In recent decades, advances in the syntheses of mechanically interlocked macromolecules, such as catenanes, have led to much greater interest in the applications of these complexes, from molecular motors and actuators to nanoscale computational memory and nanoswitches. Much remains to be understood, however, regarding how catenated ring compounds behave as a result of the effects of different solvents as well as the effects of solvent/solvent interfaces. In this work, we have investigated, using molecular dynamics simulations, the effects of solvation of poly(ethylene oxide) chains of different topologies─linear, ring, and [2]catenane─in two solvents both considered favorable toward PEO (water, toluene) and at the water/toluene interface. Compared to ring and [2]catenane molecules, the linear PEO chain showed the largest increase in size at the water/toluene interface compared to bulk water or bulk toluene. Perhaps surprisingly, observations indicate that the tendency of all three topologies to extend at the water/toluene interface may have more to do with screening the interaction between the two solvents than with optimizing specific solvent-polymer contacts.

The leap to 100 Gbps data transmission rates has relied on coherent communication technology that use dual-polarization modulation formats. While several complex modulation formats use polarization to increase data rate, it can be an unwanted degree of freedom in free space links that baseline single-polarization modulation formats. In links that are signal-to-noise ratio (SNR) limited; have receivers with limited processing resources; or rely on polarization for duplex through a shared aperture; single polarization links may be preferable. Often times, a system of polarization-maintaining (PM) fibers and PM amplifiers preserve single-polarization signals from degradation as they propagate; however, these systems can be challenging to implement due to tight tolerances on components and PMfiber splices. In this paper we present a method for recovering single-polarization signals from arbitrary polarization received signals using integrated dual-polarization coherent receivers. This removes the reliance on PM fiber components while maintaining single polarization receiver performance. The algorithm uses the received signal on both polarization channels to reconstruct the initial single-polarization coherent waveform. This is accomplished by implementing a polarization rotation and polarizing filter in digital signal processing (DSP). A feature of this method is it combines the signal energy in each of the receiver’s polarization channels while rejecting the noise energy in the polarization that is orthogonal to the signal polarization. This preserves SNR while simplifying subsequent DSP steps by eliminating the unwanted polarization mode. Perhaps most importantly, our algorithm is deterministic and can be added to established DSP processes without requiring significant processing.

Low-earth-orbit satellite constellations with hundreds to thousands of satellites are emerging as practical alternatives for providing various types of data services such as global networking and large-scale sensing. The network performance of these satellite constellations is strongly dependent on the topology of the inter-satellite links (ISLs) in such systems. This paper studies the effects of six different ISL topologies, coupled with three configurations of ground relay terminals, on path failure rate, path latency, and link transmission efficiency in an example highly-inclined Walker Delta constellation with 360 satellites. These network performance parameters are calculated in the presence of satellite failures in the constellation. Trade-offs between ISL connection density and overall performance are examined and quantified. Topologies with 4 active ISLs per satellite are shown to perform significantly better than topologies requiring fewer, especially as the average number of active ISLs per satellite becomes significantly less than three. Latencies for a topology requiring 3 active ISLs per satellite are shown to be between 15 and 60 % higher than for a 4- ISL reference topology. Path availabilities for the 3- ISL topology are shown to be on the order of 30 % lower for a benchmark case of 10 satellite failures. The performance of near-minimal topologies (e.g., an average of 2.2 active ISLs per satellite) is much worse. Latency reductions of 10-30% and path failure rate improvements on the order of 45 % are shown to be obtainable by the inclusion of 2 to 5 strategically located ground relay stations. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> DISTRIBUTION STATEMENT A. Approved for public release. Distribution is unlimited. This material is based upon work supported by the Defense Advanced Research Projects Agency under Air Force Contract No. FA8702-15-D-0001. The views, opinions and/or findings expressed are those of the authors and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.

DoD SATCOM plays a critical role in US defense communications. Current SATCOM systems are nearing capacity in an environment with multiple threat vectors that compromise availability. In response to these challenges, US Space Strategy is moving away from large, centralized platforms to distributed, flexible platforms. Future systems envision cross-linked satellites and proliferated LEO. However, it is vital that as space systems are made more resilient, ground infrastructure is also strengthened through disaggregation. This paper proposes that near term solutions ‐ provided by or before 2030 ‐ could fall into three different Courses of Action (COAs): (1) a layered managed services network, (2) commercial teleport integration, or (3) proliferated ground. The performance of each of these COAs is evaluated to assess the costs and benefits of each approach. This paper recommends that these COAs be rolled out in succession based upon feasibility. A combination of the proposed COAs will help DoD SATCOM to bridge near term systems with long term goals and keep pace with a rapidly changing battlespace.

Low-earth orbit (LEO) satellites can enable connectivity for simple, low-power user terminals and have been a significant point of research for upcoming 6G applications. These devices, however, often lack high-power amplifiers and high-gain antennas. Coupling these factors with multipath and shadow fading as well as significant path loss, the achievable signal-to-noise ratio (SNR) at the satellite can be very low in these systems. However, in dense LEO constellations, it is not uncommon for multiple satellites to be in view of a user terminal. By employing joint reception over multiple satellites and an intelligent combining scheme, the received SNR can be substantially improved. Furthermore, time diversity due to the motion of the satellites relative to the user terminal can improve the probability of message reception. In this paper, we quantify the potential performance improvements of different combining approaches, including the effects of different crosslink configurations which may limit the capabilities of combining schemes.

DOD wideband SATCOM, like other electronic communications areas, is subject to exponential growth in user demand. DOD SATCOM therefore requires commensurate growth in supply in terms of both the space segment and the Earth segment. Information dominance requires an understanding of this growth, both qualitatively and quantitatively, in the policy making, planning, and execution of DOD SATCOM systems. DOD SATCOM growth is explained qualitatively as a response to an evolution of user demands, from voice, to data, to imagery, to video, and beyond. Growth in user demand follows technology innovations which improve warfighting capabilities, as well as increased access of all fighting components to such improved warfighting capabilities. Growth has subsequently driven the migration of DOD SATCOM Earth segment architectures from those capable of less capacity to those capable of more capacity. Multiple methods are used to quantify growth in terms of average compound annual growth rates (CAGRs). DOD SATCOM link count is shown to grow at ~10%, link rate at 9-10%, link bandwidth at ~8%, total bandwidth at ~19%, and total data traffic throughput at 20-22%. All rates are in terms of compound annual growth. Careful quantitative analysis of past growth trends informs future quantitative growth expectations, which in turn inform policy, planning, procurement, and operations. Understanding and addressing growth on the ground and in space is therefore instrumental to DOD SATCOM policy, planning, research, acquisition, implementation, and operations.

An uplink non-orthogonal multiple-access communication system is developed for heterogeneous non-terrestrial networks (NTNs) that employ both low-Earth orbit (LEO) satellite constellations and high-altitude platforms (HAPs) as relays with hybrid automatic repeat request capabilities. The system is designed as a random-access and interference-resistant network to support low-rate users. A common waveform and frequency band is used for all uplink transmissions (whether the transmitter is a user terminal or a HAP). Both theoretical and simulation-based performance analysis results are provided as a function of user transmit power and packet arrival rates for channels with interference. The use of HAP relays is shown to significantly improve throughput and reduce queue size relative to direct transmission to the LEO satellites, especially for the case of low-power users in high interference environments.

Physical fitness is a pillar of U.S. Air Force (USAF) readiness and ensures that Airmen can fulfill their assigned mission and be fit to deploy in any environment. The USAF assesses the fitness of service members on a periodic basis, and discharge can result from failed assessments. In this study, a 21-feature dataset was analyzed related to 223 active-duty Airmen who participated in a comprehensive mental and social health survey, body composition assessment, and physical performance battery. Graphical analysis revealed pass/fail trends related to body composition and obesity. Logistic regression and limited-capacity neural network algorithms were then applied to predict fitness test performance using these biomechanical and psychological variables. The logistic regression model achieved a high level of significance (p < 0.01) with an accuracy of 0.84 and AUC of 0.89 on the holdout dataset. This model yielded important inferences that Airmen with poor sleep quality, recent history of an injury, higher BMI, and low fitness satisfaction tend to be at greater risk for fitness test failure. The neural network model demonstrated the best performance with 0.93 accuracy and 0.97 AUC on the holdout dataset. This study is the first application of psychological features and neural networks to predict fitness test performance and obtained higher predictive accuracy than prior work. Accurate prediction of Airmen at risk of failing the USAF fitness test can enable early intervention and prevent workplace injury, absenteeism, inability to deploy, and attrition.