The theme for Space Technology Applications International Forum II in 2013 was: when will it be possible to build craft capable of reaching the stars in reasonable lengths of time? “Reasonable” was understood to be significantly less than a human lifetime. That can only be done by implementing “exotic” technologies that are presently thought to be the stuff of science fiction. But there is at least one proposal may make such technologies practicable. It rests on “Mach’s principle” as Einstein called it. This paper, which captures the contents of the keynote talk at that conference, recapitulates how we have reached our present pass, and tells of recent experimental developments in the “Mach effects” project. Though a small-scale, table top project, steady progress has been made. For example, switching transients that may have propulsive applications are reported here. Post conference comments on claims that the quantum vacuum can be exploited for propulsive purposes are included. It is shown that such speculations are without merit.
The theory and experiments for Mach Effect Thrusters look good and are worth scaling. If it proves out and does scale with better materials and higher power levels (into the megawatt ranges) then it could enable propellantless propulsion up to 1G space drive and beyond.