Paper Session III-C - Reaction Control System Propellant Trade Study: An Application of the Analytic Hierarchy Process

Decision making is often difficult because tradeoffs must be made among competing objectives. In order to make tradeoffs, decision makers must be able to evaluate and measure each aspect of the decision - some quantitative, some qualitative, some very important, and some not so important. Uncertainties and competing interest groups also add to the complexity of decision making. The analytic hierarchy process (AHP) is a multicriterion (or mult (objective) decision support methodology. AHP makes it possible for decision makers to deal with both tangible and intangible factors. Data, thoughts, and intuition are organized in a logical, hierarchical structure. Decision makers can express their understanding and experience with pairwise comparisons about the relative importance or preference of all relevant factors. AHP allows for revision for sensitivity analyses. The results of an AHP are easily tested for sensitivities to changes in assumptions and judgments. Current Space Shuttle hypergolic propellant systems servicing is extremely hazardous and performed at three different facilities at the Kennedy Space Center (KSC). These facilities are the Orbiter Processing Facility (OPF), the Hypergolic Maintenance Facility (HMF), and Launch Complex 39 (LC-39). Propellant systems servicing in the OPF and at LC-39 must be scheduled with processing of other Space Shuttle systems. Serial processing time is incurred in any facility with hazardous operations. Alternative propellants were considered in a trade study for use on a proposed reaction control system (PCS). Specifically hydrogen peroxide (^Cy/rocket propellant 1 (RP-1) were analyzed versus the currently used nitrogen tetroxide (^O^/monomethylhydrazine (MMH). The purpose of the trade study was to identify impacts or potential savings in facilities, equipment, and processing tasks for the RCS. AHP was used as a significant decision making aid in obtaining the study results

Synapse at CAp 2017 NER challenge: Fasttext CRF

We present our system for the CAp 2017 NER challenge which is about named entity recognition on French tweets. Our system leverages unsupervised learning on a larger dataset of French tweets to learn features feeding a CRF model. It was ranked first without using any gazetteer or structured external data, with an F-measure of 58.89\%. To the best of our knowledge, it is the first system to use fasttext embeddings (which include subword representations) and an embedding-based sentence representation for NER

Above-Average Student Loan Debt for Students with Disabilities Attending Postsecondary Institutions

Black students with disabilities face more hurdles to academic success and completion than do their non-Black non-disabled peers. With an increased reliance on student loans to finance higher education, this double-at-risk population is even more vulnerable than either Black or disabled students individually. This study examines whether there is an additional debt burden to this intersectional population. The Baccalaureate and Beyond public dataset was used to explore student debt for students who graduated in 2017. This analysis found that Black students with disabilities graduated with significantly higher debt burdens than either non-disabled Black students or students with disabilities from other racial backgrounds. Implications for research, policy, and practice are discussed. Importantly, Black student veterans with disabilities were found to have student debt even with the assistance of the G.I. Bill

Paper Session III-B - A Combined Probabilistic and Expert System Approach for Assigning Repair Start-Times at the NASA Shuttle Logistics Depot

The NASA Shuttle Logistics Depot (NSLD) is tasked with the responsibility for repair and manufacture of Line Replaceable Unit (LRU) hardware and components to support the Space Shuttle Orbiter. Due to shrinking budgets, cost effective repair of LRUs becomes a primary objective. To achieve this objective, it is imperative that resources can be assigned to those LRUs which have the greatest expectation of being needed as a spare. Forecasting the times at which spares are needed requires consideration of many significant factors including, for example, failure rate, flight rate, spares availability, and desired level of support, among others. This paper summarizes the results of the research and development work that has been accomplished in producing an automated system for assisting in the assignment of effective repair start-times for LRUs at the NSLD. This system, called the Repair Start-time Assignment System (RSAS), combines probabilistic modeling and expert system technology to generate an expected future need date. The result is a mathematically calculated value that has been adjusted heuristically to produce a date for beginning the repair that has significantly greater confidence (in the sense that a desired probability of support is assured) than dates produced using other techniques. Since an important output of RSAS is the longest repair turn-around time that will ensure a desired probability of support, RSAS has the potential for being applied to operations at any repair depot where spares are on-hand and repair start-times are of interest. In addition, RSAS incorporates tenants of Just-In-Time (JIT) techniques in the connotation that the latest repair start-time (i.e., the latest time at which repair resources must be committed) may be calculated for every failed unit. This could aid in reducing the spares inventory for certain items, without significantly increasing the risk of unsatisfied demand

Power scaling analysis of fiber lasers and amplifiers based on non-silica materials

A developed formalism for analyzing the power scaling of diffraction limited fiber lasers and amplifiers is applied to a wider range of materials. Limits considered include thermal rupture, thermal lensing, melting of the core, stimulated Raman scattering, stimulated Brillouin scattering, optical damage, bend induced limits on core diameter and limits to coupling of pump diode light into the fiber. For conventional fiber lasers based upon silica, the single aperture, diffraction limited power limit was found to be 36.6kW. This is a hard upper limit that results from an interaction of the stimulated Raman scattering with thermal lensing. This result is dependent only upon physical constants of the material and is independent of the core diameter or fiber length. Other materials will have different results both in terms of ultimate power out and which of the many limits is the determining factor in the results. Materials considered include silica doped with Tm and Er, YAG and YAG based ceramics and Yb doped phosphate glass. Pros and cons of the various materials and their current state of development will be assessed. In particular the impact of excess background loss on laser efficiency is discussed

Search for Gravitational Wave Bursts from Soft Gamma Repeaters

We present the results of a LIGO search for short-duration gravitational waves (GWs) associated with Soft Gamma Repeater (SGR) bursts. This is the first search sensitive to neutron star f-modes, usually considered the most efficient GW emitting modes. We find no evidence of GWs associated with any SGR burst in a sample consisting of the 27 Dec. 2004 giant flare from SGR 1806-20 and 190 lesser events from SGR 1806-20 and SGR 1900+14 which occurred during the first year of LIGO's fifth science run. GW strain upper limits and model-dependent GW emission energy upper limits are estimated for individual bursts using a variety of simulated waveforms. The unprecedented sensitivity of the detectors allows us to set the most stringent limits on transient GW amplitudes published to date. We find upper limit estimates on the model-dependent isotropic GW emission energies (at a nominal distance of 10 kpc) between 3x10^45 and 9x10^52 erg depending on waveform type, detector antenna factors and noise characteristics at the time of the burst. These upper limits are within the theoretically predicted range of some SGR models.Comment: 6 pages, 1 Postscript figur

First LIGO search for gravitational wave bursts from cosmic (super)strings

We report on a matched-filter search for gravitational wave bursts from cosmic string cusps using LIGO data from the fourth science run (S4) which took place in February and March 2005. No gravitational waves were detected in 14.9 days of data from times when all three LIGO detectors were operating. We interpret the result in terms of a frequentist upper limit on the rate of gravitational wave bursts and use the limits on the rate to constrain the parameter space (string tension, reconnection probability, and loop sizes) of cosmic string models.Comment: 11 pages, 3 figures. Replaced with version submitted to PR

All-sky LIGO Search for Periodic Gravitational Waves in the Early S5 Data

We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50--1100 Hz and with the frequency's time derivative in the range -5.0E-9 Hz/s to zero. Data from the first eight months of the fifth LIGO science run (S5) have been used in this search, which is based on a semi-coherent method (PowerFlux) of summing strain power. Observing no evidence of periodic gravitational radiation, we report 95% confidence-level upper limits on radiation emitted by any unknown isolated rotating neutron stars within the search range. Strain limits below 1.E-24 are obtained over a 200-Hz band, and the sensitivity improvement over previous searches increases the spatial volume sampled by an average factor of about 100 over the entire search band. For a neutron star with nominal equatorial ellipticity of 1.0E-6, the search is sensitive to distances as great as 500 pc--a range that could encompass many undiscovered neutron stars, albeit only a tiny fraction of which would likely be rotating fast enough to be accessible to LIGO. This ellipticity is at the upper range thought to be sustainable by conventional neutron stars and well below the maximum sustainable by a strange quark star.Comment: 6 pages, 1 figur