roswell

its bursting diameter, the gear strikes the ground, or corrective
action is taken. Even if the extremely critical balance is intially
achieved, there will be 'Imbalance occasioned by (1) bursting of
balloons due to deterioration in the sunlight, (2) diffusion of
lifting gas from the balloons, (3) loss or gain of buoyancy "'hen
temperature inside the balloon changes with respect to the ambient
air temperature. This will result initially from radiative dif-
ferences, and after an amount of difference (superheat) has been
established, changes in ventilation will cause changes in buoyancy.
Two methods of attaching the payload to the clusters of rubber bal-
loons were tried. In the first of these (Figure 3) a long load
line was used,and short lines led from it to the individual bal-
loons. The length of such arrays was as much as 800 feet, and
this size made them difficult to launch. The single load ring
array, seen in Figure 4, proved to be much easier to handle and
is recommended for cluster lfnmchings. During ascent each of the
balloons in such an array ride separated from each other and no rub-
bing or chafing has been observed.
The controls which were associated with this balloon system were
crude and, in general, ineffective. They included (l) cutting off
balloons as the buoyancy became excessive and a preset altitude
extreme was passed, and (2) releasing part of the load in the for.m
of solid or liquid ballast whenever descent occurred. The sensi-
tivity of these elastic balloons makes it difficult to control
their altitude with any system of controls, and as controls were
developed it was found more practical to change from freely ex-
panding balloons to non-extensible cells not made of neoprene. The
tendency of neoprene to decay within a few hours when exposed to
sunlight was the most cogent argument against doing more work on
altitude controls to be used with such a system.
B. Plastic Balloons
The next attempts to control the altitude of a balloon vehicle were·
made using non-extensible plastic cells, with an open bottom to pre-
vent rupture when expansion of the lifting gas is excessive. With
a fixed maximum volume, such a system has inherent vertical insta-
bility in only one direction. When full, there is· e. pressure alti-
tude above which a given load will not be carried. The instability
of such a system is found only when an unbalanced d~nward force
exists. The development of controls and films for balloon material
proceeded concurrently, but the choice of a.non-extensible plastic
film was made before the system of control was perfected.
The properties which were given most consiaere.tion in the selection
of fabric include (l) availability and cost, (2) ease of fabrica-
tion and (3) satisfactory chemical and physical properties. Pri-
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