[MichaelNolan]

I always had the impression that the propellant transfer was the harder question than the heat shield. They have done a transfer demo from one internal tank to another, but they still need to test from one ship to another ship.

I only casually follow the news from r/spacex, but prop transfer is what I see generate the most discussion. It’s a hard requirement for all deep space missions. Where the heat shield could be refurbished between launches.

[delichon]

The heat shield may be a "we don't know how to do the physics" problem, where propellant transfer is a "complex integration of well understood components" problem. If the heat shield requires per launch refurbishment it cripples the colonization dream.

[ACCount37]

Deep space missions yes. But Starlink isn't deep space - and neither is the vast majority of commercial payloads.

Propellant transfer is relevant because it's vital for sending entire Starships to Moon and Mars - which are the exciting Starship missions. This includes Artemis. But commercially? Artemis contract isn't even a large part of SpaceX's revenue.

[panick21_]

Why do you think transfer of propellant is so difficult? We do propellant transfer all the time in space. The only real different is that the liquid is colder and Starship is just plane bigger.

But we pipe around cold stuff in space internal to space ships already quite often.

What is the fundamental limitation that you worried about?

I would say the head-shield is far harder an an unsolved problem, specially with re-use. Refurbish is not economically viable, specially not after 1 launch. That would be against every design goal of Starship. It has never been demonstrated in a practical fashion.

[mikkupikku]

Propellant transfer, with cryogenic propellants, can be done using cryocoolers. It's not too hard of a problem. Besides, Starship only needs prop transfer for Moon and Mars missions, but the later are fantasy and the former probably isn't going to happen either, and actually just regular LEO launches with a fully reusable rocket is where most of the money is anyway.

The heat shield is a huge problem though. Without the heat shield, there's simply no way SpaceX can use Starship to make money.

[idontwantthis]

Propellant transfer isn’t necessary for starlink launches.

[modeless]

Heat shield reuse is a big deal for orbital refueling too, because it requires 12+ launches in a short time frame. If you don't have heat shield reuse then you need 12+ Starships and 12+ refurbishments per mission.