A tractor beam pulls things towards it.
The Cargo Scoops/Fuel Scoops "use powerful electro-magnetic fields to guide the solar wind into their ReQax converters to fill the Witch-Space fuel condensers, and may also may be used to pick up small space debris".
The Cargo Stopper (.oxp equipment) makes use of the tractor beam which forms part of the cargo scoops. When your ship is aimed at cargo cannisters that are floating away and this device activates (this is automatic), it will use the tractor beam to bring the cargo to a stop. Cargo must be within 2km of your ship, and in the centre area of your front viewscreen, otherwise the tractor beam can't reach it. Cargo stoppers come as part of the GalCop Missions oxp.
Other tractor beams
- The Imperial Star Destroyers also have Tractor Beams, but they seem not to be implemented in the .oxp code as an offensive weapon (as used in the films).
- Coyote's Run features a good one.