Optimal Trajectories of Responsive Air - Launched Systems

Topic: Flight Dynamics) In recent years, a number of countries have shown a growing interest towards air-launched systems [1-6]as a suitable option to perform missions devoted to the responsive coverage of specific areas [7]. Air-launched systems exhibit some practical advantages with respect to conventional ground-launchedsystems [8]. First, only a limited number of ground operations is needed to integrate the launch system. Thiscircumstance greatly reduces the time required for completing all the necessary procedures before launch. Inaddition, air-launched systems are dropped at high altitudes, associated to a lower dynamical pressure, whichimplies reduced structural and thermal stresses. This circumstance allows employing advanced, (possibly)lighter materials. The engine pressure losses are also reduced, due to the fact that the expansion ratio can beincreased. Moreover, such systems are much more reliable under unfavorable weather conditions. Definitely,air-launched systems are capable of ensuring a flexible, ready-on-demand release of small payloads, becausethe delivery conditions are directly related to the aircraft dynamics and can be viewed as nearly independentof ground facilities. This work addresses the determination of the optimal trajectories for injecting a reducedsize payload into a circular orbit through an air-launched system, which is represented by a multistage rocketwith given characteristics. The control is performed through the thrust direction and magnitude. Theperformance attainable depends also on the flight path angle at rocket release, which is unspecified andtherefore is optimized. Several cases are considered, to determine the performance with respect to different(propulsive and structural) characteristics of the rocket and distinct terminal conditions at injection. Theoptimization method employed in this research is based on the conversion of the optimal control probleminto a nonlinear programming problem through the discretization of the control variables. As an illustrativeexample, the optimization process is applied to a hypothetical rocket dropped from an existing militaryaircraft. References[1] A. Ferri, “The launch of space vehicles by air-breathing lifting stages,” Vistas in Astronautics, v. 2, Pergamon Press, London, 1958[2] P. Teofilatto, and P. Cesolari, “A ready to launch system by EFA carried Small rocket,” Proceedingsof the First Conference Military Space: Questions in Europe, Paris, 25-27 April 2005.[3] T. Chen, W. Preston, W. Ferguson, and D. Deamer, J. Hensley, “Responsive air launch using F-15Global Strike Eagle,” Proceedings of the 4 Responsive Space Conference, Los Angeles, 24-27 April 2006[4] A. Degtyarev, and O. Ventskovsky, “Yuzhnoye Perspective Launch Systems,” paper IAC-06-D.2.1.04, AIAA Preston, 2006.[5] J. Woo Lee, K. Ho Noh, and Y. Hwan Byun, “Preliminary design of the hybrid air launching rocketfor nanosat,” Proceedings of the 5 International Conference on Computational Science and Applications,2007.[6] J. Summers, G. Heinsohn, and G. Hegemann, “Launch on demand; A Revolutionary Paradigm for Space Utilization,” Procedings of the 1stResponsive Space Conference, Redondo Beach, 1-3 April 2003[7] J. R. Wertz, “Coverage, Responsiveness and Accesibility for Various Responsive Orbits,” Proceedings of the 3rdResponsive Space Conference, Los Angeles, 25-28 April 2005[8] M. Labib, and T. Kaya, “A comparative Investigation of a ground and air launch of LEO-boundSmall Satellites,” paper IAC-05-E.2.2.05, AIAA Preston, 2005