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"Part of it is that the payload comparison is quite misleading; it gives LEO numbers, while neither Delta IV heavy nor Falcon Heavy are primarily designed for LEO missions. Payload to GTO (where Falcon Heavy is likely to put most of it's payloads) gives the ratio as about 3:4, and payload to direct GSO (as with most Delta IVH missions) is roughly equal. The other part is that Delta IVH doesn't make terribly good use of it's LOX/LH2 booster stage; the engines were designed for simplicity and low cost rather than performance, and only use hydrolox because that's where most of the US rocket engine expertise was in the post-shuttle era."
"How do you define "get more from using RP-1"? This isn't simply an issue of filling a different fluid into the tanks, you know.
The rocket equation doesn't care about "amounts" of something. It cares only about mass fractions. Liquid hydrogen has an extremely low density. That means in order to get a given mass of fuel, you need a huge volume to hold it, and therefore huge tanks. That's why the Delta appears so large.
The Falcon Heavy uses a propellant that's much more dense. That means it needs less tank volume to hold a given mass of fuel. In fact, due to being of similar size to the Delta, it manages to hold significantly more fuel by mass. If you compared the weight of a fully fueled Delta IV Heavy and a fully fuelled Falcon Heavy, the latter is much more massive. Wikipedia says 733,000 kg (Delta) versus 1,462,836 kg (FH). The Falcon is literally twice as heavy.
Because it has so much more propellant mass, the Falcon Heavy can lift a greater payload into low Earth orbit.
But there's a reason the Delta IV uses liquid hydrogen: it's a much better fuel. LH2/LO2 combustion (also called hydrolox for a shorthand) is by far the best (sane) rocket fuel that exists in the world, by efficiency. The RS-68A engines on the Delta get an Isp of 365s (ASL) - 414s (vac)... and that's for a fairly cheap, low-effort engine. If you really put engineering effort to it, you get something like the Space Shuttle's engine, the RS-25: Isp 366s (ASL) - 453s (vac). Now compare the Falcon Heavy that must make do with kerosene-burning Merlin engines... no matter how well you build those, they just can't compare. The Merlin 1D manages an Isp of 282s (ASL) - 311s (vac).
This is also the reason why the Falcon Heavy's performance takes such a sharp nosedive as soon as you try to go beyond low Earth orbit. The extreme Isp advantage and low weight of the hydrogen-fueled DCSS (Delta Cryogenic Second Stage) just walks all over the heavy, kerosene-fueled Falcon upper stages in space. SpaceX took a Merlin and bolted a large vacuum bell onto it, calling it Merlin 1D Vacuum ("MVac"), but that still only improves the Isp to 340s... simply not competitive with dedicated hydrogen vacuum engines which can get as high as 465s.
In other words, if you really wanted to take full advantage of the Falcon Heavy's 50 ton to LEO capability, you'd want it to lift a 50-ton hydrogen fueled spacecraft instead of trying to throw something smaller by itself."
https://forum.kerbalspaceprogram.com/index.php?/topic/113709-spacex-falcon-heavy-vs-delta-iv-heavy/Hehehe, jak się to poczyta to nie sposób się nie zgodzić z wypowiedziami z naszego forum, że FH to błąd. Że to jest rakieta, która będzie nieefektywna do zastosowań, do których będzie stosowana. A także, że lepiej, żeby jej nie było, a siły przerzucone na szybsze dokończenie Dragona 2 jako taksówki na LEO latającej zwykłym Falconem 9.
Wątek: SpaceX (Przeczytany 2012231 razy)