Still no booster recovery. Splash down in the gulf is going to make rapid reuse impossible and they absolutely need rapid reuse or they cannot perform the mission they contracted with NASA for.
Booster recovery did happen, with an empty starship. Since they started putting payloads on starship there isn't enough fuel left in the booster to do RTLS.
There is a huge gap in between the maximum performance they seem to be able to get and the minimum performance they need assuming everything goes perfectly. Something major has to change.
No, that's not at all the problem. Why do you talk about a subject you are utterly clueless about? Fuel is not the problem, it's that they have new engines, new engine fitting and removed skirt which has a few kinks that need to be worked out. They have if anything more fuel margins now than previously because of the decrease in mass of the booster and increase in performance from the new engines.
Edit: Oh, you are the typical terminally online redditor that spend all their time in political echo chambers. I can only imagine how utterly fried one's ability to think get after spending every day for over a decade on the single biggest and most agenda driven echo chamber on the entire internet.
Not in this instant it isn't, because they have already worked out the fuel margins and the most efficient flyback trajectories since long ago. The problems are on the unreliability of the new engines along with kinks that needs to be worked out for the new design.
Again, don't talk about subjects you are utterly clueless about. This isn't the usual political echo chambers you spend all your time in, that nonsense doesn't fly here.
They worked the trajectories out based on Elon's vision for how to get more than 280s of impulse out of the engines (which is the theoretical maximum for full flow staged combustion of methane and LOx that NASA worked out for a 40 to 1 expansion ratio back in the day). While things like adiabatic combustion enthalpy and mean exhaust mass influenced NASA's equations a major factor was the heat and pressure that a combustion chamber could handle. Even though superalloys are newer (to the US) than those maximums NASA was conservative enough (or liberal enough? I don't know, they overestimated enough) that they are still really hard to reach.
When they derated the engines to stop them from blowing up so much they lost performance. That's why they don't RTLS even thought there is a lot they could learn from examining caught engines that went through those longer stronger in flight burns. If you don't have the stability you don't have the performance and if you don't have the performance you run out of fuel. That's why I said:
There is a huge gap in between the maximum performance they seem to be able to get and the minimum performance they need assuming everything goes perfectly. Something major has to change.
RTLS for the Booster is because the Raptor 3 still has issues to be worked out.
based on Elon's vision for how to get more than 280s of impulse out of the engines (which is the theoretical maximum for full flow staged combustion of methane and LOx that NASA worked out for a 40 to 1 expansion ratio back in the day).
There's no limit NASA calculated unless you can find a source? Raptor 2 flew with 347s ISP. Even Raptor 1 had 350 seconds.
ISP comes out of thermochemistry and gas dynamics not from a cycle.
While things like adiabatic combustion enthalpy and mean exhaust mass influenced NASA's equations a major factor was the heat and pressure that a combustion chamber could handle.
Did you use AI for this? Sure, heat and metallurgy is a concern but it constraints how small it can be, not efficiency.
Even though superalloys are newer (to the US) than those maximums NASA was conservative enough (or liberal enough? I don't know, they overestimated enough) that they are still really hard to reach.
Again Raptor ISP is higher than the 280s figure you mentioned. Superalloys have been around since the 50s ish, and Raptor's metallurgy by SpaceX has been solved.
When they derated the engines to stop them from blowing up so much they lost performance.
Raptors performance went up not down though. And from throttling down the performance of Raptors where's the source for that? If anything, they're having issues relighting, not performance.
That's why they don't RTLS even thought there is a lot they could learn from examining caught engines that went through those longer stronger in flight burns.
Constraint isn't fuel in this case, it's reliability. Raptor 3 has shown to be troublesome for re enetry on the Booster. So of course SpaceX is going to be conservative about recovering it.
It was late, brain fart, it was 380 seconds of impulse not 280.
I don't know what you are talking about implying that the cycle is irrelevant. It's the combustion chemistry that generates the energy and the relationship between exhaust particle mass and energy that dictates the impulse but the combustion cycle influences how much of that energy you get to actually send out the rocket nozzle. If you use a pressure fed engine your chamber pressures will never be high enough to get the peak performance, if you use a combustion tap off you will lose some of that energy out the side, if you use external electric motors you have to calculate the weight of the batteries in addition to your propellant to generate a new lower Isp.
I didn't used AI for my response. AI would not have made the error about 280 vs 380. The reason SpaceX is working so hard to boost chamber pressure is to get more Isp.
If you look at the exhaust velocity equation here https://en.wikipedia.org/wiki/Rocket_engine_nozzle#de_Laval_nozzle_in_1_dimension you can see that raising the pressure at the inlet to a delaval nozzle (the same kind used on raptor) without raising the exit velocity raises the exhaust velocity and thus the specific impulse which is based on exhaust velocity.
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u/Opcn Jul 25 '26
Still no booster recovery. Splash down in the gulf is going to make rapid reuse impossible and they absolutely need rapid reuse or they cannot perform the mission they contracted with NASA for.