"The newly developed antenna, designed to be mounted on the roof of passenger vehicle, uses mechanical steering to track an Earth-orbiting satellite while the vehicle is in motion. It and other JPL-developed technologies are intended to pave the way for an eventual mobile satellite communications system."
"The system, which would be built and operated by industry, consists of one or more satellites in geosynchronous orbit and network management centers on the ground. Each of the satellites, to be deployed beginning in the early 1990s, would serve as relay station for mobile users communicating by voice and data links."
https://www.jpl.nasa.gov/news/msat-x-key-antenna-design-tested-successfully/
"It is believed to be the first time all elements of mobile satellite terminal have been tested in standard car, according to Dr. William Rafferty, manager of JPL's Communications Section, which conducts the Mobile Satellite Experiment (MSAT-X) program for NASA."
https://www.jpl.nasa.gov/news/mobile-satellite-communications-system-successfully-tested/
Still digging.