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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Long term cryogen storage in space - A feasibility study

The conduction of future space missions will require the long term storage of cryogens in space. Such missions will be performed in connection with the employment of the long life version of the Shuttle Infrared Telescope Facility (SIRTF), the Large Deployable Reflector (LDR), Gravity Probe B (GPB), Orbital Transfer Vehicles (OTVs), and the Space Station. The feasibility of building a long lifetime helium Dewar for space applications has been studied. A feasible concept was to be developed for a Shuttle-launchable 3-yr lifetime Dewar. The developed concept was to be used for the identification of key technology development areas. The desired long lifetime requires the minimization of the parasitic heat loads. It has been found that the majority of the parasitic heat load can be provided by the fiberglass-epoxy tension band supports. A new type of support system, the Passive Orbital Disconnect Strut (PODS), was developed to reduce the considered contribution to the heat load.

Kittel, P.↗
NASA NTRS1984

Magnetic reconnection in comets

Today many of the traditionally puzzling phenomena in the cometary plasma-tail environment can plausibly be linked to magnetic reconnection occurring in several regions of a comet (Niedner and Brandt, 1978 and 1980). The turn-on of these various reconnection sites appears to follow a cyclic pattern in which the plasma-tail disconnection event is the primary feature, and the periodic sector structure of the solar wind is the external driver. The purpose of this review is to discuss these different classes of cometary activity, to state the justifications for linking them to reconnection, to discuss proposed alternate (nonreconnection) models, and to suggest future tests of the hypotheses presented.

Niedner, M. B., Jr.↗
NASA NTRS1985

Effect of accuracy of wind power prediction on power system operator

This research project proposed a modified unit commitment that schedules connection and disconnection of generating units in response to load. A modified generation control is also proposed that controls steam units under automatic generation control, fast responding diesels, gas turbines and hydro units under a feedforward control, and wind turbine array output under a closed loop array control. This modified generation control and unit commitment require prediction of trend wind power variation one hour ahead and the prediction of error in this trend wind power prediction one half hour ahead. An improved meter for predicting trend wind speed variation is developed. Methods for accurately simulating the wind array power from a limited number of wind speed prediction records was developed. Finally, two methods for predicting the error in the trend wind power prediction were developed. This research provides a foundation for testing and evaluating the modified unit commitment and generation control that was developed to maintain operating reliability at a greatly reduced overall production cost for utilities with wind generation capacity.

Schlueter, R. A.↗
NASA NTRS1986

A process activity monitor for AOS/VS

With the ever increasing concern for computer security, users of computer systems are becoming more sensitive to unauthorized access. One of the initial security concerns for the Shuttle Management Information System was the problem of users leaving their workstations unattended while still connected to the system. This common habit was a concern for two reasons: it ties up resources unnecessarily and it opens the way for unauthorized access to the system. The Data General MV/10000 does not come equipped with an automatic time-out option on interactive peripherals. The purpose of this memorandum is to describe a system which monitors process activity on the system and disconnects those users who show no activity for some time quantum.

Mckosky, R. A.↗
NASA NTRS1986

Orbit Transfer Rocket Engine Technology Program: Advanced engine study, task D.1/D.3

Concepts for space maintainability of OTV engines were examined. An engine design was developed which was driven by space maintenance requirements and by a failure mode and effects (FME) analysis. Modularity within the engine was shown to offer cost benefits and improved space maintenance capabilities. Space operable disconnects were conceptualized for both engine change-out and for module replacement. Through FME mitigation the modules were conceptualized to contain the least reliable and most often replaced engine components. A preliminary space maintenance plan was developed around a controls and condition monitoring system using advanced sensors, controls, and condition monitoring concepts. A complete engine layout was prepared satisfying current vehicle requirements and utilizing projected component advanced technologies. A technology plan for developing the required technology was assembled.

Martinez, A.↗
NASA NTRS1986

Observations of Halley's Comet by the Solar Maximum Mission (SMM)

Solar Maximum Mission coronagraph/polarimeter observations of large scale phenomena in Halley's Comet are discussed. Observations of the hydrogen coma with the UV spectrometer are considered. It is concluded that coronograph/polarimeter observations of the disconnection event, in which the entire plasma tail uproots itself from the head of the comet, is convected away in the solar wind at speeds in the 50 to 100 km/sec range (relative to the head), and is replaced by a plasma tail constructed from folding ion-tail rays, are the most interesting.

Niedner, M. B.↗
NASA NTRS1986

Auroral morphology of the midday oval

Auroral displays in the noon sector were examined by using hundreds of Defense Meteorological Satellite Program auroral images, taken over the southern polar region in austral winters, in order to determine the morphology. The auroral displays in the midday part of the auroral oval can be grouped into five characteristic types, depending on the geomagnetic activity and the Bz component of the interplanetary magnetic field. An important characteristic is the clear disconnection in appearance between the noonside and the nightside discrete auroras. Also, there is the lack of correlation between the concurrent nightside substorm activity and midday discrete auroral activity. Thus, the occurrence of bright, discrete auroras in the midday oval may be caused by the local injection of the magnetosheath plasma into the dayside boundary layer. The observed discontinuity of discrete auroras between the dayside and the nightside ovals is consistent with the existence of two separated major injection regions along the auroral oval: the dayside cusp and the nightside plasma sheet.

Meng, C.-I.↗
NASA NTRS1987

Real-Time "Garbage Collection" for List Processing

Two proposed algorithmic techniques for list processing enable immediate identification of computer memory cells having become inactive through disconnection from active cells, together with addition of these inactive cells to pool of reusable cells. These two "garbage collection" techniques reduce memory requirements of list processors or increase their speed or both. With both techniques, processing continuity maintained, enabling real-time processing.

Shuler, Robert L., Jr.↗
NASA NTRS1986

International Halley Watch: Discipline specialists for large scale phenomena

The largest scale structures of comets, their tails, are extremely interesting from a physical point of view, and some of their properties are among the most spectacular displayed by comets. Because the tail(s) is an important component part of a comet, the Large-Scale Phenomena (L-SP) Discipline was created as one of eight different observational methods in which Halley data would be encouraged and collected from all around the world under the aspices of the International Halley Watch (IHW). The L-SP Discipline Specialist (DS) Team resides at NASA/Goddard Space Flight Center under the leadership of John C. Brandt, Malcolm B. Niedner, and their team of image-processing and computer specialists; Jurgan Rahe at NASA Headquarters completes the formal DS science staff. The team has adopted the study of disconnection events (DE) as its principal science target, and it is because of the rapid changes which occur in connection with DE's that such extensive global coverage was deemed necessary to assemble a complete record.

Brandt, J. C.↗
NASA NTRS1987

Space station resistojet system requirements and interface definition study

Preliminary resistojet design requirements were established based on initial technical requirements imposed by the results of NASA and Rocketdyne studies. The requirements are directed toward long life, simplicity, flexibility, and commonality with other space station components. The resistojet assembly is comprised of eight resistojets, fluid components downstream of the waste fluid storage system, a power controller, structure, and shielding. It consists of two identical subassemblies, one of which is redundant. Each subassembly consists of four 500-W resistojets, series redundant latch values, a power controller, a water vaporizer, two pressure regulators, filters, check valves, disconnects, fluid tubing, and electrical cables. All components are packaged at the end of the stinger aft of the JEM and Columbus modules. Different flow and power control methods were studied. A constant inlet pressure and a two-power setting controller were tentatively selected based on simplicity and reasonably high specific impulse for the range of waste gas compositions that are anticipated. The constant pressure is supplied by pressure regulators. The two set point power control includes individual power supplies to each resistojet heater and water vaporizer. An embedded data processor, a multiplexer-demultiplexer, and a network interface unit that are standard space station components are included in the power controller. The total dry weight of the resistojet assembly is approximately 172 lb. The total cost for design, development, test, evaluation, qualification, and flight hardware is estimated to be $16 million.

Heckert, Bruce J.↗
NASA NTRS1986

Plasma structures in Comet Halley

Large-scale plasma phenomena based on results of spacecraft probing of comets Halley and Giacobini-Zinner and on International Halley Watch are discussed. The data show that: the basic mechanism for the comets' interaction with the solar wind (Alfven, 1957) is correct; that the turn-on and turn-off of plasma activity follows the description of Mendis and Flammer (1984); and that disconnection events are associated with sector boundary crossings and an essential element in the morphology of developed plasma tails (Niedner and Brandt, 1978).

Brandt, John C.↗
NASA NTRS1986

Concepts for space maintenance of OTV engines

Concepts for space maintainability of the Orbital Transfer Vehicle (OTV) engines are examined. An engine design is developed which is driven by space maintenance requirements and by a failure modes and effects analysis (FMEA). Modularity within the engine is shown to offer cost benefits and improved space maintenance capabilities. Space-operable disconnects are conceptualized for both engine change-out and for module replacement. A preliminary space maintenance plan is developed around a controls and condition monitoring system using advanced sensors, controls, and condition monitoring concepts.

Martinez, A.↗
NASA NTRS1986

Comet Halley: The Curtis Schmidts-Isla de Pascua observations

Halley's comet plasma tail disturbances and attendant tail phenomena were observed. Nearly simultaneous exposures with two telescopes serve to correlate information obtained with the two instruments. Photographs of 14 pre-Halley comets taken on 54 nights were examined with a view to cross-interpretation of phenomena seen in Halley with the earlier comets, as recorded on a homogenous collection of plates taken with the same instrument. The tail of Halley was highly active. This contrasts sharply with pre-Halley comets where undisturbed tails are the rule. During March and April, disturbances appeared in the tail of Halley at an average of 1 new distrubance every 3.7 days. It is considered that 10 of the 11 observed disturbances had common characteristics which allow them to be characterized as disconnections.

Miller, Freeman D.↗
NASA NTRS1986

Dynamic pressure model derived from an observation by Sakigake for Comet Halley on 31 December, 1985

An outstanding disconnection event (DE)-like knot was observed on 31 Dec. 1985 in P/Halley's tail. Analysis of the Sakigake/IMF data reveals that comet Halley did not encounter the heliospheric neutral sheet on the day, demanding a new explanation of the DE-like event. During this event, the comet encountered a high-speed solar wind from a coronal hole tongue of the Sun. The event can be explained by a dynamic pressure model, according to which the DE-like plasmoid was caused by a sudden increase in the dynamic pressure of the solar wind. A simulation result is found to support this interpretation. The dynamic pressure model for a comet can be compared with the mechanism of a possible geotail disturbance during a spacecraft triggered auroral substorm.

Saito, Takao↗
NASA NTRS1986

Plasma-tail activity at the time of the Vega encounters

Physical associations are sought between Halley's plasma tail activity seen in ground-based imagery and near-comet, solar wind/IMF measurements obtained by the Vega spacecraft. Disconnection Events (DE's) and the sector boundary/frontside magnetic reconnection model (Niedner and Brandt, 1978) of their origin are discussed. Strong support for the model comes from 2 DE's: a major event whose onset, on March 7 to 8, is strongly correlated with a reversal of the comet's magnetic barrier observed by Vega-1 and Vega-2 and with an IMF sector boundary observed by Vega-1; and a minor event on March 7 which may be associated with the two-polarity (possibly reconnecting) magnetic barrier seen by Vega-1 on March 6, when the solar-wind density was low.

Niedner, Malcolm B., Jr.↗
NASA NTRS1986

A disturbance of the ion tail of Comet Halley and the heliospheric structure as observed by Sakigake

In order to study the interaction between the solar wind measured by Sakigake and ion tail disturbances of comet Halley, more than 500 photographs of the comet taken on the ground during this apparition are surveyed. The focus of the present study is the December 31, 1985, event, when various types of disturbances occurred, including an outstanding disconnection event (DE)-like knot. Analysis of the Sakigake/IMF data reveals that comet Halley did not encounter the heliospheric neutral sheet on that day, demanding a new explanation for the DE-like event, different from the Niedner-Brandt model. During this event the comet encountered a high-speed solar wind stream from a coronal hole tongue of the sun. The event can be explained by a dynamic pressure model, according to which the DE-like plasmoid was caused by a sudden increase in the dynamic pressure of the solar wind. A result of the simulation work by Ogino is found to support this interpretation.

Saito, T.↗
NASA NTRS1986

Spacecraft solid state power distribution switch

As a spacecraft performs its mission, various loads are connected to the spacecraft power bus in response to commands from an on board computer, a function called power distribution. For the Mariner Mark II set of planetary missions, the power bus is 30 volts dc and when loads are connected or disconnected, both the bus and power return side must be switched. In addition, the power distribution function must be immune to single point failures and, when power is first applied, all switches must be in a known state. Traditionally, these requirements have been met by electromechanical latching relays. This paper describes a solid state switch which not only satisfies the requirements but incorporates several additional features including soft turn on, programmable current trip point with noise immunity, instantaneous current limiting, and direct telemetry of load currents and switch status. A breadboard of the design has been constructed and some initial test results are included.

Praver, G. A.↗
NASA NTRS1986

Bidirectional solar wind electron heat flux and hemispherically symmetric polar rain

THe paper examines ISEE 3 solar wind electron data obtained concurrent with reported symmetric polar rain events and it is found that a bidirectional solar wind electron heat flux is present whenever such polar cap events occur. In contrast to the normal situation when only one of the earth's polar caps is magnetically connected to the sun, during hemispherically symmetric polar rain events either both of the earth's polar caps are magnetically connected to the sun, or else both are connected to a magnetic loop which is entirely disconnected from the sun. The relative timing between bidirectional solar wind heat flux and symmetrical polar rain events can be utilized to determine certain magnetospheric quantities such as the cross-tail convection speed.

Gosling, J. T.↗