Modelling and Open Loop Simulation of Reentry Trajectory

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

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

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

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 Guidance & Control Dynamics - Translational - Rotational - Kinematics

Inertial / Body Coordinates Inertial Coordinate System Body Coordinate System

Vehicle Attitude Coordinates Wind Axis System Euler Angles

Vehicle Models Aerodynamic Model Coefficient Based Propulsion Model Atmospheric corrections

Subsystem Models 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

Other Models Earth • Oblate Earth with zonal harmonics up to 4 th Jeffrey term considered Atmosphere • pa , r , T, Cs as functions of altitude • Flexibility of defining any atmosphere Wind • Zonal and Meridional components

Simulation Algorithm Schematic Atmospheric Model Flight Dynamics Aero Parameters Model Actuator Dynamics Mass Properties Kinematics INS Sensor Simulator Aerodynamic Model Air Data Simulator Gravity Model Earth Model RCS Simulator Flight Control GPS Simulator Navigation Package Guidance Propulsion Model

Open Loop Simulation Method v Reentry trajectory modulation by aerodynamic angles v Simulation by perturbing angles , & v Assumption: Ideal control v Parameters monitored: Input : , & Output : h, VR, ground trace (lat – / long – ) v Test cases Case-1 Case-2 Case-3 Case-4 : Bank angle = 0 : 10 o change in

Open Loop Simulation: = 0 Control Inputs

Open Loop Simulation: = 0 Time Histories

Open Loop Simulation: = 0 Ground Trace

Open Loop Simulation: = 10 Control Inputs

Open Loop Simulation: = 10 Time Histories

Open Loop Simulation: = 10 Ground Trace

Open Loop Simulation: = 10 Control Inputs

Open Loop Simulation: = 10 Time Histories

Open Loop Simulation: = 10 Ground Trace

Open Loop Simulation: = 10 Control Inputs

Open Loop Simulation: = 10 Time Histories

Open Loop Simulation: = 10 Ground Trace

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