content: Well ... here's a bit more detail, thinking through what this project would entail. A Space Fountain has a top and a bottom half.  My simple understanding of how it works is that the bottom section shoots bullets towards the top section, with enough extra kinetic energy to send the bullets (much) higher than the top section.  The top catches the bullets, magnetically, turns them around and shoots them back down at the bottom section.    Stopping the bullets from going any higher transfers the extra energy to the top section, causing it to go up (a tiny bit), and then shooting the bullet back down causes it to go up a bit more (action-reaction). The bottom does the same thing, catches the bullets, magnetically turns them around, and shoots them back up. Challenges include ... well, I need to build (at least) 2 small ... hmm, would they be coilguns? ... that fire the tiny steel/iron BBs.  At least one in the bottom section and one in the top section ... and I'm thinking a pair of them, in each section, would be better. Then, the pellet stream probably need to be contained (just, for safety, reliability, etc) ... I suppose that means plastic tubes running from the bottom section to the top section.  And that immediately introduces a problem ... if the tubes are not perfectly straight, they will impede the path of the pellets, causing them to bounce around in the tubes, lose/waste energy, and perhaps even fall back down the tubes before reaching the top section. It also needs some way to get electricity to the top section, to power the top section coilgun(s) and, perhaps, the magnets.  I suppose the electricity will need to be fed to the top section through wires on the pellet-stream tubes. Finally, I'm not clear on how the magnets would be added ... would these be simple, permanent magnets, arranged around a 180° tube?  Or am I learning how to build electro-magnets?  How strong do these need to be to catch the pellets ... more to the point, how do I figure this out? How much power will it need?  I don't know.  I suppose the main consideration is how heavy the top section ends up, once the coilguns, magnets and supporting structure are put together.  Maybe it's a pound; maybe it's 10 pounds.  How much energy is required to pull up a 1 lb or 10lb object 5 or 10 or 20 feet in the air? But more importantly, the underlying question is whether or not any of the necessary tech (coilguns, electro-magnets, sufficient power and an electrical circuit that can handle it, anything else I'm overlooking) ... if all of this is comfortably within the realm of the home project.