> SSTO configurations just aren't very good at lifting much mass to orbit, so that seems unlikely.

Depends what you mean. Performance wise they are not as efficient as multi stage expendable rockets, however they offer possibly the best operational efficiency of rocket system.

The venture star has a launch capability of 20 tons to LEO. Larger lifters like Boeing's proposed 'Big Onion' had a lift capability of 227 tons to LEO. Despite its large size, its fully reusable nature and simple design would have meant its operation would have been considerably cheaper than anything that has flown to date.

I suggest that it would be prudent to test at least one SSTO before the industry writes off the technology. Especially if we had one already 90% complete!