NeBula: Team CoSTAR's robotic autonomy solution that won phase II of DARPA Subterranean Challenge

This paper presents and discusses algorithms, hardware, and software architecture developed by the TEAM CoSTAR (Collaborative SubTerranean Autonomous Robots), competing in the DARPA Subterranean Challenge. Specifically, it presents the techniques utilized within the Tunnel (2019) and Urban (2020) competitions, where CoSTAR achieved second and first place, respectively. We also discuss CoSTAR¿s demonstrations in Martian-analog surface and subsurface (lava tubes) exploration. The paper introduces our autonomy solution, referred to as NeBula (Networked Belief-aware Perceptual Autonomy). NeBula is an uncertainty-aware framework that aims at enabling resilient and modular autonomy solutions by performing reasoning and decision making in the belief space (space of probability distributions over the robot and world states). We discuss various components of the NeBula framework, including (i) geometric and semantic environment mapping, (ii) a multi-modal positioning system, (iii) traversability analysis and local planning, (iv) global motion planning and exploration behavior, (v) risk-aware mission planning, (vi) networking and decentralized reasoning, and (vii) learning-enabled adaptation. We discuss the performance of NeBula on several robot types (e.g., wheeled, legged, flying), in various environments. We discuss the specific results and lessons learned from fielding this solution in the challenging courses of the DARPA Subterranean Challenge competition.The work is partially supported by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004), and Defense Advanced Research Projects Agency (DARPA)

Cell Adhesion for Improved Prosthetics: Determining Spatial Parameters to Allow Cell Spreading to Reach New Heights

Currently, there exists a mismatch between titanium bone replacement implants and native bone. Polyetheretherketone (PEEK) is favored as a replacement, but cells do not adhere well to untreated PEEK. This work attempts to combine 3D printing, materials properties, surface treatments, and control of structure geometries to test: 1. Is 3D printing a viable route to medical devices that promote cell in- and on-growth? 2. What dimensions allow cells to climb and perfuse on and in an entire engineered structure? To answer these questions, a porous PEEK scaffold with 800μm channels was constructed by selective laser sintering (SLS) and inspected visually and by scanning electron microscopy (SEM) for proper formation. The results indicate that these dimensions are near the minimum viable dimensions for channels in SLS PEEK, while still building successfully. A thin zirconium oxide layer was formed on the PEEK surface by chemical vapor deposition (CVD), followed by formation of a self-assembled monolayer (SAM) of diphosphonic acid. X-ray photoelectron spectroscopy (XPS) analysis of surfaces of sections of the device indicated treatment success in the device interior. Computer simulations of the discrepancy between the design of 3D parts and the finished SLS products were carried out. To assay the tolerance of cells to microstructure of devices, PEEK cell migration devices were constructed using standard machining techniques. Cell adhesion and migration were assayed on plain PEEK, zirconated PEEK, and phosphonated PEEK. Cells adhered the farthest from the center of the devices on the phosphonated surface, second farthest on the zirconated surface, and least far on plain PEEK. This work serves to characterize the parameters of manufacturing methods viable for producing bone replacement prosthetics. The influence of surface characteristics and celladhesive surface treatments on cell adhesion and migration are examined, hopefully leading to improved implant fixation and customizable shape