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130 JOURNAL OF METEOROLOGY VoLu:am 5
CONTROLLED-ALTITUDE FREE BALLOONS
By Athelstan F. Spilhaus, C. S. Schneider, and C. B. Moore
College of Engineering, New York University
(Manuscript received 4 December 1947)
ABSTRACT
The results of an experi.mental program to develop balloons with associated control devices, which will
float at constant pressure m the atmosphere, are given.
Newly dev~loped ~lastic balloons and automatic ballast equipment are described. Examples of successful
controlled-altitude fl1ghts are shown, together with a preliminary analysis of their trajectories.
The cons~?~-~evel balloon rna~ provide data not obtainable from an ordinary pilot-balloon network.
Future possibilities and plans for 1ts use are indicated.
1. Purpose
Drift bottles have been used for many years in the
study of ocean currents and have provided interesting
data. In meteorology, no corresponding device has
been available. It is evident, however, that a balloon
"which is free to move with the air currents, and yet
whose altitude can be controlled, has many important
applications in meteorology, as well as in other fields
where it may be desired to keep instruments at alti~
tude for considerable lengths of time. An example is in
the investigation of cosmic rays; here, clusters of
ordinary extensible meteorological balloons have been
used, but the constancy of altitude obtained is not
sufficient for many meteorological applications. The
purpoSe of the present investigation' was to develop
a balloon with a control system which would fly at a
predetermined constant level for periods of many
hours. Such a balloon has wider application than the
ocean drift bottle, because, whereas the latter is
limited to surface (or near surface) currents, controlled
free balloons may be set to drift at any pressure
elevation desired, or along other thermodynamically
defined surfaces, as long as the element defining the
surface changes in a monotone fashion in the vertical.
In addition to the uses for maintaining ·instruments
at high elevations, there are numerous potential appli-
cations of these balloons. Direct measurements of air
trajectories and of lateral diffusion become possible.
The balloons may also be used as vehicles to convey
and drop radiosondes over ocean areas. One problem
in this application is to obtain an absolute altitude
tie-in point, as it will be difficult to identify the point
at which the radiosonde reaches the sea surface.
2. Earlier attempts
There have been numerous attempts for various
purposes to get a balloon or group of balloons to stay
at a fairly constant altitude. Meisinger was interested
1 Sponsored by, and in cooperation with the Watson Labora~
tories of the Air Materiel Command.
in the meteorological aspects of this, using a manned
balloon. In the investigation of cosmic rays, as for
example, by Clarke and Korff (1941), clusters of
ordinary meteorological balloons, 350-gram or 700-
gram size, numbering anywhere from twenty to nearly
seventy, were utilized. No altitude-control devices
were used; the balloons were merely given different
amounts of inflation. Thus the whole train ascended
to an altitude where certain of the more highly inflated
balloons burst until the remainder just balanced the
load; thereafter, the assembly descended slowly due
to loss of lift by the diffusion of gas. The only provision
for having the system regain altitude if it descended
too low was by arranging the launching before dawn,
so that after the bursting of the first balloon and the
subst;q.uent descent, superheating of the balloons by
the nsmg sun would cause the whole assembly to rise
again, thereby increasing the duration of the flight.
The system does not have sufficient control for many
purposes.
. The much-publicized use of balloons by the Japanese
10 the last war represents an attempt which must be
considered highly suecessful from the point of view of
the length of time which the balloons stayed in the air.
He.re the objective was not to obtain any critical
altitude control, but rather to insure that the balloons
remained floating. The Japanese nonextensible bal-
loons were of two types. One type was of heavy paper,
coated to minimize diffusion, of spherical shape, about
25 ~o 30ft in diameter, and containing about 19,000
cubic feet of gas. A solid-ballast control system was
utilized and gas was valved at a low internal pressure
(about two inches of water) to prevent the balloons
from rupturing due to the increase of the internal
pressure by altitude fluctuations or radiation changes.
Such a valve tends to conserve the lifting gas but acts
as a safety device to prevent damage of the envelope
due to too great an internal pressure.
The solid-ballast system was complex; approxi-
mately 900 pounds of sand was used on each balloon
distributed in thirty-six bags. The dropping of ballas~