ASTOS 9.3 - MULTIBODY FEATURE FOR SIMULATIONS OF FLEXIBLE LAUNCHER DYNAMICS

1. ASTOS 9.3 - MULTIBODY FEATURE FOR SIMULATIONS OF FLEXIBLE LAUNCHER DYNAMICS andreas.wiegand@astos.de valerio.rossi@astos.de, sven.shaeff@astos.de, sven.weikert@astos.de

2. Outline • Company presentation • ASTOS & Multibody feature overview • Launcher flexibility • Sloshing dynamics • Stages separation • Engine propulsion oscillations • Conclusions ICATT 2018 6-9 November

3. Astos Solutions Company presentation ICATT 2018 6-9 November

4. Astos Solutions Overview • SME with sites in Unterkirnach (DE), Stuttgart (DE), Oradea/Sibiu (RO) • Spin-Off of the Univ. of Stuttgart, standalone company since 2006 • Roots of Astos Solutions go back to 1989 • Office in Stuttgart ICATT 2018 6-9 November

5. Astos Solutions’ Expertise Trajectory Optimization Multi-Disciplinary Vehicle Design Mission Analysis System Concept Analysis GNC Launch Structure & Tanks Navigation Analysis Thermal Control Sys. Launcher GNC Design Re-entry Propulsion System Link Budget Analysis Power System Robotics Low-thrust transfer Aerodynamics Coverage Analysis Data Systems Test beds Interplanetary Reference Trajectories Launch &Re-entry Safety Camera & Lidar Simulation Suborbital Asteroid Trajectory Propagation Magnetic Cleanliness Identification Pointing Error Engineering ICATT 2018 6-9 November

6. Astos Solutions’ Releveant Expertise Trajectory Optimization Multi-Disciplinary Vehicle Design Mission Analysis System Concept Analysis GNC Launch Structure & Tanks Navigation Analysis Thermal Control Sys. Launcher GNC Design Re-entry Propulsion System Link Budget Analysis Power System Robotics* Low-thrust transfer Aerodynamics Coverage Analysis Data Systems Test beds Interplanetary Reference Trajectories Launch &Re-entry Safety Camera & Lidar Simulation Suborbital Asteroid Trajectory Propagation Magnetic Cleanliness Identification Pointing Error Engineering ICATT 2018 6-9 November

7. Product Portfolio Spaceflight Design & Analysis Optimisation Testbed Visualization VESTA (OSS) ASTOS Camera/Lidar Simulator GESOP Vehicle Design ODIN MT-Aerospace dSPACE HIL-Unit SOS AMA Inc DCAP Exploration Asteroid Trajectory Propagation LOTOS WORHP SFZ GRAVMOD-2 POINT MIDACO Schlueter Magnetic Cleanliness Identification Pointing Error Engineering PEET (OSS, ESA) GAMAG ICATT 2018 6-9 November

8. Applicable Product Portfolio Spaceflight Design & Analysis Optimisation Testbed Visualization VESTA (OSS) ASTOS Camera/Lidar Simulator GESOP Vehicle Design ODIN MT-Aerospace dSPACE HIL-Unit SOS AMA Inc DCAP Exploration Asteroid Trajectory Propagation LOTOS WORHP SFZ GRAVMOD-2 POINT MIDACO Schlueter Magnetic Cleanliness Identification Pointing Error Engineering PEET (OSS, ESA) GAMAG ICATT 2018 6-9 November

9. Astos Solutions ASTOS & MULTIBODY FEATURE OVERVIEW ICATT 2018 6-9 November

10. ASTOS software • Built-in trajectory and multi-disciplinary design optimization • Performance and system concept analysis • Simulink and dSPACE interfaces for closed-loop simulations, HIL and SCOE applications • Trajectory optimization • Vehicle design optimization • Wide range of mission analysis features • Launch and re-entry safety analysis • Built-in plotting and animation tools • Built-in batch-processing engine and configuration tool ICATT 2018 6-9 November

11. DCAP software DCAP is a no-frills, rational, fast multi-body software tool, designed for assessing space systems and devices. • Symbolic order(n) dynamic formulation • Rigid and flexible bodies • Analytic flexible beam model • Transitions of hinge DOF state • Variable body properties • Gravity gradient • Contact and friction dynamics • Built-in space sensors and actuators • Non-linear devices ICATT 2018 6-9 November

12. Multibody feature overview The new multibody feature is design to address complex launcher simulations. • A launcher vehicle is a typical multibody system composed of several components. • The link ASTOS/DCAP is realised through ASCII files and dynamic libraries. • EoM are generated as auto-coded Fortran subroutines. • EoM are then compiled and linked for a fast interface with ASTOS. ICATT 2018 6-9 November

13. Multibody feature overview • DCAP computes the system dynamics and the state derivatives. • ASTOS provides the external forces such as: • gravity acceleration of each body; • aerodynamic forces; • actuators and engines output. • ASTOS finally performs the numerical integration. • The user never interacts directly with DCAP. • The post-processing is completely managed in ASTOS. ICATT 2018 6-9 November

14. Astos Solution LAUNCHER flexibility ICATT 2018 6-9 November

15. Flexible launcher structure • A launcher structure is a very long flexible slender beam. • Considering the components flexibility improves the overall launcher simulation reliability. • Structural deformations and deflections can alter the aerodynamic forces acting on the rocket. • The GNC system needs to handle those disturbances • Each component can be defined as flexible ICATT 2018 6-9 November

16. Flexibility model • A linear Euler-Bernoulli flexible beam model is used as flexibility model (no external FEM software) • Different mass distribution for liquid and solid propellant • Geometrical parameters automatically computed by ASTOS • The user inputs are: • Young modulus • Damping ratio • Number of flexible modes ICATT 2018 6-9 November

17. Mode shapes export • A dedicated export allows to compute the global mode shapes and frequencies at different point in time • This knowledge is crucial for the design of the GNC controller which takes into account also rocket deformations. Third mode shape of a flexible rocket model ICATT 2018 6-9 November

18. Astos Solution Sloshing dynamics ICATT 2018 6-9 November

19. Sloshing effect • The lateral dynamic force resulting from the motion of liquids in tanks is known as the sloshing effect. • Possible coupling between the sloshing effect, the mechanical structure and the control system leading to unstable dynamics • Computational Fluid Dynamics (CFD) model are not suitable for multibody simulation because of the high computational burden • Equivalent mechanical models are much more convenient for these applications Credits Flow Science ICATT 2018 6-9 November

20. Mechanical sloshing model Sloshing mass • Spring-mass mechanical system • Fuel is split into: • a static mass rigidly attached to the tank • one or more sloshing masses attached to the tank through spring-damper elements • One sloshing mass accounts for two flexible modes • In the ASTOS GUI, the user is required to provide only three high level inputs: • tank shape (cylindrical or spherical); • number of sloshing masses; • kinematic viscosity of the propellant. Static mass ICATT 2018 6-9 November

21. Sloshing model damping • Sloshing effect is minor when tank is almost empty • Damping coefficient depends on the tank geometry Cylindrical tank damping Spherical tank damping ICATT 2018 6-9 November

22. Astos Solution Stages separation ICATT 2018 6-9 November

23. Stages separation • The separation starts with the disconnection of two components (explosive bolts, pneumatic latches or explosive shaped charges) • A later process involves the actuators which actually separate the components (retrorockets, pneumatic thruster or elastic spring elements) ICATT 2018 6-9 November

24. Stages separation • The detachment process is achieved by a reconfiguration of the mechanical system (hinge releasing) • Separation devices: • hard-stop springs; • clamp bands; • actuators. • Clamp band separation device has been developed for payload release • Several linear springs are placed along a circumference Payload Clamp band Upper stage ICATT 2018 6-9 November

25. Clamp band separation device • High level settings • Springs misalignment and separation delay by using different mechanical properties for each spring (input table) • Simulation results of stage separation have been benchmarked with a commercial clamp band data sheet ICATT 2018 6-9 November

26. Astos Solution Engine pressure oscillations ICATT 2018 6-9 November

27. Engine pressure oscillations • The complex feedback mechanism involving vortex shedding and acoustic resonant mode produces pressure oscillations in solid rocket engines • Data available in literature shows a typical frequency around 50-60 Hz • Complex coupled CFD and FEM simulations are needed in order to estimate the frequencies involved • No equivalent mechanical models are available for multibody applications ICATT 2018 6-9 November

28. Time domain engine disturbances • Experimental or simulation data can be used in ASTOS as disturbances • Pressure oscillations contribution is added to the average engine thrust profile by superimposing a time domain signal • The signal is directly added to the average time domain Pressure oscillation (time domain) Average thrust Total engine thrust ICATT 2018 6-9 November

29. Frequency domain engine disturbances • The propulsion disturbances spectrum is associated by the user to a coloured noise and then superimposed to the average engine thrust • A red noise signal is converted into the time domain during the simulation and then added to the average thrust Pressure oscillation (red noise) Average thrust Total engine thrust ICATT 2018 6-9 November

30. Conclusions • The implementation of new EoM in ASTOS has improved the capability of the software to answer the need of aerospace engineers during the preliminary design of the vehicle. • The funding by ESA through multi-year projects made possible a comprehensive implementation in the most important areas of the vehicle design: structure and propulsion. • The dynamic coupling with DCAP opens a multitude of possibilities to use ASTOS for simulations (spacecraft with flex appendages, docking, towing, robotic arms, landing,...) • ASTOS is therefore an efficient simulation infrastructure to design launchers up to the phase B1. • This software is commercially available to all interested entities worldwide. ICATT 2018 6-9 November

31. ICATT 2018 6-9 November