Effect of different flight conditions at the release of a small spacecraft from a high performance aircraft

In recent years, mainly due to miniaturization of electronics as well as to the improvement of computer performance, small spacecraft have increased their capabilities. More and more frequently specific mission objectives can be achieved with cheap satellites of reduced size. The growing use of small satellites stimulates the development of systems specifically dedicated to orbit injection of small payloads. In this context, one option is represented by air-launched rockets. The use of an air-launched rocket for delivering a small payload into the desired orbit has several advantages. First of all, payload release is much more flexible, because the delivery conditions are directly related to the dynamics of the aircraft and can be viewed as independent of ground facilities. In addition, reduced costs are associated with higher efficiency of an aircraft in the lower layers of the atmosphere with respect to traditional ground-launched rockets. To date, air-launched rockets separate from the ail-craft in a horizontal flight condition. Then they maneuver in order to achieve the correct flight path angle for injecting into a gravity-turn arc of trajectory. Relevant losses are associated to this pitch maneuver; in addition, in this phase the rocket usually needs an aerodynamic control. Hence, the release of a rocket departing with a high flight path angle from the aircraft would avoid these losses and would simplify the control system, because in such a Situation the pitch maneuver becomes unnecessary: This paper is aimed at investigating the dynamic behavior and performance of a payload delivered from a high performance aircraft, which flies with a high flight path angle. In particular, this work is concerned with showing the differences and tradeoffs among different starting conditions of a multistage air-launched rocket related to several flight path angles of the aircraft at release. An optimal system configuration, which allows placing a micro-satellite into a specified low Earth orbit, is proposed. This configuration is selected by optimizing the release condition, the mass distribution among the stages, and the trajectory (through the determination of the optimal control law). (C) 2009 Elsevier Ltd. All rights reserved.