Just a thought: Vacuum balloons.
Vacuum balloons are a somewhat old idea and basically embodies the perfect lifting balloon.
The principle is simple: A hollow body containing a vacuum , is always lighter than what little atmosphere surrounds it and therefore floats.
The intrinsic problem is , that there are no materials lightweight and strong enough the same time to withstand the outside pressure of our atmosphere while covering the needed volume.
As we might never find such a material, capable of this, there are maybe some workarounds:
Active support: This means we use energy to stabilize the material. In its easiest form this could be a magnetic field to keep the structure in its form. The contradiction is of course, that a power supply means more weight and therefore we would have to have an even bigger hollow body to lift it up. We can however circumvent this issue, by applying the power from outside.
The next possibility to have something like a modular/staged design. While known materials aren’t able to withstand earth’s pressure, it is maybe possible to make use of this concept very high up in the atmosphere, when pressure is a small part of what it is on the ground. So those vacuum balloons only get used at certain altitudes/air pressure which would still be very useful for research on many planets with low pressure atmospheres such as mars. Usage in the upper atmosphere of earth could also be an option.
A combination of both concepts could be working as well.
Maybe somebody with a little more brain than I can do something with it...
