Right now, the F9 uses about 20 tonnes of fuel slow itself down (during the entry burn) - roughly 3 engines x 20 seconds x 330 kg/sec/engine. Likely this is done to keep the heating down to an acceptable level for the aluminum structure.So if we add a heat shield to the aluminum, assuming the engine section is already tough enough, perhaps F9 could re-enter using aerodynamic deceleration only. How much would a heat shield mass? The stage is about 41 meters long and 3.7 meters in diameter, hence about 500 m^2. Assuming a shuttle low-density tile mass of 144 kg/m^2, and a thickness of 4 cm (it's not much heating compared to shuttle entry) then the mass of the heat shield is 3 tonnes - clearly a win. A quick calculation, making the usual assumptions [ 311 First stage ISP, 436t First stage fuel, 27t First stage structure. (30t with heat shield), 26t Landing reserve (6t with heat shield), 348 Second stage ISP, 4t Mass of fairing, 107t Second stage fuel , 5.5t Second stage structure, 16t Payload ] says this would increase LEO payload by 2 tonnes. The first stage can provide about 250 m/s more, second stage 250 m/s less due to increased payload. I doubt SpaceX would do this (it's too close to F9 end of life, unless StarShip flops) but it shows that F9 could definitely be improved on.
Quote from: LouScheffer on 10/07/2022 04:07 pmRight now, the F9 uses about 20 tonnes of fuel slow itself down (during the entry burn) - roughly 3 engines x 20 seconds x 330 kg/sec/engine. Likely this is done to keep the heating down to an acceptable level for the aluminum structure.So if we add a heat shield to the aluminum, assuming the engine section is already tough enough, perhaps F9 could re-enter using aerodynamic deceleration only. How much would a heat shield mass? you have forgotten legs. You have forgotten air-dynamic issues of the cylindrical object. You have forgotten engine bells. You have forgotten mass balance particularities of the booster. Dude, why all this?
Right now, the F9 uses about 20 tonnes of fuel slow itself down (during the entry burn) - roughly 3 engines x 20 seconds x 330 kg/sec/engine. Likely this is done to keep the heating down to an acceptable level for the aluminum structure.So if we add a heat shield to the aluminum, assuming the engine section is already tough enough, perhaps F9 could re-enter using aerodynamic deceleration only. How much would a heat shield mass?
