AXBT Operation


The AXBT is deployed from the NOAA WP-3D Orion aircraft from  either an internal launch tube or from one of 22 external launch tubes (see figure axbt_load) in the belly of the aircraft. These tubes are inclined at a 45 degree angle to allow for a smooth transition of the AXBT with the external air stream.  The AXBT is encased in a protective sleeve called a Sonobuoy Launch Container (SLC) that is armed prior to flight with a CAD, a small explosive device that when activated electrically, explodes and fires the AXBT out of the SLC and into the air stream outside of the aircraft. The figure axbt1_SLC_CAD shows the CAD attached to the SLC. The CAD allows the AXBT to reach a velocity about equal to that of the air relative to the aircraft. If internally launched (see AXBT1) from within the aircraft, the top of the SLC is removed and the AXBT is allowed to slide out of the SLC as it is positioned over the internal launch tube within the aircraft, and the AXBT is literally sucked out of the aircraft. Immediately after launch, the parachute attached to the AXBT deploys and allows the AXBT to fall vertically to the surface. Figure axbt2_chute shows the parachute deployed from the AXBT. When the AXBT hits the water vertically, the impact pops off a spring-loaded bottom plate that exposes the AXBT probe. The AXBT in the water would look like the figure axbt2a_deployed2. The exploded view of the AXBT in axbt3_exploded_view shows the bottom pressure plate, a counter-weight that helps the probe enter the water vertically, the black temperature probe and wire spool cylinder and the salt-water activated battery and VHF transmitter for transmitting a radio signal containing the temperature data from the probe. The exploded view axbt4_exploded_transmit shows the small metal disc that the temperature thermistor probe is embedded in, the 300 m copper wire spool, the black plastic spool cover and the silver cylinder containing the salt water battery, transmitter and antenna along with the white plastic cover for the assembly. Figure axbt6_exploded_xmtnocover shows the same exploded view without the white plastic assembly cover. The wire spool cylinder contains a spool of thin copper wire 300 m long that stays attached to the transmitter which floats on the surface sending the radio signal back to the aircraft while the probe descends through the water. The impact of the probe on the water activates the battery and a timing circuit that warms up the transmitter and after 30 sec burns a copy retaining wire that allows the probe to start falling as the radio transmitter is turned from standby to transmit mode, which is an audio tone that can be heard to change pitch as the temperature measured by the probe changes in its descent through the water column. Figure axbt10_AXBThous_probe shows how the AXBT assembly would look as the temperature probe begins to fall from the bottom after it has stabilized in the water.