This is undergraduate engineering from Sheffield University 1985.
We start the jet as normal, and the jet engine gives off X-ray and produces helim and ozone gases, as it does Molecular Nuclear Fusion.
Incidentally, Ti plating Nimonic turbine blades double engine thrust – I used to work for INCO. Who make turbine blades.
We then feed liquid water into a hollow exhaust manifold. The 1,200oC boils off the water – we add to the combustion products. And we turn off the aviation fuel. We are flying on water.
So we obviously increase the trust by a factor of 10. We can now fly above the stratosphere, as we do not require oxygen. Until the next cold start.
We could fly to the Moon, keeping in Earth's shadow. And burrying down before the next solar dawn – named interstallar radiation will punch through 6” of lead.