You also have to make it environmentally sustainable like they did when they talked about a partnership with Prometheus fuels back in 2019, even then what's the point compared to regular planes if these "are likely to burn between 4.5 and 7.5X more fuel than subsonic aircraft in 2035." [0]
[0]: https://bsky.app/profile/rutherdan.bsky.social/post/3lgstwvv... -> 2021 NASA assessment https://ntrs.nasa.gov/citations/20205009400
