1,721,220 research outputs found
Life Cycle Cost estimation for future reusable access to space systems
Full text linkThe paper introduces an innovative Life-Cycle Cost Estimation Methodology for future reusable access to space systems to assess Research, Development, Test and Evaluation (RDTE), Production and Operating Costs. In particular, the key limitations of TransCost (i.e., the most comprehensive and noteworthy cost methodology currently applicable to Reusable Launch Vehicles (RLVs)) are discussed, highlighting the need to improve Costs Estimation Relationships (CERs) granularity level to allow a proper down-selection of the most cost-effective design options at early design stage. Therefore, the paper suggests a detailed costs breakdown structure, developed widening the more general subdivision proposed in TransCost, discussing the derivation of new CERs at the desired granularity level. Eventually, after selecting a proper case study, the new cost methodology is applied to verify the effective potential or future RLVs to reduce launch costs
A methodology to study the possible occurrence of chugging in liquid rocket engines during transient start-up
No full textAn investigation on the low frequency combustion instabilities due to the interaction of combustion chamber and feed line dynamics in a liquid rocket engine is carried out implementing a specific module in the system analysis software EcosimPro. The properties of the selected double time lag model are identified according to the two classical assumptions of constant and variable time lag. Module capabilities are evaluated on a literature experimental set up consisting of a combustion chamber decoupled from the upstream feed lines. The computed stability map results to be in good agreement with both experimental data and analytical models. Moreover, the first characteristic frequency of the engine is correctly predicted, giving confidence on the use of the module for the analysis of chugging instabilities. As an example of application, a study is carried out on the influence of the feed lines on the system stability, correctly capturing that the lines extend the stable regime of the combustion chamber and that the propellant domes play a key role in coupling the dynamics of combustion chamber and feed lines. A further example is presented to discuss on the role of pressure growth rate and of the combustion chamber properties on the possible occurrence of chug instability during engine start-up and on the conditions that lead to its damping or growth. © 2017 IA
Upgrade of HyCost methodology and tool to support LCC estimation of reusable access to space vehicles
Full text linkThis paper aims at presenting the latest upgrades to HyCost Methodology and Tool, developed by Politecnico di Torino under funding and supervision of the European Space Agency (ESA), to support Life Cycle Cost (LCC) estimation of reusable access to space vehicles. The main idea is to support the designer in cost estimation activity during conceptual and preliminary design phases, allowing the evaluation of Research, Development, Test and Evaluation (RDTE) Costs, Production Costs, as well as Direct and Indirect Operating Costs (DOC and IOC), for a wide set of aerospace systems, from supersonic civil aircraft to hypersonic and, in general, high speed vehicles. Politecnico di Torino has already proposed a LCC methodology and tool called “HyCost 1.0” specifically tailored to air-breathing high-speed transportation systems. This paper discloses the upgrades of HyCost 1.0, i.e. “HyCost 2.0” methodology, to extend the methodology and tool capability to future Reusable Access to Space Vehicles. The main goal of this research activity is to evaluate the applicability of already existing parametric cost estimation relationships (CERs) to the peculiarities of Reusable Access to Space Vehicles and if necessary, to define new equations. Specifically, this new set of equations shall be able to capture the impact of different vehicle configurations (e.g. staging strategy, staging Mach number, parallel or series configuration, etc...) onto costs, as well as the impact of the most promising propulsive solutions, ranging from scramjet and combined cycle engines to rocket engines. Ultimately, this new methodology and implemented routines are applied and validated using the SpaceX Starship case study
System analysis of low frequency combustion instabilities in liquid rocket engines
No full textIn this paper we propose an analysis of low frequency combustion instabilities, taking advantage of the software EcosimPro. We implement a specific module based on the double time lag model and investigate the coupling of combustion chamber and feed line oscillations by using a complete set of non-linear equations. We identify the characteristic time lags following two approaches: (i) a constant time lag approach and (ii) a variable time lag approach based on correlations available in open literature. To prove the module capabilities we reproduce an experimental set up consisting of a combustion chamber decoupled from the upstream feed lines. For this configuration we generate a stability map, comparing our results with literature data from both experiments and a linear double time lag model. The stability boundaries obtained with the chug module are in good agreement with those obtained in open literature, and the first characteristic frequency of the engine is well predicted. Finally, we study the influence of the feed lines on the system stability, verifying that the lines extend the stable regime of the combustion chamber and that the propellant domes play a key role in coupling the dynamics of combustion chamber and feed lines
Life-Cycle Cost Estimation for High-Speed Vehicles: from the engineers’ to the airline’s perspective
Full text linkThis paper aims at upgrading the holistic Cost Estimation methodology for High-Speed
Vehicles already developed by Politecnico di Torino and the European Space Agency (ESA)
to encompass different stakeholders’ perspectives. In details, the presented methodology
combines International Air Transport Association (IATA) best practices with a detailed Life-
Cycle Cost (LCC) assessment, which includes the evaluation of Research, Development, Test
and Evaluation (RDTE) Costs, Production costs and of Direct and Indirect Operating Costs
(DOC and IOC). The integrated approach allows to further extend the capabilities of the inhouse
developed HyCost tool to support all the actors of the product value-chain (including
engineers, manufacturers, airlines and customers) in assessing the economic sustainability of
a newly under-development high-speed vehicle. However, considering the need of providing
all these cost analyses perspectives since the early design stages, the derived Cost Estimation
Relationships are mainly derived on statistical bases. To cope with the uncertainties that affect
the initial statistical population and consequently, the CERs, this paper presents each cost
item together with the estimation of related prediction intervals. Finally, results of the
application of the upgraded cost estimation methodology and of the upgraded tool to the
LAPCAT MR2.4 high-speed civil transport are reported and discussed
Experimental investigation of the filling process in evacuated spacecraft propulsion system feedlines
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Passieve controle van hypersone grenslaag transitie op basis van ultrasone absorptie door middel van koolstof gebaseerde keramieken met willekeurige micro-structuur
No full textIn the presented work ultrasonically absorptive carbon-carbon ceramic was shown for the first time to delay hypersonic laminar to turbulent boundarylayer transition. Three 7° half-angle cones with nose radii between 0.1 mm and 5.0 mm and a total length of 1100 mm were tested at zero angle of attack in the High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR) at Mach 7.5. One model was equipped with aninhouse manufactured ultrasonically absorptive carbon-carbon ceramic insert with random microstructure covering one third of the model surface in circumferential direction. The remaining model surface consisted of polished steel and served as reference surface. The free-stream unit Reynolds number was varied over a range of 1.5e6 /m to 9.8e6 /m at stagnation enthalpies of 3.2 MJ/kg and a wall temperature to total temperature ratio of 0.1. The ultrasonic absorption properties of carbon-carbon ceramic (C/C) were assessed theoretically by means of the quasi-homogeneous absorber theory and experimentally by means of direct reflection coefficient measurements at varying ambient pressure levels. For the first time broadband ultrasonic sound transducers with resonance frequencies of up to 370 kHz were applied to directly cover the frequency range of interestwith respect to the second mode instabilities observed on cone geometries in HEG. C/C was found to absorb up to 19% of the acoustic power transmitted towards the surface. The experimental results were found to be ingood agreement with the theory. The present study revealed the second mode instability to dominate the transition process. A distinctive attenuation of instability waves and a delay of boundary layer transition on the ultrasonically absorptive carbon-carbon insert was proven by means offast-response surface pressure measurements, high speed schlieren visualization and surface heat flux measurement.status: Publishe
Experimental Investigation of the Filling Process in Evacuated Spacecraft Propulsion System Feedlines
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