Elon Musk will be doing an AMA on r/spaceX at 3pm... • /r/spacex

The question about spheres is my favourite.

I think retiring used boosters will be irrelevant when you start swapping out parts (mainly engines): On there "last flight" of the airframe, there could be a brand-new engine, recently swapped in. Many parts, like flight computers, radio's, maybe grid-fin actuators, etc. could have a life-span much longer than the air-frame, and would all be a pity to dump in the ocean.

Questions on how often boosters (or other rocket parts) are planned to be re-used are unlikely to result in a useful answer. Obviously as many times as possible, the parts are designed with some margin, but how soon wear an tear eats up those margins is very hard to predict, and future enhancements could have such a large effect on that critical wear and tear that even guessing flight numbers now is very hard. SpaceX may assume an absolute minimum number of uses to work out there economics, but we are also unlikely to receive those numbers. Maybe we can ask which part (in the current design) is expected to wear out soonest, and how that compares to the the lifetime of the carbon construction (which is almost impossible to repair).

Confirmation on F9 boosters and FH side boosters being identical enough to retrofit in one or both ways would indeed be nice.

The stressfulness of a landing should depend only on the fuel reserve. More fuel means more slowing down before hitting the atmosphere. A sea landing would save fuel, so with the same payload there is more fuel remaining for slowing down. So it depends on the payload (and target orbit), land and sea landing with little reserves are "hot", while land and sea landings with plenty if reserve fuel can slow down more, and have a cooler re-entry.

my question (feel free to ask, I may not be around tonight): Is the (first) red-dragon planned to be pressurised during the trip to Mars, or only during landing, or an "open" structure during landing? (during the unmanned trip, the atmosphere in Dragon would only be useful to help with thermal management of internal components like electronics)

edit: another question: Is SpaceX already adding and testing support for Mars travel to its Falcon-heavy/red-Dragon navigation software?

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