1. Effects of the Venus Atmosphere on Thermal Insulating Material Performance Michael Pauken, Linda Del Castillo, Jay Polk, Dannah Almasco Jet Propulsion Laboratory, California Institute of Technology 4800 Oak Grove Dr. Pasadena, CA 91109 (818 354-4242);( mpauken@jpl.nasa.gov) National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Pasadena, California www.nasa.gov National Aeronautics and Space Administration Copyright 2010. All rights reserved. Background Image: Venus - 3D Perspective View of Lavinia Planitia Photo Credit: NASA/JPL Abstract A Venus Lander thermal control system is critical to mission success because the extremely high temperature and pressure environment presents significant thermal challenges to operating lifetime. Future Venus surface missions will require advanced thermal control strategies to allow greater science return than previous missions by operating for several hours in Venus’ harsh environment. This poster describes the effects of a simulated Venus atmosphere on the thermal conductivity of insulation materials that would be placed external to the pressure vessel. The candidate insulation systems include porous silica materials, aerogel formulations and Q-fiber felt capable of handling a high temperature and high pressure gas environment while maintaining low thermal conductivity. Thermal conductivity data were measured over a range of temperature and pressure conditions up to 470°C and 92 bar pressure in carbon dioxide for the insulation material candidates. The thermal conductivity was observed to increase in the Venus- like environment over the Earth environment. This has a number of implications on the design and testing of the thermal system for a Venus Lander. Insulation Block Pieces Venus Materials Test Facility Test Methodology Oven Testing: Instrumented test article placed in oven. Temperature increased to 470°C in about 1.5 hours. Soak at temperature for 4 hours, simulate mission lifetime. Venus Chamber Testing: Test article placed in chamber. Chamber is evacuated and filled with CO2 to 30 bar. Temperature increased stepwise to 470°C, 92 bar. Short dwell at each step for k-measurements. Analysis Energy absorbed by aluminum block = energy conducted through insulation dt was taken over 10 minute intervals A(x) derived from the conduction path with variable area: A(x) = 2s 2 + 4s(0.254 + (s – s 0 )) For the test geometry this is approximated by: A(x) = 7.95x 1.35 Integration yields: Q cond = 3.555k(T ext – T al ) Discussion Oven Testing: Tests in the oven were performed to determine if the transient test method was suitable for estimating the thermal conductivity of insulating materials as an alternative to the guarded hot plate method. Reasonably good agreement was found between manufacturer’s data and test data. Venus Chamber Testing: Three different porous silica insulation materials have been tested in the Venus Chamber. Two different test methods have been employed: (1) Fixed density fluid with increasing temperature plateaus and (2) Fixed pressure fluid with increasing temperature plateaus. The 2 nd method appears to provide better data. Conclusions Insulation thermal conductivity in a Venus-like environment increases by a factor of 3 to 4 times over the earth ambient environment. Additional testing is ongoing to improve the chamber operating performance and to improve the accuracy of the thermal conductivity data. Alternate test methods such as heating the aluminum block while keeping the chamber air cooled will be used to make long duration test runs to improve accuracy. This method can achieve steady state test conditions. Acknowledgement: The research described in this poster was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Approach Measure transient temperature response of insulated aluminum block in a high temperature/pressure environment. Determine thermal conductivity of insulation using an energy balance on the control volume. Sample Preparation Each insulation block and aluminum block was weighed prior to assembly. A hole was drilled into the insulation block for inserting a single TC into the center of the aluminum block. The interior surface temperature of the insulation is assumed to be that of the aluminum block. Each assembly was wrapped with 2-mil thick type 309 annealed stainless steel foil for protecting the surface from handling damage. Stainless steel bands were used to hold the foil in place around the insulation. Stainless steel cables were used as a holder to suspend the insulation assembly in the oven and in the Venus chamber. Additional TC’s were used to measure the temperature of the insulation exterior, ambient oven air and chamber wall. Insulated Block After Oven Test