Launch vehicle mass reduction using a scramjet powered flight segment

Abstract

With the recent success of scramjet powered atmospheric flights, it may soon become possible to utilise hypersonic airbreathing stages for payload delivery to orbit. A mission is therefore investigated to deliver a 400kg payload to low earth orbit using an airbreathing flight segment. Specifically, this paper investigates the use of an upper atmospheric cruise flight, using scramjet propulsion, to accelerate a second stage vehicle to the upper limits of the scramjet operating range. It is assumed a booster is used to achieve the required scramjet ignition conditions and a third stage is used to accelerate the payload from scramjet shut-down to orbital conditions. An optimisation routine is used, coupled with a trajectory simulator, to optimise a parameterised trajectory. The angle between the lift force on the body and the free-stream velocity is used as an optimisation parameter to control a lifting trajectory, which achieves the required target conditions. The trajectory simulator includes a full spheroidal, rotating Earth model, a fourth order gravitation model and an MSISE93 atmosphere model. A fourth order Runge-Kutta integration routine is used to integrate the trajectory and a gradient projection optimisation routine is used to achieve an optimal solution. From both a gross lift-off mass and a propellant consumption point of view, a part scramjet powered vehicle is seen to have a performance advantage over a totally conventional rocket powered vehicle.