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This paper discusses the philosophy and editorial considerations behind the ongoing second revision of the ASTM F38 Committee standard on run time assurance for aircraft systems -ASTM F3269, titled "Standard Practice for Methods to Safely Bound Flight Behavior of Unmanned Aircraft Systems Containing Complex Functions". It describes the key aspects of the Run Time Assurance (RTA) architecture as depicted in the current revision of the standard and provides some insights on the design best practices suggested in the standard. RTA is a certification strategy for unmanned aircraft systems that contain complex functions, which may not be certifiable using traditional design assurance practices. This challenge may arise in part due to the inherent algorithmic complexity of these functions. It may also be due to the inability to produce design assurance artifacts according to industry standards such as RTCA DO-178C (software) or DO-254 (hardware) for commercial off-the-shelf components used on-board the aircraft. RTA adds value not only to unmanned applications, but also to manned aviationparticularly in General Aviation (GA) and Advanced Air Mobility (AAM). It has the potential to enable technologies for autonomous aircraft systems and simplified vehicle operations. The strategy will also play a role in the design assurance and certification of adaptive controllers and functions using artificial intelligence and machine learning algorithms.

Radio searches for extraterrestrial intelligence have mainly targeted the discovery of narrowband continuous-wave beacons and artificially dispersed broadband bursts. Periodic pulse trains, in comparison to the above technosignature morphologies, offer an energetically efficient means of interstellar transmission. A rotating beacon at the Galactic Center (GC), in particular, would be highly advantageous for galaxy-wide communications. Here, we present blipss, a CPU-based open-source software that uses a fast folding algorithm (FFA) to uncover channel-wide periodic signals in radio dynamic spectra. Running blipss on 4.5 hr of 4–8 GHz data gathered with the Robert C. Byrd Green Bank Telescope, we searched the central 6 ′ of our galaxy for kHz-wide signals with periods between 11 and 100 s and duty cycles (δ) between 10% and 50%. Our searches, to our knowledge, constitute the first FFA exploration for periodic alien technosignatures. We report a nondetection of channel-wide periodic signals in our data. Thus, we constrain the abundance of 4–8 GHz extraterrestrial transmitters of kHz-wide periodic pulsed signals to fewer than one in about 600,000 stars at the GC above a 7σ equivalent isotropic radiated power of ≈2 × 1018 W at δ ≃ 10%. From an astrophysics standpoint, blipss, with its utilization of a per-channel FFA, can enable the discovery of signals with exotic radio frequency sweeps departing from the standard cold plasma dispersion law.

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