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]
I'm so glad that buried deep in the HN commments in an individual who cares about the environment. In the other conversations I've seen about this no one mentions or thinks about fuel consumption. I feel like I'm taking crazy pills sometimes. It's like "Yay! We figured out another way to accelerate the disastrous consequences of climate change. Go us!"
[0]: https://bsky.app/profile/rutherdan.bsky.social/post/3lgstwvv... -> 2021 NASA assessment https://ntrs.nasa.gov/citations/20205009400