His objection isn't based on technology though. It's based on physically enveloping the problem and comparing the two cases.
His assumptions seem to be: LOX will remain cheap. The atmosphere will still have 21% oxygen. Your technology can't separate the N2 from the O2 before ingestion.
Elon says that the braking effect of ingesting that nitrogen vastly overwhelms the small benefit of having a smaller O2 tank. That's it.
This argument doesn't rely on the air-breathing stuff being more complicated or expensive or heavy (though it will be). Technology might fix those problems, but that simple kinematic fact is enough.
His objection isn't based on technology though. It's based on physically enveloping the problem and comparing the two cases.
His assumptions seem to be: LOX will remain cheap. The atmosphere will still have 21% oxygen. Your technology can't separate the N2 from the O2 before ingestion.
Elon says that the braking effect of ingesting that nitrogen vastly overwhelms the small benefit of having a smaller O2 tank. That's it.
This argument doesn't rely on the air-breathing stuff being more complicated or expensive or heavy (though it will be). Technology might fix those problems, but that simple kinematic fact is enough.