MG23: You won't get cost to orbit below a hundred dollars a kilo by throwing away your spacecraft ever time you launch.
I don't have to get the cost where you want it, to win this argument. I just have to point out that all reusable options have shown to be more expensive than using the throw-away variants. By a lot.
Our propulsion technology hasn't seen any revolutionary invention since the 60's. That's our limit. At least with dumb-boosters, we have some way to go in cost reduction via economies of scale, i.e. mass production. No such luck with SSTO. Each one (of the very few) would be build nearly by hand, and will be overbuild to take the repeated cycles and for extra fear of losing "the precious".
MG23: Would you seriously suggest that throwing away an airliner every time it flies across the Atlantic would be an economical business model?
Absolutely! If it cost less to produce a new expandable one than to recover and overhaul a reusable one that carries the same payload, then Yes!
MG23: And demonstrating new technology is precisely what NASA should be doing.
In the ideallistic world of 1960's, yes.
Enter fiscal constraints and the issues are:
1. Is
this the new technology we should be demonstrating? We can't afford to demonstrate them all. Expensive demonstrations of white elephants take away from the rest.
2. Is NASA still an efficient organisation to do it / define the goals then assign and oversee the contractors?
I think that we are heading towards JB.
Sorry Jane-DoH for this drift.
More on the subject of your Reaction Engines, they sure seem to be pushing the edges of where airbreathing engines can go.
IIUC, hellium is used as a heat circulation fluid: it moves the heat from the intake air to the cold "sink" of LH2. It won't boil until you get the
whole content of the LH2 tank above its boiling point. It is presumably large, although I imagine that this must be a concern in the final phase of the cruise.
I like their attempt at forecasting of costs, on their web page. There is an estimated R&D cost and eventual passenger ticket prices. Faster, longer legged, and cheaper than Concorde?