The discovery of Astrium-126 in the 27th century almost went unnoticed, until a laboratory accident resulted in large amounts of direct-current electricity being applied to a block of Astrium. This caused the block to suddenly accelerate in the opposite direction of the electron flow. Subsequent experiments proved that this was not due to a Newtonian reaction, but some generation of force that still remains unknown. Regardless of the cause, it didn't take long for this property to be adapted into the reactionless propulsors used in every spacecraft since.

You may install up to twenty slots of Propulsors. Each slot of Propulsor will propel the ship at 0.25 gravities, and includes sufficient volume of powerplant to generate the required electricity. Most civilian ships generate 0.75 gravities of acceleration; most military vessels will have one gravity of acceleration; cruisers frequently have a 1.5g to 2g acceleration.