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The Mars Science Laboratory contains an atmospheric data system that takes measurements of the pressure distribution on the entry body during the hypersonic and supersonic descent phases of flight. The pressure data can be combined with other onboard sensors, such as accelerometers, gyroscopes, and radar altimeters, to estimate the flight's trajectory, aerodynamics, and atmospheric profile. The number of sensors and their locations for the atmospheric data system can be optimized to increase the accuracy of the postflight reconstruction. Pressure-port placement optimization methodologies using the estimation residual and a surrogate of the observability matrix are presented, and the results of the optimization for Mars entry, descent, and landing vehicles are shown. The results of the optimization exhibited some sensor configurations that can improve upon the reconstruction performance of the Mars Science Laboratory baseline and also pointed to the number of sensors that define the point of diminishing returns with respect to estimation quality. These techniques can be subsequently applied in the design of instrumentation suites of future entry, descent, and landing vehicles.

Abstract-The U.S and the U.S.S.R. have sent seventeen successful atmospheric entry missions to Venus. Past missions to Venus have utilized rigid aeroshell systems for entry. This rigid aeroshell paradigm sets performance limitations since the size of the entry vehicle is constrained by the fairing diameter of the launch vehicle. This has limited ballistic coefficients (β) to well above 100 kg/m 2 for the entry vehicles. In order to maximize the science payload and minimize the Thermal Protection System (TPS) mass, these missions have entered at very steep entry flight path angles (γ). Due to Venus' thick atmosphere and the steep-γ, high-β conditions, these entry vehicles have been exposed to very high heat flux, very high pressures and extreme decelerations (upwards of 100 g's).Deployable aeroshells avoid the launch vehicle fairing diameter constraint by expanding to a larger diameter after the launch. Due to the potentially larger wetted area, deployable aeroshells achieve lower ballistic coefficients (well below 100 kg/m 2 ), and if they are flown at shallower flight path angles, the entry vehicle can access trajectories with far lower decelerations (~50-60 g's), peak heat fluxes (~400 W/cm 2 ) and peak pressures. The structural and TPS mass of the shallow-γ, low-β deployables are lower than their steep-γ, high-β rigid aeroshell counterparts at larger diameters, contributing to lower areal densities and potentially higher payload mass fractions. For example, at large diameters, deployables may attain aeroshell areal densities of 10 kg/m 2 as opposed to 50 kg/m 2 for rigid aeroshells. However, the low-β, shallow-γ paradigm also raises issues, such as the possibility of skip-out during entry. The shallow-γ could also increase the landing footprint of the vehicle. Furthermore, the deployable entry systems may be flexible, so there could be fluid-structure interaction, especially in the high altitude, low-density regimes. The need for precision in guidance, navigation and control during entry also has to be better understood. This paper investigates some of the challenges facing the design of a shallow-γ, low-β entry system.

Flight data from an entry, descent, and landing (EDL) sequence can be used to reconstruct the vehicle's trajectory, aerodynamic coefficients and the atmospheric profile experienced by the vehicle. Past Mars missions have contained instruments that do not provide direct measurement of the freestream atmospheric conditions. Thus, the uncertainties in the atmospheric reconstruction and the aerodynamic database knowledge could not be separated. The upcoming Mars Science Laboratory (MSL) will take measurements of the pressure distribution on the aeroshell forebody during entry and will allow freestream atmospheric conditions to be partially observable. This data provides a mean to separate atmospheric and aerodynamic uncertainties and is part of the MSL EDL Instrumentation (