AUTHOR=Oehlschlaeger Matthew A. TITLE=Grand challenges in aerospace propulsion JOURNAL=Frontiers in Aerospace Engineering VOLUME=1 YEAR=2022 URL=https://www.frontiersin.org/journals/aerospace-engineering/articles/10.3389/fpace.2022.1027943 DOI=10.3389/fpace.2022.1027943 ISSN=2813-2831