Co-Optimization of Mid Lift to Drag Vehicle Concepts for Mars Atmospheric Entry

Abstract

As NASA continues to make plans for future robotic precursor and eventual human missions to Mars, the need to characterize and develop designs for entry vehicles capable of delivering large masses to the surface of Mars will persist. In combination with this, NASA has recognized that the current heritage technology for Mars' Entry Decent and Landing (EDL) does not have the capability to land the required payload masses. Both the Thermal Protection System (TPS) and the Descent/Landing systems require new design approaches. Because of these needs, NASA has performed an Entry, Descent and Landing Systems Analysis (EDL-SA) study for high mass exploration and science missions to identify key enabling technology areas for further investment. One key technology area identified includes rigid aeroshell shapes for aerodynamic performance and controllability.In this investigation, a system optimization study of alternative aeroshell shapes for Mars exploration class payloads of approximately 40 metric tons has been conducted. This system optimization is accomplished using a Multi-disciplinary Design Optimization (MDO) framework which accounts for the aeroshell shape, trajectory, thermal protection system, and vehicle subsystem closure along with a Multi Objective Genetic Algorithm (MOGA) for the initial shape exploration. This is accomplished using a combination of engineering analysis and higher-fidelity physics based tools along with optimization methods and engineering judgment. The results of this process have shown that a proposed family of optimized mid lift-to-drag aeroshell shapes exhibit a significant improvement to the current reference entry rigid aeroshell configuration. Furthermore, a trade-off between the vehicle TPS and structural mass is identified for this class of aeroshell shapes and their corresponding trajectories. Balancing this trade-off can yield an overall decrease in the total vehicle mass or corresponding increase in landed payload, as compared to the current reference configuration. NomenclatureA = Effective projected vehicle area CD = Drag coefficient CDa = Drag Area, m 2 CL = Lift coefficient Cm = Pitching moment coefficient Cm α = Pitching moment coefficient curve slope variation with angle-of-attack, /deg. 0 = Earth's gravity constant (g 0 = 9.80665 m/s2) Isp = Specific impulse, sec (on earth) L B = Body Length, m L B_REF = Reference Body Length, m L/D = Lift-to-drag ratio m_Entry = Entry Mass, kg m_Entry REF = Reference Entry Mass, kg m payload = Payload mass, kg MaxQdot = Maximum Heat flux on the body, W/cm 2 qmax = Maximum dynamic pressure, Pa hload = Integrated heatload, J/cm 2 Re = Reynolds Number RCS = Reaction Control System RSS = Root Sum Square Swet = Wetted vehicle surface area, m 2 TPS = Thermal Protection System UWT_Body REF = Reference body structural areal mass M ∞ = Free-stream Mach number αtrim = Trim angle-of-attack, deg. ρ ∞ = Free-stream density, kg/m 3

Coupled Fluids-Radiation Analysis of a High-Mass Mars Entry Vehicle

“…2., the Ellipsled consists of a 5 m radius hemispherical cap placed on a 10 m diameter cylinder. The overall length of the Ellipsled is 30 m. The 10x30 Ellipsled was previously analyzed by Steinfeldt et al [5], Garcia et al [8], Dwyer-Cianciolo et al [3], and Engelund et al [7]. The nominal L/D for the Ellipsled was 0.5.…”

“…A fair amount of system-level analysis has been performed on high-mass Mars vehicles in Refs. [1]- [8], but to date there has been little detailed analysis of the aerothermal loads a high-mass Mars vehicle will experience while entering the Martian atmosphere. Steinfeldt et al [5] show convective heating rate results generated by the engineering-level tool CBAERO over both the 70-degree sphere cone and mid-L/D vehicles at one trajectory point.…”

“…Steinfeldt et al [5] show convective heating rate results generated by the engineering-level tool CBAERO over both the 70-degree sphere cone and mid-L/D vehicles at one trajectory point. Garcia et al [8] presented both CBAERO and computational fluid dynamic (CFD) convective heating rate solutions over mid-L/D vehicles at the peak heating point of a 7.36 km/s entry velocity trajectory. Isolated CBAERO and CFD solutions are shown in Ref.…”

“…In recent years, a number of studies have been performed to determine the vehicle and mission requirements that would enable the human exploration of Mars [1][2][3][4][5][6][7][8]. The vehicle geometries of these proposed high-mass Mars vehicles were based on 70-degree sphere cones, Apollo-type capsules, or a slender, mid lift-over-drag ratio (L/D) vehicle referred to as an Ellipsled.…”

“…No attempt was made in Refs. [3], [5], or [8] to calculate the level of radiative heating on the vehicle surface.…”