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In this question, higher altitude launches are discussed, but no one seems to address fuel consumption.

Let's take the Saturn V for example. A Saturn V rocket on the launch pad weighed approximately 3,350 tons. With the launch at sea level, it took about 39 seconds to reach 2200 m (the altitude of Santa Fe, New Mexico). At approximately 15 tons of fuel per second, the Saturn V consumes 585 tons of fuel (17.5% of its launchpad weight) just to get to an altitude that we can reach with a train.

There are other high altitude cities in the U.S., some of which are near the ocean (if that's needed). Even a not-so-high city like Salt Lake City, Utah saves the Saturn V 31 seconds of burn time and 465 tons of fuel.

I've heard arguments about transporting parts and fuel, but remember that a lot of these things were already shipped across the country just to put them in Florida.

So, from a weight and fuel consumption standpoint, why do we not attempt more high altitude launches?

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vastlysuperiorman
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  • Before anyone points it out, yes I am aware that you don't save all of that fuel. At 2.2 km Apollo 11 had a velocity of 138 m/s, where a launch from Santa Fe obviously would start at 0 m/s. But still... you'd save a lot right? – vastlysuperiorman Feb 24 '15 at 20:05
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    Because you wouldn't save much fuel at all? Remember, getting into orbit is about achieving orbital speed (here's a calculation for ISS altitude), altitude is the easy part. And gravity a bit higher up isn't that much smaller either (calculation for 30 km above mean sea level). – TildalWave Feb 24 '15 at 20:05
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    High-altitude places are located in the middle of continents, and the rocket would overfly a lot of inhabited land on its way up. – Hobbes Feb 24 '15 at 20:20
  • @TildalWave That may be true, but I'd like to know more about this. How much of a factor is altitude? Obviously if you were starting 99 mi from the surface, the rocket would not need nearly so much fuel as most of the propulsion would be "sideways". – vastlysuperiorman Feb 24 '15 at 20:22
  • Ooh, maybe I just answered my own question... yeah I guess if low earth orbit starts ~99 mi up, launching from 1.5 miles higher doesn't really make a significant difference does it? @TildalWave, I do understand--velocity is the bigger issue by far. – vastlysuperiorman Feb 24 '15 at 20:27
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    AlanSE's answer in the linked question actually does address fuel consumption, by way of delta-V; his "gravitational potential" term, saving ~300m/s with a Mount Everest launch versus a sea level launch, is what you're looking for. – Russell Borogove Feb 24 '15 at 20:53

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