Vehicle Design of a Sharp CTV Concept Using a Virtual Flight Rapid Integration Test Environment

In an effort to improve the overall aerospace vehicle design process, a design environment that merges technologies from piloted simulations, computational fluid dynamics, wind-tunnel and flight test data is currently under development at NASA Ames Research Center. The specific objective of this project, entitled Virtual Flight Rapid Integration Test Environment, was to assess the role that piloted simulations can play in the conceptual design of advanced vehicles. As a result, a conceptual design study of a Crew Transfer Vehicle was undertaken to demonstrate this rapid turn-around process. This process included aerodynamic models generated from computational fluid dynamic methods, data validation from wind-tunnel testing, and a high fidelity pilot-inthe-loop motion-based flight simulation. These vehicles were designed using multi-point numerical optimization methods coupled with an Euler flow solver. A low-speed wind-tunnel test was conducted to validate the low-speed aerodynamics database. A piloted simulation experiment was conducted to evaluate the low-speed handling qualities of the various configurations in the approach and landing phase. Six astronaut pilots evaluated each of the configurations using Cooper-Harper ratings. The knowledge gained from the simulation data and pilot evaluations was quickly returned to the design team. From these findings, a new configuration was developed and cycled back through the simulation evaluation. This paper will summarize the design process of the Virtual Flight Rapid Integration Test Environment and discuss the results of the design study including the piloted simulation experiment. Introduction The Virtual Flight Rapid Integration Test Environment (RITE) project was initiated to develop an * Aerospace Engineer, Senior Member † Aerospace Engineer, Associate Fellow ‡ Research Scientist information technology process to rapidly and easily merge data from computational fluid dynamics (CFD), wind tunnel, and/or flight test into a real-time, piloted flight simulation. The process then cycles the knowledge gained from the simulation back into the design process. To accomplish this, a new engineering design environment was constructed that combined these various data generation methods and test environments within one infrastructure. The goal of this project was to develop such a design environment to improve current design methodologies and to reduce design cycle time. Current design environments do not allow data transfer and integration to take place easily between the different technologies during the preliminary design. By providing an infrastructure that brings together all these technologies, designers will be better equipped with higherfidelity tools and methods, including simulation studies, which will lead to higher-fidelity preliminary designs. The main advantage of conducting piloted simulation studies early is to identify problems and deficiencies in aerodynamic performance, vehicle stability and control, and guidance and navigation, which can be addressed in the preliminary design phase. Simulation studies also allow for the opportunity to develop preliminary control systems early in the developmental phase. Historically, the outer mold lines of a design are defined before simulation studies and control system development can begin which may lead to expensive and complex control systems and less than optimal vehicle performance. The Space Shuttle Orbiter, which was designed in the 1970’s, is an example of such developmental problems. More recent design studies have used simulation tools in the design phase but without an infrastructure and process in place to facilitate and expedite its use. 3 Presently, the Virtual Flight RITE project has demonstrated the rapid and seamless integration of CFD, flight, and wind-tunnel data into a simulation database. During an early phase of the project, the Space Shuttle Orbiter was selected as the baseline configuration for this re-design demonstration. The radius and length of the nose of the Orbiter were altered as the design parameters. This phase of the project led AIAA Atmospheric Flight Mechanics Conference and Exhibit 5-8 August 2002, Monterey, California AIAA 2002-4881 Copyright © 2002 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner. American Institute of Aeronautics and Astronautics 2 to a successful demonstration of integrating CFD, flight and wind-tunnel data into a simulation database for rapid preliminary design work. More recently, an integrated design process augmented by the RITE process was used to develop a viable conceptual design for a Crew Transfer Vehicle (CTV). The goal of this work was to develop an optimal design for a CTV while improving the tools and techniques of the RITE process. CTV concepts are being studied as elements of various launch architectures under the 2 Generation Reusable Launch Vehicle program. NASA Ames Research Center personnel developed conceptual designs for a candidate CTV which is presented here and in Reference 4. The primary mission objectives of the CTV included orbit-to-orbit transfer and rendezvous with the International Space Station (ISS). The Ames preliminary designs included the ultrahigh temperature ceramic (UHTC) material. This new UHTC material enabled the use of sharp leading edges and nose geometries during hypersonic flight. Historically, re-entry space vehicles have been designed using blunt-body concepts to meet the temperature constraints of current thermal protection material. Because of unique structural, thermal and chemical properties, UHTC’s are capable of nonablating operation approaching 5100 deg. F. Using this new material, designers were allowed to use sharpbodied concepts in the conceptual designs. As has been reported, sharp-bodied designs for reentry can greatly improve the crossrange, allowing significantly greater flexibility in selecting re-entry trajectories and landing sites. However, achieving good transonic and subsonic flight characteristics for this class of vehicle presented a challenge to the designers, which warranted the study of the approach and landing characteristics. The RITE process was ideally suited for this design study because it provided the infrastructure needed for simulation studies to be integrated into this design process. For this reason, the CTV design was selected as the next case study under the RITE process. This paper will present the results of this study and process, which included vehicle design optimization, CFD, wind tunnel and a full-motion simulation experiment conducted in the NASA Ames Vertical Motion Simulator (VMS) facility. The objectives of this experiment were to evaluate the approach and landing flight characteristics of the CTV and to develop a control system optimization tool for use in the RITE process. Six astronaut pilots evaluated the handling qualities of the CTV configurations and for comparison purposes, also evaluated the handling qualities of the Space Shuttle Orbiter and NASA-Langley’s HL20 design. The details of this simulation experiment and significant results will be summarized in this paper. This paper will also contain a detailed summary of the overall integrated design process including the RITE process used in developing a design for the CTV vehicle concept. Integrated Design Process Various sharp-bodied design concepts for the CTV were developed for study using an integrated design framework developed under the High Performance Computing and Communication Program (HPCCP) and Information Technology (IT) Base Programs. This integrated design process was further augmented by the RITE process to evaluate concepts during approach and landing through piloted simulations. A summary of this integrated design process including the RITE process is outlined in Figure 1. Initially, the configurations were designed using a Newtonian-based aerodynamic method in the hypersonic speed regime. Surface geometry was defined using the Rapid Aircraft Modeler (RAM), ProEngineer and Gridgen computer programs. Volume grids for the new geometry were generated using CART3D for the unstructured, cartesian Euler solutions, MESH3D for the unstructured tetrahedral Euler-flow solutions, and Gridgen for the structured Navier-Stokes flow solutions. Data generation methods included methods of various levels of fidelity including vortex lattice methods, Euler methods and