[hnick]

I don't really know where else to ask, so I'll ask here.

Another topic of research is very rapid sub-orbital passenger flight. Are there any numbers on proposed fuel efficiency for that? I'd expect you gain a lot by removing hours and hours of wind resistance, but getting up to speed and out of the atmosphere probably (gut feel) uses more.

[davedx]

I also haven't seen numbers, but I imagine the energy usage even to reach sub-orbital altitude would be pretty huge compared to a jet plane takeoff -> cruising altitude. Sub-orbital means you also have to bring your own oxygen too (rocket vs jet engine), which can approximately double your fuel mass...

[umeshunni]

No numbers, but you might have seen the SpaceX proposal / video here: https://www.youtube.com/watch?v=zqE-ultsWt0