The Space Development Agency (SDA) is developing the Proliferated Warfare Space Architecture (PWSA) – a constellation of hundreds of satellites in low earth orbit delivering space-based capabilities to the joint warfighter. The PWSA is a mesh network of optically connected satellites providing low-latency data transport and missile warning/tracking capabilities. SDA capitalizes on a unique business model that values speed and lowers costs by harnessing commercial development. The Optical Communications Terminal (OCT) standard was created to provide optical interoperability specifications, enable a strong marketplace, and to drive advancements in optical communication capabilities to terrestrial, maritime, and airborne warfighting elements. As part of the spiral development process, the OCT standard evolves with PWSA deployment phases. SDA has incorporated feedback as well as advancements to the OCT standard, resulting in the release of version 3.1.0. In this paper we discuss key aspects of the OCT standard, such as wavelength, modulation, data rates, polarization, link distance, error correction coding, pointing, acquisition and tracking, and position, navigation, and timing.
The DARPA Space-Based Adaptive Communications Node (Space-BACN) optical terminal will be a low-cost reconfigurable optical intersatellite link (OISL) terminal capable of supporting up to 100 Gbps low-earth-orbit (LEO) links. Rapid and reliable pointing, acquisition, and tracking (PAT) is critical to OISL performance, especially in cross-plane LEO links, where contacts can be short. The Space-BACN optical terminal will demonstrate a novel reconfigurable acquisition implementation, which can be dynamically configured to operate in one of three acquisition modes: in-band, out-of-band, and synthesized beacon. Here, we review the features, implementation, performance analysis, and verification approaches for each of the three acquisition modes.
Ionic polymers are a class of electromechanically coupled materials that can be used as flexible transducers. When set up in the cantilever configuration, the actuators exhibit a large bending deflection when an electric field is applied across their thickness. Being a relatively new research topic, the governing physical and chemical mechanisms are not yet fully understood. Experimental results have demonstrated nonlinear dynamic behavior. The nonlinear dynamics can be seen in the response of current, displacement, and velocity of the actuator. This work presents results for the nonlinear identification of ionic polymer actuator systems driven at a specific frequency. Identification results using a 5th-degree Volterra expansion show that the nonlinear distortion can be accurately modeled. Using such a high power in the series expansion is necessary to capture the most dominant harmonics, as evidenced when examining the power spectral density of the response. An investigation of how nonlinearities enter into the response is also performed. By analyzing both the actuation current and tip velocity, results show that both the voltage to current and current to velocity stages influence the nonlinear response, but the voltage to current stage is more dominantly nonlinear.
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