roswell

132
BALLAST INI.IT TUBE
FIG. 2.. \utomatic ballast valve.
a diaphragm-operated needle valve which jettisons
liquid ballast whenever the balloon is below the alti-
tude at which the control is actuated. This is shown in
fig. 2. The ballast reservoir (fig. 3), in general, can
hold 15 kilograms of the liquid ballast-usually com-
pass fluid, a highly refined kerosene-type petroleum
product. When the atmospheric pressure outside the
diaphragm is 5 millibars above the internal pressure,
160 grams of ballast per minute flow under a one-foot
head. When the automatic ballast valve is wide open,
which is after 6.5 millibars increase over the internal
pressure, 300 grams per minute flow. These values may
be compared with a diffusion loss of lift of the order
of magnitude of 10 grams per hour from the thicker
15-ft balloon described below. Quite positive altitude
control can be obtained.
Efforts are made to cause the static rate of leakage,
i.e., the leakage which proceeds when the automatic
ballast valve is closed, to exceed slightly the rate of
loss of lift due to the diffusion of the lifting gas from
the balloon. To facilitate setting the fixed leak, a
manually operated ballast valve, consisting of a leak
adjustable by means of a fine needle valve, is added to
the ballast-release assembly. 4
C. lJ;finimum pressure switch.-0bvious1y, the auto-
matic ballast valve must not be in operation while the
balloon is rising, as this would be a waste of ballast.
Therefore the automatically operated needle valve is
closed until the balloon reaches altitude. This is ac-
complished by having the loaded diaphragm of the
altitude control open to the atmosphere until the
balloon descends from a minimum pressure ..-\t this
time, an electrical contact is made and a squib6 cuts a
' Since this manuscript was written, the procedure has been
simplified. Only a simple fixed leak is used for daytime flights.
The automati~ ballast valve is used alone for Rights through
sunset or sunnse.
1 A small electrically detonated charge.
VoLUME 5
restraining cord and allows a needle valve to seal off
the diaphragm from any further access to the air
(fig. 2). The capsule then contains a volume of air
which has been trapped at the existing pressure an'd
temperature, at the time of operation of the sealing
switch. Thereafter the aneroid will withdraw the
ballast-control needle valve when the ambient pressure
increases to the point where the entrapped air is com-
pressed below this volume.
Fig. 4 shows the minimum pressure switch which
makes the electrical contact at the time of seal-off. It
consists of a trapped volume of air that is allowed to
escape through a mercury pool as long as the outside
pressure is decreasing. As soon as the exterior pressure
increases once more, however, mercury is drawn into
the tube, making the seal-off contact between two
electrodes.
4. Height determination
Up to the present time, the standard radiosonde has
been used in order to determine the altitude at which
the balloon is flying. This permits a regular radiosonde
ascent to be obtained during the period that the bal-
loon is rising. Thereafter, as the balloon remains at
approximately the same altitude, it becomes somewhat
difficult to identify the radiosonde contact, but utiliz-
ing both the temperature and pressure indication, this
is possible. A special radiosonde modulator of the
Olland type has been designed (fig. 5). The pressure
BATTERY BOX
VENT TUBE
DISCHARGE TUBE
FIG. 3. Ballast-release assembly.