DSMC simulations of blunt body flows for Mars entries - Mars Pathfinder and Mars Microprobe capsules

Abstract

ABSflRACTThe hypersonic transitional flow aerodynamics of the Mars Pathfinder and Mars Microprobe capsules are simulated with the direct simulation Monte Carlo method. Calculations of axial, normal, and static pitching coefficients were obtained over an angle of attack range comparable to actual flight requirements.Comparisons are made with modified Newtonian and free-molecular-flow calculations. Aerothermal results were also obtained for zero incidence entry conditions. NOMENCLATURE acceleration axial force coefficient drag coefficient heat transfer coefficient mass fraction of species i normal force coefficient pitching moment coefficient about center of gravity pitching moment coefficient about nose maximum probe diameter Knudsen number pressure heat transfer rate afterbody radius maximum probe radial dimension comer radius *Aerospace Engineer, Aerothermodynamics Branch, Aero-and Gas-Dynamics Division, Fellow AIAA. +Aerospace Engineer, Aerothermodynamics Branch, Aero-and Gas Dynamics Division, Senior Member AIAA *Aerospace Engineer, Aerothermodynamics Branch, Aero-and Gas Dynamics Division. INTRODUCTIONDuring the next decade, mapping and inspection missions to Mars will occur with considerable frequency utilizing orbiters, landers and penemtors. The NASA Planetary Exploration Program plans for a pair of spacecraft to be sent to Mars every twentysix months for the next five years. This activity was initiated in late 1996 with two successful launches: first, the Mars Global Surveyor spacecraft which will provide an orbiting platform and, second, the Mars Pathfinder scheduled for a Mars landing July 4, 1997.The Mars Pathfinder mission will demonstrate a low-cost delivery system** to the surface of Mars while providing unique opportunities for scientific exploration. The entry vehicle contains a scientific instrument platform and a small rover that will be placed on the surface of Mars. Pathfinder is viewed as is statically unstable for the k molecular and much of the transitional flow regime, that is, the flow regime bounded by fke molecular and continuum flow. However, as shown from trajectory calculations, the gyroscopic effect of the vehicle spin is adequate for preventing unacceptable increases in vehicle attitude during the transitional portion of entry. A second requirement for Pathfinder rarefied aerodynamics is to support the atmospheric structure experiment where data obtained from accelerometer measurements will allow the extraction of atmospheric density as well as pressure and temperature. Accuracy of the atmospheric structure experiment depends directly on the accuracy of the probe axial force coefficients.Upon arrival at Mars, the Microprobes will be released from the Surveyor spacecraft and begin a k fall to the surface. The capsule forebody is a spherically blunted 45" half angle cone followed by a hemispherical backshield with a maximum body diameter of 0.35 m. A unique aspect of the Microprobes' entries is that the vehicles will encounter Mars' outer atmosphere in a random state, potentially t...

Prediction and validation of Mars Pathfinder hypersonic aerodynamic data base

“…al. 11 predicted static instabilities in the transitional regime for Path nder as a function of Knudsen number variation.…”

Analysis of Entry Vehicle Aerothermodynamics Using the Direct Simulation Monte Carlo Method

“…The moment curve slope increases with gas rarefaction and even changes sign. 13,14 Thus, the vehicle's pitch stability goes from being statically unstable to statically stable as it descends into the atmosphere. The figure does not consider the effect of changing the accommodation coefficient.…”

All-Particle Multiscale Computation of Hypersonic Rarefied Flow

“…For example, the Mars Pathfinder directly entered the Martian atmosphere as an entry capsule [1,2]. It was released from the spacecraft at 130.9km and began a descent to the surface.…”