>>12667034>either that or something with the pluming the fuelIts that.
Rockets have only ignited when upright, and gravity keeps fuel at the bottom of the tank. The exception is a 2nd stage in orbit, but they use helium to keep it together because the fuel becomes weightless in orbit.
The huge problem with both SN8 and SN9 is that the heavy fuel is being pulled "down" against the side of the fuel tank when starship is horizontal. This makes it awkward to keep fuel going to the raptors while trying to relight.
"Why not light earlier?" Raptors pull a LOT of fuel when actually generating thrust as opposed to firing up. If you attempt to ignite early, and both raptors spool up, they can choke out the little bit of pressure that does exist to get them going. Not to mention that when SS is horizontal, thrust makes it move laterally, which isn't wanted.
"Ok, light 3 raptors then." Three points of failure as opposed to only 2. Plus, that is 50% more fuel required to attempt relight. You're backtracking into the previous issue here.
This is why they are doing real-live testing. There is no data or experience out there for what SpaceX is attempting. They can do the math and maybe some minor simulating, but much like the landing of the Falcon9, they have to try it first and collect data so they can really start putting the puzzle together.
The flip maneuver is actually quite sensitive to thrust made by the raptors. SN8 had both raptors reignite, flipped properly, then lost fuel pressure on the way down. SN9 only had one raptor properly ignite, so when the pre-programmed maneuver executed, there wasn't enough raptor thrust to balance out the flip. Hence the last-second photo of SN9 doing its banana-peel slip. It kept rotating.
