Passive orbit control for space-based geo-engineering

In this Note we consider using solar sail propulsion to stabilize a spacecraft about an artificial libration point. It has been demonstrated that the constant acceleration from a solar sail can be used to generate artificial libration points in the Earth-Sun three-body problem. This is achieved by directing the thrust due to the sail such that it adds to the centripetal and gravitational forces. These libration points have the potential for future space physics and Earth observation missions. Of particular interest is the possibility of placing solar reflectors at the L1 artificial libration point to offset natural and human driven climate change. One engineering challenge that presents itself is that these artificial libration points are highly unstable and require active control for station-keeping. Previous work has shown that it is possible to stabilize a solar sail about artificial libration points using variations in both pitch and yaw angles. However, in a practical sense, solar sails are large structures and active control of the sail's attitude is a challenging engineering problem. Passive stabilization of such reflectors is to be investigated here to reduce the complexity of space-based geo-engineering schemes

A pedagogical proposal in an area of epistemological uncertainty

IV Projetar 2009: PROJETO COMO INVESTIGAÇÃO: ENSINO, PESQUISA E PRÁTICA FAU-UPM SÃO PAULO BRASIL, Outubro 2009In professional areas in which there is an element of design practice, such as architecture and urbanism, the academic model of knowledge has not been clearly articulated. This means that often the values held in professional practice run counter to the traditional models of knowledge and research that are adopted. As a result there is a problem in accounting for research in these areas in ways that will be recognised and valued by both communities. There is an ongoing debate about the best way of dealing with and reflecting these values that are, from the academic viewpoint, non-traditional. The debate has substantiated an emergent type of research that is specific to areas of design practice that is called ‘Practice-based Research’ (PbR). PbR claims that design practice has an instrumental role in research in areas such as design and urban planning. This role is different from the role of experimentation in traditional empirical research, and different from the role of practice in professional design practice. This paper describes the development and delivery of a research methods training course in the department of spatial planning and design (Stedenbouw) at the Technical University Delft (TU Delft, Netherlands) that builds on research by the ‘Non-traditional Knowledge and Communication’ project (NtKC) at the University of Hertfordshire (UK). The paper will analyse the way in which research and practice are problematized in the TU Delft course. We claim that the problem of PbR manifests the differences between the worldviews of academic research and professional practice, with their differing aims and values. As a result, training and expertise in the professional values of design practice is insufficient for academic research, leading to a need for specific training as a researcher that recognises these differences. This need has been accepted at an institutional level in many universities in Europe, and the TU Delft course represents one such training programme

An international collaboration for the development of a research training course in an emergent academic discipline

Proceedings of INTED2010 Conference. 8-10 March 2010, Valencia, Spain.In professional areas such as the creative and performing arts and design, the academic model of research has not been clearly articulated. This means that often the values held in advanced professional practice run counter to the traditional models of knowledge and research that are adopted in academia. As a result, there is a problem in accounting for research in these areas in ways that will be recognised and valued by both communities. There is an ongoing debate about the best way of dealing with and reflecting these professional values in academic research. This debate has substantiated an emergent type of research that is called ‘Practice-based Research’ (PbR). PbR introduces the claim that creative practice has an instrumental role in academic research in areas such as design and urban planning. This role is different from the one of experimentation in traditional empirical research, and different from the one of practice in professional creative practice. This paper describes the development and delivery of a research methods training course in the department of spatial planning and design (Stedenbouw) at the Technical University Delft (TU Delft, Netherlands) that engages directly with these fundamental problems. The course, Research and Design Methods, has served as a testing ground for many ideas stemming from the cooperation between TU Delft and the University of Hertfordshire (UH, UK). As part of the international knowledge transfer initiative, a member of staff from TU Delft has been working at the UH for a year. One of the outcomes of this collaboration is the design and delivery of a new course at TU Delft, which tackles the relationship between academic research and planning and design, through a dialogue between different views on the activities of the urban planner and the designer. There are challenges that arise when structuring a course within an area for which the epistemological, ontological and methodological questions are still under discussion by the community. The broad aim was to offer insight into non-traditional academic research tools and methods for different areas of urban design and planning within a broader academic context. This included the analysis of different academic traditions that were relevant for urban planning and design. We define research as a systematic investigation of a subject that leads to the production of explicit knowledge, and adds to the existing body of knowledge about the subject. In the paper, we analyse the way in which research and practice are problematized in the TU Delft course and claim that PbR manifests the differences between the worldviews of academic research and professional practice, with their different aims and values. As a result, training and expertise in the professional values of creative practice is insufficient for academic research. There is therefore a need for specific research training that addresses these differences. This need for discipline specific research training has been recognized in the Bologna Process and the TU Delft course represents one such training programme.otherPeer reviewe

Vegetation-soil relations in a highly sodic landscape, Yelarbon, southern Queensland

Soil and vegetation data were collected from a sodic-scald near Yelarbon in southern Queensland. The surface of the landscape includes relatively light textured pedestals of the A-horizon with slightly alkaline pH and slopes leading down to scalded basement representing the surface of the strongly alkaline B-horizon. The strongest gradient within the floristic patterns was associated with wetland vegetation in drainage lines, but a secondary and orthogonal gradient was related to soil pH, which was probably a function of lower alkalinity on the more stable and weathered A-horizons. There were few significant differences between soil or vegetation characteristics from plot data comparing parts of the landscape with differing historical grazing regimes. Sites included stock routes heavily grazed between the 1920s and 1970s, and subsequently almost ungrazed; and grazed paddocks that have had moderate use throughout this period. There is clear evidence that the area is naturally active in terms of erosion and deposition during flooding regardless of grazing

Unevenly-sampled signals: a general formalism of the Lomb-Scargle periodogram

The periodogram is a popular tool that tests whether a signal consists only of noise or if it also includes other components. The main issue of this method is to define a critical detection threshold that allows identification of a component other than noise, when a peak in the periodogram exceeds it. In the case of signals sampled on a regular time grid, determination of such a threshold is relatively simple. When the sampling is uneven, however, things are more complicated. The most popular solution in this case is to use the "Lomb-Scargle" periodogram, but this method can be used only when the noise is the realization of a zero-mean, white (i.e. flat-spectrum) random process. In this paper, we present a general formalism based on matrix algebra, which permits analysis of the statistical properties of a periodogram independently of the characteristics of noise (e.g. colored and/or non-stationary), as well as the characteristics of sampling.Comment: 10 pages, 11 figures, Astronomy and Astrophysics, in pres

Baby Boomers & adult Ageing: Issues for Social and Public policy

This paper provides a critical assessment of academic and policy approaches to population ageing with an emphasis on the baby boomer cohort and constructions of late-life identity. It is suggested that policy towards an ageing population has shifted in focus, away from particular social hazards and towards an attempt to re-engineer the meaning of legitimate ageing and social participation in later life. Three themes are identified: constructing the baby boomers as a force for social change, a downward drift of the age associated with 'older people' and a shift away from defining ageing identities through consumption, bacl towards work and production. The paper concludes with a discussion of the implications for future social and public policy

The Age-shift: observations on social policy, ageism and the dynamics of the adult lifecourse

Through a critical engagement with policy trends, we ask how shifts in ideologies of ageing might influence the possibilities available to adults as they grow older. Of particular interest are the implications for how people are being encouraged to think about the adult lifecourse. We address these questions by looking at policy development, taking the 2000–2005 period in the UK as a case example, and by comparing this period to wider regional and international trends. Finally, we assess the implications of contemporary policy, from a psychodynamic point of view, for the maintenance of a viable identity in later life and for intergenerational relationships

Solar sail formation flying for deep-space remote sensing

In this paper we consider how 'near' term solar sails can be used in formation above the ecliptic plane to provide platforms for accurate and continuous remote sensing of the polar regions of the Earth. The dynamics of the solar sail elliptical restricted three-body problem (ERTBP) are exploited for formation flying by identifying a family of periodic orbits above the ecliptic plane. Moreover, we find a family of 1 year periodic orbits where each orbit corresponds to a unique solar sail orientation using a numerical continuation method. It is found through a number of example numerical simulations that this family of orbits can be used for solar sail formation flying. Furthermore, it is illustrated numerically that Solar Sails can provide stable formation keeping platforms that are robust to injection errors. In addition practical trajectories that pass close to the Earth and wind onto these periodic orbits above the ecliptic are identified

Control of solar sail periodic orbits in the elliptic three-body problem

A solar sail essentially consists of a large mirror that uses the momentum change due to photons reflecting off the sail for its impulse. Solar sails are therefore unique spacecraft, as they do not require fuel for propulsion [1]. In this Note we consider using the solar sail to continuously maintain a periodic orbit above the ecliptic plane using variations in the sail's orientation. Positioning a spacecraft continuously above the ecliptic would allow continuous observation and communication with the poles