Direct Simulation Monte Carlo Simulations of Ballute Aerothermodynamics Under Hypersonic Rarefied Conditions

Abstract

This paper presents computational results obtained with the direct simulation Monte Carlo method for towed ballute applications. A ballute is an inflatable drag device that can be used to create a large amount of drag at high altitudes. Consequently, ballutes provide a potential technology for achieving aerocapture when the primary spacecraft velocity reduction ( V) is achieved at much higher altitudes than with the conventional rigid aeroshell. Because the V is achieved at relatively high altitudes, rarefaction can be significant and is the motivation for the current study with the direct simulationMonte Carlo method. Computed surface and flowfield results are presented for a toroidal ballute, isolated tethers when exposed to freestream flow conditions, and the flow interactions resulting from a toroidal ballute when towed by a 6 m diameter Mars Pathfinder shaped (without tethers) spacecraft. All results presented are for Earth entry at velocities of 14 to 7 km=s (primary focus is at 8:55 km=s, same as some previous Titan aerocapture studies) and altitudes of 200 to 100 km. Variations of drag and heating coefficients as a function of rarefaction are presented. Adescription of theflow structure is provided and also an explanation of how it is affected by shock interactions produced solely by the ballute and those resulting from the two body combination of towed ballute and spacecraft is also given.