About 20 years ago, I briefly considered what it would take to use heliostats focussed on a heat exchanger to the same effect.
The mistake I made then was thinking fuel was expensive, so I assumed similar performance to existing rockets as if I was using it to superheat cheap water to the combustion temperature of hydrogen-oxygen — the problem with this being that it's pumping the equivalent of the entire electrical power demand of the United Kingdom into an engine the size of a truck for 6 minutes without it exploding.
(Similarly, it's possible to push against Earth's magnetic field but if you use copper the resistive losses will vaporise you launch vehicle. And you can make a much stronger artificial field on the ground, but the way magnetic fields reduce with distance means the current loop on the ground has to be significantly larger than CERN's LHC).
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