[cwkoss]

Even without the weight of the first stage, I'd imagine this would have to be a massive quantity of balloons. Lifting an adult human takes a house-sized amount of balloons. Fun to imagine dragging a stadium sized quantity of hydrogen balloons a mile up before detonating them with the engines, but likely impractical. Perhaps rockets could be launched from the top of a giant zeppelin once it reaches altitude? (~4 orders of magnitude larger than the Hindenberg)?

I've always been curious as to how effective a hydraulic lift could be at reducing necessary launch weight. A disproportionate amount of fuel is used at the beginning of the first stage when it is the heaviest, so seems like the benefit would be quadratic - Saturn V took 12 seconds to clear the tower. Would require major infrastructure, but if you could "throw" the rocket so it starts at a greater initial speed, seems like you could bend the rocket equation favorably. Perhaps even a giant underground potato-canon or railgun.

[sevencolors]

NASA has done tests for a railgun style launch. Project probably died. But i feel it's a strong possibility for the future

https://www.nasa.gov/topics/technology/features/horizontalla...

[aw1621107]

> I've always been curious as to how effective a hydraulic lift could be at reducing necessary launch weight.

I suppose you'd be able to approximate the effect by comparing the delta v needed to launch from a sea-level site (Cape Canaveral, Kourou, etc.) with that needed to launch from one of China's inland sites (e.g., Taiyuan, which sits at 1500m). I have no idea whether this data is publically available, though. I'd guess the bulk of your performance improvements would come from increased engine performance due to the lower ambient pressure (~0.83 atm according to Wolfram Alpha) rather than the increased altitude, since most of the energy is needed for horizontal acceleration [0]. The increased thrust would mean lower gravity losses, but I wouldn't be able to say how much.

[0]: https://what-if.xkcd.com/58/