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It's not crazy complicated. And the Shuttle was fed by an external tank as well. The way it will work with the Falcon Heavy (when that much payload capacity is

It's not crazy complicated. And the Shuttle was fed by an external tank as well. The way it will work with the Falcon Heavy (when that much payload capacity is desired) is that the 3 engines on each side in the center booster will each feed from the nearest outer cores during liftoff. When those cores are empty the feed will be stopped, those 6 engines will shut down, the outer cores will separate, and then the 6 engines will come online again fueled by the center core. It's mostly just valve work, to be honest. Also, even if it doesn't work it's not a huge deal long term. It means that we'll be deprived of the highest payload capacities for an expendable Falcon Heavy but we'll still have a fairly high (20+ tonne to LEO) capacity booster in a reusable configuration, which will probably be more impactful in the long run than the expendable configuration.

hga 13y ago
Ah ha! In the back of my mind I knew this wasn't entirely unprecedented, just couldn't remember where. The scheme, as described in more details by you, is a lot simpler, and less concerning than I was envisioning (figures, given this is Space X). There's no cross tanking, that is, feeding the tanks of the central core from the sides. Hmmm, although as I remember, when they had to shut down one engine during an ascent, it shed debris because of the pressure imposed by the adjacent engines. But I note the Merlin 1D, while producing significantly more thrust at sea level (nearly 50%), can throttle between 70-100 percent. Obviously they've thought through these stresses, and of course there are structural implications in making them highly reusable, they're willing to trade off weight penalties for durability, and therefore likely strength. Anyway, thanks for the details, and all the contributions you've made to this topic!
- InclinedPlane 13y ago
  That's a good point about the engine problem after it was shut down. However, there are a few important issues that are relevant. On further investigation the engine damage was due to fuel leakage, it wouldn't necessarily be expected that a healthy engine would react the same way if shut down under the same conditions. Also, that failure occurred at Max-Q (maximum dynamic pressure), and normally it would be expected that the stage separation would occur under much, much less strenuous aerodynamic conditions (farther down range and higher altitude, much lower atmospheric pressure).

hga 13y ago

Ah ha! In the back of my mind I knew this wasn't entirely unprecedented, just couldn't remember where. The scheme, as described in more details by you, is a lot simpler, and less concerning than I was envisioning (figures, given this is Space X). There's no cross tanking, that is, feeding the tanks of the central core from the sides. Hmmm, although as I remember, when they had to shut down one engine during an ascent, it shed debris because of the pressure imposed by the adjacent engines. But I note the Merlin 1D, while producing significantly more thrust at sea level (nearly 50%), can throttle between 70-100 percent. Obviously they've thought through these stresses, and of course there are structural implications in making them highly reusable, they're willing to trade off weight penalties for durability, and therefore likely strength. Anyway, thanks for the details, and all the contributions you've made to this topic!

InclinedPlane 13y ago
That's a good point about the engine problem after it was shut down. However, there are a few important issues that are relevant. On further investigation the engine damage was due to fuel leakage, it wouldn't necessarily be expected that a healthy engine would react the same way if shut down under the same conditions. Also, that failure occurred at Max-Q (maximum dynamic pressure), and normally it would be expected that the stage separation would occur under much, much less strenuous aerodynamic conditions (farther down range and higher altitude, much lower atmospheric pressure).