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Abstract: The Radio Aurora Explorer (RAX) is a triple CubeSat that launched on November 19, 2010. RAX was designed to study plasma irregularities in the polar lower ionosphere (80–300km), and is the first CubeSat mission funded by the United States National Science Foundation. The scientific mission requires attitude knowledge within 5° (), and a custom attitude determination subsystem was developed for the mission. The subsystem utilizes rate gyros, magnetometers, coarse sun sensors, and an extended Kalman filter, and was designed to be a simple, low cost solution to meet the attitude determination requirements. In this paper, we describe the design, implementation, and testing of the RAX attitude determination subsystem, including derivation of the determination requirements, sensor selection, the integrated hardware design, pre-flight sensor calibration, and attitude estimation algorithms. The paper is meant to serve as a resource for others in the small satellite and nanosatellite communities, as well as a critical reference for those analyzing RAX data. Lessons learned from the design and performance of the RAX determination subsystem will be used in future designs of attitude determination systems for small satellites and similar platforms, such as high altitude balloons and autonomous aerial vehicles. [Copyright &y& Elsevier]

Abstract: Altruism has previously been proposed as a topic for interstellar communication, because it begins to describe one important class of human and non-human behaviors, and because it can be modeled in mathematical and physical terms. Prior research has focused on altruism toward close relatives. The current paper explains how we could communicate basic principles of reciprocal altruism, in which one entity undergoes short-term self-sacrifice for the benefit of another, as well as for long-term self-interest. After providing an algorithmic description of the loss of mass involved in the evolution of stars—a phenomenon that should be familiar to extraterrestrial astronomers—an analogous process is described at a human scale, where the maintenance or loss of mass represents the maintenance or loss of health, and ultimately life. An adaptation of the Prisoner''s Dilemma game is communicated, showing limitations of both cooperation and defection as strategies for interacting with other agents. For the overall stability of a population, there are significant advantages for entities not always either cooperating or defecting in their responses; we end by modeling a more flexible strategy discussed by game theorists, known as Tit For Tat. [Copyright &y& Elsevier]