A new engine could bring back supersonic air-travel

I'm more interested in the part at the end where they talk about how to eliminate (or reduce) the sonic boom being heard from the ground.

Mach cut-off [...] involves directing the sonic boom in such a way as to refract it through layers of thicker air at lower altitude. Refract it enough and it will, in effect, be reflected—never arriving at ground level. Feeding the autopilot information about where the relevant layers are would let the plane steer itself in a way which maximised Mach cut-off.

I wonder if a new engine could work with only water injection instead of afterburning. It would certainly be much cheaper and delivers an impressive boost in thrust. Quite a few cargo jets use it for takeoffs, especially when heavily loaded on hot days and high altitude.

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