Operations Planning and Formation Flying: Analyzing Resource Usage in Formation Assembly

Increasing interest in small spacecraft has fostered a variety of new mission concepts. Within this busy framework, one particular family of mission concepts is taking shape - spacecraft formations. Formation flying entails the organized collection of satellites in a region of space to do a certain job. Missions of this kind pose some interesting design challenges. Most notably, active control of a formation is a fairly popular topic. The aim of s.uch research is to devise a means of stabilizing a loosely bound system while conserving valuable resources. Another area, which seems to be lagging in attention, is the area of formation assembly. Formation assembly involves getting the vehicles to some rendezvous point prior to actually constructing the formation. Equal care should be taken with system resources at this stage. In this paper, a brief overview of these formation flying concepts will be given. The discussion will then focus on analyzing a hypothesized formation assembly strategy. The emphasis will be on using precious resources such as time and fuel as a performance metric for the strategy under various conditions. The derived relations will provide insight about what one might expect to achieve operationally when attempting to assemble a group of satellites

The Orion Microsatellite Mission: A Testbed for Command, Control, and Communications for Formation Fleets

The Orion microsatellite, under development at Stanford University, will fly along with two other Stanford satellites (“Emeralds”) as part of a NASA-funded project. The primary objective is to demonstrate, for the first time, the use of carrier-phase differential GPS (CDGPS) for the relative sensing, navigation and coordinated control of satellites to form a virtual spacecraft bus. Launch of this mission has been tentatively scheduled for late 2001. Formation flying offers an exciting new approach to conducting space science missions. Instead of employing a single, large satellite, a fleet of similar, smaller spacecraft is coordinated to perform mission-related tasks. While formation flying architectures have a significant amount of operational flexibility, the internal system complexity increases with the number of satellites in the fleet. In addition, constraints on satellite resources play a particularly key role. This paper is a summary of work conducted at Stanford to investigate the influence of resource constraints on mission and current-task planning. By making efficient use of knowledge associated with mission goals and operations, optimal strategies can be used to increase fleet life-cycle performance. In addition to discussing this topic, the role of the Orion mission as a testbed for these concepts is included

The Orion Microsatellite: A Demonstration of Formation Flying In Orbit

The Orion microsatellite project is funded by NASA Goddard Space Flight Center. The goals of the project are to demonstrate determination of position and attitude of spacecraft in a formation using carrier phase differential GPS, and closed loop autonomous control of the formation. The mission is designed so it can be performed with a constellation of three or more Orion spacecraft, or a constellation of one Orion spacecraft and the Emerald spacecraft. The spacecraft are designed and built by the Formation Flying Laboratory and the Space Systems Development Laboratory, both at Stanford. The Orion spacecraft will build on the heritage of prior Stanford satellites: Sapphire and Opal. The bus will be cube shaped, 0.5 meters on the side. The command and data handler is the SpaceQuest CPU, based on the NEC V-53 microprocessor. In addition there will be another StrongARM based CPU performing mission specific, CPU intensive calculations. This second CPU could be combined with the GPS computer. The Orion spacecraft will use a cold-gas propulsion system, using Nitrogen gas. The onboard propellant will provide 40 mls delta V. Kiraly, Engberg, Busse, Prof. Twiggs and How Magnetic torquer coils will be used for detumbling after deployment. The subsystems will be connected using an 12C serial data bus. The GPS receiver and computer is in development at Stanford. A single Orion spacecraft is slated to fly with the University Nanosatellite mission

Effects of Normobaric Hypoxia on Oculomotor Dynamics of Aviator Students during a Simulated Flight Task

Hypoxia occurs when the body\u27s tissues are unable to obtain adequate oxygen supply and is the primary environmental factor present when pilots are exposed to increasing altitude levels. Hypoxia leads to impaired vision, cognition, and motor control function, which can negatively affect performance and become deadly if a pilot becomes incapacitated. Thus, objective identification of early-onset hypoxia is critical to increase the time of useful consciousness and prevent physiological episodes. Of the few studies utilizing eye-tracking, there is disagreement and mixed results concerning saccadic eye metrics as a means to measure and detect hypoxia. Therefore, the purpose of this study was to investigate saccadic velocity changes driven by acute normobaric hypoxia. Using a noninvasive infrared-based eye-tracking device, we recorded saccadic average peak velocity during flight tasks at simulated altitudes of 0 ft, 12,500 ft, and 19,000 ft. No changes were observed in saccadic average peak velocity among different altitude exposures. As time on task increased, saccadic average peak velocity decreased, suggesting that eye metrics can serve as an indicator of mental fatigue

Pathways to clinical CLARITY: volumetric analysis of irregular, soft, and heterogeneous tissues in development and disease

AbstractThree-dimensional tissue-structural relationships are not well captured by typical thin-section histology, posing challenges for the study of tissue physiology and pathology. Moreover, while recent progress has been made with intact methods for clearing, labeling, and imaging whole organs such as the mature brain, these approaches are generally unsuitable for soft, irregular, and heterogeneous tissues that account for the vast majority of clinical samples and biopsies. Here we develop a biphasic hydrogel methodology, which along with automated analysis, provides for high-throughput quantitative volumetric interrogation of spatially-irregular and friable tissue structures. We validate and apply this approach in the examination of a variety of developing and diseased tissues, with specific focus on the dynamics of normal and pathological pancreatic innervation and development, including in clinical samples. Quantitative advantages of the intact-tissue approach were demonstrated compared to conventional thin-section histology, pointing to broad applications in both research and clinical settings.</jats:p

Self-love and sociability: the ‘rudiments of commerce’ in the state of nature

Istvan Hont’s classic work on the theoretical links between the seventeenth-century natural jurists Hugo Grotius and Samuel Pufendorf and the eighteenth-century Scottish political economists remains a popular trope among intellectual and economic historians of various stamps. Despite this, a common criticism levelled at Hont remains his relative lack of engagement with the relationship between religion and economics in the early modern period. This paper challenges this aspect of Hont’s narrative by drawing attention to an alternative, albeit complementary, assessment of the natural jurisprudential heritage of eighteenth-century British political economy. Specifically, the article attempts to map on to Hont’s thesis the Christian Stoic interpretation of Grotius and Pufendorf which has gained greater currency in recent years. In doing so, the paper argues that Grotius and Pufendorf’s contributions to the ‘unsocial sociability’ debate do not necessarily lead directly to the Scottish school of political economists, as is commonly assumed. Instead, it contends that a reconsideration of Grotius and Pufendorf as neo-Stoic theorists, particularly via scrutiny of their respective adaptations of the traditional Stoic theory of oikeiosis, steers us towards the heart of the early English ‘clerical’ Enlightenment

The OPAL Satellite Project: Continuing the Next Generation of Small Satellite Development

The Satellite Systems Development Laboratory (SSDL) in the Department of Aeronautics and Astronautics at Stanford University was created in an effort to promote a new philosophy about building satellites. The main tenets of this philosophy include the design and construction of reliable spacecraft that are smaller, developed within a one year time frame, and employ cheaper off-the-shelf parts. As a result of these criteria, one must take an alternative approach to the engineering project, including rapid prototyping of hardware, careful evaluation of mission requirements, and an overall approach which emphasizes development of the whole system rather than individual subsystems. The result is the Satellite QUick Research Testbed, or SQUIRT class of satellites. These smaller SQUIRTs are limited of course, weighing only 25 pounds and having the size restrictions of a 16 inch diameter by 9 inch high hexagon. However, the range of applications still available to these small wonders has hardly been scratched. These satellites still have the traditional major subsystems, such as power, communications, and data & command processing, which allow them a great deal of flexibility in supporting a wide variety of payloads, both scientific and otherwise. The first satellite being developed in this laboratory is SAPPHIRE, which carries on board specially machined infrared micro sensors, as well as a camera and a voice synthesizer which can broadcast messages over amateur radio frequencies. This paper will discuss the design of the SSDL\u27s second SQUIRT satellite, OPAL (Orbiting Picosatellite Automated Launcher). The main focus of this satellite will be to attempt to demonstrate the feasibility of launching and communicating with a smaller secondary satellite. An introduction to SSDL and this project will be given, followed by a background and short review of the technical aspects of the main payload, the picosatellite module. A brief overview of the remaining system architecture will then be discussed. A few conclusions will describe the near-future plans for this project

Small Satellite Capability Analysis: A Systems Approach for Defining Translational Performance in Small Satellites

With recent technological advances, small satellite systems have evoked great interest from both commercial and military sectors. These systems offer reductions in both development time and mission cost, which make them attractive alternatives to the large systems in use today, especially for developing space nations. Small satellites are inherently less capable due to their resource constraints, yet as technology advances, a widening array of supportable missions may be enabled. Due to this, it is important for future Space Situational Awareness (SSA) applications to understand and analyze the capabilities and limitations of these small systems. In order to achieve this, a subsystem-by-subsystem analysis approach may be employed to define the capabilities of each sub-system that may be found in a small satellite. This study is intended to analyze the propulsion sub-system and define an upper bound for translational performance in micro-satellites. During the study, each element of the propulsion subsystem was characterized in terms of the satellite size to define the metrics that have the greatest effect on the overall performance. Both monopropellant and cold gas propulsion, which are proven and viable options for small satellites, were chosen for the analysis. From this study, conclusions can be drawn for both systems that identify the upper bounds of available Delta-V in terms of the sub-system and overall satellite size

A High Stiffness Boom to Increase the Moment-Arm for a Propulsive Attitude Control System on FalconSAT-3

Small satellite missions requiring attitude control can realize significant mass savings by extending the moment arm of a propulsion-based system. Replacing traditional torque rods and reaction wheels with small thrusters on extendable booms can significantly reduce the mass of the ACS. Small satellite buses pose significant integration challenges when incorporating electric micro-thrusters. Generally these satellites have low power capability and small geometries. This impacts attitude determination and control system (ADACS) thruster performance significantly, as it results in low thrust capability (due to power limitations) and small torque moment arms (due to size limitations). To address these technical challenges, the Air Force Research Laboratory is developing a lightweight deployable boom for extending the moment arm of Busek Inc.’s Micro-Propulsion Attitude Control System (MPACS). Specific engineering requirements include increased stiffness, integrated power, and a telemetry wiring harness embedded within the boom’s multi-functional structure. A major design goal is to standardize a modular integration with satellites using the Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter (ESPA). Therefore, the boom is designed to stow within the ESPA interface port, a surface region that is generally unused on ESPA satellites. Deployment of the boom is accomplished with a series of elastic-memory composite (EMC) hinges that extend a multi-functional composite structure to a total length of 4 meters. Gravity-gradient stabilization for tip and roll control is abetted by a 6.2-kg tip mass, comprised of the MPACS micro-thrusters and integrated batteries used to power the boom deployment. The boom design effort is currently underway for the United States Air Force Academy’s (USAFA) FalconSAT-3 (FS3) satellite, manifested for launch in 2006 as a secondary payload on the MLV-06 Space Test Program ESPA flight

National Automated Surveillance of Hospital-Acquired Bacteremia in Denmark Using a Computer Algorithm

BACKGROUNDIn 2015, Denmark launched an automated surveillance system for hospital-acquired infections, the Hospital-Acquired Infections Database (HAIBA).OBJECTIVETo describe the algorithm used in HAIBA, to determine its concordance with point prevalence surveys (PPSs), and to present trends for hospital-acquired bacteremiaSETTINGPrivate and public hospitals in DenmarkMETHODSA hospital-acquired bacteremia case was defined as at least 1 positive blood culture with at least 1 pathogen (bacterium or fungus) taken between 48 hours after admission and 48 hours after discharge, using the Danish Microbiology Database and the Danish National Patient Registry. PPSs performed in 2012 and 2013 were used for comparison.RESULTSNational trends showed an increase in HA bacteremia cases between 2010 and 2014. Incidence was higher for men than women (9.6 vs 5.4 per 10,000 risk days) and was highest for those aged 61–80 years (9.5 per 10,000 risk days). The median daily prevalence was 3.1% (range, 2.1%–4.7%). Regional incidence varied from 6.1 to 8.1 per 10,000 risk days. The microorganisms identified were typical for HA bacteremia. Comparison of HAIBA with PPS showed a sensitivity of 36% and a specificity of 99%. HAIBA was less sensitive for patients in hematology departments and intensive care units. Excluding these departments improved the sensitivity of HAIBA to 44%.CONCLUSIONSAlthough the estimated sensitivity of HAIBA compared with PPS is low, a PPS is not a gold standard. Given the many advantages of automated surveillance, HAIBA allows monitoring of HA bacteremia across the healthcare system, supports prioritizing preventive measures, and holds promise for evaluating interventions.Infect Control Hosp Epidemiol 2017;38:559–566</jats:sec