Comment Re:It's almost like the Concord verses the 747 aga (Score 1) 157
The main advantage to hydrogen would be overcoming the Kantrowitz choking effect caused by supersonic flow;
Yes, understood, and any design choice that further lowers the density of gas in the tube requires more compressor work for the air bearings, which require a fixed mass per second flow.
I don't think that's right. The air bearings function based on pressure, not mass density. 50Pa air + 50Pa H2 would keep the overall tube pressure the same, so the compressors' job wouldn't change. In fact, since the H2 (in my proposed design) would be injected into the ski air stream post-compression, the compressors would have less work to do, not more. The required mass flow to the skis using an air/H2 mix would actually be substantially less than in the Alpha proposal. Again, the pressure is what's important (averaging 7kPa under the skis), not the mass per se.