Reconstruction of Mars Pathfinder Aeroheating and Heat Shield Response Using Inverse Methods

The Mars Pathfinder probe entered the Martian atmosphere in 1997 and contained instrumentation that provided measurements of the superlight ablator (SLA) heat shield subsurface temperature at different locations during the entry sequence. These measurements represented the first Martian aeroheating flight data since the Viking Lander missions. The objective of this paper is to reconstruct the Pathfinder entry vehicle's aerothermal heating and heat shield material response using updated modeling tools and approaches in both direct and inverse manners. The direct approach consists of performing updated computational fluid dynamics calculations on a newly reconstructed entry trajectory to characterize the vehicle's heating environment. From the calculated heating boundary conditions, the heat shield in-depth temperature response is computed using an updated thermal response and ablation model for the SLA material. These predictions are compared directly to the flight data. In addition to the direct comparison approach, inverse methods are used to estimate boundary conditions that result in a closer match between the flight data and subsurface temperature predictions. The unblown surface heat transfer coefficient is reconstructed as a function of time using whole-time domain least-squares methods in conjunction with regularization techniques.