Assembly was used to support both internal (intercom) and external crew communications onboard the space shuttle and was used for flight qualification testing. $1275 shipped within US.The headset interface unit has separate push-to-talk buttons for transmit and intercom modes and a volume control that determines the level of sound heard through the crewmember's ear piece. Push to talk means that a push button must be depressed to allow a flight crew member to talk through the system.
The headset interface unit is a portable microphone switch that was considered part of the communications carrier umbilical. It provided volume control and push-to-talk capabilities to the CCA Snoopy cap used for EVA, to the CAPS and to the wireless crew communication unit as a backup.
The HIU has a clip that attaches to the crew's flight suits. The unit has a three-position rocker switch and a volume control knob. The switch positions are xmit; icom; and an unlabeled, spring-loaded-off center position. The xmit position allowed access to intercom and external circuits, while the icom position is for intercom only.