Physics object slowing down

I have a skeletal mesh (Spacecraft) with a physics body and no gravity , I add an impulse to it and it starts moving as per its mass say at 600 units/sec veclocity.

Over time the skeletal mesh is slowing down at a uniform rate for no apparent reason, there is nothing touching it.

I’m watching the velocity using “Print String” and its falling down from initial speed at about 2-3 units per second or so.

Why is it slowing down? How do I disable it to make friction-less motion effect in space.