Present and future models for NASA's Heatshield Design
Ioana Cozmuta
2:30 PM on 2008-04-11
209 Akerman Hall
Abstract:
Spacecrafts that enter a planetary atmosphere (i.e. Earth, Mars) require the use of a thermal protection system (TPS) to protect them from aerodynamic heating. The aerodynamic heating is generated at the surface of an entering object due to the combination of compression and surface friction of the atmospheric gas. The vehicle's configuration and entry trajectory in combination with the type of thermal protection system used define the temperature distribution on the vehicle. The TPS system usually employs surface materials with a high temperature capability in combination with an underlying thermal insulation to inhibit the conduction of heat to the interior of the vehicle. The temperature limit a reusable TPS may withstand is lower than for ablative TPS. For reusable TPS, the main mechanism of dissipation for the heat developed from the aerodynamic heating process is by re-radiating it into space by virtue of the high surface temperature. For ablative TPS, pyrolysis (internal decomposition of the solid leading to release of gaseous species) and ablation (combination of processes which consume heatshield surface material) are the dominant mechanisms of efficient rejection of aerothermal heat load. Due to the wide variation of these surface temperatures the TPS selection is customized for each spacecraft and is composed of many different materials. Each material's temperature capability, durability and weight determine the extent of its application on the vehicle. A typical process for the evaluation of a new vehicle concept is usually based on the following steps: geometric representation, aerodynamic and aerothermal analysis, trajectory optimization, TPS selection and sizing, and weight and sizing evaluation. For design and sizing of spacecraft TPS materials it is imperative to have flexible and reliable numerical procedures which apply to both reusable and ablating TPS and which can compute surface mediated chemical interactions, internal temperature histories (conduction), surface recession rate and in-depth pyrolysis (the latter two being applied for ablative TPS only). To improve thermal protection material and vehicle performance, highly desired features of these materials are more durability, higher temperature capability, greater thermal shock resistance and lower thermal conductivity.
This talk will present an overview of NASA’s currently employed Thermal Protection System analysis and design capability as applied to ablative materials with the attempt to identify and discuss fundamental research that is highly desired to increase accuracy and reliability of existing modeling techniques.
Ioana Cozmuta received her PhD from University of Groningen, the Netherlands in 2001. During her PhD, she developed, using experimental and computational methods, a model for transport of radionuclides in porous media directly coupled with the time evolution of the microstructure. This work, performed under the supervision of prof. R. J. de Meijer and dr. E. R. van der Graaf has been used as correction for indoor-air pollution models employed within the Radiation Performance Index Standard of the Dutch building codes. Following her Ph.D., she has joined the Material and Process Simulation Center at California Institute of Technology headed by prof. W. A. Goddard, where her research focus has been the application of computational chemistry methods to polymeric and polymer-based nanocomposite systems. Next, her research work at Stanford and at the Center for Nanotechnology at NASA Ames, CA has addressed the design of a solid-state nanopore for DNA sequencing using large-scale molecular dynamics and mesoscale simulations. Recently, she has joined as a Senior Research Scientist the Reacting Flow Environments Branch at NASA Ames Research Center to perform material response modeling, Thermal Protection System (TPS) sizing, analysis and design and model development of surface catalycity employing reactive and non-reactive atomistic scale in support of the CEV mission and Stardust post-flight analysis. Over the past five years, her research has focused on implementing and developing novel multi-scale, hierarchical modeling techniques to systematically understand the macroscopic response of various complex systems based on their fundamental, atomistic structure.