Tractor beam

A tractor beam is an attenuated linear graviton beam used by starships and space stations to control the movement of external objects. The beam places spatial stresses on the object in specific areas allowing the ship using the tractor beam to hold the object in a fixed location or alter its position or trajectory. While tractor beams are normally used to pull objects towards the beam source, or to tow objects, they can also be set to repel objects. 

Tractor beams are generally only used at sub-warp velocities. To safely tow a vessel at warp speed, the target vessel's engines must be deactivated to avoid shearing forces against towing vessel. Using a tractor beam can be done at warp speed only if both vessels' speeds are exactly matched.