The theory and practice of unmanned aerial vehicle (UAV) capture and control via Global Positioning System (GPS) signal spoofing are analyzed and demonstrated. The goal of this work is to explore UAV vulnerability to deceptive GPS signals. Specifically, this paper (1) establishes the necessary conditions for UAV capture via GPS spoofing, and (2) explores the spoofer's range of possible post-capture control over the UAV. A UAV is considered captured when a spoofer gains the ability to eventually specify the UAV's position and velocity estimates. During post-capture control, the spoofer manipulates the true state of the UAV, potentially resulting in the UAV flying far from its flight plan without raising alarms. Both overt and covert spoofing strategies are considered, as distinguished by the spoofer's attempts to evade detection by the target GPS receiver and by the target navigation system's state estimator, which is presumed to have access to non-GPS navigation sensor data. GPS receiver tracking loops are analyzed and tested to assess the spoofer's capability for covert capture of a mobile target. The coupled dynamics of a UAV and spoofer are analyzed and simulated to explore practical post-capture control scenarios. A field test demonstrates capture and rudimentary control of a rotorcraft UAV, which results in unrecoverable navigation errors that cause the UAV to crash. C 2014 Wiley Periodicals, Inc.

Abstract-A proposal for civil GPS navigation message authentication (NMA) is presented with sufficient specificity to enable near-term implementation. Although previous work established the practicality and efficacy of NMA for civil GPS signal authentication, there remains a need for a detailed proposal that addresses several outstanding considerations regarding implementation. In particular, this paper (1) provides a definitive evaluation of the tradeoffs involved in the choice of cryptographic protocol, and (2) optimizes the placement of digital signature bits in the GPS CNAV message stream. By offering GPS engineers and policymakers a detailed blueprint for civil NMA, this work advances the possibility of NMA implementation on modernized civil GPS signals.

Fiber-reinforced hydrogels are a class of soft composite materials that has seen increased use across a wide variety of biomedical applications. However, existing fabrication techniques for these hydrogels are unable to realize biologically relevant macro/meso-scale geometries. To address this limitation, this paper presents a novel air-assisted, dual-polarity electrospinning printhead that converges high-strength electric fields, with low velocity air flow to remove the collector dependency seen with traditional far-field electrospinning setups. The use of this printhead, in conjunction with different configurations of deformable collection templates has resulted in the production of three classes of fiber-reinforced hydrogel prototype geometries, viz. (i) tubular geometries with bifurcations and meso-scale texturing; (ii) hollow, non-tubular geometries with single and dual-entrances; and (iii) 3D printed flat geometries with varying fiber density. All three classes of prototype geometries were mechanically characterized to have properties that were in line with those observed in living soft tissues. With the realization of this printhead, biologically relevant macro/meso-scale geometries can be realized using fiber-reinforced hydrogels to aid a wide array of biomedical applications.

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