The Future of the Microsatellite Program in Canada

The Canadian Space Agency (CSA) began an initiative to develop a microsatellite bus for generic application with the release of an RFP in August 2004. Phase A for this program is now completed and demonstrates, a multimission adaptable satellite bus that will be capable of satisfying at least three particular missions. The Near Earth Object Surveillance Satellite (NEOSSat), a joint CSA-DRDC (Defense Research and Development Canada) program, is scheduled as the first mission to be launched nominally in the first quarter of 2008. The second mission is nominally expected to launch two years later, in 2010, and will contain a radar altimeter payload whose objective is to measure the height of waves in the oceans. The third mission is expected to launch another two years later, in 2012, and is expected to be a technology demonstration mission to provide a dedicated satellite to space qualify advanced newly developed technology. The design for a microsatellite bus to satisfy the requirements for all three missions is presented. The design centers on a set of modular avionics that can be used as required for the various missions, housed in a set of aluminum trays that form a tray stack as the primary structure of the satellite

Modular Attitude Control System for Microsatellites with Stringent Pointing Requirements

Advancing technology has allowed for the development of low cost attitude control hardware for microsatellites. However, the attitude control design and software development remain a significant cost driver. The Dynacon High Performance Attitude Control system is a modular control system that makes use of reusable algorithm modules enabling the attitude control system to be applied to several different spacecraft missions with very different performance requirements. The High Performance Attitude Control system is described in this paper, and simulation results are shown for a variety of spacecraft

Dynamic Reconstruction and Multivariable Control for Force-Actuated, Thin Facesheet Adaptive Optics

The Multiple Mirror Telescope (MMT) under development at the University of Arizona takes a new approach in adaptive optics placing a large (0.65 m) force-actuated, thin facesheet deformable mirror at the secondary of an astronomical telescope, thus reducing the effects of emissivity which are important in IR astronomy. However, The large size of the mirror and low stiffness actuators used drive the natural frequencies of the mirror down into the bandwidth of the atmospheric distortion. Conventional adaptive optics takes a quasi-static approach to controlling the, deformable mirror. However, flexibility within the control bandwidth calls for a new approach to adaptive optics. Dynamic influence functions are used to characterize the influence of each actuator on the surface of the deformable mirror. A linearized model of atmospheric distortion is combined with dynamic influence functions to produce a dynamic reconstructor. This dynamic reconstructor is recognized as an optimal control problem. Solving the optimal control problem for a system with hundreds of actuators and sensors is formidable. Exploiting the circularly symmetric geometry of the mirror, and a suitable model of atmospheric distortion, the control problem is divided into a number of smaller decoupled control problems using circulant matrix theory. A hierarchic control scheme which seeks to emulate the quasi-static control approach that is generally used in adaptive optics is compared to the proposed dynamic reconstruction technique. Although dynamic reconstruction requires somewhat more computational power to implement, it achieves better performance with less power usage, and is less sensitive than the hierarchic technique

Flight Results of the Attitude Determination and Control System for the NEMO-HD Earth Observation Microsatellite

NEMO-HD is an Earth observation microsatellite designed and built at the Space Flight Laboratory at the University of Toronto Institute for Aerospace Studies (SFL) in collaboration with the Slovenian Centre of Excellence for Space Sciences and Technologies (SPACE-SI) who owns and operates the spacecraft. The mission was launched successfully into a circular Sun-synchronous orbit with 10:30 LTDN at an altitude of 535 km, aboard the VEGA VV16 mission from French Guiana on September 2, 2020. The primary payload is an optical imager, providing still imagery on its panchromatic (PAN) channel with 2.8 m ground sample distance (GSD), 5.6 m GSD on its four multi-spectral channels (R,G,B,NIR), and high definition video with 1920x1080 resolution. To achieve the precise pointing and stability requirements required for high quality optical imagery, the spacecraft is three-axis stabilized using reaction wheels for attitude control, and dual star trackers for attitude determination. The spacecraft has three targeting modes for imaging: inertial pointing, nadir-pointing, and ground target tracking; the exact mode selection depends upon the type of imagery desired. In this paper we discuss spacecraft attitude determination and control system design, and present the detailed attitude determination and control system pointing performance results for the mission in each of the primary operational modes, using one of the two star trackers as the “true” reference attitude

Tracking the provenance of Greenland-sourced, Holocene aged, individual sand-sized ice-rafted debris using the Pb-isotope compositions of feldspars and 40Ar/39Ar ages of hornblendes

The provenance of sand-sized ice-rafted debris (IRD) sourced from Greenland is currently difficult to determine. Such knowledge, if it could be ascertained with a high degree of certainty, could be applied to the Greenland-proximal marine records to improve both our understanding of modern-day spatial patterns of iceberg rafting and the past history of the Greenland Ice Sheet (GIS). Recent studies have highlighted the utility of the Pb-isotope composition of individual sand-sized feldspars and the 40Ar/39Ar ages of individual sand-sized hornblendes in this regard. However, before any such provenance toolkit can be applied to the palaeo-record, it is necessary first to determine whether this approach can be used to track the sources of known recent Greenland-proximal IRD deposition. To this end we present new records of the Pb-isotope composition and the 40Ar/39Ar ages of individual sand-sized grains of feldspars and hornblendes, respectively, from modern Greenland glacifluvial and fjord sands and Holocene to modern Greenland-proximal marine sediments. These new data demonstrate that sand-sized feldspars and hornblendes glacially eroded by the GIS exhibit distinct intra- and inter-tectonic terrane differences in their Pb-isotope compositions and ages and that these differences are clearly expressed in the geochemistry and geochronology of sand-sized IRD deposited in marine sediments around Greenland. Although overlap exists between some Greenland-proximal IRD ‘source fields’ defined by these data, our approach has the potential to both better understand spatial patterns of Greenland-derived IRD in the modern day as well as during past episodes of iceberg calving

The positive transcriptional elongation factor (P-TEFb) is required for neural crest specification

Regulation of gene expression at the level of transcriptional elongation has been shown to be important in stem cells and tumour cells, but its role in the whole animal is only now being fully explored. Neural crest cells (NCCs) are a multipotent population of cells that migrate during early development from the dorsal neural tube throughout the embryo where they differentiate into a variety of cell types including pigment cells, cranio-facial skeleton and sensory neurons. Specification of NCCs is both spatially and temporally regulated during embryonic development. Here we show that components of the transcriptional elongation regulatory machinery, CDK9 and CYCLINT1 of the P-TEFb complex, are required to regulate neural crest specification. In particular, we show that expression of the proto-oncogene c-Myc and c-Myc responsive genes are affected. Our data suggest that P-TEFb is crucial to drive expression of c-Myc, which acts as a ‘gate-keeper’ for the correct temporal and spatial development of the neural crest

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

Effect of a Perioperative, Cardiac Output-Guided Hemodynamic Therapy Algorithm on Outcomes Following Major Gastrointestinal Surgery A Randomized Clinical Trial and Systematic Review

Importance: small trials suggest that postoperative outcomes may be improved by the use of cardiac output monitoring to guide administration of intravenous fluid and inotropic drugs as part of a hemodynamic therapy algorithm.Objective: to evaluate the clinical effectiveness of a perioperative, cardiac output–guided hemodynamic therapy algorithm.Design, setting, and participants: OPTIMISE was a pragmatic, multicenter, randomized, observer-blinded trial of 734 high-risk patients aged 50 years or older undergoing major gastrointestinal surgery at 17 acute care hospitals in the United Kingdom. An updated systematic review and meta-analysis were also conducted including randomized trials published from 1966 to February 2014.Interventions: patients were randomly assigned to a cardiac output–guided hemodynamic therapy algorithm for intravenous fluid and inotrope (dopexamine) infusion during and 6 hours following surgery (n=368) or to usual care (n=366).Main outcomes and measures: the primary outcome was a composite of predefined 30-day moderate or major complications and mortality. Secondary outcomes were morbidity on day 7; infection, critical care–free days, and all-cause mortality at 30 days; all-cause mortality at 180 days; and length of hospital stay.Results: baseline patient characteristics, clinical care, and volumes of intravenous fluid were similar between groups. Care was nonadherent to the allocated treatment for less than 10% of patients in each group. The primary outcome occurred in 36.6% of intervention and 43.4% of usual care participants (relative risk [RR], 0.84 [95% CI, 0.71-1.01]; absolute risk reduction, 6.8% [95% CI, ?0.3% to 13.9%]; P?=?.07). There was no significant difference between groups for any secondary outcomes. Five intervention patients (1.4%) experienced cardiovascular serious adverse events within 24 hours compared with none in the usual care group. Findings of the meta-analysis of 38 trials, including data from this study, suggest that the intervention is associated with fewer complications (intervention, 488/1548 [31.5%] vs control, 614/1476 [41.6%]; RR, 0.77 [95% CI, 0.71-0.83]) and a nonsignificant reduction in hospital, 28-day, or 30-day mortality (intervention, 159/3215 deaths [4.9%] vs control, 206/3160 deaths [6.5%]; RR, 0.82 [95% CI, 0.67-1.01]) and mortality at longest follow-up (intervention, 267/3215 deaths [8.3%] vs control, 327/3160 deaths [10.3%]; RR, 0.86 [95% CI, 0.74-1.00]).Conclusions and relevance: in a randomized trial of high-risk patients undergoing major gastrointestinal surgery, use of a cardiac output–guided hemodynamic therapy algorithm compared with usual care did not reduce a composite outcome of complications and 30-day mortality. However, inclusion of these data in an updated meta-analysis indicates that the intervention was associated with a reduction in complication rate

Physical rehabilitation interventions for adult patients with critical illness across the continuum of recovery:an overview of systematic reviews protocol

Background: Patients admitted to the intensive care unit with critical illness often experience significant physical\ud impairments, which typically persist for many years following resolution of the original illness. Physical rehabilitation\ud interventions that enhance restoration of physical function have been evaluated across the continuum of recovery\ud following critical illness including within the intensive care unit, following discharge to the ward and beyond hospital\ud discharge. Multiple systematic reviews have been published appraising the expanding evidence investigating these\ud physical rehabilitation interventions, although there appears to be variability in review methodology and quality. We\ud aim to conduct an overview of existing systematic reviews of physical rehabilitation interventions for adult intensive\ud care patients across the continuum of recovery.\ud Methods/design: This protocol has been developed according to the Preferred Reporting Items for Systematic\ud Reviews and Meta-Analyses Protocol (PRISMA-P) guidelines. We will search the Cochrane Systematic Review Database,\ud Database of Abstracts of Reviews of Effectiveness, Cochrane Central Register of Controlled Trials, MEDLINE, Excerpta\ud Medica Database and Cumulative Index to Nursing and Allied Health Literature databases. We will include systematic\ud reviews of randomised controlled trials of adult patients, admitted to the intensive care unit and who have received\ud physical rehabilitation interventions at any time point during their recovery. Data extraction will include systematic\ud review aims and rationale, study types, populations, interventions, comparators, outcomes and quality appraisal\ud method. Primary outcomes of interest will focus on findings reflecting recovery of physical function. Quality of\ud reporting and methodological quality will be appraised using the PRISMA checklist and the Assessment of Multiple\ud Systematic Reviews tool.\ud Discussion: We anticipate the findings from this novel overview of systematic reviews will contribute to the synthesis\ud and interpretation of existing evidence regarding physical rehabilitation interventions and physical recovery in post-critical\ud illness patients across the continuum of recovery