Return of a falcon9 stage fails

[burkhard]

(12-08-2018 12:33 AM)Jim Horn Wrote:  I suspect that reentry from near space at high speed would damage the engines which aren't protected by a heat shield, so a significant burn is needed anyway. Landing at a given spot under a parachute is unlikely with any significant surface winds. The structure is also designed for compressive loads while a parachute would apply large tensile loads. Finally, since the vast majority of the fuel and oxygen are already used, the lower stage is very light compared to at liftoff, minimizing the amount of fuel needed to propel it at high accelerations to bring it back. All told, the weight difference may be less than you'd expect with the tradeoff being high control of the return.

You raise some good points Jim, although the issue of tensile v. compressive loading depends on where the parachute cables are ultimately anchored and applying force when they are under load. If they mount to the top of the structure, yes, it is tensile. If they actually mount near the bottom and are merely guided up through the center, it's a compressive load, just like the engine firing.

In any event, I wouldn't box oneself into thinking only parachutes either, nor would I expect it to be wholly without *any* engine firing. I'm talking about reducing the work the engines do, not eliminating it.

There are all sorts of extendable panels which could add some free drag, and yet still allow the engines to do 50% (or more) of the work and handle guidance on descent. On Earth, atmospheric drag is there for the taking. They let the thing fall like a stone (picking up kinetic energy which they later have to thrust like mad to reduce) for a while before even firing the engines at any significant level, don't they?

I'd like to get a couple of SpaceX engineers out for some adult beverages and after a few hours get some straight unfiltered opinions out of them. Musk is a master showman and viral internet direct marketer. I can't help but think that the burn-only landing is strongly influenced by his hand and his flair for the dramatic rather than by pure engineering judgement.