This is air launch—using a balloon is just one variant. All of the schemes I’ve seen seem to have fairly small payloads, I assume the trade-offs don’t work well above some threshold.
If we’re talking about orbital propellant depots, the individual launches of fuel don’t have to be very big, as long as the price per kilogram to LEO is favorable. Rockoons are but one method of circumventing the rocket equation. Many others are known, with some being more realistic than others in the short term.
Then why not launch from high-altitude balloons?
This is air launch—using a balloon is just one variant. All of the schemes I’ve seen seem to have fairly small payloads, I assume the trade-offs don’t work well above some threshold.
If we’re talking about orbital propellant depots, the individual launches of fuel don’t have to be very big, as long as the price per kilogram to LEO is favorable. Rockoons are but one method of circumventing the rocket equation. Many others are known, with some being more realistic than others in the short term.