It's hip to be square : The CubeSat revolution

With the launch of the UK’s first commercial CubeSat, UKube-1, on the horizon, Malcolm Macdonald and Christopher Lowe look at what the future holds for this standardised spacecraft platform

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

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

Methodologies for the analysis of value from delay-tolerant inter-satellite networking

In a world that is becoming increasingly connected, both in the sense of people and devices, it is of no surprise that users of the data enabled by satellites are exploring the potential brought about from a more connected Earth orbit environment. Lower data latency, higher revisit rates and higher volumes of information are the order of the day, and inter-connectivity is one of the ways in which this could be achieved. Within this dissertation, three main topics are investigated and built upon. First, the process of routing data through intermittently connected delay-tolerant networks is examined and a new routing protocol introduced, called Spae. The consideration of downstream resource limitations forms the heart of this novel approach which is shown to provide improvements in data routing that closely match that of a theoretically optimal scheme. Next, the value of inter-satellite networking is derived in such a way that removes the difficult task of costing the enabling inter-satellite link technology. Instead, value is defined as the price one should be willing to pay for the technology while retaining a mission value greater than its non-networking counterpart. This is achieved through the use of multi-attribute utility theory, trade-space analysis and system modelling, and demonstrated in two case studies. Finally, the effects of uncertainty in the form of sub-system failure are considered. Inter-satellite networking is shown to increase a system's resilience to failure through introduction of additional, partially failed states, made possible by data relay. The lifetime value of a system is then captured using a semi-analytical approach exploiting Markov chains, validated with a numerical Monte Carlo simulation approach. It is evident that while inter-satellite networking may offer more value in general, it does not necessarily result in a decrease in the loss of utility over the lifetime.In a world that is becoming increasingly connected, both in the sense of people and devices, it is of no surprise that users of the data enabled by satellites are exploring the potential brought about from a more connected Earth orbit environment. Lower data latency, higher revisit rates and higher volumes of information are the order of the day, and inter-connectivity is one of the ways in which this could be achieved. Within this dissertation, three main topics are investigated and built upon. First, the process of routing data through intermittently connected delay-tolerant networks is examined and a new routing protocol introduced, called Spae. The consideration of downstream resource limitations forms the heart of this novel approach which is shown to provide improvements in data routing that closely match that of a theoretically optimal scheme. Next, the value of inter-satellite networking is derived in such a way that removes the difficult task of costing the enabling inter-satellite link technology. Instead, value is defined as the price one should be willing to pay for the technology while retaining a mission value greater than its non-networking counterpart. This is achieved through the use of multi-attribute utility theory, trade-space analysis and system modelling, and demonstrated in two case studies. Finally, the effects of uncertainty in the form of sub-system failure are considered. Inter-satellite networking is shown to increase a system's resilience to failure through introduction of additional, partially failed states, made possible by data relay. The lifetime value of a system is then captured using a semi-analytical approach exploiting Markov chains, validated with a numerical Monte Carlo simulation approach. It is evident that while inter-satellite networking may offer more value in general, it does not necessarily result in a decrease in the loss of utility over the lifetime

The Fox/Forkhead transcription factor family of the hemichordate Saccoglossus kowalevskii

Background: The Fox gene family is a large family of transcription factors that arose early in organismal evolution dating back to at least the common ancestor of metazoans and fungi. They are key components of many gene regulatory networks essential for embryonic development. Although much is known about the role of Fox genes during vertebrate development, comprehensive comparative studies outside vertebrates are sparse. We have characterized the Fox transcription factor gene family from the genome of the enteropneust hemichordate Saccoglossus kowalevskii, including phylogenetic analysis, genomic organization, and expression analysis during early development. Hemichordates are a sister group to echinoderms, closely related to chordates and are a key group for tracing the evolution of gene regulatory mechanisms likely to have been important in the diversification of the deuterostome phyla. Results: Of the 22 Fox gene families that were likely present in the last common ancestor of all deuterostomes, S. kowalevskii has a single ortholog of each group except FoxH, which we were unable to detect, and FoxQ2, which has three paralogs. A phylogenetic analysis of the FoxQ2 family identified an ancestral duplication in the FoxQ2 lineage at the base of the bilaterians. The expression analyses of all 23 Fox genes of S. kowalevskii provide insights into the evolution of components of the regulatory networks for the development of pharyngeal gill slits (foxC, foxL1, and foxI), mesoderm patterning (foxD, foxF, foxG), hindgut development (foxD, foxI), cilia formation (foxJ1), and patterning of the embryonic apical territory (foxQ2). Conclusions: Comparisons of our results with data from echinoderms, chordates, and other bilaterians help to develop hypotheses about the developmental roles of Fox genes that likely characterized ancestral deuterostomes and bilaterians, and more recent clade-specific innovations

Co-option of an anteroposterior head axis patterning system for proximodistal patterning of appendages in early bilaterian evolution

AbstractThe enormous diversity of extant animal forms is a testament to the power of evolution, and much of this diversity has been achieved through the emergence of novel morphological traits. The origin of novel morphological traits is an extremely important issue in biology, and a frequent source of this novelty is co-option of pre-existing genetic systems for new purposes (Carroll et al., 2008). Appendages, such as limbs, fins and antennae, are structures common to many animal body plans which must have arisen at least once, and probably multiple times, in lineages which lacked appendages. We provide evidence that appendage proximodistal patterning genes are expressed in similar registers in the anterior embryonic neurectoderm of Drosophila melanogaster and Saccoglossus kowalevskii (a hemichordate). These results, in concert with existing expression data from a variety of other animals suggest that a pre-existing genetic system for anteroposterior head patterning was co-opted for patterning of the proximodistal axis of appendages of bilaterian animals

Detection and characterisation of Eemian marine tephra layers within the sapropel S5 sediments of the Aegean and Levantine Seas

The Eemian was the last interglacial period (~130 to 115 ka BP) to precede the current interglacial. In Eastern Mediterranean marine sediments, it is marked by a well-developed and organic-rich “sapropel” layer (S5), which is thought to reflect an intensification and northward migration of the African monsoon rain belt over orbital timescales. However, despite the importance of these sediments, very little proxy-independent stratigraphic information is available to enable rigorous correlation of these sediments across the region. This paper presents the first detailed study of visible and non-visible (cryptotephra) layers found within these sediments at three marine coring sites: ODP Site 967B (Levantine Basin), KL51 (South East of Crete) and LC21 (Southern Aegean Sea). Major element analyses of the glass component were used to distinguish four distinct tephra events of Santorini (e.g., Vourvoulos eruption) and possible Anatolian provenance occurring during the formation of S5. Interpolation of core chronologies provides provisional eruption ages for the uppermost tephra (unknown Santorini, 121.8 ± 2.9 ka) and lowermost tephra (Anatolia or Kos/Yali/Nisyros, 126.4 ± 2.9 ka). These newly characterised tephra deposits have also been set into the regional tephrostratigraphy to illustrate the potential to precisely synchronise marine proxy records with their terrestrial counterparts, and also contribute to the establishment of a more detailed volcanic history of the Eastern Mediterranean

Neural Predictive Control of Broiler Chicken Growth

Active control of the growth of broiler chickens has potential benefits for farmers in terms of improved production efficiency, as well as for animal welfare in terms of improved leg health. In this work, a differential recurrent neural network (DRNN) was identified from experimental data to represent broiler chicken growth using a recently developed nonlinear system identification algorithm. The DRNN model was then used as the internal model for nonlinear model predicative control (NMPC) to achieve a group of desired growth curves. The experimental results demonstrated that the DRNN model captured the underlying dynamics of the broiler growth process reasonably well. The DRNN based NMPC was able to specify feed intakes in real time so that the broiler weights accurately followed the desired growth curves ranging from $-12$ to +12% of the standard curve. The overall mean relative error between the desired and achieved broiler weight was 1.8% for the period from day 12 to day 51