MDO – Multidisciplinary Design Optimization for Launchers and Entry Vehicles

Project Objectives

The objective of the MDO framework is to provide an industrial grade tool which provides all functionality for the multidisciplinary vehicle design optimization of launch and reentry vehicles. The type of launcher shall be flexible with respect to number of stages, strap ons and chosen material and propellant. The used discipline models shall be selected such that All-At-Once optimization shall be possible and that the final design is robust against the inaccuracy of the discipline models. This required a clear improvement first of all for mass estimation models, second for propulsion system models and third for aerodynamic models in case launchers. In addition it is important to provide analysis functions to evaluate the quality of the design considering, e.g. the controllability, and a link of the MDO workflow to other workflows like GNC design or detailed structural and propulsion system design. Therefore the user shall be able to specify the following design requirements:

• Target orbit(s) and payload(s) and launch site(s)
• Number of stages, strap-on boosters and stage under fairing
• Propellant type
• Engine cycle of propulsion systems
• Specification of substructures (material and stiffening concept)
• Kind of tank

The output of the MDO framework presents

• Optimal design of stages and engines
• Dimensioning load cases for each substructure on level of cylinders, cones, bulkheads
• Statements about controllability and stability
• Finite element model export for purpose of frequency analysis
• Performance values of the propulsion systems
• Sizing of solid motor engines
• Graphical representation of the launcher design

Architecture

The MDO framework builds up on the existing ASTOS software, which has been extended for basic MDO functionality in the frame of ESA contract 22047/08/NL/ST. Within this MDO project ASTOS will be further improved in various disciplines and analysis methods. Especially ASTOS will be linked with the structural optimization software ODIN and the rocket propulsion analysis software RPA. While ASTOS is responsible for the whole scenario definition, the optimization itself and the analysis, ODIN is used first of all to compute mass regression tables to be used during the ASTOS optimization, second for the validation of ASTOS' structural design analysing the safety margins and third for the export of a FE-model.

Features

ASTOS is a general purpose astronautics software for mission and system analysis and trajectory and vehicle design analysis. The sophisticated graphical user interface provides rapid configuration and post-analysis capabilities. The figure below shows a screen shot of ASTOS, which presents in the left tree view an overview of the different input sections of ASTOS. The main window presents the selected Vehicle Builder of the launch vehicle, which allows assembling the launcher components and equipment such as thrusters.

ASTOS provides:

• Data driven setup of the scenario with the Model Browser
• Online help function
• Automatic reporting function
• Batch mode inspector for e.g. sensitivity analysis
• A set of optimization algorithm for various purpose
• Definition of all constraints and cost functions
• Definition of control laws for the optimal control, which are typically yaw and pitch in case of ascent scenarios

• Overview with graphical representation of the launch vehicle
• Trajectory
• COM and MOI evolution
• Key Trajectory Events comprising time points of maximum loads and of dimensioning line loads
• Final Orbit
• Table of substructures with stiffening concept, dimensions, mass and comparison with ODIN mass
• Plots of flux and pressure over x position for each dimensioning load case

Detailed documentation and tutorials are provided with ASTOS, which is commercialized as COTS software.

ODIN (Optimal Design INvestigations) is an answer to the need for a quick structural sizing tool within the MDO process. It is designed to perform a pre-dimensioning of main structural components basing on well-known numerical methods, thus providing a first assessment with respect to stage/launcher mass budget and consequently to launcher performance. The pre-dimensioning performed by ODIN relies on the usage of a random search method in order to assess a mass optimised design fulfilling user defined safety criteria. User inputs of ODIN are material, stiffening concept, geometry and dimension load case of shell structures like cylinder, cone, bulkhead, y-ring and strut cone. The objectives of ODIN are

• Mass estimation for the MDO process
• Analytical pre-dimensioning of main structural components and mass estimation for trade off purposes and phase A studies
• Preliminary sizing close to final design solution to reduce the number of FEM-calculations
• Export of a rough FEM-model for a complete stage
• Time reduction of preliminary designs from weeks to days
• Cost reduction of preliminary designs and reduced reaction time during tender processes