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enter image description here What could the Kozlov’s Aerosmena project blimp add to fuel saving if space rockets were launched from it? Where would you place the rocket and airship on this chart?

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    $\begingroup$ fuel usage per km is not a useful metric for space vehicles $\endgroup$ May 9 at 19:02
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    $\begingroup$ Rockets can travel as far as you are willing to wait, and the optimal time to reach a destination is driven by orbital mechanics, independent of vehicle. This chart is basically useless for space travel, it only means something for vehicles that spend their time crawling around on a planetary surface or through its oceans/atmosphere. $\endgroup$ May 9 at 19:26
  • $\begingroup$ To reiterate what has been said in many places. When you want to reach the orbit, gaining altitude is not the problem. The real problem is that you need to accelerate to the speed of 8 kilometers per second sideways. True, it is marginally easier to do that if you don't have to fight the extra drag of the thicker atmosphere the first few kilometers, but A) a rocket lifting off does not spend much time at low altitudes, B) its speed while there is "slow". $\endgroup$ May 10 at 7:24
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    $\begingroup$ @JyrkiLahtonen also, from what I could find, the maximum altitude of these blimps is only 3000 m. That's probably not when carrying their maximum payload. You're basically launching from a really expensive and weather-sensitive ground pad. $\endgroup$ May 10 at 13:00
  • $\begingroup$ @OrganicMarble This graphic has nothing to do with space travel - what is called "Stage" here are just different stages of engine development. $\endgroup$
    – asdfex
    May 11 at 7:49
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If a rocket using cryogenic fuel and oxidizer is launched from a blimp, no fuel will be saved.

During the blimp flight from ground to launch height, the rocket will loose a lot of fuel by evaporation.

A rocket to reach an orbit at 400 km height and 8 km/s speed saves only very, very little fuel when launched from about 10 km height provided by a blimb.

So much more fuel is wasted by evaporation than saved by the increased launch height.

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    $\begingroup$ It certainly would receive at least a modest benefit launching from 10 km altitude! Max-Q would be much smaller and at a higher altitude, less propellants necessary, etc. A topping-off and helium bubbling system that you describe here could be added to the balloon's payload as long as the ballon's ascent rate were fast enough. Weight savings by launching from 10 km could be used to add more insulation to the rocket to lower evaporation, and the increase in diameter is less important because starting at 10 km body drag issues will be much lower $\endgroup$
    – uhoh
    May 10 at 2:41
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    $\begingroup$ @uhoh it's now clear to me why this design has shown such wide acceptance in the world's space launch systems! $\endgroup$ May 10 at 2:45
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    $\begingroup$ @OrganicMarble you are being sarcastic. "no fuel will be saved" is simply not correct, but "this is much better and everyone should do it" does not follow from that. Answers to previous versions of the question point out several operational and logistical reasons why launching from the ground is better than the top of a mountain or a balloon. But that's not what this question asked. $\endgroup$
    – uhoh
    May 10 at 2:47

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