ALASS
ALASS is
a meteorological sampling system which provides temperature, barometric pressure,
humidity, and Omega position data in remote ocean areas for ballistic missile tests. The
system provides this weather data for missile RV data reduction and provides wind data
used to calculate sonobuoy launch points during a
Sonobuoy
Missile Impact Location System (SMILS) mission.
Mission Description
During a mission where SMILS is
utilized, the ARIA deploys an ALASS probe through the B-size gravity drop tube
approximately 60 miles out from the DOT array center at an altitude of between 4,000 and
9,000 feet. The probe descends to approximately 50 feet above the ocean where it releases
an Omega weathersonde attached to a helium balloon. The sonde then ascends to an altitude
of between 60,000 and 100,000 feet (until the balloon bursts) as it transmits its
meteorological and position data back to the aircraft on a frequency of between 400 and
406 MHz at a maximum range of approximately 200 nautical miles.
System Description
The system consists of an ALASS
probe, receiver/processor, disk recorder, and printer.
ALASS Probe
The ALASS probe is a spun fiberglass
canister which stands 5 feet tall, 8 inches in diameter, and weighs approximately 55
pounds. It contains a radiosonde (VLF Omega weathersonde) connected to a helium balloon, a
tank of compressed helium to inflate the balloon, a drogue chute to stabilize the
ballistic flight of the probe, a parachute which deploys at 4,000 feet altitude to slow
the probe descent, a water sensor to activate the sonde deployment, and an electronic
timer to control the entire system.
Radiosonde
The radiosonde uses capacitive
sensors (which detect atmospheric pressure, temperature, and humidity) to vary the
frequency of a local oscillator. The output of this oscillator is mixed with received
Omega navigation signals and used to modulate the RF carrier. The sensors are factory
calibrated, and this calibration data is supplied on a paper tape which is read by the
receiver/processor unit to enable highly accurate data recovery.
Receiver/Processor
The receiver/processor receives the
RF signal from the radiosonde, demodulates it, digitizes the data, interprets and displays
the data, and outputs the data serially to a printer and a disk drive.
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