3-DOF Entry Descent and Landing Simulations of a Conceptual Entry Vehicle for Human Missions to Mars

Abstract

Landing humans on Mars for the purpose of exploring and expanding our knowledge of the solar system is one of the future goals of NASA. To do so will require a focus on entry, descent and landing systems. In support of that effort a Martian Entry Descent Landing Simulator (MEDLS) was developed and implemented in Matlab for the purpose of examining the entry trajectory of a spacecraft and understanding the size of an entry descent and landing (EDL) system required primarily for landing a crew on Mars. This was a two part effort involving the creation of MEDLS which is a nonlinear Newtonian entry dynamic model of three degree-of-freedom (DOF) that uses the Mars Global Reference Atmospheric Model (Mars-GRAM) output to model the Martian atmosphere, a gravitational force model treating Mars as a spheroid and Newtonian impact theory to model aerodynamic forces. The second part of the effort involved running simulations with a conceptual vehicle using an Orion Crew Module (CM) as the basis for the vehicle with a "modified" Service Module (SM) equipped to handle entry. EDL system size was restricted to an aeroshell no larger than 15 m in diameter, a parachute no larger than 30 m and a descent propulsion system designed to have constant thrust and bring the spacecraft to a landing speed of less than 2 m/s at 0 km in altitude. The entry trajectories were carried out first with a vehicle mass of 25000 kg (25 t) and second with a mass of 50000 kg (50 t) from an entry interface altitude of 125 km based on a Mars parking orbit arising from an opposition class Mars mission. This preliminary examination of entry trajectories shows that the 25 t conceptual spacecraft could deliver a maximum of 5928 kg of payload while the 50 t conceptual spacecraft could deliver a maximum of 10814 kg. Nomenclature A= heading angle, deg a I = inertial acceleration, m/s 2 α = angle of attack, deg C p = coefficient of pressure C τ = coefficient of shear stress C D = coefficient of drag C L = coefficient of lift C Y = coefficient of side force C Dfm = coefficient of drag free molecular flow C Lfm = coefficient of lift free molecular flow C DC = coefficient of drag continuum flow regime C LC = coefficient of lift continuum flow regime C Dp = parachute coefficient of drag e = eccentricity erf = error function ε = angle with respect to x-axis in wind coordinate reference frame , deg f D = force due to drag, N f T = force due to thrust, N f P = force due to parachute, N GM = Mars gravitational constant, km 3 /s 2 g r = radial direction of gravity vector, m/s 2 g δ = transverse direction of gravity vector, m/s 2 1 Project Engineer, Orion MPCV Program, Lockheed Martin, Houston, TX, Member AIAA. 2 g 0 = gravitational constant (Earth), m/s 2 h P = periapsis Altitude, km Isp = specific Impulse, s i = inclination, deg m = mass, kg = mass flow rate, kg/s θ = angle between velocity vector and vehicle surface, deg ϕ = flight path angle, deg δ = latitude, deg λ = longitude, deg σ N = normal momentum accommodation coefficient σ T = tangential momentum accommodation...