PDRS was an agency or title held by a Starfleet officer at Starfleet Command's Fleet Operations Center, Sol Sector.
In January of 2155, Starfleet officers T. Scott, G. Agalsoff, and D. Baker were working in or as PDRS. It and the officers' names were listed on directory placards. (ENT: "Demons", directories)
PDRS, like many of the other agencies or titles on the listing, was a reference to NASA and ISS terminology, in this case, the "Payload Deployment and Retrieval System".