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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2022

Characterizing Minimum Admissible Separation Distances in Heavy Duty Vehicle Platoons

Heavy duty (HD) vehicles platooning under highway operating conditions, have been projected to provide significant fuel economy (FE) gains based on aerodynamic drag reduction of the platooning vehicles. Realizing these benefits under real-world operating conditions have several challenges. This paper (the second as part of series) quantifies the minimum admissible separation distance between platooning vehicles in HD commercial vehicle (CV) applications. This distance must be set up such that no collision occurs with leading vehicles under all deceleration conditions. In this paper key interactions to characterize this distance are demonstrated. These include, road surface conditions, grade, inter-vehicle communication delays, air-brake lag time, vehicle speed, weight, and aerodynamic drag. It is seen that characterizing the vehicle and road dynamics will be critical in establishing required deceleration or stopping distances for each vehicle in a platoon. The results of the study also necessitate vehicle control systems that can dynamically adjust not only the separation distances but also the braking reference points based on road conditions. The narrative provides application decision personnel with a well-defined set of admissible separation distance impact factors to consider as part of their architecture selection process.

Sujan, Vivek↗

DOE OSTI2026

A Panspermia Origin for Venus Cloud Life

Decades of study have hinted at the astrobiological potential of Venus's cloud layers. This potential is often cast as stemming from the idea that the Venusian surface was clement in the past. As the climate changed, life then remained in, or perhaps evolved and migrated to, the last habitable niche: the altitudes above ∼50 km with Earth-like temperatures and pressures today. Here we explore an alternative scenario where life was delivered to Venus' clouds from Earth or Mars (“panspermia”). This process requires a life-containing bolide to enter the atmosphere, without experiencing complete sterilization, and then be dispersed at high altitude in fragments small enough to dwell in the clouds. We adapt a widely used model of bolide-atmosphere interaction to investigate the fate of bolides delivered to Venus from Earth and Mars. Starting at the top of the atmosphere, bolides ablate and fragment. Aerodynamic drag spreads these fragments horizontally, forming a “pancake” with an increased effective cross-section, causing rapid deceleration. An airburst occurs when the bolide deposits its highest amount of kinetic energy in the atmosphere. Observations of terrestrial meteorites provide a scaling law for the distribution of post-airburst fragment sizes. Inspired by the “Venus Life Equation,” we present a framework for calculating the rate at which panspermia delivers microbial life to the clouds of Venus. Our best estimate is an average of ∼100 cells dispersed in the clouds per Earth-year. Whether this life can survive and thrive in its new home remains an open question.

Guinan, Emma [Arizona State Univ., Tempe, AZ (Unit↗

DOE OSTI2026

Urban Land Surface Effects on Summertime Clouds and Moist Convection in Houston Under Different Synoptic Conditions

Urban landscapes modify cloud formation and convection through complex thermodynamic and aerodynamic processes; however, their influence under different synoptic regimes remains poorly understood. This study investigates the impact of the Houston metropolitan area on summertime cloud cover and convective cell characteristics using a combination of satellite observations, radar data, and high-resolution process-based modeling. We isolate urban effects by comparing model simulations with realistic urban land cover against hypothetical scenarios where all urban areas are replaced by rural vegetation. Results reveal that Houston's land cover consistently enhances cloud fraction and convective activity relative to surrounding rural areas, altered by large-scale meteorological forcing. Under weakly forced conditions, enhanced surface heat flux primarily contributes to driving low-level convergence and vertical ascent, leading to over 8% cloud fraction increase between 2 and 6 km over the city. Under strongly forced conditions, urban influences manifest differently depending on cloud type. For non-convective clouds, the city acts as a barrier that decelerates and lifts moist southerly inflow, increasing low cloud cover over the urban core, while decreasing it downwind the city. For convective clouds, both synoptic ascent and urbanization modulate moisture redistribution and cloud structure, producing modest cloud enhancement over the city and slight suppression over the downwind area. Urbanization exerts small changes in the intensity of the convective cells; however, it significantly decreases their duration and traveling distance. This work highlights the importance of accounting for land surface heterogeneity in modeling clouds and precipitation and demonstrates that urban impacts on clouds are highly regime-dependent.

Liu, Ye [Pacific Northwest National Laboratory (PN↗