I have always wondered if a kind of blimp-like spacecraft would not be our answer for some kind of futuristic spacecraft design.
Imagine this: a blimp-like spacecraft is loaded with cargo on the ground, then starts to rise into the sky. As it goes up, it begins to collect and compress oxygen from the atmosphere, which it will use it on the second stage. As is rises, the helium inside will expand, so it will need to recapture it and store it compressed.
When it reaches the limit of our atmosphere, it would burn a mixture of fuel and the capturated oxygen. Shape would only be a minor problem now, since the atmosphere is so thin. The oxygen would only be used when it reaches the no-oxygen area, and only for orientation.
Once the spacecraft finishes its mission and has to go back to the ground, it would undock from the mothership and target Earth. When it re-enters the atmosphere, the helium should be restored in its interior, which would help reduce the re-entry speed. Once the atmosphere is thick enough, it would need some heat shield for sure, but once it's fully inside the Earth's atmosphere, the helium would slow down the fall. The spacecraft could return safely by controlling the amount of helium inside, again using compressors and reducing the amount of helium inside the hull.
I am interested in the math. Is this possible with current technology?