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Dante80

Junior Member
Registered Member
If I understand you right, you just described why I asked the question. How could FH which lacks the two extra upper stages send GTO payload of 3 times of one F9. In other words, due to lack of 2 extra upper stages, FH should not be able to send 26.7t to GTO IMO, but around 15t.
It is the same way that theoretically the Delta IV Heavy had more than triple the GTO performance of a Delta IV Medium+ (5,2) with the GEMs removed, even if you accounted for the larger fairing the Heavy had.

You are thinking the two (payload-less) stages as adding more fuel and range. It's the exact opposite, they simply add more mass and drag to the equation.

Delta IV is again a good example. Delta IV Medium+ (4,2) has a GTO capacity of 6,150 kilograms. The bigger Delta IV Medium+ (5,2), due to the larger 5-meter (16 ft) DCSS upper stage gets 5,072 kilograms. Even when it has a lot more fuel.
 
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Dante80

Junior Member
Registered Member
In a two stage rocket the ideal ratio is the lower stage should be 10x bigger than the upper stage. That is why Falcon 9 has 9 lower stage engines. 9 is the closest number to 10 for which you can still build a symmetrical engine arrangement. They are using the same engine on both stages.

This ratio is broken on Falcon Heavy. The upper stage for it is underpowered. Period.
It's the other way around btw.

Falcon 9 has a first stage weighing ~440 tons wet, and a second stage weighing ~110 tons. That gives you a ratio of around 4.
Falcon 9 has an abnormally large and overpowered second stage, and it stages low and slow so it has to do most of the work to get a payload to orbit.

Falcon Heavy has a first stage weighing ~445 tons wet, two boosters weighing about ~433 tons and an upper stage weighing ~110 tons. That gives you a ratio of around 12. Which is better for high energy orbits/missions.
 
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