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An analysis of optical scintillation and fade on long slant-path atmospheric channels is presented via a direct comparison between wave-optics-based numerical simulations and experimental flight data from a ground-to-aircraft optical communication link. In addition to physically modeling the propagation through slant-path atmospheric turbulence, the numerical simulations include simultaneously the effects of mechanical pointing jitter, aperture-averaging, and first-order scattering/absorption models. The power spectral density, fade probability, and mean fade time of the simulated power fluctuations are studied and validated against measurements taken at slant-path distances ranging from 60 to 113 km and aircraft speeds up to 70 m / s.

We describe the design, development, and field demonstration of a high-throughput E-band communication link between a ground station and a Cessna aircraft flying at an altitude of 7km and a top speed of 463km/h. The link achieved a peak data rate of 40Gbps bi-directional (80Gbps combined simultaneously), and robustly maintained a sustained data rate of 40Gbps in downlink and 36Gbps in uplink direction for the 12km air-to-ground slanted path. The average power consumption of the flight terminal prototype was measured at 363 Watts in average, and mass at 11.8kg. We also report the results of a test campaign in Quillayute, WA to spot-check the ITU models for rain and cloud attenuation over an air-to-ground link. Using the proven system performance and ITU path loss models, we show that the terminal could be used to provide the maximum bidirectional 40Gbps data rates up to an altitude of 28km and 10Gbps up to 310km. To the best of the authors' knowledge, the very high capacity (> 10Gbps in each direction) millimeter wave communication link system between a ground station and a fast-moving aerial platform over significant ranges (> 10km slanted range) is a world first.

Mobile satellite antennas are gimbal-mounted with an active control system to keep the antenna pointed at the target satellite. Short time-scale antenna stabilization is achieved with gyroscope feedback. Long time-scale tracking of the satellite is maintained by scanning the antenna: The beam is intentionally nutated and the resulting change in signal strength is used to estimate how well the antenna is aligned to the satellite. We review the basic architectures for tracking with an outer control loop, assuming that the system is built upon a fast inner stabilization loop. The problem is formulated in a generic mathematical way, not specific to RF satellite communication. Approaches and nomenclature from other fields faced with the same problem of peak-seeking control are discussed. One common and simple technique for tracking is analyzed in detail to reveal the shortcomings that lead to degraded performance. An improvement is suggested and subjected to the same transient analysis to show the improvement. Implications to the overall closed-loop tracking systems are discussed.

As pointing system performances continue to increase while gimbal and vehicle weights decrease, structural considerations of the gimbal-base interface become more problematic and important. We begin by presenting the generalized structural transfer function equation in modal superposition form. We emphasize that the reaction torque of an actuator must be included in practice. From this theoretical basis, we assume stiff gimbal structures and evaluate the structural coupling due only to mount flexure. We show that in some inertially stabilized precision pointing systems the effect of the actuator reaction torques cannot be ignored. We show that structural stiffness is less important than properties of the mount symmetry. In particular, asymmetries in the system mount (the structure between the reaction torque and the base) allow dangerous coupling between gimbal axes. The observed coupling may depend on the angles of the gimbals, making experimental testing and validation more challenging.

The FCC recently issued final regulations on the operation of Ku-band mobile satellite communication antennas mounted to ground vehicles. The “Vehicle-Mounted Earth Station” (VMES) regulations set limits on the transmitted power density broadcast to an adjacent satellite by the mobile, satcom-on-the-move (SOTM) antenna. The challenge presented by these requirements varies depending on the configuration of the SOTM antenna as well other factors, such as satellite elevation and vehicle operating conditions, but in any case these challenges are not trivial. A brief overview of the requirements is provided. Several classes of antennas are defined, including pointing versus tracking antennas, and mechanically steered versus electronically steered. For each class of antenna, standardized servo performance metrics are defined and their relation to the VMES requirements derived and discussed.

Just as the Wright brothers implemented controls to achieve stable airplane flight, flying insects have evolved behavioral strategies that ensure recovery from flight disturbances. Pioneering studies performed on tethered and dissected insects demonstrate that the sensory, neurological, and musculoskeletal systems play important roles in flight control. Such studies, however, cannot produce an integrative model of insect flight stability because they do not incorporate the interaction of these systems with free-flight aerodynamics. We directly investigate control and stability through the application of torque impulses to freely flying fruit flies ( Drosophila melanogaster ) and measurement of their behavioral response. High-speed video and a new motion tracking method capture the aerial “stumble,” and we discover that flies respond to gentle disturbances by accurately returning to their original orientation. These insects take advantage of a stabilizing aerodynamic influence and active torque generation to recover their heading to within 2° in

Flying insects have evolved sophisticated sensory–motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities. We describe a theory that predicts the instability growth rate in body pitch from flapping-wing aerodynamics and reveals two ways of achieving balanced flight: active control with sufficiently rapid reactions and passive stabilization with high body drag. By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability. Moreover, we find that fruit flies with their control sensors disabled can keep upright if high-drag fibres are also attached to their bodies, an observation consistent with our prediction for the passive stability condition. Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots.