I think 1) and 3) are the only ones that do not require advances in fundamental science to achieve.
Space based energy requires a way to send the energy to the surface for monetization. The three ways to do this would be
1) Wireless transmission -- infeasible with current level tech at the distances required.
2) Wired transmission -- requires materials with very high tensile strength in quantities never before produced.
3) Deorbit batteries -- You spend more energy launching/deorbiting and distributing batteries than you gain.
High speed transport (ground to orbit, and interplanetary) have huge problems in scaling, but it mostly can be solved with current level engineering.
Space based energy requires a way to send the energy to the surface for monetization. The three ways to do this would be 1) Wireless transmission -- infeasible with current level tech at the distances required. 2) Wired transmission -- requires materials with very high tensile strength in quantities never before produced. 3) Deorbit batteries -- You spend more energy launching/deorbiting and distributing batteries than you gain.
High speed transport (ground to orbit, and interplanetary) have huge problems in scaling, but it mostly can be solved with current level engineering.