1,720,976 research outputs found
Performance comparison of green propulsion systems for future Orbital Transfer Vehicles
No full textThis paper explores the relevance of a new class of upper stages commonly referred to as Orbital Transfer Vehicles (OTVs) or Kick-Stages, and the importance of green propellants in the development of such systems.
Orbital Transfer Vehicles are currently developed for diverse applications by many entities and are expected to
have a major impact in the future of space missions and overall space sector. Such systems are commonly
connected to the topic of On-Orbit Servicing with the promise of unlocking new missions, including active space
debris removal, multi-payload to multi-orbit delivery, in-orbit experiments, in-orbit refuelling and other generic
services. Green propulsion is an increasingly prevalent trend in the space industry that has experienced significant growth in recent decades with the main objective of identifying suitable alternatives to commonly used,
toxic liquid propellants for in-space applications. The study investigates the synergies between the two themes,
underlining the advantages that a widespread use of green technologies could bring to the overall sector, but also
examining the final benefits to the system design of OTVs. Due to the numerous and challenging propulsive
system requirements associated with these systems, green technologies are analysed to determine their advantages and disadvantages in comparison with current concepts, outlining current trends and expected future
developments. The focus is on attainable performances of propulsion systems with respect to the required dry
and inert mass. Various architectures of the different green alternatives based on hydrogen peroxide and the
more peculiar self-pressurized propellants are proposed, exploring green propellants-based designs that can offer
synergies and advantages over classical ones. These new architectures offer performance comparable to classical
and widely available toxic alternatives and present the important advantage of using easy-to-handle propellants.
The development of such new options has the potential to enable innovative future designs by improving mass
and size requirements of new propulsion systems, thereby enhancing the current landscape
A holistic approach for efficient greener in-space propulsion
No full textThis paper presents a comprehensive framework for designing in-space propulsion systems, integrating four
criteria: global propulsive performance, environmental impact, cost efficiency, and architectural reliability. The
study focuses on the emerging class of Orbital Transfer Vehicles to illustrate the application of this method. By
examining the synergistic potential of OTVs and greener propellants, the paper addresses different mission
scenarios, including LEO, GEO, and lunar missions, with both scientific and commercial objectives. The proposed
framework aims to go beyond traditional cost-centric approaches, offering a more complete evaluation method
for early design phases. A case study comparing three liquid bipropellant options, pressure-fed MON-3/MMH,
98%-HTP/RP-1, and self-pressurizing N2O/Ethane, demonstrates the utility of the tool. Findings suggest that
scientific missions benefit most from 98%-HTP/RP-1, while traditional propellants remain preferable for costdriven commercial missions to GEO and the Moon, though greener alternatives are competitive for less
demanding LEO missions. This innovative framework aims to guide the selection of propulsion systems to
achieve greener space missions, aligning traditional performance figures with environmental responsibility
Experimental investigation of combustion performance of a green hypergolic bipropellant based on hydrogen peroxide
No full textThe present study examines the advancements of a promising low-toxicity hypergolic propellant combination
called HIP_11 for in-space applications, developed as alternative to common hypergolic toxic propellants. The
fuel is based on an ionic liquid, storable, stable and simple to handle at ambient conditions, developed at the
Institute of Space Propulsion, German Aerospace Centre (DLR). The compound shows hypergolicity behaviour
when in contact with Hydrogen Peroxide and is a promising substitution to conventional hypergolic propellants.
The present work describes the advancements in the development of HIP_11 through a dedicated experimental
investigation of various components, analysing and investigating the performances. The experiments are based
on a small modulable thruster that allowed to study the efficiency and stability of combustion of the propellant
combination while varying various design parameters of the thruster. Specifically, the effects of different injector
designs, as well as variations in combustion chamber shape, characteristic length, and operating pressure have
been thoroughly examined and analysed
Assessment of Propulsion System Architectures for Green Propellants-based Orbital Stages
Full text linkGreen Propulsion is a recurring trend in the space sector that has grown exponentially over the last decades. The researchers’ shared goal is to find good alternatives to current liquid propellants, usually toxic and hard-to-manage during ground operations. The current toxic leading compounds are Hydrazine and its derivatives that covered and still cover a key role in the space propulsion arena: as a matter of fact, despite the well-known complications for incompatibilities with human health, and despite the dozens of proposed replacements, the propellants still have some advantages over many of the suggested alternatives and are commonly used. The main and natural application of green technologies is doubtlessly the in-space propulsion since the main features of long-term storability, stability and acceptable performance are a perfect match for engines working outside the atmosphere and far from the support of ground operations.
In this study, the identified most attractive technologies are evaluated on their applicability to upper stages. A specific class of systems, often referred to as kick-stages, are taken as reference. These systems are designed, as usually, to remain as light as possible to carry more payload, but concomitantly to be able to fulfil a very diverse type of missions.
Between others: active space debris removal, multi-payload to multi-orbit delivery, in-orbit experiments with a few providers planning also the reusability and return to the ground. With such diverse and arduous purposes, it is clear that, in terms of propulsive system requirements, the challenges are many. The analysis expands on utilization of green technologies for these systems, outlining advantages and disadvantages in comparison with current concepts. Particular focus is dedicated to the attainable performance with respect to required dry mass. In particular, it is analysed the different inert mass rate of various architectures considering also full-green-propellants-based designs that can offer synergies and advantages respect to classical ones
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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