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I'm assuming a majority of the fuel used in a rocket to say get to the moon is involved in escaping earth's gravity.

So why can't we create a smaller weighing rocket, with less fuel to carry and attach it to several huge balloons and have them float high into earths atmosphere then once there the balloons release the rocket and it launches the rest of the way saving a bunch of fuel and cost.

Is this a realistic idea.. if not why?

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"Escaping Earth's gravity" does not primarily mean reaching a certain altitude, it means reaching enough horizontal speed to achieve orbit (I.e. going fast enough horizontally so the trajectory does not intersect witg the ground). Reaching even a low Earth orbit altitude changes this required orbital speed by less than 10%. Therefore for an orbital rocket, launching via balloon does not add much benefit.

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  • $\begingroup$ But other missions (say to Moon or Mars or elsewhere in the Solar system) do not involve getting into Earth's orbit. Would this be beneficial for those? $\endgroup$
    – Vilx-
    Jan 17, 2023 at 7:18
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    $\begingroup$ @Vilx- no. In practice, almost all missions – including those headed for deep space – first inject into a low Earth orbit, and then accelerate (with or without pause) further from there to raise their apogee and ultimately escape from Earth's gravity. The kinetic energy of the initial orbit is part of the energy that's used to escape. It would theoretically be possible to just accelerate upwards, but it's not efficient (you lose a lot of Δv in fighting gravity, instead of letting the side-velocity do that for you), and also a parking orbit gives you more time to target the destination. $\endgroup$ Jan 17, 2023 at 8:28
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    $\begingroup$ Obligatory XKCD reference (really What If, but still): Space isn't like this, it's more like this. $\endgroup$
    – Arthur
    Jan 17, 2023 at 9:38
  • $\begingroup$ avoiding atmospheric drag is still a significant benefit, even if you don't have the horizontal velocity $\endgroup$
    – Tristan
    Jan 17, 2023 at 10:07
  • $\begingroup$ @Tristan It's significant for sounding rockets that do most of their accelerating in a very brief burn after ignition. It's not so significant for rockets going to orbit and beyond, where the burn is long enough that most of it takes place high enough that drag is negligible. $\endgroup$
    – John Doty
    Jan 17, 2023 at 13:04
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Been done for sounding rockets. It helps to reduce the atmospheric drag at the beginning of the flight. However, your rocket still has to accelerate to whatever velocity the mission requires, so it doesn't save much fuel.

Stratospheric balloons are difficult to make and launch. That adds to the cost and complexity of a rockoon versus an ordinary rocket. It's usually simpler and easier to just carry enough fuel to do the job from the ground.

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