Direct Simulation Monte Carlo Investigation of Hyperthermal Oxygen Beam Exposures

Pulsed sources of hyperthermal O-atoms are now being extensively used to simulate low-Earth-orbit (LEO) surface exposure environments. The peak flux of these sources is many orders of magnitude larger than the corresponding LEO flux. Although it is desirable to accelerate the test by using higher fluxes than found in LEO, even commonly used fluxes are large enough to produce multicollision effects by causing a buildup of gas at the sample surface. We characterize the physical consequences to the experiment using the direct simulation Monte Carlo (DSMC) method. DSMC allows us to extract the distributions of energy and impact angle for the O-atoms that reach the surface and to record how strongly the gas buildup at the target assembly deflects flux from downstream instrumentation. By considering a range of source fluxes, we determine the onset conditions and severity of these multicollision effects. We find that, depending on the target properties, even at common experimental fluxes with a normally incident beam striking a flat surface sample, the energy distribution of incident O-atoms can broaden and develop a significant low-energy tail. The distribution of the angle of impact can also broaden significantly, and the number of O-atoms that reach downstream instrumentation can be attenuated by as much as ∼50%. These simulations will aid in the calibration of ground-based O-atom measuremehts and provide a model for the energy and angular distributions of O-atoms that actually impinge on surface samples.

[1]  M. M. Finckenor,et al.  Material Selection Guidelines to Limit Atomic Oxygen Effects on Spacecraft Surfaces , 1999 .

[2]  Graham S. Arnold.  Spacecraft contamination model development , 1998, Optics & Photonics.

[3]  Matthew Braunstein,et al.  Simulations of Ground and Space-Based Oxygen Atom Experiments , 2003 .

[4]  S. Koontz,et al.  Flight mass-spectrometer calibration in a high-velocity atomic-oxygen beam , 1995 .

[5]  Timothy K. Minton,et al.  DYNAMICS OF ATOMIC-OXYGEN-INDUCED POLYMER DEGRADATION IN LOW EARTH ORBIT , 2001 .

[6]  L. S. Bernstein,et al.  The Theory Behind the SOCRATES Code , 1992 .

[7]  Amy Brunsvold,et al.  Erosion of Kapton ® H by Hyperthermal Atomic Oxygen , 2006 .

[8]  Timothy K. Minton,et al.  Reactive and inelastic scattering dynamics of hyperthermal oxygen atoms on a saturated hydrocarbon surface , 2002 .

[9]  R. Tennyson.  Atomic oxygen effects on polymer-based materials , 1991 .

[10]  G. Bird.  Molecular Gas Dynamics and the Direct Simulation of Gas Flows , 1994 .

[11]  Graeme A. Bird,et al.  MONTE-CARLO SIMULATION IN AN ENGINEERING CONTEXT , 1980 .

[12]  Matthew Braunstein,et al.  Direct simulation Monte Carlo modeling of high energy chemistry in molecular beams: Chemistry models and flowfield effects , 2002 .

[13]  A. Hedin.  MSIS‐86 Thermospheric Model , 1987 .

[14]  B. Banks,et al.  Scattered atomic oxygen effects on spacecraft materials , 2003 .

[15]  Bruce A. Banks,et al.  Monte Carlo Computational Modeling of the Energy Dependence of Atomic Oxygen Undercutting of Protected Polymers , 2001 .

[16]  Nobuo Ohmae,et al.  Impingement angle dependence of erosion rate of polyimide in atomic oxygen exposures , 2002 .

[17]  Amy Brunsvold,et al.  Measurements and simulations of high energy O(3P) + Ar(1S) angular scattering: single and multi-collision regimes. , 2004, The Journal of chemical physics.

[18]  Bruce A. Banks,et al.  Atomic-oxygen undercutting of Long Duration Exposure Facility atomized-Kapton multilayer insulation , 1994 .