> Also, do we really have better propulsion technology to make space travel more efficient? It’s not really the propulsion technology that’s the key, it’s not

> Also, do we really have better propulsion technology to make space travel more efficient? It’s not really the propulsion technology that’s the key, it’s not throwing away a whole bunch of rocket engines every time, just to launch something once. So it’s really a design methodology as much as the technology. Having said that I think a key contributor to reusability is computation. As far as I’m aware all the experiments with propulsive landing in the 60s and 70s were manual. You could compute optimal thrust profiles given enough time and ideal conditions, but the conditions for an actual landing are never ideal. Particularly issues like atmospheric conditions such as air pressure by altitude, the effect of humidity, wind conditions and allows for the variability of turbulence around the vehicle. Modern automation of such must be vastly more efficient than manual control, but I don’t know when this became viable.