A Distributed Computing Architecture for Small Satellite and Multi-Spacecraft Missions

Distributed computing architectures offer numerous advantages in the development of complex devices and systems. This paper describes the design, implementation and testing of a distributed computing architecture for low-cost small satellite and multi-spacecraft missions. This system is composed of a network of PICmicro® microcontrollers linked together by an I2C serial data communication bus. The system also supports sensor and component integration via Dallas 1-wire and RS232 standards. A configuration control processor serves as the external gateway for communication to the ground and other satellites in the network; this processor runs a multitasking real-time operating system and an advanced production rule system for on-board autonomy. The data handling system allows for direct command and data routing between distinct hardware components and software tasks. This capability naturally extends to distributed control between spacecraft subsystems, between constellation satellites, and between the space and ground segments. This paper describes the technical design of the aforementioned features. It also reviews the use of this system as part of the two-satellite Emerald and QUEST university small satellite missions

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure fl ux through the autophagy pathway (i.e., the complete process including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defi ned as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (inmost higher eukaryotes and some protists such as Dictyostelium ) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the fi eld understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation it is imperative to delete or knock down more than one autophagy-related gene. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways so not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field

Smaller than Small, Faster than Fast, Cheaper than Cheap: The BARNACLE Satellite Project

The BARNACLE micro-satellite is an extremely simple low-cost space vehicle for the characterization of electronic instruments in space. The satellite was developed in less than one year by a group of seven undergraduate engineering students with no previous spacecraft design experience. The satellite was built for under $2,000 of the students own money with most of the hardware donated by industry and university sponsors. The craft includes a Motorola 68HC11 microprocessor-based subsystem for system control, with a logic system to back up the processor in the case of failure. Power is regulated by high-efficiency switching mode regulators in the power subsystem. Communications between the craft and ground stations is handled by the communications subsystems providing full-duplex AFSK communications at 1200 baud. The instruments are interfaced to the control core logic and microprocessor through the sensor interface subsystem. After testing, the satellite will be launched in a tube configuration aboard a non-orbital sounding rocket in August 1998. A cube configuration of the same satellite is being considered for an orbital launch in 1999

A Standardized, Distributed Computing Architecture: Results from Three Universities

At the 16th AIAA/USU Conference on Small Satellites, researchers at Santa Clara University (SCU) proposed a distributed computing architecture for small or multi-spacecraft missions. This architecture extended existing I2C, Dallas 1-wire and RS232 data protocols and was adaptable to a number of microcontrollers. Since then, that architecture has been implemented on six university-class space missions at three different universities. As “early adopters”, these universities had the typical challenges of working with a new, evolving standard and adapting the standard to their hardware and mission needs. Each faced additional, program-specific challenges related to project size, scope and infrastructure as well as the student background/training. Still, because of this architecture, every school saw three improvements: accelerated integration and training of new students; rapid modifications of existing systems; and school-wide collaboration among robotics projects. This paper reviews SCU’s distributed computing architecture, discusses the details of its implementation at all three universities, and provides lessons learned/lessons applied to six spacecraft programs: Akoya-A/Bandit-A & Akoya- B/Bandit-C at Washington University in St. Louis, EMERALD & ONYX at SCU, and FASTRAC and ARTEMIS at the University of Texas-Austin. The merits of adopting this architecture as a standard for university-class spacecraft are also reviewed