29,686 research outputs found

    Conceptions of geographic information systems (GIS) held by senior geography students in Queensland

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    Geographical Information Systems (GIS) represent one of the major contributions to spatial analysis and planning of the new technologies. While teachers and others have viewed its potential contribution to geographical education as considerable, it has not been known with any certainty whether they present a valuable educational tool that aids geographical education. The value of GIS to geographical education is viewed as depending on a geographical education being, in itself, valuable. Within this context, synergetic focus groups are employed to explore the conceptions of GIS held by 109 secondary school students studying Senior Geography in metropolitan and regional Queensland, Australia. A phenomenographic approach is adopted to identify the six qualitatively different ways, or conceptions, in which the participating students experience GIS as: 1. Maps and a source of maps in geography. 2. Mapping in geography: a way to use and create maps. 3. A professional mapping tool: exceeding the needs of senior geography. 4. Frustrating geography: irksome and presenting many challenges to the student-user. 5. Relevant geography: within and beyond the school experience. 6. A better geography: offering a superior curriculum, and broader geographical education, when contrasted to a senior geography that omits its use. The structural and referential elements of each of these conceptions are elucidated within corresponding Categories of Description. The qualitatively different ways in which the conceptions may be experienced are illustrated through an Outcome Space, comprising a metaphoric island landscape. This structural framework reveals that for the Senior Geography students who participated in this investigation, the extent to which GIS may augment the curriculum is influenced by the nature of students' individual understandings of how GIS manages spatial data. This research project is a response to repeated calls in the literature for teachers of geography themselves to become researchers and for a better understanding of GIS within geography education. It reviews the salient literature with respect to geography and geography education generally, and GIS within geographical education specifically. The investigation has confirmed that qualitatively different conceptions of GIS exist amongst students and that these are not consistently aligned with assumptions about its use and benefits as presented by current literature. The findings of the study contribute to knowledge of the potential educational outcomes associated with the use of GIS in geography education and decisions related to current and potential geography curricula. It provides guidance for future curriculum development involving GIS and argues for additional research to inform educators and the spatial sciences industry about the actual and perceived role of GIS within geography education

    Advanced Launch Vehicle Upper Stages Using Liquid Propulsion and Metallized Propellants

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    Metallized propellants are liquid propellants with a metal additive suspended in a gelled fuel or oxidizer. Typically, aluminum (Al) particles are the metal additive. These propellants provide increase in the density and/or the specific impulse of the propulsion system. Using metallized propellant for volume-and mass-constrained upper stages can deliver modest increases in performance for low earth orbit to geosynchronous earth orbit (LEO-GEO) and other earth orbital transfer missions. Metallized propellants, however, can enable very fast planetary missions with a single-stage upper stage system. Trade studies comparing metallized propellant stage performance with non-metallized upper stages and the Inertial Upper Stage (IUS) are presented. These upper stages are both one- and two-stage vehicles that provide the added energy to send payloads to altitudes and onto trajectories that are unattainable with only the launch vehicle. The stage designs are controlled by the volume and the mass constraints of the Space Transportation System (STS) and Space Transportation System-Cargo (STS-C) launch vehicles. The influences of the density and specific impulse increases enabled by metallized propellants are examined for a variety of different stage and propellant combinations

    Upper stages using liquid propulsion and metallized propellants

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    Metallized propellants are liquid propellants with a metal additive suspended in a gelled fuel. Typically, aluminum particles are the metal additive. These propellants increase the density and/or the specific impulse of the propulsion system. Using metallized propellants for volume- and mass-constrained upper stages can deliver modest increases in performance for low Earth orbit to geosynchronous Earth orbit (LEO-GEO) and other Earth-orbital transfer missions. However, using metallized propellants for planetary missions can deliver great reductions in flight time with a single-stage, upper-stage system. Tradeoff studies comparing metallized propellant stage performance with nonmetallized upper stages and the Inertial Upper Stage (IUS) are presented. These upper stages, launched from the STS and STS-C, are both one- and two-stage vehicles that provide the added energy to send payloads to high altitude orbits and onto interplanetary trajectories that are unattainable with only the Space Transportation System (STS) and the Space Transportation System-Cargo (STS-C). The stage designs are controlled by the volume and the mass constraints of the STS and STS-C launch vehicles. The influences of the density and specific impulse increases enabled by metallized propellants are examined for a variety of different stage and propellant combinations

    Advanced launch vehicle propulsion at the NASA Lewis Research Center

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    Several programs are investigating the benefits of advanced propellant and propulsion systems for future launch vehicles and upper stages. The two major research areas are the Metallized Propellants Program and the Advanced Concepts Program. Both of these programs have theoretical and experimental studies underway to determine the system-level performance effects of these propellants on future NASA vehicles

    Atomic hydrogen as a launch vehicle propellant

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    An analysis of several atomic hydrogen launch vehicles was conducted. A discussion of the facilities and the technologies that would be needed for these vehicles is also presented. The Gross Liftoff Weights (GLOW) for two systems were estimated; their specific impulses (I sub sp) were 750 and 1500 lb(sub f)/s/lb(sub m). The atomic hydrogen launch vehicles were also compared to the currently planned Advanced Launch System design concepts. Very significant GLOW reductions of 52 to 58 percent are possible over the Advanced Launch System designs. Applying atomic hydrogen propellants to upper stages was also considered. Very high I(sub sp) (greater than 750 lb(sub f)/s/lb(sub m)) is needed to enable a mass savings over advanced oxygen/hydrogen propulsion. Associated with the potential benefits of high I(sub sp) atomic hydrogen are several challenging problems. Very high magnetic fields are required to maintain the atomic hydrogen in a solid hydrogen matrix. The magnetic field strength was estimated to be 30 kilogauss (3 Tesla). Also the storage temperature of the propellant is 4 K. This very low temperature will require a large refrigeration facility for the launch vehicle. The design considerations for a very high recombination rate for the propellant are also discussed. A recombination rate of 210 cm/s is predicted for atomic hydrogen. This high recombination rate can produce very high acceleration for the launch vehicle. Unique insulation or segmentation to inhibit the propellant may be needed to reduce its recombination rate

    Advanced chemical propulsion at NASA Lewis: Metallized and high energy density propellants

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    Two of the programs at the NASA Lewis Research Center investigating advanced systems for future space missions are the Metallized Propellant Program and the Advanced Concepts Program. Each program includes both experimental and theoretical studies of future propellants and the associated vehicle impacts and significant payload benefits for many types of space transportation. These programs are described

    Metallized Propellants for the Human Exploration of Mars

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    Advanced chemical propulsion using Metallized Propellants (MP) can lead to significant reductions in launch mass for piloted Mars missions. MP allow the propellant density or the specific impulse I(sub sp) of the propulsion system, or both, to increase. It can reduce the propellant mass and the propulsion system dry mass. Detailed mass-scaling equations and estimates of the I(sub sp) for several MP combinations are presented. The most significant savings with MP are derived from increasing the payload delivered to Mars. For the mass in low Earth orbit (LEO), a metallized Mars transfer vehicle can deliver 20 to 22 percent additional payload. This 20-percent payload increase reduces the total number of Mars flights and therefore significantly reduces the number of Space Transportation System-Cargo launches for the entire Mars architecture. Using MP to reduce the mass in LEO per flight is not as effective as increasing the payload delivery capacity. The mass saving per flight, while delivering the same payload with a higher I(sub sp) system, is much smaller. Using MP in all of the Mars propulsion systems would produce a modest 3.3 percent LEO mass saving. This translates into a saving of 38,000 kg over the mass required with O2/H2 propulsion. A Mars excursion vehicle using Earth- or space-storable propellants for the ascent can be an alternative to storing cryogenic H2 on Mars. A space-storable system using oxygen/monomethyl hydrazine/aluminum (O2/MMH/Al) would deliver the lowest mass penalty over O2/H2. For lower-energy expedition missions the LEO mass penalty for using metallized O2/MMH/Al would be only 3 to 5 percent
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