1. Modelling and Open Loop Simulation of Reentry Trajectory for RLV Missions Ashok Joshi and K. Sivan Department of Aerospace Engineering Indian Institute of Technology Bombay 4 TH International Symposium on ATMOSPHERIC REENTRY VEHICLES & SYSTEMS ARCACHON, FRANCE, 21-23 March 2005

2. Motivation, Aim and Scope Atmospheric reentry phase is expected to dissipate large orbital energy, efficiently Reentry phase is also an uncertain domain with respect to aerodynamics, propulsion and control Present study proposes mathematical models that reflect the complexity and at the same time retain the ease of their simulation A generic RLV is taken up for development of model and verification through simulations

3. RLV Configuration Wing-Body Configuration with both Aerodynamic and Reaction Control System Both FADS and SIGI Sensors Total of seven aerodynamic control surfaces i.e. 4 Elevons, one each of Body Flap, Rudder and Speed Brake

4. Generic RLV Dynamic Model Coordinate Systems Definition Vehicle Attitude Definition Coordinate Transformation Environmental Model - Earth shape - Gravity - Atmosphere - Wind Vehicle Model - Aerodynamics - Propulsion - Mass Properties Subsystem Model - Sensors - Navigation - Actuators Dynamics - Translational - Rotational - Kinematics Guidance & Control

5. Inertial Coordinate System Body Coordinate System Inertial / Body Coordinates

6. Wind Axis System Vehicle Attitude Coordinates Euler Angles

7. Aerodynamic Model Coefficient Based Propulsion Model Atmospheric corrections Vehicle Models

8. Sensors 2 nd order dynamics Navigation 2 Error Models Larger errors for pure inertial Navigation Smaller errors for combined Navigation Actuators 2 nd order dynamics Subsystem Models

9. Other Models Earth Oblate Earth with zonal harmonics up to 4 th Jeffrey term considered Atmosphere p a, r, T, C s as functions of altitude Flexibility of defining any atmosphere Wind Zonal and Meridional components

10. Simulation Algorithm Schematic

11. Open Loop Simulation Method  Reentry trajectory modulation by aerodynamic angles  Simulation by perturbing angles ,  &   Assumption: Ideal control  Parameters monitored: Input : ,  &  Output: h, V R, ground trace (lat –  / long –  )  Test cases Case-1: Bank angle = 0 Case-2: 10 o change in  Case-3: 10 o change in  Case-4: 10 o change in 

12. Open Loop Simulation:  = 0 Control Inputs

13. Open Loop Simulation:  = 0 Time Histories

14. Open Loop Simulation:  = 0 Ground Trace

15. Open Loop Simulation:  = 10 Control Inputs

16. Open Loop Simulation:  = 10 Time Histories

17. Open Loop Simulation:  = 10 Ground Trace

18. Open Loop Simulation:  = 10 Control Inputs

19. Open Loop Simulation:  = 10 Time Histories

20. Open Loop Simulation:  = 10 Ground Trace

21. Open Loop Simulation:  = 10 Control Inputs

22. Open Loop Simulation:  = 10 Time Histories

23. Open Loop Simulation:  = 10 Ground Trace

24. Conclusions Generalized 6-DOF Reentry Flight Dynamic Model of a Generic RLV is evolved Multiple coordinate systems are used for ease of representation Both RCS and Aerodynamic control surfaces are included, along with Flush Air Data Sensor and GPS 3-DOF Comparison with literature data validates the model & solution methodology Open loop simulations provide adequacy and sensitivity of the model presented