roswell

or sunset outs off the superheat is so large that it is not possible
to carry enough ballast to sustain ,the system unQ.er these condi-
tions. On the other hand, the loss of buoyancy through a sealed-off
Seyfang balloon at 4100 feet MSL is of the orQ.er of 60 grams per
hour Which is significantly less than the loss expected from a 20-
foot, 1 mil polyethylene cell in flight conditiona. (With the appendix
aperture sealed, .such a cell shows a loss of lift of about 40 grams
per hour when one-fifth inf~ated at sea level).
One other type of balloon which has been used as a super-pressure
balloon is the neoprene J2000 balloon of Dewey and Almy, surrounded
by nylon cloth shroud. The rubber balloon normally would expand
until it reached bursting diameter, but when enshrouded, it is
limited to the volume of the shroud. The difficulties in launching
and flying this balloon are not unusually great, but on each of the
several tests which have been made to date improper handling has
been a possible cause of the early rupture of the balloon. It is
believed, however, that such a balloon is not especially suitable
t~ long flights because of the deterioration which occurs in the
neoprene in the presence of sunlight. Perhaps a shroud of material
which would filter out the ultraviolet rays would protect ana
lengthen the lite of such a balloon.
Despite the success of the Japanese silk or rice-paper balloons,
which were constructed on a super-pressure principle, it is not be-
lieved practical at this time to develop a balloon of such strength
that it would successfully withstand and retain press\lre increases
corresponding to the temperature changes from night to day as the
superheat of absorbed sunlight is gained. The super-pressure with
a neoprene-coated nylon balloon, for example, would be approximaitiy
0.6 psi. That such a balloon could be built is unquestioned. The
cost of production, however, appears at this time to be unwarranted.
D. Altitude Controls
Beginning with the arrays of rubber balloons which were first used,
various systems of dropping ballast, both solid and liquid, have
been attempted with the aim of exactly compensating for the loss of
buoyancy which is occasioned as the lifting gas diffuses or leaks
through the balloon. On the early rubber balloons only rough incre-
mental ballast dropping was emPbyed. At that time it W$S decided not
to use sand as ballast since most sand contains some water which
may freeze while aloft. Further, it is easier to control the flow
of a liquid ballast than it is to control sand particles. In the
investigations for a suitable liquid ballast the petroleum product
known commercially as Mobil Aero compass fluid was finally settled
upon. These investigations included tests of cloud point, freezing
point, and also density and viscosity over a large range of tempera-
tures. The compass fluid is especially suitable for ballast work
-16-