Modelling and Open Loop Simulation of Reentry Trajectory for RLV Missions

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 4TH International Symposium on ATMOSPHERIC REENTRY VEHICLES & SYSTEMS ARCACHON, FRANCE, 21-23 March 2005

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 Motivation, Aim and Scope

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

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

Inertial / Body Coordinates Inertial Coordinate System Body Coordinate System

Vehicle Attitude Coordinates Wind Axis System Euler Angles

Vehicle Models Aerodynamic ModelCoefficient Based Propulsion ModelAtmospheric corrections

Subsystem Models Sensors2nd order dynamics Navigation2 Error Models Larger errors for pure inertial Navigation Smaller errors for combined Navigation Actuators2nd order dynamics

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

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

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

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

Modelling and Open Loop Simulation of Reentry Trajectory for RLV Missions