Weight savings in aerospace vehicles through propellant scavenging

Vehicle payload benefits of scavenging hydrogen and oxygen propellants are addressed. The approach used is to select a vehicle and a mission and then select a scavenging system for detailed weight analysis. The Shuttle 2 vehicle on a Space Station rendezvous mission was chosen for study. The propellant scavenging system scavenges liquid hydrogen and liquid oxygen from the launch propulsion tankage during orbital maneuvers and stores them in well insulated liquid accumulators for use in a cryogenic auxiliary propulsion system. The fraction of auxiliary propulsion propellant which may be scavenged for propulsive purposes is estimated to be 45.1 percent. The auxiliary propulsion subsystem dry mass, including the proposed scavenging system, an additional 20 percent for secondary structure, an additional 5 percent for electrical service, a 10 percent weight growth margin, and 15.4 percent propellant reserves and residuals is estimated to be 6331 kg. This study shows that the fraction of the on-orbit vehicle mass required by the auxiliary propulsion system of this Shuttle 2 vehicle using this technology is estimated to be 12.0 percent compared to 19.9 percent for a vehicle with an earth-storable bipropellant system. This results in a vehicle with the capability of delivering an additional 7820 kg to the Space Station

Advanced APS Impacts on Vehicle Payloads

Advanced auxiliary propulsion system (APS) technology has the potential to both, increase the payload capability of earth-to-orbit (ETO) vehicles by reducing APS propellant mass, and simplify ground operations and logistics by reducing the number of fluids on the vehicle and eliminating toxic, corrosive propellants. The impact of integrated cryogenic APS on vehicle payloads is addressed. In this system, launch propulsion system residuals are scavenged from integral launch propulsion tanks for use in the APS. Sufficient propellant is preloaded into the APS to return to earth with margin and noncomplete scavenging assumed. No propellant conditioning is required by the APS, but ambient heat soak is accommodated. High temperature rocket materials enable the use of the unconditioned hydrogen/oxygen in the APS and are estimated to give APS rockets specific impulse of up to about 444 sec. The payload benefits are quantified and compared with an uprated monomethyl hydrazine/nitrogen tetroxide system in a conservative fashion, by assuming a 25.5 percent weight growth for the hydrogen/oxygen system and a 0 percent weight growth for the uprated system. The combination and scavenging and high performance gives payload impacts which are highly mission specific. A payload benefit of 861 kg (1898 lbm) was estimated for a Space Station Freedom rendezvous mission and 2099 kg (4626 lbm) for a sortie mission, with payload impacts varying with the amount of launch propulsion residual propellants. Missions without liquid propellant scavenging were estimated to have payload penalties, however, operational benefits were still possible

Windows Into Public Attitudes Towards Redistribution

redistribution, income taxation, public opinion

Hydrogen/oxygen auxiliary propulsion technology

A survey is provided of hydrogen/oxygen (H/O) auxiliary propulsion system (APS) concepts and low thrust H/O rocket technology. A review of H/O APS studies performed for the Space Shuttle, Space Tug, Space Station Freedom, and Advanced Manned Launch System programs is given. The survey also includes a review of low thrust H/O rocket technology programs, covering liquid H/O and gaseous H/O thrusters, ranging from 6600 N (1500 lbf) to 440 mN (0.1 lbf) thrust. Ignition concepts for H/O thrusters and high temperature, oxidation resistant chamber materials are also reviewed

An efficient counting method for the colored triad census

The triad census is an important approach to understand local structure in network science, providing comprehensive assessments of the observed relational configurations between triples of actors in a network. However, researchers are often interested in combinations of relational and categorical nodal attributes. In this case, it is desirable to account for the label, or color, of the nodes in the triad census. In this paper, we describe an efficient algorithm for constructing the colored triad census, based, in part, on existing methods for the classic triad census. We evaluate the performance of the algorithm using empirical and simulated data for both undirected and directed graphs. The results of the simulation demonstrate that the proposed algorithm reduces computational time many-fold over the naive approach. We also apply the colored triad census to the Zachary karate club network dataset. We simultaneously show the efficiency of the algorithm, and a way to conduct a statistical test on the census by forming a null distribution from 1,000 realizations of a mixing-matrix conditioned graph and comparing the observed colored triad counts to the expected. From this, we demonstrate the method's utility in our discussion of results about homophily, heterophily, and bridging, simultaneously gained via the colored triad census. In sum, the proposed algorithm for the colored triad census brings novel utility to social network analysis in an efficient package

Improving the accuracy of simple runoff estimates : the role of parameter resolution and data collection

This research project collected, compared, and analyzed rainfall and runoff data from two similar small watersheds within Knoxville\u27s Second Creek drainage area. The primary reason for the study was to determine the most efficient way to increase the accuracy of two well known and simple runoff estimation models: the Rational and SCS Curve Number Methods. This was accomplished by investigating the impact that incorporating different amounts and types of information had on the accuracy of the models. An important component of this investigation was to examine the relative cost-benefit ratios of the different techniques that were attempted. To optimize the models, the investigation took a three-pronged approach. First, the a priori model parameters and the parameter selection methods were optimized by using increasingly higher-resolution data to characterize the watersheds. The second step of the research was to see by what degree collecting rain and/or runoff data improved model estimations on that watershed. The process began by using the least possible data and incrementally increasing it. The final approach was to investigate whether the measured rainfall-runoff records from one watershed enhanced the estimates on another similar, nearby watershed. Once those steps had been accomplished, a benefit-cost analysis was performed to determine which techniques and data most efficiently improved the models. For the peak flow estimates, the results showed that fine-tuning the parameters with high-resolution data did not result in better estimates. In fact, for these watersheds the highest resolution parameters produced some of the poorest estimates. Using observed runoff data, however, substantially decreased the estimate errors. Errors were reduced up to 90% using data collected within the watershed. Using data collected from a similar watershed to cross-calibrate the model reduced errors by up to 70%. In addition, the results indicated that more data further improved the estimates. However, the larger amounts of data tended to have a lower benefit to cost ratio. The results from the volume estimates were not as clear-cut. While all the techniques appeared to work, the evaluation was hampered by the limited observations of storm events. Thus, the first two techniques, the a priori and the calibrated estimates were unreliable. Even so, the third technique, which used data from the similar watershed to calibrate the model, reduced errors by approximately 60 %. This research provides engineers, hydrologists, and others needing quick and simple runoff estimates with techniques that increase the models\u27 accuracy. This should aid in the sizing of stormwater conveyances, determining mass contaminant loads, making land management decisions, and other actions requiring accurate runoff volumes and peak flows. Because these techniques allow more accurate estimations while maintaining the simplicity and cost effectiveness of the models, it is expected to primarily benefit those in smaller communities, suburban, and rural areas. However, anyone who uses the Rational and SCS Curve Number Methods should find the techniques applicable. Keywords: Surface Runoff Estimations, Rational Method, SCS Curve Number Method, Representative Watershed, Paired Watershed, Data Collection and Accuracy, Calibration Techniques, A Priori Parameter Resolution, Rainfall and Runoff Data, Calibration Data from a Similar Watershed , Peak Flow, Volumes, Cross-watershed Calibrations, Time of Concentration, Benefit-Cost Ratio

The Design and Implementation of the Dynamic Ionosphere Cubesat Experiment (Dice) Science Instruments

Dynamic Ionosphere Cubesat Experiment (DICE) is a satellite project funded by the National Science Foundation (NSF) to study the ionosphere, more particularly Storm Enhanced Densities (SED) with a payload consisting of plasma diagnostic instrumentation. Three instruments onboard DICE include an Electric Field Probe (EFP), Ion Langmuir Probe (ILP), and Three Axis Magnetometer (TAM). The EFP measures electric fields from 8V and consists of three channels a DC to 40Hz channel, a Floating Potential Probe (FPP), and an spectrographic channel with four bands from 16Hz to 512Hz. The ILP measures plasma densities from 1x104 cm-3 to 2x107 cm-3. The TAM measures magnetic field strength with a range 0.5 Gauss with a sensitivity of 2nT. To achieve desired mission requirements careful selection of instrument requirements and planning of the instrumentation design to achieve mission success. The analog design of each instrument is described in addition to the digital framework required to sample the science data at a 70Hz rate and prepare the data for the Command and Data Handing (C&DH) system. Calibration results are also presented and show fulfillment of the mission and instrumentation requirements

Impacts of Trogocytosis-Mediated Intracellular Signaling on CD4+ T cell Effector Cytokine Production and Differentiation

Trogocytosis is the direct intercellular transfer of membrane and membrane associated molecules. Unlike other passive-membrane transfer events, trogocytosed molecules may remain fully functional and become re-expressed on the surface of the trogocytosis-positive (trog+) recipient. This phenomenon commonly occurs between various cell types, including those of the immune system. CD4+ T cell trogocytosis occurs during their activation by antigen presenting cells (APC). Consequently, the acquired molecules include ligands for signaling receptors on the T cell. The impacts of CD4+ trogocytosis on the immune response are largely unknown. While it has been demonstrated that trog+ cells can present trogocytosed peptide:MHC (pMHC), and costimulatory molecules to activate other T cells, the consequences of trogocytosis on the individual trog+ CD4+ T cell have not been studied in-depth. We previously reported that trog+ cells perform cell-autonomous signaling by trogocytosed ligands engaging surface receptors, referred here to as trogocytosis-mediated signaling. This signaling led to the enhanced survival of trog+ cells in vitro compared to trog– cells after APC removal. Because the duration of T cell signaling influences the activation, lineage determination, and effector functionality of CD4+ T cells; trogocytosis-mediated signaling has the potential to uniquely modulate the effector-cytokine production and differentiation of trog+ CD4+ T cell after separation from APC. Examining this possibility is the foundation for this dissertation. Here, I will report my findings that: 1. Between 0-72 hrs post-separation from APC, trogocytosis-mediated signaling drives IL-4 and GATA-3 expression, consistent with T helper type-2 (TH2) differentiation; 3. Extended trogocytosis-mediated signaling (\u3e72 hrs) leads to the expression of Bcl-6, PD-1, CXCR5, and IL-21, consistent with T follicular helper (TFH) differentiation; 4. In absence of exogenous antigen (Ag), trogocytosis-mediated signaling is critical for the survival of the activated CD4+ T cells with high memory-potential. Despite the critical role for CD4+ T cells in generating protective immunity in the host, much remains unknown about the differentiation of CD4+ T cell effector subsets. The findings here present a novel mechanism for CD4+ T cell activation and differentiation via trogocytosis-mediated signaling, demonstrating the broad implications for such signaling in matters of public health

Studying the effects of in-vehicle information systems on driver visual behaviour – implications for design

In-vehicle information systems (IVIS) are a common feature in modern vehicles. The interaction of drivers with IVIS when driving must be considered to minimise distraction whilst maintaining the benefits provided. This research investigates the glance behaviours of drivers, assessed from video data, when using two functions – a personal navigation device (study 1) and a green driving advisory device (study 2). The main focus was to establish the number of glances of 2 seconds or more to the IVIS and relate this to driver safety (as stipulated in new guidelines for use of IVIS proposed by NHTSA). In study 1, the percentage of eyes- off-road time for drivers was much greater in the experimental (with device) condition compared to the baseline condition (14.3% compared to 6.7%) but, whilst glances to the personal navigation device accounted for the majority of the increase, there were very few which exceeded 2 seconds. Drivers in study 2 spent on average 4.3% of their time looking at the system, at an average of 0.43 seconds per glance; no glances exceeded 2 seconds. The research showed that ordinary use of IVIS (excluding manual interaction) does not lead to driver visual distraction and therefore the impact on safety is minimal. The results of the study have important design implications for future in-vehicle information systems