Originally designed to assist in assembling large ships and orbital installations, the salvage rig's gantry and manipulators are used to assist in recovering derelict hulks and scavenging useful material from wreckage and debris fields. The rig itself has no cargo or fuel capacity and requires ample supply to maintain. Increases non-combat salvage gained, with more difficult operations being able to make use of more rigs.
As a destroyer-sized class the Salvage Rig receives a 25% salvage bonus from its Salvage Gantry hullmod compared to the 10% salvage bonus on the Frigate sized Shepherd class. Hovewer it requires other ships to provide for its logistical needs as it has no cargo capacity and is unable to meet its own skeleton crew requirements.
For more information about how salvaging bonuses work see the Salvage Gantry article.