1,720,973 research outputs found
Small Spacecraft Solar Sail Missions for Multiple Near-Earth Object Prospection: Remote Sensing, In-Situ Characterization and Sample Return
No full textSolar sail technology has been developed by the German Aerospace Center (DLR) since the 1990s, culminating in a successful (20 m)² sail ground demonstrator deployment test in 1999 at DLR Cologne. In the last years a further development of the technology for controlled deployment of gossamer spacecraft was made in the DLR GOSSAMER-1 Project.
The DLR-ESTEC GOSSAMER roadmap originally envisaged the extremely fast-paced development of solar sailing technology by a series of successively leapfrogging low-cost demonstrator flights leading towards the technological basis for first science missions. In this framework, the GOSSAMER-1 deployment demonstrator for a (5 m)² sail structure in low Earth orbit dominated by drag was to be followed by the (20 m)² sail effect and attitude control demonstrator GOSSAMER-2 for higher Earth orbits dominated by solar radiation pressure, and the (50 m)² GOSSAMER-3 sailcraft proving the principle within the Earth-Moon system. It was to demonstrate sufficient trajectory and attitude control for science missions using a simple lightweight camera for timed pointing and localization reference imaging and a magnetometer to study the space environment around a sail. Since the first Roadmap studies, the expected payload capability increased from a few to several kg.
Three scientific mission types which are exclusively feasible with the unique capabilities of solar sail propulsion were identified and studied in detail by science working groups as candidates for a first science mission. These studies were based on the expected performance of solar sail technology developed in the Roadmap. Each mission was to be completed within 10 years:
• Multiple Near-Earth Asteroids (NEA) Rendezvous (MNR) & station-keeping, with optional Near-Earth Object (NEO) fly-bys of opportunity,
• Displaced Lagrange point 1 (DL1) solar storm early warning at twice L1 distance from Earth,
• Solar Polar Orbiters (SPO) for solar wind and coronal research and/or spectroscopic imaging of the Sun.
For MNR, trajectories for several triple-rendezvous missions were calculated assuming near-term 1st-generation sailcraft performance. Notably, a solar sail based mission can change target NEAs in flight whenever new knowledge triggers a change of interest. The science payload of 12 kg included a multispectral imager, a vis-NIR point spectrometer, an IR radiometer, and three 1U-CubeSat-sized drop probes. The spacecraft was expected to fit a standard ESPA or ASAP ‘micro’ piggy-back payload launch envelope. The ‘mini’-class ENEAS missions with launch masses from 150 to 750 kg studied a decade earlier based on similar sail performance estimates include single- and triple-sample-return mission profiles. Sailcraft with a performance between MNR and ENEAS could carry a single MASCOT-type or several CubeSat-like landers to each rendezvous target. Sharing of the science payload between lander and sailcraft may be feasible for missions focusing more on a single target.
With the technology available already now, it would be possible to develop a lightweight solar sail that fulfills the mission requirements of a 10-year multiple NEO rendezvous mission, thereby providing the means to study, prospect, or even deflect such potentially mineable or dangerous objects. In recent years, DLR has gained significant experience in realizing small spacecraft based projects on very short timelines with a high degree of strategic re-use of proven components between projects such as MASCOT and its successors, GOSSAMER-1, ROBEX, the ADEO dragsail, the GOSSAMER successor project GOSOLAR for very large scale photovoltaics, and others. Also, the infrastructure has been expanded to include facilities for functional and qualification testing, and the study and testing of critical effects of the space environment on new types of structures such as sail foils and thin-film photovoltaics
Efficient Massively Parallel Prospection for ISRU by Multiple Near-Earth Asteroid Rendezvous using Near-Term Solar Sails and 'Now-Term' Small Spacecraft Solutions
Get PDFPhysical interaction with small solar system bodies (SSSB) is key for in-situ resource utilization (ISRU). The design of mining missions requires good understanding of SSSB properties, including composition, surface and interior structure, and thermal environment. But as the saying goes "If you've seen one asteroid, you've seen one Asteroid": Although some patterns may begin to appear, a stable and reliable scheme of SSSB classification still has to be evolved. Identified commonalities would enable generic ISRU technology and spacecraft design approaches with a high degree of re-use. Strategic approaches require much broader in-depth characterization of the SSSB populations of interest to the ISRU community. The DLR-ESTEC GOSSAMER Roadmap Science Working Groups identified target-flexible Multiple Near-Earth asteroid (NEA) Rendezvous (MNR) as one of the missions only feasible with solar sail propulsion, showed the ability to access any inclination and a wide range of heliocentric distances as well as continuous operation close to Earth's orbit where low delta-v objects reside
Using emergent order to shape a space society
Get PDFA fast-growing movement in the scientific community is reshaping the way that we view the world around us. The short-hand name for this movement is 'chaos'. Chaos is a science of the global, nonlinear nature of systems. The center of this set of ideas is that simple, deterministic systems can breed complexity. Systems as complex as the human body, ecology, the mind or a human society. While it is true that simple laws can breed complexity, the other side is that complex systems can breed order. It is the latter that I will focus on in this paper. In the past, nonlinear was nearly synonymous with unsolvable because no general analytic solutions exist. Mathematically, an essential difference exists between linear and nonlinear systems. For linear systems, you just break up the complicated system into many simple pieces and patch together the separated solutions for each piece to form a solution to the full problem. In contrast, solutions to a nonlinear system cannot be added to form a new solution. The system must be treated in its full complexity. While it is true that no general analytical approach exists for reducing a complex system such as a society, it can be modeled. The technical involves a mathematical construct called phase space. In this space stable structures can appear which I use as analogies for the stable structures that appear in a complex system such as an ecology, the mind or a society. The common denominator in all of these systems is that they rely on a process called feedback loops. Feedback loops link the microscopic (individual) parts to the macroscopic (global) parts. The key, then, in shaping a space society, is in effectively using feedback loops. This paper will illustrate how one can model a space society by using methods that chaoticists have developed over the last hundred years. And I will show that common threads exist in the modeling of biological, economical, philosophical, and sociological systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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