Low Thrust Augmented Spacecraft Formation-Flying

Ballistic spacecraft formation-flying with zero thrust has great utility, but it is limited to a comparatively small set of relative trajectories. However, through the application of continuous low thrust, rich new families of formation-flying trajectories can be accessed. This new and novel problem provides a wide range of potentially useful alternatives to natural ballistic formationflying. In this paper, the standard Clohessy-Wiltshire approximation of relative spacecraft motion is used to investigate the motion of a chase spacecraft about a target spacecraft which is in a circular Earth orbit. Families of non-Keplerian relative motion are systematically explored, generating analytical representations of the relative motion trajectories and the required thrust commands for both simple static formations and more complex new forced relative orbits. It is found that the impulse, and therefore propellant, required for maintenance of such relative orbits is small, and so the concept of low thrust augmented formation-flying is deliverable in the near term with existing thruster technology

Staying in the science stream: patterns of participation in A-level science subjects in the UK.

This paper describes patterns of participation and attainment in A-level physics, chemistry and biology from 1961 to 2009. The A-level has long been seen as an important gateway qualification for higher level study, particularly in the sciences. This long term overview examines how recruitment to these three subjects has changed in the context of numerous policies and initiatives that seek to retain more young people in the sciences. The results show that recruitment to the pure sciences has stagnated, general trends have hardly varied and the track record of government policy in influencing change is not strong. There is no evidence for increasing achievement gaps between the sexes at A-level and even national policy requiring that all young people study science up to the age of 16 appears to have had little impact on recruitment at this leve

Alien Registration- Arnot, Meta (Winthrop, Kennebec County)

https://digitalmaine.com/alien_docs/16105/thumbnail.jp

Women workers and trade union participation in Scotland 1919-1939

This thesis seeks to provide an assessment of women’s work, their participation in the trade union movement and the extent of women’s strike activity n Scotland in the period 1919-1939. It will highlight the position of women in the labour market, their continuing confinement to a narrow range of industries and occupations and the low paid and low status nature of their work. The weakness of trade union organisation among women workers in the inter-war period will be an important consideration. It will be shown that despite the massive influx of women in to the trade unions in the First World War and the attempts by trade unions and the Scottish Trades Union Congress (STUC) to encourage greater numbers of women into the trade union movement, organisation among women in most industries remained weak throughout the entirety of the inter-war period. Therefore, this thesis will seek to offer a number of explanations for the lack of extensive trade union organisation among women during this period. These will include the occupational and industrial distribution of women workers, their low earnings, the impact of the depression, high unemployment and the failure of the General Strike. However, it will also be suggested that one of the reasons for the low level of trade union organisation among women may have been related to trade union policies and practices. The argument to be developed is that despite recruitment drives undertaken by trade unions and the STUC, trade unions themselves could often be very hostile to women workers and the failure to address issues of importance to women and the remoteness of the movement from the needs of potential women members could mean that there was very often little incentive for women to join trade unions. In order to support this argument, it will be shown that trade unions employed exclusionary tactics either by limiting the entry of women into certain areas of work, attempting to exclude women from work altogether, via agreements with employers, or by excluding women from trade union membership

The Evolutionary Ecology of Menopause

Despite appearing to be maladaptive, the human menopause and prolonged post-reproductive lifespan are thought to have been shaped in our evolutionary history by natural selection. As a result, there has been a great deal of research looking at the inclusive fitness benefits of a post-reproductive lifespan. However, there are still many things we do not know about menopause, such as whether current variation in menopause timing is the result of evolutionary trade-offs, whether menopause symptoms require an evolutionary explanation, and how post-reproductive care functions in a sample of women from the United Kingdom. This thesis focuses on trying to fill these identified gaps in the literature using data from the United Kingdom, United States, and China. I find no evidence for menopause symptoms being facultative, nor that menopause timing varies in the way predicted by current evolutionary models. However, I do find that a later menopause is predicted by an increased likelihood of pregnancy, suggesting an energetic trade-off. Further, I show that menopause symptoms predictably vary relative to one’s ecology, with a more stressful environment predicting worse symptoms. When looking at caring behaviour, I found evidence in favour of it being facultative relative to fecundity status, with pre-menopausal women caring more for their parents, while post-menopausal women spent more time caring for their grandchildren. Finally, I present evidence for an earlier menopause predicting a greater number of grandchildren, suggesting that women are able to offset the costs of being post-reproductive by increasing indirect fitness. Results from this thesis suggest that many aspects of the menopausal transition are plastic, and often vary in a way predicted by evolutionary theory. Through understanding these trends, it may those who experience menopause more autonomy over the transition. Further, my research on fecundity status and caring behaviours demonstrates the behavioural implications of energetic trade-offs

Orbit period modulation for relative motion using continuous low thrust in the two-body and restricted three-body problems

This paper presents rich new families of relative orbits for spacecraft formation flight generated through the application of continuous thrust with only minimal intervention into the dynamics of the problem. Such simplicity facilitates implementation for small, low-cost spacecraft with only position state feedback, and yet permits interesting and novel relative orbits in both two- and three-body systems with potential future applications in space-based interferometry, hyperspectral sensing, and on-orbit inspection. Position feedback is used to modify the natural frequencies of the linearised relative dynamics through direct manipulation of the system eigenvalues, producing new families of stable relative orbits. Specifically, in the Hill–Clohessy–Wiltshire frame, simple adaptations of the linearised dynamics are used to produce a circular relative orbit, frequency-modulated out-of-plane motion, and a novel doubly periodic cylindrical relative trajectory for the purposes of on-orbit inspection. Within the circular restricted three-body problem, a similar minimal approach with position feedback is used to generate new families of stable, frequency-modulated relative orbits in the vicinity of a Lagrange point, culminating in the derivation of the gain requirements for synchronisation of the in-plane and out-of-plane frequencies to yield a singly periodic tilted elliptical relative orbit with potential use as a Lunar far-side communications relay. The Δv requirements for the cylindrical relative orbit and singly periodic Lagrange point orbit are analysed, and it is shown that these requirements are modest and feasible for existing low-thrust propulsion technology