""completely reuseable" TPS cannot at present work."
Are we sure? That was forty years old technology - it was designed and built in the 1970s. The Shuttle was tested without unmanned launches, no surprise some issue arose.
Are we sure synthetic material technology of today can't deliver a simpler (less tiles) and easier to maintain heath shield?
The X-37 is said having an "improved" thermal protection - what is it using?
Ablative shields are surely cheaper, and for small capsule, not costly to replace.