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NASA NTRS2001

Novel Directional Solidification of Hypermonotectic Alloys

There are many metal alloy systems that separate into two different liquids upon cooling from a higher temperature. Uniform microstructural development during solidification of these immiscible liquids on Earth is hampered by inherent density differences between the phases. Microgravity processing minimizes settling but segregation still occurs due to gravity independent wetting and coalescence phenomena. Experiments with the transparent organic, metal analogue, succinonitrile-glycerol system were conducted in conjunction with applied ultrasonic energy. The processing parameters associated with this technique have been evaluated in view of optimizing dispersion uniformity. Characterization of the experimental results in terms of an initial modeling effort will also be presented.

Grugel, R. N.↗
NASA NTRS2001

Numerical Modeling of Liquid-Vapor Phase Change

We implemented a two- and three-dimensional finite difference/front tracking technique to solve liquid-vapor phase change problems. The mathematical and the numerical features of the method were explained in great detail in our previous reports, Briefly, we used a single formula representation which incorporated jump conditions into the governing equations. The interfacial terms were distributed as singular terms using delta functions so that the governing equations would be the same as conventional conservation equations away from the interface and in the vicinity of the interface they would provide correct jump conditions. We used a fixed staggered grid to discretize these equations and an unstructured grid to explicitly track the front. While in two dimensions the front was simply a connection of small line segments, in three dimensions it was represented by a connection of small triangular elements. The equations were written in conservative forms and during the course of computations we used regriding to control the size of the elements of the unstructured grid. Moreover, we implemented a coalescence in two dimensions which allowed the merging of different fronts or two segments of the same front when they were sufficiently close. We used our code to study thermocapillary migration of bubbles, burst of bubbles at a free surface, buoyancy-driven interactions of bubbles, evaporation of drops, rapid evaporation of an interface, planar solidification of an undercooled melt, dendritic solidification, and a host of other problems cited in the reference.

Esmaeeli, Asghar↗
NASA NTRS1994

The Relationship Between Constraint and Ductile Fracture Initiation as Defined by Micromechanical Analyses

The use of small laboratory specimens to predict the integrity of large, complex structures relies on the validity of single parameter fracture mechanics. Unfortunately, the constraint loss associated with large scale yielding, whether in a laboratory specimen because of its small size or in a structure because it contains shallow flaws loaded in tension, can cause the breakdown of classical fracture mechanics and the loss of transferability of critical, global fracture parameters. Although the issue of constraint loss can be eliminated by testing actual structural configurations, such an approach can be prohibitively costly. Hence, a methodology that can correct global fracture parameters for constraint effects is desirable. This research uses micromechanical analyses to define the relationship between global, ductile fracture initiation parameters and constraint in two specimen geometries (SECT and SECB with varying a/w ratios) and one structural geometry (circumferentially cracked pipe). Two local fracture criteria corresponding to ductile fracture micromechanisms are evaluated: a constraint-modified, critical strain criterion for void coalescence proposed by Hancock and Cowling and a critical void ratio criterion for void growth based on the Rice and Tracey model. Crack initiation is assumed to occur when the critical value in each case is reached over some critical length. The primary material of interest is A516-70, a high-hardening pressure vessel steel sensitive to constraint; however, a low-hardening structural steel that is less sensitive to constraint is also being studied. Critical values of local fracture parameters are obtained by numerical analysis and experimental testing of circumferentially notched tensile specimens of varying constraint (e.g., notch radius). These parameters are then used in conjunction with large strain, large deformation, two- and three-dimensional finite element analyses of the geometries listed above to predict crack initiation loads and to calculate the associated (critical) global fracture parameters. The loads are verified experimentally, and microscopy is used to measure pre-crack length, crack tip opening displacement (CTOD), and the amount of stable crack growth. Results for A516-70 steel indicate that the constraint-modified, critical strain criterion with a critical length approximately equal to the grain size (0.0025 inch) provides accurate predictions of crack initiation. The critical void growth criterion is shown to considerably underpredict crack initiation loads with the same critical length. The relationship between the critical value of the J-integral for ductile crack initiation and crack depth for SECT and SECB specimens has been determined using the constraint-modified, critical strain criterion, demonstrating that this micromechanical model can be used to correct in-plane constraint effects due to crack depth and bending vs. tension loading. Finally, the relationship developed for the SECT specimens is used to predict the behavior of circumferentially cracked pipe specimens.

Panontin, Tina L.↗
NASA NTRS2001

Measurements and Predictions for a Distributed Exhaust Nozzle

The acoustic and aerodynamic performance characteristics of a distributed exhaust nozzle (DEN) design concept were evaluated experimentally and analytically with the purpose of developing a design methodology for developing future DEN technology. Aerodynamic and acoustic measurements were made to evaluate the DEN performance and the CFD design tool. While the CFD approach did provide an excellent prediction of the flowfield and aerodynamic performance characteristics of the DEN and 2D reference nozzle, the measured acoustic suppression potential of this particular DEN was low. The measurements and predictions indicated that the mini-exhaust jets comprising the distributed exhaust coalesced back into a single stream jet very shortly after leaving the nozzles. Even so, the database provided here will be useful for future distributed exhaust designs with greater noise reduction and aerodynamic performance potential.

Kinzie, Kevin W.↗
NASA NTRS2001

Solidification Processing of Immiscible Liquids in the Presence of Applied Ultrasonic Energy

Uniform microstructural distribution during solidification of immiscible liquids (e.g., oil and water; aluminum and lead) on Earth is hampered by inherent density differences between the phases. Microgravity processing minimizes settling but segregation still occurs due to gravity independent wetting and coalescence phenomena. Experiments with the transparent organic, metal analogue, succinonitrile-glycerol system were conducted in conjunction with applied ultrasonic energy. The processing parameters associated with this technique have been evaluated in view of optimizing dispersion uniformity. Characterization of the experimental results in terms of a modeling effort will also be presented,

Grugel, R. N.↗
NASA NTRS2001

The Green Ocean Over the Amazon: Implications for Cloud Electrification

A convective regime with distinct maritime characteristics (weak updraft, low CCN, prevalent coalescence and rainout, weak mixed phase reflectivity, low glaciation temperature, and little if any lightning) is documented over the Amazon basin of the South American continent, and dubbed the "green ocean". Radar, lightning, thermodynamic and AVHRR satellite observations are examined to shed light on the roles of updraft and aerosol in providing departures from the green ocean regime toward continental behavior. Extreme case studies are identified in which the updraft control is dominant and in which the aerosol control is dominant. The tentative conclusion gives importance to both updrafts and aerosol in shaping the electrification of tropical convection.

Williams, E.↗
NASA NTRS2001

Responses of Precipitation and Hydrologic Processes to Tropical SST

The goal of the research is to identify the mechanisms in the response of tropical precipitation and atmospheric hydrologic cycle to sea surface temperature (SST) variability at seasonal-to-interannual time scales, and to utilize the knowledge for better understanding of climate feedback processes relevant to global change. As a first step to achieve the goal, we characterize the inter-relationship among convective/stratiform rain, ice/water clouds water vapor, and SST using TRMM satellite data and a cloud-resolving model. We examined the daily hydrologic variables [column water vapor (PW), cloud liquid water (CW), rainfall rates (RR)] as a function of SST using high-resolution data (0.25 x 0.25, daily) derived from TRMM satellite measurements. Comparing the winter of 97/98 (El Nino condition) against the winter of 99/00 (La Nina condition), area-mean values of all four hydrologic variables in cloudy areas within the tropical Pacific are higher in the El Nino winter than in the La Nina winter. This is consistent with previous observational analyses and SST warming experiments (idealized or ENSO-like) that showed the interaction between hydrologic cyclic and radiation at the seasonal to interannual time scales leads to intensified tropical circulation and hydrologic cycle. However, there is evidence that the enhanced hydrologic cycle over the warm pool is accompanied by an expansion of radiatively -driven subsidence in response to a stronger SST gradient between warm pool and surrounding cold pool. The expanding subsidence effectively reduces cloud amounts over the warm pool. Our analysis of daily variability further indicates a more vigorous water cycle characterized by higher PW, CW, and RR in response to overall warming. This is expected from the Clausius Clapeyron relation as a thermodynamic response to warming. However cloudy areas decrease in response to overall warming. This may be due to factors that are fundamentally different. One possibility is that in a warmer climate, there may be alteration in the microphysical processes in clouds, e.g., increased coalescence of cloud size droplets and increased entrainment of dry air from above due to the invigorated convective motions in response to overall warming. As a result, cloud amounts are less. Another interpretation is that, in colder air masses, more ice particles will be produced and, because of their lower densities, are less likely to precipitate, hence the higher cloud amount. This suggests that, when averaged over a sufficiently large area covering both the rising and sinking branches of the tropical circulation, there maybe an increase in the precipitation efficiency in stratiform clouds, in conjunction with increased subsidence in an enhanced water cycle. This is supported by the residence time at different rainrates.

Sui, C.-H.↗
NASA NTRS2000

Cloud Microphysics in Hurricane Outflows: Observations in 'Bonnie' (1998) at 12 km Altitude

The water balance of a hurricane is controlled by boundary layer inflow, near vertical motion in the eyewall causing coalescence precipitation at above and residual ice precipitation at below freezing temperatures, and cirrus outflow at below -40 C aloft. In this paper we address the question of efficiency of water removal by this cirrus outflow which is important for the release of latent heat at high altitudes and its role in the dynamic flow at that level. During NASA's 1998 Convection and Moisture Experiment campaign we acquired microphysical outflow data in order to (1) determine the release and redistribution of latent heat near the top of hurricanes, (2) aid in TRMM algorithm development for remote sensing of precipitation, and (3) determine the optical/radiative characteristics of hurricane outflow. The data were acquired with Particle Measuring Systems two dimensional imaging spectrometers. On 23 August and again during the hurricane's landfall on 26 August, 1998, the NASA DC-8 aircraft penetrated hurricane 'Bonnie' four times each near 200 hPa pressure altitude. The eye crossing times were determined by (1) zero counts of cloud particles, (2) approximately 5 C increases in static and potential temperatures, and (3) minima in speeds and changes of direction of horizontal winds. The vertical winds showed shear between -6 m per second and +4 m per second and tangential winds approached 30 m per second in the eyewall. The particle volumes in the eyewall (determined by the pixels the particles shadowed in the direction of flight [x-direction] and normally to it by the number of diodes that they shadowed [y-direction]) ranged between 0.5 and 5.0 cubic centimeters per cubic meter. With a particle density near 0.2 g per cubic centimeter (determined from in situ melting and evaporation on a surface collector), the 1.0 g per meter corresponding mass of cloud ice ranged between 0.27 and 2.7 g per kilograms yielding horizontal fluxes between 8.1 and 81 g per square meters per second. The outflow ice was concentrated in crystals of a modal size of 190 micrometers. The particle size distributions were heavily skewed toward sizes with 98% of all cirrus particles smaller than the modal size comprising, however, only 20% of the mass. Thus the smaller than modal size particles dominantly affected the optical/radiative characteristics of the cloud, whereas the larger than modal size crystals determined the ice mass, hence dominated latent heating. Questions to be addressed relate to the origin of individual ice particles as the hurricane evolved and the likelihood of pristine and aggregate particle formation under the complicated conditions of rotation and outflow in the eyewall.

Pueschel, Rudolf F.↗
NASA NTRS2001

Distributed Exhaust Nozzles for Jet Noise Reduction

The main objective of this study is to validate the jet noise reduction potential of a concept associated with distributed exhaust nozzles. Under this concept the propulsive thrust is generated by a larger number of discrete plumes issuing from an array of small or mini-nozzles. The potential of noise reduction of this concept stems from the fact that a large number of small jets will produce very high frequency noise and also, if spaced suitably, they will coalesce at a smaller velocity to produce low amplitude, low frequency noise. This is accomplished through detailed acoustic and fluid measurements along with a Computational Fluidic Dynamic (CFD) solution of the mean (DE) Distributed Exhaust nozzle flowfield performed by Northrop-Grumman. The acoustic performance is quantified in an anechoic chamber. Farfield acoustic data is acquired for a DE nozzle as well as a round nozzle of the same area. Both these types of nozzles are assessed numerically using Computational Fluid Dynamic (CFD) techniques. The CFD analysis ensures that both nozzles issued the same amount of airflow for a given nozzle pressure ratio. Data at a variety of nozzle pressure ratios are acquired at a range of polar and azimuthal angles. Flow visualization of the DE nozzle is used to assess the fluid dynamics of the small jet interactions. Results show that at high subsonic jet velocities, the DE nozzle shifts its frequency of peak amplitude to a higher frequency relative to a round nozzle of equivalent area (from a S(sub tD) = 0.24 to 1. 3). Furthermore, the DE nozzle shows reduced sound pressure levels (as much as 4 - 8 dB) in the low frequency part of the spectrum (less than S(sub tD) = 0.24 ) compared to the round nozzle. At supersonic jet velocities, the DE nozzle does not exhibit the jet screech and the shock-associated broadband noise is reduced by as much as 12 dB.

Ahuja, K. K.↗
NASA NTRS2001

Using Climate Models to Evaluate Mechanisms of Glacial Inception

The initiation and subsequent growth of an ice sheet or large glacier is based on two primary factors: 1. Most fundamentally, a region must exist with a positive net snow accumulation, that is, cold season snowfall exceeds warm season snowmelt. Because snow can melt very rapidly, in a practical sense this probably means that little or no snow melt should occur in the warm season (mountain glaciers being one possible exception). 2. When sufficient ice builds in a region with a positive net snow accumulation, the ice will flow into adjoining regions with a negative mass balance. Feedbacks can also then arise between the emerging ice sheet and the overall climate, which, among other effects, may cause the mass balance in that region to turn positive. A key question is the relative importance of these two factors. In particular, is it possible for a large lowland region to experience a positive mass balance, such that the ice sheet can arise largely 'in-situ'? Or instead are uplands necessary, such that essentially mountain glaciers form first, and then, under the right conditions, grow and coalesce, eventually spreading out into the lowlands? This is probably the single most fundamental question to be addressed in the modeling of glacial inception. Other key questions then focus on how the (upland or low-land) positive mass balance is obtained at some times, but not others (the ice sheets are not continuously present). For Northern Hemisphere ice sheets in particular, what climatic conditions can lead to abundant winter snowfall in the Canadian Arctic and northern Labrador in conjunction with cool summertime conditions? Are both required, or will cool summer conditions alone suffice? Conversely, are a few years of abnormally heavy snowfall all that is required to trigger glacial inception? A major need at present is for carefully constructed climate model studies aimed at addressing these questions. A successful strategy will almost certainly require more than just a global model; while the global climate model might be necessary to properly simulate large-scale forcing, such models have insufficient spatial resolution to adequately address the roles of topography and the nature of the land surface. Necessary also is the use of a high-resolution regional climate model (in conjunction with a global model). Possible forcing mechanisms of Pleistocene ice ages are well known (e.g., orbital forcing; CO2 fluctuations) but we must understand and be able to successfully model the actual processes involved in glacial inception before we can fully understand the true roles played by these forcing mechanisms.

Oglesby, Robert J.↗
NASA NTRS1995

Speed Discrimination: Multiple Stimuli Appear Better Than One

We reported that for a 21FC task with multiple moving grating patches (Gabors) in each interval, thresholds for speed discrimination decreased with the number of patches, while increasing the area of a single grating produced no such effect. Furthermore, this decrease occurred regardless of the spacing of the patches about a circle of eccentricity 4 degrees, i.e., whether they were maximally separated or almost touching. These results suggest that it is the multiple, discrete grating patches that cause thresholds to decrease, rather than the spatial arrangement. To test this hypothesis, we measured the effect of dividing a large grating into four quadrants, by superimposing a mean-luminance cross on it. The mean speed discrimination thresholds (Weber Fractions) for four observers were 19, 15, and 11 plus or minus 2%, for the single large grating, the grating with cross, and the 4 maximally-separated, small gratings, respectively. Thus, breaking up a single large grating into multiple parts caused thresholds to improve, despite the fact that less of the original patch was visible. To investigate the possible contribution of total bounding contour length, we measured the effect of coalescing three small grating patches into a single banana-shaped patch, while keeping the total contour length constant. These two conditions were compared to a single, circular Gabor patch of equivalent area that had (necessarily) a smaller contour length. Preliminary data from 3 of 4 observers were similar for the small-grating and banana configurations, but increased for the single, large grating, suggesting that contour length might play a role. We are also investigating the role of low-level factors pertinent to the large grating, such as the pooling of signals from motion units at different eccentricities, and the stimulation of extended inhibitory motion surrounds, as well as the possible contribution of topdown influences that segment the stimulus into distinct objects.

Verghese, Preeti↗
NASA NTRS1995

Soot Aerosol In The Atmosphere: Pole-to-Pole Distribution And Contributions by Aircraft

Interest in the distribution of black carbon (soot) aerosol (BCA) in the atmosphere is warranted for the following reasons: (1) BCA has the highest absorption cross section of any compound known, thus it can absorb solar radiation to cause atmospheric warming; (2) BCA is a strong adsorber of gases, thus it can catalyze heterogeneous chemical reactions to modify the chemical composition of the atmosphere; (3) If aircraft emission is the major source of atmospheric BCA, it can serve as an atmospheric tracer of aircraft exhaust. We collect BCA particles greater than or equal to 0.02 micrometer diameter by wires mounted on both the DC-8 and ER-2 aircraft. After return to the laboratory, the wires are examined with a field emission scanning electron microscope to identify BCA particles by their characteristic morphology. Typically, BCA exists in the atmosphere as small particles of complex morphology. The particle sizes at the source are measured in tens of Angstrom units; after a short residence time in the atmosphere, individual particles coalesce to loosely packed agglomerates of typical dimensions 0.01 to 0.1 micrometer. We approximate the size of each BCA aggregate by that of a sphere of equivalent volume. This is done by computing the volume of a sphere whose diameter is the mean between averaged minimum and maximum dimensions of the BCA particle. While this procedure probably underestimates the actual surface area, it permits us to compare BCA size distributions among themselves and with other types of aerosols. When statistically justified, we fit lognormal distributions to the data points to determine number concentrations, geometric mean radii, standard deviations, BCA surface areas and volumes. Results to date permit the following conclusions: (1) BCA concentration in the northern stratosphere averages 0.6 ng per cubic meters. This amount is one part in 10(exp 4) after a volcanic eruption (e.g., Pinatubo) increasing to about one percent during volcanic quiescence. In the northern troposphere, BCA concentration averages 3.2 ng per cubic meters, or 0.3 percent of the background aerosol. (2) Applying an BCA emission index EI(BCA)=5 x 10(exp -5), measured in the exhaust wake of a Concorde supersonic jet aircraft, to realistic estimates of fuel burnt by the current and projected fleets permits us to conclude that: (i) Most BCA in the northern stratosphere results from aircraft emissions; (ii) Most BCA in the northern troposphere results from other sources than aircraft; (iii) A projected supersonic fleet will increase the northern stratospheric BCA concentration by one order of magnitude, unless the emission index is substantially reduced. (3) A strong gradient between the northern and southern hemispheres indicates that mixing across the equator is greatly inhibited in relation to atmospheric residence times of BCA. (4) The single scatter albedo of BCA/"background" aerosol mixtures suggests a cooling effect for most of the globe; an exemption is the Arctic because of the high surface albedo of the snow/ice covered earth's surface.

Pueschel, R. F.↗
NASA NTRS1995

Soot Aerosols in the Atmosphere: Contributions by Aircraft

Interest in the distribution of black carbon (soot) aerosol (BCA) in the atmosphere is based on the following: (1) Because BCA has the highest absorption cross section of any compound know, it can absorb solar radiation to cause atmospheric warming; (2) Because BCA is a strong adsorber of gases, it can catalyze heterogeneous chemical reactions to modify the chemical composition of the atmosphere; (3) If aircraft emission is the major source of BCA, it can serve as an atmospheric tracer of aircraft exhaust. We collect BCA particles as small as 0.02 micrometers by wires mounted on both the DC-8 and ER-2 aircraft. After return to the laboratory, the wires are examined with a field emission scanning electron microscope to identify BCA particles by their characteristics morphology, Typically, BCA exists in the atmosphere as small particles of complex morphology. The particle sizes at the source are measured in tens of Angstrom units; after a short residence time in the atmosphere, individual particles coalesce to loosely packed agglomerates of typical dimensions 0.01 to 0.1 micrometer. We approximate the size of each BCA aggregate by that of a sphere of equivalent volume. This is done by computing the volume of a sphere whose diameter is the mean between averaged minimum and maximum dimensions of the BCA particle. While this procedure probably underestimates the actual surface area, it permits us to compare BCA size distributions among themselves and with other types of aerosols.

Pueschel, R. F.↗
NASA NTRS2002

Behavior of Rapidly Sheared Bubble Suspensions

An experiment to be carried out aboard the International Space Station is described. A suspension consisting of millimeter-sized bubbles in water containing some dissolved salt, which prevents bubbles from coalescing, will be sheared in a Couette cylindrical cell. Rotation of the outer cylinder will produce centrifugal force which will tend to accumulate the bubbles near the inner wall. The shearing will enhance collisions among bubbles creating thereby bubble phase pressure that will resist the tendency of the bubbles to accumulate near the inner wall. The bubble volume fraction and velocity profiles will be measured and compared with the theoretical predictions. Ground-based research on measurement of bubble phase properties and flow in vertical channel are described.

Sangani, A. S.↗
NASA NTRS2002

Micro-Mechanical Modeling of Ductile Fracture in Welded Aluminum-Lithium Alloys

This study describes a 3-D computational framework to model stable extension of a macroscopic crack under mode I conditions in ductile metals. Material separation occurs through a local fracture mechanism based on the growth and coalescence of micro voids dispersed in the material. The Gurson-Tvergaard plasticity model for void materials describes the eventual loss of material stress capacity under sustained loading. Fixed-sized computational cell elements defined on a thin layer adjacent to the crack plane provide an implicit length scale for continuum damage model. Outside this layer, the material remains undamaged by void growth, consistent with metallurgical observations. The key micro-mechanics parameters are D, the thickness of cell layer, and f 0 , the initial cell porosity.

Ahmed Ibrahim↗
NASA NTRS2002

The Effect of Friction on Penetration in Friction Stir Welding

"Friction stir butt welding," as it was originally termed by Wayne Thomas and Christopher Dawes, in the early 1990s, but now commonly called "friction stir welding," has made great progress as a new welding technique. Commercially, friction stir welding (FSW) is finding many applications. Marine Aluminum of Norway is using the process for welding 20-meter aluminum sheets for ferry construction. Japan is using the technique in development work on bullet trains. Sapa of Sweden utilizes FSW in the landing of refrigeration units for cargo ships. In the United States, Boeing is using the technique in the production of Delta rockets. Eclipse Aviation Corporation plans to use FSW to produce a business jet available in August, 2003. Marshall Space Flight Center has been investigating the use of FSW for assembly of the Shuttle's external fuel tank since the late 1990s and hopes to have the process in use by the summer of 2002. In FSW, a cylindrical pin tool of hardened steel, is rotated and plunged into the abutting edges of the parts to be joined. The tool is plunged into the weldment to within about .050 in of the bottom to assure full penetration. As the tool moves along the joint, the tool shoulder helps produce frictional heating, causing the material to plasticize. The metal of the two abutting plates flows from the front of the tool to the back where it cools and coalesces to form a weld in the solid phase.

Steve Rapp↗
NASA NTRS1998

Isosurface Extraction in Time-Varying Fields Using a Temporal Hierarchical Index Tree

Many high-performance isosurface extraction algorithms have been proposed in the past several years as a result of intensive research efforts. When applying these algorithms to large-scale time-varying fields, the storage overhead incurred from storing the search index often becomes overwhelming. this paper proposes an algorithm for locating isosurface cells in time-varying fields. We devise a new data structure, called Temporal Hierarchical Index Tree, which utilizes the temporal coherence that exists in a time-varying field and adoptively coalesces the cells' extreme values over time; the resulting extreme values are then used to create the isosurface cell search index. For a typical time-varying scalar data set, not only does this temporal hierarchical index tree require much less storage space, but also the amount of I/O required to access the indices from the disk at different time steps is substantially reduced. We illustrate the utility and speed of our algorithm with data from several large-scale time-varying CID simulations. Our algorithm can achieve more than 80% of disk-space savings when compared with the existing techniques, while the isosurface extraction time is nearly optimal.

Shen, Han-Wei↗
NASA NTRS2002

A Multi-Function Guidance, Navigation and Control System for Future Earth and Space Missions

Over the past several years the Guidance, Navigation and Control Center (GNCC) at NASA's Goddard Space Flight Center (GSFC) has actively engaged in the development of advanced GN&C technology to enable future Earth and Space science missions. The Multi-Function GN&C System (MFGS) design presented in this paper represents the successful coalescence of several discrete GNCC hardware and software technology innovations into one single highly integrated, compact, low power and low cost unit that simultaneously provides autonomous real time on-board attitude determination solutions and navigation solutions with accuracies that satisfy many future GSFC mission requirements. The MFGS is intended to operate as a single self-contained multifunction unit combining the functions now typically performed by a number of hardware units on a spacecraft. However, recognizing the need to satisfy a variety of future mission requirements, design provisions have been included to permit the unit to interface with a number of external remotely mounted sensors and actuators such as magnetometers, sun sensors, star cameras, reaction wheels and thrusters. The result is a highly versatile MFGS that can be configured in multiple ways to suit a realm of mission-specific GN&C requirements. It is envisioned that the MFGS will perform a mission enabling role by filling the microsat GN&C technology gap. In addition, GSFC believes that the MFGS could be employed to significantly reduce volume, power and mass requirements on conventional satellites.

Gambino, Joel↗