The Cryogenic, Conformal, Composite, Common-Bulkhead, Aerogel-Insulated Tank project, or CBAT, is part of the development of Airframe Technologies for Advanced Space Transportation. Demonstration of all these technology elements (cryogenic, conformal, composite, common, and aerogel) together in one engineering development unit (EDU) is the overall objective of this project, which is being led by the Marshall Space Flight Center (MSFC). A key part of the prototype launch vehicle tank-set is the thermally insulating structural panel between fuel (kerosene) and oxidizer (liquid oxygen) tanks. Thermal performance testing of candidate insulation panels under cryogenic vacuum conditions was performed at the Cryogenics Test Laboratory of the NASA Kennedy Space Center.

The steady-state liquid nitrogen boiloff method of calorimetry was used to determine the apparent thermal conductivity (k-value) of the test specimens. Cryostat-4, a flat-plate insulation test apparatus for comparative k-value measurement, was used for all tests. A liquid nitrogen cold mass maintained the cold boundary temperature (CBT) at approximately 78 kelvin (K). The warm boundary temperature (WBT) was maintained at approximately 293 K using an external heater. The mean temperature was therefore about 186 K (-87 degrees Celsius). Vacuum environments included the following three cases: high vacuum (HV), soft vacuum (SV), and no vacuum (NV). Nitrogen was the residual gas within the vacuum chamber.

The 8-inch-nominal-diameter test specimens, shown in figure 1, include evacuated, nonevacuated, and krypton-filled insulation panels manufactured by NanoPore Inc. The core material is Nanogel, a trademark of Cabot Corporation. Values for thickness and density for the installed condition are given in the table. A summary graph of the calibrated k-value as a function of CVP is presented in figure 2. The curves for polystyrene and aerogel beads are shown for reference. The evacuated panel tests, test series F102 and F106, show that the compressive load of approximately 50 pounds per square inch causes a significant increase in the heat transfer rate. The krypton-filled panel F104 shows remarkably good performance relative to the air-filled panel F103 as expected because the thermal conductivity of krypton is much lower.

Although the KSC task for CBAT has concluded, the research work continues in a related area. Plans for 2002 call for working with Technology Applications, Inc., to develop structural insulating panels for cryogenic piping. The core material for this insulation system will be glass microspheres for their excellent combination of mechanical, thermal, and low-mass properties. Potential applications include thermal protection system for reusable launch vehicles, common bulkhead propellant tanks for spacecraft, underwater fuel transfer lines, shipping containers for frozen foods or biological tissues, refrigerated transport, replacement for conventional cellular glass or foam insulants on liquid oxygen piping and tanks, and cold boxes for manufacturing processes.

Contact: J.E. Fesmire (James.Fesmire-1@ksc.nasa.gov), YA-C2, (321) 867-7557
Participating Organizations: Dynacs Inc. (K.W. Heckle) and NASA MSFC (G. Smithers)