1. Satellite Drag in the Re-entry Region Brian Argrow Dept. Aerospace Engineering Sciences University of Colorado NADIR MURI 21 October 2008

2. Focus Area VIII: Satellite Drag in the Re-Entry Region Motivation Accurate knowledge of satellite C D is essential for accurate prediction of satellite drag, and for inferring densities from accelerometer measurements Insufficient knowledge exists about C D in the transition and slip-flow regimes (i.e., < 150 km) Objective: To significantly advance understanding of satellite drag in the transition and near-continuum regimes using state-of-the art numerical modeling, and to provide C D predictions under a broadened range of conditions Brian Argrow and Jeff Forbes (CU)

3. High-Altitude Simulations with the Direct Simulation Monte Carlo (DSMC) Method 130 km 100 km Methodology –Direct Simulation Monte Carlo (DSMC) with calibrated gas-surface interaction models –Bird’s DS3V –NASA DSMC Analysis Code (DAC) –Investigate gas surface interaction models and produce calibrated modules to couple with DSMC

4. 0.010.1110100 Discrete Particle or Molecular Model Continuum Model Collisionless Boltzmann Equation Boltzmann Equation Euler Eqs. Navier-Stokes Equations 0 ∞ Conservation Equations Do Not Form A Closed Set Free-Molecule Limit Inviscid Limit Local Knudsen Number Flow Regimes and Governing Equations* *Bird, G., Molecular Gas Dynamics and the Direct Simulation of Gas Flows Why DSMC? Local Kn often violates the global free-molecular flow assumption

5. Milestones and Deliverables YrMilestonesDeliverables 1DAC-based simulations of simple 3-D geometries with candidate GSI models. DSMC/GSI with atmosphere model 2Down-select/calibrate GSI models w/ satellite data DSMC/GSI w/ calibrated GSI options 3DSMC computation of transition-regime aerodynamic coefficients Code to compute C D in slip/ transition flows for range of geometries 4Create database of altitude-dependent C D for representative satellites in transition flow. Integrated simulation environment code to produce C D database 5Complete DSMC/GSI code for trajectory simulations w/ direct modeling of flow environment Integrated simulation environment code to simulate real-time application

6. DS3V Example: 1-m, 75  Delta Wing

7. Input: 75  Delta Wing,  = 2  L = 1 m V  = 7.6 km/s H = 120 km Non-reacting Air (20% O 2, 80% N 2 ) T  = 360 K Kn  = 3.3 Fully diffuse reflection T surf = 300 K Output: Total Force F x = 1.2 N F y = -1.5 × 10 -3 N F z = -9.1 × 10 -5 N Pressure F x = 1.4 × 10 -4 N F y = 2.0 × 10 -3 N F z = -5.1 × 10 -4 N Shear F x = 1.2 N F y = -4.6 × 10 -4 N F z = 4.2 × 10 -4 N

8. DSMC Example: 2-m Sphere

9. Input: L = 2 m V  = 7.6 km/s H = 120 km Non-reacting Air (20% O 2, 80% N 2 ) T  = 360 K Kn  = 1.7 Fully diffuse reflection T surf = 300 K Output: Total Force F x = 4.2 N F y = -6 × 10 -3 N F z = -1 × 10 -3 N Pressure F x = 2.3 N F y = -6 × 10 -4 N F z = -1 × 10 -3 N Shear F x = 1.9 N F y = -1 × 10 -4 N F z = 1 × 10 -3 N

10. Current Status Year 1 Summary –Hywapyong Ko, PhD candidate (started Aug 08) –Simulations of simple geometries with DS3V –Paperwork completed for DAC97 (July 08) –Dedicated 8-processor workstation Year 2 Focus –Development of DAC + gas/surface modeling –New course on Molecular Gas Dynamics (Sp 09)