Dual seal insulation, consisting of an inner layer of sealed-cell Mylar honeycomb core and an outer helium purge channel of fiber glass reinforced phenolic honeycomb core, is used as a thin, lightweight insulation for external surfaces of cryogenic-propellant tanks

Dumire, P. E.

Middleton, R. L.

Schell, J. T.

Stuckey, J. M.

English

NASA Technical Reports Server

rated Phenolic 
jcomb Core 
ied Epoxy Adhesive 
Epoxy 
Adhesi 
June 1966
	 Brief 66-10183 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Insulation for Cryogenic Tanks Has Reduced Thickness and Weight 
Polyuretndile	 Honeycomb Core 
Adhesive
Mylar Film 
Tank Skin
complished by the condensation (cryopump) of the air 
trapped within them when the back surface of the in-
sulation reaches —423'F as the propellant tank is 
filled with liquid hydrogen. 
The honeycothb core used in the helium purge 
channel is perforated during fabrication, resulting in 
a 1/16-inch-diameter hole in each side of the cell. 
These holes allow helium to flow through the entire 
outer channel. This channel is separated from the 
inner core by a low permeability aluminum film which 
is bonded to the inner and outer cores. Another alumi-
num film, which serves as the outer skin of the insula-
tion, is bonded to the phenolic core with an epoxy 
phenolic adhesive. A Mylar film is bonded with a 
polyurethane adhesive to the bottom surface of the 
Mylar core to form the sealed cell lower insulation. 
The polyurethane adhesive is also used for bonding 
the insulation to the tank wall. 
In the event that both the outer and inner seals 
are punctured, helium gas from the outer core will 
flow through the puncture in the outer seal, prevent-
ing air from entering the insulation until repairs are 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States 
The problem: 
To develop a thin, lightweight insulation for use 
on external surfaces of cryogenic propellant tanks. In 
a particular application, the outer surface of the in-
sulation will be exposed to aerodynamic heating which 
will raise its temperature to approximately 400° F for 
a short time, while the inner surface, approximately 
0.6 inch away, will be at the temperature of liquid 
hydrogen (-423° F). 
The solution: 
A dual seal insulation having a weight of approxi-
mately 0.5 lb/ft2 and a thermal conductivity of 0.2 
Btu/in./hr/ft-/ F. The dual seal insulation consists 
of an inner layer of sealed cell Mylar honeycomb core 
and an outer helium purge channel of fiberglass rein-
forced phenolic honeycomb core. Each cell in the 
Mylar honeycomb core is a hermetically sealed unit 
so that gases-cannot permeate cell to cell. 
How it's done: 
The operating principle of this system is based upon 
the self-evacuation of the sealed cells, which is ac-
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000182 2020-03-11T17:30:34+00:00Z
made. The helium will also enter any damaged cells 
in the lower core through the puncture in the inner 
seal. However, since each cell in the lower core 
is individually sealed, the helium is confined to the 
affected cells. Thus there is no degradation in thermal 
conductivity in large areas due to local damage. 
Notes: 
I. The sealed cell Mylar honeycomb is the part of 
the system that provides the cryogenic insulation. 
However, the Mylar core softens at a little over 
2000 F. The heat resistant, phenolic honeycomb 
core or purge channel portion, is provided to pro-
tect the Mylar core from higher temperatures due 
to aerodynamic heating. 
2. Effective applications would require the backface 
temperature to be low enough to condense the 
air entrapped in the sealed cells to create a vacuum. 
It has been found that by fabricating the sealed 
cell portion in a carbon dioxide or fluorocarbon 
gas environment, the system could be used for in-
sulating liquid nitrogen or liquid oxygen con-
tainers.
3. This material has been applied to surfaces with 
compound curvatures and around cryogenic trans-
fer lines or pipes down to 1.5 inches in diameter. 
4. Further information concerning this invention is 
given in NASA SP-5030, "Symposium on Tech-
nology Status and Trends," Huntsville, Alabama, 
April 21-23, 1965, available from the Clearing-
house for Federal Scientific and Technical Infor-
mation, Springfield, Virginia, 22151. Inquiries may 
also be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama, 35E12 
Reference: B66-10183 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C., 20546. 
Source: R. L. Middleton, J. T. Schell, 
P. E. Dumire, J. M. Stuckey, et al
(M-FS-326) 
Brief 66-10183	 Category 02


Insulation for cryogenic tanks has reduced thickness and weight

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