[rbanffy]

They are testing a lot of things at once - it's a new metal (for rockets, at least, it hasn't been used since the Mercury times) with new assembly techniques and new structural demands. It'll fly with new engines that have never flown before and, finally, the full-scale article will need to do something nobody has ever done before - come back from orbit and do a propulsive landing.

I dislike the active cooling part (which they'll probably start to test along the rest with this vehicle). Everything "active" will eventually fail at the worst possible time.

[sgc]

Since the alternative is basically use of insulating tiles, which as we know are not free of significant concerns, I have come to accept that it is required complexity.

[rbanffy]

If we had science-fiction engines, we could do a propulsive brake and skip messing with the atmosphere altogether.

[Klathmon]

Doesn't "the tyranny of the rocket equation" kind of make the idea of fully propulsive braking systems kind of infeasible?

I know it's possible, but when you have an atmosphere not using it would be just throwing away potential weight that you could be using for the mission at hand.

I'm not rocket scientist, but it sounds like solving that problem using other means (like active cooling) gives you a good amount of weight to play with before it even begins to equal the cost of propulsive braking. And that means you can have a lot of redundancy or can use less efficient but simpler to operate/manufacturer/fix.

[rbanffy]

It all depends on how much mass you can eject how quickly. If you have good enough propulsion you can save on thermal shielding (and propellant mass).

And, if you have a true science-fiction-grade engine, you may not even need propellant. ;-)