar operates at a frequency of 53.5 MHz in a valley in the Harz mountains, Germany, 90 km from Hanover. The radar controller, which is programmed by a 16-bit computer holds 1024 program steps in core and controls, via 8 channels, the whole radar system: in particular the master oscillator, the transmitter, the transmit-receive-switch, the receiver, the analog to digital converter, and the hardware adder. The high-sensitivity receiver has a dynamic range of 70 dB and a video bandwidth of 1 MHz. Phase coding schemes are applied, in particular for investigations at mesospheric heights, in order to carry out measurements with the maximum duty cycle and the maximum height resolution. The computer takes the data from the adder to store it in magnetic tape or disc. The radar controller is programmed by the computer using simple FORTRAN IV statements. After the program has been loaded and the computer has started the radar controller, it runs automatically, stopping at the program end. In case of errors or failures occurring during the radar operation, the radar controller is shut off caused either by a safety circuit or by a power failure circuit or by a parity check system.

Schmidt, G.↗

NASA NTRS1983

Extensions of the discrete-average models for converter power stages

An improved power converter model is developed by combining the average and discrete modeling techniques. The parameter determination of the proposed discrete-average model is shown to be dependent on the type of duty cycle control law, and the accuracy of the model is shown to depend on the nature of the error processor used in the feedback loop.

Shortt, D. J.↗

NASA NTRS1983

Free-piston stirling engine endurance test program

The Free-Piston Stirling Engine (FPSE) has the potential to be a long-lived, highly reliable, power conversion device attractive for many product applications such as space, residential, or remote-site power. The purpose of endurance testing the FPSE is to demonstrate its potential for long life. The endurance program was directed at obtaining 1000 operational hours under various test conditions: low power, full stroke, duty cycle, and stop/start. Critical performance parameters were measured to note any change and/or trend. Inspections were conducted to measure and compare critical seal/bearing clearance. The engine performed well throughout the program, completing the 1000 hours. Hardware inspection, including the critical clearances, showed no significant change in hardware or clearance dimensions. The performance parameters did not exhibit any increasing or decreasing trends. The test program confirms the potential for long-life FPSE applications. Additional testing is planned to increase the test hours to 10,000.

Dochat, G.↗

NASA NTRS1984

A Summary Description of a Computer Program Concept for the Design and Simulation of Solar Pond Electric Power Generation Systems

A solar pond electric power generation subsystem, an electric power transformer and switch yard, a large solar pond, a water treatment plant, and numerous storage and evaporation ponds. Because a solar pond stores thermal energy over a long period of time, plant operation at any point in time is dependent upon past operation and future perceived generation plans. This time or past history factor introduces a new dimension in the design process. The design optimization of a plant must go beyond examination of operational state points and consider the seasonal variations in solar, solar pond energy storage, and desired plant annual duty-cycle profile. Models or design tools will be required to optimize a plant design. These models should be developed in order to include a proper but not excessive level of detail. The model should be targeted to a specific objective and not conceived as a do everything analysis tool, i.e., system design and not gradient-zone stability.

Source record↗

NASA NTRS1985

Study of high performance alloy electroforming

More panels electroformed with intentional variations of pulse plating parameters are being made. Pulse plating frequency was noted to have a significant effect regarding mechanical properties. The use of a high pulse frequency (assuming fixed duty cycles) results in an increase in ductility and a decrease in ultimate and yield strengths. Electroforming to intermediate frequencies is being done to obtain the best possible combination of ductility and strength. Results of some tests from high frequency specimens are tabulated.

Malone, G. A.↗

NASA NTRS1984

Miniature electrooptical air flow sensor

A sensor for measuring flow direction and airspeed that is suitable, because of its small size, for rapid instrumentation of research airplanes is described. A propeller driven sphere rotating at a speed proportional to airspeed presents a reflective target to an electro-optical system such that the duty cycle of the resulting electrical output is proportional to yaw angle and the frequency is proportional to airspeed.

Kershner, D. D.↗

NASA NTRS1984

Spectral Information from Gapped Data. a Comparison of Technique

The fast Fourier transformations (FFT) is used to estimate power spectra of continuous signals evenly sampled on discrete domains. The problem of finding power spectra on unevenly sampled domains, in particular a regularly spaced domain with gaps is discussed. The analysis of the ACRIM solar bolometric intensity data, obtained with a 3/5 on and 2/5 off duty cycle of approximately 100 minutes, would benefit from the techniques. The comparative effectiveness of three different analysis techniques applied to synthetic data generated on gapped domain is reported.

Kuhn, J. R.↗

NASA NTRS1984

Study of high performance alloy electroforming

Using the two nickel-manganese alloy electroforming baths of near identical compositions, panels were electroformed under the same deposition parameters of current density, bath temperature, pH, and pulse plating conditions of duty cycle and frequency. By changing the electrolyte agitation conditions, significant effects on mechanical properties were noted. Since electrolyte agitation conditions on the typical flat panels studied to date will not be identical to those existing on a complex curved shape such as the SSME combustion chamber simulation, it is most important that these effects be evaluated prior to Phase B studies. The subscale chamber has been fabricated and shield support tooling is being made. Electroforming of optimized alloy test bars is being deferred until the electrolyte agitation effects are more fully appraised.

Malone, G. A.↗

NASA NTRS1985

Thrust chamber life prediction

The reusable life of the Space Shuttle main engine (SSME) is influenced by the cyclic life of the regeneratively liquid cooled main combustion chamber (MCC). During an operational duty cycle the MCC liner is subjected to a large transient thermal gradient that imparts a high thermal cyclic strain to the liner hot gas wall. Life predictions of such chambers have usually been based on low cycle fatigue (LCF) evaluations. Hot-fire testing, however, has shown significant mid-channel wall deformation and thinning during accrued cyclic testing. This phenomenon is termed cyclic creep and appears to be significantly accelerated at elevated temperatures. An analytical method that models the cyclic creep phenomenon and its application to thrust chamber life prediction is presented. The chamber finite element geometry is updated periodically to account for accrued wall thinning and distortion. Failure is based on the tensile instability failure criterion. Cyclic life results for several chamber life enhancing coolant channel designs are compared to the typically used LCF analysis that neglects cyclic creep. The results show that the usable cyclic creep life is approximately 30 to 50% of the commonly used LCF life.

Kasper, H. J.↗