A system of hypersonic drag mitigation is proposed. It is based on injection of light and/or hot gas in a new, isobaric mode, in order to form a "gaseous fore body" and to protect the frontal part of the surface of a hypersonic vehicle from formation of the hypersonic boundary layer. The effectivity of application of the proposed system depends on whether the advantages of the drag mitigation outweigh the drawbacks of storing of the additional gas. The question was studied with help of complex (integral) modeling of the hypersonic flying vehicles. There were compared two designs of hypersonic vehicles, which were able to implement the same mission. One of the designs included a solid propellant rocket engine to compensate the hypersonic aerodynamic drag, the other one applied the system of hypersonic drag mitigation with a continuous injection of helium. The complex models took into account the internal (engine) and external gas dynamics with the shock wave drag and surface friction, flight dynamics in the exponential atmosphere, mass change, flight control, etc. Computations have demonstrated that the start mass of the first vehicle was approximately twice as big as that of the second one. An additional advantage of the system of hypersonic drag mitigation is a considerable growth of the available coolant, which can provide comfortable thermal onboard conditions. Thus, there are cases, for which it is advantageous to apply the proposed system of hypersonic drag mitigation.