Builds the antennas, networks and software that talk to spacecraft.

Every command and every byte of telemetry passes through the ground segment. Ground systems engineers own the stations, the scheduling, the links and the software that turns a radio signal into something an operator can read.
RF, networks or software emphasis all work.
Station maintenance is a genuine entry point with progression into engineering.
Software developers, quality assurance analysts, and testers · US Bureau of Labor Statistics, Occupational Outlook Handbook, May 2024 wages and 2024–34 projections.
Ground segment work spans software and electronics; the software occupation is the nearest published fit and covers a vastly larger population than space ground systems.
Nobody notices the ground segment until a pass fails, and then everybody does. The systems are long-lived, which means maintaining software older than some of the people using it.