Parametric CubeSat flight simulation architecture

This paper presents the architecture of a system of models that provides realistic simulation of the dynamic, in-orbit behaviour of a CubeSat. Time-dependent relationships between sub-systems and between the satellite and external nodes (ground stations and celestial bodies) are captured through numerical analysis of a multi-disciplinary set of state variables including position, attitude, stored energy, stored data and system temperature. Model-Based Systems Engineering and parametric modelling techniques are employed throughout to help visualise the models and ensure flexibility and expandability. Operational mode states are also incorporated within the design, allowing the systems engineer to assess flight behaviour over a range of mission scenarios. Finally, both long and short term dynamics are captured using a coupled-model philosophy; described as Lifetime and Operations models. An example mission is analysed and preliminary results are presented as an illustration of early capabilities

SOFTC: A Software Correlator for VLBI

SOFTC is an advanced software implementation of a signal correlator for very-long-baseline interferometry (VLBI) for measuring positions of natural celestial objects and distant spacecraft. Because of increases in processing speeds of general-purpose computers, software VLBI correlators have become viable alternatives to hardware ones. The input to SOFTC consists of digitized samples of raw VLBI-antenna received- signal voltages. Optionally, SOFTC also tracks calibration tones superimposed on the received signals. The outputs of SOFTC are (1) phases and amplitudes as functions of time and frequency for cross-correlated received signals and (2) phases and amplitudes as functions of time, station, and tone number for the calibration tones. SOFTC was created to be as accurate as possible, capable of processing essentially any VLBI data, pass strong debugging tests, have a simple user interface, and have no platform dependencies. SOFTC is written modularly in the C programming language. The great advantage of implementing a correlator in software, in contradistinction to hardware, is that it becomes relatively easy and much less expensive and time-consuming to adapt, modify, improve, and update the correlator

Through-life modelling of nano-satellite power system dynamics

This paper presents a multi-fidelity approach to finding optimal, mission-specific power system configurations for CubeSats. The methodology begins with propagation of the orbit elements over the mission lifetime, via a continuous-time model, accounting for orbital perturbations (drag, solar radiation and non-spherical geo-potential). Analytical sizing of the power system is then achieved at discrete long-term intervals, to account for the effects of variations in environmental conditions over the mission life. This sizing is based on worst case power demand and provides inputs to a numerical assessment of the in-flight energy collection for each potential solar array deployment configuration. Finally, two objective functions (minimum deviation about the orbit average power and maximum average power over the entire mission) are satisfied to identify the configurations most suitable for the specific mission requirement. Most Nano-satellites are designed with relatively simple, static-models only and tend to be over-engineered as a result, often leading to a power-limited system. The approach described here aims to reduce the uncertainty in energy collection during flight and provide a robust approach to finding the optimal solution for a given set of mission requirements

Experts and evidence in deliberation: scrutinising the role of witnesses and evidence in mini-publics, a case study

Experts hold a prominent position in guiding and shaping policy-making; however, the nature of expert input to decision-making is a topic of public debate. A key aspect of deliberative processes such as citizens’ juries is the provision of information to participants, usually from expert witnesses. However, there is currently little guidance on some of the challenges that organisers and advocates of citizens’ juries must consider regarding expert involvement, including the role of the witness, issues around witness identification and selection, the format of evidence provision, the evidence itself, and how these factors affect the experience of the participants and the witnesses. Here, we explore these issues through detailed case study of three citizens’ juries on onshore wind farm development in Scotland, including interviews with the witnesses involved. This is complemented by examining a cohort of mini-publics held on energy and the environment topics, and, where possible, discussion with the program organisers. We identify a series of issues and sensitivities that can compromise the effectiveness and fairness of the evidence-giving in mini-publics, for the participants, the witnesses and the organisers. We recommend approaches and areas for future work to address these challenges. This is the first time that the ways of involving witnesses in such processes have been so comprehensively examined, and is timely given the increasing interest in democratic innovations such as mini-publics and the current discourse concerning experts

Developing know-how for the improvement and sustainable management of teak genetic resources

The project had the following objectives: To trace and quantify genetic diversity of teak within its natural range, DNA markers were used to assay the current distribution of genetic diversity within and between populations, investigate its mating system and establish historical migration patterns. To evaluate the amount of contemporary gene flow through pollen and seed, hypervariable microsatellite DNA markers have been developed for parentage analysis. The molecular work was complemented by field observations of teak flower insect pollinators. To assess the influence of human disturbance, the genetic diversity in teak forests that have been undisturbed, lightly or heavily disturbed have been assessed and compared for both population genetic diversity and contemporary gene flow processes

Tidal synchronous orbit : A novel approach to remote sensing of oceanic regions

To-date space-based remote sensing of oceans and coastal regions has principally been conducted from platforms in Sun-Synchronous Low Earth Orbit (LEO). Such a trajectory, while beneficial in terms of solar illumination angle, has limitations in that geometric patterns driven primarily by tidal variation (such as coastal bathymetry and suspended sediment reflectance) may not be captured effectively. As such, tidal-synchronous observations can be expected to provide enhanced remote sensing of oceanic regions where tidal variation plays a key role. This paper introduces the concept of Tidal synchronism, defining it as when the orbit period of a platform is synchronised with the rotation period of the Earth such that a repeat ground-track is achieved after an integer number of ‘tidal periods’ (twice the ‘principal lunar semi-diurnal’ constituent). Such a Tidal-Synchronous platform would facilitate analysis of specific locations, at specific times in the regular tidal sequence, resulting in improved monitoring of evolving patterns as a function of tidal variation. Whilst a Sun-Synchronous orbit has been necessary for the majority of large, multi-functional Earth Observation platforms (e.g. ENVISAT), specific mission applications realised through smaller, specialised technologies are becoming increasingly common, for which a tidal synchronous orbit is found to be beneficial. For the first time, this paper introduces the concept of a Tidal-Synchronous orbit and describes the astrodynamic properties of such a trajectory under the influence of natural perturbations (J2) via a set of Modified Equinoctial Elements. Analytical solutions for low thrust propulsive station-keeping are presented, for the general case of orbit and repeat parameter combinations, indicating the applicability of such a mission to small, resource limited spacecraft. It is shown that a repeat ground-track can be achieved every 28 tidal periods with a single platform, through exploitation of natural perturbations alone (imager field of view would govern temporal resolution over any given region). A constellation of satellites could be deployed to achieve greater temporal resolution (additional satellites in an orbit plane) and greater number of ground-track repeats at specific tidal times (additional orbit planes). It is also shown that orbit parameters attributed to a repeat ground-track after exactly 57 tidal periods are almost identical to those required for a Sun-Synchronous orbit (approximately 5deg drift in relative solar angle per year). In this case, benefits from each class of synchronism could be exploited in order to achieve high quality, reliable visible imaging data at regular times in the tidal sequence

Metabolic, inflammatory and haemostatic effects of a low-dose continuous combined HRT in women with type 2 diabetes: potentially safer with respect to vascular risk?

BACKGROUND Conventional hormone replacement therapy (HRT) containing conjugated equine oestrogen (CEE) and medroxyprogesterone acetate (MPA) increases triglyceride, C- reactive protein (CRP) and coagulation Factor VII concentrations, potentially explaining their increased coronary heart disease (CHD) and stroke risk. OBJECTIVE To assess the metabolic effects of a continuous combined HRT containing 1 mg oestradiol and 0.5 mg norethisterone or matching placebo. DESIGN Double-blind, randomized placebo-controlled trial. PATIENTS Fifty women with type 2 diabetes. MEASUREMENTS Classical and novel risk factors for vascular disease. RESULTS Triglyceride concentration was not altered (P = 0.31, change in active arm relative to placebo) and low-density lipoprotein (LDL) cholesterol concentration declined 13% (P = 0.018). IL-6 concentration (mean difference -1.42 pg/ml, 95% CI: -2.55 to - 0.29 IU/dl, P = 0.015), Factor VII (-32 IU/dl, -43 to -21 IU/l, P lt 0.001) and tissue plasminogen activator antigen (by 13%, P = 0.005) concentrations fell, but CRP was not significantly altered (P = 0.62). Fasting glucose (P = 0.026) also declined significantly, but there are no significant effects on HBA1c, Factor IX or APC resistance. CONCLUSIONS HRT containing 1 mg oestradiol and 0.5 mg norethisterone may avoid the adverse metabolic effects potentially implicated in the elevated CHD and stroke risk induced by conventional higher dose HRT. This type of preparation may therefore be more suitable than conventional HRT for women at elevated CHD risk such as those with type 2 diabetes. Large randomized controlled trials of such low dose preparations, powered for cardiovascular end points, are now needed

Statistical Studies of Giant Pulse Emission from the Crab Pulsar

We have observed the Crab pulsar with the Deep Space Network (DSN) Goldstone 70 m antenna at 1664 MHz during three observing epochs for a total of 4 hours. Our data analysis has detected more than 2500 giant pulses, with flux densities ranging from 0.1 kJy to 150 kJy and pulse widths from 125 ns (limited by our bandwidth) to as long as 100 microseconds, with median power amplitudes and widths of 1 kJy and 2 microseconds respectively. The most energetic pulses in our sample have energy fluxes of approximately 100 kJy-microsecond. We have used this large sample to investigate a number of giant-pulse emission properties in the Crab pulsar, including correlations among pulse flux density, width, energy flux, phase and time of arrival. We present a consistent accounting of the probability distributions and threshold cuts in order to reduce pulse-width biases. The excellent sensitivity obtained has allowed us to probe further into the population of giant pulses. We find that a significant portion, no less than 50%, of the overall pulsed energy flux at our observing frequency is emitted in the form of giant pulses.Comment: 19 pages, 17 figures; to be published in Astrophysical Journa