The key components in communications satellite payloads are the high-power amplifiers that amplify the received signal so that it can be accurately transmitted to the intended end user. In this study, we examine 26 amplifier anomalies and quantify the high-energy electron environment for periods of time prior to the anomalies. Building on the work of Lohmeyer and Cahoy (2013), we find that anomalies occur at a rate higher than just by chance when the >2 MeV electron fluence accumulated over 14 and 21 days is elevated. To try to understand "why," we model the amplifier subsystem to assess whether the dielectric material in the radio frequency (RF) coaxial cables, which are the most exposed part of the system, is liable to experience electrical breakdown due to internal charging. We find that the accumulated electric field over the 14 and 21 days leading up to the anomalies is high enough to cause the dielectric material in the coax to breakdown. We also find that the accumulated voltages reached are high enough to compromise components in the amplifier system, for example, the direct current (DC) blocking capacitor. An electron beam test using a representative coaxial cable terminated in a blocking capacitor showed that discharges could occur with peak voltages and energies sufficient to damage active RF semiconductor devices.

Several studies have investigated whether vestibular signals can be processed to determine the magnitude of passive body motions. Many of them required subjects to report their perceived displacements offline, i.e., after being submitted to passive displacements. Here, we used a protocol that allowed us to complement these results by asking subjects to report their introspective estimation of their displacement continuously, i.e., during the ongoing body rotation. To this end, participants rotated the handle of a manipulandum around a vertical axis to indicate their perceived change of angular position in space at the same time as they were passively rotated in the dark. The rotation acceleration (Acc) and deceleration (Dec) lasted either 1.5 s (peak of 60°/s2, referred to as being “High”) or 3 s (peak of 33°/s2, referred to as being “Low”). The participants were rotated either counter-clockwise or clockwise, and all combinations of acceleration and deceleration were tested (i.e., AccLow-DecLow; AccLow-DecHigh; AccHigh-DecLow; AccHigh-DecHigh). The participants’ perception of body rotation was assessed by computing the gain, i.e., ratio between the amplitude of the perceived rotations (as measured by the rotating manipulandum’s handle) and the amplitude of the actual chair rotations. The gain was measured at the end of the rotations, and was also computed separately for the acceleration and deceleration phases. Three salient findings resulted from this experiment: (i) the gain was much greater during body acceleration than during body deceleration, (ii) the gain was greater during High compared to Low accelerations and (iii) the gain measured during the deceleration was influenced by the preceding acceleration (i.e., Low or High). These different effects of the angular stimuli on the perception of body motion can be interpreted in relation to the consequences of body acceleration and deceleration on the vestibular system and on higher-order cognitive processes.

Two algorithms that coordinate activities across a resource-constrained, Earth-observing CubeSat constellation are presented. The Resource-Aware SmallSat Planner algorithm performs online planning of activities for a satellite while keeping the satellite's resources within constraints. The Limited Communication Constellation Coordinator algorithm performs coordination of observations across the constellation to reduce average revisit times for a set of targets. The algorithms are simulated for 24 h with an 18 satellite LEO constellation. Three orbital geometries are examined, with different configurations of intersatellite and satellite-to-ground communications links to share planning information. Results indicate that coordination through Resource-Aware SmallSat Planner/Limited Communication Constellation Coordinator and a background communications constellation improves observation performance, with sensor-averaged revisit times of 197, 203, and 225 min (over three orbital geometries) versus 204, 211, and 240 min for a baseline random sensor selection method. The results also reveal that the constellations studied perform poorly at sharing planning information via only downlinks and crosslinks and point to the need for a method of calculating the information sharing utility of such links in a coordinated constellation. These findings are relevant for Federated Satellite Systems because they provide guidance on next steps toward integrating large networks of heterogeneous small satellites into large-scale, coordinated, Earth-observing systems. I. IntroductionI N THIS paper, we assess the feasibility of automated onboard coordination of Earth observations across a constellation of resource-constrained CubeSats. We analyze the utility of coordinated observations while varying both the constellation's orbital geometry and the use of communications links for sharing planning information. This work is relevant for the Federated Satellite Systems community in that it takes a step toward the integrated planning of Earth remote sensing and communications link usage, two key attributes of future Earth-orbiting satellite systems. We assess the results from two newly developed planning algorithms and describe important items of future work for a full-scale planning system.Traditional Earth-observing space missions use a single, monolithic spacecraft to take measurements and communicate with ground stations. This architecture limits geospatial and temporal spacing of an instrument's measurements because it provides only a single space-time location for them to be taken. Large-scale, Earth-orbiting constellations offer great benefits due to the additional spatial and temporal diversity they provide. Such large constellations are rapidly emerging as a real possibility with the advance of small satellite and CubeSat technology. A CubeSat is a class of small satellite built of multiple 10 × 10 × 10 cm units each with a mass around 1.3 kg and designed to a standardized launch vehicle interface [1]. The CubeSat form factor impose...

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One of the most challenging yet poorly defined aspects of engineering a complex aerospace system is behavior engineering, including definition, specification, design, implementation, and verification and validation of the system's behaviors. This is especially true for behaviors of highly autonomous and intelligent systems. Behavior engineering is more of an art than a science. As a process it is generally ad-hoc, poorly specified, and inconsistently applied from one project to the next. It uses largely informal representations, and results in system behavior being documented in a wide variety of disparate documents. To address this problem, JPL has undertaken a pilot project to apply its institutional capabilities in Model-Based Systems Engineering to the challenge of specifying complex spacecraft system behavior. This paper describes the results of the work in progress on this project. In particular, we discuss our approach to modeling spacecraft behavior including 1) requirements and design flowdown from system-level to subsystem-level, 2) patterns for behavior decomposition, 3) allocation of behaviors to physical elements in the system, and 4) patterns for capturing V&V activities associated with behavioral requirements. We provide examples of interesting behavior specification patterns, and discuss findings from the pilot project.

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