Can Turborockets replace Pure Rockets?
Turborockets are hybrid systems that aim to use atmospheric oxygen as oxidizer instead of carrying it on board and thereby improve performance. While they do have a real chance of replacing the conventional rockets in use today, there are a number of engineering challenges to be overcome before they become viable.


These hybrid systems basically use a gas turbine inside the atmosphere (ramjets/scramjets have also been proposed) to produce thrust. The issue is that the jet engine becomes dead weight outside the atmosphere, so its weight has to be minimized. Skylon uses a slightly different method with a heat exchanger using helium, but the problem is the same.
The air intake has to operate over a wide range of speeds, from subsonic to hypersonic; the best option is to have a variable air intake, which adds weight and complexity.
The nozzle has the same problem. The area ratio of the nozzle has to vary significantly to cope with widely differing flow conditions.
If the vehicle has to take off under its own power, it has to have lifting surfaces, which are dead weight (eating into payload) once out of the atmosphere.
The integration of all these extra systems also causes a significant weight penalty.


The addition of all these systems increases weight more than the weight of the oxidizer they replace. This demands extremely high performance materials and very high efficiency systems for the vehicle to be commercially viable.