Aerogel insulation applications for liquid hydrogen launch vehicle tanks

Abstract

Aerogel based insulation systems for ambient pressure environments were developed for liquid hydrogen (LH2) tank applications. Solutions to thermal insulation problems were demonstrated for the Space Shuttle External Tank (ET) through extensive testing at the Cryogenics Test Laboratory. Demonstration testing was performed using a 1/10th scale ET LH2 intertank unit and liquid helium as the coolant to provide the 20 K cold boundary temperature. Cryopumping tests in the range of 20K were performed using both constant mass and constant pressure methods. Long-duration tests (up to 10 hours) showed that the nitrogen mass taken up inside the intertank is reduced by a factor of nearly three for the aerogel insulated case as compared to the un-insulated (bare metal flight configuration) case. Test results including thermal stabilization, heat transfer effectiveness, and cryopumping confirm that the aerogel system eliminates free liquid nitrogen within the intertank. Physisorption (or adsorption) of liquid nitrogen within the fine pore structure of aerogel materials was also investigated. Results of a mass uptake method show that the sorption ratio (liquid nitrogen to aerogel beads) is about 62 percent by volume. A novel liquid nitrogen production method of testing the liquid nitrogen physical adsorption capacity of aerogel beads was also performed to more closely approximate the actual launch vehicle cooldown and thermal stabilization effects within the aerogel material. The extraordinary insulating effectiveness of the aerogel material shows that cryopumping is not an open-cell mass transport issue but is strictly driven by thermal communication between warm and cold surfaces. The new aerogel insulation technology is useful to solve heat transfer problem areas and to augment existing thermal protection systems on launch vehicles. Examples are given and potential benefits for producing launch systems that are more reliable, robust, reusable, and efficient are outlined.

Hydrophobic and thermal insulation properties of silica aerogel/epoxy composite

“…Therefore, they have many potential applications in thermal, acoustic, electronic and catalytic fields, especially in thermal insulation [1][2][3][4]. However, hydrophilicity and powder or the granule form of silica aerogels limits their applications.…”

“…Silica aerogels are excellent nanoporous materials with high specific surface area (500-1200 m 2 /g), low density (0.003-0.1 g/cm 3 ), low dielectric constant (1.1-2.0) and low thermal conductivity (0.013-0.04 W/m k). Therefore, they have many potential applications in thermal, acoustic, electronic and catalytic fields, especially in thermal insulation [1][2][3][4].…”

Prediction of the gaseous thermal conductivity in aerogels with non-uniform pore-size distribution

“…In most cases, the total effective thermal conductivity of the aerogel is less than that of the free air at room temperature, and thus many aerogels have been directly used as thermal insulation materials especially in extreme conditions [4][5][6][7][8]. In the researches [9][10][11][12], we can find that gaseous thermal conductivity in the aerogel has significant contribution to the total thermal conductivity under normal ambient conditions.…”

Flexible and Transparent Silica Aerogels: An Overview

“…Aerogel has been considered as a potential candidate to act as a heat shield in these cryogenic systems such as liquid-hydrogen (LH 2 ) tanks and liquid-oxygen (LO 2 ) feedlines because of its fully breathable and hydrophobic characteristics [152]. Furthermore, experiments in [153] have shown that liquid nitrogen (LN 2 ) can be prevented from accumulating within the intertank of the space shuttle by using an insulation system consisting of a bulk-fill aerogel material. The key phases to assess the performance of cryogenic insulation systems are at lift-off and reentry into the atmosphere when there are sudden changes in temperature and pressure.…”